Arginine Deiminase in Giardia lamblia and its novel role as peptidyl-arginine deiminase during the encystation process

VRANYCH, CV; MERINO, MC; TOUZ, MC; ROPOLO, AS

Mar del Plata

Congreso; IX Congreso Argentino de Protozoología y Enfermedades Parasitarias; 2011

Sociedad Argentina de Protozoología

A crucial characteristic of eukaryotic cell physiology is the regulation of the expressed genome, a complex process controlled by several molecular mechanisms that include posttranscriptional modulation at mRNA levels. Posttranslational modifications are one of the most effective ways by which evolution has increased the versatility in protein function, providing the cell flexibility to respond to a broad range of stimuli. An interesting feature of parasites is its ability to efficiently adapt to changes of the environment. G. lamblia is a parasitic protozoan early divergent in the evolutionary history with multiple mechanisms of adaptation; therefore it turns a useful model to study biological processes of higher eukaryotes. Arginine Deiminase (gADI) is an important enzyme in the survival and differentiation of Giardia. Considering the ancestral character of this parasite and the different conditions along its life cycle it is not strange that Giardia modify the function of its enzymes according to the requirements of the environment. Previous studies determined that gADI plays a role in the energy metabolism and acts as a Peptidyl Arginine Deiminase (PAD) on variant-specific surface proteins regulating the antigenic variation process. Besides during the encystation process, gADI translocate to the nuclei of the parasite both in wild-type and gADI-HA transfected trophozoites. Wild-type cells only showed the presence of nuclear gADI late during encystation. Interestingly, the transgenic cells showed a clear translocation of gADI-HA to the nuclei had few if any encystation-specific secretory vesicles and at the same time the number of cyst produced is very low. Also, our results indicate that gADI is a sumoylated protein based on “in silico” data, Western blotting and IPP. This protein modification may be essential in the nuclear translocation of gADI in order to accomplish its function during encystation, since the 85 kDa-gADI was mainly located in the nuclear subfractions. Therefore we made site-specific mutation on the site of sumoylation of gADI and we observed that in these cells gADI did not localize to the nuclei nor the number of cyst was reduced. These results confirmed that the sumoylation of gADI is crucial for gADI in order to fulfill its function. Then we analyzed which was the function of gADI in the nucleus, and we found that gADI is able to citrullinate the Histone H2. On the whole, these results indicate that gADI shows a regulatory role during encystation where both sumoylation of gADI and citrullination of histones are key players.