C3, HUMAN

The Uses of C3, HUMAN

Complement C3 is important in complement activation through the classical and alternative pathways. Complement C3 has been used in studies of bacterial defense against the complement system. Research on streptococcus infection has shown that Streptococcal pyrogenic exotoxin B (SPE B), a cysteine protease, can prevent phagocytic activity via cleavage of the C3 and impairing the pathways of the compliment system. C3 deficiency can result in recurrent infections and immune complex disorders. Recent research has shown that inherited C3 deficiency can occur either through homozygous mutations or through compound heterozygous mutations,

Biochem/physiol Actions

Complement C3 is the third and most abundant component of the complement pathway. It plays a central role in complement activation, being involved in both the classical and alternative pathways. C3 or its proteolytic fragments mediate many biological functions such as opsonization and anaphylatoxin activities. Pro-C3 is synthesized as a large single chain of 185 kDa and is processed to a disulfide-linked heterodimer consisting of an α-chain (115 kDa) and a β-chain (70 kDa) in the plasma. C3 is cleaved by the C3 convertases in either pathway (C4b2a, C3iBb, C3bBb) to C3b (176 kDa) comprised of the large C-terminal portion of the α-chain and the β-chain. C3b interacts with other complement components to initiate the amplification cascade. Studies of C3 function have been facilitated by experimentally induced C3 deficiency in animals by injection of cobra venom factor and more recently with gene ablation technology.