The region Ser333-Arg356of the α-chain of human C4b-binding protein is involved in the binding of complement C4b

Abstract
Human C4b‐binding protein (C4BP) functions as a cofactor to factor I in the degradation of C4b and accelerates the decay rate of the C4b2a complex. In this study we describe a monoclonal antibody directed against the α‐chain of C4BP that inhibits the binding of C4b to C4BP. In order to identify the structural domain of the a‐chain of C4BP that interacts with C4b, tryptie fragments of C4BP were generated. Amino acid sequence analysis of the fragments revealed that the residues Ser333‐Arg356 of the α‐chain of C4BP contain the epitope of this antibody, and as a consequence, that this part of the α‐chain of C4BP is likely to be involved in the interaction with C4b.