Cathepsin B Activity Regulation

Abstract

It has been shown that lysosomal cysteine protein-ases, specially cathepsin B, has been implicated in a variety of diseases involving tissue remodeling states, such as inflammation, parasite infection, and tumor me-tastasis, by degradation of extracellular matrix components. Recently, we have shown that heparin and hepa-ran sulfate bind to papain specifically; this interaction induces an increase of its-helix content and stabilizes the enzyme structure even at alkaline pH (Almeida, P. C., Nantes, I. L., Rizzi, C. C. A., Jú dice, W. A. S., Chagas, J. R., Juliano, L., Nader, H. B., and Tersariol, I. L. S. (1999) J. Biol. Chem. 274, 30433-30438). In the present work, a combination of circular dichroism analysis, affinity chromatography, cathepsin B mutants, and flu-orogenic substrate assays were used to characterize the interaction of human cathepsin B with glycosaminogly-cans. The nature of the cathepsin B-glycosaminoglycans interaction was sensitive to the charge and type of po-lysaccharide. Like papain, heparin and heparan sulfate bind cathepsin B specifically, and this interaction reduces the loss of cathepsin B-helix content at alkaline pH. Our data show that the coupling of cathepsin B with heparin or heparan sulfate can potentiate the endopep-tidase activity of the cathepsin B, increasing 5-fold the half-life (t1 ⁄2) of the enzyme at alkaline pH. Most of these effects are related to the interaction of heparin and heparan sulfate with His 111 residue of the cathepsin B occluding loop. These results strongly suggest that heparan sulfate may be an important binding site for cathepsin B at cell surface, reporting a novel physiological role for heparan sulfate proteoglycans.