Millisecond-scale molecular dynamics simulation of spike RBD structure reveals evolutionary adaption of SARS-CoV-2 to stably bind ACE2

The Receptor Binding Domain (RBD) of the SARS-CoV-2 surface spike (S) protein interacts with host angiotensin converting enzyme 2 (ACE2) to gain entry to host cells and initiate infection ^1–3 . Detailed, accurate understanding of key interactions between S RBD and ACE2 provides critical information that may be leveraged in the development of strategies for the prevention and treatment of COVID-19. Utilizing the published sequences and cryo-EM structures of both the viral S RBD and ACE2 ^4,5 , we performed in silico molecular dynamics (MD) simulations of free S RBD and of its interaction with ACE2 over the exceptionally long durations of 2.9 and 2 milliseconds, respectively, to elucidate the nature and relative affinity of S RBD surface residues for the ACE2 binding region. Our findings reveal that free S RBD has assumed an optimized ACE2 binding-ready conformation, incurring little entropic penalty for binding, an evolutionary adaptation that contributes to its high affinity for the receptor ⁶ . We further identified high probability molecular binding interactions that inform both vaccine design and therapeutic development, which may include recombinant ACE2-based spike decoys ⁷ and/or allosteric S RBD-ACE2 binding inhibitors ^8,9 to prevent or arrest infection and thus disease.