Characterization of a new thioredoxin system from Entamoeba histolytica.

ARIAS, DIEGO; IGLESIAS, ALBERTO A.; GUERRERO, SERGIO A.

Mar del Plata – Buenos Aires - Argentina

Congreso; SAIB - XLIII Reunión Anual; 2007

The thioredoxin system, composed by thioredoxin and thioredoxin reductase, serves as a reduction equivalents donor in the reduction of disulfides. Entamoeba histolytica, a unicellular parasite, usually lives and multiplies within the human gut, under reduced oxygen pressure. During tissue invasion, it is exposed to increased amounts of reactive oxygen species, which are highly toxic for the parasite. The metabolic pathways used by this organism to cope with such environmental changes and redox homeostasis is a matter of our work. Recently, we characterized in E. histolytica its functional thioredoxin system (EhTRXR/EhTRX41). In this work, we present the cloning, expression and characterization of a new thioredoxin from E. histolytica (EhTRX8). EhTRX8 was evaluated in its ability to catalyse the NADPH dependent reduction of cystine (k = 124,7 M-1s-1), GSSG (k = 55.23 M-1s-1), TS2 (k = 118,56 M-1s-1) and insulin (k = 2435.13 M-1s-1). In addition, the EhTRXR/EhTRX8 system was able to work together to EhP29 (a typical 2CysPrx) in the NADPH dependent reduction of hydroperoxides. The standard redox potential of EhTRX8 (-0.282 V) was estimated by equilibrium with NADPH/NADP at pH 7.0. This work strongly supports the occurrence in E. histolytica of a new thioredoxin, which was not previously described in the parasite. Granted by UNL, CAI+D 2002; ANPCyT, PICT´03 01-14733, PAV´03 137.