ticle cryo-electron microscopy (cryo-EM). The results for HIV-1 Env were reproduced directly from Berndsen et al.51 while the previously published SARS 2P dataset52 was reprocessed for this study. Although cryo-EM datasets of fully glycosylated MERS S41 and chimpanzee simian immunodeficiency virus (SIVcpz)53 are also available, only the HIV and SARS data were of sufficient quality (Fig. 5). We recently showed51 that dynamics in surface exposed gly