title: Mapping of the properdin-binding site in the third component of complement.
abstract: The properdin-binding site in the human third complement component (C3) was mapped by using isolated C3b, C3c, alpha- and beta-chains of C3 and C3 polypeptide fragments and an enzyme-linked-immunosorbent-assay procedure. The C3 chains and the polypeptide fragments were purified to homogeneity by preparative sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The alpha-chain polypeptides included a 68 kDa and a 43 kDa polypeptide, which were generated by cleavage of C3b with factors I and H, and a 40 kDa, 33 kDa (C3d) and 27 kDa polypeptide, which were generated by cleavage of C3b with porcine elastase. It was shown that properdin binds to C3b, C3c, alpha-chain, and to the 43 kDa (factor-I + H-derived), as well as to 40 kDa (elastase-derived) alpha-chain fragment, but not to the beta-chain 68 kDa, 33 kDa (C3d) and 27 kDa alpha-chain fragments. Thus the binding site for properdin resides on the 40-43 kDa C-terminal alpha-chain fragment of C3.
mesh_terms: D001665:Binding Sites; D003176:Complement C3 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008956:Models, Chemical; D010446:Peptide Fragments / Q000378:metabolism; D011414:Properdin / Q000378:metabolism*
chemical_list: D003176:Complement C3; D010446:Peptide Fragments; D011414:Properdin