Grid-Based Surface Generalized Born Model for Calculation of Electrostatic Binding Free Energies

Fast and accurate calculation of solvation free energies is central to many applications, such as rational drug design. In this study, we present a grid-based molecular surface implementation of "R6" flavor of the generalized Born (GB) implicit solvent model, named GBNSR6. The speed, accuracy relative to numerical Poisson-Boltzmann treatment, and sensitivity to grid surface parameters are tested on a set of 15 small protein-ligand complexes and a set of biomolecules in the range of 268 to 25099 atoms. Our results demonstrate that the proposed model provides a relatively successful compromise between the speed and accuracy of computing polar components of the solvation free energies (ΔG) and binding free energies (ΔΔG). The model tolerates a relatively coarse grid size h = 0.5 Å, where the grid artifact error in computing ΔΔG remains in the range of kT ∼ 0.6 kcal/mol. The estimated ΔΔGs are well correlated (r = 0.97) with the numerical Poisson-Boltzmann reference, while showing virtually no systematic bias and RMSE = 1.43 kcal/mol. The grid-based GBNSR6 model is available in Amber (AmberTools) package of molecular simulation programs.