Procathepsin L degrades extracellular matrix proteins in the presence of glycosaminoglycans in vitro.

The processing of procathepsin L on the surfaces of physiological glycosaminoglycans, heparan sulfate, chondroitin sulfate, etc., as well as dextran derivatives were studied. All glycosaminoglycans and dextran derivatives including dextran T-500 and DEAE dextran examined in this study accelerated the conversion of procathepsin L to processed cathepsin L in vitro with different time courses. Further, we examined whether procathepsin L digests protein substrates in the presence or absence of the surface materials. Laminin was degraded by both procathepsin L itself and the 31-kDa processed form in the presence of surface materials with the same profiles. In contrast, fibronectin was digested by procathepsin L without processing in the presence of surface materials. The proteolytic profiles of fibronectin by the processed form differed from those by procathepsin L. This is the first evidence that the proform of a cysteine proteinase proteolyzes protein substrates.