C4b Protein

C4b is derived from native C4 upon cleavage and release of C4a. It is prepared by cleavage of purified C4 with the classical pathway activated protease C1s enzyme (#A104) . Native human C4b is a glycosylated (~7.3%) polypeptide containing three disulfide-linked chains. C4b is central to the function of two of the three pathways of complement. Both the classical and lectin pathways of complement activation generate surface-bound active proteases that cleave C4 (C1s in the classical pathway and MASP1/2 in the lectin pathway) . These enzymes cleave a peptide bond in C4 releasing the anaphylatoxin C4a and activating C4b. For a fraction of a second after proteolytic activation C4b can covalently attach to the surface of the target.