Graduate School of Science, Nagoya University, Nagoya, Japan.
Biophys J. 2013 Jan 22;104(2):377-85. doi: 10.1016/j.bpj.2012.12.018.
Halorhodopsin from Natronomonas pharaonis (pHR), a retinylidene protein that functions as a light-driven chloride ion pump, is converted into a proton pump in the presence of azide ion. To clarify this conversion, we investigated light-induced structural changes in pHR using a C2 crystal that was prepared in the presence of Cl(-) and subsequently soaked in a solution containing azide ion. When the pHR-azide complex was illuminated at pH 9, a profound outward movement (∼4 Å) of the cytoplasmic half of helix F was observed in a subunit with the EF loop facing an open space. This movement created a long water channel between the retinal Schiff base and the cytoplasmic surface, along which a proton could be transported. Meanwhile, the middle moiety of helix C moved inward, leading to shrinkage of the primary anion-binding site (site I), and the azide molecule in site I was expelled out to the extracellular medium. The results suggest that the cytoplasmic half of helix F and the middle moiety of helix C act as different types of valves for active proton transport.
嗜盐菌视紫红质（pHR）是一种视黄醛蛋白，作为光驱动氯离子泵起作用，在叠氮离子存在下转化为质子泵。为了阐明这种转化，我们使用在 Cl(-)存在下制备的 C2 晶体研究了 pHR 的光诱导结构变化，然后将其浸泡在含有叠氮离子的溶液中。当 pHR-叠氮复合物在 pH 9 下被照射时，EF 环朝向开放空间的亚基中的螺旋 F 的细胞质半部分观察到明显的外向移动（约 4 Å）。这种运动在视黄醛席夫碱和细胞质表面之间创建了一个长的水通道，质子可以沿着该通道运输。同时，螺旋 C 的中间部分向内移动，导致主要阴离子结合位点（位点 I）收缩，而位于位点 I 的叠氮分子被排出到细胞外介质中。结果表明，螺旋 F 的细胞质半部分和螺旋 C 的中间部分充当主动质子运输的不同类型的阀门。
