Structural insight into the assembly and D antigenicity of polio type 1 stabilized virus-like particles

The inherent instability of poliovirus capsids presents a formidable challenge for developing next-generation vaccines suitable for a post-eradication world. Here, we address this by engineering a thermally stabilized virus-like particle (sVLP) derived from the poliovirus serotype 1 (PV1) Mahoney-SC7 mutant and elucidating its atomic-level structure. Produced at remarkably high yields in Pichia pastoris yeast, our engineered sVLP maintains a native, D-antigenic conformation and elicits a potent neutralizing antibody response in mice, in sharp contrast to unstable wild-type VLP (wtVLP) which adopts an expanded, non-immunogenic form. Our 2.43 Å resolution cryo-EM structure reveals precisely how seven stabilizing mutations cooperatively enhance inter-protomer contacts and rigidify surface loops to lock the particle in its immunogenic state. We further define a critical D-antigenic epitope by determining the 2.60 Å structure of the sVLP in complex with a novel D-antigen-specific, neutralizing monoclonal antibody, 3G10, elucidating the structural mechanisms of D-antigen recognition and virus neutralization by 3G10. These findings provide a definitive structural blueprint for engineering stable, immunogenic vaccines for PVs and other enteroviruses and also deliver a vital reagent for ensuring vaccine quality control.