Covalent structure of collagen: Amino acid sequence of three cyanogen bromide-derived peptides from human α1(V) collagen chain

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Type V collagen was prepared from human amnionic/chorionic membranes and separated into α1(V) and α2(V) polypeptide chains. The α1(V) chain was digested with cyanogen bromide and nine peptides were obtained and purified. Three of the peptides, α1(V)CB1, CB4, and CB7 having molecular weights of 5000, 8000, and 6000, respectively, were further analyzed by amino acid sequence analysis and thermolytic or tryptic digestions. CB1 contained 54 amino acids and identification of its complete sequence was aided by thermolysin digestion and isolation of two peptides, Th1 and Th2. CB4 contained 81 amino acids and sequence analysis of intact CB4 and five tryptic peptides provided us with its complete amino acid sequence. The peptide CB7 contained 67 amino acids and was cleaved into four tryptic peptides that were used for complete sequence analysis. The above results represent the first available covalent structure information on the α1(V) collagen chain. These data enabled us to establish the location of these peptides within the helical structure of other collagen chains. CB4 was homologous to residues 66–145 in the collagen chain while CB1 represented residues 146–200 and CB7 was homologous with residues 201–269. This alignment was facilitated by identification of a helical collagen crossing site consisting of Hyl-Gly-His-Arg located at positions 87–90 in all collagen chains of this size thus far identified. Seventy-one percent homology (excluding Gly residues) was found between amino acids in this region of the α1(XI) and of α1(V) collagen chains while only 21 and 19% identity was calculated for the same region of α2(V) and α1(I) collagen chains, respectively.