High-level expression and immunogenicity of porcine circovirus type 2b capsid protein without nuclear localization signal expressed in Hansenula polymorpha

Currently, porcine circovirus type 2b (PCV2b) is the dominant PCV2 genotype causing postweaning multi systemic wasting disease (PMWS) in pigs worldwide. Efforts have been made to develop various recombinant capsid proteins of PCV2b used in vaccines against PCV2b. However, the nuclear localization signal (NLS) of PCV2b capsid protein (CP) was found to inhibit the expression of the whole length capsid protein in E. coli. Here, we expressed a NLS-deleted capsid protein (ACP) of PCV2b in Hansenula polymorpha based on the capsid protein of PCV2b strain Y-7 isolated in China. Comparatively, the ACP was expressed at a higher level than the CP. The purified ACP could self-assemble into virus like particles (VLPs) with similar morphology of the VLPs formed by CP. The purified ACP could be recognized by the anti-sera derived from the mice immunized by inactivated PCV2b particles. Furthermore, it induced higher levels of PCV2b specific antibodies than the purified CP in mice. These results showed that the ACP, a recombinant PCV2b capsid protein without nuclear localization signal sequence, could be efficiently expressed in Hansenula polymorpha, and used as a candidate antigen for the development of PCV2b vaccines.