Complement Component 4 Binding Protein Alpha
C4-binding protein alpha (C4BPA), encoded by the C4BPA gene, is the principal subunit of the plasma complement regulator C4BP. In circulation, seven alpha chains assemble around a single beta chain through disulfide bridges, forming the octameric, spider-shaped glycoprotein that carries most of the complex's regulatory activity. Each alpha chain presents eight complement control protein (CCP) modules, whose N-terminal CCP domains mediate cofactor activity for factor I-mediated cleavage of C4b and accelerate decay of the classical and lectin pathway C3 convertases. Produced mainly by hepatocytes, it protects host surfaces, binds heparin and phospholipids, and limits complement-mediated damage; altered levels accompany inflammatory and thrombotic conditions.
