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Complete primary structure of rainbow trout type I collagen consisting of α1(I)α2(I)α3(I) heterotrimers

Saito, Masataka, Takenouchi, Yoshitaka, Kunisaki, Naomichi, Kimura, Shigeru
European journal of biochemistry 2001 v.268 no.10 pp. 2817-2827
Oncorhynchus mykiss, amino acids, cDNA libraries, collagen, complementary DNA, denaturation, digestion, fibroblasts, fish, heat, imino acids, muscles, phylogeny, temperature
The subunit compositions of skin and muscle type I collagens from rainbow trout were found to be α1(I)α2(I)α3(I) and [α1(I)]2α2(I), respectively. The occurrence of α3(I) has been observed only for bonyfish. The skin collagen exhibited more susceptibility to both heat denaturation and MMP‐13 digestion than the muscle counterpart; the former had a lower denaturation temperature by about 0.5 °C than the latter. The lower stability of skin collagen, however, is not due to the low levels of imino acids because the contents of Pro and Hyp were almost constant in both collagens. On the other hand, some cDNAs coding for the N‐terminal and/or a part of triple‐helical domains of proα(I) chains were cloned from the cDNA library of rainbow trout fibroblasts. These cDNAs together with the previously cloned collagen cDNAs gave information about the complete primary structure of type I procollagen. The main triple‐helical domain of each proα(I) chain had 338 uninterrupted Gly‐X‐Y triplets consisting of 1014 amino acids and was unique in its high content of Gly‐Gly doublets. In particular, the bonyfish‐specific α(I) chain, proα3(I) was characterized by the small number of Gly‐Pro‐Pro triplets, 19, and the large number of Gly‐Gly doublets, 38, in the triple‐helical domain, compared to 23 and 22, respectively, for proα1(I). The small number of Gly‐Pro‐Pro and the large number of Gly‐Gly in proα3(I) was assumed to partially loosen the triple‐helical structure of skin collagen, leading to the lower stability of skin collagen mentioned above. Finally, phylogenetic analyses revealed that proα3(I) had diverged from proα1(I). This study is the first report of the complete primary structure of fish type I procollagen.