RNA dependent RNA polymerase (RdRp) as a drug target for SARS-CoV2

RNA-dependent RNA polymerase (RdRp), also called nsp12, is considered a promising but challenging drug target for inhibiting replication and hence, the growth of various RNA-viruses. In this report, a computational study is performed to offer insights on the binding of Remdesivir and Galidesivir with SARS-CoV2 RdRp with natural substrate, ATP, as the control. It was observed that Remdesivir and Galidesivir exhibited similar binding energies for their best docked poses, -6.6 kcal/mole and -6.2 kcal/mole, respectively. ATP also displayed comparative and strong binding free energy of -6.3 kcal/mole in the catalytic site of RdRp. However, their binding locations within the active site are distinct. Further, the interaction of catalytic site residues (Asp760, Asp761, and Asp618) with Remdesivir and Galidesivir is comprehensively examined. Conformational changes of RdRp and bound molecules are demonstrated using 100 ns explicit solvent simulation of the protein-ligand complex. Simulation suggests that Galidesivir binds at the non-catalytic location and its binding strength is relatively weaker than ATP and Remdesivir. Remdesivir also binds at the catalytic site and showed high potency to inhibit the function of RdRp. Binding of co-factor units nsp7 and nsp8 with RdRp (nsp12) complexed with Remdesivir and Galidesivir was also examined. MMPBSA binding energy for all three complexes has been computed across the 100 ns simulation trajectory. Overall, this study suggests, Remdesivir has anti-RdRp activity via binding at a catalytic site. In contrast, Galidesivir may not have direct anti-RdRp activity but it can induce a conformational change in the RNA polymerase.