Schistosomiasis is a major
neglected tropical disease (NTD) and considered the most important of the human
helminthiases in terms of morbidity and mortality. Whereas treatment with
praziquantel has been effective since the 1980s, the potential for the emergence of drug resistance has propelled the search for new interventions. Studies have revealed key roles of
proteases in parasitic helminths during establishment of
infection, tissue invasion, immune evasion, parasite feeding and development throughout the different developmental stages, pinpointing them as possible candidates. The
leucine aminopeptidases (LAPs), members of the M17 family of Zn-
metalloproteases, preferentially cleave
leucine (Leu) residues at the N-terminal end of
proteins and short
peptides. These
enzymes display broad proteolytic activities beyond Leu hydrolysis and are involved in processing, maturation, activation and/or degradation of substrates. As a
vaccine immunogen, LAP induces protection against
infection with the liver fluke Fasciola hepatica. Herein, two LAPs, SmLAP1 (Smp_030000) and SmLAP2 (Smp_083870) of the human blood fluke Schistosoma mansoni were cloned, expressed, purified and biochemically characterized. The
enzymes differed in activity against diagnostic substrates, including
leucine,
methionine and
arginine, with an optimal pH of 8.0. The activity increased in the presence of Mg+2 and Mn+2, and was inhibited by
bestatin, a specific inhibitor of
aminopeptidase. In addition,
1,10-phenanthroline and
EDTA inhibited the enzymatic activity of SmLAP2. Finally, immunolocalization using
antibodies specific for SmLAP1 and SmLAP2 identified the expression of these
proteases in the egg and adult developmental stages of S. mansoni, and in intestinal epithelia, vitelline cells and sub-tegumental regions of the parasite. Characterization of schistosome
proteases not only enhances understanding of the biology of schistosomes and
schistosomiasis, but may also provide novel intervention approaches.