Time-resolved x-ray diffraction reveals multiple conformations in the M-N transition of the bacteriorhodopsin photocycle
Abstract
We measured the M-N transition of wild-type bacteriorhodopsin (pH 9, 10°C) by time-resolved x-ray diffraction study at SPring8 BL45XU-A. We confirmed the accumulation of M and N intermediates by absorbance measurements, and we found that the time resolution of x-ray diffraction experiments (244 ms) was sufficient to resolve the M-N transition. From the x-ray diffraction data, three components were decomposed by singular value decomposition analysis. The existence of three components in the M→N→BR reaction revealed that BR changes its structure during the M-N transition. Moreover, the difference Fourier maps of reconstituted fast and slow decay components clearly showed that the electron density distributions of the F helix changes in the M-N transition. The observed structural change at the F helix will increase access of the Schiff base and D96 to the cytoplasmic surface and facilitate the proton transfer steps that begin with the decay of the M state.
- Publication:
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Proceedings of the National Academy of Science
- Pub Date:
- December 2000
- DOI:
- 10.1073/pnas.260504897
- Bibcode:
- 2000PNAS...9714278O
- Keywords:
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- Biophysics