This paper is part of the Proceedings of the 12th International Conference on Retinal Proteins held at Awaji Island, Hyogo, Japan on 4–8 June 2006.
Pressure-induced Isomerization of Retinal on Bacteriorhodopsin as Disclosed by Fast Magic Angle Spinning NMR†
Article first published online: 27 FEB 2007
Photochemistry and Photobiology
Volume 83, Issue 2, pages 346–350, March/April 2007
How to Cite
Kawamura, I., Degawa, Y., Yamaguchi, S., Nishimura, K., Tuzi, S., Saitô, H. and Naito, A. (2007), Pressure-induced Isomerization of Retinal on Bacteriorhodopsin as Disclosed by Fast Magic Angle Spinning NMR. Photochemistry and Photobiology, 83: 346–350. doi: 10.1562/2006-06-20-RC-941
- Issue published online: 27 FEB 2007
- Article first published online: 27 FEB 2007
- Received 20 June 2006; accepted 18 October 2006; published online 24 October 2006
Bacteriorhodopsin (bR) is a retinal protein in purple membrane of Halobacterium salinarum, which functions as a light-driven proton pump. We have detected pressure-induced isomerization of retinal in bR by analyzing 15N cross polarization-magic angle spinning (CP-MAS) NMR spectra of [ζ-15N]Lys-labeled bR. In the 15N-NMR spectra, both all-trans and 13-cis retinal configurations have been observed in the Lys Nζ in protonated Schiff base at 148.0 and 155.0 ppm, respectively, at the MAS frequency of 4 kHz in the dark. When the MAS frequency was increased up to 12 kHz corresponding to the sample pressure of 63 bar, the 15N-NMR signals of [ζ-15N]Lys in Schiff base of retinal were broadened. On the other hand, other [ζ-15N]Lys did not show broadening. Subsequently, the increased signal intensity of [ζ-15N]Lys in Schiff base of 13-cis retinal at 155.0 ppm was observed when the MAS frequency was decreased from 12 to 4 kHz. These results showed that the equilibrium constant of [all-trans-bR]/[13-cis-bR] in retinal decreased by the pressure of 63 bar. It was also revealed that the structural changes induced by the pressure occurred in the vicinity of retinal. Therefore, microscopically, hydrogen-bond network around retinal would be disrupted or distorted by a constantly applied pressure. It is, therefore, clearly demonstrated that increased pressure induced by fast MAS frequencies generated isomerization of retinal from all-trans to 13-cis state in the membrane protein bR.