Structural Changes in Bacteriorhodopsin following Retinal Photoisomerization from the 13-Cis Form
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- 作者：Noriko Mizuide ; Mikihiro Shibata ; Noga Friedman ; Mordechai Sheves ; Marina Belenky ; Judith Herzfeld ; Hideki Kandori
- 刊名：Biochemistry
- 出版年：2006
- 出版时间：September 5, 2006
- 年：2006
- 卷：45
- 期：35
- 页码：10674 - 10681
- 全文大小：140K
- 年卷期：v.45,no.35(September 5, 2006)
- ISSN：1520-4995
文摘
Bacteriorhodopsin (BR), a light-driven proton pump in Halobacterium salinarum, accommodatestwo resting forms of the retinylidene chromophore, the all-trans form (AT-BR) and the 13-cis,15-synform (13C-BR). Both isomers are present in thermal equilibrium in the dark, but only the all-trans formhas proton-pump activity. In this study, we applied low-temperature Fourier-transform infrared (FTIR)spectroscopy to 13C-BR at 77 K and compared the local structure around the chromophore before andafter photoisomerization with that in AT-BR. Strong hydrogen-out-of-plane (HOOP) vibrations wereobserved at 964 and 958 cm-1 for the K state of 13C-BR (13C-BRK) versus a vibration at 957 cm-1 forthe K state of AT-BR (AT-BRK). In AT-BRK, but not in 13C-BRK, the HOOP modes exhibit isotopeshifts upon deuteration of the retinylidene at C15 and at the Schiff base nitrogen. Whereas the HOOPmodes of AT-BRK were significantly affected by the mutation of Thr89, this was not the case for theHOOP modes of 13C-BRK. These observations imply that, while the chromophore distortion is localizednear the Schiff base in AT-BRK, it is located elsewhere in 13C-BRK. By use of [
-15N]lysine-labeled BR,we identified the N-D stretching vibrations of the 13C-BR Schiff base (in D2O) at 2173 and 2056 cm-1,close in frequency to those of AT-BR. These frequencies indicate strong hydrogen bonding of the Schiffbase in 13C-BR, presumably with a water molecule as in AT-BR. In contrast, the N-D stretching vibrationappears at 2332 and 2276 cm-1 in 13C-BRK versus values of 2495 and 2468 cm-1 for AT-BRK, suggestingthat the rupture of the Schiff base hydrogen bond that occurs in AT-BRK does not occur in 13C-BRK.Rotational motion of the Schiff base upon retinal isomerization is probably smaller in magnitude for13C-BR than for AT-BR. These differences in the primary step are possibly related to the absence oflight-driven proton pumping by 13C-BR.
-15N]lysine-labeled BR,we identified the N-D stretching vibrations of the 13C-BR Schiff base (in D2O) at 2173 and 2056 cm-1,close in frequency to those of AT-BR. These frequencies indicate strong hydrogen bonding of the Schiffbase in 13C-BR, presumably with a water molecule as in AT-BR. In contrast, the N-D stretching vibrationappears at 2332 and 2276 cm-1 in 13C-BRK versus values of 2495 and 2468 cm-1 for AT-BRK, suggestingthat the rupture of the Schiff base hydrogen bond that occurs in AT-BRK does not occur in 13C-BRK.Rotational motion of the Schiff base upon retinal isomerization is probably smaller in magnitude for13C-BR than for AT-BR. These differences in the primary step are possibly related to the absence oflight-driven proton pumping by 13C-BR.