F734236355625ED9BEC6C3B326FE210797EF30A2EBEA50ACF82F5277A6D22F5453DA11DD18BBD8FBE09A33026ABD3693

C1s B chain is a serine protease that combines with C1q and C1r to form C1, the first component of the classical pathway of the complement system. C1r activates C1s so that it can, in turn, activate C2 and C4 (By similarity).

Source:http://purl.uniprot.org/SHA-384/F734236355625ED9BEC6C3B326FE210797EF30A2EBEA50ACF82F5277A6D22F5453DA11DD18BBD8FBE09A33026ABD3693