Identification of peptides inhibitory to recombinant cysteine proteinase, CPB, of Leishmania mexicana

We have identified peptides that are relatively resistant to hydrolysis by a recombinant cysteine proteinase, CPB2.8 Delta CTE, of Leishmania mexicana, and yet exhibit inhibition constant (K-i) values in the nanomolar range. Common to these peptides is a basic-hydrophobic-hydrophobic motif in the P-3-P-1 sites, which is also present in the pro-region of the enzyme. A nine-amino acid stretch, FAA (RYL) under bar NGA, which has good homology to the pro-region of mammalian cathepsin L was identified as the part of the pro-region most likely to interact with the active site of the parasite enzyme. This peptide is not hydrolyzed by CPB2.8 Delta CTE and inhibited it with a K-i of 4 muM. Extension of this sequence at both the N- and C-termini and the introduction of ortho-aminobenzoic acid at the N-terminal site reduced the K-i value to 30 nM. The best substrate for CPB2.8 Delta CTE was also well hydrolyzed by cathepsin L, however the best inhibitor of the parasite enzyme inhibit poorly cathepsin L, with K-i value two order of magnitude higher than against the parasite enzyme. These promising data provide insights into the peculiar specificity of the parasite enzyme and M ill aid the design of antiparasitic drugs directed against the leishmanial enzyme. (C) 2001 Elsevier Science B.V. All rights reserved.