Interaction Analyses on SARS-CoV-2 Spike Protein Based on Large-Scale Correlated Fragment Molecular Orbital Calculations

At the stage of SARS-CoV-2 infection to human cell, the spike protein consisting of three chains, A, B and C, with a total of 3.3 thousand residues plays the key role, and thus its nature have attracted considerable interests. Here, we report interaction analyses on the spike protein of both closed (PDB-ID: 6VXX) and open (6VYB) structures, based on large-scale fragment molecular orbital (FMO) calculations at the level of up to the fourth-order Møller-Plesset perturbation with singles, doubles and quadruples (MP4(SDQ)). Inter-chain interaction energies were evaluated for both structures, and mutual comparison indicated considerable losses of stabilization energies in the open structure, especially in the receptor binding domain (RBD) of chain-B. By two separate calculations for the RBD complexes with angiotensin converting enzyme 2 (ACE2) (6M0J) and B38 Fab antibody (7BZ5), it was found that this stabilization loss of RBD was partially compensated by the binding with ACE2 or antibody.