ORGN 943 |
| Recent literature (Nature, 2004, 430, 101) shows that backbone hydrogen bonds make context-dependent contribution to protein stability. We hypothesized that hydrophobic packing and H-bonding may stabilize the protein structure synergistically; that is, upon protein folding, hydrophobic packing buries H-bonds and strengths them, which further enhances the hydrophobic effect which is established to be an important contributor to protein stability. The hypothesis was tested in both alpha-helical (B domain of protein A) and beta-sheet (PIN WW domain) folds using a double mutant cycle analysis approach. A side chain proximal to the H-bond of interest was changed to alter the solvent accessibility of the H-bond, such that there is a variant whose large side chain protects the H-bond from solvent interaction and another whose small side chain allows solvent access. Amide-to-ester mutations were used to assess H-bond strength in the case of the large and the small side chain variants. Double mutant cycle analysis revealed that H-bonds are significantly stronger when excluded from solvent contact by bulky hydrophobic side chains. The increased H-bond strength accounts for at least 30% of the overall protein stability gain when a small hydrophobic side chain is replaced by a larger one. Our results indicate that the hydrophobic effect and H-bonding are thermodynamically linked in protein structures and that only a few residues make substantial contributions to protein stability. |
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Proteins, Peptides, Amino Acids, and Enzyme Inhibitors
1:00 PM-5:00 PM, Thursday, 14 September 2006 Moscone Center -- Room 131, Oral
Division of Organic Chemistry |