Mmapping the neutralizing epitope on the coat protein of fish nodavirus.

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The striped jack nervous necrosis virus (SJNNV), the causative agent of viral nervous necrosis in marine fish, is a members of fish nodaviruses. The fish nodavirus is an isometric virus consisting of a single type of coat protein and two positive-sense RNA molecules, and is divided into four different genotypes (SJ, TP, BF and RG types) based on the nucleotide sequence of the coat protein gene (RNA2). In this study, two different regions of the coat protein gene of SJNNV and other genotypes of fish nodaviruses were cloned into expression vector plasmids for analysis of the serological relationships and mapping the neutralizing epitope on SJNNV.The four different genotypes of nodaviruses were confirmed to be distinguishable from each other easily by the hybridization with DIG labeled DNA probes. Furthermore, by western blot analysis with A/S SJNNV and MAbs having neutralizing activities against SJNNV, it was revealed that SJNNV and other fish nodaviruses shared a significant number of antigenic determinants with other genotype viruses, although SJNNV was serologically distinguishable from them. And it was suggested that the antigenic determinant of SJNNV for the neutralizing MAbs was a liner epitope, which consisted of a repeated amino acid sequence at the coat protein. It was considered that one of the neutralizing epitopes of SJNNV was PAN (aa 254-256). The other genotypes of fishnodaviruses, TP, BF and RG types, have a PPG, PEG and/or PDG at the same amino acid position as SJNNV coat protein, thus it was considered that the four different genotypes of fish nodaviruses were also serologically different from each other.