ARGININE DEIMINASE: A SUMOYLATED ENZYME INVOLVED IN THE MECHANISMS OF SURVIVAL OF THE PARASITE GIARDIA LAMBLIA.

VRANYCH CV; RIVERO MR; TOUZ MC; RÓPOLO AS

Rosario. Santa Fe

Congreso; VIII Congreso Argentino de Protozoología y Enfermedades Parasitarias. Sociedad Argentina de Protozoología; 2008

Sociedad Argentina de Protozoología.

Giardia lamblia is a protozoan parasite that colonize the upper part of the small intestine of humans and other vertebrates, causing acute as chronic infections. Here, we describe the functions played by the enzyme arginine deiminase (ADI) during the mechanims of Giardia adaptation to survive inside and outside the host. It is widely known that, during Giardia growth in the intestine of the host, the trophozoite acquire free arginine from the extracellular medium and by way of ADI it is converted in citrulline, with ATP production occuring at the final enzymatic step of the ADH pathway. Also, ADI is released to the extracellular space when the trophozoites are in contact with human epithelial cells and compete with the oxide nitric sinthase for the free arginine, thereby reducing the production of nitric oxide. We found that ADI also acts as a peptidyl arginine deiminase producing post-translational citrullination in the citoplasmic tail of the variant-specific surface proteins. This modification directly controls the VSP swithching involved in the process of antigenic variation and cell death. During encystation ADI translocates to the nucleus and has a regulatory role in the expression of encystation specific genes. Also, we found that arginine deiminase is a sumoylated protein based on the results of Western blot and immunoprecipitation assays both employing anti-SUMO mAb. This protein modification may be essential in the nuclear translocation of ADI during encystation. Our findings reveal multiple physiological roles played by ADI and define novel regulatory pathways used by Giardia for survival.