UniprotKB/SwissProt ID: P09871 (P09871)
Gene Name:
C1S
Organism: Homo sapiens (Human)
Function: 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:11445589, PubMed:16169853, PubMed:417728, PubMed:467643, PubMed:6271784, PubMed:6282646, PubMed:6319179, PubMed:70787, PubMed:9422791). C1S is activated following association of the C1 complex with immunoglobulins (IgG or IgM) complexed with antigens to form antigen-antibody complexes on the surface of pathogens (PubMed:34155115). C1S is cleaved and activated by C1R to generate C1s subcomponent heavy and light chains (PubMed:11445589, PubMed:6271784). C1s subcomponent light chain then cleaves and activates C2 and C4, the next components of the classical complement pathway (PubMed:16169853, PubMed:467643, PubMed:6282646, PubMed:6319179, PubMed:6906228, PubMed:70787, PubMed:9422791) Serine protease component of the complement C1 complex, which catalyzes cleavage and activation of C2 and C4, the next components of the classical complement pathway (PubMed:16169853, PubMed:22949645, PubMed:417728, PubMed:467643, PubMed:6282646, PubMed:6319179, PubMed:70787, PubMed:9422791). Also able to cleave C1 inhibitor (SERPING1) in vitro; additional evidence is however required to confirm this result in vivo (PubMed:16169853). Also cleaves IGFBP5 and thereby inhibits the trophic effects of IGF1 (PubMed:18930415)
Other Modifications: View all modification sites in dbPTM
Protein Subcellular Localization: Secreted. Cell surface
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