Theoretical insights into the binding interaction of Nirmatrelvir with SARS-CoV-2 Mpro mutants (C145A and C145S): MD simulations and binding free-energy calculation to understand drug resistance.

M^pro, the main protease and a crucial enzyme in SARS-CoV-2 is the most fascinating molecular target for pharmacological treatment and is also liable for viral protein maturation. For antiviral therapy, no drugs have been approved clinically to date. Targeting the M^pro with a compound having inhibitory properties against it can hinder viral replication. The therapeutic potential of the antiviral compound Nirmatrelvir (NMV) against SARS-CoV-2 M^pro was investigated using a systematic approach of molecular docking, MD simulations, and binding free energy calculation based on the MM-GBSA method. NMV, a covalent inhibitor with a recently revealed chemical structure, is a promising oral antiviral clinical candidate with significant in vitro anti-SARS-CoV-2 action in third-phase clinical trials. To explore the therapeutic ability and possible drug resistance, the M^pro system was studied for WT and two of its primary mutants (C145A & C145S). The protein-ligand (M^pro/NMV) complexes were further examined through long MD simulations to check the possible drug resistance in the mutants. To understand the binding affinity, the MM-GBSA method was applied to the M^pro/NMV complexes. Moreover, PCA analysis confirms the detachment of the linker region from the major domains in C145S and C145A mutants allowing for conformational alterations in the active-site region. Based on the predicted biological activities and binding affinities of NMV to WT and mutant (C145A & C145S) M^pro, it can be stipulated that NMV may have conventional potency to act as an anti-viral agent against WT M^pro, while the catalytic-dyad mutations may show substantial mutation-induced drug resistance.Communicated by Ramaswamy H. Sarma.