Homology modelling, molecular docking, and molecular dynamics simulations reveal the inhibition of <italic>Leishmania donovani</italic> dihydrofolate reductase-thymidylate synthase enzyme by Withaferin-A.

Objective: Present in silico study was carried out to explore the mode of inhibition of <italic>Leishmania donovani</italic> dihydrofolate reductase-thymidylate synthase (<italic>Ld</italic> DHFR-TS) enzyme by Withaferin-A, a withanolide isolated from <italic>Withania somnifera</italic>. Withaferin-A (WA) is known for its profound multifaceted properties, but its antileishmanial activity is not well understood. The parasite's DHFR-TS enzyme is diverse from its mammalian host and could be a potential drug target in parasites. Results: A 3D model of <italic>Ld</italic> DHFR-TS enzyme was built and verified using Ramachandran plot and SAVES tools. The protein was docked with WA-the ligand, methotrexate (MTX)-competitive inhibitor of DHFR, and dihydrofolic acid (DHFA)-substrate for DHFR-TS. Molecular docking studies reveal that WA competes for active sites of both <italic>Hu</italic> DHFR and TS enzymes whereas it binds to a site other than active site in <italic>Ld</italic> DHFR-TS. Moreover, Lys 173 residue of DHFR-TS forms a H-bond with WA and has higher binding affinity to <italic>Ld</italic> DHFR-TS than <italic>Hu</italic> DHFR and <italic>Hu</italic> TS. The MD simulations confirmed the H-bonding interactions were stable. The binding energies of WA with <italic>Ld</italic> DHFR-TS were calculated using MM-PBSA. Homology modelling, molecular docking and MD simulations of <italic>Ld</italic> DHFR-TS revealed that WA could be a potential anti-leishmanial drug. [ABSTRACT FROM AUTHOR]