MMPBSA calculations were conducted by GMXPBSA 2.1 a suite based on Bash/Perl scripts for streamlining MMPBSA calculations on structural ensembles derived from GROMACS trajectories and to automatically calculate binding free energies for protein-protein or ligand-protein interactions . GMXPBSA 2.1 calculates diverse MMPBSA energy contributions from molecular mechanics (MM) and electrostatic contribution to solvation (PB) and non-polar contribution to solvation (SA). This tool combines the capability of MD simulations (GROMACS) and the Poisson-Boltzmann equation (APBS) for calculating solvation energy (Baker et., 2001). The g_mmpbsa tool in GROMACS was used after molecular dynamics simulations, the output files obtained were used to post-process binding free energies by the singletrajectory MMPBSA method. In the current study, we used 100 frames at equal distances from 20ns trajectory files.