Hydrogen-bonding alterations of the protonated Schiff base and water molecule in the chloride pump of Natronobacterium pharaonis.
Hydrogen-bonding alterations of the protonated Schiff base and water molecule in the chloride pump of Natronobacterium pharaonis.
复制标题
DOI：
10.1021/bi050726d
复制
发表时间：
2005-08
期刊：
影响因子：
2.9
通讯作者：
Mikihiro Shibata;N. Muneda;Takanori Sasaki;K. Shimono;N. Kamo;M. Demura;H. Kandori
中科院分区：
文献类型：
--
作者：
Mikihiro Shibata;N. Muneda;Takanori Sasaki;K. Shimono;N. Kamo;M. Demura;H. Kandori
Halorhodopsin 是一种光驱动的氯离子泵。氯离子结合在视网膜发色团的席夫碱区域，单向氯离子转运可能是通过与质子化席夫碱和内部水分子的特定氢键相互作用来加强的。在本文中，我们通过分别分配 D(2)O 中的 N-D 和 O-D 伸缩振动来研究法老嗜盐杆菌 (pHR) 盐视紫红质 (pHR) 中席夫碱和水分子的氢键变化。高精度低温傅立叶变换红外光谱表明，席夫碱和水分子的氢键在未光解状态下很弱，而在视网膜光异构化时它们会增强。卤化物对伸缩振动的依赖性使我们得出结论，希夫碱仅在 K 中间体中与 Cl(-) 形成直接氢键。 L(1)中间体中希夫碱的氢键进一步加强，而卤化物依赖性表明受体不是Cl(-)，而可能是水分子。由此可见，席夫碱与Cl(-)之间的氢键相互作用并不是Cl(-)运动的驱动力。相反，去除其与希夫碱和水的氢键使得L(1)中间体中Cl(-)周围的环境极性降低，这可能驱动Cl(-)从其结合位点运动到细胞质结构域。
Halorhodopsin is a light-driven chloride ion pump. Chloride ion is bound in the Schiff base region of the retinal chromophore, and unidirectional chloride transport is probably enforced by the specific hydrogen-bonding interaction with the protonated Schiff base and internal water molecules. In this article, we study hydrogen-bonding alterations of the Schiff base and water molecules in halorhodopsin of Natronobacterium pharaonis (pHR) by assigning their N-D and O-D stretching vibrations in D(2)O, respectively. Highly accurate low-temperature Fourier transform infrared spectroscopy revealed that hydrogen bonds of the Schiff base and water molecules are weak in the unphotolyzed state, whereas they are strengthened upon retinal photoisomerization. Halide dependence of the stretching vibrations enabled us to conclude that the Schiff base forms a direct hydrogen bond with Cl(-) only in the K intermediate. Hydrogen bond of the Schiff base is further strengthened in the L(1) intermediate, whereas the halide dependence revealed that the acceptor is not Cl(-), but presumably a water molecule. Thus, it is concluded that the hydrogen-bonding interaction between the Schiff base and Cl(-) is not a driving force of the motion of Cl(-). Rather, the removal of its hydrogen bonds with the Schiff base and water(s) makes the environment around Cl(-) less polar in the L(1) intermediate, which presumably drives the motion of Cl(-) from its binding site to the cytoplasmic domain.