N-terminal truncation of the foot-and-mouth disease virus VP0 protein promotes soluble co-expression and particle assembly stability of viral capsid proteins in Escherichia coli.

BACKGROUND: Foot-and-mouth disease (FMD), caused by foot-and-mouth disease virus (FMDV), is an acute, highly contagious, and economically devastating disease affecting cloven-hoofed animals worldwide. Vaccination remains the cornerstone of FMD control strategies. To increase the production yield and structural stability of virus-like particles (VLPs), we investigated the effects of the N-terminal truncation of VP0 on the soluble co-expression of three capsid proteins, and the stability of the assembled particles.

RESULTS: A series of VP0 variants with progressive N-terminal truncations (5-20 amino acids) were co-expressed with VP3 and VP1 via a single plasmid in the Escherichia coli (E. coli) expression system by fusing these proteins with a small ubiquitin-like modifier (SUMO) tag. The assembly characteristics of the co-expressed fusion proteins were systematically characterized. Our findings show that all engineered fusion proteins were successfully co-expressed, and truncations between residues 10 and 20 yielded significantly higher expression levels and purification efficiencies than those of full-length VP0. The 031-VP0 dN10, 031-VP0 dN15, and 031-VP0 dN20 exhibited increased stability of the assembly and retained the native morphology. An in vitro binding assay for neutralizing antibodies against FMDV indicated that all VLPs maintained wild-type-like antigenic properties, demonstrating preserved conformational epitopes. Pigs immunized with VLPs-based vaccines exhibited humoral and cellular immune responses, with the 031-VP0 dN20 variant eliciting significantly stronger cellular immunity.

CONCLUSIONS: Collectively, our findings establish a robust platform for the efficient production of structurally stable FMDV VLPs in E. coli, providing a valuable framework for developing soluble expression systems for other FMDV serotypes.