Virtual screening and molecular dynamics simulation studies to predict the binding of Sisymbrium irio L. derived phytochemicals against Staphylococcus aureus dihydrofolate reductase (DHFR)

The discovery of antibiotics initiated the era of drug innovation and implementation for human and animal health. Very soon, antibiotic resistance started evolving due to over-prescription and heavy usage of drugs leading to deleterious side effects. However, using plant extracts or medicinal plants has emerged as a new approach to dealing with the current problem. One such medicinal plant Sisymbrium irio L. is widely used in Unani therapy as an antimicrobial, analgesic, antipyretic, antioxidant, anti-inflammatory, hepatoprotective, bronchoprotective etc. The phytochemicals extracted from the aerial part of the plant have been used as a natural compound library and screened against a well-known anti-bacterial drug target Dihydrofolate reductase (DHFR)  enzyme of Staphylococcus aureus. The top two phytochemicals with lower docking score along with the positive control were subjected to molecular dynamics (MD) simulation studies to examine the stabilities of the complexes over 100 ns, followed by binding free energy estimation. The Root Mean Square Deviation (RMSD), Root Mean Square Fluctuation (RMSF) and Radius of Gyration (Rg) yielded established results throughout the MD run. Moreover, the derived phytochemicals exhibited lower binding free energy values than the positive control that can be tested for its in vitro efficacy, followed by further optimization to attain a potent therapeutic against S. aureus. Taken together, the present study suggests two promising phytochemicals derived from the aerial part of the plant S. irio with stable MD simulation results, strong binding affinity and no side effects.