Photosynthetic organisms have developed mechanisms to regulate light reactions in response to varying light conditions. Photosynthetic electron transport leads to the formation of a ΔpH across the thylakoid membrane, which is crucial for regulating electron transport. However, other pH modulators remain to be identified, particularly in cyanobacteria. In this study, we evaluated the potential involvement of six Na+/H+ antiporters (NhaS1–NhaS6) in control of pH in the cyanobacterium Synechocystis sp. PCC 6803. Synechocystis showed a strong requirement for Na+ at high light intensities, with ΔnhaS1 and ΔnhaS2 strains unable to grow under high light conditions. We analyzed Na+ efflux–driven H+-uptake activities of NhaS1–NhaS6 in inverted membranes of Escherichia coli. Biological fractionation and immunoelectron microscopy revealed that NhaS1 localizes to both the plasma and thylakoid membranes while NhaS2 localizes to the plasma membrane. Measurement of photosynthesis activity indicated that NhaS2 promotes ATP production and electron transport from PQ to P700. Measurements of pH outside of the cells and in the cytoplasm suggested that both NhaS1 and NhaS2 are involved in plasma membrane–mediated light-dependent H+ uptake and cytoplasmic acidification. NhaS1 and NhaS2 were also found to prevent photoinhibition under high light treatment. These results indicate that H+ transport mediated by NhaS1 and NhaS2 plays a role in regulating intracellular pH and maintaining photosynthetic electron transport.

中文翻译：

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Na+/H+ 逆向转运蛋白对 Na+ 驱动的 pH 调节可促进蓝藻的光合效率


光合生物已经开发出响应不同光照条件调节光反应的机制。光合电子传递导致在类囊体膜上形成 ΔpH，这对于调节电子传递至关重要。然而，其他 pH 调节剂仍有待鉴定，尤其是在蓝细菌中。在这项研究中，我们评估了六种 Na + / H + 逆向转运蛋白 （NhaS1-NhaS6） 在蓝藻集胞藻属 PCC 6803 中控制 pH 值的潜在参与。集胞藻在高光强度下表现出对 Na+ 的强烈需求，而 ΔnhaS1 和 ΔnhaS2 菌株在强光条件下无法生长。我们分析了大肠杆菌倒置膜中 NhaS1-NhaS6 的 Na+ 外排驱动的 H+ 摄取活性。生物分级和免疫电子显微镜显示，NhaS1 定位于质膜和类囊体膜，而 NhaS2 定位于质膜。光合作用活性的测量表明，NhaS2 促进 ATP 的产生和从 PQ 到 P700 的电子传递。细胞外和细胞质中 pH 值的测量表明，NhaS1 和 NhaS2 都参与质膜介导的光依赖性 H+ 摄取和细胞质酸化。还发现 NhaS1 和 NhaS2 在强光处理下可防止光抑制。这些结果表明，NhaS1 和 NhaS2 介导的 H+ 转运在调节细胞内 pH 值和维持光合电子转运中发挥作用。