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A family of receptors for venom phospholipases A2
474
Abstracts
than the overall structure of the enzyme molecules. As a result, activity changes generally precede unfolding of the molecules. The induced fit hypothesis by Koshland implies that the existence of multi-conformational states of enzyme molecules and the substrate perturbation of the different states is an integral part of the catalytic process. It is evidently required that the different conformation states shift rapidly from one to another and consequently relative flexibility at the active site is essential for the full expression of the catalytic activities of enzymes. A.ftimily qfrecepiors,/tir uenomphospholipases A?. G. Lambeau, P. Ancian, J. Barhanin, S. Beiboer, J. P. Nicolas. H. Verheij, E. Zwaritch and M. Lazdunski (Institut de Pharmacologic Moleculaire et Cellulaire CNRS, 660 route des Lucioles. Sophia-Antipolis, 06560 Valbonne, France). Venom phospholipases AI (vPLA>s) display a large spectrum of toxic effects including neurotoxicity and myotoxicity, and hypotensive, anticoagulant and proinflammatory effects. We have shown that these different types of effect are apparently linked to the existence of a variety of very high affinity receptors (R values as low as I.5 PM) for these toxic enzymes, Mammalian secretory PLAzs (msPLA2s) are now implicated in many biological functions besides digestion, such as airway and vascular smooth muscle contraction, cell proliferation, and a variety of diseases associated with inflammation, such as rheumatoid arthritis, endotoxic shock, and respiratory distress syndromes. Several different types of receptor (N and M) have been identified for vPLA?s, one of which (180,000 mol. wt, called M) has been cloned and sequenced in rabbit and humans. It is a membrane protein with a N-terminal cysteine-rich domain, a Iibronectin type II domain, eight repeats of a carbohydrate recognition domain, a unique transmembrane domain and an intracellular C-terminal domain. When expressed in transfected cells it binds msPLA*s (synovial PLA>, Kd - l-10 nM), indicating that the receptors for toxic PLA: are the normal targets of endogenous msPLAl involved in a variety of diseases. Residues within or close to the Ca*+-binding loop of sPLA2 are crucially involved in the binding step, although the presence of Ca’+, which is essential for the enzymatic activity, is not required for binding to the receptor. The molecular domain in charge of vPLA2 binding in the M-type receptor has been identified. The M-type receptor is an endocytic receptor. Myotoxic phospholipases ,from snake venoms: general myoglobinuric and local myonecrotic toxins. P. Gopalakrishnakone (Venom and Toxin Research Group, Faculty of Medicine, National University of Singapore, Singapore 119260). The term myotoxin is used by toxinologists to describe a toxin which causes deleterious effect/s on skeletal muscle as shown by either biochemical, pharmacological or morphological evidence. However, this general term includes two classes of toxins, such as general myotoxin, which causes systemic myotoxicity and myoglobinurea, and local myotoxin or myonecrotic toxin, which causes muscle degeneration when injected locally. For example, crotoxin, taipoxin, notexin and mojave toxin produce muscle degeneration locally when injected i.m., whereas PLA? enzymes from the venoms of Enhydrina schistosa and Australian elapids of the genus Pseudechis produce systemic myotoxicity, characterized by generalized muscle damage and myoglobinuria. Muscle damage observed by lightand electron-microscopic methods includes dilatation of sarcoplasmic reticulum, vacuolation, oedema within 4 hr of injection of toxin, followed by disruption and hypercontraction of the fibres with inflammatory changes by about 6 hr. The inflammatory reaction characterized by infiltration by phagocytic cells is maximally seen between I2 and 24 hr. Evidence of regeneration starts by 36 hr and complete regeneration is seen by 7-10 days. The mechanism by which these toxins cause muscle damage is not fully understood. However, the disruption of one sarcolemmal membrane, increase in influx of Ca?+ into sarcoplasm, and Ca’+-activated neutral proteases play a vital role in this process. Clinical challenge of‘ tjenomous bites and stings in the Asia-Pac$c area. D. A. Warrell Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, U.K.).
(Centre
for Tropical
In the Asia-Pacific region, snakebite is an occupational hazard for farmers, plantation workers, hunters, herdsmen and those who handle snakes for culinary purposes. Medically important species include: Elapidae [kraits (Bungurus), cobras (Naja), death adders (Acanthophis), taipan (Oxyuranus)]; and Viperidae [Russell’s vipers (Daboia), saw-scaled vipers (Echis), pit vipers (Agkistrodon-Gloydius, Calloselasma, Deinagkistrodon and Trimeresurus)]. Local envenoming by cobras and Viperidae can result in acute life-threatening hypovolaemia, gangrene, septicaemia, and persisting ulceration, osteomyelitis, malignant transformation and physical handicap. Systemic envenoming can kill through respiratory paralysis (Elapidae and some Agkistrodon species), shock, coagulopathy and bleeding (Viperidae and Australasian Elapidae). The incidence of bites from sea snakes appears to have declined with mechanization of fishing methods. Challenging aspects of clinical treatment include appropriate first-aid treatment, provision of affordable, effective and safe specific antivenoms, ancillary treatments such as the use of anticholinesterases for neurotoxicity and support of respiratory, circulatory and renal failure. New ovine Fab fragment antivenoms are now being developed for envenoming by &his, Daboia and Pseudonaja. Preventive strategies include protective clothing, avoidance of high-risk habitats and community education. Many species of venomous scorpions, spiders, centipedes, ticks, insects (Hymenoptera) and leeches occur in the region, but only the Indian red scorpion (Mesobuthus tam&s) envenoming, Hymenoptera sting anaphylaxis, and mass attacks by large Vespidae and Apidae constitute significant medical problems.
Abstracts
than the overall structure of the enzyme molecules. As a result, activity changes generally precede unfolding of the molecules. The induced fit hypothesis by Koshland implies that the existence of multi-conformational states of enzyme molecules and the substrate perturbation of the different states is an integral part of the catalytic process. It is evidently required that the different conformation states shift rapidly from one to another and consequently relative flexibility at the active site is essential for the full expression of the catalytic activities of enzymes. A.ftimily qfrecepiors,/tir uenomphospholipases A?. G. Lambeau, P. Ancian, J. Barhanin, S. Beiboer, J. P. Nicolas. H. Verheij, E. Zwaritch and M. Lazdunski (Institut de Pharmacologic Moleculaire et Cellulaire CNRS, 660 route des Lucioles. Sophia-Antipolis, 06560 Valbonne, France). Venom phospholipases AI (vPLA>s) display a large spectrum of toxic effects including neurotoxicity and myotoxicity, and hypotensive, anticoagulant and proinflammatory effects. We have shown that these different types of effect are apparently linked to the existence of a variety of very high affinity receptors (R values as low as I.5 PM) for these toxic enzymes, Mammalian secretory PLAzs (msPLA2s) are now implicated in many biological functions besides digestion, such as airway and vascular smooth muscle contraction, cell proliferation, and a variety of diseases associated with inflammation, such as rheumatoid arthritis, endotoxic shock, and respiratory distress syndromes. Several different types of receptor (N and M) have been identified for vPLA?s, one of which (180,000 mol. wt, called M) has been cloned and sequenced in rabbit and humans. It is a membrane protein with a N-terminal cysteine-rich domain, a Iibronectin type II domain, eight repeats of a carbohydrate recognition domain, a unique transmembrane domain and an intracellular C-terminal domain. When expressed in transfected cells it binds msPLA*s (synovial PLA>, Kd - l-10 nM), indicating that the receptors for toxic PLA: are the normal targets of endogenous msPLAl involved in a variety of diseases. Residues within or close to the Ca*+-binding loop of sPLA2 are crucially involved in the binding step, although the presence of Ca’+, which is essential for the enzymatic activity, is not required for binding to the receptor. The molecular domain in charge of vPLA2 binding in the M-type receptor has been identified. The M-type receptor is an endocytic receptor. Myotoxic phospholipases ,from snake venoms: general myoglobinuric and local myonecrotic toxins. P. Gopalakrishnakone (Venom and Toxin Research Group, Faculty of Medicine, National University of Singapore, Singapore 119260). The term myotoxin is used by toxinologists to describe a toxin which causes deleterious effect/s on skeletal muscle as shown by either biochemical, pharmacological or morphological evidence. However, this general term includes two classes of toxins, such as general myotoxin, which causes systemic myotoxicity and myoglobinurea, and local myotoxin or myonecrotic toxin, which causes muscle degeneration when injected locally. For example, crotoxin, taipoxin, notexin and mojave toxin produce muscle degeneration locally when injected i.m., whereas PLA? enzymes from the venoms of Enhydrina schistosa and Australian elapids of the genus Pseudechis produce systemic myotoxicity, characterized by generalized muscle damage and myoglobinuria. Muscle damage observed by lightand electron-microscopic methods includes dilatation of sarcoplasmic reticulum, vacuolation, oedema within 4 hr of injection of toxin, followed by disruption and hypercontraction of the fibres with inflammatory changes by about 6 hr. The inflammatory reaction characterized by infiltration by phagocytic cells is maximally seen between I2 and 24 hr. Evidence of regeneration starts by 36 hr and complete regeneration is seen by 7-10 days. The mechanism by which these toxins cause muscle damage is not fully understood. However, the disruption of one sarcolemmal membrane, increase in influx of Ca?+ into sarcoplasm, and Ca’+-activated neutral proteases play a vital role in this process. Clinical challenge of‘ tjenomous bites and stings in the Asia-Pac$c area. D. A. Warrell Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, U.K.).
(Centre
for Tropical
In the Asia-Pacific region, snakebite is an occupational hazard for farmers, plantation workers, hunters, herdsmen and those who handle snakes for culinary purposes. Medically important species include: Elapidae [kraits (Bungurus), cobras (Naja), death adders (Acanthophis), taipan (Oxyuranus)]; and Viperidae [Russell’s vipers (Daboia), saw-scaled vipers (Echis), pit vipers (Agkistrodon-Gloydius, Calloselasma, Deinagkistrodon and Trimeresurus)]. Local envenoming by cobras and Viperidae can result in acute life-threatening hypovolaemia, gangrene, septicaemia, and persisting ulceration, osteomyelitis, malignant transformation and physical handicap. Systemic envenoming can kill through respiratory paralysis (Elapidae and some Agkistrodon species), shock, coagulopathy and bleeding (Viperidae and Australasian Elapidae). The incidence of bites from sea snakes appears to have declined with mechanization of fishing methods. Challenging aspects of clinical treatment include appropriate first-aid treatment, provision of affordable, effective and safe specific antivenoms, ancillary treatments such as the use of anticholinesterases for neurotoxicity and support of respiratory, circulatory and renal failure. New ovine Fab fragment antivenoms are now being developed for envenoming by &his, Daboia and Pseudonaja. Preventive strategies include protective clothing, avoidance of high-risk habitats and community education. Many species of venomous scorpions, spiders, centipedes, ticks, insects (Hymenoptera) and leeches occur in the region, but only the Indian red scorpion (Mesobuthus tam&s) envenoming, Hymenoptera sting anaphylaxis, and mass attacks by large Vespidae and Apidae constitute significant medical problems.