Strongly hydrogen-bonded water molecule present near the retinal chromophore of Leptosphaeria rhodopsin, the bacteriorhodopsin-like proton pump from a eukaryote.
Strongly hydrogen-bonded water molecule present near the retinal chromophore of Leptosphaeria rhodopsin, the bacteriorhodopsin-like proton pump from a eukaryote.
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DOI：
10.1021/bi0513498
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发表时间：
2005-10
期刊：
影响因子：
2.9
通讯作者：
Masayo Sumii;Y. Furutani;S. Waschuk;L. Brown;H. Kandori
中科院分区：
文献类型：
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作者：
Masayo Sumii;Y. Furutani;S. Waschuk;L. Brown;H. Kandori
Leptosphaeria rhodopsin （LR）是一种在真菌中发现的古菌型视紫红质，是第一个来自真核生物的光驱动质子泵视网膜蛋白。LR以一种类似于细菌视紫红质（BR）的方式泵质子，细菌视紫红质是一种光驱动质子泵的盐古菌。LR的氨基酸序列与NR （Neurospora rhodopsin， BR）更为相似，而NR没有质子泵活性。这些事实提出了质子泵送功能是如何实现的问题。本文利用低温傅里叶变换红外光谱（FTIR）研究了LR在视网膜光异构化后的结构变化，并与BR和NR的光谱进行了比较。LR、BR和NR之间普遍存在全反式光异构化到13顺式光异构化的现象。我们发现，在视网膜和蛋白质的详细振动带方面，LR的结构变化更接近于BR，而不是NR。最显著的差异是水O-D拉伸振动（以D2O测量）。LR在2257 cm（-1）处表现出水的O-D延伸，表明存在强氢键水分子。BR中存在这种强氢键水分子（O-D拉伸<2400 cm(-1)），而NR中没有。对BR突变体和古细菌视紫红质的综合研究表明，强氢键水分子仅存在于具有质子泵送活性的蛋白质中，这表明强氢键水分子及其结合的短暂减弱对视紫红质的质子泵送功能至关重要。这一观察结果为古细菌紫红质强氢键水分子与质子泵送活性之间的相关性提供了额外的实验证据。
Leptosphaeria rhodopsin (LR) is an archaeal-type rhodopsin found in fungi, and is the first light-driven proton-pumping retinal protein from eukaryotes. LR pumps protons in a manner similar to that of bacteriorhodopsin (BR), a light-driven proton pump of haloarchaea. The amino acid sequence of LR is more homologous to that of Neurospora rhodopsin (NR) than BR, whereas NR has no proton-pumping activity. These facts raise the question of how the proton-pumping function is achieved. In this paper, we studied structural changes of LR following the retinal photoisomerization by means of low-temperature Fourier transform infrared (FTIR) spectroscopy, and compared the obtained spectra with those for BR and NR. While the light-induced photoisomerization from the all-trans to 13-cis form was commonly observed among LR, BR, and NR, we found that the structural changes of LR are closer to those of BR than to those of NR in terms of detailed vibrational bands of retinal and protein. The most prominent difference was seen for the water O-D stretching vibrations (measured in D2O). LR exhibits an O-D stretch of water at 2257 cm(-1), indicating the presence of a strongly hydrogen-bonded water molecule. Such strongly hydrogen-bonded water molecules (O-D stretch at <2400 cm(-1)) were observed for BR, but not for NR. Comprehensive studies of BR mutants and archaeal rhodopsins have revealed that strongly hydrogen-bonded water molecules are found only in the proteins exhibiting proton-pumping activity, suggesting that strongly hydrogen-bonded water molecules and transient weakening of their binding are essential for the proton-pumping function of rhodopsins. This observation for LR provided additional experimental evidence of the correlation between strongly hydrogen-bonded water molecules and proton-pumping activity of archaeal rhodopsins.