cruzi contains many genes homologous reference 2 to those encoding proteases which are con sidered virulence factors in other pathogens. However, only a few of these enzymes have been functionally characterized to date. Among them, cathepsin L, which is known as cruzipain, is associated with both T. cruzi development and infection. Oligopeptidase B and POP Tc80, which are members of the prolyl oligopepti dase family of serine proteases, play important roles during parasite entry into mammalian cells. T. cruzi differentiation depends on proteasome activity, while antibodies against surface metalloproteases par tially block infection by trypomastigotes. Addi tionally, the cysteine protease cathepsin B, a serine carboxipeptidase, and, more recently, two cytosolic metallocarboxypeptidases, a serine oligopeptidase and two aspartyl proteases have been biochemically charac terized.

In contrast, the study of aminopepti dases has been limited to the detection of such activity in cell extracts of T. cruzi epimastigotes. Leucyl aminopeptidases are metal loaminopeptidases that catalyse the removal of N term inal amino acid residues, preferentially leucine, from proteins and peptides. LAPs comprise a diverse set of enzymes with different biochemical and biophysical properties, are found in animals, plants and microorgan isms, and play important roles in physiological pro cesses, such as the catabolism of endogenous and exogenous proteins, peptide and protein turnover and processing, modulation of gene expression, antigen pro cessing and defence.

LAPs in the peptidase family M17 show two unrelated domains, with the active site in the C terminal domain. Their activities require two metal ions, are found to be maximal at neutral basic pH, and are sensitive to bestatin and amastatin. Because of their essential functions in the life cycle of microorganisms such as Plasmodium, Fusobacterium nucleatum, and the African trypanosome, LAPs are emerging as novel and promising pathogen targets for drug design. Furthermore, LAPs are considered potential vaccine candidates, as evidenced by specific immune protection of sheep and cattle against fasciolia sis. The aim of this study was to examine leucyl amino peptidase activity present in the developmental forms of T. cruzi. We report the identification, purification and characterization of the major leucyl aminopeptidolytic activity mediated by a hexameric 330 kDa leucyl amino peptidase of T.

cruzi, whose assembly does not depend on interchain disulfide bonds. Its molecular and enzymatic properties lead us to classify LAPTc as an archetypal member of the peptidase Drug_discovery family M17. Differ ent from its recombinant form that is alkaline and ther mophilic, LAPTc purified from epimastigotes is neutral, mesophilic, and retains its oligomeric structure after los ing activity at 80 C. Our data suggest that the enzyme localizes within vesicles in the cytoplasm of epimasti gostes, trypomastigotes and amastigotes of T. cruzi.