CLEAVAGE OF TYPE-I PROCOLLAGEN BY HUMAN MAST-CELL CHYMASE INITIATES COLLAGEN FIBRIL FORMATION AND GENERATES A UNIQUE CARBOXYL-TERMINAL PROPEPTIDE

The ability of human mast cell chymase and tryptase to process procoll agen was examined. Purified human intestinal smooth muscle cell procol lagen was incubated with human mast cell tryptase or human mast cell c hymase, Purified chymase, but not tryptase, exhibited procollagen prot einase activity in the presence of EDTA Addition of purified porcine h eparin over a range of 0.1-100 mu g/ml did not affect either the rate or the products of procollagen chymase cleavage, The cleavage site of chymase on the pro-alpha 1(I) collagen carboxyl terminus was found to be in the propeptide region at Leu-1248-Ser-1249. Cleavage at this sit e suggested that the collagen products would form fibrils and confirme d the production of a unique carboxyl-terminal propeptide. Turbidometr ic fibril formation assay demonstrated de novo formation of chymase-ge nerated collagen fibrils with characteristic lag, growth, and plateau phases. When observed by dark, field microscopy, these fibrils were si milar to fibrils formed by the action of procollagen proteinases. Thus , mast cell chymase, but not tryptase, exhibits procollagen peptidase- like activity as evidenced by its ability to process procollagen to fi bril-forming collagen with concurrent formation of a unique carboxyl-t erminal propeptide, These data demonstrate that mast cell chymase has a potential role in the regulation of collagen biosynthesis and in the pathogenesis of fibrosis.