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X-ray diffraction of bacteriorhodopsin photocycle intermediates
1Department of Physiology and Biophysics, University of California, Irvine, CA 92697, USA. jlanyi@orion.oac.uci.edu
Molecular Membrane Biology
|June 19, 2004
Summary
Structural insights into bacteriorhodopsin reveal how light-driven proton pumping involves atomic-level changes in retinal, protein, and water. This mechanism of local-global conformational coupling may unify transporters and receptors.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Bacteriorhodopsin is a light-driven proton pump crucial for energy transduction.
- Understanding its mechanism requires atomic-level structural data of its photochemical cycle intermediates.
Purpose of the Study:
- To elucidate the atomic mechanisms of proton translocation in bacteriorhodopsin.
- To provide structural models for all intermediates of the bacteriorhodopsin photochemical cycle.
Main Methods:
- X-ray diffraction on trapped photostationary states in bacteriorhodopsin crystals.
- Analysis of selected mutant structures for uncharacterized intermediates.
Main Results:
- Structural models for all photochemical cycle intermediates were obtained.
- Atomic details show retinal isomerization triggers Schiff base deprotonation and protein conformational changes.
- Two distinct conformational cascades, one leading to proton release and the other to proton uptake, were identified.
Conclusions:
- Local-global conformational coupling, initiated by retinal photoisomerization, drives proton pumping in bacteriorhodopsin.
- This mechanism of propagating conformational changes may be a fundamental principle shared by transporters and receptors.