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Pressure‐induced Isomerization of Retinal on Bacteriorhodopsin as Disclosed by Fast Magic Angle Spinning NMR †
Author(s) -
Kawamura Izuru,
Degawa Yoshiaki,
Yamaguchi Satoru,
Nishimura Katsuyuki,
Tuzi Satoru,
Saitô Hazime,
Naito Akira
Publication year - 2007
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/2006-06-20-rc-941
Subject(s) - bacteriorhodopsin , retinal , chemistry , isomerization , magic angle spinning , schiff base , retinaldehyde , membrane , crystallography , photochemistry , nuclear magnetic resonance spectroscopy , stereochemistry , rhodopsin , organic chemistry , biochemistry , catalysis
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 15 N cross polarization‐magic angle spinning (CP‐MAS) NMR spectra of [ζ‐ 15 N]Lys‐labeled bR. In the 15 N‐NMR spectra, both all‐ trans and 13‐ cis retinal configurations have been observed in the Lys N ζ 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 15 N‐NMR signals of [ζ‐ 15 N]Lys in Schiff base of retinal were broadened. On the other hand, other [ζ‐ 15 N]Lys did not show broadening. Subsequently, the increased signal intensity of [ζ‐ 15 N]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.