Leishmania mexicana: Identification and characterization of an aspartyl proteinase activity

An aspartyl proteinase activity was detected in the soluble fraction (SF) of Leishmania mexicana promastigotes by the use of the synthetic substrate benzoyl-Arg-Gly-Phe-Phe-Leu-4-methoxy-β-naphthylamide selective for Cathepsin D like aspartyl-proteinases. This peptide was hydrolyzed with an apparent Km of 2.3 ± 0.3 μM. The classic inhibitor of aspartyl-proteinases, diazo-acetyl-norleucinemethylester (DAN) inhibited the proteolytic activity with an IC50 of 400 μM. The soluble fraction degraded (in absence of thiol groups) human fibrinogen with a specific activity of 533 U/mg protein. When tested for the ability to inhibit the “in vitro” proliferation of L. mexicana promastigotes, DAN showed concentration dependent anti-proliferative effects with a LD50 of 466 μM at 48 h, with a significant fall in this value to 22 μM after 72 h. This is the first characterization of an aspartyl-proteinase activity in Leishmania, calling for further studies directed towards the physiologic role of these enzymes in the parasite. The anti-proliferative effect of its inhibition makes this enzyme a putative new target for the development of leishmanicidal drugs.