Importance of the alpha 3-fragment of complement C4 for the binding with C4b-binding protein.
The human regulatory complement component C4b-binding protein (C4BP) is a multimeric plasma protein, which regulates the classical pathway of the complement system. C4BP functions as a cofactor to factor 1 in the degradation of C4b and accelerates the decay rate of the C4b2a complex. Previously, we have demonstrated that monoclonal antibodies (C4-2 and 9) directed against the alpha'-chain of C4b inhibit the binding of C4b to C4BP. In order to identify the structural domain of C4b that binds C4BP, proteolytic fragments of C4 were generated with trypsin and Staphylococcus aureus V8 protease. Sodium dodecyl sulfate polyacrylamide gel electrophoresis, immunoblotting and amino acid sequence analysis of the proteolytic fragments reactive with the anti-C4 mAb's revealed that the residues Ala738-Arg826 of the alpha 3-fragment of C4b are important for the interaction with C4BP.
Hessing
M
M
Department of Biology, Faculty of Science, Kyushu University, Fukuoka, Japan.
van 't Veer
C
C
Hackeng
T M
TM
Bouma
B N
BN
Iwanaga
S
S
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D001665:Binding Sites; D002352:Carrier Proteins / Q000032:analysis*; D003181:Complement C4 / Q000032:analysis*; D003169:Complement Inactivator Proteins; D000939:Epitopes / Q000032:analysis; D006023:Glycoproteins; D006801:Humans; D008969:Molecular Sequence Data; D011489:Protein Denaturation; D012697:Serine Endopeptidases
D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; D003181:Complement C4; D003169:Complement Inactivator Proteins; D000939:Epitopes; D006023:Glycoproteins; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase