The Covalent Binding Reaction of Complement Component C3

Mihaela Gadjeva, Alister W. Dodds, Aiko Taniguchi-Sidle, Antony C. Willis, David E. Isenman, S. K. Alex Law
1998 Journal of Immunology  
The covalent binding of C3 to target molecules on the surfaces of pathogens is crucial in most complement-mediated activities. When C3 is activated, the acyl group is transferred from the sulfhydryl of the internal thioester to the hydroxyl group of the acceptor molecule; consequently, C3 is bound to the acceptor surface by an ester bond. It has been determined that the binding reaction of the B isotype of human C4 uses a two-step mechanism. Upon activation, a His residue first attacks the
more » ... nal thioester to form an acyl-imidazole bond. The freed thiolate anion of the Cys residue of the thioester then acts as a base to catalyze the transfer of the acyl group from the imidazole to the hydroxyl group of the acceptor molecule. In this article, we present results which indicate that this two-step reaction mechanism also occurs in C3.
doi:10.4049/jimmunol.161.2.985 fatcat:6w2svmyxyng6hhn5yi3kfhlwbm