Characterization of a lysosomal serine carboxypeptidase from Trypanosoma cruzi

Trypanosoma cruzi, the flagellate protozoan which is the causative agent of the American trypanosomiasis, Chagas disease has carboxypeptidase activity. The enzyme has been purified to protein homogeneity, and shown to be a lysosomal monomeric glycoprotein with a molecular mass of about 54kDa. The enzyme has an optimum acidic pH (4.5 with furyl acryloyl-Phe-Phe as substrate), is highly specific for hydrophobic C-terminal amino acid residues, and is strongly inhibited by 3,4-dichloroisocoumarin (IC(50) value 0.3 microM). The enzyme is encoded by a number of genes arrayed in head-to-tail tandems; one of these genes has been cloned and sequenced. Sequence comparisons indicate that the enzyme belongs to the C group of serine carboxypeptidases, within the S10 serine peptidase family, and shows the higher similarity to plant and yeast enzymes. The residues involved in catalysis and most of those involved in substrate binding are conserved in the T. cruzi enzyme as well as 8 out of 10 Cys residues known to be involved in disulfide bridges in the yeast enzyme. This is the first report of an S10 family enzyme in trypanosomatids. The presence of serine carboxypeptidases is not restricted to T. cruzi, being possibly a general character of trypanosomatids.