Structure-based virtual screening suggests inhibitors of 3-Chymotrypsin-Like Protease of SARS-CoV-2 from Vernonia amygdalina and Occinum gratissimum

Abstract

An in-house library of 173 phytocompound structures from Vernonia amygdalina and Occinum gratissimum was screened against the active region of 3-Chymotrypsin-Like Protease (3CLpro) of SARS-CoV-2 in silico. Based on docking scores and reference inhibitors, a hit- list of 21 phytocompounds, with binding energies ranging from − 7.2 to -8.0 kcal/mol, was initially generated. Further docking against the 3CLpro of related coronaviruses (SARS-CoV and MERS-CoV), docking to 5 different representative conformations generated from the cluster analysis of SARS-CoV-2 3CLpro molecular dynamics simulation (MDS) trajectories, and in silico drug-likeness analyses, revealed two drug-like terpenoid structures as promising non-covalent inhibitors of SARS-CoV-2 3CLPro viz: neoandrographolide and vernolide. These terpenoid structures are accommodated within the substrate-binding pocket, and interacted with the catalytic dyad, the oxyanion loop (residues 138–145), and the S1/S2 subsites of the enzyme active site. With the aid of an array of hydrogen bonds and hydrophobic interactions with residues 142–145, these phytocompounds may stabilize the conformation of the flexible oxyanion loop; and thereby interfere with the tetrahedral oxyanion intermediate formation during proteolytic cleavage. Molecular dynamics simulation and binding free energy calculation further revealed that the terpenoid-enzyme complexes exhibit strong interactions and structural stability, which could be adapted for experimental models.