Cleavage of type I and type II procollagens by type I/II procollagen N-proteinase. Correlation of kinetic constants with the predicted conformations of procollagen substrates.

The kinetic constants were examined for the cleavage of several types of procollagen by type I/II procollagen N-proteinase.The K , values were essentially the same (0.2 PM) for chick type I procollagen, human type I procollagen, and chick type I1 procollagen.However, the V , , values differed over a 14-fold range.As reported previously, the enzyme did not cleave denatured type I or I1 procollagen.Also, it did not cleave human type I11 procollagen which contains the same scissle -Pro-Gln-bond as the pro-al(I) chain of type I procollagen.To explain the observations, Chou-Fasman rules were used to compare the secondary structures of the cleavage sites in the procollagens.The results supported a previous suggestion (Helseth, D. L., Jr., Lechner, J. L., and Veis, A. ( 1979) Biopolymers 18, 3005-3014) that the region carboxyl-terminal to cleavage site in the pro-al(1) chain of type I procollagen was in a hairpin conformation consisting of a 8sheet, &turn, and &sheet.In both chick and human type I procollagen, the hairpin loop in the pro-al(1) chain consisted of about 18 amino acids.The cleavage site itself was in a short a-helical structure of four or five amino acids.The pro-a2(1) chains had a similar hairpin loop of about 14 amino acids and a-helix of four or five amino acids containing the cleavage site.Chick type I1 procollagen, which had the highest V , , value, had a longer hairpin structure of 22 amino acids, and the cleavage site was in a longer a-helical domain of 10 amino acids.In contrast, type I11 procollagen had a random-coil conformation in the same region.The results help to explain the unusual substrate requirements of type I/II N-proteinase.They also help explain why mutations that produce in-frame deletions of amino acids 84 or more residues carboxyl-terminal to the cleavage site make the protein resistant to the enzyme.Collagens are a family of over 10 structural proteins that consist primarily of three polypeptide chains in a characteristic a triple helix.Type I, type 11, and type I11 collagens are the major fibrillar collagens (Prockop and Kivirikko, 1984;Cheah, 1985;Miller, 1985).