| Abstract
| - Alanine scanning of protein−protein interfaces has shown that there are some residues in the protein−proteininterfaces, responsible for most of the binding free energy, which are called hot spots. Hot spots tend to existin densely packed central clusters, and a hypothesis has been proposed that considers that inaccessibility tothe solvent must be a necessary condition to define a residue as a binding hot spot. This O-ring hypothesisis mainly based on the analysis of the accessible surface area (ASA) of 23 static, crystallographic structuresof protein complexes. It is known, however, that protein flexibility allows for temporary exposures of buriedinterfacial groups, and even though the ASA provides a general trend of the propensity for hydration, protein/solvent-specific interactions or hydrogen bonding cannot be considered here. Therefore, a microscopic level,atomistic picture of hot spot solvation is needed to support the O-ring hypothesis. In this study, we began byapplying a computational alanine-scanning mutagenesis technique, which reproduces the experimental resultsand allows for decomposing the binding free energy difference in its different energetic factors. Subsequently,we calculated the radial distribution function and residence times of the water molecules near the hot/warmspots to study the importance of the water environment around those energetically important amino acidresidues. This study shows that within a flexible, dynamic protein framework, the warm/hot spot residuesare, indeed, kept sheltered from the bulk solvent during the whole simulation, which allows a better interactingmicroenvironment.
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