Protein-Bound Water Molecules in Primate Red- and Green-Sensitive Visual Pigments
Protein-Bound Water Molecules in Primate Red- and Green-Sensitive Visual Pigments
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DOI：
10.1021/bi201676y
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发表时间：
2012-02-14
期刊：
影响因子：
2.9
通讯作者：
Kandori, Hideki
中科院分区：
文献类型：
--
作者：
Katayama, Kota;Furutani, Yuji;Kandori, Hideki
蛋白质结合水分子在蛋白质的结构和功能中起着至关重要的作用。在X射线晶体学、傅里叶变换红外光谱（FTIR）和辐射分解标记方法的基础上，已经讨论了水分子在视紫红质（微光视觉的光传感器）中的功能作用，但对我们的彩色视觉色素中的蛋白质结合沃茨一无所知。在这里，我们适用于低温FTIR光谱猴子红（MR）和绿色（MG）敏感的彩色颜料在77 K，并成功地识别水的振动使用D2 O和（D2 O）-O-18在整个中红外区域。所观察到的水的振动为6-8 MR和MG，表明几个水分子存在于视网膜发色团附近，并改变其氢键后，视网膜光异构化。从这个意义上说，彩色视色素具有与视紫红质基本相似的蛋白质结合水分子。MR和MG在2550 cm（-1）处不存在强氢键水分子（O-D拉伸）。其次，在视网膜光异构化后，观察到全反式形式的强氢键水分子（MR为2303 cm（-1），MG为2308 cm（-1）），而视紫红质的情况并非如此。MR和MG的这些具体特征可以通过Cl-结合位点中存在水分子来解释，所述Cl-结合位点位于视网膜发色团的位置C11和C9附近。MR和MG观察到的水O-D伸缩振动的平均频率随着λ（max）的红移而降低，这表明水分子参与了我们视觉的颜色调节。
Protein-bound water molecules play crucial roles in the structure and function of proteins. The functional role of water molecules has been discussed for rhodopsin, the light sensor for twilight vision, on the basis of X-ray crystallography, Fourier transform infrared (FTIR) spectroscopy, and a radiolytic labeling method, but nothing is known about the protein-bound waters in our color visual pigments. Here we apply low-temperature FTIR spectroscopy to monkey red (MR)- and green (MG)-sensitive color pigments at 77 K and successfully identify water vibrations using D2O and (D2O)-O-18 in the whole midinfrared region. The observed water vibrations are 6-8 for MR and MG, indicating that several water molecules are present near the retinal chromophore and change their hydrogen bonds upon retinal photoisomerization. In this sense, color visual pigments possess protein-bound water molecules essentially similar to those of rhodopsin. The absence of strongly hydrogen-bonded water molecules (O-D stretch at 2550 cm(-1) for both MR and MG. Second, strongly hydrogen-bonded water molecules (2303 cm(-1) for MR and 2308 cm(-1) for MG) are observed for the all-trans form after retinal photoisomerization, which is not the case for rhodopsin. These specific features of MR and MG can be explained by the presence of water molecules in the Cl--biding site, which are located near positions C11 and C9 of the retinal chromophore. The averaged frequencies of the observed water O-D stretching vibrations for MR and MG are lower as the lambda(max) is red-shifted, suggesting that water molecules are involved in the color tuning of our vision.