The High Transmission of SARS-CoV-2 Omicron (B.1.1.529) Variant is Not Only Due to Its hACE2 binding: A Free Energy of Perturbation Study

The mutations in the spike protein of SARS-CoV-2 Omicron variant (B.1.1.529 lineage) gave rise to questions, but the data on the mechanism of action at the molecular level is limited. In this study, we present the Free energy of perturbation (FEP) data about the RBD-hACE2 binding of this new variant.

We identified two groups of mutations located close to the most contributing substitutions Q498R and Q493R, which altered significantly the RBD-hACE2 interactions. The Q498R, Y505H and G496S mutations, in addition to N501Y, highly increased the binding to hACE2. They enhanced the binding by 98, 14 and 13 folds, respectively, which transforms the S1-RBD to a picomolar binder. However, in contrast to the case in mice the Q493R/K mutations, in a combination with K417N and T478K, dramatically reduced the S1 RBD binding by over 100 folds. The N440K, G446S and T478K substitutions had lesser contribution. Thus, the total effect of these nine mutations located on the interaction surface of RBD-hACE2 turns out to be similar to that observed in the Alpha variant. In a special circumstances it could be further altered by the E484A and S477N mutations and even lower binding capacity is likely to be detected. Finally, we provide a structural basis of the observed changes in the interactions.

These data may explain only partially the observed in South Africa extremely high Omicron spread and is in support to the hypothesis for multiple mechanisms of actions involved in the transmission.