Fig. 3.

Acidic groups with increased burial in the locked form are predicted to give a mild acidic pH-dependence. (a) Order/disorder is illustrated with stacked histograms (1/0) for the 6 sub-groups of spike trimers. Differences of d-SASA between sub-groups are more extensive than are those of order/disorder, illustrated with cumulative plots of the closed form subtracted from the 5 other sub-groups (b). The magnitude of locked to closed difference is larger than that of open to closed. All sub-groups other than D614Gset consist of either all RBD down or all RBD up S trimers. The small difference between D614Gset and closed sub-groups reflects an average over substantial variation in D614Gset (Fig. 2a). (c) A heat map of predicted conformational stability change from pH 7.5 to 5, for each sub-group (labelled), with stabilising (red) or destabilising (blue) indicated. Amino acids that differ the most between sub-groups are indicated at the bottom of the plot, together with additional grey vertical bars aligned with the heat map. Panels (a) and (b) are in register. Panel (c), with only ionisable groups, is approximately in register with the full sequence plots. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)