FTIR Spectroscopy of the all-trans form of Anabaena sensory rhodopsin at 77 K:: Hydrogen bond of a water between the Schiff base and Asp75
FTIR Spectroscopy of the all-trans form of Anabaena sensory rhodopsin at 77 K:: Hydrogen bond of a water between the Schiff base and Asp75
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DOI：
10.1021/bi050841o
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发表时间：
2005-09-20
期刊：
影响因子：
2.9
通讯作者：
Kandori, H
中科院分区：
文献类型：
--
作者：
Furutani, Y;Kawanabe, A;Kandori, H
鱼腥藻感觉视紫红质（ASR）是真细菌中发现的古细菌型视紫红质，并且被认为作为与14 kDa可溶性蛋白相互作用的光传感器起作用。视网膜结合口袋中的大多数残基在ASR中是相似的，除了脯氨酸206，其中其他古菌型视紫红质中的相应氨基酸是高度保守的天冬氨酸，其构成带正电荷的质子化席夫碱的互补复合物。最近测定的ASR的X射线晶体学结构揭示了席夫碱和Asp 75之间的水分子[Vogeley，L.，西涅舍科夫岛一、Trivedi，V.D.，佐佐木，J.，Spudich，J. L.，和Luecke，H.（2004）Science 306，1390-1393]，以及细菌视紫红质（BR）的情况，细菌视紫红质是一种典型的转运视紫红质，用作质子泵。在这项研究中，我们应用低温傅里叶变换红外光谱（FTIR）在77 K的ASR的全反式形式，并比较了当地的结构周围的发色团和他们的结构变化后，视网膜光异构化与BR。的K中间减去ASR差光谱基本上类似于BR的那些，表明光异构化产生的扭曲的13-顺式形式的形成。与此相反，很少酰胺I带观察到ASR。脯氨酸特异性振动带的存在表明，肽骨架的改变仅限于ASR的K态中的Pro206部分。希夫碱在ASR中的N-D伸缩推测位于2163（-）和2125（-）cm（-1）处，表明希夫碱在ASR中的氢键强度与BR中的相似。ASR和BR在水纹上有显著差异。虽然ASR具有像BR一样的水分子桥，但水分子的O-D伸缩仅在ASR的>2500 cm（-1）区域观察到。我们解释了席夫碱与Asp 75之间的桥水的弱氢键来源于它们的几何构型。由于ASR不泵质子，我们的研究结果支持的工作假设，即存在强氢键的水分子是必不可少的古细菌视紫红质的质子泵活性。
Anabaena sensory rhodopsin (ASR) is an archaeal-type rhodopsin found in eubacteria, and is believed to function as a photosensor interacting with a 14 kDa soluble protein. Most of the residues in the retinal binding pocket are similar in ASR except proline 206, where the corresponding amino acid in other archaeal-type rhodopsins is highly conserved aspartate that constitutes the counterion complex of the positively charged protonated Schiff base. The recently determined X-ray crystallographic structure of ASR revealed a water molecule between the Schiff base and Asp75 [Vogeley, L., Sineshchekov, O. A., Trivedi, V. D., Sasaki, J., Spudich, J. L., and Luecke, H. (2004) Science 306, 1390-1393], as well as the case for bacteriorhodopsin (BR), a typical transport rhodopsin working as a proton pump. In this study, we applied low-temperature Fourier transform infrared (FTIR) spectroscopy to the all-trans form of ASR at 77 K, and compared the local structure around the chromophore and their structural changes upon retinal photoisomerization with those of BR. The K intermediate minus ASR difference spectra were essentially similar to those for BR, indicating that photoisomerization yields formation of the distorted 13-cis form. In contrast, little amide I bands were observed for ASR. The presence of the proline-specific vibrational bands suggests that peptide backbone alterations are limited to the Pro206 moiety in the K state of ASR. The N-D stretching of the Schiff base is presumably located at 2163 (-) and 2125 (-) cm(-1) in ASR, suggesting that the hydrogen bonding strength of the Schiff base in ASR is similar to that in BR. A remarkable difference between ASR and BR was revealed from water bands. Although ASR possesses a bridged water molecule like BR, the O-D stretching of water molecules was observed only in the >2500 cm(-1) region for ASR. We interpreted that the weak hydrogen bond of the bridged water between the Schiff base and Asp75 originates from their geometry. Since ASR does not pump protons, our result supports the working hypothesis that the existence of strongly hydrogen bonded water molecules is essential for proton pumping activity in archaeal rhodopsins.