Complement component 4 binding protein alpha chain (C4BPA)

Complement component 4 binding protein alpha chain (C4BPA) is the major subunit of C4b-binding protein (C4BP), a large, multimeric, soluble glycoprotein primarily synthesized in the liver and found in plasma. C4BP contains seven identical alpha chains and one beta chain, and acts as a potent regulator of the classical and lectin pathways of the complement system, serving as a cofactor for factor I–mediated inactivation of C4b and C3b, thereby damping excessive complement activation and inflammation. C4BPA also plays a significant role in coagulation and interacts with multiple serum and cell-surface proteins, including protein S and serum amyloid P component. Altered function or expression of C4BPA is relevant in immune response modulation, infection (where pathogens may hijack C4BP to evade complement-mediated killing), and diseases such as atypical hemolytic uremic syndrome and other inflammatory or coagulopathy-associated conditions. Recent studies indicate additional roles in lipid metabolism and fat regulation in certain cell types.

Other names

C4b-binding protein alpha chainC4BP alphaC4BPC4bpProline-rich proteinPRPC4b-binding proteinComplement component 4 binding proteinC4b-binding protein alpha

Inhibition/modulation of complement activation (classical pathway); Enhancement of cofactor activity for factor I–mediated proteolysis of C4b and C3b