Desolvation Costs of Salt Bridges across Protein Binding Interfaces: Similarities and Differences between Implicit and Explicit Solvent Models

The prevalence of salt bridges across protein binding interfaces is surprising given the significant costs of desolvating the two charged groups upon binding. These desolvation costs, which are difficult to examine using laboratory experiments, have been computed in previous studies using the Poisson-Boltzmann (PB) implicit solvent model. Here for the first time, we directly compare the PB implicit solvent model with several explicit water models in computing the desolvation penalties of salt bridges across protein-protein interfaces. We report both overall agreement as well as significant differences between the implicit and explicit solvent results. These differences highlight challenges to be faced in the application of implicit solvent methods.