C4 Binding Protein Alpha (C4BPa)

C4b-binding protein is involved in regulation of the complement system. It is a multimeric protein comprising 7 identical alpha chains, encoded by C4BPA, and a single beta chain, encoded by C4BPB. The alpha and beta chains have molecular masses of 70 and 45 kD, respectively. Both subunits belong to a superfamily of proteins composed predominantly of tandemly arranged short consensus repeats (SCR) of approximately 60 amino acids in length (Aso et al., 1991).Brodeur et al. (2003) identified a 23-kD protein that bound CD40 as C4BP-alpha. Flow cytometric analysis demonstrated binding of C4BP to human B-cell lines expressing CD40, but not to cells from CD40-deficient patients.Aso et al. (1991) found that the C4BPA gene comprises 12 exons and spans about 40 kb.