Complement C1s

**Definition:** A 77-kDa subcomponent of complement C1, encoded by gene C1S, is a SERINE PROTEASE existing as a proenzyme (homodimer) in the intact complement C1 complex. Upon the binding of COMPLEMENT C1Q to antibodies, the activated COMPLEMENT C1R cleaves C1s into two chains, A (heavy) and B (light, the serine protease), linked by disulfide bonds yielding the active C1s. The activated C1s, in turn, cleaves COMPLEMENT C2 and COMPLEMENT C4 to form C4b2a (CLASSICAL C3 CONVERTASE).

**Tree numbers:** - D08.811.277.300.290 - D12.776.124.486.274.045.290 - D12.776.124.486.274.050.290

**Synonyms:** - Complement 1s - C 1 Esterase - Complement 1 Esterase - Complement Component 1s - C1s Complement - C1 Esterase