CR1

Chapter 28

CR1 Ionita Ghiran, Anne Nicholson-Weller Beth Israel Deaconess Medical Center, Boston, MA, United States

OTHER NAMES Complement receptor 1, CD35, immune adherence receptor, C3b/C4b receptor.

PHYSICOCHEMICAL PROPERTIES CR1 is a type I transmembrane glycoprotein of 2039 amino acids; the leader sequence is between amino acids 1 and 41.1,2 The mature peptide is located between position 42 and 2039, with a 25 amino acid transmembrane domain, between position 1972–1996, and with a 43 amino acid C-terminal domain, containing two PDZ motifs.3 There are four major structural allotypes recognised in humans: 1 (F, fast or A), 2 (S, slow or B), 3 (Cor F) and 4 (D). The most abundant is allotype 1, CR1*1, which will be used for all the subsequent descriptions. The isoelectric point of CR1 is 6.57. The relative molecular mass of CR1 depends on the cellular source of CR1, type of electrophoresis system and buffers used. CR1 obtained from nucleated blood cells run higher than CR1 from red cells, due to altered N-glycosylation.2 Allotype

Relative Molecular Mass (Mr, kDa, Reduced)

Relative Molecular Mass (Mr, kDa, Unreduced)

CR1*1 CR1*2 CR1*3 CR1*4

220–250 250–280 190–220 Over 280

190–210 220–250 160–190 Over 250

There are 21 glycosylation sites on mature CR1 molecule, with the following locations: Asn 56, Asn 156, Asn 252, Asn 410, Asn 447, Asn 509, Asn 578, Asn 702, Asn 860, Asn 897, Asn 959, Asn 1028, Asn 1152, Asn 1310, Asn 1481, Asn 1504, Asn 1534, Asn 1540, Asn 1605, Asn 1763, Asn 1908. Glycosylation contributes with 20–25 kDa to the molecular mass of CR1. Radiolabelled experiments using tagged glucosamine indicate lack of O-linked oligosaccharide on CR1.4 The Complement FactsBook. http://dx.doi.org/10.1016/B978-0-12-810420-0.00028-6 Copyright © 2018 Elsevier Ltd. All rights reserved.

295

296  PART | V  Regulatory Proteins

STRUCTURE The extracellular domain of CR1 is comprised of 30 short consensus repeats (SCRs), SCRs are also known as complement control protein repeats or Sushi domains (Fig. 28.1). Extracellular SCRs are further grouped in four, tandem large homologous repeats, LHR-A, LHR-B, LHR-C and LHR-D, each 45 kDa in size, and composed of seven SCRs.5 There are two unassigned SCRs near the plasma membrane, SCR 29 and 30. The homology between the four LHRs varies between 60% and 99%.5 The S variant of CR1, CR1*2, has an additional LHR-S inserted between LHR-B and LHR-C. The transmembrane domain, higher primates, baboons and macaques have GPI-anchored version of CR1 with identical extracellular portions. The crystal structure is shown for the first two domains (Fig. 28.2).

FUNCTION In humans, the main function of CR1 is binding of complement fragments C3b, C4b, C1q and MBL (mannan-binding protein).6 The interaction between CR1 and iC3b is weak. CR1 on circulating red blood cells (RBCs) binds complement-opsonised immune complexes and microbes present in blood and delivers them to tissue-resident macrophages in liver and spleen through a process called immune adhesion clearance. By preventing immune complexes to persist in circulation, and directly interact with nucleated blood cells, RBC CR1 contributes to maintaining an anti-inflammatory environment in blood. Following the transfer of immune complexes, RBCs along with CR1 are returned to circulation. EBV (Epstein–Barr virus) binds to CR1 by activating classical complement pathway in the absence of antibody,7 as well as by direct protein–protein interaction.8 CR1 also served as an adhesion for Plasmodium falciparum.9 In rodents, immune clearance is performed by platelets and soluble factor H.10 Complement-opsonised particles are phagocytosed by neutrophils and circulating monocytes, but only after priming. On T cells and dendritic cells, CR1 participates in antigen presentation. In RBCs, CR1 promotes Ca++ influx and increases membrane deformability.11 CR1 modulates B cell function and is involved in polarisation of Tregs. The complement regulatory function of CR1 depends on soluble factor I, which acts as a cofactor during degradation of complement fragment C3b to iC3b and C3f, and of iC3b to C3c and C3d,g.12 In the presence of factor I, CR1 also cleaves C4b to C4c and C4d and accelerates the degradation of the C3 and C5 convertases of the classical and alternative complement activation pathways.13

FIGURE 28.1  Diagram of protein domains for CR1.

CR1 Chapter | 28  297

FIGURE 28.2  Diagram of crystal structure for CR1. (A) Ribbon diagram of the solution NMR structure of complement receptor type 1 (CR1) CCP1-CCP2 domains (PDB ID: 2MCZ). (B) Schematic representation of the single-chain CR1 domains.

TISSUE DISTRIBUTION In blood, CR1 is expressed on RBCs, neutrophils, monocytes, B cells, subpopulation of T and activated NK cells.14–16 In tissue, CR1 is found on podocytes, activated endothelial cells, neurons, astrocytes and follicular dendritic cells.17 A soluble form of CR1, with concentration ranging 13–81 ng/mL, exists in plasma that could be either actively secreted by the cells, likely circulating neutrophils, or the product of enzymatic cleavage.18,19 The soluble form of CR1 may play a protective role during inflammatory conditions.20

298  PART | V  Regulatory Proteins

REGULATION OF EXPRESSION While the expression levels of CR1 on circulating RBCs is genetically determined, during the 120 days life cycle in circulation, RBCs lose about 40% of their original CR1 numbers. During acute and chronic inflammatory conditions, such as systemic lupus erythematosus (SLE), lepromatous leprosy, AIDS, autoimmune haemolytic anaemias, circulating RBCs lose CR1 at an accelerated rate due to abnormally high immune clearance process. The low CR1 expression level on circulating RBCs is a consequence of the disease, and not a predisposition. In blood neutrophils, most of the CR1 is stored in secretory vesicles and becomes exposed at the plasma membrane only upon activation.21

PROTEIN SEQUENCE MGASSPRSPE PVGPPAPGLP FCCGGSLLAV VVLLALPVAW GQCNAPEWLP

50

FARPTNLTDE FEFPIGTYLN YECRPGYSGR PFSIICLKNS VWTGAKDRCR

100

TVIWDNETPI CDRIPCGLPP TITNGDFIST NRENFHYGSV VTYRCNPGSG

200

RKSCRNPPDP VNGMVHVIKG IQFGSQIKYS CTKGYRLIGS SSATCIISGD GRKVFELVGE PSIYCTSNDD QVGIWSGPAP QCIIPNKCTP PNVENGILVS

DNRSLFSLNE VVEFRCQPGF VMKGPRRVKC QALNKWEPEL PSCSRVCQPP

PDVLHAERTQ RDKDNFSPGQ EVFYSCEPGY DLRGAASMRC TPQGDWSPAA PTCEVKSCDD FMGQLLNGRV LFPVNLQLGA KVDFVCDEGF QLKGSSASYC

VLAGMESLWN SSVPVCEQIF CPSPPVIPNG RHTGKPLEVF PFGKTVNYTC DPHPDRGTSF DLIGESTIRC TSDPQGNGVW SSPAPRCGIL GHCQAPDHFL FAKLKTQTNA SDFPIGTSLK YECRPEYYGR PFSITCLDNL VWSSPKDVCK

RKSCKTPPDP VNGMVHVITD IQVGSRINYS CTTGHRLIGH SSAECILSGN AAHWSTKPPI CQRIPCGLPP TIANGDFIST NRENFHYGSV VTYRCNPGSG

GRKVFELVGE PSIYCTSNDD QVGIWSGPAP QCIIPNKCTP PNVENGILVS DNRSLFSLNE VVEFRCQPGF VMKGPRRVKC QALNKWEPEL PSCSRVCQPP

PDVLHAERTQ RDKDNFSPGQ EVFYSCEPGY DLRGAASMRC TPQGDWSPAA PTCEVKSCDD FMGQLLNGRV LFPVNLQLGA KVDFVCDEGF QLKGSSASYC

VLAGMESLWN SSVPVCEQIF CPSPPVIPNG RHTGKPLEVF PFGKAVNYTC DPHPDRGTSF DLIGESTIRC TSDPQGNGVW SSPAPRCGIL GHCQAPDHFL

150 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950

FAKLKTQTNA SDFPIGTSLK YECRPEYYGR PFSITCLDNL VWSSPKDVCK 1000

RKSCKTPPDP VNGMVHVITD IQVGSRINYS CTTGHRLIGH SSAECILSGN 1050 TAHWSTKPPI CQRIPCGLPP TIANGDFIST NRENFHYGSV VTYRCNLGSR 1100 GRKVFELVGE PSIYCTSNDD QVGIWSGPAP QCIIPNKCTP PNVENGILVS 1150 DNRSLFSLNE VVEFRCQPGF VMKGPRRVKC QALNKWEPEL PSCSRVCQPP 1200 PEILHGEHTP SHQDNFSPGQ EVFYSCEPGY DLRGAASLHC TPQGDWSPEA 1250 PRCAVKSCDD FLGQLPHGRV LFPLNLQLGA KVSFVCDEGF RLKGSSVSHC 1300 VLVGMRSLWN NSVPVCEHIF CPNPPAILNG RHTGTPSGDI PYGKEISYTC 1350 DPHPDRGMTF NLIGESTIRC TSDPHGNGVW SSPAPRCELS VRAGHCKTPE 1400 QFPFASPTIP INDFEFPVGT SLNYECRPGY FGKMFSISCL ENLVWSSVED 1450 NCRRKSCGPP PEPFNGMVHI NTDTQFGSTV NYSCNEGFRL IGSPSTTCLV 1500

SGNNVTWDKK APICEIISCE PPPTISNGDF YSNNRTSFHN GTVVTYQCHT 1550

CR1 Chapter | 28  299

PROTEIN SEQUENCE—Continued GPDGEQLFEL VGERSIYCTS KDDQVGVWSS PPPRCISTNK CTAPEVENAI 1600 RVPGNRSFFT LTEIIRFRCQ PGFVMVGSHT VQCQTNGRWG PKLPHCSRVC 1650

QPPPEILHGE HTLSHQDNFS PGQEVFYSCE PSYDLRGAAS LHCTPQGDWS 1700 PEAPRCTVKS CDDFLGQLPH GRVLLPLNLQ LGAKVSFVCD EGFRLKGRSA 1750

SHCVLAGMKA LWNSSVPVCE QIFCPNPPAI LNGRHTGTPF GDIPYGKEIS 1800 YACDTHPDRG MTFNLIGESS IRCTSDPQGN GVWSSPAPRC ELSVPAACPH 1850 PPKIQNGHYI GGHVSLYLPG MTISYICDPG YLLVGKGFIF CTDQGIWSQL 1900 DHYCKEVNCS FPLFMNGISK ELEMKKVYHY GDYVTLKCED GYTLEGSPWS 1950 QCQADDRWDP PLAKCTSRTH DALIVGTLSG TIFFILLIIF LSWIILKHRK 2000 GNNAHENPKE VAIHLHSQGG SSVHPRTLQT NEENSRVLP

The leader sequence (residues 1–46) is underlined and the potential N-linked glycosylation sites.

PROTEIN MODULES 1 or 6–46 47–106 107–168 169–238 239–300 301–360 361–423 424–496 497–556 557–618 619–688 669–750 751–810 811–873 874–946 947–1006 1007–1068 1069–1138 1139–1200 1201–1260 1261–1323 1324–1399 1400–1459 1460–1521 1522–1591 1592–1653 1654–1713 1714–1776 1777–1851 1852–1911 1912–1972 1977–2001 2002–2044

Leader peptide CCP1, start LHR-A CCP2 CCP3 CCP4 CCP5 CCP6 CCP7, end LHR-A CCP8, start LHR-B CCP9 CCP10 CCP11 CCP12 CCP13 CCP14, end LHR-B CCP15, begin LHR-C CCP16 CCP17 CCP18 CCP19 CCP20 CCP21, end LHR-C CCP22, begin LHR-D CCP23 CCP24 CCP25 CCP26 CCP27 CCP28, end of LHR-D CCP29 CCP30 Transmembrane region Cytoplasmic domain

exon 1 exon 2 exons 3/4 exons 5 exon 5 exon 6 exons 7/8 exon 9 exon 10 exons 11/12 exon 13 exon 13 exon 14 exons 15/16 exon 17 exon 18 exons 19/20 exon 21 exon 21 exon 22 exons 23/24 exon 25 exon 26 exons 27/28 exon 29 exon 29 exon 30 exons 31/32 exon 33 exon 34 exon 35 exons 36/37 exon 38

300  PART | V  Regulatory Proteins

LIGAND BINDING SITES 47–300

CCPs 1–4

LHR-A

C4b-binding site; C3b, low affinity

497–750

CCPs 8–11

LHR-B

947–1200

CCPs 15–18

LHR-C

C3b-binding site, C4b low affinity C3b-binding site, C4b low affinity

PROTEIN–PROTEIN INTERACTION SITES 2040–2043

Cytoplasmic domain type-1 PDZ-motif, interaction with FAP-1.

CHROMOSOMAL LOCATION Human: chromosome 1q, 32.2 (Ensembl). Telomere … CD46 … CR1 … CR2 … CD55 … C4bp … Centromere. Mouse analogue (CR1/CR2): chromosome 1q, 40. Telomere … Crry … CR1/CR2 … Cfh … C4bp … Centromere.

HUMAN cDNA SEQUENCE TTTTGTCCCG GAACCCCGCA GCCCTCCCCA CACTCTGGGC GCGGAGCACA ATGATTGGTC

60

ACTCCTATTT TCGCTGAGCT TTTCCTCTTA TTTCAGTTTT CTTCGAGATC AAATCTGGTT

120

TGTAGATGTG CTTGGGGAGA ATGGGGGCCT CTTCTCCAAG AAGCCCGGAG CCTGTCGGGC

180

CGCCGGCGCC CGGTCTCCCC TTCTGCTGCG GAGGATCCCT GCTGGCGGTT GTGGTGCTGC

240

TTGCGCTGCC GGTGGCCTGG GGTCAATGCA ATGCCCCAGA ATGGCTTCCA TTTGCCAGGC

300

CTACCAACCT AACTGATGAA TTTGAGTTTC CCATTGGGAC ATATCTGAAC TATGAATGCC

360

GCCCTGGTTA TTCCGGAAGA CCGTTTTCTA TCATCTGCCT AAAAAACTCA GTCTGGACTG

420

GTGCTAAGGA CAGGTGCAGA CGTAAATCAT GTCGTAATCC TCCAGATCCT GTGAATGGCA

480

TGGTGCATGT GATCAAAGGC ATCCAGTTCG GATCCCAAAT TAAATATTCT TGTACTAAAG

540

GATACCGACT CATTGGTTCC TCGTCTGCCA CATGCATCAT CTCAGGTGAT ACTGTCATTT

600

GGGATAATGA AACACCTATT TGTGACAGAA TTCCTTGTGG GCTACCCCCC ACCATCACCA

660

ATGGAGATTT CATTAGCACC AACAGAGAGA ATTTTCACTA TGGATCAGTG GTGACCTACC

720

GCTGCAATCC TGGAAGCGGA GGGAGAAAGG TGTTTGAGCT TGTGGGTGAG CCCTCCATAT

780

ACTGCACCAG CAATGACGAT CAAGTGGGCA TCTGGAGCGG CCCCGCCCCT CAGTGCATTA

840

TACCTAACAA ATGCACGCCT CCAAATGTGG AAAATGGAAT ATTGGTATCT GACAACAGAA

900

GCTTATTTTC CTTAAATGAA GTTGTGGAGT TTAGGTGTCA GCCTGGCTTT GTCATGAAAG

960

  

CR1 Chapter | 28  301

HUMAN cDNA SEQUENCE—Continued GACCCCGCCG TGTGAAGTGC CAGGCCCTGA ACAAATGGGA GCCGGAGCTA CCAAGCTGCT 1020 CCAGGGTATG TCAGCCACCT CCAGATGTCC TGCATGCTGA GCGTACCCAA AGGGACAAGG 1080 ACAACTTTTC ACCTGGGCAG GAAGTGTTCT ACAGCTGTGA GCCCGGCTAC GACCTCAGAG 1140 GGGCTGCGTC TATGCGCTGC ACACCCCAGG GAGACTGGAG CCCTGCAGCC CCCACATGTG 1200 AAGTGAAATC CTGTGATGAC TTCATGGGCC AACTTCTTAA TGGCCGTGTG CTATTTCCAG 1260 TAAATCTCCA GCTTGGAGCA AAAGTGGATT TTGTTTGTGA TGAAGGATTT CAATTAAAAG 1320 GCAGCTCTGC TAGTTACTGT GTCTTGGCTG GAATGGAAAG CCTTTGGAAT AGCAGTGTTC 1380 CAGTGTGTGA ACAAATCTTT TGTCCAAGTC CTCCAGTTAT TCCTAATGGG AGACACACAG 1440 GAAAACCTCT GGAAGTCTTT CCCTTTGGGA AAACAGTAAA TTACACATGC GACCCCCACC 1500 CAGACAGAGG GACGAGCTTC GACCTCATTG GAGAGAGCAC CATCCGCTGC ACAAGTGACC 1560 CTCAAGGGAA TGGGGTTTGG AGCAGCCCTG CCCCTCGCTG TGGAATTCTG GGTCACTGTC 1620 AAGCCCCAGA TCATTTTCTG TTTGCCAAGT TGAAAACCCA AACCAATGCA TCTGACTTTC 1680 CCATTGGGAC ATCTTTAAAG TACGAATGCC GTCCTGAGTA CTACGGGAGG CCATTCTCTA 1740 TCACATGTCT AGATAACCTG GTCTGGTCAA GTCCCAAAGA TGTCTGTAAA CGTAAATCAT 1800 GTAAAACTCC TCCAGATCCA GTGAATGGCA TGGTGCATGT GATCACAGAC ATCCAGGTTG 1860 GATCCAGAAT CAACTATTCT TGTACTACAG GGCACCGACT CATTGGTCAC TCATCTGCTG 1920 AATGTATCCT CTCGGGCAAT GCTGCCCATT GGAGCACGAA GCCGCCAATT TGTCAACGAA 1980 TTCCTTGTGG GCTACCCCCC ACCATCGCCA ATGGAGATTT CATTAGCACC AACAGAGAGA 2040 ATTTTCACTA TGGATCAGTG GTGACCTACC GCTGCAATCC TGGAAGCGGA GGGAGAAAGG 2100 TGTTTGAGCT TGTGGGTGAG CCCTCCATAT ACTGCACCAG CAATGACGAT CAAGTGGGCA 2160 TCTGGAGCGG CCCGGCCCCT CAGTGCATTA TACCTAACAA ATGCACGCCT CCAAATGTGG 2220 AAAATGGAAT ATTGGTATCT GACAACAGAA GCTTATTTTC CTTAAATGAA GTTGTGGAGT 2280 TTAGGTGTCA GCCTGGCTTT GTCATGAAAG GACCCCGCCG TGTGAAGTGC CAGGCCCTGA 2340 ACAAATGGGA GCCGGAGCTA CCAAGCTGCT CCAGGGTATG TCAGCCACCT CCAGATGTCC 2400 TGCATGCTGA GCGTACCCAA AGGGACAAGG ACAACTTTTC ACCCGGGCAG GAAGTGTTCT 2460 ACAGCTGTGA GCCCGGCTAT GACCTCAGAG GGGCTGCGTC TATGCGCTGC ACACCCCAGG 2520 GAGACTGGAG CCCTGCAGCC CCCACATGTG AAGTGAAATC CTGTGATGAC TTCATGGGCC 2580 AACTTCTTAA TGGCCGTGTG CTATTTCCAG TAAATCTCCA GCTTGGAGCA AAAGTGGATT 2640 TTGTTTGTGA TGAAGGATTT CAATTAAAAG GCAGCTCTGC TAGTTATTGT GTCTTGGCTG 2700 GAATGGAAAG CCTTTGGAAT AGCAGTGTTC CAGTGTGTGA ACAAATCTTT TGTCCAAGTC 2760 CTCCAGTTAT TCCTAATGGG AGACACACAG GAAAACCTCT GGAAGTCTTT CCCTTTGGAA 2820 AAGCAGTAAA TTACACATGC GACCCCCACC CAGACAGAGG GACGAGCTTC GACCTCATTG 2880 GAGAGAGCAC CATCCGCTGC ACAAGTGACC CTCAAGGGAA TGGGGTTTGG AGCAGCCCTG 2940 CCCCTCGCTG TGGAATTCTG GGTCACTGTC AAGCCCCAGA TCATTTTCTG TTTGCCAAGT 3000 TGAAAACCCA AACCAATGCA TCTGACTTTC CCATTGGGAC ATCTTTAAAG TACGAATGCC 3060

  

Continued

302  PART | V  Regulatory Proteins

HUMAN cDNA SEQUENCE—Continued GTCCTGAGTA CTACGGGAGG CCATTCTCTA TCACATGTCT AGATAACCTG GTCTGGTCAA 3120 GTCCCAAAGA TGTCTGTAAA CGTAAATCAT GTAAAACTCC TCCAGATCCA GTGAATGGCA 3180 TGGTGCATGT GATCACAGAC ATCCAGGTTG GATCCAGAAT CAACTATTCT TGTACTACAG 3240 GGCACCGACT CATTGGTCAC TCATCTGCTG AATGTATCCT CTCAGGCAAT ACTGCCCATT 3300 GGAGCACGAA GCCGCCAATT TGTCAACGAA TTCCTTGTGG GCTACCCCCA ACCATCGCCA 3360 ATGGAGATTT CATTAGCACC AACAGAGAGA ATTTTCACTA TGGATCAGTG GTGACCTACC 3420 GCTGCAATCT TGGAAGCAGA GGGAGAAAGG TGTTTGAGCT TGTGGGTGAG CCCTCCATAT 3480 ACTGCACCAG CAATGACGAT CAAGTGGGCA TCTGGAGCGG CCCCGCCCCT CAGTGCATTA 3540 TACCTAACAA ATGCACGCCT CCAAATGTGG AAAATGGAAT ATTGGTATCT GACAACAGAA 3600 GCTTATTTTC CTTAAATGAA GTTGTGGAGT TTAGGTGTCA GCCTGGCTTT GTCATGAAAG 3660 GACCCCGCCG TGTGAAGTGC CAGGCCCTGA ACAAATGGGA GCCAGAGTTA CCAAGCTGCT 3720 CCAGGGTGTG TCAGCCGCCT CCAGAAATCC TGCATGGTGA GCATACCCCA AGCCATCAGG 3780 ACAACTTTTC ACCTGGGCAG GAAGTGTTCT ACAGCTGTGA GCCTGGCTAT GACCTCAGAG 3840 GGGCTGCGTC TCTGCACTGC ACACCCCAGG GAGACTGGAG CCCTGAAGCC CCGAGATGTG 3900 CAGTGAAATC CTGTGATGAC TTCTTGGGTC AACTCCCTCA TGGCCGTGTG CTATTTCCAC 3960 TTAATCTCCA GCTTGGGGCA AAGGTGTCCT TTGTCTGTGA TGAAGGGTTT CGCTTAAAGG 4020 GCAGTTCCGT TAGTCATTGT GTCTTGGTTG GAATGAGAAG CCTTTGGAAT AACAGTGTTC 4080 CTGTGTGTGA ACATATCTTT TGTCCAAATC CTCCAGCTAT CCTTAATGGG AGACACACAG 4140 GAACTCCCTC TGGAGATATT CCCTATGGAA AAGAAATATC TTACACATGT GACCCCCACC 4200 CAGACAGAGG GATGACCTTC AACCTCATTG GGGAGAGCAC CATCCGCTGC ACAAGTGACC 4260 CTCATGGGAA TGGGGTTTGG AGCAGCCCTG CCCCTCGCTG TGAACTTTCT GTTCGTGCTG 4320 GTCACTGTAA AACCCCAGAG CAGTTTCCAT TTGCCAGTCC TACGATCCCA ATTAATGACT 4380 TTGAGTTTCC AGTCGGGACA TCTTTGAATT ATGAATGCCG TCCTGGGTAT TTTGGGAAAA 4440 TGTTCTCTAT CTCCTGCCTA GAAAACTTGG TCTGGTCAAG TGTTGAAGAC AACTGTAGAC 4500 GAAAATCATG TGGACCTCCA CCAGAACCCT TCAATGGAAT GGTGCATATA AACACAGATA 4560 CACAGTTTGG ATCAACAGTT AATTATTCTT GTAATGAAGG GTTTCGACTC ATTGGTTCCC 4620 CATCTACTAC TTGTCTCGTC TCAGGCAATA ATGTCACATG GGATAAGAAG GCACCTATTT 4680 GTGAGATCAT ATCTTGTGAG CCACCTCCAA CCATATCCAA TGGAGACTTC TACAGCAACA 4740 ATAGAACATC TTTTCACAAT GGAACGGTGG TAACTTACCA GTGCCACACT GGACCAGATG 4800 GAGAACAGCT GTTTGAGCTT GTGGGAGAAC GGTCAATATA TTGCACCAGC AAAGATGATC 4860 AAGTTGGTGT TTGGAGCAGC CCTCCCCCTC GGTGTATTTC TACTAATAAA TGCACAGCTC 4920 CAGAAGTTGA AAATGCAATT AGAGTACCAG GAAACAGGAG TTTCTTTACC CTCACTGAGA 4980 TCATCAGATT TAGATGTCAG CCCGGGTTTG TCATGGTAGG GTCCCACACT GTGCAGTGCC 5040 AGACCAATGG CAGATGGGGG CCCAAGCTGC CACACTGCTC CAGGGTGTGT CAGCCGCCTC 5100

  

CR1 Chapter | 28  303

HUMAN cDNA SEQUENCE—Continued CAGAAATCCT GCATGGTGAG CATACCCTAA GCCATCAGGA CAACTTTTCA CCTGGGCAGG 5160 AAGTGTTCTA CAGCTGTGAG CCCAGCTATG ACCTCAGAGG GGCTGCGTCT CTGCACTGCA 5220 CGCCCCAGGG AGACTGGAGC CCTGAAGCCC CTAGATGTAC AGTGAAATCC TGTGATGACT 5280 TCCTGGGCCA ACTCCCTCAT GGCCGTGTGC TACTTCCACT TAATCTCCAG CTTGGGGCAA 5340 AGGTGTCCTT TGTTTGCGAT GAAGGGTTCC GATTAAAAGG CAGGTCTGCT AGTCATTGTG 5400 TCTTGGCTGG AATGAAAGCC CTTTGGAATA GCAGTGTTCC AGTGTGTGAA CAAATCTTTT 5460 GTCCAAATCC TCCAGCTATC CTTAATGGGA GACACACAGG AACTCCCTTT GGAGATATTC 5520 CCTATGGAAA AGAAATATCT TACGCATGCG ACACCCACCC AGACAGAGGG ATGACCTTCA 5580 ACCTCATTGG GGAGAGCTCC ATCCGCTGCA CAAGTGACCC TCAAGGGAAT GGGGTTTGGA 5640 GCAGCCCTGC CCCTCGCTGT GAACTTTCTG TTCCTGCTGC CTGCCCACAT CCACCCAAGA 5700 TCCAAAACGG GCATTACATT GGAGGACACG TATCTCTATA TCTTCCTGGG ATGACAATCA 5760 GCTACATTTG TGACCCCGGC TACCTGTTAG TGGGAAAGGG CTTCATTTTC TGTACAGACC 5820 AGGGAATCTG GAGCCAATTG GATCATTATT GCAAAGAAGT AAATTGTAGC TTCCCACTGT 5880 TTATGAATGG AATCTCGAAG GAGTTAGAAA TGAAAAAAGT ATATCACTAT GGAGATTATG 5940 TGACTTTGAA GTGTGAAGAT GGGTATACTC TGGAAGGCAG TCCCTGGAGC CAGTGCCAGG 6000 CGGATGACAG ATGGGACCCT CCTCTGGCCA AATGTACCTC TCGTACACAT GATGCTCTCA 6060 TAGTTGGCAC TTTATCTGGT ACGATCTTCT TTATTTTACT CATCATTTTC CTCTCTTGGA 6120 TAATTCTAAA GCACAGAAAA GGCAATAATG CACATGAAAA CCCTAAAGAA GTGGCTATCC 6180 ATTTACATTC TCAAGGAGGC AGCAGCGTTC ATCCCCGAAC TCTGCAAACA AATGAAGAAA 6240 ATAGCAGGGT CCTTCCTTGA CAAAGTACTA TACAGCTGAA GAACATCTCG AATACAATTT 6300 TGGTGGGAAA GGAGCCAATT GATTTCAACA GAATCAGATC TGAGCTTCAT AAAGTCTTTG 6360 AAGTGACTTC ACAGAGACGC AGACATGTGC ACTTGAAGAT GCTGCCCCTT CCCTGGTACC 6420 TAGCAAAGCT CCTGCCTCTT TGTGTGCGTC ACTGTGAAAC CCCCACCCTT CTGCCTCGTG 6480 CTAAACGCAC ACAGTATCTA GTCAGGGGAA AAGACTGCAT TTAGGAGATA GAAAATAGTT 6540 TGGATTACTT AAAGGAATAA GGTGTTGCCT GGAATTTCTG GTTTGTAAGG TGGTCACTGT 6600 TCTTTTTTAA AATATTTGTA ATATGGAATG GGCTCAGTAA GAAGAGCTTG GAAAATGCAG 6660 AAAGTTATGA AAAATAAGTC ACTTATAATT ATGCTACCTA CTGATAACCA CTCCTAATAT 6720 TTTGATTCAT TTTCTGCCTA TCTTCTTTCA CATATGTGTT TTTTTACATA CGTACTTTTC 6780 CCCCTTAGTT TGTTTCCTTT TATTTTATAG AGCAGAACCC TAGTCTTTTA AACAGTTTAG 6840 AGTGAAATAT ATGCTATATC AGTTTTTACT TTCTCTAGGG AGAAAAATTA ATTTACTAGA 6900 AAGGCATGAA ATGATCATGG GAAGAGTGGT TAAGACTACT GAAGAGAAAT ATTTGGAAAA 6960 TAAGATTTCG ATATCTTCTT TTTTTTTGAG ATGGAGTCTG GCTCTGTCTC CCAGGCTGGA 7020 GTGCAGTGGC GTAATCTCGG CTCACTGCAA GCTCCGCCTC CCGGGTTGAC ACCATTTTCC 7080 TGCCTCAGCC TCCTGAGTAG TTGGGATTAC CAGTAGATGG GACTACAGGC ACCTGCCAAC 7140 ACGCCCGGCT AATTTTTTTG TATTTTTAGT AGAGACGGGG TTTCACCATG TTAGCCAGGA 7200

  

Continued

304  PART | V  Regulatory Proteins

HUMAN cDNA SEQUENCE—Continued TGGTCTGGAT CTCCTGACCT CGTGATCCAC CTGCCTCGGC CTCCCAAAGT GCTGCGATTA 7260

CAGGCATGAG CCACCGCGCC TGGCCGCTTT CGATATTTTC TAAACTTTAA TTCAAAAGCA 7320 CTTTGTGCTG TGTTCTATAT AAAAAACATA ATAAAAATTG AAATGAAAGA ATAATTGTTA 7380 TTATAAAAGT ACTAGCTTAC TTTTGTATGG ATTCAGAATA TACTAAATTA ACTTTTTAAA 7440 ACACAACTTT TAAAAAATGT ATCAAAATAA TAAACGTGTT CTGATATTTT TAAAATAAGT 7500 GACCTTGTGT TCTTTAACCA GTCCACATCT TTAGAGAACA AAAATGTGTT ATGATATTAT 7560 GGGCCATGCT AATGACCTCT AGAAAACATC AGAATATTTC TGGATATTTA ATAATAGCTT 7620 TATATATGAC TAATGCTCAT TTCTATGTAA TTCTGTTTAA TAGTTGCTTT AAAGGTGAAT 7680 TTTGCCACAT TTACTTTGAC AGCAGTATAA GGAGTGAGAT AGACATGAAC CTGAATTTCA 7740 ATTTAAAATC ATGGAAGAGA GGGAAAAAAA ACCAGCTTAA GAAAAATCAA CTGATAAACT 7800 GCAAGAAAAA AATGCAACTT ACATCACAAA AGCTAATTGC TTTATTATTT AGAGAGTACT 7860 TAAAAATTAA AGACCAAACT TCTCTCCACC CAACAAAAAT GGGCAAAGGA CATACAGCTA 7920 GGTCACCAAG AAAGAAGGGC AAATAGGTGG TGAGTATATG TAAAGATACT TGATAGGACT 7980 TTTGCTTAGT TGAATCTTTA GCAAATCTCT TTTATTTCTT GGGATTTTGA AGAAGTAATT 8040 TTTAAAGGAG GACTAGAAAC TAAGTGATTG GGAATTGGCC TTTTTAGAAT TAAAATTTCC 8100 CATTACAAGA AAAAAAAATC CTGTGTTCTT TTTTTTTTCC AGAATGGAGT AGGTCAGTGA 8160 GCAATGTGAT TAATAAATAT TTCAATGTCT GTGACTTTTG ATTTATTTTG GAGACAGGGT 8220 CTTGCTCTGT TACCCAGGCT GGAGTGCAGT GGTGCTATCT AGGCTTACTG CAACCTCACC 8380 TGTCACTTTT TAATTGCAAG AAAGCTGAAA GGTTTTTTTC TATTATATCA GTTATAATGA 8440 TAAATACTGT ATATACTAAC TATGAGTAAA ATACTATATT GCCTAACTTG TATTATTAAG 8500 CAATTCTGCT AACCTGTGAC CTTACATTTT CATCTGAAAA GCAGGGGCTG GACACCAATT 8460 GCCCTATGAA GCTATTGCTA GTCCTAACAT TCTTTGTTTT GTTTGCTTTT TTGGCACACT 8520 TAAGTGTGTA CTATGAAGTT TATGATGCTT TAATGAAATT TTCTGTCTCT ACCATTGTAA 8580 TGAGAAAGGA ATAAAATACT TTATTTTGCA AATCTAAAAA AAAAAAAAA

The first nucleotides in each exon are underlined. The two possible initiation codons (ATG, methionine) are underlined and so are the termination codon (TGA) and the polyadenylation site (AATAAA).

GENOMIC STRUCTURE The gene for CR1 is found on chromosome 1, in the cluster of RCA (regulators of complement activation) region. The gene presented here (allotype F or 1) is the most common transcript, extends 133 kb and encodes 39 exons. The second most abundant form, allotype S or 2, is larger, 150–160 kb and spans 47 exons. The additional eight exons form an additional long homologue repeat (LHR-S) (Fig. 28.3).

CR1 Chapter | 28  305 LHR-S found in allotype S or 2 1

39

Allotype F or 1

FIGURE 28.3  Diagram of the genomic structure for CR1. Allotype F or 1 has 39 exons, while allotype Sor 2, has an additional LHR containing 8 exons.

ACCESSION NUMBERS Human Chimpanzee Baboon Mouse

CR1 CR1 CR1 CR1/CR2

Mouse

Crry

Rat

Crry

cDNA

Genomic

Y000816 L24920–L24922 L39791 M61132 M36470 M29281 M35684 J04153 M33527 U17123–U17128 X98171 M23529 M34164–M34173 L36532 D42115

L17390–L17430

DEFICIENCY To date, there are no known individuals with innate CR1 deficiency. Acquired CR1 deficiency, seen as low expression levels of CR1 on circulating RBCs, is seen during pregnancy22 and in chronic inflammatory conditions such as HIV, SLE, sepsis and acute respiratory syndrome due to generation and clearance of abnormally large numbers of circulating immune complexes.23 Innate low expression of CR1 on circulating RBCs is seen in individuals expressing Knops group antigens (Knops, McCoy, Swain-Langley and York) on CR1 that also have circulating anti-CR1 antibodies.

POLYMORPHIC VARIANTS CR1 polymorphism due to insertion, duplication and deletion in CR1 gene has triple consequences: (1) structural, detected as variation in molecular mass of CR1 variants, (2) functional, with altered binding avidity for C3b due to changes in LHR-B segments, and changes in the cofactor activity effectiveness,24 and (3) quantitative, with H allotype having expression levels of CR1 on circulating RBCs over ten times larger compared to the L allotype. In general population, RBC CR1 levels vary between 100 in L allotype expresser to

306  PART | V  Regulatory Proteins

600 in mixed HL allotype and 1200 in H allotype expressers.18 The expression levels of CR1 in circulating neutrophils do not display an H/L allotype variation. Allotype S of CR1 has been found to be associated with increased risk of Alzheimer disease.25

POLYMORPHISM FREQUENCIES26 Structural Alleles

White Population

African Americans

Mexican Americans

Chinese Taiwanese

CR1*1 CR1*2 CR1*3 CR1*4

0.86–0.93 0.07–0.26 0–0.02 <0.01

0.82–0.84 0.11–0.12 0.04–0.06 <0.01

0.89 0.11 0 <0.01

0.96 0.03 0.01 0

Quantitative Allele

White Population

African Americans

Mexican Americans

Chinese Taiwanese

H L

0.75–0.78 0.25–0.22

0.85 0.15

0.80 0.20

0.71 0.28

Knops Phenotype

White Population

African Americans

Mexican Americans

Chinese Taiwanese

Kn(a+) McC(a+) McC(b+) SL(a+) Yk(a+)

0.98 0.98 0.01 0.99 0.98

0.99 0.94 0.51 0.65 0.92

Unknown Unknown Unknown Unknown Unknown

0.99 1.00 0.02 0.97 Unknown

MUTANT ANIMALS In mice, CR1/CR2 knockout animals were generated by mutation of Cr2 genes in embryonic stem cells by homologous recombination.27 Functional studies of the mice have demonstrated the role of CR1 and CR2 in B cell activation, regulation of B cell-specific humoral immune response cell defects and increased risk to develop cardiomyopathy, altered IgG3 antibody production and expression of significant defects in T cell functions.27–30

REFERENCES 1. Fearon DT. Identification of the membrane glycoprotein that is the C3b receptor of the human erythrocyte, polymorphonuclear leukocyte, B lymphocyte and monocyte. J Exp Med 1980;152:20–30. 2. Klickstein LB, Moulds JM. CR1. In: Morley BJ, Walport MJ, editors. The complement facts book. New York: Academic Press; 2000. p. 136–45. 3. Ghiran I, Glodek AM, Weaver G, Klickstein LB, Nicholson-Weller A. Ligation of erythrocyte CR1 induces its clustering in complex with scaffolding protein FAP-1. Blood 2008;112(8):3465–73.

CR1 Chapter | 28  307 4. Lublin DM, Griffith RC, Atkinson JP. Influence of glycosylation on allelic and cell-specific Mr variation, receptor processing, and ligand binding of the human complement C3b/C4b receptor. J Biol Chem 1986;261(13):5736–44. 5. Klickstein LB, Wong WW, Smith JA, Weis JH, Wilson JG, Fearon DT. Human C3b/C4b receptor (CR1). Demonstration of long homologous repeating domains that are composed of the short consensus repeats characteristics of C3/C4 binding proteins. J Exp Med 1987;165(4):1095–112. 6. Birmingham DJ, Hebert LA. CR1 and CR1-like: the primate immune adherence receptors. Immunol Rev 2001;180:100–11. 7. Martin H, McConnell I, Gorick B, Hughes-Jones NC. Antibody-independent activation of the classical pathway of complement by Epstein-Barr virus. Clin Exp Immunol 1987;67(3):531–6. 8. Ogembo JG, Kannan L, Ghiran I, Nicholson-Weller A, Finberg RW, Tsokos GC, et al. Human complement receptor type 1/CD35 is an Epstein–Barr Virus receptor. Cell Rep 2013;3(2):371–85. 9. Rowe JA, Moulds JM, Newbold CI, Miller LH. P. Falciparum rosetting mediated by a parasite-variant erythrocyte membrane protein and complement-receptor 1. Nature 1997;388(6639):292–5. 10. Alexander JJ, Hack BK, Cunningham PN, Quigg RJ. A protein with characteristics of factor H is present on rodent platelets and functions as the immune adherence receptor. J Biol Chem 2001;276(34):32129–35. 11. Glodek AM, Mirchev R, Golan DE, Khoory JA, Burns JM, Shevkoplyas SS, et al. Ligation of complement receptor 1 increases erythrocyte membrane deformability. Blood 2010;116(26):6063–71. 12. Ross GD, Lambris JD, Cain JA, Newman SL. Generation of three different fragments of bound C3 with purified factor I or serum. I. Requirements for factor H vs. CR1 cofactor activity. J Immunol 1982;129(5):2051–60. 13. Daha MR, Fearon DT, Austen KF. C3 requirements for formation of alternative pathway C5 convertase. J Immunol 1976;117(2):630–4. 14. Collard CD, Bukusoglu C, Agah A, Colgan SP, Reenstra WR, Morgan BP, et al. Hypoxiainduced expression of complement receptor type 1 (CR1, CD35) in human vascular endothelial cells. Am J Physiol 1999;276:C450–8. 15. Min X, Liu C, Wei Y, Wang N, Yuan G, Liu D, et al. Expression and regulation of complement receptors by human natural killer cells. Immunobiology 2014;219(9):671–9. 16. Cohen JH, Atkinson JP, Klickstein LB, Oudin S, Subramanian VB, Moulds JM. The C3b/C4b receptor (CR1, CD35) on erythrocytes: methods for study of the polymorphisms. Mol Immunol 1999;36(13–14):819–25. 17. Sim RB, Malhotra V, Day AJ, Erdei A. Structure and specificity of complement receptors. Immunol Lett 1987;14(3):183–90. 18. Yoon SH, Fearon DT. Characterization of a soluble form of the C3b/C4b receptor (CR1) in human plasma. J Immunol 1985;134(5):3332–8. 19. Pascual M, Duchosal MA, Steiger G, Giostra E, Pechere A, Paccaud JP, et al. Circulating soluble CR1 (CD35). Serum levels in diseases and evidence for its release by human leukocytes. J Immunol 1993;151(3):1702–11. 20. Mulligan MS, Yeh CG, Rudolph AR, Ward PA. Protective effects of soluble CR1 in complement- and neutrophil-mediated tissue injury. J Immunol 1992;148:1479–85. 21. Olesen B, Thomsen BS, Kristensen HS. Loss of erythrocyte complement receptors (CR1; CD35) in patients with acute episodes of septicaemia or bacterial meningitis. Scand J Infect Dis 1992;24(2):189–95.

308  PART | V  Regulatory Proteins 22. Imrie HJ, McGonigle TP, Liu DT, Jones DR. Reduction in erythrocyte complement receptor 1 (CR1, CD35) and decay accelerating factor (DAF, CD55) during normal pregnancy. J Reprod Immunol 1996;31(3):221–7. 23. Larcher C, Schulz TF, Hofbauer J, Hengster P, Romani N, Wachter H, et al. Expression of the C3d/EBV receptor and of other cell membrane surface markers is altered upon HIV-1 infection of myeloid, T, and B cells. J Acquir Immune Defic Syndr 1990;3(2):103–8. 24. Wong WW, Farrell SA. Proposed structure of the F’ allotype of human CR1. Loss of a C3b binding site may be associated with altered function. J Immunol 1991;146:656–62. 25. Mahmoudi R, Kisserli A, Novella JL, Donvito B, Drame M, Reveil B, et al. Alzheimer’s disease is associated with low density of the long CR1 isoform. Neurobiol Aging 2015;36(4). 1766 e5–1766 e12. 26. Moulds JM, Brai M, Cohen J, Cortelazzo A, Cuccia M, Lin M, et al. Reference typing report for complement receptor 1 (CR1). Exp Clin Immunogenet 1998;15(4):291–4. 27. Molina H, Holers VM, Li B, Fung Y, Mariathasan S, Goellner J, et al. Markedly impaired humoral immune response in mice deficient in complement receptors 1 and 2. Proc Natl Acad Sci USA 1996;93(8):3357–61. 28. Boackle SA, Culhane KK, Brown JM, Haas M, Bao L, Quigg RJ, et al. CR1/CR2 deficiency alters IgG3 autoantibody production and IgA glomerular deposition in the MRL/lpr model of SLE. Autoimmunity 2004;37(2):111–23. 29. Fang Y, Xu C, Fu YX, Holers VM, Molina H. Expression of complement receptors 1 and 2 on follicular dendritic cells is necessary for the generation of a strong antigen-specific IgG response. J Immunol 1998;160(11):5273–9. 30. Fairweather D, Frisancho-Kiss S, Njoku DB, Nyland JF, Kaya Z, Yusung SA, et al. Complement receptor 1 and 2 deficiency increases coxsackievirus B3-induced myocarditis, dilated cardiomyopathy, and heart failure by increasing macrophages, IL-1beta, and immune complex deposition in the heart. J Immunol 2006;176(6):3516–24.