Covalent structure of collagen: amino acid sequence of cyanogen bromide peptides from the amino-terminal segment of type III collagen of human liver

Abstract

Human liver type III collagen was prepared by limited pepsin digestion, differential salt precipitation and carboxymethylcellulose chromatography. Cyanogen bromide digestion of purified type III collagen chains yielded 9 distinct peptides. Three peptides, .alpha.1(III)-CB3, .alpha.1(III)-CB7 and .alpha.1(III)-CB6, were isolated by carboxymethylcellulose chromatography and Sephadex G-50 SF gel filtration. Automated Edman degradation together with selective hydroxylamine cleavage and chymotrypsin and trypsin digestion enable determination of their complete amino acid sequence. Compared with type I collagen, the data show tentative homology of .alpha.1(III)-CB3 with .alpha.1(I)-CB1, .alpha.1(I)-CB2 and .alpha.1(I)-CB4; .alpha.1(III)-CB7 with .alpha.1(I)-CB5; and .alpha.1(III)-CB6 with the amino-terminal portion of .alpha.1(I)-CB8. Close interspecies homology was found between the sequences presented here with 90 residues of .alpha.1(III)-CB3 and26 of .alpha.1(III)-CB8 of calf aorta. The amino acid sequence was established of 229 residues near the amino terminus or nearly 1/4 of the type III collagen chains. The disaccharide, Glc-Gal, was convalently bound to hydroxylsine at a position corresponding to the same location in the .alpha.1(I) chain.