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Victor Ginsburg's influence on my research of the role of sialic acids in biological recognition
ABB Archives of Biochemistry and Biophysics 426 (2004) 132–141 www.elsevier.com/locate/yabbi
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Victor GinsburgÕs influence on my research of the role of sialic acids in biological recognitionq Roland Schauer* Biochemisches Institut, Christian-Albrechts-Universit€at, Olshausenstr. 40, Kiel D-24098, Germany Received 5 January 2004, and in revised form 27 February 2004 Available online 12 April 2004
Abstract Sialic acids are monosaccharides with relatively strong acidity which belong to the most important molecules of higher animals and also occur in some microorganisms. They are bound to complex carbohydrates and occupy prominent positions, especially in cell membranes. Their structural diversity is high and, correspondingly, the mechanisms for their biosynthesis complex. Sialic acids are involved in a great number of cell functions. Due to their cell surface location these acidic molecules shield macromolecules and cells from enzymatic and immunological attacks and thus contribute to innate immunity. In contrast to this masking role, enabling, for example, blood cells and serum glycoproteins a longer life-time, sialic acids also represent recognition sites for various physiological receptors, such as the selectins and siglecs, as well as for toxins and microorganisms and thus allow their colonization. The recognition function of sialic acids can again be masked by O-acetylation, which modifies the interaction with receptors. Many viruses use sialic acids for the infection of cells. As sialic acids play also a decisive role in tumor biology, they prove to be rather versatile molecules that modulate biological and pathological cellular events in a sensitive way. Thus, they are most prominent representatives of mediators of molecular and cellular recognition. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Sialic acids; Chemical variety; N-Acetyl hydroxylation; O-acetylation; Masking effect; Ligand function; Cellular communication; Bacterial and viral adhesion; Innate immunity
Although carbohydrates have been known for long not only in the form of starch or glucose as primary source of energy, but as components of cell membranes forming a thick coat called glycocalyx, their biological role was not understood. Victor Ginsburg and colleagues made the pioneering observation that cell surface carbohydrates play a crucial role in the interaction of cells: the behavior of rat lymphocytes in the circulation changed dramatically after treatment with fucosidase or sialidase. The white blood cells accumulated in the liver instead of the spleen and lymph nodes [1]. It was believed that the carbohydrate residues may play a role in the recognition of lymphocytes by cells lining the q
Based on a lecture delivered at the Symposium on Glycobiology, dedicated to the Memory of Dr. Victor Ginsburg, NIH, Bethesda, MD, November 10, 2003. * Fax: +49-431-8802238. E-mail address: [email protected]. 0003-9861/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.abb.2004.03.008
capillary vessels as well as in controlling the passage of the lymphocytes from blood into lymphoid tissue. The group of Moscona discovered that the substances involved in the aggregation of sponge cells are glycoproteins and that species-specific aggregation may depend on the carbohydrate moiety of these cell surface glycoproteins [2]. Another milestone in the elucidation of the role of protein-bound carbohydrates was the observation made by Morell et al. [3] that desialylation of serum glycoproteins leads to binding and endocytosis of these macromolecules by hepatocytes. The reason was the exposure of galactose residues by sialidase treatment followed by recognition of these subterminal monosaccharides by a galactose receptor [4]. I had started my research work in the laboratory of Hans Faillard at the newly founded Ruhr-University of Bochum in March 1967 and focussed first on the isolation and analysis of different types of sialic acids including their susceptibility to sialidase and lyase action.
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Later on we discovered the enzymes hydroxylating the N-acetyl group of N-acetylneuraminic acid (Neu5Ac) yielding N-glycolylneuraminic acid (Neu5Gc) or Oacetylating these sialic acids at the pyranose ring or the sialic acid glycerol side chain (reviewed in [5,6]). Stimulated by the discoveries cited above which showed the involvement of glycans in molecular and cellular interactions, we became interested in the biological role of sialic acids positioned on the outer surface of the cell coat in high density. Furthermore, we addressed the question: Why are there so many different kinds of sialic acids?
The diversity of sialic acids Sialic acids are derivatives of neuraminic acid (5-amino-3,5-dideoxy-D -glycero-D -galacto-2-nonulopyranosonic acid) and occur in higher animals and some microorganisms [6,7]. They have also been found in developing insects [8] and a recent report demonstrates their expression in cell cultures from Arabidopsis thaliana [9]. They contribute to the impressive structural diversity of complex carbohydrates which are major constitutents mostly of proteins and lipids of cell membranes and secreted macromolecules [10]. Sialic acids are prominently positioned usually at the outer end of these molecules. The diversity of glycan chains is much increased by the biosynthesis of various kinds of sialic acids [11,12], thus potentiating the complexity of the ‘‘third language of life’’ represented by glycoconjugates. About 50 members of this unique monosaccharide family have been identified. They carry various substituents at the amino or hydroxyl groups (Fig. 1) [6,7,11– 16]. The amino group of neuraminic acid is acetylated or glycolylated, while at all non-glycosidic hydroxyl residues one or various acetyl groups may occur. Usually, there is only one O-acetyl group, mostly at O-9, but diand tri-O-acetylated sialic acids are known, especially in mucins from bovine submandibular gland and human colon [13]. At O-9 lactyl or phosphoryl residues and at O-8 methyl or sulfate groups can occur. All these different substituents may be combined, e.g., 8-O-methyl with 9-O-acetyl and N-glycolyl, yielding the manifold types of sialic acids found throughout the animal kingdom. Besides these sialic acids in various biological sources unsaturated sialic acids as well as anhydro- and lactone forms have been identified. 5-Desamino-5-hydroxy-neuraminic acid or 2-keto-3-deoxy-nononic acid (Kdn)1 [17] is increasingly detected in microorganisms and animals. Neuraminic acid itself (Neu), the de-Nacetylated product of Neu5Ac, is a further component of mammalian glycoconjugates. The sialic acid most 1
Abbreviations used: Kdn, 2-keto-3-deoxy-nononic acid; PSA, polysialic acids; IgSF, Immunoglobulin superfamily; EST, expressed sequence tags; MAG, myelin-associated-glycoprotein.
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recently discovered is the 1-tauryl derivative of Neu5Ac, isolated from the brain of patients suffering from TaySachs disease [18]. The sialic acids, except unsaturated sialic acids (2deoxy-2,3-didehydro sialic acids) and N -acetylneuraminic acid-9-phosphate (Neu5Ac9P), usually occur in glycosidic linkages of oligosaccharides, polysaccharides (polysialic acids), glycoproteins, gangliosides, and lipopolysaccharides [6,7,13,19]. Neu5Ac9P is an intermediate in sialic acid biosynthesis [20]. Neu5Ac, Neu5Gc, and N -acetyl-9-O-acetylneuraminic acid (Neu5,9Ac2 ) are the three most frequently occurring members of the sialic acid family. Only Neu5Ac is ubiquitous, while the others are not found in all species. The best investigated example next to Neu5Ac is Neu5Gc, which is found often in animals including the great apes, but not in healthy human tissues in significant quantities, with the exception of some tumors [21,22]. It was not detected in bacteria, but in Arabidopsis cells, as mentioned [9]. Neu5Gc is formed from CMP-Neu5Ac by a cytosolic hydroxylase which requires several electron-transferring cofactors and oxygen [21]. The enzyme has been isolated from starfish and various mammals and their primary structures were elucidated, showing that it is highly conserved in the deuterostome branch [23,24]. Man has lost Neu5Gc expression due to a gene mutation [25]. The small amount of Neu5Gc found in some tumors is discussed to be derived from the diet or it may be due to an unknown alternative biosynthetic pathway [21,22]. O-acetylated sialic acids are widespread, too. Sialic acids O-acetylated at the side-chain, mainly at C-9, are most predominant in animals from the echinoderms onwards, in human and in some bacteria, while 4-Oacetylation seems to be randomly occurring in individual species throughout the animal kingdom from echidnas to the horse [6,7,12,26]. The subcellular site and mechanism of O-acetylation of sialic acids seem to be more complex than the biosynthesis of Neu5Gc and resisted full elucidation. The enzymes involved, the acetyl-CoA:sialate-4-O-acetyltransferase and the corresponding 7(9)-O-acetyltransferase, are firmly attached to the Golgi membranes and were only recently solubilized by detergents and partially purified from bovine submandibular gland (Lrhorfi et al., unpublished) and guinea-pig liver [27]. Although the substrate specificities and kinetic properties of these enzymes have been studied, knowledge about their structural properties is scant, and expression cloning and mutagenesis experiments have failed to reveal the gene structures [28]. With regard to the mechanism of sialate O-acetylation a hypothesis has been developed that in a protein complex the CMP-Neu5Ac transporter, the O-acetyltransferases esterifying CMP-Neu5Ac, and the sialyltransferases transferring the O-acetylated product to nascent glycoconjugates are cooperating in the Golgi apparatus,
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Fig. 1. The family of naturally occurring sialic acids. The nomenclature, abbreviations, and references are listed in [6,16,91]. The residues on the neuraminic acid (Neu) molecule may be combined depending on the species or tissues. For further details and distribution see the text.
perhaps by inclusion of an acetylated intermediate [29,30]. Nothing is known of the enzymology and molecular biology of the enzymes involved in 9-O-lactylation and 8-O-sulfation of sialic acids [12]. While the former modification is ubiquitous, found also in human and best studied in trout liver, the latter seems to be restricted to some starfish species [6]. Only the enzyme for 8-O-methylation, which is bound to subcellular membranes, has been solubilized and isolated from the gonades of Asterias rubens [31]. Only in echinoderms, best studied in A. rubens, larger amounts of 8-Omethylated sialic acids are found. The occurrence of minor quantities of this sialic acid, as well as of 8-Osulfated species, in mucins of higher animals was reported [15]. Never have all kinds of sialic acids been found in one cell or organism. The distribution depends on the animal and cell species as well as on the function of a cell and seems to be strongly regulated on the gene level. In submandibular gland mucin of cow, 15 species of sialic acids were detected, most of them being Oacetylated in the sialic acid side-chain, but also 9-Olactylated as well as N-acetylated or N-glycolylated [6,32]. In human the number of sialic acid types is smaller, with Neu5Ac prevailing and followed by derivatives O-acetylated and O-lactylated at the sialic acid side chain. Rich sources of different sialic acids are the echinoderms [6].
The significance of sialic acids in molecular and cellular interactions The external position of sialic acids on glycoproteins and gangliosides, either alone or in oligo- or polymeric form, and correspondingly on the outer cell membranes implies a strong influence in cell biology. These acidic monosaccharides can most easily interact with the components of other cell surfaces, extracellular substances, and effector molecules. Evidence is increasing that they are involved in a multiplicity of cell signalling events. When considering their functions, sialic acids may be divided into more general classes, irrespective of the variability of their structures, and into those exerted by chemical modifications of these acidic monosaccharides [6,7]. Also, the biology of sialic acids may be viewed from their dual role, that is that they either mask recognition sites, or, in contrast, represent a biological target, allowing recognition by a receptor protein, a lectin, thus representing a ligand or counter-receptor (Fig. 2) [19,33,34]. The latter role may be again modulated or even abolished by sialic acid substituents, most effectively by O-acetyl groups. These multiple possibilities make thorough understanding of the sialic acids difficult. This is even more pronounced, since the environment of these monosaccharides and the nature of the molecule to which they are bound may influence the biological effects. However, the present knowledge in
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Fig. 2. The dual role of sialic acids. Association and dissociation of cells are regulated by the loss and restoration of sialic acids by the action of sialidases and sialyltransferases, respectively. Only after the demasking of a sufficient number of galactose residues (a ‘‘cluster’’) attachment to another cell via galactose-recognizing receptors is possible. O-Acetyl groups may inhibit the enzymatic release of sialic acids or the interaction of these monosaccharides with sialic acid-recognizing receptors, e.g., siglecs. These ester groups are incorporated by sialate-O-acetyltransferases into the sialic acid side chain or the pyranose ring and can be removed by specific esterases. The O-acetylation of sialic acids can mask ligand functions of sialic acids or make a masking sialic acid residue available for binding of, for example, viruses and lectins. Other sialic acid modifications, such as N acetyl hydroxylation (Neu5Gc), may also modify the masking or ligand function. Examples are given in the text.
this area allows the prediction of biological events, if the amount of sialic acids on cells increases or decreases, or if the nature of sialic acids, typical for a given cell or tissue, changes. In the following, drawing from our own experience, some light will be shed on this situation, showing that sialic acids are ideal mediators of finetuning of cell behavior. With regard to the more general effects, due to their negative charge, sialic acids are involved in the binding and transport of positively charged molecules including pharmaceuticals as well as in the attraction and repulsion of cells and molecules [6,34]. An example for repulsion are erythrocytes in the bloodstream. In this way, as components of glycoproteins, sialic acids contribute to the high viscosity of mucins lining and protecting endothelia, for instance in the intestine or on the surface of fish or of frog eggs. Similarly, they influence the conformation of, for example, gangliosides and contribute to the supramolecular structures in cell membranes, thus influencing the functions of the membrane components, such as ion channels or hormone receptors.
These physico-chemical properties of sialic acids may be modulated by hydrophobic substituents such as O-acetyl or O-methyl groups or by hydroxylation of the N -acetyl moiety. By sulfation, as observed in echinoderms, a very acidic sialic acid is produced. The negative charge of these sugars also contributes to their anti-proteolytic effect in glycoproteins and also hinders the action of some endoglycosidases [6]. The anti-recognition effects of sialic acids are explained by the negative charge in combination with the bulky, hydrophilic molecule. This is a very important research field comprising the masking of the penultimate sugars which nature has designated to be recognized by receptors, such as galactose, or the shielding of antigenic sites in macromolecules soluble or bound to cell membranes [34]. Desialylation, in the first case, leads to recognition by galactose-specific lectins and, in the second case, to recognition of macromolecules and cells by the complement or immune system. The purpose of the first effect is to target molecules and cells to specific sites, often to promote degradation, which may be of physiological or pathological
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importance. The first reported and very stimulating example for this phenomenon was the disturbance of the homing of lymphocytes after glycosidase treatment [1] and the uptake of desialylated serum glycoproteins by hepatocytes [5] as discussed in Introduction. A similar function was observed on the interaction between liver, spleen, and peritoneal macrophages and erythrocytes, first observed with human red blood cells [35,36] which had lost part of their surface sialic acids (1– 2 107 molecules/cell). After sialidase treatment of
Fig. 3. Survival of chromium-labelled human erythrocytes in circulation after sialidase treatment (half-life time about 2 h). C, control experiment; S, sialidase-treated erythrocytes. (From [36]; with permission of the publishers, Walter de Gruyter, Berlin).
mammalian erythrocytes and reinjection, most of the modified cells disappear from the bloodstream within a few hours, although their normal survival time in human is about 120 days (Fig. 3). They are phagocytosed by liver Kupffer cells and spleen macrophages as was studied with rabbits in vivo (Fig. 4) [37,38]. Sialidasetreated thrombocytes experience the same fate, as studied with rat peritoneal macrophages and autologous blood platelets [39]. Sialidase-treated lymphocytes also attach to macrophages by this mechanism, however, they are not engulfed but are released after about one day incubation probably due to resialylation of the cell surface (Fig. 5) [40]. This explains why T-lymphocytes that mediate delayed-type hypersensitivity to sheep red blood cells in mice did not immigrate sites of antigen deposition but accumulated in liver after sialidase or periodate treatment of the lymphocytes [41]. Trapping of lymphocytes in liver was transient and they were released after 24 h showing restored immunological activity. These experiments were in accordance with and extended the earlier observations by Gesner and Ginsburg [1] and by Woodruff and Gesner [42]. On these blood cells sialic acid is bound to galactose or N -acetylgalactosamine, which can be recognized by corresponding lectins after the enzymatic release of the sialic acid moieties. The red blood cells bind via their demasked galactose residues to a galactose-specific receptor of phagocytes and ultimately are taken up and degraded [43]. Correspondingly, trapping of sialidasetreated erythrocytes can be inhibited by galactose or more efficiently by galactosides [43,44]. This mechanism can work without the involvement of immunoglobulin or complement and appears to be involved in the sequestration process of aged red cells (reviewed in [44]).
Fig. 4. Binding of sialidase-treated rabbit erythrocytes to liver Kupffer cells in vivo. The scanning electron micrograph is taken from [37] with permission by Springer-Verlag.
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Fig. 5. Interaction between sialidase-treated rat lymphocytes (L) and homologous peritoneal macrophages in vitro. The firm attachment of the lymphocyte membranes to the macrophage surface and the beginning of encirclement of the lymphocytes are visible (from [92], modified).
It was demonstrated that old erythrocytes expose more galactose residues than younger cells [45]. In human 3–5 million red blood cells are phagocytosed per second [44]. The galactose-recognizing receptor, belonging to the C-type lectins, responsible for the binding of blood cells was isolated from rat peritoneal macrophages by Kelm and Schauer [46] and represented one of the first characterized mammalian galactose receptors after the hepatocyte receptor. Since then large gene families encoding for the galectins and other proteins recognizing galactose were found in microorganisms, plants, and animals [34,47,48]. The molecular characterization of the rat Kupffer cell glycoprotein receptor has been reported [49]. Malignant cells can also be eliminated in this way by macrophages, and it is understandable that oversialylation, often observed in such cells, protects them from humoral and cellular defense systems and thus increases their malignancy. The strategy to increase sialylation
over physiological levels has been used to create a ‘‘hyper-erythropoietin’’ by insertion of more glycosylation sites which exhibits better pharmacokinetic properties due to an extended life-time in blood serum [50]. In this regard, polysialic acids (PSA) found on some bacteria and on mammalian cells are strongly antiadhesive thus regulating cell adhesion and cellular movements (see 19,51] for reviews). PSA enhance virulence in, e.g., Escherichia coli and in higher animals play a crucial role in development, especially of neuronal tissues and are involved in the maintenance of neuronal plasticity. They also facilitate tumor growth and spreading. Sialylation of microorganisms follows a similar strategy, allowing better survival in the host organisms and thus enhancing virulence. This can be achieved in different ways, such as total synthesis of sialic acids and sometimes their polymeric form, colominic acid, in E. coli strains, the acquisition of sialic acids from the host with the aid of trans-sialidases in some trypanosomal
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strains or the transfer of sialic acids from CMP-glycoside from the host by a sialyltransferase expressed by the pathogenic bacterium, for example gonococci [52,53]. Similar to the binding of blood cells after demasking of their galactose residues, many, and often pathogenic, bacteria attach to mucous endothelia via galactose-recognizing lectins, for example, the oro-gastro-intestinal tract after desialylation of the endothelial cells and exposure of penultimate galactose residues [34]. Such bacteria secrete sialidase which removes the protecting sialic acid moieties and can thus be considered as spreading or virulence factor. Many efforts are presently undertaken to synthesize inhibitors of this glycosidase or soluble ligands to prevent adhesion. A second group of examples for the masking effect of sialic acid is the production of auto-antibodies after cell membrane desialylation by bacterial or viral sialidases. This exposure of cellular antigens may lead to chronic diseases such as glomerulonephritis [54]. Carbohydrates, including sialic acids, may be antigenic determinants, especially in gangliosides, but they more often shield antigenic sites and thus weaken the immuno-reactivity. Sialic acids render cells as ‘‘self,’’ not allowing recognition by the immune system or by, e.g., macrophage lectins. The loss of these monosaccharides makes these cells ‘‘non-self’’ and therefore vulnerable. Therefore, sialic acids can be considered as members of the innate immune system. Other acidic carbohydrates may take over this function in lower animals [55]. The work of Victor Ginsburg and his colleagues was pioneering in elucidation of the role of sialic acids as antigenic determinants. A monoclonal IgM associated with Waldenstr€ om macroglobulinemia, which binds at low temperature to sialylated glycoproteins and glycolipids of human erythrocytes was characterized in 1977 [56]. This group was the first to apply antibodies and sialic acid-binding toxins to TLC immunostaining, e.g., the detection of the ganglioside GM1 with cholera toxin [57]. This technique is still in wide use. The characterization of tumor-associated antigens presenting sialic acids as part of the immunogenic epitopes was a further important landmark. In 1981, a monosialoganglioside was recognized as an antigen of colon carcinoma [58] and one year later sialylated lacto-N -fucopentaose II, a hapten of the human Lea blood group antigen, was isolated as component of a monosialoganglioside from gastrointestinal cancer [59]. In further studies, this antigen was found to be recognized by the leucocyte adhesion molecule of endothelial cells ELAM-1 [60,61], later denominated E-selectin (see below). In contrast to masking, sialic acid molecules take part directly in a variety of recognition processes. This may be the most important role of these monosaccharides. This was first noted in microorganisms, which in most cases use cell surface carbohydrates for binding to their host cells [34,62]. Sialic acids appear to be the most
frequent ligands for pathogenic and non-pathogenic viruses, bacteria, and protozoa. The best known and longest studied example are influenza viruses. Hirst observed in 1942 [63] the binding of influenza A virus to human erythrocytes and mucins of the respiratory tract. The attachment, mediated by a viral lectin called hemagglutinin, was reversible and accompanied by the release of an acidic sugar-like substance by a viral ‘‘receptor-destroying enzyme,’’ later named neuraminidase, resp. sialidase. The infection mechanism includes binding of the virus to endothelial cells of the respiratory tract, followed by penetration, multiplication, and exocytosis of such viruses. Viral sialidase seems to facilitate the spreading of the viruses in tissues by preventing their further attachment to the cells and to mucus layers protecting epithelia of the respiratory tract. Using this knowledge it was possible to synthesize a very strong inhibitor (2,3-didehydro-2,4-dideoxy-4guanidinyl-N -acetylneuraminic acid) of the viral sialidase based on a natural sialidase inhibitor and exact knowledge of the three-dimensional structure of the enzyme [64]. This substance and derivatives thereof are active also in vivo and are being successfully used for the treatment of influenza. Many other viruses (see [34] for a review) also attach to cells via sialic acids and the number of examples is growing [65]. The most prominent ones are corona, polyoma, adenoma, and rota viruses, and on infection with HIV viruses sialylated glycans both from the virus and the cellular receptors are involved. Some viruses only recognize modified Sia such as human influenza C virus and mouse hepatitis virus, which exclusively bind to Neu5,9Ac2 [66] and Neu4,5Ac2 [67], respectively. The infectious salmon anemia virus also binds to the 4-Oacetylated sialic acid [68]. Bacteria produce carbohydrate-specific adhesins which are frequently located on their fimbriae or pili. Prominent examples for colonization via sialic acids are pathogenic bacteria such as strains of E. coli, Streptococci and Helicobacter pylori [34,62]. A very recent example is Flavobacterium psychrophilum [69]. Earlier examples, described by Victor Ginsburg and collaborators, are the sialic acid-dependent adhesion of Mycoplasma pneumoniae to glycoproteins [70] and binding of the E. coli strain K99 from piglet small intestine to Neu5Gc-containing gangliosides [71]. Especially H. pylori, often found in human stomach and responsible for gastric inflammation and possibly also cancer, is intensively studied. Mahdavi et al. [72] published the structure of its sialic acid-recognizing adhesin. Knowledge about such adhesion mechanisms enables a biologybased therapy of diseases caused, e.g., by H. pylori and may save the use of antibiotics [73]. By this alternative strategy, receptor–ligand interactions are inhibited with soluble ligands such as sialylated oligosaccharides or glycoproteins. Such oligosaccharides occur in a rela-
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tively high concentration in milk, especially the colostrum. The milk from each mammal contains different and more or less sialylated glycans [74]. These carbohydrates are considered to regulate the species-specific colonization of the intestine with microorganisms and to hinder the attachment of pathogenic bacteria such as E. coli and Helicobacter strains or pathogenic viruses, for example rota viruses, which is most important in newborns. Correspondingly, the application of sialo-oligosaccharides in soluble forms or as dendritic polymers is a new strategy to fight microbial infections [75–77]. It should be noted that a high sialic acid content in human milk, especially in the first days after birth, was shown to increase the sialic acid content of brain gangliosides in rat and human and is discussed to promote higher permanently intelligence [78]. Also bacterial toxins, such as cholera, tetanus, and diphtheria toxin, firmly adhere to sialic acids, mostly of gangliosides, as basis of their pathophysiological activity ([57], and summarized in [34]). A variety of sialic acid-recognizing lectins were isolated from plants and lower animals (reviewed in [34,47,48,79]). They are assumed to be involved in mechanisms of innate immunity. Some evidence that sialic acids are recognized not only by microorganisms, plants, and lower animals, but also by mammalian receptor proteins was obtained by Lee et al. [80]. When we studied the interaction of the galactose-recognizing receptor from rat peritoneal macrophages with ligands containing terminal galactose residues such as desialylated blood cells or glycoproteins, we observed that this interaction can specifically be inhibited by Neu5Ac. An allosteric influence of sialic acid on the binding of galactose by the receptor was discussed. Shortly thereafter, Paul Crocker, Jim Paulson, and Sørge Kelm, one of the authors of this publication by Lee et al. [80] and collaborators, obtained firm evidence that sialic acids are directly involved in recognition processes by functioning as ligands also in animals. A sialic acid-binding receptor was discovered in murine bone marrow cells and called ‘‘sialoadhesin’’ [81]. It is a member of the ‘‘siglecs,’’ which belong to the immunoglobulin superfamily (IgSF) with repeating extracellular domains of variable length, of which 11 members were discovered in the past few years due to the increased availability of expressed sequence tags (EST) and genomic DNA sequences [34,82]. The first well-characterized species are the macrophage sialoadhesin, involved in binding and nursing of maturing blood cells, the CD22 on B-lymphocytes, responsible for the ‘‘cross-talk’’ of these cells with Tlymphocytes, and the myelin-associated-glycoprotein (MAG) on oligodendrocytes and Schwann cells, participating in the growth and myelination of neurites. Most of the other siglecs are involved in the regulation of recognition phenomena of various white blood cell types and macrophages and thus are regulators of the
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immune system (see [83–85]). They also vary in the recognition of different sialic acids and can distinguish glycosidic linkages. For example, sialoadhesin and MAG only bind to a2,3-linked sialic acids, while CD22 recognizes a2,6-bonds. While N -acetyl hydroxylation (Neu5Gc) can modify the affinity, sialic acid-O-acetylation (Neu5,9Ac2 ) abolishes it [34]. Another group of mammalian sialic acid-recognizing lectins are the selectins found on endothelial cells, which also possess repeating domains (for reviews see [34,86]). They participate in the initial stage of adhesion of white blood cells to endothelia, along which they begin to roll and eventually penetrate into the tissue below, which may be damaged by the lack of oxygen, in, for example, transplants or infarcts, or which are inflamed. Cytokines play here an essential role. Selectins preferably recognize sialylated Lewis structures (Sia-Lex ), a tetrasaccharide, which is bound to glycoproteins or glycolipids. Since these oligosaccharide moieties also occur on tumor cells [87–89], selectins can be involved in the formation of metastases. To avoid further tissue damage by evading lymphocytes or to prevent metastasis of tumors, great efforts are being undertaken to prevent cell adhesion to endothelia by the application of either selectin antibodies or Sia-Lex analogues. Since sialic acids are involved in such a wealth of biological phenomena, change of their concentration or of their chemical structure may alter the biology of cells. This has a great impact in fertilization, development and tumorigenesis, immunological reactions, life-time of cells including apoptosis, transmembrane signalling events, microbial and non-microbial inflammations, and many other cell biological and pathological events. Sialic acids seem to be indispensable for the life of higher organisms, since inhibition of their biosynthesis during early development of mice is lethal, as was shown by inactivation of UDP-N -acetylglucosamine-2-epimerase/ N -acetylmannosamine kinase, the key enzyme of sialic acid biosynthesis [90]. The main role of sialic acids with their outstanding position on molecules and cells and their chemical diversity seems to be the fine-tuning of a multitude of cellular events which may be explained by the capacity of sialic acids to regulate molecular interactions. We are grateful to Victor Ginsburg and colleagues for having opened the gate to study these special functions of carbohydrates.
References [1] B.M. Gesner, V. Ginsburg, Proc. Natl. Acad. Sci. USA 52 (1964) 750–755. [2] E. Margoliash, J.R. Schenck, M.P. Hargie, S. Burokas, W.R. Richter, G.H. Barlow, A.A. Moscona, Biochem. Biophys. Res. Commun. 20 (1965) 383–388. [3] A.G. Morell, G. Gregoriadis, I.H. Scheinberg, J. Hickman, G. Ashwell, J. Biol. Chem. 246 (1971) 1461–1467.
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[4] G. Ashwell, A.G. Morell, Adv. Enzymol. 41 (1974) 99–128. [5] C. Traving, R. Schauer, Cell. Mol. Life Sci. 54 (1998) 1330–1349. [6] R. Schauer, J.P. Kamerling, in: J. Montreuil, J.F.G. Vliegenthart, H. Schachter (Eds.), Glycoproteins II, Elsevier Science, Amsterdam, 1997, pp. 243–402. [7] A. Varki, Glycobiology 2 (1992) 25–40. [8] R. Schauer, Trends Glycosci. Glycotechnol. 13 (2001) 507–517. [9] M.M. Shah, K. Fujiyama, C.R. Flynn, L. Joshi, Nat. Biotechnol. 21 (2003) 1470–1471. [10] A. Varki, R. Cummings, J. Esko, H. Freeze, G. Hart, J. Marth (Eds.), Essentials of Glycobiology, Cold Spring Harbor, New York, 1999. [11] R. Schauer, Glycoconjugate J. 17 (2000) 485–499. [12] R. Schauer, in: B. Ernst, G.W. Hart, P. Sina€y, (Eds.), Carbohydrates in Chemistry and Biology. Part II. Biology of Saccharides, vol. 3, Wiley-VCH, Weinheim, 2000, pp. 227–243. [13] A.P. Corfield, R. Schauer, in: R. Schauer (Ed.), Sialic Acids— Chemistry, Metabolism and Function, Springer, Wien, New York, 1982, pp. 5–50. [14] C.S. Alviano, L.R. Travassos, R. Schauer, Glycoconjugate J. 16 (1999) 545–554. [15] J.-P. Zanetta, A. Pons, M. Iwersen, C. Mariller, Y. Leroy, P. Timmerman, R. Schauer, Glycobiology 11 (2001) 663–676. [16] T. Angata, A. Varki, Chem. Rev. 102 (2002) 439–469. [17] D. Nadano, M. Iwasaki, S. Endo, K. Kitajima, S. Inoue, Y. Inoue, J. Biol. Chem. 261 (1986) 11550–11557. [18] Y.-T. Li, K. Maskos, C.-W. Chou, R.B. Cole, S.-C. Li, J. Biol. Chem. 278 (2003) 35286–35291. [19] M. M€ uhlenhoff, M. Eckhardt, R. Gerardy-Schahn, Curr. Opin. Struct. Biol. 8 (1998) 558–564. [20] A.P. Corfield, R. Schauer, in: R. Schauer (Ed.), Sialic Acids— Chemistry, Metabolism and Function, Springer, Wien, New York, 1982, pp. 195–261. [21] Y.N. Malykh, R. Schauer, L. Shaw, Biochimie 83 (2001) 623– 4634. [22] P. Tangvoranuntakul, P. Gagneux, S. Diaz, M. Bardor, N. Varki, A. Varki, E. Muchmore, Proc. Natl. Acad. Sci. USA 100 (2003) 12045–12050. [23] W. Schlenzka, L. Shaw, R. Schauer, Glycobiology 4 (1994) 675– 683. [24] I. Martensen, R. Schauer, L. Shaw, Eur. J. Biochem. 268 (2001) 5157–5166. [25] A. Irie, S. Koyama, Y. Kozutsumi, T. Kawasaki, A. Suzuki, J. Biol. Chem. 273 (1998) 15866–15871. [26] R. Schauer, H. Schmid, J. Pommerencke, M. Iwersen, G. Kohla, in: A.M. Wu (Ed.), The Molecular Immunology of Complex Carbohydrates 2, Adv. Exp. Med. Biol., vol. 491, Kluwer Academics/Plenum Publishers, New York, 2001, pp. 325–342. [27] M. Iwersen, H. Schmid, S. Gasa, G. Kohla, R. Schauer, Biol. Chem. 384 (2003) 1035–1047. [28] W.X. Shi, R. Chammas, A. Varki, Glycobiology 8 (1998) 199–205. [29] H.H. Higa, C. Butor, S. Diaz, A. Varki, J. Biol. Chem. 264 (1989) 19427–19434. [30] J. Tiralongo, R. Schauer, Trends Glycosci. Glycotechnol. 16, 2004 (in press). [31] A. Kelm, L. Shaw, R. Schauer, G. Reuter, Eur. J. Biochem. 251 (1998) 874–884. [32] A. Klein, S. Diaz, I. Ferreira, G. Lamblin, P. Roussel, A.E. Manzi, Glycobiology 7 (1997) 421–432. [33] R. Schauer, Trends Biochem. Sci. 10 (1985) 357–360. [34] S. Kelm, R. Schauer, Int. Rev. Cytol. 175 (1997) 137–240. [35] J. Jancik, R. Schauer, Hoppe-SeylerÕs Z. Physiol. Chem. 355 (1974) 395–400. [36] J. Jancik, R. Schauer, H.-J. Streicher, Hoppe-SeylerÕs Z. Physiol. Chem. 356 (1975) 1329–1331. [37] J.M. Jancik, R. Schauer, K.H. Andres, M. von D€ uring, Cell Tissue Res. 186 (1978) 209–226.
[38] H. Kolb, C. Schudt, V. Kolb-Bachofen, H.A. Kolb, Exp. Cell Res. 113 (1978) 319–325. [39] A. Kluge, G. Reuter, H. Lee, B. Ruch-Heeger, R. Schauer, Eur. J. Cell. Biol. 59 (1992) 12–20. [40] C. Fischer, S. Kelm, B. Ruch, R. Schauer, Carbohydr. Res. 213 (1991) 263–273. [41] S.H.E. Kaufmann, R. Schauer, H. Hahn, Immunobiology 160 (1981) 184–195. [42] J.J. Woodruff, B.M. Gesner, J. Exp. Med. 129 (1969) 551–567. [43] E. M€ uller, C. Schr€ oder, R. Schauer, N. Sharon, Hoppe-SeylerÕs Z. Physiol. Chem. 364 (1983) 1419–1429. [44] D. Bratosin, J. Mazurier, J.P. Tissier, J. Estaquier, J.J. Huart, J.C. Ameisen, D. Aminoff, J. Montreuil, Biochimie 80 (1998) 173–195. [45] D. Bratosin, J. Mazurier, H. Debray, M. Lecocq, B. Boilly, C. Alonso, M. Moisei, C. Motas, J. Montreuil, Glycoconjugate J. 12 (1995) 258–267. [46] S. Kelm, R. Schauer, Biol. Chem. Hoppe-Seyler 369 (1988) 693– 704. [47] N. Sharon, H. Lis (Eds.), Lectins, second ed., Kluwer Academic Publishers, Dordrecht, 2003. [48] H.-J. Gabius, S. Gabius (Eds.), Lectins and Glycobiology, Springer, Berlin, 1993. [49] A.J. Fadden, O.J. Holt, K. Drickamer, Glycobiology 13 (2003) 529–537. [50] W. Jelkmann, Eur. J. Haematol. 69 (2002) 265–274. [51] K. Angata, M. Fukuda, Biochimie 85 (2003) 195–206. [52] L. Gao, L. Linden, N.J. Parsons, J.A. Cole, H. Smith, Microb. Pathogenesis 28 (2000) 257–266. [53] E. Vimr, C. Lichtensteiger, Trends Microbiol. 10 (2002) 254–257. [54] T. Corfield, Glycobiology 6 (1992) 509–521. [55] H. Faillard, R. Schauer, in: A. Gottschalk (Ed.), Glycoproteins— Their Composition, Structure and Function, BBA Library 5, Elsevier Publ. Company, Amsterdam, 1972, pp. 1246–1267. [56] C.M. Tsai, D.A. Zopf, R.K. Yu, R. Wistar Jr., V. Ginsburg, Proc. Natl. Acad. Sci. USA 74 (1977) 4591–4594. [57] J.L. Magnani, D.F. Smith, V. Ginsburg, Anal. Biochem. 109 (1980) 399–402. [58] J.L. Magnani, M. Brockhaus, D.F. Smith, V. Ginsburg, M. Blaszczyk, K.F. Mitchell, Z. Steplewski, H. Koprowski, Science 212 (1981) 55–56. [59] J.L. Magnani, B. Nilsson, M. Brockhaus, D. Zopf, Z. Steplewski, H. Koprowski, V. Ginsburg, J. Biol. Chem. 257 (1982) 14365– 14369. [60] E.L. Berg, M.K. Robinson, O. Mansson, E.C. Butcher, J.L. Magnani, J. Biol. Chem. 266 (1991) 14869–14872. [61] A. Takada, K. Ohmori, N. Takahashi, K. Tsuyuoka, A. Yago, K. Zenita, A. Hasegawa, R. Kannagi, Biochem. Biophys. Res. Commun. 179 (1991) 713–719. [62] I. Ofek, J. Doyle (Eds.), Bacterial Adhesion to Cells and Tissues, Chapman & Hall, New York, 1994. [63] G.K. Hirst, J. Exp. Med. 76 (1942) 195–209. [64] M. von Itzstein, W.-Y. Wu, B. Jin, Carbohydr. Res. 259 (1994) 301–305. [65] B. Tsai, J.M. Gilbert, T. Stehle, W. Lencer, T.L. Benjamin, T.A. Rapoport, EMBO J. 22 (2003) 4346–4355. [66] G. Herrler, G. Reuter, R. Rott, H.-D. Klenk, R. Schauer, Biol. Chem. Hoppe-Seyler 368 (1987) 451–454. [67] G. Regl, A. Kaser, M. Iwersen, H. Schmid, G. Kohla, B. Strobl, U. Vilas, R. Schauer, R. Vlasak, J. Virol. 73 (1999) 4721–4727. [68] A. Hellebø, U. Vilas, K. Falk, R. Vlasak, J. Virol., 78 (2004) 3055–3062. [69] J.D. Møller, J.L. Larsen, L. Madsen, I. Dalsgaard, Appl. Environ. Microbiol. 69 (2003) 5275–5280. [70] D.D. Roberts, L.D. Olson, M.F. Barile, V. Ginsburg, H.C. Krivan, J. Biol. Chem. 264 (1989) 9289–9293. [71] M. Kyogashima, V. Ginsburg, H.C. Krivan, Arch. Biochem. Biophys. 270 (1989) 391–397.
R. Schauer / Archives of Biochemistry and Biophysics 426 (2004) 132–141 [72] J. Mahdavi, B. Sonden, M. Hurtig, F.O. Olfat, L. Forsberg, N. Roche, J. Angstr€ om, T. Larsson, S. Teneberg, K.-A. Karlsson, S. Altraja, T. Wadstr€ om, D. Kersulyte, D.E. Berg, A. Dubois, C. Petersson, K.-E. Magnusson, T. Norberg, F. Lindh, B.B. Lundskog, A. Arnqvist, L. Hammarstr€ om, T. Boren, Science 297 (2002) 573–578. [73] M. Gerhard, S. Hirmo, T. Wadstr€ om, H. Miller-Podraza, S. Teneberg, K.-A. Karlsson, B. Appelmelk, S. Odenbreit, R. Haas, A. Arnqvist, T. Boren, in: S. Suerbaum (Ed.), Helicobacter pylori: Molecular and Cellular Biology, Horizon Scientific Press, Wymondham, UK, 2001, pp. 185–206. [74] W. Sumiyoshi, T. Urashima, T. Nakamura, I. Arai, T. Saito, N. Tsumura, B. Wang, J. Brand-Miller, Y. Watanabe, K. Kimura, Brit. J. Nutr. 89 (2003) 61–69. [75] T. Urashima, T. Saito, T. Nakamura, M. Messer, Glycoconjugate J. 18 (2001) 357–371. [76] J.J. Landers, Z. Cao, I. Lee, L.T. Piehler, P.P. Myc, A. Myc, T. Hamouda, A.T. Galecki, J.R. Baker Jr., J. Infect. Diseases 186 (2002) 1222–1230. [77] A. Kobata, Chang Gung Med. J. 26 (2003) 620–635. [78] B. Wang, J. Brand-Miller, Eur. J. Clin. Nutr. 57 (2003) 1351– 1369. [79] A. Varki, FASEB J. 11 (1997) 248–255. [80] H. Lee, S. Kelm, J.-C. Michalski, R. Schauer, Biol. Chem. HoppeSeyler 371 (1990) 307–316.
141
[81] P.R. Crocker, S. Kelm, C. Dubois, B. Martin, A.S. McWilliam, D.M. Shotton, J.C. Paulson, S. Gordon, EMBO J. 10 (1991) 1661–1669. [82] T. Angata, E.C.M. Brinkman-Van der Linden, Biochim. Biophys. Acta 1572 (2002) 294–316. [83] P.R. Crocker, A. Varki, Trends Immunol. 22 (2001) 337–342. [84] H. Aizawa, N. Zimmermann, P.E. Carrigan, J.J. Lee, M.E. Rothenberg, B.S. Bochner, Genomics 82 (2003) 521–530. [85] A. Bhunia, V. Jayalakshmi, A.J. Benie, O. Schuster, S. Kelm, N. Rama Krishna, T. Peters, Carbohydr. Res. 339 (2004) 259–267. [86] R. Kannagi, Curr. Opin. Struct. Biol. 12 (2002) 599–608. [87] Y.J. Kim, L. Borsig, N.M. Varki, A. Varki, Proc. Natl. Acad. Sci. USA 95 (1998) 9325–9330. [88] P. Grabowski, B. Mann, U. Mansmann, N. L€ ovin, H.-D. Foss, G. Berger, H. Scher€ ubl, E.-O. Riecken, H.-J. Buhr, C. Hanski, Int. J. Cancer 88 (2000) 281–286. [89] L. Borsig, R. Wong, J. Feramisco, D.R. Nadeau, N.M. Varki, A. Varki, Proc. Natl. Acad. Sci. USA 98 (2001) 3352–3357. [90] M. Schwarzkopf, K.-P. Knobeloch, E. Rohde, S. Hinderlich, N. Wiechens, L. Lucka, I. Horak, W. Reutter, R. Horstkorte, Proc. Natl. Acad. Sci. USA 99 (2002) 5267–5270. [91] Y.-T. Li, K. Maskos, C.-W. Chou, R.B. Cole, S.-C. Li, J. Biol. Chem. 278 (2003) 35286–35291. [92] S.e-D. Jibril, B. von Gaudecker, S. Kelm, R. Schauer, Biol. Chem. Hoppe-Seyler 368 (1987) 819–829.
Minireview
Victor GinsburgÕs influence on my research of the role of sialic acids in biological recognitionq Roland Schauer* Biochemisches Institut, Christian-Albrechts-Universit€at, Olshausenstr. 40, Kiel D-24098, Germany Received 5 January 2004, and in revised form 27 February 2004 Available online 12 April 2004
Abstract Sialic acids are monosaccharides with relatively strong acidity which belong to the most important molecules of higher animals and also occur in some microorganisms. They are bound to complex carbohydrates and occupy prominent positions, especially in cell membranes. Their structural diversity is high and, correspondingly, the mechanisms for their biosynthesis complex. Sialic acids are involved in a great number of cell functions. Due to their cell surface location these acidic molecules shield macromolecules and cells from enzymatic and immunological attacks and thus contribute to innate immunity. In contrast to this masking role, enabling, for example, blood cells and serum glycoproteins a longer life-time, sialic acids also represent recognition sites for various physiological receptors, such as the selectins and siglecs, as well as for toxins and microorganisms and thus allow their colonization. The recognition function of sialic acids can again be masked by O-acetylation, which modifies the interaction with receptors. Many viruses use sialic acids for the infection of cells. As sialic acids play also a decisive role in tumor biology, they prove to be rather versatile molecules that modulate biological and pathological cellular events in a sensitive way. Thus, they are most prominent representatives of mediators of molecular and cellular recognition. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Sialic acids; Chemical variety; N-Acetyl hydroxylation; O-acetylation; Masking effect; Ligand function; Cellular communication; Bacterial and viral adhesion; Innate immunity
Although carbohydrates have been known for long not only in the form of starch or glucose as primary source of energy, but as components of cell membranes forming a thick coat called glycocalyx, their biological role was not understood. Victor Ginsburg and colleagues made the pioneering observation that cell surface carbohydrates play a crucial role in the interaction of cells: the behavior of rat lymphocytes in the circulation changed dramatically after treatment with fucosidase or sialidase. The white blood cells accumulated in the liver instead of the spleen and lymph nodes [1]. It was believed that the carbohydrate residues may play a role in the recognition of lymphocytes by cells lining the q
Based on a lecture delivered at the Symposium on Glycobiology, dedicated to the Memory of Dr. Victor Ginsburg, NIH, Bethesda, MD, November 10, 2003. * Fax: +49-431-8802238. E-mail address: [email protected]. 0003-9861/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.abb.2004.03.008
capillary vessels as well as in controlling the passage of the lymphocytes from blood into lymphoid tissue. The group of Moscona discovered that the substances involved in the aggregation of sponge cells are glycoproteins and that species-specific aggregation may depend on the carbohydrate moiety of these cell surface glycoproteins [2]. Another milestone in the elucidation of the role of protein-bound carbohydrates was the observation made by Morell et al. [3] that desialylation of serum glycoproteins leads to binding and endocytosis of these macromolecules by hepatocytes. The reason was the exposure of galactose residues by sialidase treatment followed by recognition of these subterminal monosaccharides by a galactose receptor [4]. I had started my research work in the laboratory of Hans Faillard at the newly founded Ruhr-University of Bochum in March 1967 and focussed first on the isolation and analysis of different types of sialic acids including their susceptibility to sialidase and lyase action.
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Later on we discovered the enzymes hydroxylating the N-acetyl group of N-acetylneuraminic acid (Neu5Ac) yielding N-glycolylneuraminic acid (Neu5Gc) or Oacetylating these sialic acids at the pyranose ring or the sialic acid glycerol side chain (reviewed in [5,6]). Stimulated by the discoveries cited above which showed the involvement of glycans in molecular and cellular interactions, we became interested in the biological role of sialic acids positioned on the outer surface of the cell coat in high density. Furthermore, we addressed the question: Why are there so many different kinds of sialic acids?
The diversity of sialic acids Sialic acids are derivatives of neuraminic acid (5-amino-3,5-dideoxy-D -glycero-D -galacto-2-nonulopyranosonic acid) and occur in higher animals and some microorganisms [6,7]. They have also been found in developing insects [8] and a recent report demonstrates their expression in cell cultures from Arabidopsis thaliana [9]. They contribute to the impressive structural diversity of complex carbohydrates which are major constitutents mostly of proteins and lipids of cell membranes and secreted macromolecules [10]. Sialic acids are prominently positioned usually at the outer end of these molecules. The diversity of glycan chains is much increased by the biosynthesis of various kinds of sialic acids [11,12], thus potentiating the complexity of the ‘‘third language of life’’ represented by glycoconjugates. About 50 members of this unique monosaccharide family have been identified. They carry various substituents at the amino or hydroxyl groups (Fig. 1) [6,7,11– 16]. The amino group of neuraminic acid is acetylated or glycolylated, while at all non-glycosidic hydroxyl residues one or various acetyl groups may occur. Usually, there is only one O-acetyl group, mostly at O-9, but diand tri-O-acetylated sialic acids are known, especially in mucins from bovine submandibular gland and human colon [13]. At O-9 lactyl or phosphoryl residues and at O-8 methyl or sulfate groups can occur. All these different substituents may be combined, e.g., 8-O-methyl with 9-O-acetyl and N-glycolyl, yielding the manifold types of sialic acids found throughout the animal kingdom. Besides these sialic acids in various biological sources unsaturated sialic acids as well as anhydro- and lactone forms have been identified. 5-Desamino-5-hydroxy-neuraminic acid or 2-keto-3-deoxy-nononic acid (Kdn)1 [17] is increasingly detected in microorganisms and animals. Neuraminic acid itself (Neu), the de-Nacetylated product of Neu5Ac, is a further component of mammalian glycoconjugates. The sialic acid most 1
Abbreviations used: Kdn, 2-keto-3-deoxy-nononic acid; PSA, polysialic acids; IgSF, Immunoglobulin superfamily; EST, expressed sequence tags; MAG, myelin-associated-glycoprotein.
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recently discovered is the 1-tauryl derivative of Neu5Ac, isolated from the brain of patients suffering from TaySachs disease [18]. The sialic acids, except unsaturated sialic acids (2deoxy-2,3-didehydro sialic acids) and N -acetylneuraminic acid-9-phosphate (Neu5Ac9P), usually occur in glycosidic linkages of oligosaccharides, polysaccharides (polysialic acids), glycoproteins, gangliosides, and lipopolysaccharides [6,7,13,19]. Neu5Ac9P is an intermediate in sialic acid biosynthesis [20]. Neu5Ac, Neu5Gc, and N -acetyl-9-O-acetylneuraminic acid (Neu5,9Ac2 ) are the three most frequently occurring members of the sialic acid family. Only Neu5Ac is ubiquitous, while the others are not found in all species. The best investigated example next to Neu5Ac is Neu5Gc, which is found often in animals including the great apes, but not in healthy human tissues in significant quantities, with the exception of some tumors [21,22]. It was not detected in bacteria, but in Arabidopsis cells, as mentioned [9]. Neu5Gc is formed from CMP-Neu5Ac by a cytosolic hydroxylase which requires several electron-transferring cofactors and oxygen [21]. The enzyme has been isolated from starfish and various mammals and their primary structures were elucidated, showing that it is highly conserved in the deuterostome branch [23,24]. Man has lost Neu5Gc expression due to a gene mutation [25]. The small amount of Neu5Gc found in some tumors is discussed to be derived from the diet or it may be due to an unknown alternative biosynthetic pathway [21,22]. O-acetylated sialic acids are widespread, too. Sialic acids O-acetylated at the side-chain, mainly at C-9, are most predominant in animals from the echinoderms onwards, in human and in some bacteria, while 4-Oacetylation seems to be randomly occurring in individual species throughout the animal kingdom from echidnas to the horse [6,7,12,26]. The subcellular site and mechanism of O-acetylation of sialic acids seem to be more complex than the biosynthesis of Neu5Gc and resisted full elucidation. The enzymes involved, the acetyl-CoA:sialate-4-O-acetyltransferase and the corresponding 7(9)-O-acetyltransferase, are firmly attached to the Golgi membranes and were only recently solubilized by detergents and partially purified from bovine submandibular gland (Lrhorfi et al., unpublished) and guinea-pig liver [27]. Although the substrate specificities and kinetic properties of these enzymes have been studied, knowledge about their structural properties is scant, and expression cloning and mutagenesis experiments have failed to reveal the gene structures [28]. With regard to the mechanism of sialate O-acetylation a hypothesis has been developed that in a protein complex the CMP-Neu5Ac transporter, the O-acetyltransferases esterifying CMP-Neu5Ac, and the sialyltransferases transferring the O-acetylated product to nascent glycoconjugates are cooperating in the Golgi apparatus,
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Fig. 1. The family of naturally occurring sialic acids. The nomenclature, abbreviations, and references are listed in [6,16,91]. The residues on the neuraminic acid (Neu) molecule may be combined depending on the species or tissues. For further details and distribution see the text.
perhaps by inclusion of an acetylated intermediate [29,30]. Nothing is known of the enzymology and molecular biology of the enzymes involved in 9-O-lactylation and 8-O-sulfation of sialic acids [12]. While the former modification is ubiquitous, found also in human and best studied in trout liver, the latter seems to be restricted to some starfish species [6]. Only the enzyme for 8-O-methylation, which is bound to subcellular membranes, has been solubilized and isolated from the gonades of Asterias rubens [31]. Only in echinoderms, best studied in A. rubens, larger amounts of 8-Omethylated sialic acids are found. The occurrence of minor quantities of this sialic acid, as well as of 8-Osulfated species, in mucins of higher animals was reported [15]. Never have all kinds of sialic acids been found in one cell or organism. The distribution depends on the animal and cell species as well as on the function of a cell and seems to be strongly regulated on the gene level. In submandibular gland mucin of cow, 15 species of sialic acids were detected, most of them being Oacetylated in the sialic acid side-chain, but also 9-Olactylated as well as N-acetylated or N-glycolylated [6,32]. In human the number of sialic acid types is smaller, with Neu5Ac prevailing and followed by derivatives O-acetylated and O-lactylated at the sialic acid side chain. Rich sources of different sialic acids are the echinoderms [6].
The significance of sialic acids in molecular and cellular interactions The external position of sialic acids on glycoproteins and gangliosides, either alone or in oligo- or polymeric form, and correspondingly on the outer cell membranes implies a strong influence in cell biology. These acidic monosaccharides can most easily interact with the components of other cell surfaces, extracellular substances, and effector molecules. Evidence is increasing that they are involved in a multiplicity of cell signalling events. When considering their functions, sialic acids may be divided into more general classes, irrespective of the variability of their structures, and into those exerted by chemical modifications of these acidic monosaccharides [6,7]. Also, the biology of sialic acids may be viewed from their dual role, that is that they either mask recognition sites, or, in contrast, represent a biological target, allowing recognition by a receptor protein, a lectin, thus representing a ligand or counter-receptor (Fig. 2) [19,33,34]. The latter role may be again modulated or even abolished by sialic acid substituents, most effectively by O-acetyl groups. These multiple possibilities make thorough understanding of the sialic acids difficult. This is even more pronounced, since the environment of these monosaccharides and the nature of the molecule to which they are bound may influence the biological effects. However, the present knowledge in
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Fig. 2. The dual role of sialic acids. Association and dissociation of cells are regulated by the loss and restoration of sialic acids by the action of sialidases and sialyltransferases, respectively. Only after the demasking of a sufficient number of galactose residues (a ‘‘cluster’’) attachment to another cell via galactose-recognizing receptors is possible. O-Acetyl groups may inhibit the enzymatic release of sialic acids or the interaction of these monosaccharides with sialic acid-recognizing receptors, e.g., siglecs. These ester groups are incorporated by sialate-O-acetyltransferases into the sialic acid side chain or the pyranose ring and can be removed by specific esterases. The O-acetylation of sialic acids can mask ligand functions of sialic acids or make a masking sialic acid residue available for binding of, for example, viruses and lectins. Other sialic acid modifications, such as N acetyl hydroxylation (Neu5Gc), may also modify the masking or ligand function. Examples are given in the text.
this area allows the prediction of biological events, if the amount of sialic acids on cells increases or decreases, or if the nature of sialic acids, typical for a given cell or tissue, changes. In the following, drawing from our own experience, some light will be shed on this situation, showing that sialic acids are ideal mediators of finetuning of cell behavior. With regard to the more general effects, due to their negative charge, sialic acids are involved in the binding and transport of positively charged molecules including pharmaceuticals as well as in the attraction and repulsion of cells and molecules [6,34]. An example for repulsion are erythrocytes in the bloodstream. In this way, as components of glycoproteins, sialic acids contribute to the high viscosity of mucins lining and protecting endothelia, for instance in the intestine or on the surface of fish or of frog eggs. Similarly, they influence the conformation of, for example, gangliosides and contribute to the supramolecular structures in cell membranes, thus influencing the functions of the membrane components, such as ion channels or hormone receptors.
These physico-chemical properties of sialic acids may be modulated by hydrophobic substituents such as O-acetyl or O-methyl groups or by hydroxylation of the N -acetyl moiety. By sulfation, as observed in echinoderms, a very acidic sialic acid is produced. The negative charge of these sugars also contributes to their anti-proteolytic effect in glycoproteins and also hinders the action of some endoglycosidases [6]. The anti-recognition effects of sialic acids are explained by the negative charge in combination with the bulky, hydrophilic molecule. This is a very important research field comprising the masking of the penultimate sugars which nature has designated to be recognized by receptors, such as galactose, or the shielding of antigenic sites in macromolecules soluble or bound to cell membranes [34]. Desialylation, in the first case, leads to recognition by galactose-specific lectins and, in the second case, to recognition of macromolecules and cells by the complement or immune system. The purpose of the first effect is to target molecules and cells to specific sites, often to promote degradation, which may be of physiological or pathological
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importance. The first reported and very stimulating example for this phenomenon was the disturbance of the homing of lymphocytes after glycosidase treatment [1] and the uptake of desialylated serum glycoproteins by hepatocytes [5] as discussed in Introduction. A similar function was observed on the interaction between liver, spleen, and peritoneal macrophages and erythrocytes, first observed with human red blood cells [35,36] which had lost part of their surface sialic acids (1– 2 107 molecules/cell). After sialidase treatment of
Fig. 3. Survival of chromium-labelled human erythrocytes in circulation after sialidase treatment (half-life time about 2 h). C, control experiment; S, sialidase-treated erythrocytes. (From [36]; with permission of the publishers, Walter de Gruyter, Berlin).
mammalian erythrocytes and reinjection, most of the modified cells disappear from the bloodstream within a few hours, although their normal survival time in human is about 120 days (Fig. 3). They are phagocytosed by liver Kupffer cells and spleen macrophages as was studied with rabbits in vivo (Fig. 4) [37,38]. Sialidasetreated thrombocytes experience the same fate, as studied with rat peritoneal macrophages and autologous blood platelets [39]. Sialidase-treated lymphocytes also attach to macrophages by this mechanism, however, they are not engulfed but are released after about one day incubation probably due to resialylation of the cell surface (Fig. 5) [40]. This explains why T-lymphocytes that mediate delayed-type hypersensitivity to sheep red blood cells in mice did not immigrate sites of antigen deposition but accumulated in liver after sialidase or periodate treatment of the lymphocytes [41]. Trapping of lymphocytes in liver was transient and they were released after 24 h showing restored immunological activity. These experiments were in accordance with and extended the earlier observations by Gesner and Ginsburg [1] and by Woodruff and Gesner [42]. On these blood cells sialic acid is bound to galactose or N -acetylgalactosamine, which can be recognized by corresponding lectins after the enzymatic release of the sialic acid moieties. The red blood cells bind via their demasked galactose residues to a galactose-specific receptor of phagocytes and ultimately are taken up and degraded [43]. Correspondingly, trapping of sialidasetreated erythrocytes can be inhibited by galactose or more efficiently by galactosides [43,44]. This mechanism can work without the involvement of immunoglobulin or complement and appears to be involved in the sequestration process of aged red cells (reviewed in [44]).
Fig. 4. Binding of sialidase-treated rabbit erythrocytes to liver Kupffer cells in vivo. The scanning electron micrograph is taken from [37] with permission by Springer-Verlag.
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Fig. 5. Interaction between sialidase-treated rat lymphocytes (L) and homologous peritoneal macrophages in vitro. The firm attachment of the lymphocyte membranes to the macrophage surface and the beginning of encirclement of the lymphocytes are visible (from [92], modified).
It was demonstrated that old erythrocytes expose more galactose residues than younger cells [45]. In human 3–5 million red blood cells are phagocytosed per second [44]. The galactose-recognizing receptor, belonging to the C-type lectins, responsible for the binding of blood cells was isolated from rat peritoneal macrophages by Kelm and Schauer [46] and represented one of the first characterized mammalian galactose receptors after the hepatocyte receptor. Since then large gene families encoding for the galectins and other proteins recognizing galactose were found in microorganisms, plants, and animals [34,47,48]. The molecular characterization of the rat Kupffer cell glycoprotein receptor has been reported [49]. Malignant cells can also be eliminated in this way by macrophages, and it is understandable that oversialylation, often observed in such cells, protects them from humoral and cellular defense systems and thus increases their malignancy. The strategy to increase sialylation
over physiological levels has been used to create a ‘‘hyper-erythropoietin’’ by insertion of more glycosylation sites which exhibits better pharmacokinetic properties due to an extended life-time in blood serum [50]. In this regard, polysialic acids (PSA) found on some bacteria and on mammalian cells are strongly antiadhesive thus regulating cell adhesion and cellular movements (see 19,51] for reviews). PSA enhance virulence in, e.g., Escherichia coli and in higher animals play a crucial role in development, especially of neuronal tissues and are involved in the maintenance of neuronal plasticity. They also facilitate tumor growth and spreading. Sialylation of microorganisms follows a similar strategy, allowing better survival in the host organisms and thus enhancing virulence. This can be achieved in different ways, such as total synthesis of sialic acids and sometimes their polymeric form, colominic acid, in E. coli strains, the acquisition of sialic acids from the host with the aid of trans-sialidases in some trypanosomal
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strains or the transfer of sialic acids from CMP-glycoside from the host by a sialyltransferase expressed by the pathogenic bacterium, for example gonococci [52,53]. Similar to the binding of blood cells after demasking of their galactose residues, many, and often pathogenic, bacteria attach to mucous endothelia via galactose-recognizing lectins, for example, the oro-gastro-intestinal tract after desialylation of the endothelial cells and exposure of penultimate galactose residues [34]. Such bacteria secrete sialidase which removes the protecting sialic acid moieties and can thus be considered as spreading or virulence factor. Many efforts are presently undertaken to synthesize inhibitors of this glycosidase or soluble ligands to prevent adhesion. A second group of examples for the masking effect of sialic acid is the production of auto-antibodies after cell membrane desialylation by bacterial or viral sialidases. This exposure of cellular antigens may lead to chronic diseases such as glomerulonephritis [54]. Carbohydrates, including sialic acids, may be antigenic determinants, especially in gangliosides, but they more often shield antigenic sites and thus weaken the immuno-reactivity. Sialic acids render cells as ‘‘self,’’ not allowing recognition by the immune system or by, e.g., macrophage lectins. The loss of these monosaccharides makes these cells ‘‘non-self’’ and therefore vulnerable. Therefore, sialic acids can be considered as members of the innate immune system. Other acidic carbohydrates may take over this function in lower animals [55]. The work of Victor Ginsburg and his colleagues was pioneering in elucidation of the role of sialic acids as antigenic determinants. A monoclonal IgM associated with Waldenstr€ om macroglobulinemia, which binds at low temperature to sialylated glycoproteins and glycolipids of human erythrocytes was characterized in 1977 [56]. This group was the first to apply antibodies and sialic acid-binding toxins to TLC immunostaining, e.g., the detection of the ganglioside GM1 with cholera toxin [57]. This technique is still in wide use. The characterization of tumor-associated antigens presenting sialic acids as part of the immunogenic epitopes was a further important landmark. In 1981, a monosialoganglioside was recognized as an antigen of colon carcinoma [58] and one year later sialylated lacto-N -fucopentaose II, a hapten of the human Lea blood group antigen, was isolated as component of a monosialoganglioside from gastrointestinal cancer [59]. In further studies, this antigen was found to be recognized by the leucocyte adhesion molecule of endothelial cells ELAM-1 [60,61], later denominated E-selectin (see below). In contrast to masking, sialic acid molecules take part directly in a variety of recognition processes. This may be the most important role of these monosaccharides. This was first noted in microorganisms, which in most cases use cell surface carbohydrates for binding to their host cells [34,62]. Sialic acids appear to be the most
frequent ligands for pathogenic and non-pathogenic viruses, bacteria, and protozoa. The best known and longest studied example are influenza viruses. Hirst observed in 1942 [63] the binding of influenza A virus to human erythrocytes and mucins of the respiratory tract. The attachment, mediated by a viral lectin called hemagglutinin, was reversible and accompanied by the release of an acidic sugar-like substance by a viral ‘‘receptor-destroying enzyme,’’ later named neuraminidase, resp. sialidase. The infection mechanism includes binding of the virus to endothelial cells of the respiratory tract, followed by penetration, multiplication, and exocytosis of such viruses. Viral sialidase seems to facilitate the spreading of the viruses in tissues by preventing their further attachment to the cells and to mucus layers protecting epithelia of the respiratory tract. Using this knowledge it was possible to synthesize a very strong inhibitor (2,3-didehydro-2,4-dideoxy-4guanidinyl-N -acetylneuraminic acid) of the viral sialidase based on a natural sialidase inhibitor and exact knowledge of the three-dimensional structure of the enzyme [64]. This substance and derivatives thereof are active also in vivo and are being successfully used for the treatment of influenza. Many other viruses (see [34] for a review) also attach to cells via sialic acids and the number of examples is growing [65]. The most prominent ones are corona, polyoma, adenoma, and rota viruses, and on infection with HIV viruses sialylated glycans both from the virus and the cellular receptors are involved. Some viruses only recognize modified Sia such as human influenza C virus and mouse hepatitis virus, which exclusively bind to Neu5,9Ac2 [66] and Neu4,5Ac2 [67], respectively. The infectious salmon anemia virus also binds to the 4-Oacetylated sialic acid [68]. Bacteria produce carbohydrate-specific adhesins which are frequently located on their fimbriae or pili. Prominent examples for colonization via sialic acids are pathogenic bacteria such as strains of E. coli, Streptococci and Helicobacter pylori [34,62]. A very recent example is Flavobacterium psychrophilum [69]. Earlier examples, described by Victor Ginsburg and collaborators, are the sialic acid-dependent adhesion of Mycoplasma pneumoniae to glycoproteins [70] and binding of the E. coli strain K99 from piglet small intestine to Neu5Gc-containing gangliosides [71]. Especially H. pylori, often found in human stomach and responsible for gastric inflammation and possibly also cancer, is intensively studied. Mahdavi et al. [72] published the structure of its sialic acid-recognizing adhesin. Knowledge about such adhesion mechanisms enables a biologybased therapy of diseases caused, e.g., by H. pylori and may save the use of antibiotics [73]. By this alternative strategy, receptor–ligand interactions are inhibited with soluble ligands such as sialylated oligosaccharides or glycoproteins. Such oligosaccharides occur in a rela-
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tively high concentration in milk, especially the colostrum. The milk from each mammal contains different and more or less sialylated glycans [74]. These carbohydrates are considered to regulate the species-specific colonization of the intestine with microorganisms and to hinder the attachment of pathogenic bacteria such as E. coli and Helicobacter strains or pathogenic viruses, for example rota viruses, which is most important in newborns. Correspondingly, the application of sialo-oligosaccharides in soluble forms or as dendritic polymers is a new strategy to fight microbial infections [75–77]. It should be noted that a high sialic acid content in human milk, especially in the first days after birth, was shown to increase the sialic acid content of brain gangliosides in rat and human and is discussed to promote higher permanently intelligence [78]. Also bacterial toxins, such as cholera, tetanus, and diphtheria toxin, firmly adhere to sialic acids, mostly of gangliosides, as basis of their pathophysiological activity ([57], and summarized in [34]). A variety of sialic acid-recognizing lectins were isolated from plants and lower animals (reviewed in [34,47,48,79]). They are assumed to be involved in mechanisms of innate immunity. Some evidence that sialic acids are recognized not only by microorganisms, plants, and lower animals, but also by mammalian receptor proteins was obtained by Lee et al. [80]. When we studied the interaction of the galactose-recognizing receptor from rat peritoneal macrophages with ligands containing terminal galactose residues such as desialylated blood cells or glycoproteins, we observed that this interaction can specifically be inhibited by Neu5Ac. An allosteric influence of sialic acid on the binding of galactose by the receptor was discussed. Shortly thereafter, Paul Crocker, Jim Paulson, and Sørge Kelm, one of the authors of this publication by Lee et al. [80] and collaborators, obtained firm evidence that sialic acids are directly involved in recognition processes by functioning as ligands also in animals. A sialic acid-binding receptor was discovered in murine bone marrow cells and called ‘‘sialoadhesin’’ [81]. It is a member of the ‘‘siglecs,’’ which belong to the immunoglobulin superfamily (IgSF) with repeating extracellular domains of variable length, of which 11 members were discovered in the past few years due to the increased availability of expressed sequence tags (EST) and genomic DNA sequences [34,82]. The first well-characterized species are the macrophage sialoadhesin, involved in binding and nursing of maturing blood cells, the CD22 on B-lymphocytes, responsible for the ‘‘cross-talk’’ of these cells with Tlymphocytes, and the myelin-associated-glycoprotein (MAG) on oligodendrocytes and Schwann cells, participating in the growth and myelination of neurites. Most of the other siglecs are involved in the regulation of recognition phenomena of various white blood cell types and macrophages and thus are regulators of the
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immune system (see [83–85]). They also vary in the recognition of different sialic acids and can distinguish glycosidic linkages. For example, sialoadhesin and MAG only bind to a2,3-linked sialic acids, while CD22 recognizes a2,6-bonds. While N -acetyl hydroxylation (Neu5Gc) can modify the affinity, sialic acid-O-acetylation (Neu5,9Ac2 ) abolishes it [34]. Another group of mammalian sialic acid-recognizing lectins are the selectins found on endothelial cells, which also possess repeating domains (for reviews see [34,86]). They participate in the initial stage of adhesion of white blood cells to endothelia, along which they begin to roll and eventually penetrate into the tissue below, which may be damaged by the lack of oxygen, in, for example, transplants or infarcts, or which are inflamed. Cytokines play here an essential role. Selectins preferably recognize sialylated Lewis structures (Sia-Lex ), a tetrasaccharide, which is bound to glycoproteins or glycolipids. Since these oligosaccharide moieties also occur on tumor cells [87–89], selectins can be involved in the formation of metastases. To avoid further tissue damage by evading lymphocytes or to prevent metastasis of tumors, great efforts are being undertaken to prevent cell adhesion to endothelia by the application of either selectin antibodies or Sia-Lex analogues. Since sialic acids are involved in such a wealth of biological phenomena, change of their concentration or of their chemical structure may alter the biology of cells. This has a great impact in fertilization, development and tumorigenesis, immunological reactions, life-time of cells including apoptosis, transmembrane signalling events, microbial and non-microbial inflammations, and many other cell biological and pathological events. Sialic acids seem to be indispensable for the life of higher organisms, since inhibition of their biosynthesis during early development of mice is lethal, as was shown by inactivation of UDP-N -acetylglucosamine-2-epimerase/ N -acetylmannosamine kinase, the key enzyme of sialic acid biosynthesis [90]. The main role of sialic acids with their outstanding position on molecules and cells and their chemical diversity seems to be the fine-tuning of a multitude of cellular events which may be explained by the capacity of sialic acids to regulate molecular interactions. We are grateful to Victor Ginsburg and colleagues for having opened the gate to study these special functions of carbohydrates.
References [1] B.M. Gesner, V. Ginsburg, Proc. Natl. Acad. Sci. USA 52 (1964) 750–755. [2] E. Margoliash, J.R. Schenck, M.P. Hargie, S. Burokas, W.R. Richter, G.H. Barlow, A.A. Moscona, Biochem. Biophys. Res. Commun. 20 (1965) 383–388. [3] A.G. Morell, G. Gregoriadis, I.H. Scheinberg, J. Hickman, G. Ashwell, J. Biol. Chem. 246 (1971) 1461–1467.
140
R. Schauer / Archives of Biochemistry and Biophysics 426 (2004) 132–141
[4] G. Ashwell, A.G. Morell, Adv. Enzymol. 41 (1974) 99–128. [5] C. Traving, R. Schauer, Cell. Mol. Life Sci. 54 (1998) 1330–1349. [6] R. Schauer, J.P. Kamerling, in: J. Montreuil, J.F.G. Vliegenthart, H. Schachter (Eds.), Glycoproteins II, Elsevier Science, Amsterdam, 1997, pp. 243–402. [7] A. Varki, Glycobiology 2 (1992) 25–40. [8] R. Schauer, Trends Glycosci. Glycotechnol. 13 (2001) 507–517. [9] M.M. Shah, K. Fujiyama, C.R. Flynn, L. Joshi, Nat. Biotechnol. 21 (2003) 1470–1471. [10] A. Varki, R. Cummings, J. Esko, H. Freeze, G. Hart, J. Marth (Eds.), Essentials of Glycobiology, Cold Spring Harbor, New York, 1999. [11] R. Schauer, Glycoconjugate J. 17 (2000) 485–499. [12] R. Schauer, in: B. Ernst, G.W. Hart, P. Sina€y, (Eds.), Carbohydrates in Chemistry and Biology. Part II. Biology of Saccharides, vol. 3, Wiley-VCH, Weinheim, 2000, pp. 227–243. [13] A.P. Corfield, R. Schauer, in: R. Schauer (Ed.), Sialic Acids— Chemistry, Metabolism and Function, Springer, Wien, New York, 1982, pp. 5–50. [14] C.S. Alviano, L.R. Travassos, R. Schauer, Glycoconjugate J. 16 (1999) 545–554. [15] J.-P. Zanetta, A. Pons, M. Iwersen, C. Mariller, Y. Leroy, P. Timmerman, R. Schauer, Glycobiology 11 (2001) 663–676. [16] T. Angata, A. Varki, Chem. Rev. 102 (2002) 439–469. [17] D. Nadano, M. Iwasaki, S. Endo, K. Kitajima, S. Inoue, Y. Inoue, J. Biol. Chem. 261 (1986) 11550–11557. [18] Y.-T. Li, K. Maskos, C.-W. Chou, R.B. Cole, S.-C. Li, J. Biol. Chem. 278 (2003) 35286–35291. [19] M. M€ uhlenhoff, M. Eckhardt, R. Gerardy-Schahn, Curr. Opin. Struct. Biol. 8 (1998) 558–564. [20] A.P. Corfield, R. Schauer, in: R. Schauer (Ed.), Sialic Acids— Chemistry, Metabolism and Function, Springer, Wien, New York, 1982, pp. 195–261. [21] Y.N. Malykh, R. Schauer, L. Shaw, Biochimie 83 (2001) 623– 4634. [22] P. Tangvoranuntakul, P. Gagneux, S. Diaz, M. Bardor, N. Varki, A. Varki, E. Muchmore, Proc. Natl. Acad. Sci. USA 100 (2003) 12045–12050. [23] W. Schlenzka, L. Shaw, R. Schauer, Glycobiology 4 (1994) 675– 683. [24] I. Martensen, R. Schauer, L. Shaw, Eur. J. Biochem. 268 (2001) 5157–5166. [25] A. Irie, S. Koyama, Y. Kozutsumi, T. Kawasaki, A. Suzuki, J. Biol. Chem. 273 (1998) 15866–15871. [26] R. Schauer, H. Schmid, J. Pommerencke, M. Iwersen, G. Kohla, in: A.M. Wu (Ed.), The Molecular Immunology of Complex Carbohydrates 2, Adv. Exp. Med. Biol., vol. 491, Kluwer Academics/Plenum Publishers, New York, 2001, pp. 325–342. [27] M. Iwersen, H. Schmid, S. Gasa, G. Kohla, R. Schauer, Biol. Chem. 384 (2003) 1035–1047. [28] W.X. Shi, R. Chammas, A. Varki, Glycobiology 8 (1998) 199–205. [29] H.H. Higa, C. Butor, S. Diaz, A. Varki, J. Biol. Chem. 264 (1989) 19427–19434. [30] J. Tiralongo, R. Schauer, Trends Glycosci. Glycotechnol. 16, 2004 (in press). [31] A. Kelm, L. Shaw, R. Schauer, G. Reuter, Eur. J. Biochem. 251 (1998) 874–884. [32] A. Klein, S. Diaz, I. Ferreira, G. Lamblin, P. Roussel, A.E. Manzi, Glycobiology 7 (1997) 421–432. [33] R. Schauer, Trends Biochem. Sci. 10 (1985) 357–360. [34] S. Kelm, R. Schauer, Int. Rev. Cytol. 175 (1997) 137–240. [35] J. Jancik, R. Schauer, Hoppe-SeylerÕs Z. Physiol. Chem. 355 (1974) 395–400. [36] J. Jancik, R. Schauer, H.-J. Streicher, Hoppe-SeylerÕs Z. Physiol. Chem. 356 (1975) 1329–1331. [37] J.M. Jancik, R. Schauer, K.H. Andres, M. von D€ uring, Cell Tissue Res. 186 (1978) 209–226.
[38] H. Kolb, C. Schudt, V. Kolb-Bachofen, H.A. Kolb, Exp. Cell Res. 113 (1978) 319–325. [39] A. Kluge, G. Reuter, H. Lee, B. Ruch-Heeger, R. Schauer, Eur. J. Cell. Biol. 59 (1992) 12–20. [40] C. Fischer, S. Kelm, B. Ruch, R. Schauer, Carbohydr. Res. 213 (1991) 263–273. [41] S.H.E. Kaufmann, R. Schauer, H. Hahn, Immunobiology 160 (1981) 184–195. [42] J.J. Woodruff, B.M. Gesner, J. Exp. Med. 129 (1969) 551–567. [43] E. M€ uller, C. Schr€ oder, R. Schauer, N. Sharon, Hoppe-SeylerÕs Z. Physiol. Chem. 364 (1983) 1419–1429. [44] D. Bratosin, J. Mazurier, J.P. Tissier, J. Estaquier, J.J. Huart, J.C. Ameisen, D. Aminoff, J. Montreuil, Biochimie 80 (1998) 173–195. [45] D. Bratosin, J. Mazurier, H. Debray, M. Lecocq, B. Boilly, C. Alonso, M. Moisei, C. Motas, J. Montreuil, Glycoconjugate J. 12 (1995) 258–267. [46] S. Kelm, R. Schauer, Biol. Chem. Hoppe-Seyler 369 (1988) 693– 704. [47] N. Sharon, H. Lis (Eds.), Lectins, second ed., Kluwer Academic Publishers, Dordrecht, 2003. [48] H.-J. Gabius, S. Gabius (Eds.), Lectins and Glycobiology, Springer, Berlin, 1993. [49] A.J. Fadden, O.J. Holt, K. Drickamer, Glycobiology 13 (2003) 529–537. [50] W. Jelkmann, Eur. J. Haematol. 69 (2002) 265–274. [51] K. Angata, M. Fukuda, Biochimie 85 (2003) 195–206. [52] L. Gao, L. Linden, N.J. Parsons, J.A. Cole, H. Smith, Microb. Pathogenesis 28 (2000) 257–266. [53] E. Vimr, C. Lichtensteiger, Trends Microbiol. 10 (2002) 254–257. [54] T. Corfield, Glycobiology 6 (1992) 509–521. [55] H. Faillard, R. Schauer, in: A. Gottschalk (Ed.), Glycoproteins— Their Composition, Structure and Function, BBA Library 5, Elsevier Publ. Company, Amsterdam, 1972, pp. 1246–1267. [56] C.M. Tsai, D.A. Zopf, R.K. Yu, R. Wistar Jr., V. Ginsburg, Proc. Natl. Acad. Sci. USA 74 (1977) 4591–4594. [57] J.L. Magnani, D.F. Smith, V. Ginsburg, Anal. Biochem. 109 (1980) 399–402. [58] J.L. Magnani, M. Brockhaus, D.F. Smith, V. Ginsburg, M. Blaszczyk, K.F. Mitchell, Z. Steplewski, H. Koprowski, Science 212 (1981) 55–56. [59] J.L. Magnani, B. Nilsson, M. Brockhaus, D. Zopf, Z. Steplewski, H. Koprowski, V. Ginsburg, J. Biol. Chem. 257 (1982) 14365– 14369. [60] E.L. Berg, M.K. Robinson, O. Mansson, E.C. Butcher, J.L. Magnani, J. Biol. Chem. 266 (1991) 14869–14872. [61] A. Takada, K. Ohmori, N. Takahashi, K. Tsuyuoka, A. Yago, K. Zenita, A. Hasegawa, R. Kannagi, Biochem. Biophys. Res. Commun. 179 (1991) 713–719. [62] I. Ofek, J. Doyle (Eds.), Bacterial Adhesion to Cells and Tissues, Chapman & Hall, New York, 1994. [63] G.K. Hirst, J. Exp. Med. 76 (1942) 195–209. [64] M. von Itzstein, W.-Y. Wu, B. Jin, Carbohydr. Res. 259 (1994) 301–305. [65] B. Tsai, J.M. Gilbert, T. Stehle, W. Lencer, T.L. Benjamin, T.A. Rapoport, EMBO J. 22 (2003) 4346–4355. [66] G. Herrler, G. Reuter, R. Rott, H.-D. Klenk, R. Schauer, Biol. Chem. Hoppe-Seyler 368 (1987) 451–454. [67] G. Regl, A. Kaser, M. Iwersen, H. Schmid, G. Kohla, B. Strobl, U. Vilas, R. Schauer, R. Vlasak, J. Virol. 73 (1999) 4721–4727. [68] A. Hellebø, U. Vilas, K. Falk, R. Vlasak, J. Virol., 78 (2004) 3055–3062. [69] J.D. Møller, J.L. Larsen, L. Madsen, I. Dalsgaard, Appl. Environ. Microbiol. 69 (2003) 5275–5280. [70] D.D. Roberts, L.D. Olson, M.F. Barile, V. Ginsburg, H.C. Krivan, J. Biol. Chem. 264 (1989) 9289–9293. [71] M. Kyogashima, V. Ginsburg, H.C. Krivan, Arch. Biochem. Biophys. 270 (1989) 391–397.
R. Schauer / Archives of Biochemistry and Biophysics 426 (2004) 132–141 [72] J. Mahdavi, B. Sonden, M. Hurtig, F.O. Olfat, L. Forsberg, N. Roche, J. Angstr€ om, T. Larsson, S. Teneberg, K.-A. Karlsson, S. Altraja, T. Wadstr€ om, D. Kersulyte, D.E. Berg, A. Dubois, C. Petersson, K.-E. Magnusson, T. Norberg, F. Lindh, B.B. Lundskog, A. Arnqvist, L. Hammarstr€ om, T. Boren, Science 297 (2002) 573–578. [73] M. Gerhard, S. Hirmo, T. Wadstr€ om, H. Miller-Podraza, S. Teneberg, K.-A. Karlsson, B. Appelmelk, S. Odenbreit, R. Haas, A. Arnqvist, T. Boren, in: S. Suerbaum (Ed.), Helicobacter pylori: Molecular and Cellular Biology, Horizon Scientific Press, Wymondham, UK, 2001, pp. 185–206. [74] W. Sumiyoshi, T. Urashima, T. Nakamura, I. Arai, T. Saito, N. Tsumura, B. Wang, J. Brand-Miller, Y. Watanabe, K. Kimura, Brit. J. Nutr. 89 (2003) 61–69. [75] T. Urashima, T. Saito, T. Nakamura, M. Messer, Glycoconjugate J. 18 (2001) 357–371. [76] J.J. Landers, Z. Cao, I. Lee, L.T. Piehler, P.P. Myc, A. Myc, T. Hamouda, A.T. Galecki, J.R. Baker Jr., J. Infect. Diseases 186 (2002) 1222–1230. [77] A. Kobata, Chang Gung Med. J. 26 (2003) 620–635. [78] B. Wang, J. Brand-Miller, Eur. J. Clin. Nutr. 57 (2003) 1351– 1369. [79] A. Varki, FASEB J. 11 (1997) 248–255. [80] H. Lee, S. Kelm, J.-C. Michalski, R. Schauer, Biol. Chem. HoppeSeyler 371 (1990) 307–316.
141
[81] P.R. Crocker, S. Kelm, C. Dubois, B. Martin, A.S. McWilliam, D.M. Shotton, J.C. Paulson, S. Gordon, EMBO J. 10 (1991) 1661–1669. [82] T. Angata, E.C.M. Brinkman-Van der Linden, Biochim. Biophys. Acta 1572 (2002) 294–316. [83] P.R. Crocker, A. Varki, Trends Immunol. 22 (2001) 337–342. [84] H. Aizawa, N. Zimmermann, P.E. Carrigan, J.J. Lee, M.E. Rothenberg, B.S. Bochner, Genomics 82 (2003) 521–530. [85] A. Bhunia, V. Jayalakshmi, A.J. Benie, O. Schuster, S. Kelm, N. Rama Krishna, T. Peters, Carbohydr. Res. 339 (2004) 259–267. [86] R. Kannagi, Curr. Opin. Struct. Biol. 12 (2002) 599–608. [87] Y.J. Kim, L. Borsig, N.M. Varki, A. Varki, Proc. Natl. Acad. Sci. USA 95 (1998) 9325–9330. [88] P. Grabowski, B. Mann, U. Mansmann, N. L€ ovin, H.-D. Foss, G. Berger, H. Scher€ ubl, E.-O. Riecken, H.-J. Buhr, C. Hanski, Int. J. Cancer 88 (2000) 281–286. [89] L. Borsig, R. Wong, J. Feramisco, D.R. Nadeau, N.M. Varki, A. Varki, Proc. Natl. Acad. Sci. USA 98 (2001) 3352–3357. [90] M. Schwarzkopf, K.-P. Knobeloch, E. Rohde, S. Hinderlich, N. Wiechens, L. Lucka, I. Horak, W. Reutter, R. Horstkorte, Proc. Natl. Acad. Sci. USA 99 (2002) 5267–5270. [91] Y.-T. Li, K. Maskos, C.-W. Chou, R.B. Cole, S.-C. Li, J. Biol. Chem. 278 (2003) 35286–35291. [92] S.e-D. Jibril, B. von Gaudecker, S. Kelm, R. Schauer, Biol. Chem. Hoppe-Seyler 368 (1987) 819–829.