Proton-pumping rhodopsins are light-driven proton transporters that have been discovered from various microbiota. They are categorized into two groups: outward-directed and inward-directed proton pumps. Although the directions of transport are opposite, they are active proton transporters that create an H+ gradient across a membrane. Here, we aimed to study the driving force of the proton-pumping rhodopsins and the effect of ΔΨ and ΔpH on their pumping functions. We systematically characterized the H+ transport properties of nine different rhodopsins, six outward-directed H+ pumps and three inward-directed pumps, by patch-clamp measurements after expressing them in mammalian cells. The driving force of each pump was estimated from the slope of the current-voltage relations (I-V plot). Notably, among the tested rhodopsins, we found a large variation in driving forces, ranging from 83 to 399 mV. The driving force and decay rate of each pump current exhibited a good correlation. We determined driving forces under various pHs. pH dependency was less than predicted by the Nernst potential in most of the rhodopsins. Our study demonstrates that the H+-pumping rhodopsins from different organisms exhibit various pumping properties in terms of driving force, kinetics, and pH dependency, which could be evolutionarily derived from adaptations to their environments.

中文翻译：

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质子泵视紫红质的驱动力


质子泵式视紫红质是从各种微生物群中发现的光驱动质子转运蛋白。它们分为两组：外向质子泵和内向质子泵。尽管传输方向相反，但它们是活性质子转运蛋白，可在膜上产生 H+ 梯度。在这里，我们旨在研究质子泵送视紫红质的驱动力以及 ΔΨ 和 ΔpH 对其泵送功能的影响。在哺乳动物细胞中表达 9 种不同的视紫红质、6 种外向 H+ 泵和 3 种内向泵后，我们通过膜片钳测量系统表征了它们的 H+ 转运特性。每个泵的驱动力是根据电流-电压关系的斜率 （I-V 图） 估计的。值得注意的是，在测试的视紫红质中，我们发现驱动力变化很大，范围从 83 到 399 mV。各泵浦电流的驱动力和衰减率均表现出良好的相关性。我们确定了各种 pH 值下的驱动力。在大多数视紫红质中，pH 依赖性低于 Nernst 电位的预测。我们的研究表明，来自不同生物体的 H+ 泵送视紫红质在驱动力、动力学和 pH 依赖性方面表现出不同的泵送特性，这可能是从对环境的适应进化得出的。