a Model of the glycosylated Spike protein trimer (based on Woo et al.9) depicting its insertion through a lipid bilayer and the relative position of a receptor binding domain in an ‘up’ position of the blue/cyan chain (other S chains coloured light and dark grey). b Close-up depicting the positioning of the solvent-accessible S1/S2 cleavage site (residues R685-S686) as well as the recessed and glycan-protected position of the D614 residue. c Cut-away view of the D614 interface with the adjacent S chain in grey. D614 can hydrogen bond with T859 and form a salt bridge with K854. A D614G mutation is expected to disrupt both these interactions.