Expression and self-assembly of Heterocapsa circularisquama RNA virus-like particles synthesized in Pichia pastoris

Heterocapsa circularisquama RNA virus （HcRNAV） is the first single-stranded RNA virus to be characterized that infects dinoflagellates. The ability of HcRNAV coat protein （HcRNAV CP） to self-assemble into virus-like particles （VLPs） in vitro suggested that heterologous expression was possible, and that the VLPs might be ideal nanocontainers for the targeted delivery of genes and chemicals. In this paper, we report the expression of a codon-optimized HcRNAV 109 CP gene in Pichia pastoris and the produc- tion of self-assembled HcRNAV VLPs using large-scale fermentation. The HcRNAV 109 CP gene was synthesized according to the codon preference of P. pastoris and cloned into a pPICZA vector. The recombinant plasmid pPICZA-CPsyns was transformed into P. pastoris by electroporation. The resulting yeast colonies were screened by PCR and analyzed for protein expression by SDS polyacrylarnide gel electrophoresis. After large-scale fermentation, the yield of HcRNAV CPsyns reached approximately 2.5 g L-1 within. 4 d. The HcRNAV VLPs were purified using PEG precipitation followed by cesium chloride density gradient ultracentrifugation, and were subsequently analyzed using UV spectrophotometry and transmission electron microscopy. Fluores- cence dye-labeled myoglobin was loaded into the cages of the HcRNAV VLPs and the encapsulation was confirmed by fluores- cence spectroscopy. The results point to the possible utilization in pharmacology or nanotechnology of HcRNAV VLPs produced by P. pastoris fermentation.