1s54
|
Thr24Ala Bacteriorhodopsin
OverviewOverview
Hydrogen bonds involving a carbon donor are very common in protein structures, and energy calculations suggest that C-H···O hydrogen bonds could be about one-half the strength of traditional hydrogen bonds. It has therefore been proposed that these nontraditional hydrogen bonds could be a significant factor in stabilizing proteins, particularly membrane proteins as there is a low dielectric and no competition from water in the bilayer core. Nevertheless, this proposition has never been tested experimentally. Here, we report an experimental test of the significance of C-H···O bonds for protein stability. Thr24 in bacteriorhodopsin, which makes an interhelical C-H···O hydrogen bond to the C of Ala51, was changed to Ala, Val, and Ser, and the thermodynamic stability of the mutants was measured. None of the mutants had significantly reduced stability. In fact, T24A was more stable than the wild-type protein by 0.6 kcal/mol. Crystal structures were determined for each of the mutants, and, while some structural changes were seen for T24S and T24V, T24A showed essentially no apparent structural alteration that could account for the increased stability. Thus, Thr24 appears to destabilize the protein rather than stabilize. Our results suggest that C-H···O bonds are not a major contributor to protein stability.
About this StructureAbout this Structure
1S54 is a Single protein structure of sequence from Halobacterium salinarum with RET as ligand. Full crystallographic information is available from OCA.
ReferenceReference
A C alpha-H...O hydrogen bond in a membrane protein is not stabilizing., Yohannan S, Faham S, Yang D, Grosfeld D, Chamberlain AK, Bowie JU, J Am Chem Soc. 2004 Mar 3;126(8):2284-5. PMID:14982414
Page seeded by OCA on Wed Nov 21 02:06:40 2007