Structure and Function characterization of ubiquitin like protein of Singapore grouper iridovirus

Abstract

Singapore grouper iridovirus (SGIV) containing 162 open reading frames causes the sleepy disease in grouper fish with unknown mechanism. This virus encodes putative ubiquitin like protein with 75% of similarity with animal ubiquitin. The question is why this virus needs its own ubiquitin? To address this question, we firstly confirmed the biological function of SGIV ubiquitin by in vitro ubiquitination assay. The NMR experiment was conducted to determine the structure of the viral ubiquitin. The structure of SGIV ubiquitin presented the common protein foldings of ubiquitin. Although ubiquitin is one the most conserved protein, our comparative analysis of different viral ubiquitin DNA and protein sequences reveales some viral unique regions. On the other hand, the Itraq experiment interestingly showed that ubiquitin is up regulated after virus infection. To further elucidate the function of viral ubiquitin, we are focussing on distinguishing viral and host ubiquitin. The viral unique ubiquitin peptide sequence is used for raising antibody specific for viral ubiquitin. Western blot experiment has showed bands of ubiquitinated proteins up regulated after virus infection. We are futher investingating those changes using 2D gel and Mass spectrometry approach.