Complete primary structure of the human alpha 2 type V procollagen COOH-terminal propeptide

Recently we presented the partial covalent structure of a type V collagen chain. Analysis of amino acids 796-1020 in the human alpha 2(V) Gly-X-Y region showed strong conservation of charged positions with the interstitial collagens but also revealed substitutions unique to type V. To gain more information about this procollagen and primarily to resolve the ambiguous nature of the 3' noncollagenous propeptide, we sequenced several cDNA clones coding for amino acids adjacent to the carboxyl end of the alpha chain. Here we report the complete primary structure of the alpha 2(V) COOH-terminal propeptide. In general, the latter sequence (270 residues) bears a greater degree of similarity to those of the interstitial rather than the basement membrane procollagens. Compared to the interstitial procollagens, however, more divergence has occurred in alpha 2(V) surrounding the conserved N-asparaginyl-linked carbohydrate attachment site at residues 171-173, and alpha 2(V) possesses an additional potential glycosylation site (Asn-Lys-Thr) located in a hypervariable region near the NH2 terminus. Although certainly premature to form any rigid hypothesis, a pattern emerges that may be characteristic of alpha 2 versus alpha 1 chains. Both the alpha 2(I) and alpha 2(V) telopeptides are devoid of a lysine, which in alpha 1 chains forms an interchain cross-link with residue 87 of the collagenous region. Also in contrast to the interstitial alpha 1 carboxyl propeptides is the absence in alpha 2(I) and alpha 2(V) of a cysteine that probably participates in an interchain disulfide bond. Therefore, one can speculate that those alpha 2 chains, represented only once in procollagen trimers, may not be under the same selective pressure as alpha 1 chains to maintain certain residues responsible for stabilizing the triple helical molecules.