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- SARS-CoV-2, the causative virus for COVID-19 has now super-mutated into the Omicron (Om) variant. On its spike (S) glycoprotein alone, more than 30 substitutions have been characterized with 15 within the receptor binding domain (RBD); It therefore calls to question the transmissibility and antibody escapability of Omicron. This study was setup to investigate the Omicron RBD’s interaction with ACE2 (host receptor) and a SARS-CoV-2 neutralizing monoclonal antibody (mAb). In-silico mutagenesis was used to generate the Om-RBD in complex with ACE2 or mAb from the wildtype. HDOCK server was used to redock and score the mAbs in Om-RBD bound state relative to the wildtype. Stability of interaction between all complexes were investigated using all-atom molecular dynamics (MD). Analyses of trajectories showed that Om-RBD has evolved into an efficient ACE2 binder, via pi-pi (Om-RBD-Y501/ACE2-Y41) and salt-bridge (Om-RBD-K493/ACE2-Y41) interactions. Conversely, in binding mAb, it has become less efficient (Center of mass distance of RBD from mAb complex, wildtype ≈ 30 Å, Omicron ≈ 41 Å). Disruption of Om-RBD/mAb complex resulted from loose interaction between Om-RBD and the light chain complementarity-determining region residues. Omicron is expected to be better transmissible and less efficiently interacting with neutralizing convalescent mAbs with consequences on transmissibility provided other mutations within the S protein similarly promote cell fusion and viral entry.
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- The development of clinically actionable pharmaceuticals against coronavirus disease (COVID-19); an infectious disease caused by the SARS-CoV-2 virus is very important for ending the pandemic. Coronavirus spike glyco protein (GP)-Receptor Binding Domain (RBD) and its interaction with host receptor angiotensin converting enzyme 2 (ACE2) is one of the most structurally understood but therapeutically untapped aspect of COVID-19 pathogenesis. Binding interface based on previous x-ray structure of RBD/ACE2 were virtually screened to identify fragments with high-binding score from 12,000 chemical building blocks. The hit compound was sub jected to fingerprint-based similarity search to identify compounds within the FDA-approved drug library con taining the same core scaffold. Identified compounds were then re-docked into of RBD/ACE2. The best ranked compound was validated for RBD/ACE2 inhibition using commercial kit. Molecular dynamics simulation was conducted to provide further insight into the mechanism of inhibition. From the original 12000 chemical building blocks, benzimidazole (BAZ) scaffold was identified. Fingerprint-based similarity search of the FDA- approved drug library for BAZ-containing compounds identified 12 drugs with the benzimidazole-like sub structure. When these compounds were re—docked into GP/ACE2 interface, the consensus docking identified bazedoxifene as the hit. In vitro RBD/ACE2 inhibition kinetics showed micromolar IC50 value (1.237 μM) in the presence of bazedoxifene. Molecular dynamics simulation of RBD/ACE2 in the presence BAZ resulted in loss of contact and specific hydrogen-bond interaction required for RBD/ACE2 stability. Taken together, these findings identified benzimidazole scaffold as a building block for developing novel RBD/ACE2 complex inhibitor and provided mechanistic basis for the use of bazedoxifene as a repurposable drug for the treatment of COVID-19 acting at RBD/ACE2 interface.
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- D614G spike glycoprotein (sgp) mutation in rapidly spreading severe acute respiratory syndrome coronavirus‐2 (SARS‐COV‐2) is associated with enhanced fitness and higher transmissibility in new cases of COVID‐19 but the underlying mechanism is unknown. Here, using atomistic simulation, a plausible mechanism has been delineated. In G614 sgp but not wild type, increased D(G)614‐T859 Cα‐distance within 65 ns is interpreted as S1/S2 protomer dissociation. Overall, ACE2‐binding, post‐fusion core, open‐state and sub‐optimal antibody‐binding conformations were preferentially sampled by the G614 mutant, but not wild type. Furthermore, in the wild type, only one of the three sgp chains has optimal communication route between residue 614 and the receptor‐binding domain (RBD); whereas, two of the three chains communicated directly in G614 mutant. These data provide evidence that D614G sgp mutant is more available for receptor binding, cellular invasion and reduced antibody interaction; thus, providing framework for enhanced fitness and higher transmissibility in D614G SARS‐COV‐2 mutant.
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