Real-time Conformational Dynamics of SARS-CoV-2 Spikes on Virus Particles

Lu, Maolin; Uchil, Pradeep D.; Li, Wenwei; Zheng, Desheng; Terry, Daniel S.; Gorman, Jason; Shi, Wei; Zhang, Baoshan; Zhou, Tongqing; Ding, Shilei; Gasser, Romain; Prévost, Jérémie; Beaudoin-Bussières, Guillaume; Anand, Sai Priya; Laumaea, Annemarie; Grover, Jonathan R.; Liu, Lihong; Ho, David D.; Mascola, John R.; Finzi, Andrés; Kwong, Peter D.; Blanchard, Scott C.; Mothes, Walther

SARS-CoV-2 spike (S) mediates viral entry into cells and is critical for vaccine development against COVID-19. Structural studies have revealed distinct conformations of S, but real-time information that connects these structures, is lacking. Here we apply single-molecule Fluorescence (Förster) Resonance Energy Transfer (smFRET) imaging to observe conformational dynamics of S on virus particles. Virus-associated S dynamically samples at least four distinct conformational states. In response to human receptor Angiotensin-Converting Enzyme 2 (hACE2), S opens sequentially into the hACE2-bound S conformation through at least one on-path intermediate. Conformational preferences observed upon expsoure to convalescent plasma or antibodies suggest mechanisms of neutralization involving either competition with hACE2 for binding to the receptor-binding domain (RBD) or allosteric interference with conformational changes required for entry. Our findings inform on mechanisms of S recognition and conformations for immunogen design.