Structural changes of water molecules during the photoactivation processes in bovine rhodopsin
Structural changes of water molecules during the photoactivation processes in bovine rhodopsin
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DOI：
10.1021/bi034592k
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发表时间：
2003-08-19
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;Shichida, Y;Kandori, H
视紫红质的内部水分子在稳定由质子化的视网膜希夫碱及其抗衡离子组成的关键离子对方面发挥着重要作用。先前对古细菌视紫红质的低温FTIR光谱观察到D2O中水O-D伸缩振动在2400-2100 cm(-1)处，对应于强氢键。由于水分子桥接质子化的席夫碱和古细菌视紫红质中的天冬氨酸，因此观察到的水分子可能会水合席夫碱区域的负电荷。相比之下，牛视紫红质的 FTIR 光谱数据表明，在强氢键条件下（在 2500 cm(-1) 区域，对应于弱氢键），水分子没有光谱变化。这些结果意味着脊椎动物视觉视紫红质中的离子对状态以与古细菌视紫红质不同的方式稳定。此外，水合负电荷的内部水分子在光活化中不起重要作用。在形成 Meta II 时，观察到 β-折叠的 H-D 可交换肽酰胺的结构变化，这表明 β-折叠的运动与从希夫碱到其抗衡离子的质子转移反应耦合。
Internal water molecules of rhodopsins play an important role in stabilizing the crucial ion pair comprised by the protonated retinal Schiff base and its counterion. Previous low-temperature FTIR spectroscopy of archaeal rhodopsins observed water O-D stretching vibrations at 2400-2100 cm(-1) in D2O, corresponding to strong hydrogen bonds. Since a water molecule bridges the protonated Schiff base and an aspartate in archaeal rhodopsins, the observed water molecules presumably hydrate the negative charges in the Schiff base region. In contrast, the FTIR spectroscopy data of bovine rhodopsin presented here revealed that there are no spectral changes of water molecules under strongly hydrogen-bonding conditions (in the range 2500 cm(-1) region that corresponds to weak hydrogen bonding. These results imply that the ion pair state in vertebrate visual rhodopsins is stabilized in a manner different from that in archaeal rhodopsins. In addition, the internal water molecules that hydrate the negative charges do not play important role in the photoactivation processes of rhodopsin that involve proton transfer from the Schiff base to Glu113 upon formation of Meta II. Structural changes of the H-D exchangeable peptide amide of a beta-sheet are observed upon formation of metarhodopsin II, suggesting that motion of a beta-sheet is coupled to the proton transfer reaction from the Schiff base to its counterion.