Complement cascade (Homo sapiens)

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11, 12, 59, 82, 8615, 546, 8337599, 193619, 224, 453, 48595452, 6142, 62, 6961792744595932, 7617, 25, 42, 63, 67...49, 51, 534, 31, 4510, 16, 4144, 5919, 24, 4720, 46, 57, 723, 482, 62, 692157, 58, 81715744, 595218, 28, 38, 43, 50...59137, 39, 65, 70, 7834, 44, 64493, 74563530, 51, 55855, 14, 264829, 36, 58, 715266, 68234818, 33, 40, 43, 50...54Cell surfaceC4bC2a MASP1 dimer MBL-II tetramer deamidated-Q1013-C4A-derived C4b Ig Antibody Light Chain C4b Complement factor I deamidated-Q1013-C4B-derived C4b MCP, CR1C4bC3b complexes C3b deamidated-Q1013-C4B-derived C4b Cell surfaceFH,FHR3C3b MBL-II tetramer Cell surfaceC3bFactor BbProperdin Complement factor ICell surfaceFH,FHR3C3b deamidated-Q1013-C4B-derived C4b C4b MBL-IIActivated MASP-1 dimerActivated MASP-2 dimer complex C4b MASP2 dimer Complement factor I C3Complement factor 5 deamidated-Q1013-C4A-derived C4b MASP2 dimer thioester-C1010-Q1013-C4b C4b-binding protein C3b C3IgG VTNC5bC6C7C8C9 FCN3 subunit C3b C5bC6C7C8 complex C5b cytosolVTNC5bC6C7 C3b C4b-binding protein C3b Ig Kappa Light Chain V Region deamidated-Q1013-C4A-derived C4b Activated MASP-2 dimer Ficolin-1 tetramer C3b Host cell surface Ig Lambda C region C3b MASP2 dimer MBL bound to mannose-based carbohydrates on bacterial surfaces FCN3 subunit FCN3 ligand Ig Lamda Light Chain V Region IgG C region CR1C3b Ig Kappa Light Chain V Region C3b C4b deamidated-Q1013-C4A-derived C4b C4 binding proteinprotein S thioester-C1010-Q1013-C4B-derived C4b MASP1 dimer Factor HC3b MASP1 dimer deamidated-Q1013-C4A-derived C4b C3b Immunoglobulin Lambda Light Chain C5b Ficolin-1 tetramer Cell surfaceC3b C1 complement factor FCN2MASPsCa2+FCN2 ligand FCN2MASP2 dimerMASP1 dimer C8 iC3b Cell surfaceC3bFactor Bb Cell surfaceC4b Factor IMCP, CR1C4b, C3b complexes FCN2 subunit C4b CR1C4b FCN1 subunit deamidated-Q1013-C4A-derived C4b Ig Heavy Chain V Region Ficolin-3 hexamer deamidated-Q1013-C4B-derived C4b IgG Heavy Chain Complement factor I Complement factor I C-reactive protein pentamerphosphocholineC1Q IgG C region deamidated-Q1013-C4B-derived C4b deamidated-Q1013-C4B-derived C4b C3b FCN1 ligand C3b Cell surfaceC3b Cell surfaceC4b FCN3MASP2 dimerMASP1 dimer DAFC3b C5bC6C7 complex Antigen antibody C1 C3b C3b C1SC1R tetramer Cell surfaceC3bFactor Bb Ficolin-2 tetramer FCN3MASP2 dimerMASP1 dimer C3b Ig Antibody Light Chain C5bC6 complex C3b deamidated-Q1013-C4A-derived C4b FCN3MASPsCa2+FCN3 ligand C8 Activated C1R Cell surfaceC4b C3MBLactivated MASPsmannose-based carbohydrates MBL subunit Cell surfaceC4bC2a C4b-binding protein C3Cell surfaceC4b C1Q CD59C5b-C9 C3bFactor BbC3bProperdin complex Membrane Attack Complex C4b-binding protein C4b C4b Cell surfaceC4b Antigen-antibody complex MBL subunit C4b FCN2 ligand Antigen antibody C1 Cell surfaceC4b MASP1 dimer Complement factor I FCN1MASP2 dimerMASP1 dimer MASP1 dimer thioester-C1010-Q1013- C4A-derived C4b MASP2 dimer Cell surfaceC4b MCPC4b C4b-binding protein MCPC3b Activated C1S C3b Ig Lambda C region C5b C5bC6C7 complex FCN1MASP2 dimerMASP1 dimer C5b FCN1MASPsCa2+FCN1 ligand MASP2 dimer IgG Immunoglobulin Kappa Light Chain Cell surfaceC3b CR1C4b C4bC2aC3b C3b MCPC4b C1Q subunit C4-binding proteinC4b C5bC6C7C8 complex Immunoglobulin Kappa Light Chain C5b C1 complement factor DAFC4b deamidated-Q1013-C4A-derived C4b Immunoglobulin Lambda Light Chain Ficolin-2 tetramer MCPC3b C5b deamidated-Q1013-C4A-derived C4b VTNC5bC6C7 Antigen-antibody complex MBL-IIMASP-2 dimerMASP-1 dimer complex Cell surfaceC4b Factor HC3b C1 complement factor Activated C1Sactivated C1R tetramer deamidated-Q1013-C4B-derived C4b Cell surfaceFH,FHR3C3bBb MASP1 dimer C3IgG MASP2 dimer Immunoglobulin Kappa Light Chain deamidated-Q1013-C4A-derived C4b Cell surfaceC3bFactor BbProperdin Host cell surface thioester-C1010-Q1013-C4B-derived C4b FCN1 subunit thioester-C1010-Q1013-C4b Ig Lambda C region IgG Heavy Chain Ig Heavy Chain V Region MASP2 dimer C1Q thioester-C1010-Q1013- C4A-derived C4b deamidated-Q1013-C4B-derived C4b C1Q subunit IgG C region Factor HHost cell surface Cell surfaceC4bC2a Ig Heavy Chain V Region C4b MBL-II tetramer FCN2MASP2 dimerMASP1 dimer C3c iC3b Cell surfaceC3b MBL-IIMASP-2 dimerMASP-1 dimer complex IgG Heavy Chain C4b C5b Activated MASP-1 dimer C4 binding proteinC4bC2a C8 iC3b MASP2 dimer C1Q subunit C-reactive protein pentamerphosphocholine Cell surfaceC3b Immunoglobulin Lambda Light Chain C8 MBL subunit C5bC6C7 complex Cell surfaceC4bC2a CR1iC3b Cell surfaceC3bFactor Bb C3b deamidated-Q1013-C4B-derived C4b thioester-C1010-Q1013-C4b Cell surfaceC3bFactor B complex C1Q subunit C5b C4-binding proteinC4b Cell surfaceC4b Ficolin-3 hexamer Cell surfaceFH,FHR3C3b Antigen antibody C1 complex C5bC6C7 complex FCN2 subunit Ig Kappa Light Chain V Region Antigen-antibody complex C-reactive protein homopentamer C3thioester-C1010-Q1013-C4B-derived C4b C8 C5b Cell surfaceC3b Ig Lamda Light Chain V Region C4b-binding proteinFactor I Activated C1R thioester-C1010-Q1013- C4A-derived C4b C1Q MASP1 dimer C1Q C3b Complement factor IFactor HC3b CR1C3b Cell surfaceC4b C1Sactivated C1R tetramer C3b Ig Antibody Light Chain MASP1 dimer Ig Lamda Light Chain V Region deamidated-Q1013-C4B-derived C4b C3b Complement factor 3 C3 beta chain Ig kappa chain V-III region CLL Ig lambda chain V-II region BO C7dNQ-C4AC2a C3b alpha' Ig heavy chain V-II region HE Ig kappa chain V-III region VG Ig lambda chain V-II region TOG C4A beta dNQ-C4AIg kappa chain V-I region Roy Ig heavy chain V-I region WOL Ig lambda chain V-I region WAH Ig lambda chain V-V region DEL dNQ-C4AdNQ-C4BC4A gamma C4B beta IGHV7-81IGLC1FCN3 Ig lambda chain V-II region TRO Ig lambda chain V-I region HA IGLC2C4aCFBIg kappa chain V-II region RPMI 6410 Ig kappa chain V-III region WOL C7H2OIg lambda chain V-II region TOG C3b alpha' Cell surfaceC3bFactor BbIGLC6IGHG3 Ig lambda chain V-I region HA C4A gamma Ig kappa chain V-I region Rei thioester-C1010-Q1013-C4bMASP2-1 dNQ-C4BIGLC1Ig heavy chain V-III region JON C3b alpha' IGHG4Ig heavy chain V-I region HG3 C4B gamma Ig lambda chain V-I region NEWM MASP1IgH heavy chain V-III region VH26 precursor IGKV1-5Sialic acid Ig heavy chain V-III region NIE Ig heavy chain V-II region COR Ig kappa chain V-I region Lay IGHG2C5b alpha' Ig kappa chain V-III region WOL Ig heavy chain V-III region BUT Cell surfaceC3bC4BPA C4B gamma C4A gamma Ig kappa chain V-IV region Len C3b alpha' IGLV3-22CD59Ig lambda chain V-IV region Kern Ig lambda chain V-VI region EB4 FCN3 C4B beta Ig kappa chain V-III region HAH C4A gamma C3 beta chain C5 beta MBL2 C4A beta Ig lambda chain V-VII region MOT Ig kappa chain V-I region Daudi Ig heavy chain V-I region HG3 Ig lambda chain V-III region LOI Ig kappa chain V-I region Scw Ig heavy chain V-III region BUR IGHV7-81C3 beta chain IGLV1-36Ig lambda chain V-II region NEI C3C4A gamma CD55Ig heavy chain V-III region JON IGLV7-43Ig heavy chain V-III region GAL Ig heavy chain V-III region ZAP Ig heavy chain V-I region ND Ig lambda chain V-III region SH C3 beta chain Ig kappa chain V-I region EU Ig kappa chain V-I region CAR N-acetylgalactosamine thioester-C1010-Q1013-C4bIGLV8-61Ig kappa chain V-III region VH IGKCFCN2 ligandMASP2-1 C8B Ig heavy chain V-III region GAL C4b-binding proteinFactor IC4A beta C4B gamma Ig kappa chain V-II region RPMI 6410 Ig heavy chain V-II region HE IGKVA18Ig kappa chain V-II region Cum Ig lambda chain V-IV region Bau IGLV3-27IGLV5-37C3 beta chain C8A Ig kappa chain V-II region FR CFIC1QBIg kappa chain V-I region Roy CFBIGLV2-18Cell surfaceC4bC2aC4A beta C5 beta Ig kappa chain V-IV region STH Ig kappa chain V-I region WAT C3b alpha' C4BPB IGLV7-46Ig kappa chain V-I region WEA C7Ig heavy chain V-III region BUR IGLV7-46C4 activatorIg kappa chain V-I region Hau C8A Ig heavy chain V-II region MCE dNQ-C4BIg kappa chain V-I region Kue CFBIg lambda chain V-VI region AR IGLV2-23Ig heavy chain V-I region WOL Ig kappa chain V-II region GM607 C1S C-terminal fragment IGLVIGLV3-25Ig lambda chain V region 4A C4B beta MCP, CR1IGLV2-18C4B gamma IGLV4-3Ig kappa chain V-II region MIL Ig kappa chain V-III region HIC Cell surfaceC3bFactor BbProperdinC4-binding proteinC4bIg heavy chain V-I region HG3 Ig lambda chain V-VII region MOT C5b alpha' C4A gamma MASP2-1 Cell surfaceC4bC2aIg heavy chain V-I region WOL Ig kappa chain V-III region HAH IGKCC4B alpha chain fragment b Complement factor 3Ig kappa chain V-I region AU Ig kappa chain V-I region Ka C3 beta chain Ig heavy chain V-III region CAM Ig kappa chain V-I region CAR C5bC6C7 complexIg heavy chain V-II region ARH-77 IGLV1-44C4B beta IGLV3-16MASP1Ig lambda chain V-IV region X C3b alpha' Ig heavy chain V-III region GA C4BPA VTNC5bC6C7C8 complexIg kappa chain V-I region Mev Ig kappa chain V-I region AG Complement factor IC6 FCN1MASP2 dimerMASP1 dimerC4B beta C8G Ca2+ C3bC3b alpha' C3 beta chain Ig heavy chain V-III region GA Ig heavy chain V-III region WEA Ig heavy chain V-II region SESS D-fucose Ig kappa chain V-I region DEE C4BPB Ig lambda chain V-II region TRO C4A beta C3b alpha' C6 Ig lambda chain V-I region EPS C5b alpha' C4cIGLV7-43FCN2 N-acetylgalactosamine Ig lambda chain V-VI region EB4 Ig kappa chain V-II region MIL C3 beta chain Ig kappa chain V-I region AG C1QC CFBIg kappa chain V-II region MIL Ig kappa chain V-I region CAR CFIC1SCFBComplement Factor 4CR1 C3b alpha' Ig kappa chain V-III region Ti IGHG2IGLV1-40FCN3 ligandIg lambda chain V-II region VIL Ig kappa chain V-I region OU C6 Ig heavy chain V-III region HIL Ig heavy chain V-III region POM Ig kappa chain V-IV region STH Ig heavy chain V-III region BUT FCN3MASPsCa2+FCN3 ligandIg kappa chain V-III region GOL CD55 IGLV1-36N-acetyl-D-glucosamine MASP2-1 C5b alpha' Ig heavy chain V-III region BUR Ig lambda chain V-III region SH Ig kappa chain V-I region Lay C2aIg kappa chain V-III region WOL FCN3MASP2 dimerMASP1 dimerIGLV2-33Ig kappa chain V region EV15 Ig kappa chain V-III region VG H2OIg kappa chain V-I region Ka C3c alpha' chain fragment 2 Ig heavy chain V-III region HIL C3b alpha' IGLV3-22Ig heavy chain V-II region COR IGLC7Ig heavy chain V-III region TEI C5 convertasesIg heavy chain V-II region DAW C4B alpha chain fragment b C3 beta chain Ig heavy chain V-III region DOB dNQ-C3C8B Ig lambda chain V-II region NEI IGLV1-40Ig lambda chain V-II region MGC C3c alpha' chain fragment 1 DAFC4bC1R N-terminal fragment IGLV7-46C4BPB C3b alpha' C3 beta chain C9C4B beta Ig kappa chain V-I region Roy Ig heavy chain V-II region DAW MASP2-1 Ig kappa chain V-I region AG C2a Ig heavy chain V-III region ZAP C4dC3bIg lambda chain V-II region WIN C3b alpha' N-acetyl-D-glucosamine C4b, C3bC7Ig kappa chain V-I region DEE Ig kappa chain V-I region BAN Ig heavy chain V-II region COR IgH heavy chain V-III region VH26 precursor Ig kappa chain V-III region NG9 C4B gamma CFBC4A gamma Ig lambda chain V-I region VOR C1SC3c alpha' chain fragment 1 precursor C3aCFH CD55 C3b alpha' C4 binding proteinprotein SIg heavy chain V-III region NIE Ig heavy chain V-III region BRO C3b alpha' Ig kappa chain V-III region B6 IGLV3-25CFIIg kappa chain V-II region RPMI 6410 IGLV2-23Ig lambda chain V-VI region AR CR1C3bBb, C4bC2a complexesIg lambda chain V-VII region MOT IGLV5-45FCN1 iC3bCell surfaceC3bC8A dNQ-C4AIg kappa chain V-III region VG C3 beta chain Ig lambda chain V-IV region Hil C2aIg kappa chain V-III region CLL C2a Ig lambda chain V-II region BO Complement factor DIg kappa chain V-I region Bi C3c alpha' chain fragment 1 precursor C3b alpha' Ig kappa chain V-I region DEE Ig heavy chain V-III region GA IGLV2-33C3 beta chain Ig kappa chain V-II region TEW Complement factor ICell surfaceFH,FHR3C3bC8B Ig kappa chain V-III region IARC/BL41 IGLV11-55IGLC3IGLC2C4BPB Bacterial mannose-based carbohydrate surface patternCFIC9Ig heavy chain V-III region POM C1QBIGKVA18Ig kappa chain V-I region Daudi IGLV3-25Ig kappa chain V-III region VH C3bFactor BbC3bProperdin complexIGLV10-54Ig kappa chain V-I region HK101 Cell surfaceFH,FHR3C3bBbIGLV7-43dNQ-C4BC8G Ig lambda chain V-IV region X Ig heavy chain V-II region ARH-77 IGKV4-1Complement factor 5C1RIg kappa chain V-III region NG9 Heparins Ig heavy chain V-III region CAM CR1 IGHVIg lambda chain V-II region BUR Ig kappa chain V-III region SIE Ig heavy chain V-II region MCE C5bC6C7 complexMASP1Ig kappa chain V-III region HAH Ig lambda chain V-IV region MOL Ig kappa chain V-IV region STH dNQ-C4BN-acetyl-D-glucosamine FCN1MASPsCa2+FCN1 ligandIg lambda chain V-VI region AR IGLV4-60C4A gamma Ig heavy chain V-III region JON Ig kappa chain V-I region EU Ig heavy chain V-III region KOL IGHVIGLC7C4A beta CFIIGLV3-12IGLV2-11Cell surfaceC4bC1QC Ig kappa chain V-I region WAT IGLV8-61Ig kappa chain V-I region Wes Ca2+ C4A gamma C3b alpha' IGLV3-27CFIIg lambda chain V-I region NIG-64 Ig lambda chain V-I region NEW C4B gamma FCN2 Ig kappa chain V-I region WEA Ig kappa chain V-I region Rei IGLV10-54C4B gamma IGLV3-12Ig heavy chain V-II region OU IGLV4-60CR1iC3bC3 beta chain IGLV1-44CR1IGLV3-16Ig lambda chain V-II region BOH Ig heavy chain V-III region WAS MASP1Ig heavy chain V-III region TUR dNQ-C4BIg heavy chain V-I region EU Ig kappa chain V-I region WEA Ig kappa chain V-I region Wes IgH heavy chain V-III region VH26 precursor Ig lambda chain V-I region BL2 C8G Antigen antibody C1 Ig lambda chain V-VI region EB4 Ig lambda chain V-I region WAH C5 beta C4B gamma IGHV7-81IGLC3IGLV4-60C1R N-terminal fragment Ig heavy chain V-II region WAH Ig lambda chain V-II region VIL IGLVC4BPA Ig kappa chain V-III region Ti FH, FHR-3C4B alpha chain fragment b IGLV11-55MBL2 Ig lambda chain V-I region VOR C1QA Ig heavy chain V-II region NEWM IGHG4Ig lambda chain V-II region TRO Heparins C4A beta Ig heavy chain V-III region TIL Ig lambda chain V-II region WIN IGKVA18Ig lambda chain V-II region NIG-58 Ig lambda chain V-VI region SUT Antigen antibody C1 complexIg heavy chain V-III region WEA C4A beta C7IGLV2-11PCho IGLV4-3Ig heavy chain V-III region ZAP C3 convertasesC3b alpha' C3 beta chain IGLC1C7C4A gamma C6 C3 beta chain Ig kappa chain V-III region GOL dNQ-C4AIg heavy chain V-I region Mot Ig kappa chain V-I region Bi Ig kappa chain V-II region GM607 Ig kappa chain V-IV region B17 Cell surfaceC3bFactor BbIg heavy chain V-III region TIL C1QC CD46 Ig kappa chain V-I region Gal C3FCN2MASPsCa2+FCN2 ligandIGLV1-44Ig kappa chain V-III region VH iC3bC-reactive protein pentamerphosphocholineC1QC4B gamma CD46 CFIIg heavy chain V-III region TRO Lipoteichoic acid IGLV2-23C5 beta C3 beta chain Ig kappa chain V-I region Ni IGKV4-1Ig kappa chain V-I region Lay C3c alpha' chain fragment 2 Ig heavy chain V-III region WEA dNQ-C4AMASP1Ig heavy chain V-III region LAY C9Ig kappa chain V-III region CLL C3 beta chain IGLV4-69Ig heavy chain V-III region TIL Ig lambda chain V-IV region X CFICFIIg lambda chain V-VI region WLT C3c alpha' chain fragment 1 precursor Ig heavy chain V-II region OU CR1C4bIGLVIg lambda chain V-III region LOI MCP, CR1C4bC3b complexesIg lambda chain V-VI region NIG-48 Ig lambda chain V-III region SH Ig kappa chain V-I region Ni C5 beta C3 beta chain VTNC4B beta Ig kappa chain V-I region HK101 IGLV3-12C3fIg kappa chain V-III region POM CFIC4A beta Ig kappa chain V-I region Kue Ig lambda chain V-I region NIG-64 CR1C3bIg lambda chain V-VI region WLT dNQ-C4BIGLV8-61Ig heavy chain V-III region TUR Ig lambda chain V-I region VOR C3 beta chain Ig lambda chain V-I region BL2 Ig lambda chain V-I region MEM Ig kappa chain V-I region AU C4 binding proteinC4bC2aC4b with hydrolysed thioesterCa2+ Ig heavy chain V-III region NIE C4BPA Factor HC3bIg kappa chain V-II region GM607 MBL-IIMASP-2 dimerMASP-1 dimer complexIg kappa chain V-III region HIC C1QA CFBC7Ig heavy chain V-II region NEWM CR1 C1QBIg heavy chain V-I region Mot C5 beta C3dgIg kappa chain V-III region SIE CFBIg kappa chain V-I region Scw C3C4A alpha b Ig kappa chain V-I region Mev dNQ-C4BIg heavy chain V-III region POM Ig heavy chain V-II region WAH C3Ig kappa chain V-II region FR C7Ig kappa chain V-III region POM Ig kappa chain V-I region WAT Ig heavy chain V-III region BRO Ig kappa chain V-I region OU MBL2 C9IGLV3-27IGLV4-69Ig kappa chain V-II region Cum C4B beta IGKV4-1CFH Ig lambda chain V-IV region Hil Ig kappa chain V-III region B6 Ig lambda chain V-IV region MOL Factor IMCP, CR1C4b, C3b complexesC4bC2a, C3bBbIg heavy chain V-I region Mot C4B gamma Ig lambda chain V-I region MEM C5b alpha' Ig kappa chain V-III region Ti Ig lambda chain V-II region BOH C4B beta Ig kappa chain V-I region Walker Ig lambda chain V-IV region Bau C3b alpha' Cell surfaceC4bC5bC3aC4A alpha b C3 beta chain C5 beta MASP2-1IGLC3C1R C-terminal fragment Ig kappa chain V-III region IARC/BL41 CFIC5 beta Ig heavy chain V-I region ND C4A gamma Ig lambda chain V-IV region Kern Ig kappa chain V-I region Gal C4BPB Ig kappa chain V-II region FR IGLV11-55Ig lambda chain V-I region EPS Ig lambda chain V-I region NIG-64 Sialic acid 11xCbxE-PROS1CFH C3 beta chain IGLV5-45Ig heavy chain V-III region WAS Ig heavy chain V-III region BUT Ig lambda chain V-II region MGC C5aIg heavy chain V-I region ND Ig heavy chain V-II region SESS C1S N-terminal fragment Ig heavy chain V-II region MCE Ig heavy chain V-III region KOL IGLV1-36C4A beta Ig kappa chain V-III region HIC Ig lambda chain V-IV region MOL C2aIg kappa chain V-I region Kue dNQ-C4BVTNC4B beta VTNC5bC6C7IGKV1-5Cell surfaceMBLactivated MASPsmannose-based carbohydratesC8A C3c alpha' chain fragment 2 CR1 C2bCa2+ Ig lambda chain V-II region BO IGHG2IGLV5-45C3c alpha' chain fragment 2 C3 beta chain C6 IGHG1Ig kappa chain V-IV region JI Ig kappa chain V-III region IARC/BL41 IGHG3 Ig kappa chain V-I region Bi Ig lambda chain V-I region EPS dNQ-C4AC6 11xCbxE-PROS1 Ig kappa chain V-I region Rei Ig kappa chain V-I region OU CFHIg kappa chain V-I region Mev Sialic acid IGLV2-11MASP1Ig heavy chain V-II region ARH-77 Ig kappa chain V-I region BAN C1QC C8B Ig lambda chain V-III region LOI C5 alpha C4B beta IGLC2Ig kappa chain V-IV region Len MBL/FicolinMASPs bound to carbohydrate patternsC5b alpha' Ig heavy chain V-II region NEWM IGLV2-18C5b alpha' CFBIg lambda chain V-II region NEI C2aMASP1Ig kappa chain V-I region Hau Ig heavy chain V-II region WAH Antigen antibody C1 dNQ-C4AIg lambda chain V region 4A Ig lambda chain V-II region BUR C3 convertasesIGLC6dNQ-C4BIg heavy chain V-II region OU dNQ-C4AC1R C-terminal fragment C3 beta chain Ig kappa chain V region EV15 Ig kappa chain V-I region HK101 Ig lambda chain V-I region NEW C2a Ig kappa chain V-I region EU IGLV4-3Ig lambda chain V-II region BOH Ig kappa chain V-II region TEW Host cell surfaceFCN1 ligandVTNC5bC6C7C8C9IGLV10-541,3-beta-D-glucan Ig kappa chain V-III region NG9 Ig lambda chain V-I region MEM MASP2-1MCPC4bC2aIg lambda chain V-VI region SUT C4d, iC3bCa2+ CFIIg kappa chain V-III region SIE C4b-binding proteinIg lambda chain V-II region TOG Factor HHost cell surfaceIg lambda chain V region 4A C3 beta chain Ig lambda chain V-I region WAH Ig lambda chain V-IV region Kern C5 beta C3bIg lambda chain V-VI region WLT DAFC3 convertase complexesIg lambda chain V-II region NIG-84 C3bIg lambda chain V-II region WIN Ig kappa chain V-I region Daudi C4c, C3fC1QA IGLV5-37dNQ-C3IGLV3-22Ig heavy chain V-I region EU C5b alpha' IGLV3-16Ca2+ C8G Ca2+C2IGHG1MASP2-1 Ig lambda chain V-II region VIL Ig kappa chain V-I region AU IGKV1-5dNQ-C4AC4A alpha b C3 beta chain C3 beta chain C3 beta chain Ig heavy chain V-II region DAW C8G C3b alpha' Ig heavy chain V-II region HE C8A MBL bound to mannose-based carbohydrates on bacterial surfacesC9C1QA Ig heavy chain V-I region EU Ig kappa chain V-III region GOL C3 beta chain Properdin oligomerC8B Ig lambda chain V-II region NIG-84 CD59 Ig lambda chain V-I region NEWM Cell surfaceCD59C5b-C9C4B beta IGLV5-37Ig heavy chain V-I region SIE C3 beta chain Ig lambda chain V-IV region Bau Ig heavy chain V-III region KOL dNQ-C3Ig kappa chain V-I region BAN CFBIg lambda chain V-I region NEW Ig lambda chain V-IV region Hil Ig heavy chain V-II region SESS Ig kappa chain V region EV15 IGHG4Cell surfaceC3bFactor B complexComplement factor IFactor HC3bIGLV1-40Ig kappa chain V-I region Gal Ig lambda chain V-II region NIG-58 C5bC6 complexC4A gamma CRPCD46 CFBMASP2-1 C5b alpha' Ig lambda chain V-I region NEWM MASP1C3b alpha' Ig heavy chain V-III region WAS Ig lambda chain V-II region NIG-58 C4B gamma Ig lambda chain V-VI region NIG-48 Ig heavy chain V-I region SIE Ig heavy chain V-III region TRO C4A gamma IGLV2-33C6 Ig heavy chain V-III region LAY DAFC3bIg lambda chain V-I region HA Ig kappa chain V-II region Cum C6 FCN2MASP2 dimerMASP1 dimerIGKCC6CFDC8IGLC6Ig heavy chain V-III region BRO Ig kappa chain V-IV region Len Ig kappa chain V-IV region B17 C4A beta Ig lambda chain V-VI region NIG-48 FCN1 MASP2-1 Ig kappa chain V-IV region B17 C1QBIg kappa chain V-I region Hau Ig kappa chain V-II region TEW Ig heavy chain V-III region TUR Ig lambda chain V-V region DEL Ig kappa chain V-IV region JI Ig kappa chain V-III region POM C3cIg heavy chain V-III region DOB C4B gamma Ig heavy chain V-III region TRO Ig kappa chain V-I region Ka Ig lambda chain V-II region MGC Ig heavy chain V-III region CAM IGLV4-69C4B gamma Cell surfaceFH,FHR3C3bMembrane Attack ComplexIg kappa chain V-III region B6 IGHG3 MCPC3bIGLC7C4A beta IGHG1C3 alpha chain C3b alpha' C5 beta Ig kappa chain V-IV region JI Ig heavy chain V-III region GAL Ig kappa chain V-I region Wes Ig heavy chain V-III region TEI MASP1CD46Ig heavy chain V-I region SIE Ig kappa chain V-I region Walker Ig kappa chain V-I region Walker C4BPA Ig lambda chain V-II region BUR dNQ-C3C3 beta chain C4A beta Ig heavy chain V-III region LAY Ig kappa chain V-I region Scw Ig heavy chain V-III region DOB Ig heavy chain V-III region TEI Ig heavy chain V-III region HIL Ig lambda chain V-VI region SUT C4bC2aC3bIg lambda chain V-II region NIG-84 Ig lambda chain V-V region DEL C4B beta MASP1IGHVIg kappa chain V-I region Ni MBL/FCNactivated MASPcarbohydrate patternsIg lambda chain V-I region BL2 6957736018, 28843, 8014, 2655718806718


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The complement system is a biochemical cascade, so named because it 'complements' the ability of antibodies to clear pathogens. It is part of the innate immune system. Complement system proteins circulate in the blood as inactive precursors (pro-proteins). When triggered by the presence of microbes, complement proteases cleave complement proteins, initiating a cascade of further cleavages. The end-result of this activation is the activation of the Membrane Attack Complex and cell lysis. The C3 and C5 components also lead to phagocytosis by leukocytes.

There are three branches that lead to activation of the complement system: the classical complement pathway, the alternative complement pathway, and the mannose-binding lectin pathway. Complement proteins are always present in the blood and a small percentage spontaneously activate. Innapropriate activation leads to host cell damage, so the activation process is tightly controlled by several regulatory mechanisms.


N.B. Originally the larger fragment of Complement Factor 2 (C2) was designated C2a. However, complement scientists decided that the smaller of all C fragments should be designated with an 'a', the larger with a 'b', changing the nomenclature for C2. Recent literature may use the updated nomenclature and refer to the larger C2 fragment as C2b, and refer to the classical C3 convertase as C4bC2b. Throughout this pathway Reactome adheres to the original convention to agree with the current (Feb 2012) Uniprot names for C2 fragments.
Original Pathway at Reactome: http://www.reactome.org/PathwayBrowser/#DB=gk_current&FOCUS_SPECIES_ID=48887&FOCUS_PATHWAY_ID=166658

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Bibliography

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  115. Arlaud GJ, Reboul A, Sim RB, Colomb MG.; ''Interaction of C1-inhibitor with the C1r and C1s subcomponents in human C1.''; PubMed Europe PMC Scholia

History

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CompareRevisionActionTimeUserComment
115062view17:00, 25 January 2021ReactomeTeamReactome version 75
113506view11:58, 2 November 2020ReactomeTeamReactome version 74
112706view16:10, 9 October 2020ReactomeTeamReactome version 73
101621view11:49, 1 November 2018ReactomeTeamreactome version 66
101157view21:35, 31 October 2018ReactomeTeamreactome version 65
100683view20:08, 31 October 2018ReactomeTeamreactome version 64
100233view16:53, 31 October 2018ReactomeTeamreactome version 63
99785view15:18, 31 October 2018ReactomeTeamreactome version 62 (2nd attempt)
99338view12:47, 31 October 2018ReactomeTeamreactome version 62
93740view13:33, 16 August 2017ReactomeTeamreactome version 61
93254view11:18, 9 August 2017ReactomeTeamreactome version 61
86332view09:15, 11 July 2016ReactomeTeamreactome version 56
83391view11:06, 18 November 2015ReactomeTeamVersion54
81582view13:07, 21 August 2015ReactomeTeamVersion53
77042view08:34, 17 July 2014ReactomeTeamFixed remaining interactions
76747view12:11, 16 July 2014ReactomeTeamFixed remaining interactions
76072view10:13, 11 June 2014ReactomeTeamRe-fixing comment source
75782view11:30, 10 June 2014ReactomeTeamReactome 48 Update
75419view10:07, 29 May 2014LifishModified description
75132view14:08, 8 May 2014AnweshaFixing comment source for displaying WikiPathways description
74779view08:52, 30 April 2014ReactomeTeamReactome46
44996view14:41, 6 October 2011MartijnVanIerselOntology Term : 'signaling pathway in the innate immune response' added !
42021view21:50, 4 March 2011MaintBotAutomatic update
39824view05:51, 21 January 2011MaintBotNew pathway

External references

DataNodes

View all...
NameTypeDatabase referenceComment
1,3-beta-D-glucan MetaboliteCHEBI:37671 (ChEBI)
11xCbxE-PROS1 ProteinP07225 (Uniprot-TrEMBL)
11xCbxE-PROS1ProteinP07225 (Uniprot-TrEMBL)
Antigen 
antibody
C1 		ComplexREACT_8066 (Reactome)
Antigen 
antibody
C1 		ComplexREACT_8973 (Reactome)
Antigen 
antibody
C1 complex		ComplexREACT_8034 (Reactome)
Bacterial mannose-based carbohydrate surface patternREACT_8923 (Reactome)
C-reactive protein pentamer

phosphocholine

C1Q		ComplexREACT_25403 (Reactome)
C1QA ProteinP02745 (Uniprot-TrEMBL)
C1QBProteinP02746 (Uniprot-TrEMBL)
C1QC ProteinP02747 (Uniprot-TrEMBL)
C1R C-terminal fragment ProteinP00736 (Uniprot-TrEMBL)
C1R N-terminal fragment ProteinP00736 (Uniprot-TrEMBL)
C1RProteinP00736 (Uniprot-TrEMBL)
C1S C-terminal fragment ProteinP09871 (Uniprot-TrEMBL)
C1S N-terminal fragment ProteinP09871 (Uniprot-TrEMBL)
C1SProteinP09871 (Uniprot-TrEMBL)
C2ProteinP06681 (Uniprot-TrEMBL)
C2a ProteinP06681 (Uniprot-TrEMBL)
C2aProteinP06681 (Uniprot-TrEMBL)
C2bProteinP06681 (Uniprot-TrEMBL)
C3 alpha chain ProteinP01024 (Uniprot-TrEMBL)
C3 beta chain ProteinP01024 (Uniprot-TrEMBL)
C3 convertasesREACT_8751 (Reactome)
C3ComplexREACT_8268 (Reactome)
C3ComplexREACT_8649 (Reactome)
C3ComplexREACT_8857 (Reactome)
C3aProteinP01024 (Uniprot-TrEMBL)
C3b

Factor Bb C3b

Properdin complex		ComplexREACT_8784 (Reactome)
C3b alpha' ProteinP01024 (Uniprot-TrEMBL)
C3bComplexREACT_8621 (Reactome) Linked by disulphide bond between positions 559 and 816.
C3c alpha' chain fragment 1 ProteinP01024 (Uniprot-TrEMBL)
C3c alpha' chain fragment 1 precursor ProteinP01024 (Uniprot-TrEMBL)
C3c alpha' chain fragment 2 ProteinP01024 (Uniprot-TrEMBL)
C3cComplexREACT_164188 (Reactome)
C3dgProteinP01024 (Uniprot-TrEMBL)
C3fProteinP01024 (Uniprot-TrEMBL)
C4 activatorREACT_8154 (Reactome)
C4 binding protein C4bC2aComplexREACT_120190 (Reactome)
C4 binding protein protein SComplexREACT_119894 (Reactome)
C4-binding protein C4bComplexREACT_118966 (Reactome)
C4A alpha b ProteinP0C0L4 (Uniprot-TrEMBL) C4 alpha chain has a thioester bond between Cys 1010 and Gln 1013
C4A beta ProteinP0C0L4 (Uniprot-TrEMBL)
C4A gamma ProteinP0C0L4 (Uniprot-TrEMBL)
C4B alpha chain fragment b ProteinP0C0L5 (Uniprot-TrEMBL)
C4B beta ProteinP0C0L5 (Uniprot-TrEMBL)
C4B gamma ProteinP0C0L5 (Uniprot-TrEMBL)
C4BPA ProteinP04003 (Uniprot-TrEMBL)
C4BPB ProteinP20851 (Uniprot-TrEMBL)
C4aProteinREACT_25991 (Reactome)
C4b

C2a

C3b		ComplexREACT_8556 (Reactome)
C4b with hydrolysed thioesterComplexREACT_164040 (Reactome)
C4b, C3bComplexREACT_119260 (Reactome)
C4b-binding protein Factor IComplexREACT_119445 (Reactome)
C4b-binding proteinComplexREACT_120080 (Reactome)
C4bC2a, C3bBbComplexREACT_119171 (Reactome)
C4c, C3fComplexREACT_119917 (Reactome)
C4cComplexREACT_119729 (Reactome)
C4d, iC3bProteinREACT_119732 (Reactome)
C4dProteinREACT_119059 (Reactome)
C5 alpha ProteinP01031 (Uniprot-TrEMBL)
C5 beta ProteinP01031 (Uniprot-TrEMBL)
C5 convertasesREACT_8864 (Reactome)
C5aProteinP01031 (Uniprot-TrEMBL)
C5b

C6 C7

C8 complex		ComplexREACT_8352 (Reactome)
C5b

C6

C7 complex		ComplexREACT_8333 (Reactome)
C5b

C6

C7 complex		ComplexREACT_8454 (Reactome)
C5b C6 complexComplexREACT_8500 (Reactome)
C5b alpha' ProteinP01031 (Uniprot-TrEMBL)
C5bComplexREACT_8814 (Reactome) Linked by disulphide bond between positions 559 and 816.
C6 ProteinP13671 (Uniprot-TrEMBL)
C6ProteinP13671 (Uniprot-TrEMBL)
C7ProteinP10643 (Uniprot-TrEMBL)
C8A ProteinP07357 (Uniprot-TrEMBL)
C8B ProteinP07358 (Uniprot-TrEMBL)
C8G ProteinP07360 (Uniprot-TrEMBL)
C8ComplexREACT_8563 (Reactome)
C9ProteinP02748 (Uniprot-TrEMBL)
CD46 ProteinP15529 (Uniprot-TrEMBL)
CD46ProteinP15529 (Uniprot-TrEMBL)
CD55 ProteinP08174 (Uniprot-TrEMBL)
CD55ProteinP08174 (Uniprot-TrEMBL)
CD59 C5b-C9ComplexREACT_164087 (Reactome)
CD59 ProteinP13987 (Uniprot-TrEMBL)
CD59ProteinP13987 (Uniprot-TrEMBL)
CFBProteinP00751 (Uniprot-TrEMBL)
CFDProteinP00746 (Uniprot-TrEMBL)
CFH ProteinP08603 (Uniprot-TrEMBL)
CFHProteinP08603 (Uniprot-TrEMBL)
CFIProteinP05156 (Uniprot-TrEMBL)
CR1 C3bBb, C4bC2a complexesComplexREACT_120030 (Reactome)
CR1 C3bComplexREACT_119014 (Reactome)
CR1 C4bComplexREACT_119535 (Reactome)
CR1 iC3bComplexREACT_164751 (Reactome)
CR1 ProteinP17927 (Uniprot-TrEMBL)
CR1ProteinP17927 (Uniprot-TrEMBL)
CRPProteinP02741 (Uniprot-TrEMBL)
Ca2+ MetaboliteCHEBI:29108 (ChEBI)
Ca2+MetaboliteCHEBI:29108 (ChEBI)
Cell surface

C3b

Factor B complex		ComplexREACT_8205 (Reactome)
Cell surface

C3b Factor Bb

Properdin		ComplexREACT_8531 (Reactome)
Cell surface

C3b

Factor Bb		ComplexREACT_8668 (Reactome)
Cell surface C3bComplexREACT_26114 (Reactome)
Cell surface

C4b

C2a		ComplexREACT_8917 (Reactome)
Cell surface C4bComplexREACT_25739 (Reactome)
Cell surface

FH,FHR3

C3bBb		ComplexREACT_118983 (Reactome)
Cell surface

FH,FHR3

C3b		ComplexREACT_119386 (Reactome)
Cell surfaceREACT_26575 (Reactome) This entity is intended to represent any molecule that might be at the outer cell surface of any cell, host or microbial.
Complement Factor 4ComplexREACT_26761 (Reactome)
Complement factor 3ComplexREACT_8213 (Reactome) Linked by disulphide bond between positions 559 and 816.
Complement factor 5ComplexREACT_8215 (Reactome)
Complement factor DProteinREACT_161511 (Reactome) This CandidateSet contains sequences identified by William Pearson's analysis of Reactome catalyst entities. Catalyst entity sequences were used to identify analagous sequences that shared overall homology and active site homology. Sequences in this Candidate set were identified in an April 24, 2012 analysis.
Complement factor I

Cell surface FH,FHR3

C3b		ComplexREACT_119579 (Reactome)
Complement factor I

Factor H

C3b		ComplexREACT_119450 (Reactome)
Complement factor IComplexREACT_119465 (Reactome)
D-fucose MetaboliteCHEBI:28847 (ChEBI)
DAF C3 convertase complexesComplexREACT_119393 (Reactome)
DAF C3bComplexREACT_119929 (Reactome)
DAF C4bComplexREACT_119228 (Reactome)
FCN1

MASP2 dimer

MASP1 dimer		ComplexREACT_164741 (Reactome)
FCN1

MASPs Ca2+

FCN1 ligand		ComplexREACT_165421 (Reactome)
FCN1 ProteinO00602 (Uniprot-TrEMBL)
FCN1 ligandMetaboliteREACT_165133 (Reactome)
FCN2

MASP2 dimer

MASP1 dimer		ComplexREACT_165253 (Reactome)
FCN2

MASPs Ca2+

FCN2 ligand		ComplexREACT_164948 (Reactome)
FCN2 ProteinQ15485 (Uniprot-TrEMBL)
FCN2 ligandMetaboliteREACT_164334 (Reactome)
FCN3

MASP2 dimer

MASP1 dimer		ComplexREACT_165152 (Reactome)
FCN3

MASPs Ca2+

FCN3 ligand		ComplexREACT_164302 (Reactome)
FCN3 ProteinO75636 (Uniprot-TrEMBL)
FCN3 ligandMetaboliteREACT_165296 (Reactome)
FH, FHR-3ProteinREACT_119141 (Reactome)
Factor H C3bComplexREACT_120113 (Reactome)
Factor H Host cell surfaceComplexREACT_119254 (Reactome)
Factor I

MCP, CR1

C4b, C3b complexes		ComplexREACT_120091 (Reactome)
H2OMetaboliteCHEBI:15377 (ChEBI)
Heparins MetaboliteCHEBI:24505 (ChEBI)
Host cell surfaceComplexREACT_119096 (Reactome)
IGHG1ProteinP01857 (Uniprot-TrEMBL)
IGHG2ProteinP01859 (Uniprot-TrEMBL)
IGHG3 ProteinP01860 (Uniprot-TrEMBL)
IGHG4ProteinP01861 (Uniprot-TrEMBL)
IGHV7-81ProteinQ6PIL0 (Uniprot-TrEMBL)
IGHVProteinA2KUC3 (Uniprot-TrEMBL)
IGKCProteinP01834 (Uniprot-TrEMBL)
IGKV1-5ProteinP01602 (Uniprot-TrEMBL)
IGKV4-1ProteinP06312 (Uniprot-TrEMBL)
IGKVA18ProteinA2NJV5 (Uniprot-TrEMBL)
IGLC1ProteinP0CG04 (Uniprot-TrEMBL)
IGLC2ProteinP0CG05 (Uniprot-TrEMBL)
IGLC3ProteinP0CG06 (Uniprot-TrEMBL)
IGLC6ProteinP0CF74 (Uniprot-TrEMBL)
IGLC7ProteinA0M8Q6 (Uniprot-TrEMBL)
IGLV1-36ProteinQ5NV67 (Uniprot-TrEMBL)
IGLV1-40ProteinQ5NV69 (Uniprot-TrEMBL)
IGLV1-44ProteinQ5NV81 (Uniprot-TrEMBL)
IGLV10-54ProteinQ5NV86 (Uniprot-TrEMBL)
IGLV11-55ProteinQ5NV87 (Uniprot-TrEMBL)
IGLV2-11ProteinQ5NV84 (Uniprot-TrEMBL)
IGLV2-18ProteinQ5NV65 (Uniprot-TrEMBL)
IGLV2-23ProteinQ5NV89 (Uniprot-TrEMBL)
IGLV2-33ProteinQ5NV66 (Uniprot-TrEMBL)
IGLV3-12ProteinQ5NV85 (Uniprot-TrEMBL)
IGLV3-16ProteinQ5NV64 (Uniprot-TrEMBL)
IGLV3-22ProteinQ5NV75 (Uniprot-TrEMBL)
IGLV3-25ProteinQ5NV90 (Uniprot-TrEMBL)
IGLV3-27ProteinQ5NV91 (Uniprot-TrEMBL)
IGLV4-3ProteinQ5NV61 (Uniprot-TrEMBL)
IGLV4-60ProteinQ5NV79 (Uniprot-TrEMBL)
IGLV4-69ProteinQ5NV92 (Uniprot-TrEMBL)
IGLV5-37ProteinQ5NV68 (Uniprot-TrEMBL)
IGLV5-45ProteinQ5NV82 (Uniprot-TrEMBL)
IGLV7-43ProteinQ5NV80 (Uniprot-TrEMBL)
IGLV7-46ProteinQ5NV83 (Uniprot-TrEMBL)
IGLV8-61ProteinQ5NV62 (Uniprot-TrEMBL)
IGLVProteinA2NXD2 (Uniprot-TrEMBL)
Ig heavy chain V-I region EU ProteinP01742 (Uniprot-TrEMBL)
Ig heavy chain V-I region HG3 ProteinP01743 (Uniprot-TrEMBL)
Ig heavy chain V-I region Mot ProteinP06326 (Uniprot-TrEMBL)
Ig heavy chain V-I region ND ProteinP01744 (Uniprot-TrEMBL)
Ig heavy chain V-I region SIE ProteinP01761 (Uniprot-TrEMBL)
Ig heavy chain V-I region WOL ProteinP01760 (Uniprot-TrEMBL)
Ig heavy chain V-II region ARH-77 ProteinP06331 (Uniprot-TrEMBL)
Ig heavy chain V-II region COR ProteinP01815 (Uniprot-TrEMBL)
Ig heavy chain V-II region DAW ProteinP01816 (Uniprot-TrEMBL)
Ig heavy chain V-II region HE ProteinP01818 (Uniprot-TrEMBL)
Ig heavy chain V-II region MCE ProteinP01817 (Uniprot-TrEMBL)
Ig heavy chain V-II region NEWM ProteinP01825 (Uniprot-TrEMBL)
Ig heavy chain V-II region OU ProteinP01814 (Uniprot-TrEMBL)
Ig heavy chain V-II region SESS ProteinP04438 (Uniprot-TrEMBL)
Ig heavy chain V-II region WAH ProteinP01824 (Uniprot-TrEMBL)
Ig heavy chain V-III region BRO ProteinP01766 (Uniprot-TrEMBL)
Ig heavy chain V-III region BUR ProteinP01773 (Uniprot-TrEMBL)
Ig heavy chain V-III region BUT ProteinP01767 (Uniprot-TrEMBL)
Ig heavy chain V-III region CAM ProteinP01768 (Uniprot-TrEMBL)
Ig heavy chain V-III region DOB ProteinP01782 (Uniprot-TrEMBL)
Ig heavy chain V-III region GA ProteinP01769 (Uniprot-TrEMBL)
Ig heavy chain V-III region GAL ProteinP01781 (Uniprot-TrEMBL)
Ig heavy chain V-III region HIL ProteinP01771 (Uniprot-TrEMBL)
Ig heavy chain V-III region JON ProteinP01780 (Uniprot-TrEMBL)
Ig heavy chain V-III region KOL ProteinP01772 (Uniprot-TrEMBL)
Ig heavy chain V-III region LAY ProteinP01775 (Uniprot-TrEMBL)
Ig heavy chain V-III region NIE ProteinP01770 (Uniprot-TrEMBL)
Ig heavy chain V-III region POM ProteinP01774 (Uniprot-TrEMBL)
Ig heavy chain V-III region TEI ProteinP01777 (Uniprot-TrEMBL)
Ig heavy chain V-III region TIL ProteinP01765 (Uniprot-TrEMBL)
Ig heavy chain V-III region TRO ProteinP01762 (Uniprot-TrEMBL)
Ig heavy chain V-III region TUR ProteinP01779 (Uniprot-TrEMBL)
Ig heavy chain V-III region WAS ProteinP01776 (Uniprot-TrEMBL)
Ig heavy chain V-III region WEA ProteinP01763 (Uniprot-TrEMBL)
Ig heavy chain V-III region ZAP ProteinP01778 (Uniprot-TrEMBL)
Ig kappa chain V region EV15 ProteinP06315 (Uniprot-TrEMBL)
Ig kappa chain V-I region AG ProteinP01593 (Uniprot-TrEMBL)
Ig kappa chain V-I region AU ProteinP01594 (Uniprot-TrEMBL)
Ig kappa chain V-I region BAN ProteinP04430 (Uniprot-TrEMBL)
Ig kappa chain V-I region Bi ProteinP01595 (Uniprot-TrEMBL)
Ig kappa chain V-I region CAR ProteinP01596 (Uniprot-TrEMBL)
Ig kappa chain V-I region DEE ProteinP01597 (Uniprot-TrEMBL)
Ig kappa chain V-I region Daudi ProteinP04432 (Uniprot-TrEMBL)
Ig kappa chain V-I region EU ProteinP01598 (Uniprot-TrEMBL)
Ig kappa chain V-I region Gal ProteinP01599 (Uniprot-TrEMBL)
Ig kappa chain V-I region HK101 ProteinP01601 (Uniprot-TrEMBL)
Ig kappa chain V-I region Hau ProteinP01600 (Uniprot-TrEMBL)
Ig kappa chain V-I region Ka ProteinP01603 (Uniprot-TrEMBL)
Ig kappa chain V-I region Kue ProteinP01604 (Uniprot-TrEMBL)
Ig kappa chain V-I region Lay ProteinP01605 (Uniprot-TrEMBL)
Ig kappa chain V-I region Mev ProteinP01612 (Uniprot-TrEMBL)
Ig kappa chain V-I region Ni ProteinP01613 (Uniprot-TrEMBL)
Ig kappa chain V-I region OU ProteinP01606 (Uniprot-TrEMBL)
Ig kappa chain V-I region Rei ProteinP01607 (Uniprot-TrEMBL)
Ig kappa chain V-I region Roy ProteinP01608 (Uniprot-TrEMBL)
Ig kappa chain V-I region Scw ProteinP01609 (Uniprot-TrEMBL)
Ig kappa chain V-I region WAT ProteinP80362 (Uniprot-TrEMBL)
Ig kappa chain V-I region WEA ProteinP01610 (Uniprot-TrEMBL)
Ig kappa chain V-I region Walker ProteinP04431 (Uniprot-TrEMBL)
Ig kappa chain V-I region Wes ProteinP01611 (Uniprot-TrEMBL)
Ig kappa chain V-II region Cum ProteinP01614 (Uniprot-TrEMBL)
Ig kappa chain V-II region FR ProteinP01615 (Uniprot-TrEMBL)
Ig kappa chain V-II region GM607 ProteinP06309 (Uniprot-TrEMBL)
Ig kappa chain V-II region MIL ProteinP01616 (Uniprot-TrEMBL)
Ig kappa chain V-II region RPMI 6410 ProteinP06310 (Uniprot-TrEMBL)
Ig kappa chain V-II region TEW ProteinP01617 (Uniprot-TrEMBL)
Ig kappa chain V-III region B6 ProteinP01619 (Uniprot-TrEMBL)
Ig kappa chain V-III region CLL ProteinP04207 (Uniprot-TrEMBL)
Ig kappa chain V-III region GOL ProteinP04206 (Uniprot-TrEMBL)
Ig kappa chain V-III region HAH ProteinP18135 (Uniprot-TrEMBL)
Ig kappa chain V-III region HIC ProteinP18136 (Uniprot-TrEMBL)
Ig kappa chain V-III region IARC/BL41 ProteinP06311 (Uniprot-TrEMBL)
Ig kappa chain V-III region NG9 ProteinP01621 (Uniprot-TrEMBL)
Ig kappa chain V-III region POM ProteinP01624 (Uniprot-TrEMBL)
Ig kappa chain V-III region SIE ProteinP01620 (Uniprot-TrEMBL)
Ig kappa chain V-III region Ti ProteinP01622 (Uniprot-TrEMBL)
Ig kappa chain V-III region VG ProteinP04433 (Uniprot-TrEMBL)
Ig kappa chain V-III region VH ProteinP04434 (Uniprot-TrEMBL)
Ig kappa chain V-III region WOL ProteinP01623 (Uniprot-TrEMBL)
Ig kappa chain V-IV region B17 ProteinP06314 (Uniprot-TrEMBL)
Ig kappa chain V-IV region JI ProteinP06313 (Uniprot-TrEMBL)
Ig kappa chain V-IV region Len ProteinP01625 (Uniprot-TrEMBL)
Ig kappa chain V-IV region STH ProteinP83593 (Uniprot-TrEMBL)
Ig lambda chain V region 4A ProteinP04211 (Uniprot-TrEMBL)
Ig lambda chain V-I region BL2 ProteinP06316 (Uniprot-TrEMBL)
Ig lambda chain V-I region EPS ProteinP06888 (Uniprot-TrEMBL)
Ig lambda chain V-I region HA ProteinP01700 (Uniprot-TrEMBL)
Ig lambda chain V-I region MEM ProteinP06887 (Uniprot-TrEMBL)
Ig lambda chain V-I region NEW ProteinP01701 (Uniprot-TrEMBL)
Ig lambda chain V-I region NEWM ProteinP01703 (Uniprot-TrEMBL)
Ig lambda chain V-I region NIG-64 ProteinP01702 (Uniprot-TrEMBL)
Ig lambda chain V-I region VOR ProteinP01699 (Uniprot-TrEMBL)
Ig lambda chain V-I region WAH ProteinP04208 (Uniprot-TrEMBL)
Ig lambda chain V-II region BO ProteinP01710 (Uniprot-TrEMBL)
Ig lambda chain V-II region BOH ProteinP01706 (Uniprot-TrEMBL)
Ig lambda chain V-II region BUR ProteinP01708 (Uniprot-TrEMBL)
Ig lambda chain V-II region MGC ProteinP01709 (Uniprot-TrEMBL)
Ig lambda chain V-II region NEI ProteinP01705 (Uniprot-TrEMBL)
Ig lambda chain V-II region NIG-58 ProteinP01713 (Uniprot-TrEMBL)
Ig lambda chain V-II region NIG-84 ProteinP04209 (Uniprot-TrEMBL)
Ig lambda chain V-II region TOG ProteinP01704 (Uniprot-TrEMBL)
Ig lambda chain V-II region TRO ProteinP01707 (Uniprot-TrEMBL)
Ig lambda chain V-II region VIL ProteinP01711 (Uniprot-TrEMBL)
Ig lambda chain V-II region WIN ProteinP01712 (Uniprot-TrEMBL)
Ig lambda chain V-III region LOI ProteinP80748 (Uniprot-TrEMBL)
Ig lambda chain V-III region SH ProteinP01714 (Uniprot-TrEMBL)
Ig lambda chain V-IV region Bau ProteinP01715 (Uniprot-TrEMBL)
Ig lambda chain V-IV region Hil ProteinP01717 (Uniprot-TrEMBL)
Ig lambda chain V-IV region Kern ProteinP01718 (Uniprot-TrEMBL)
Ig lambda chain V-IV region MOL ProteinP06889 (Uniprot-TrEMBL)
Ig lambda chain V-IV region X ProteinP01716 (Uniprot-TrEMBL)
Ig lambda chain V-V region DEL ProteinP01719 (Uniprot-TrEMBL)
Ig lambda chain V-VI region AR ProteinP01721 (Uniprot-TrEMBL)
Ig lambda chain V-VI region EB4 ProteinP06319 (Uniprot-TrEMBL)
Ig lambda chain V-VI region NIG-48 ProteinP01722 (Uniprot-TrEMBL)
Ig lambda chain V-VI region SUT ProteinP06317 (Uniprot-TrEMBL)
Ig lambda chain V-VI region WLT ProteinP06318 (Uniprot-TrEMBL)
Ig lambda chain V-VII region MOT ProteinP01720 (Uniprot-TrEMBL)
IgH heavy chain V-III region VH26 precursor ProteinP01764 (Uniprot-TrEMBL)
Lipoteichoic acid MetaboliteCHEBI:28640 (ChEBI)
MASP1ProteinP48740 (Uniprot-TrEMBL)
MASP2-1 ProteinO00187-1 (Uniprot-TrEMBL)
MASP2-1ProteinO00187-1 (Uniprot-TrEMBL)
MBL

activated MASPs

mannose-based carbohydrates		ComplexREACT_8515 (Reactome)
MBL bound to mannose-based carbohydrates on bacterial surfacesComplexREACT_8711 (Reactome)
MBL-II

MASP-2 dimer

MASP-1 dimer complex		ComplexREACT_8380 (Reactome)
MBL/FCN

activated MASP

carbohydrate patterns		ComplexREACT_165602 (Reactome)
MBL/Ficolin MASPs bound to carbohydrate patternsComplexREACT_165125 (Reactome)
MBL2 ProteinP11226 (Uniprot-TrEMBL)
MCP C3bComplexREACT_119903 (Reactome)
MCP C4bComplexREACT_119237 (Reactome)
MCP, CR1

C4b

C3b complexes		ComplexREACT_120251 (Reactome)
MCP, CR1ProteinREACT_119720 (Reactome) CR1 and MCP are widely distributed cell surface molecules that bind C4b and C3b, and act as cofactors for Complement factor I, thereby regulating the classical and alternative C3 convertases.
Membrane Attack ComplexComplexREACT_8325 (Reactome)
N-acetyl-D-glucosamine MetaboliteCHEBI:28009 (ChEBI)
N-acetylgalactosamine MetaboliteCHEBI:40356 (ChEBI)
PCho MetaboliteCHEBI:36700 (ChEBI)
Properdin oligomerREACT_8730 (Reactome)
Sialic acid MetaboliteCHEBI:28879 (ChEBI)
VTN

C5b C6 C7 C8

C9		ComplexREACT_164606 (Reactome)
VTN

C5b C6

C7		ComplexREACT_165289 (Reactome)
VTNProteinP04004 (Uniprot-TrEMBL)
dNQ-C3ProteinP01024 (Uniprot-TrEMBL)
dNQ-C4AProteinP0C0L4 (Uniprot-TrEMBL)
dNQ-C4BProteinP0C0L5 (Uniprot-TrEMBL)
iC3bComplexREACT_119218 (Reactome)
iC3bComplexREACT_120169 (Reactome)
thioester-C1010-Q1013-C4bComplexREACT_26471 (Reactome)

Annotated Interactions

View all...
SourceTargetTypeDatabase referenceComment
11xCbxE-PROS1REACT_118836 (Reactome)
Antigen 
antibody
C1 complex		mim-catalysisREACT_7978 (Reactome)
Antigen 
antibody
C1 		mim-catalysisREACT_7977 (Reactome)
Bacterial mannose-based carbohydrate surface patternREACT_7983 (Reactome)
C-reactive protein pentamer

phosphocholine

C1Q		ArrowREACT_7978 (Reactome)
C2aArrowREACT_118584 (Reactome)
C2aArrowREACT_118641 (Reactome)
C2aArrowREACT_118692 (Reactome)
C2aArrowREACT_118738 (Reactome)
C2aArrowREACT_7959 (Reactome)
C2aREACT_8014 (Reactome)
C2bArrowREACT_7959 (Reactome)
C3 convertasesmim-catalysisREACT_7990 (Reactome)
C3ArrowREACT_118641 (Reactome)
C3ArrowREACT_7981 (Reactome)
C3REACT_8013 (Reactome)
C3aArrowREACT_7948 (Reactome)
C3aArrowREACT_7986 (Reactome)
C3aArrowREACT_7990 (Reactome)
C3b

Factor Bb C3b

Properdin complex		ArrowREACT_7986 (Reactome)
C3bArrowREACT_118641 (Reactome)
C3bArrowREACT_7948 (Reactome)
C3bArrowREACT_7990 (Reactome)
C3bREACT_118712 (Reactome)
C3bREACT_25075 (Reactome)
C3cArrowREACT_163860 (Reactome)
C3dgArrowREACT_163860 (Reactome)
C3fArrowREACT_118650 (Reactome)
C3fArrowREACT_118841 (Reactome)
C3mim-catalysisREACT_7948 (Reactome)
C4 activatormim-catalysisREACT_7959 (Reactome)
C4 activatormim-catalysisREACT_8002 (Reactome)
C4-binding protein C4bArrowREACT_118738 (Reactome)
C4-binding protein C4bREACT_118647 (Reactome)
C4aArrowREACT_8002 (Reactome)
C4b, C3bREACT_118575 (Reactome)
C4b-binding proteinArrowREACT_118719 (Reactome)
C4b-binding proteinREACT_118752 (Reactome)
C4b-binding proteinREACT_118763 (Reactome)
C4b-binding proteinREACT_118836 (Reactome)
C4bC2a, C3bBbREACT_118580 (Reactome)
C4bC2a, C3bBbREACT_118782 (Reactome)
C4c, C3fArrowREACT_118673 (Reactome)
C4cArrowREACT_118719 (Reactome)
C4d, iC3bArrowREACT_118673 (Reactome)
C4dArrowREACT_118719 (Reactome)
C5 convertasesmim-catalysisREACT_7989 (Reactome)
C5aArrowREACT_7989 (Reactome)
C5b

C6 C7

C8 complex		REACT_163829 (Reactome)
C5b

C6 C7

C8 complex		REACT_7988 (Reactome)
C5b

C6

C7 complex		REACT_163759 (Reactome)
C5b

C6

C7 complex		REACT_7946 (Reactome)
C5b C6 complexREACT_7950 (Reactome)
C5bArrowREACT_7989 (Reactome)
C5bREACT_7976 (Reactome)
C6REACT_7976 (Reactome)
C7REACT_7950 (Reactome)
C8REACT_163870 (Reactome)
C8REACT_7946 (Reactome)
C9REACT_163829 (Reactome)
C9REACT_163870 (Reactome)
C9REACT_7988 (Reactome)
CD46REACT_118575 (Reactome)
CD55REACT_118782 (Reactome)
CD59REACT_163829 (Reactome)
CFBArrowREACT_118584 (Reactome)
CFBArrowREACT_118641 (Reactome)
CFBArrowREACT_118692 (Reactome)
CFBArrowREACT_118727 (Reactome)
CFBArrowREACT_7981 (Reactome)
CFBArrowREACT_8026 (Reactome)
CFBREACT_7966 (Reactome)
CFBREACT_8013 (Reactome)
CFHArrowREACT_118650 (Reactome)
CFHREACT_118604 (Reactome)
CFHREACT_118712 (Reactome)
CFIREACT_118674 (Reactome)
CR1 C3bArrowREACT_118692 (Reactome)
CR1 C4bArrowREACT_118692 (Reactome)
CR1ArrowREACT_163860 (Reactome)
CR1REACT_118580 (Reactome)
Ca2+REACT_163715 (Reactome)
Ca2+REACT_163747 (Reactome)
Ca2+REACT_163758 (Reactome)
Ca2+REACT_7983 (Reactome)
Cell surface

C3b Factor Bb

Properdin		REACT_7986 (Reactome)
Cell surface

C3b Factor Bb

Properdin		mim-catalysisREACT_7986 (Reactome)
Cell surface

C3b

Factor Bb		ArrowREACT_8026 (Reactome)
Cell surface

C3b

Factor Bb		REACT_118710 (Reactome)
Cell surface

C3b

Factor Bb		REACT_8018 (Reactome)
Cell surface C3bREACT_118815 (Reactome)
Cell surface C3bREACT_7966 (Reactome)
Cell surface C3bREACT_8022 (Reactome)
Cell surface

C4b

C2a		ArrowREACT_118641 (Reactome)
Cell surface

C4b

C2a		REACT_118752 (Reactome)
Cell surface

C4b

C2a		REACT_8022 (Reactome)
Cell surface C4bArrowREACT_118641 (Reactome)
Cell surface C4bREACT_8014 (Reactome)
Cell surface

FH,FHR3

C3b		ArrowREACT_118727 (Reactome)
Cell surface

FH,FHR3

C3b		REACT_118844 (Reactome)
Cell surfaceREACT_25075 (Reactome)
Cell surfaceREACT_25166 (Reactome)
Complement factor 3REACT_7986 (Reactome)
Complement factor 3REACT_8007 (Reactome)
Complement factor Dmim-catalysisREACT_7981 (Reactome)
Complement factor Dmim-catalysisREACT_8026 (Reactome)
Complement factor I

Cell surface FH,FHR3

C3b		mim-catalysisREACT_118841 (Reactome)
Complement factor I

Factor H

C3b		mim-catalysisREACT_118650 (Reactome)
Complement factor IArrowREACT_118650 (Reactome)
Complement factor IArrowREACT_118673 (Reactome)
Complement factor IArrowREACT_118719 (Reactome)
Complement factor IArrowREACT_118841 (Reactome)
Complement factor IREACT_118583 (Reactome)
Complement factor IREACT_118631 (Reactome)
Complement factor IREACT_118647 (Reactome)
Complement factor IREACT_118844 (Reactome)
DAF C3bArrowREACT_118584 (Reactome)
DAF C4bArrowREACT_118584 (Reactome)
FCN1

MASP2 dimer

MASP1 dimer		REACT_163715 (Reactome)
FCN1 ligandREACT_163715 (Reactome)
FCN2

MASP2 dimer

MASP1 dimer		REACT_163747 (Reactome)
FCN2 ligandREACT_163747 (Reactome)
FCN3

MASP2 dimer

MASP1 dimer		REACT_163758 (Reactome)
FCN3 ligandREACT_163758 (Reactome)
FH, FHR-3ArrowREACT_118841 (Reactome)
FH, FHR-3REACT_118710 (Reactome)
FH, FHR-3REACT_118815 (Reactome)
Factor H C3bREACT_118583 (Reactome)
Factor H Host cell surfaceArrowREACT_118710 (Reactome)
Factor H Host cell surfaceArrowREACT_118815 (Reactome)
Factor I

MCP, CR1

C4b, C3b complexes		mim-catalysisREACT_118673 (Reactome)
H2OREACT_163768 (Reactome)
H2OREACT_8007 (Reactome)
Host cell surfaceREACT_118604 (Reactome)
MBL-II

MASP-2 dimer

MASP-1 dimer complex		REACT_7983 (Reactome)
MCP C3bArrowREACT_118575 (Reactome)
MCP C4bArrowREACT_118575 (Reactome)
MCP, CR1

C4b

C3b complexes		REACT_118631 (Reactome)
MCP, CR1ArrowREACT_118673 (Reactome)
Properdin oligomerArrowREACT_118641 (Reactome)
Properdin oligomerREACT_8018 (Reactome)
REACT_118575 (Reactome) Membrane cofactor protein (MCP; CD46) is a widely distributed C3b/C4b-binding cell surface glycoprotein which is a cofactor for Complement factor I.
REACT_118580 (Reactome) Complement Receptor 1 (CR1) is a widely distributed cell surface protein that is a decay accelerating factor for the conventional (C4bC2a) and alternative (C3bBb) C3 convertases (Coico & Sunshine 2009).
REACT_118583 (Reactome) Complement factor I binds the factor H:C3b complex.
REACT_118584 (Reactome) Decay accelerating factor (DAF, CD55) is a widely distributed membrane protein. It accelerates the dissociation of C3bBb and C4C2a, thereby inhibiting the amplification of complement. DAF can bind C3b and Bb but must bind both for efficient decay acceleration. The regulatory function of DAF is believed to be inhibition of activated C3 convertase enzymes rather than binding of inactive proenzymes (Harris et al. 2007).
REACT_118604 (Reactome) Factor H preferentially binds to host cells and surfaces that have negatively charged cell surface polyanions such as heparin and sialic acid commonly found on host cells (Kazatchkine et al. 1979, Meri & Pangburn 1990). This mediates protection of plasma-exposed host structures.
REACT_118631 (Reactome) Membrane cofactor protein (MCP) and Complement Receptor 1 (CR1) act as cofactors for the protease activity of complement factor I which binds MCP or CR1 complexes with C3b or C4b, inactivating C3b/C4b.
REACT_118641 (Reactome) C3b:Bb is naturally labile with a half-life of ~90 s. unless bound to properdin on the cell surface (Medicus et al. 1976). C4bC2a is also unstable, lasting at best a few minutes (Kerr et al. 1980). Decay is associated with the release of the Bb or C2a fragments respectively into the fluid phase. The liberated C3b/C4b is able to re-bind Bb/C2a if Factor B/C2 are present.
REACT_118647 (Reactome) C4b-binding protein is a cofactor for Complement Factor I, allowing it to bind and thereby mediating C4b proteolysis.
REACT_118650 (Reactome) Complement factor I cleaves the alpha chain of C3b at two positions, generating inactivated C3b (iC3b) and a small fragment C3f which is released. The majority of the alpha chain is retained as two fragments which are tethered by disulphide bonds. iC3b is proteolytically inactive.
REACT_118673 (Reactome) Factor I cleaves the truncated alpha (a') chain of C4b between Arg-1336 and Asn-1337 and then again between Arg-956 and Thr-957, producing a 16 kDa fragment known as alpha4, derived from the C terminus of the a' chain, followed by a 27 kDa alpha3 fragment. The remaining alpha 2 (C4d) fragment stays covalently bound to the cell membrane while the complex of disulfide-linked alpha3, alpha4, beta chain and gamma chain are released (C4c) into the fluid phase (Fujita et al. 1978).
REACT_118674 (Reactome) Complement factor I (CFI) is a complex of one heavy and one light chain, both cleaved from the same precursor peptide. It inactivates complement subcomponents C3b, iC3b and C4b by proteolytic cleavage of the alpha chains of C4b and C3b in the presence of cofactors such as Factor H, C4b binding protein, Complement receptor 1 (CR1) or MCP (CD46).
REACT_118692 (Reactome) Complement Receptor 1 (CR1) displaces the activated enzyme components Bb and C2a from the conventional and alternative C3 convertases C4bC2a and C3bBb, respectivley.
REACT_118710 (Reactome) Factor H (FH) binds to C3bBb, leading to displacement of Bb. Complement factor H-related protein 3 (FHR-3) has also been reported to bind C3Bb leading to inhibition of C3Bb C3 convertase activity (Fritsche et al. 2010). FH also acts as a cofactor for the factor I-mediated proteolytic inactivation of C3b to iC3b.
REACT_118712 (Reactome) Factor H (FH) regulates the alternative pathway C3 convertase C3bBb and its C3b component both in plasma and at host cell surfaces. FH binds to plasma C3b, making it unavailable, and acts as a cofactor for the factor I-mediated proteolytic inactivation of C3b to iC3b.
REACT_118719 (Reactome) C4b-binding protein is a cofactor in Factor I mediated C4b proteolysis. C4b is cleaved, releasing C4c, leaving C4d bound to the cell surface.
REACT_118727 (Reactome) Factor H greatly accelerates the displacement (decay) of Complement factor Bb from C3b.
REACT_118738 (Reactome) C4 binding protein accelerates the decay of C4bC2a in a dose-dependent fashion. The mechanism of this is poorly understood, but is distinct from Factor I mediated degradation of C4b and believed to represent the displacement of C2a from specific binding sites on C4b (Gigli et al. 1979).
REACT_118752 (Reactome) C4 binding protein accelerates the decay of C4bC2a in a dose-dependent fashion, without causing degradation of C4b, and is presumed to bind to the convertase to mediate this effect.
REACT_118763 (Reactome) The most abundant form of C4b-binding protein (C4BP) consists of seven alpha-chains (70kDa) and one beta-chain (45kDa) all linked by disulphide bonds to form a native protein with a molecular weight of 570kDa (Hilarp et al. 1989). Each alpha chain can bind C4b; it is not known whether full occupancy is necessary for subsequent events. The beta chain binds and inactivates Protein S, a component of the coagulation system. C4BP down-regulates complement activity in several ways: It binds to C4b thus inhibiting the formation of the classical pathway C3 convertase C4bC2a; it acts as a decay accelerating factor for existing convertases, probably by promoting dissociation of C2a; it is a cofactor in Factor I mediated C4b proteolysis.
REACT_118782 (Reactome) Decay-accelerating-factor (DAF, CD55) is a membrane- bound complement regulatory protein that inhibits autologous complement cascade activation. It is expressed on all cells that are in close contact with serum complement proteins, but also on cells outside the vascular space and on tumour cells. DAF binds to C3bBb and C4bC2a on cell surfaces, accelerating their dissociation and thereby inhibiting the amplification of complement. DAF can bind C3b and Bb, and must bind both for efficient decay acceleration. Although it can bind the inactive proenzymes C3b and C4b, the regulatory function of DAF is believed to be inhibition of activated C3 convertase enzymes (Harris et al. 2007).
REACT_118815 (Reactome) Factor H (FH) regulates the alternative pathway C3 convertase C3bBb and its C3b component both in plasma and at host cell surfaces. FH binds to membrane-associated C3b, competing with Factor B and thereby preventing formation of the active C3 convertase C3bBb. In addition, it acts as a cofactor for the Factor I-mediated proteolytic inactivation of C3b to iC3b.
REACT_118836 (Reactome) The beta subunit of C4b binding protein binds and inactivates Protein S, a vitamin K dependent anticoagulation factor. This may represent part of a mechanism for fine-tuning the process of phagocytosis (Kask et al. 2004).
REACT_118841 (Reactome) Following the displacement of Bb from C3bBb, Factor I cleaves Factor H-bound C3b producing iC3b, which remains bound to the membrane. The majority of the C3b alpha chain is retained as two fragments which are tethered to the beta chain by disulphide bonds. iC3b is proteolytically inactive and cannot contribute to the complement cascade process, though it still contributes to opsonization.
REACT_118844 (Reactome) Complement factor I binds to the Factor H:C3b complex.
REACT_163715 (Reactome) Ficolin-1 (M-ficolin or FCN1) was shown to localize at the cell surface of circulating monocytes and granulocytes, despite lacking an obvious transmembrane domain, (Teh C et al. 2000; Honore C et al. 2010). Ficolin-1 has also been found in human plasma (Honore C et al. 2008; Wittenborn T et al. 2010; Kjaer TR et al. 2011). Monocytes and macrophages, but not immature dendritic cells were reported to secrete Ficolin-1 into the serum (Honore C et al. 2010). Moreover, early studies revealed its presence in secretory granules of peripheral blood monocytes and granulocytes (Liu Y et al. 2005). Soluble Ficolin-1 was found to form a complex with MASP2, while cell surface-bound Ficolin-1 did not associate with MASP (Honore C et al. 2010; Kjaer TR et al. 2011).

Ficolin-1 specifically recognizes sialic acid and can bind to acetylated compounds such as N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc) (Garlatti V et al. 2007; Gout E et al. 2010; Kjaer TR et al. 2011).

REACT_163747 (Reactome) Human ficolin-2 (L-ficolin, P35 or FCN2) is synthesised in the liver and secreted into the bloodstream where it recognizes various capsulated bacteria and exhibits binding specificity for diverse ligands, such as lipoteichoic acid, 1,3-beta-d-glucan, and acetylated compounds [Lynch NJ et al. 2004; Aoyagi Y et al. 2008; Ma YG et al. 2004; Garlatti V et al. 2007; Gout E et al 2010]. Ficolin-2 also binds to apoptotic HL60, U937, and Jurkat cells [Kuraya M, et al. 2005].
REACT_163758 (Reactome) Ficolin-3 (H-ficolin, FCN3 or Hakata antigen) activates the lectin pathway of complement similar to mannose-binding lectin. Ficolin-3 is composed by a collagen-like strand and three C-terminal recognition domains which bind to carbohydrates on the target surface. Ficolin-3 circulates in plasma associated with mannan-binding lectin-associated serine proteases (MASPs). Upon ligand binding ficolin-3:MASPs complex triggers activation of the lectin pathway [Matsushita M et al. 2002; Teillet F et al. 2008; Zacho RM et al. 2012]. Ficolin-3 (FCN3 or H-ficolin) can specifically recognize Aerococcus viridans [Tsujimura M et al. 2002; Zacho RM et al. 2012]. Ficolin-3 has been shown to bind to patterns of bacterial polysaccharides such as d-fucose and galactose [Garlatti V et al. 2007]. In adition to pathogenic ligands ficolin-3 was reported to bind to apoptotic Jurkat cells [Kuraya M et al. 2005].
REACT_163759 (Reactome) Vitronectin interacts with C5b:C6:C7 complex preventing it from the binding with the cell membrane
REACT_163768 (Reactome) Cleavage of C4 exposes a highly reactive thioester bond on the C4b molecule. The thioester bond is rapidly inactivated by hydrolysis if C4b does not bind to the target cell surface [Sepp A et al 1993].
REACT_163829 (Reactome) CD59, the major inhibitor of the complement membrane attack complex, is an 18–20 kDa glycoprotein, linked to the membrane via a glycosylphosphatidylinositol (GPI)-anchor. It interacts with complement components C8 and C9 during assembly of the membrane attack complex (MAC) and inhibits C9 polymerization, thus preventing the formation of MAC [Lehto T and Meri S. 1993;Rollins SA et al 1991]
REACT_163860 (Reactome) Factor I (FI) inactivates C3 convertase activity by cleavage C3b producing iC3b, which remains bound to the membrane. A final proteolytic cleavage converts iC3b into two molecules, C3c, which is released into solution, and C3dg, which remains attached to the membrane. This cleavage requires CR1, which serves as a cofactor for cleavage of iC3b by factor I (Medof ME et al. 1982).

iC3b and C3dg are active molecules, that can bind CR2 (CD21) to enhance B-cell immunity (Tuveson DA et al.1991; Sarrias MR et al. 2001).

REACT_163870 (Reactome) Complement proteins C8 and C9 can bind to VTN:C5b:C6:C7 to form soluble C5b-C9 complex in plasma. The vitronectin binding to C5b-C9 complex prevents C9 polymerization by rendering it water-soluble and lytic inactive.
REACT_25075 (Reactome) Metastable C3b can bind a wide variety of proteins and carbohydrates expressed on biological surfaces (Coico & Sunshine, 2009; Kimball 2010). This is an essentially random event (Dodds & Law, 1998); binding may be to host or microorganism. However, certain surface sugars have greater C3b binding rates, perhaps explaining variations in microorganism suceptibility (Pangburn, M. in The Complement System, Ed. Rother et al. 1998).
REACT_25166 (Reactome) The cleavage of C4 into C4a and C4b releases an acyl group from the intrachain thioester bond, allowing C4b to bond covalently to any adjacent biological substrates (Dodds & Law 1998). C4 is encoded at two loci, C4A and C4B. The C4b proteins derived from these genes are not identical and have different binding preferences (Law et al 1984, Sepp et al. 1993); C4A-derived C4b binds more efficiently than C4B-derived C4b to amino groups, while C4B-derived C4b is more effective than C4A in binding to hydroxyl groups. The site of C4b deposition is not clearly established (Møller-Kristensen et al. 2003) but generally accepted to be the activating cell membrane surface, though it may be the activating complex itself.
REACT_7946 (Reactome)
REACT_7948 (Reactome) C3(H2O):Factor Bb is a C3 convertase, sometimes referred to as the initial C3 convertase (iC3). The Factor Bb component catalyzes the hydrolysis of C3 to produce C3b and C3a. This reaction is not known to be directly coupled to the association of C3b complexes with a cell surface. It is believed that a small proportion of C3b spontaneously associates with the cell surface, otherwise it is rapidly inactivated (Muller-Eberhard 1988).
REACT_7950 (Reactome)
REACT_7959 (Reactome) C2 is cleaved into the large C2a and the small C2b fragment. This irreversible, extracellular reaction can be catalyzed by activated MBL, generated through the lectin pathway of complement activation (Vorup-Jensen et al. 2000), and by activated C1, generated through the classical pathway (Nasagawa and Stroud 1977). N.B. Early literature refers to the larger fragment of C2 as C2a. However, complement scientists decided that the smaller of all C fragments should be designated with an 'a', the larger with a 'b', changing the nomenclature for C2. For this reason recent literature may refer to the larger C2 fragment as C2b, and the classical C3 convertase as C4bC2b. Throughout this pathway, Reactome uses the current (Feb 2012) Uniprot names which adhere to the original naming practice.
REACT_7965 (Reactome) MBL or ficolins binding to carbohydrates on the target surface results in conformational changes in the lectin:MASPs complex. It in turn promotes a cleavage of proenzyme form of MASP between the CCP2 and the serine protease domains, which results in the generation of the active form. The active form of MASP-2 is able to cleave C4 and C2 to generate the C3 convertase (Vorup-Jensen T et al. 2000; Chen CB and Wallis R 2004). The active form of MASP-1 was shown to facilitate the complement activation by either direct cleavage of complex-bound MASP-2 or cleavage of C2 bound to C4 (Matsushita M et al. 2000; Heja D et al. 2012).
REACT_7966 (Reactome) C3b on a surface binds Factor B from solution to form a complex (Schreiber et al. 1978; Muller-Eberhard 1988).
REACT_7976 (Reactome)
REACT_7977 (Reactome) In this irreversible reaction, the activated C1r subunit of the C1:antibody:antigen complex cleaves the C1s subunit of the complex, activating it in turn (Ziccardi and Cooper 1976). The resulting complex is a C4 activator.
REACT_7978 (Reactome) C1 activation requires interaction with two separate Fc domains, so pentavalent IgM antibody is far more efficient at complement activation than IgG antibody (Muller-Eberhard and Kunkel 1961). Antibody binding results in a conformational change in the C1r component of the C1 complex and a proteolytic cleavage of C1r, activating it (Ziccardi and Cooper 1976). This reaction is irreversible under physiological conditions.
REACT_7981 (Reactome) Factor D, a constitutively active serine protease found in trace amounts in the blood, cleaves a specific Arg-Lys bond in the Factor B component of the soluble C3(H2O):Factor B complex, yielding C3(H2O):Factor Bb and an inactive polypeptide, Factor Ba (Fearon and Austin 1975; Lesavre and Muller-Eberhard 1978; Lesavre et al. 1979; Schreiber et al. 1978).
REACT_7982 (Reactome)
REACT_7983 (Reactome) The MBL polypeptide chain consists of a short N-terminal cysteine-rich region, a collagen-like region comprising 19 Gly-X-Y triplets, a 34-residue hydrophobic stretch, and a C-terminal C-type lectin domain. MBL monomers associate via their cysteine-rich and collagen-like regions to form homotrimers, and these in turn associate into oligomers. The predominant oligomers found in human serum contain three (MBL-I) or four (MBL-II) homotrimers (Fujita et al. 2004; Teillet et al. 2005). Extracellular MBL oligomers circulate in plasma in complexes with MASP1/2. The carbohydrate recognition domain (CRD) of MBL binds carbohydrates with 3- and 4- OH groups in the pyranose ring, such as mannose and N-acetyl-D-glucosamine, in the presence of Ca2+. Such motifs occur on the surfaces of viruses, bacteria, fungi and protozoa. The affinity of any one MBL binding site for a carbohydrate ligand is low, but interaction between multiple binding sites on an MBL oligomer and a repetitive carbohydrate motif on a target surface allow high-avidity binding. The specificity of the MBL binding site (it does not bind glucose or sialic acid) and the requirement for a repeated target motif may account for the failure of MBL to bind human glycoproteins under normal conditions (Petersen et al. 2001). This reaction in particular represents the interaction of MBL with bacterial mannose repeats.
REACT_7986 (Reactome) The complex of C3b:Factor Bb, stabilized on the cell surface by properdin, catalyzes the cleavage of C3 to yield C3b and C3a. The C3b is recruited to the C3b:Factor B complex through its interaction with properdin (Daha et al. 1976; Medicus et al. 1976; Hourcade 2006), yielding the alternate C5 convertase.
REACT_7988 (Reactome) The membrane attack complex is composed of one C5:C6:C7:C8 complex and between 12-15 C9 molecules (Podack et al. 1982 - 12 represented in this reaction).
REACT_7989 (Reactome) The same complexes as for C3 activation are employed for the cleavage of C5. C3 convertases with an additional C3b molecule covalently deposited in the immediate vicinity form the C5 convertases C3bBbC3b and C4b2aC3b, respectively. The second C3b acts like an anvil for C5: it interacts with C5 and presents C5 in the correct conformation for cleavage by the C2a or Bb enzyme.
REACT_7990 (Reactome) C4b and C2a bind to form the classical pathway C3-convertase (C4b2a complex), C3b and the Bb fragment of Factor B form the alternative pathway C3 convertase. The C3(H2O):Bb C3 convertase is sometimes called the initiating convertase, and the C5 convertases also have C3 convertase activity (Rawal & Pangburn 2001).
REACT_8002 (Reactome) The alpha chain of C4 is cleaved, releasing an N-terminal portion of this chain as C4a. The beta and gamma chains are not cleaved and remain linked to the alpha chain by disulfide bonds (Nagasawa et al. 1976, 1980). The resulting C4b heterotrimer undergoes a gross conformational change; the internal thioester in C4b becomes exposed and able to form covalent bonds with surrounding molecules (Law and Dodds 1997). A large proportion of the bonds formed are with water, but some will attach C4b to biological surfaces (Rother et al. 1998). This irreversible reaction can be catalyzed by activated MBL, generated through the lectin pathway of complement activation (Fujita et al. 2004; Hajela et al. 2002), and by activated C1, generated through the classical pathway (Muller-Eberhard and Lepow 1965).

N.B. Humans have two highly polymorphic loci for Complement factor 4, C4A and C4B. C4A alleles carry the Rodgers (Rg) blood group antigens while the C4B alleles carry the Chido (Ch) blood group antigens. The two loci encode non identical C4 peptides; C4 derived from C4A reacts more rapidly with the amino groups of peptide antigens while C4B allotypes react more rapidly with the hydroxyl group of carbohydrate antigens. The names of the two loci are always represented in uppercase. C4a and C4b refer to the peptide products of Complement Factor 4 cleavage.
REACT_8007 (Reactome) The thioester linkage between cysteine residue 1010 and glutamine residue 1013 in the alpha chain of Complement factor 3 (C3) can spontaneously hydrolyze, yielding so-called C3(H2O) (Tack et al. 1980; Pangburn & Muller-Eberhard 1980; Pangburn et al. 1981). Thioester bond hydrolysis causes conformational rearrangements that give C3(H2O) the ability to bind Factor B. The spontaneous hydrolysis rate of C3 under physiological conditions and temperature is about l% per hour, thus the C3b-like properties of C3(H2O) provide a continuous low level initiation of the alternative pathway of complement activation (Pangburn & Muller-Eberhard 1983). If not bound by Factor B, C3(H2O) binds Factor H and is inactivated by Factor I
REACT_8013 (Reactome) Thioester bond hydrolysis causes conformational rearrangements that give C3(H2O) the ability to bind Factor B (Schreiber et al. 1978). The spontaneous hydrolysis rate of C3 under physiological conditions and temperature is about l% per hour, thus the C3b-like properties of C3(H2O) provide a continuous low level initiation of the alternative pathway of complement activation (Pangburn & Muller-Eberhard 1983).
REACT_8014 (Reactome) C4b and C2a form a complex termed the classical pathway C3 convertase (Muller-Eberhard et al. 1967). C2a that fails to bind C4b is rapidly inactivated.
REACT_8018 (Reactome) C3b:Bb is naturally labile with a half-life of ~90 s; association of the complex with properdin extends the half-life to ~30 min. (Medicus et al. 1976). Properdin is found in the blood as a mixture of multivalent oligomers: 30% dimers, 45% trimers, 10% tetramers, and 15% higher oligomers. Monomers associate with one another in a head-to-tail arrangement, producing closed circular structures (Smith et al. 1984). These features suggest that the properdin oligomer associated with a C3b:Bb complex on a surface such as a cell membrane can facilitate recruitment of additional C3b:Bb complexes to the site (Farries et al. 1988; Hourcade 2006).
REACT_8022 (Reactome) C5 convertases are serine proteases that cleave C5 with high efficiency; the C3 convertases can cleave C5 but have a poor affinity for C5, with a Km of 6-9 microM. The high affinity C5 convertases are generated when the low affinity C3/C5 convertases such as C4b:C2a deposit C3b by cleaving native C3. These C3b-containing C3/C5 convertases have Km values of 0.005 microM, well below the normal concentration of C5 in blood (0.37 microM). They have very low Vmax rates, just one C5 cleaved per 1–4 min per enzyme (Rawal & Pangburn 1998).
REACT_8026 (Reactome) Factor D, a constitutively active serine protease found in trace amounts in the blood, cleaves a specific Arg-Lys bond in the Factor B component of the cell surface-associated C3b:Factor B complex, yielding the alternate C3 convertase C3bBb on the surface and releasing an inactive polypeptide, Factor Ba (Lesavre and Muller-Eberhard 1978; Lesavre et al. 1979; Schreiber et al. 1978).
VTN

C5b C6

C7		REACT_163870 (Reactome)
VTNREACT_163759 (Reactome)
iC3bArrowREACT_118650 (Reactome)
iC3bArrowREACT_118841 (Reactome)
thioester-C1010-Q1013-C4bArrowREACT_8002 (Reactome)
thioester-C1010-Q1013-C4bREACT_118763 (Reactome)
thioester-C1010-Q1013-C4bREACT_163768 (Reactome)
thioester-C1010-Q1013-C4bREACT_25166 (Reactome)
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