Abstract
Nervous necrosis virus (NNV) is a pathogenic fish virus belonging to family Nodaviridae. The objective of this study was to analyze stabilities of NNV surface protrusion and free coat protein (CP) conformational structures by analyzing changes of NNV infectivity and antigenicity after incubation at moderate-low temperatures. When cultured NNV suspension was incubated at 45 °C, its infectivity declined gradually but its antigenicity maintained. In contrast, both infectivity and antigenicity of purified NNV declined after incubation at 45 °C. After heat-treatment, surface protrusions of NNV particles disappeared completely, although viral particle structures maintained. Therefore, the reduction in NNV infectivity appeared to specifically occur as a result of heat-denaturation of virus surface protrusions. The loss of NNV infectivity in the presence of fetal bovine serum (FBS) was delayed compared to virus heated in the absence of FBS, demonstrating that FBS could function as a stabilizer for conformational structures of NNV surface protrusions. Moreover, the stabilizing function of FBS changed depending on salt concentration. Continued maintenance of antigenicity for heated cultured NNV suspension containing free-CPs may suggest that conformational structures corresponding to protrusion-domain of free-CP are more heat-stable than those of surface protrusions on NNV particles.
Highlights
Nervous necrosis virus (NNV), a member of the genus Betanodavirus in the Nodaviridae family, can infect more than 120 fish species and cause high mortality in aquaculture facilities worldwide[1,2,3]
By using Focused ion beam scanning electron microscopic (FIB-SEM), we were able to show that NNV surface protrusions were completely denatured after incubation at 45 °C, NNV particle structures were reliably preserved (Fig. 6)
The NNV antiserum used in this study can recognize heat-sensitive conformational structures of NNV surface protrusions[37]
Summary
Nervous necrosis virus (NNV), a member of the genus Betanodavirus in the Nodaviridae family, can infect more than 120 fish species and cause high mortality in aquaculture facilities worldwide[1,2,3]. NNV-neutralizing antibodies could not be detected in these convalescent fish despite the fact that these fish are strongly protected against re-infection by NNV20 This suggests that there might be some slight differences in antigenicity between inactivated and naïve NNV particles. Trimeric P-domains can form 60 protrusions on the NNV particle surface[21,22] These surface protrusions play a crucial role in the antigenicity and receptor interactions during virus infection[22]. It is drastically curtailed at ≥60 °C35,36 This could be due to denaturation of NNV surface protrusions because these protrusions have heat-sensitive conformational structures[37]. The objective of this study was to determine stabilities of NNV surface protrusions and free-CPs by analyzing both infectivity and antigenicity after incubation at moderate-low temperatures. Influence of fetal bovine serum (FBS) on stability of NNV surface protrusions was investigated
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