Heparin Modulates the Endopeptidase Activity of Leishmania mexicana Cysteine Protease Cathepsin L-Like rCPB2.8

Abstract

Background: Cysteine protease B is considered crucial for the survival and infectivity of the Leishmania in its human host. Several microorganism pathogens bind to the heparin-like glycosaminoglycans chains of proteoglycans at host-cell surface to promote their attachment and internalization. Here, we have investigated the influence of heparin upon Leishmania mexicana cysteine protease rCPB2.8 activity.Methodology/Principal Findings: the data analysis revealed that the presence of heparin affects all steps of the enzyme reaction: (i) it decreases 3.5-fold the k(1) and 4.0-fold the k(-1), (ii) it affects the acyl-enzyme accumulation with pronounced decrease in k(2) (2.7-fold), and also decrease in k(3) (3.5-fold). the large values of triangle G = 12 kJ/mol for the association and dissociation steps indicate substantial structural strains linked to the formation/dissociation of the ES complex in the presence of heparin, which underscore a conformational change that prevents the diffusion of substrate in the rCPB2.8 active site. Binding to heparin also significantly decreases the alpha-helix content of the rCPB2.8 and perturbs the intrinsic fluorescence emission of the enzyme. the data strongly suggest that heparin is altering the ionization of catalytic (Cys(25))-S-/(His(163))-Im(+) H ion pair of the rCPB2.8. Moreover, the interaction of heparin with the N-terminal pro-region of rCPB2.8 significantly decreased its inhibitory activity against the mature enzyme.Conclusions/Significance: Taken together, depending on their concentration, heparin-like glycosaminoglycans can either stimulate or antagonize the activity of cysteine protease B enzymes during parasite infection, suggesting that this glycoconjugate can anchor parasite cysteine protease at host cell surface.