A novel virus-like particle based on hepatitis B core antigen and substrate-binding domain of bacterial molecular chaperone DnaK

Hepatitis B virus core (HBc) protein has been proved to be an attractive carrier for foreign epitopes, and can display green fluorescent protein (GFP) on its surface. The structure of substrate-binding domain of DnaK [DnaK (394-504 aa), DnaK SBD] is similar to GFP, we therefore reasoned that DnaK SBD might also be tolerated. Electron microscopic observations suggested that the chimeric proteins containing the truncated HBc (HBcΔ) and DnaK SBD could self-assemble into virus-like particle (VLP). Then the accessibility of DnaK SBD and the adjuvanticity of VLP HBcΔ-SBD were demonstrated by two recombinant peptide vaccines against gonadotropin-releasing hormone (GnRH), GhM and GhMNR. The latter carries in addition the peptide motif NRLLLTG which is known to bind to DnaK and DnaK SBD. The combination of VLP HBcΔ-SBD and GhMNR elicited stronger humoral responses and caused further testicular atrophy than the combinations of VLP HBcΔ and GhMNR or VLP HBcΔ-SBD and GhM in Balb/c mice. These findings indicate VLP HBcΔ-SBD might serve as an excellent carrier for GhMNR and some other peptide vaccines.