Cathepsin B activity regulation - Heparin-like glycosaminoglycans protect human cathepsin B from alkaline pH-induced inactivation

It has been shown that lysosomal cysteine proteinases, specially cathepsin B, has been implicated in a variety of diseases involving tissue remodeling states, such as inflammation, parasite infection, and tumor metastasis, by degradation of extracellular matrix components. Recently, we have shown th at heparin and heparan sulfate bind to papain specifically; this interactio n induces an increase of its alpha -helix content and stabilizes the enzyme structure even at alkaline pH (Almeida, P. C., Nantes, I. L,, Rizzi, C, C. A., Judice, W.A.S., Chagas, J. R., Juliano, L., Nader, H. B., and Tersario l, I. L. S. (1999) J. Biol. Chem. 274, 30433-30438). In the present work, a combination of circular dichroism analysis, affinity chromatography, cathe psin B mutants, and fluorogenic substrate assays were used to characterize the interaction of human cathepsin B with glycosaminoglycans. The nature of the cathepsin B-glycosaminoglycans interaction was sensitive to the charge and type of polysaccharide, Like papain, heparin and heparan sulfate bind cathepsin B specifically, and this interaction reduces the loss of cathepsi n B alpha -helix content at alkaline pH. Our data show that the coupling of cathepsin B with heparin or heparan sulfate can potentiate the endopeptida se activity of the cathepsin B, increasing B-fold the half-life (t(1/2)) of the enzyme at alkaline pH, Most of these effects are related to the intera ction 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 n ovel physiological role for heparan sulfate proteoglycans.