Complement Component 6 (C6)

C6 is 1 of 5 late-acting proteins of complement that participate in assembly and function of the MAC (DiScipio and Hugli, 1989). The deduced C6 protein contains 934 amino acids, including a 21-amino acid N-terminal signal sequence and 2 N-glycosylation sites. The mature 913-amino acid C6 protein shares 29% amino acid identity with C7 , and 55 of 56 cysteines in C7 match those in C6.

The C6 polypeptide chain is cross-linked by 32 disulfide bonds, and most cysteines are located in short, discrete segments that exhibit homology with a variety of proteins, including thrombospondin, low density lipoprotein receptor(LDLR), epidermal growth factor (EGF), and complement factors H (CFH) and I (CFI ).