3.6.6.  Solvent accessible surface area (SASA)
SASA is a measure of the receptor exposure to the solvent environment during the simulation. The hydrophobic residues that got exposed to the solvent environment upon binding with the ligand molecules contribute to the SASA values. The plot of the SASA for the proteins and their ligand-bound form is presented in Figure 8. The analysed average SASA values for the RBD Spro, RBD Spro-Piperine, Mpro and Mpro-Piperine are 106.976 ± 1.602 nm2, 107.235 ± 1.667 nm2, 150.698 ± 2.565 nm2 and 151.022 ± 2.207 nm2, respectively. There is no significant change observed for the averaged SASA values of the complex as compared to only protein suggesting their stability after binding to the drug molecule.
Figure 8.  Solvent accessible surface area (SASA) plots of (a) RBD Spro (black) and RBD Spro-Piperine (red); (b) Mpro (black) and Mpro-Piperine (blue).