SAR and QSAR of COVID-19 Main Protease-Inhibitor Interactions of Recently X-ray Crystalized Complexes.

COVID-19 is still widespread worldwide and up to now there is no established antiviral able to control the disease. Main protease is responsible for the viral replication and transcription; thus, its inhibition is a promising route to control virus proliferation. The present study aims to examine detail interactions between main protease and recently reported ninety-seven inhibitors with available X-ray crystallography to define factors enhance inhibition activity; thirty-two of most potent inhibitors were examined to identify sites and types of interaction. The study showed formation of covalent bond, H-bond and hydrophobic interaction with key residues in the active side. Covalent bond is observed in seventeen complexes, all of them by attack of the 145Cys thiol group on Michael acceptor, aldehyde or its hydrate, α-ketoamide, double bond or acetamide methyl group; the latter type requires H-bonding between acetamide carbonyl oxygen and at least one of 143Gly, 144Ser or 145Cys. Potent inhibitors, disulfiram and ebselen docked in the same binding site. Accordingly, factors identify inhibition include forming covalent bond and existing terminal hydrophobic groups and amidic or peptidomimetic structure. Binding affinity was found correlated with topological diameter up to 24 bond, molecular size, branching, polar surface area up to 199 Å2 and hydrophilicity. Supplementary Information: The online version contains supplementary material available at 10.1007/s40011-021-01338-8.

Evaluation of SARS-CoV-2 main protease and inhibitor interactions using dihedral angle distributions and radial distribution function.

In order to evaluate the interactions between a potential drug candidate like inhibitor N3 and the residues in substrate binding site of SARS-CoV-2 main protease ( M pro ), we used molecular docking and dynamics simulations. The structural features describing the degrees of folding states of M pro formed by beta-barrels and alpha-helices were analyzed by means of root mean square deviation, root mean square fluctuation, radius of gyration, residue velocity, H-bonding, dihedral angle distributions and radial distribution function. All of the residues forming ligand binding domain (LBD) of M pro lie within the allowed region of the dihedral angle distributions as observed from the equilibrating best pose of M pro -N3 system. Sharp peaks of radial distribution function (RDF) for H-bonding atom pairs (about 2 Å radial distance apart) describe the strong interactions between inhibitor and SARS-CoV-2 M pro . During MD simulations, HSE163 has the lowest residue speed offering a sharp RDF peak whereas GLN192 has the highest residue speed resulting a flat RDF peak for the H-bonding atom pairs of M pro -N3 system. Along with negative values of coulombic and Lenard-Jones energies, MM/PBSA free energy of binding contributed by the non-covalent interactions between M pro and N3 has been obtained to be -19.45 ± 3.6 kcal/mol. These physical parameters demonstrate the binding nature of an inhibitor in M pro -LBD. This study will be helpful in evaluating the drug candidates which are expected to inhibit the SARS-CoV-2 structural proteins.