Time-resolved x-ray diffraction reveals multiple conformations in the M-N transition of the bacteriorhodopsin photocycle.
We measured the M-N transition of wild-type bacteriorhodopsin (pH 9, 10 degrees 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.
Oka
T
T
Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan. kataoka@ms.aist-nara.ac.jp
Yagi
N
N
Fujisawa
T
T
Kamikubo
H
H
Tokunaga
F
F
Kataoka
M
M
D001436:Bacteriorhodopsins / Q000737:chemistry*; D017440:Photoperiod; D011487:Protein Conformation; D018717:Purple Membrane / Q000737:chemistry*; D013997:Time Factors; D014961:X-Ray Diffraction / Q000379:methods
D001436:Bacteriorhodopsins