Virus-like particles (VLPs) are multiprotein structures that mimic naturally occurring virions but lack genetic material and, therefore, are unable to replicate and cause infection. The major application of VLPs is vaccines and delivery of drugs, other bio- and nanomaterials [1]. Being known for cost-effective cultivation, high levels of protein expression and rapid cell growth, Escherichia coli is the most widely used bacterial expression system for VLP synthesis [2].
Two species of the virus family Totiviridae, L-A and L-BC, are presently known to infect Saccharomyces cerevisiae. They are double-stranded RNA viruses which pack their genomes into a capsid composed of a single major coat protein Gag and Gag-Pol fusion protein. Previous research has shown that Gag modification by Mak3-Mak10-Mak31 N-acetyltransferase complex is essential for L-A viral assembly, while L-BC can persist in host cells which lack the N-acetyltransferase complex [3]. Since L-BC Gag protein does not require N-acetylation, attempts to produce its VLPs in bacteria have been made.
The main aim of this study was to synthesize recombinant L-BC Gag protein that would successfully self-assemble into VLPs in E. coli. The L-BC Gag encoding sequence was incorporated into a bacterial expression vector and protein synthesis was initiated by double inducing system. The particles were purified from E. coli lysate by ultracentrifugation through sucrose cushion and cesium chloride, with a yield of 0.34 mg protein/g dry cell weight. Dynamic light scattering (DLS) method confirmed that L-BC Gag protein self-assembled into VLPs, the diameter of which was found to be 40.4±1.57 nm. This result is comparable to the diameter of native L-BC virions (38.5 nm), recently observed in another study [4]. Further research regarding cytotoxicity and stability of the synthesized VLPs is in progress before considering these VLPs as nanodelivery system.