Background |
Aliases: complement factor D, CFD, Adipsin, AND, C3 convertase activator. Complement factor D, also known as adipsin, is a serine protease that is required for the initiation of the alternative pathway of complement. Human complement factor D is a 253 amino acid (aa) precursor protein consisting of a signal peptide, a five-residue activation-/ pro-peptide, and the mature chain. Under physiological conditions, mature factor D lacking the activation peptide circulates as an inactive enzyme and requires interaction with its natural substrate, C3b-bound factor B, for activation of its catalytic activity. Active factor D functions to cleave the C3b-bound factor B, resulting in the formation of C3bBb complex, the alternative pathway C3 convertase. Factor D is expressed in multiple tissues, including monocyte/ macrophages, muscle, sciatic nerve, endometrium, kidney, intestine, and at especially high levels in adipocytes. Pathologically, Complement factor D deficiency is associated with low activity of the alternative complement pathway and low capacity to opsonize bacteria. |