1S54: Thr24ala Bacteriorhodopsin

Hydrogen bonds involving a carbon donor are very common in protein structures, and energy calculations suggest that Calpha-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 Calpha-H...O bonds for protein stability. Thr24 in bacteriorhodopsin, which makes an interhelical Calpha-H...O hydrogen bond to the Calpha 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 Calpha-H...O bonds are not a major contributor to protein stability.
PDB ID: 1S54Download
MMDB ID: 26604
PDB Deposition Date: 2004/1/19
Updated in MMDB: 2012/11
Experimental Method:
x-ray diffraction
Resolution: 2.2  Å
Source Organism:
Similar Structures:
Biological Unit for 1S54: monomeric; determined by author
Molecular Components in 1S54
Label Count Molecule
Protein (1 molecule)
Bacteriorhodopsin(Gene symbol: VNG_RS05715)
Molecule annotation
Chemical (1 molecule)
* Click molecule labels to explore molecular sequence information.

Citing MMDB