Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Saga 840-8502, Japan.
Phys Chem Chem Phys. 2021 Jan 28;23(3):2072-2079. doi: 10.1039/d0cp05652a.
We carried out the low-temperature Raman measurement of a sodium pump rhodopsin from Indibacter alkaliphilus (IaNaR) and examined the primary structural change for the light-driven Na+ pump. We observed that photoexcitation of IaNaR produced the distorted 13-cis retinal chromophore in the presence of Na+, while the structural distortion was significantly relaxed in the absence of Na+. This structural difference of the chromophore with/without Na+ was attributed to the Na+ binding to the protein, which alters the active site. Using the spectral sensitivity to the ion binding, we found that IaNaR had a second Na+ binding site in addition to the one already specified on the extracellular surface. To date, the Na+ binding has not been considered as a prerequisite for Na+ transport. However, this study provides insight that the protein structural change induced by the ion binding involved the formation of an R108-D250 salt bridge, which has critical importance in the active transport of Na+.
我们对来自嗜堿盐杆菌（Indibacter alkaliphilus）的钠泵视紫红质（IaNaR）进行了低温喇曼测量，并研究了光驱动 Na+泵的主要结构变化。我们观察到，在有 Na+存在的情况下，IaNaR 的光激发产生了扭曲的 13-顺式视黄醛发色团，而在没有 Na+的情况下，结构扭曲明显得到缓解。这种有/没有 Na+的发色团的结构差异归因于 Na+与蛋白质的结合，这种结合改变了活性部位。利用对离子结合的光谱灵敏度，我们发现除了已经在细胞外表面指定的一个 Na+结合位点外，IaNaR 还有第二个 Na+结合位点。到目前为止，Na+结合尚未被认为是 Na+运输的先决条件。然而，这项研究提供了一个见解，即离子结合诱导的蛋白质结构变化涉及 R108-D250 盐桥的形成，这在 Na+的主动运输中具有至关重要的意义。
