Comparative biochemical and functional properties of two leucine aminopeptidases of Clonorchis sinensis.

Leucine aminopeptidases (LAP; EC 3.4.11.1) are a group of metalloexopeptidases, which catalyze the sequential removal of leucine amino acids from the N-termini of the polypeptides or proteins. In this study, we identified two novel genes that encode LAPs of Clonorchis sinensis (CsLAP1 and CsLAP2) and characterized their biochemical and functional properties. Multiple sequence alignment of the deduced amino acid sequences of CsLAP1 and CsLAP2 with those of other organisms revealed that typical metal-binding coordinating and active site residues for LAPs were well conserved in CsLAP1 and CsLAP2. Recombinant CsLAP1 and CsLAP2 showed similar biochemical properties such as pH optima at pH 8.0 and stability at neutral pHs. Both enzymes were specifically inhibited by bestatin and showed preferential substrate specificity for Leu-MCA. However, the enzymes differed in that they required different metal ions for maximum activity. Expressions of CsLAP1 and CsLAP2 were detected throughout the various developmental stages of C. sinensis, and their transcription levels increased gradually in accordance with the maturation of the parasite. Both enzymes were identified in soluble worm extract of C. sinensis, but not in excretory and secretory products. Immunolocalization studies showed that both enzymes were co-localized to the intestinal epithelial cells and gastrodermis of the parasite. These results collectively suggest that CsLAP1 and CsLAP2 are synthesized in the intestinal epithelial and gastrodermal cells of C. sinensis and may be involved in the final digestion of peptides that hydrolyzed within intestinal lumen followed by absorbed into gastrodermal cells of the parasite.