Design, cloning and expression of a synthetic gene encoding a grouper iridovirus major capsid protein

Abstract

Synthetic biology approaches can be adopted to successfully redesign, clone and express recalcitrant proteins from viruses in a bacterial expression system. The grouper iridovirus major capsid proteins (GI-MCP) is a surface coat protein which has the potential for application as an antigen for the development of vaccines which confer immunity against GI. The native amino acid coding region of the GI-MCP does not lend itself to expression in the Escherichia coli (BL21) (DE3) platform due to the presence of internal motifs which represent the start and stop codons as well as secondary structures. This manuscript reports on the redesigning, cloning and expression of a synthetic GI-MCP in E. coli. The native GI-MCP protein coding region was retrieved from the NCBI GenBank. The sequence was codon optimized, internal start and stop codons were modified and potential secondary structures were resolved. Both the native and modified GI-MCP coding DNA sequences were synthesized and ligated onto an expression plasmid, pET22b (+) followed by transformation, cloning and expression in E. coli (BL21) (DE3). Induction of protein expression was carried out at 12°C, 20°C and 37°C to assess protein solubility. The gene encoding the native GI-MCP failed to express under any of the culture conditions, however, the modified synthetic gene encoding the GI-MCP expressed the recombinant iridovirus coat protein (rGI-MCP) under all the conditions. Gene design and synthesis offer an ideal solution for the recombinant expression of viral proteins in bacterial expression systems for the industrial production of viral antigens.