Revisiting "Reverse Hydrophobic Effect": Applicable Only to Coil Mutations at the Surface

In a seminal paper, Pakula and Sauer (Nature, 1990, 344, 363-364) demonstrated that the increase in sidechain hydrophobicity has a reverse relationship with protein stability. We have addressed this problem with several examples of mutants that span at different locations in protein structure based on secondary structure and solvent accessibility We confirmed that the stability change upon single coil mutation at exposed region is reversely correlated with hydrophobicity with a single exception. In addition, we found the existence of such relationship in partially buried coil mutants. The stability of exposed helical mutants is governed by conformational properties. In buried and partially buried helical and strand mutants properties reflecting hydrophobicity have direct relationship with stability, whereas all opposite relationship was obtained with entropy and flexibility The structural analysis of partially buried/exposed mutants showed that the surrounding residues are important for the stability change upon mutation. These results provide insights to understand the general behavior for the stability of proteins upon amino acid substitutions. (C) 2009 Wiley Periodicals, Inc. Biopolymers 91: 591-599, 2009.