Partial characterization of cDNA clones encoding the three distinct pro alpha chains of type I collagen from rainbow trout

The major fibrillar collagen of rainbow trout skin, type I, was found to ha ve a subunit composition of alpha 1(I)alpha 2(I)alpha 3(I); or alpha 3(I) i s known to be a unique subunit of bonyfish type I collagen. To investigate the primary structure of these a(I) chains, a cDNA library was prepared fro m mRNA of rainbow trout fibroblast and screened by use of a cDNA collagen p robe. Three distinct cDNAs coding for fibrillar collagen pro alpha chains w ere cloned and polypeptides encoded by these clones were denoted as RtCOL1A 1, RtCOL1A2, and RtCOL1A3. Each clone encompassed 2.5 or 3.0 kb and was fou nd to code for more than the C-terminal half of pro alpha chains. On the ot her hand, the alpha 1(I), alpha 2(I), and alpha 3(I) chains of rainbow trou t skin type I collagen were isolated and characterized by sequencing of sel ected tryptic peptides with subsequent comparison of these sequences with t he deduced amino acid sequences of rainbow trout collagen cDNAs. From these results, RtCOL1A1, RtCOL1A2, and RtCOL1A3 were identified as parts of the pro alpha 1(I), pro alpha 2(I), and pro alpha 3(I) chains of rainbow trout type I collagen, respectively. When compared with human fibrillar collagens , each of RtCOL1A1 and RtCOL1A3 was found to have the highest level of amin o acid sequence homology to human pro alpha 1(I), while RtCOL1A2 had the hi ghest homology to human pro alpha 2(I). Furthermore, RtCOL1A3 resembled RtC OL1A1 rather than RtCOL1A2; particularly, distribution of the highly conser ved cysteine residues and putative crosslinking sites indicated that RtCOL1 A3 was diverged from RtCOL1A1. As far as we know, this study is the first r eport of fish type I collagen cDNAs.