Transmission of allosteric response within the homotrimer of SARS-CoV-2 spike upon recognition of ACE2 receptor by the receptor-binding domain

The pathogenesis of novel SARS-CoV-2 virus initiates through recognition of ACE2 receptor (Angiotensin-converting enzyme 2) of the host cells by the receptor-binding domain (RBD) located at spikes of the virus. Following receptor-recognition, proteolytic cleavage between S1 and S2 subunits of the spike protein occurs with subsequent release of fusion peptide. Here, we report our study on allosteric communication within RBD that propagates the signal from ACE2-binding site towards allosteric site for the post-binding activation of proteolytic cleavage. Using MD simulations, we have demonstrated allosteric crosstalk within RBD in apo- and receptor-bound states where dynamic correlated motions and electrostatic energy perturbations contribute. While allostery, based on correlated motions, dominates inherent distal communication in apo-RBD, electrostatic energy perturbations determine favorable crosstalk within RBD upon binding to ACE2. Notably, allosteric path is constituted with evolutionarily conserved residues pointing towards their biological relevance. As revealed from recent structures, in the trimeric arrangement of spike, RBD of one copy interacts with S2 domain of another copy. Interestingly, the allosteric site identified is in direct contact (H-bonded) with a region in RBD that corresponds to the interacting region of RBD of one copy with S2 of another copy in trimeric constitution. Apparently, inter-monomer allosteric communication orchestrates concerted action of the trimer. Based on our results, we propose the allosteric loop of RBD as a potential drug target.