コラーゲン様補体成分C1qの構造と機能に関する研究 : ウシおよびヒトC1qの比較研究

Abstract

In order to find a clue to the molecular evolution mechanism of collagen-like molecules, comparative studies on the function and the structure of human and bovine C1q, a collagen-like complement component, were carried out. The hemolytic activity of bovine C1q was conspicuously higher than that of human C1q. On the other hand, the ability of bovine C1q to bind to Fc of immune complexes was a little lower than that of human C1q. However, these activities were interchangeable between them. Both the N-terminal collagen-like (CLF) and the C-terminal globular fragments (GF) of these C1q were highly purified by enzymic digestion followed by gel filtration, and their physicochemical and antigenic characterization was performed. Polyacrylamide gel electrophoresis (PAGE) analyses have shown that not only whole molecules of both C1q but also CLFs and GFs seem to be composed of essentially the same peptide structures. Some similarities between amino acid compositions of both CLFs and great similarities between those of both GFs were found. Moreover, great similarities of amino acid compositions were found among three non-covalently linked chains of each GF as well as between the corresponding chains of both GFs. Immunodiffusion analyses and radioimmune inhibition tests have shown that the definitive antigenic cross-reactivity is present between these two C1q molecules, and that the regions participating in interspecies cross-reactions are located in both CLF and GF of C1q. These results suggest that both CLF and GF on the C1q molecule remained highly conserved in their evolution, and that the hemolytic activity and the Fc-binding ability evolved independently to some extent. The possible relation of the C1q evolution to that of collagen molecules has been also discussed.