Structures and distributions of SARS-CoV-2 spike proteins on intact virions

Ke, Zunlong; Oton, Joaquin; Qu, Kun; Cortese, Mirko; Zila, Vojtech; McKeane, Lesley; Nakane, Takanori; Zivanov, Jasenko; Neufeldt, Christopher J; Cerikan, Berati; Lu, John M; Peukes, Julia; Xiong, Xiaoli; Kräusslich, Hans-Georg; Scheres, Sjors H W; Bartenschlager, Ralf; Briggs, John A G

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virions are surrounded by a lipid bilayer from which spike (S) protein trimers protrude1. Heavily glycosylated S trimers bind to the angiotensin-converting enzyme 2 receptor and mediate entry of virions into target cells2-6. S exhibits extensive conformational flexibility: it modulates exposure of its receptor-binding site and subsequently undergoes complete structural rearrangement to drive fusion of viral and cellular membranes2,7,8. The structures and conformations of soluble, overexpressed, purified S proteins have been studied in detail using cryo-electron microscopy2,7,9-12, but the structure and distribution of S on the virion surface remain unknown. Here we applied cryo-electron microscopy and tomography to image intact SARS-CoV-2 virions and determine the high-resolution structure, conformational flexibility and distribution of S trimers in situ on the virion surface. These results reveal the conformations of S on the virion, and provide a basis from which to understand interactions between S and neutralizing antibodies during infection or vaccination.