A heat-induced Mutation on VP1 of FMDV Serotype O Enhanced Capsid Stability and the Immunogenicity.

Foot-and-mouth disease (FMD) is a highly contagious viral disease affecting cloven-hoofed animals that cause a significant economic burden globally. Vaccination is the most effective FMD control strategy. However, FMDV particles are prone to dissociate when appropriate physical or chemical conditions are unavailable, such as an incomplete cold chain. Such degraded vaccines result in compromised herd vaccination. Therefore, thermostable FMD particles are needed for use in vaccines. This study generated thermostable FMDV mutants (M3 and M10) by serial passages at high temperature, subsequent amplification, and purification. Both mutants contained an alanine to threonine mutation at position 13 in VP1 (A1013T), although M3 contained 3 additional mutations. The selected mutants showed improved stability and immunogenicity in neutralizing antibody titers, compared with the wild-type (wt) virus. The sequencing analysis and cryo-electron microscopy showed that the mutation of alanine to threonine at the 13th amino acid (aa) in VP1 protein (A1013T) is critical for the capsid stability of FMDV. Virus-like particles (VLPA1013T) containing A1013T also showed significantly improved stability to heat treatment. This study demonstrated that Thr at the 13th amino acid of VP1 could stabilize the capsid of FMDV. Our findings will facilitate the development of a stable vaccine against FMDV serotype O.IMPORTANCEFoot-and-mouth disease (FMD) serotype O is one of the global epidemic serotypes, and cause significant economic loss. Vaccination plays a key role in the prevention and control of FMD. However, the success of vaccination mainly depends on the quality of the vaccine. Here, the thermostable FMDV mutants (M3 and M10) were selected through thermal-screening at high temperatures with improved stability and immunogenicity compared to the wild-type virus. The results of multi-sequence alignment and Cryo-EM analysis showed that the "Thr" substitution at the 13th amino acid in VP1 protein is critical for the capsid stability of FMDV. For thermolabile type O FMDV, this major discovery will aid the development of its thermostable vaccine.