Fig. 1.

a The structure of the Spike (S) protein from Covid-19 (PDB code 6VSB) showing its three subunit conformation. In red is chain A in the “up” position, and chains B and C (blue and green respectively) are in the “down” position (see text for specific details). b Chain A in the up position and c chain B in the same orientation as A, in the down position. These are coloured according to the structural differences between them where red indicates the most significant of these differences, using 2StrucCompare [10]. Structure coloured grey only exists in chain B