Here, the ''Desmond 2.4 Package'' [39] was adopted to study the internal motions of the receptor-ligand system. According to the software, the OPLS 2005 force fields [64, 65] was used to build aqueous biological systems, and the TIP3P model [66] was used to simulate water molecules. The orthorhombic periodic boundary conditions were set up to specify the shape and size of the repeating unit. In order to get an electrically neutral system, the minimum number of sodium and chloride ions needed to balance the system charge was placed randomly in the solvated system, and 0.15 mol/L sodium and chloride were then added to mimic the osmotic effect of water. Molecular dynamics simulations were carried out with the periodic boundary conditions in the NPT ensemble. The temperature and pressure were kept at 300 K and 1 atmospheric pressure using Nose-Hoover temperature coupling and isotropic scaling [67] . After all restrains were removed via the 3ns (nanosecond or 10 29 of a second) system minimization and relaxation, the operation was followed by running the 10 ns NPT production simulation and saving the configurations thus obtained in 2ps (picosecond or 10 212 of a second) intervals. All the molecular dynamics simulations were performed with a time step of 2fs (femtosecond or 10 215 of a second).