Investigation of proteins from infectious pancreatic necrosis virus important for protection in Atlantic salmon (Salmo salar)
Infectious Pancreatic Necrosis Virus (IPNV) belongs to the birnavirus genes, family Birnaviridae, and has classically been shown to be virulent to salmonid fish, including Atlantic salmon (Salmo salar). This study was oriented around this pathogen; it’s structural proteins in particular, namely viral proteins 2 and 3 (VP2 and VP3). Two VP2 fragments were expressed in E. coli and full length VP3 was expressed in Pichia. These proteins were tested for their abilities to confer protection against IPNV in an Atlantic salmon trial. The serum was analysed by ELISA against whole virus, and in neutralisation assays. Differences in level of response were found between the groups at the various timepoints depending on the vaccination group in all analyses. The findings from this trial suggested that VP3 had the strongest virus neutralising abilities as indicated from the 1/320 serum dilutions. VP2 has been the protein that has attracted most interest for its potential as a vaccine component. The findings of this project suggest that the importance of VP3 in protection of Atlantic salmon against IPNV has been underestimated. Another aspect of this study involved the investigation of signal sequence selection on the expression levels of the viral proteins. The outcome of this work indicated that expression of the viral proteins using the alpha mating factor signal could not be optimised. A random signal sequence library was constructed with the view to finding a novel signal(s) that was capable of yielding a higher VP3 protein expression level than that obtained by using the alpha mating factor. One sequence was discovered that was able to express VP3, which had 98% identity with the alpha mating factor signal.