Altered interaction between RBD and ACE2 receptor contributes towards the increased transmissibility of SARS CoV-2 delta, kappa, beta, and gamma strains with RBD double mutations.

The COVID-19 pandemics by SARS-CoV-2 causes catastrophic damage for global human health. The initial step of SARS-CoV-2 infection is the binding of the receptor-binding domain (RBD) in its spike protein to ACE2 receptor in host cell membrane. The evolving of SARS-CoV-2 constantly generates new mutations across its genome including RBD. Besides the well-known single mutation in RBD, the recent new mutation strains with RBD "double mutation" is causing new outbreaks globally, as represented by the delta strain containing RBD L452R/T478K. Although it is considered that the increased transmissibility of the double mutated strains could be attributed to the alteration of mutated RBD to ACE2 receptor, the molecular details remains to be unclear. Using the methods of molecular dynamics simulation, superimposed structural comparison, free binding energy estimation and antibody escaping, we investigated the relationship between ACE2 receptor and the RBD double mutant L452R/T478K (delta), L452R/E484Q (kappa) and E484K/N501Y (beta, gamma). The results demonstrated that each of the three RBD double mutants altered RBD structure, led to enhanced binding affinity of mutated RBD to ACE2 receptor, leading to increased transmissibility of SARS-CoV-2 to the host cells.