Chromatographically-purified capsid proteins of red-spotted grouper nervous necrosis virus expressed in Saccharomyces cerevisiae form virus-like particles.

Nervous necrosis viruses (NNVs) cause mass mortality of marine fish, leading to large economic losses for aquaculturists. A promising vaccine candidate for preventing NNV infection is the NNV virus-like particle (VLP), which is a structure resulting from assembly of recombinant NNV capsid protein. NNV capsid proteins have been expressed in insect cells and the Escherichia coli expression system, and purified by non-scalable protocols such as ultracentrifugation on sucrose and cesium chloride density gradients. In this study, we expressed red-spotted grouper NNV (RGNNV) capsid proteins in Saccharomyces cerevisiae (S. cerevisiae) and developed a chromatography-based method with potential for large-scale vaccine production. The RGNNV capsid protein was successfully purified by a single-step of heparin chromatography. Transmission electron microscopy (TEM) confirmed the high quality of the purified RGNNV capsid protein: it was in the form of VLPs with mean diameters of 25nm, in homogeneous suspension without any aggregation. Moreover, the RGNNV capsid protein elicited anti-RGNNV capsid protein antibodies in mice. We suggest that RGNNV capsid protein expressed in S. cerevisiae and purified by heparin chromatography, is of sufficient quality for use as a vaccine.