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. 2023 Mar 14;14:1421. doi: 10.1038/s41467-023-36745-0

Fig. 6. Spike priming for fusion.

Fig. 6

a Regions manifesting increased HDX in spikes bound to ACE2 are superimposed and coloured in red on a single protomer of the structure of D614 spike with one RBD bound (PDB: 7a9514); regions with increased HDX only in spike of alpha and omicron variants bound to ACE2 are coloured in magenta. b The magnitude of the destabilization of the core helices is represented by differential colouring (red scale) for the various spike trimers. The HR1 region (962–982) manifesting HDX bimodality is framed in grey. c The bimodal isotopic envelopes of a model peptide of the HR1 region 962–982 are shown at 15 s and 1 min time points for spike (S) variants in the ACE2-bound state and for omicron spike alone, to exemplify the priming for fusion upon receptor engagement. Bimodal envelopes manifest in omicron spike also in the absence of ACE2, indicating it as pre-primed for fusion.