Complement C1q subcomponent subunit C
1_MDVGP 6_ SSLPH 11_ LGLKL 16_ LLLLL 21_ LLPLR 26_ GQANT 31_ GCYGI 36_ PGMPG 41_ LPGAP 46_ GKDGY 51_ DGLPG 56_ PKGEP 61_ GIPAI 66_ PGIRG 71_ PKGQK 76_ GEPGL 81_ PGHPG 86_ KNGPM 91_ GPPGM 96_ PGVPG 101_ PMGIP 106_ GEPGE 111_ EGRYK 116_ QKFQS 121_ VFTVT 126_ RQTHQ 131_ PPAPN 136_ SLIRF 141_ NAVLT 146_ NPQGD 151_ YDTST 156_ GKFTC 161_ KVPGL 166_ YYFVY 171_ HASHT 176_ ANLCV 181_ LLYRS 186_ GVKVV 191_ TFCGH 196_ TSKTN 201_ QVNSG 206_ GVLLR 211_ LQVGE 216_ EVWLA 221_ VNDYY 226_ DMVGI 231_ QGSDS 236_VFSGF
1: Core component of the complement C1 complex, a multiprotein complex that initiates the classical pathway of the complement system, a cascade of proteins that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:12847249, PubMed:19006321, PubMed:24626930, PubMed:29449492, PubMed:3258649, PubMed:34155115, PubMed:6249812, PubMed:6776418). The classical complement pathway is initiated by the C1Q subcomplex of the C1 complex, which specifically binds IgG or IgM immunoglobulins complexed with antigens, forming antigen-antibody complexes on the surface of pathogens: C1QA, together with C1QB and C1QC, specifically recognizes and binds the Fc regions of IgG or IgM via its C1q domain (PubMed:12847249, PubMed:19006321, PubMed:24626930, PubMed:29449492, PubMed:3258649, PubMed:6776418). Immunoglobulin-binding activates the proenzyme C1R, which cleaves C1S, initiating the proteolytic cascade of the complement system (PubMed:29449492). The C1Q subcomplex is activated by a hexamer of IgG complexed with antigens, while it is activated by a pentameric IgM (PubMed:19706439, PubMed:24626930, PubMed:29449492). The C1Q subcomplex also recognizes and binds phosphatidylserine exposed on the surface of cells undergoing programmed cell death, possibly promoting activation of the complement system (PubMed:18250442)