LEISHMANIA-MAJOR - MOLECULAR MODELING OF CYSTEINE PROTEASES AND PREDICTION OF NEW NONPEPTIDE INHIBITORS

The crystal structures of papain, cruzain, and human liver cathepsin B were used to build homology-based enzyme models of a cathepsin L-Like cysteine protease (cpL) and a cathepsin B-like cysteine protease (cpB ) from the protozoan parasite Leishmania major. Although structurally a member of the cathepsin B subfamily, the L. major cpB is not able to cleave synthetic substrates having an arginine in position P-2. This biochemical property correlates with the prediction of a glycine inste ad of a glutamic acid at position 205 (papain numbering). The modeled active sites of the L. major cpB and cpL were used to screen the Avail able Chemicals Directory (a database of about 150,000 commercially ava ilable compounds) for potential cysteine protease inhibitors, using DO CK3.5. Based on both steric and force field considerations, 69 compoun ds were selected. Of these, 18 showed IC50's between 50 and 100 mu M a nd 3 had IC50's below 50 mu M. A secondary library of compounds, origi nally derived from a structural screen against the homologous protease of Plasmodium falciparum (falcipain), and subsequently expanded by co mbinatorial chemistry, was also screened. Three inhibitors were identi fied which were not only effective against the L. major protease but a lso inhibited parasite growth at 5-50 mu M. (C) 1997 Academic Press.