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

Abstract

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.

Evolution of collagens

“…In contrast, the central triple helix of hydra fibrillar ␣ chains is relatively poor in proline residues (15% compared to 23% in vertebrate ␣ chains), and this feature of hydra collagen may be correlated with the flexible properties of its ECM . In addition, several studies have indicated that Gly-Xaa-Gly and Gly-Gly-Yaa triplets are more abundant in invertebrate and lower vertebrate ␣ chains than in their mammalian counterparts (Su et al, 1991;Exposito et al, 1992a;Yoneda et al, 1999;Saito et al, 2001). These triplets have been described as destabilizing triplets (Shah et al, 1997), and are also found in vertebrate collagens.…”

“…It is worth noting that in type I-III collagens, the cleavage site for mammalian collagenase is near a flexible region characterized by a low amino acid content (Fields, 1991). The best example of Gly-Gly-containing triplets is probably that of rainbow trout type I collagen (Saito et al, 2001). As indicated by Saito et al (2001), the three ␣ chains making up type I collagen are rich in Gly-Gly pairs (11% for the ␣3(I) chain), and this situation may be correlated with the low thermal stability of type I collagen from this poikilothermic animal.…”

“…The best example of Gly-Gly-containing triplets is probably that of rainbow trout type I collagen (Saito et al, 2001). As indicated by Saito et al (2001), the three ␣ chains making up type I collagen are rich in Gly-Gly pairs (11% for the ␣3(I) chain), and this situation may be correlated with the low thermal stability of type I collagen from this poikilothermic animal. Hence, depending on the environment and the ability to regulate body temperature, distinct selective features have been used during evolution.…”

“…Several phylogenic studies using this domain have been performed, and the major result is that vertebrate fibrillar collagen chains can be divided into two groups: the A group, including types I-III and the pro␣2(V) chains; and the B group, including the pro␣1(V), pro␣1(XI), and pro␣2(XI) chains (Sicot et al, 1997;Saito et al, 2001;Vä lkkilä et al, 2001), and probably also the pro␣3(V) chain. This subdivision reflects the divergence of the exon-intron organization observed for the genes encoding these two groups (Takahara et al, 1995;Vuoristo et al, 1995).…”

A Major IgE Epitope of Rainbow Trout Collagen α2 Chain

“…All three a chains of collagen have been completely sequenced for only two species of fish, rainbow trout 13) and zebrafish Danio rerio 14) . Rainbow trout is an important edible fish that is widely consumed, while zebrafish is often used as a model fish in biology, but is not edible.…”