The occurrence of two types of collagen pro alpha-chain in the abalone Haliotis discus muscle

Acid-soluble collagens were prepared from connective tissues in the abalone Haliotis discus foot and adductor muscles with limited proteolysis using p epsin. Collagen preparation solubilized with 1% pepsin contained two types of ct-chains which were different in their N-terminal amino acid sequences. Accordingly, two types of full-length cDNAs coding for collagen pro alpha- chains were isolated from the foot muscle of the same animal and these prot eins were named Hdcols (Haliotis discus collagens) la and 2 alpha. The two N-terminal amino acid sequences of the abalone pepsin-solubilized collagen preparation corresponded to either of the two sequences deduced from the cD NA clones. In addition, several tryptic peptides prepared from the pepsin-s olubilized collagen and fractionated by HPLC showed N-terminal amino acid s equences identical to those deduced from the two cDNA clones. Hdcols 1 alph a and 2 alpha consisted of 1378 and 1439 amino acids, respectively, showing the primary structure typical to those of fibril-forming collagens. The N- terminal propeptides of the two collagen proa-chains contained cysteine-ric h globular domains. It is of note that Hdcol l alpha completely lacked a sh ort Gly-X-Y triplet repeat sequence in its propeptide, An unusual structure such as this has never before been reported for any fibril-forming collage n. The main triple-helical domains for both chains consisted of 1014 amino acids, where a supposed glycine residue in the triplet at the 598th positio n from the N-terminus was replaced by alanine in Hdcol la and by serine in Hdcol 2a. Both proa-chains of abalone collagens contained six cysteine resi dues in the carboxyl-terminal propeptide, lacking two cysteine residues usu ally found in vertebrate collagens. Northern blot analysis demonstrated tha t the mRNA levels of Hdcols 1 alpha and 2 alpha in various tissues includin g muscles were similar to each other.