Covalent structure of mouse type-IV collagen. Isolation, order and partial amino-acid sequence of cyanogen-bromide and tryptic peptides of pepsin fragment P1 from the alpha 1(IV) chain.

Fragment P1 (Mr = 55 000) which is located in the carboxy-terminal portion of the triple-helical segment of the alpha 1(IV) chain was purified from a pepsin digest of a mouse tumor basement membrane. Peptides produced from P1 by cleavage with cyanogen bromide and trypsin were purified and characterised with respect to their size, composition and partial amino acid sequence. Fragment patterns and overlapping sequences allowed the ordering of these peptides within the P1 segment. About 70% of the sequence was determined by Edman degradation. Segments of seven or eight amino acid residues, which lacked the triple-helical sequence Gly-Xaa-Yaa, were found at both ends of fragment P1, explaining the susceptibility of native type IV collagen to pepsin. Two further interruptions of the triple helix were indicated by single deletions of GLy or Yaa positions in the triplet structure (Gly-Xaa-Yaa)n. The two 3-hydroxyproline residues were found in position Xaa and are surrounded by homologous sequences.