FUNCTIONAL STUDY OF SINGAPORE GROUPER IRIDOVIRUS PROTEINS

Abstract

Singapore grouper iridovirus (SGIV) is a major pathogen that causes significant economic losses in grouper aquaculture. The virus contains a dsDNA genome of about 140kb predicted to encode 162 open reading frames (ORFs). In this project, we demonstrated that suppression of ORF075R expression, an abundant viral structural protein, can result in a significant reduction of viral infectivity in grouper embryonic cells. We also revealed that ORF075R had four distinct protein isoforms with slightly different molecular mass and pI. The post-translational modification of ORF075R was due to phosphorylation. The phosphorylation sites were characterized by MS. In addition, the phosphorylation profiles of ORF075R changed in different phases of SGIV infection. ORF075R was localized in the host cell cytoplasm. We hypothesize that multi-phosphorylation of ORF075R may play different roles in viral morphogenesis and viral-host interaction. We have attempted to crystallize this protein or its truncated fragments without success. The protein crystallization work may help us to further investigate the structure and function of ORF075R. This study was the first report to study the alteration of protein expression in SGIV infected zebrafish cell line instead of the grouper cell line. Many novel zebra fish proteins have been identified. The proteomic results therefore provided vast valuable information for host cells response to SGIV infection.