Identification and partial characterization of excretory/secretory products with proteolytic activity in Giardia intestinalis

This report examines the presence of proteolytic activity detected in media collected from in vitro cultures of Giardia intestinalis, and the partial characterization by gelatin-substrate polyacrylamide gel electrophoresis an d inhibition studies. Gelatin-substrate polyacrylamide gel electrophoresis revealed 6 bands with proteolytic activity, with estimated molecular weight s of 36, 59, 63, 72, 103, and 175 kDa. These bands were not present in the control medium. On the other hand, G. intestinalis trophozoite lysates show ed proteolytic bands at 16, 20, 66, 82, 108, and 120 kDa, thus indicating t hat intracellular proteases could be different from the excretory/secretory (E/S) products. Based on inhibition studies, 2 bands of 59 and 63 kDa were inhibited by iodoacetic acid, indicating the presence of cysteine protease s. Partial inhibition of a band of 36 kDa was found with EDTA, a metal-chel ating agent, suggesting the possible presence of metalloproteases. The pres ence of aspartic and serine proteases were not detected under the assay con ditions used. As G. intestinalis E/S may be involved in differentiation mec hanisms of the parasite and also be responsible for the mucosal alterations that occur in giardiasis, the characterization of these proteases may faci litate their evaluation as targets in the therapy of the disease.