Tsujii Masaru, Kobayashi Ayumu, Kano Ayaka, Kera Kota, Takagi Tomoko, Nagata Noriko, Kojima Seiji, Hikosaka Kouki, Oguchi Riichi, Sonoike Kintake, Azai Chihiro, Inagaki Tomomi, Ishimaru Yasuhiro, Uozumi Nobuyuki
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan.
Department of Chemical and Biological Sciences, Faculty of Science, Japan Women's University, Bunkyo-ku, Tokyo 112-8681, Japan.
Plant Physiol. 2024 Dec 23;197(1). doi: 10.1093/plphys/kiae562.
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 (TM), 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 to 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 to NhaS6 in inverted membranes of Escherichia coli. Biological fractionation and immunoelectron microscopy revealed that NhaS1 localizes to both the plasma and TMs, while NhaS2 localizes to the plasma membrane (PM). 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 PM-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.
光合生物已经进化出一些机制，以响应不同的光照条件来调节光反应。光合电子传递导致类囊体膜（TM）两侧形成ΔpH，这对于调节电子传递至关重要。然而，其他pH调节剂仍有待确定，尤其是在蓝细菌中。在本研究中，我们评估了六种Na+/H+反向转运蛋白（NhaS1至NhaS6）在蓝细菌聚球藻属PCC 6803的pH控制中的潜在作用。聚球藻在高光强度下对Na+有强烈需求，ΔnhaS1和ΔnhaS2菌株在高光条件下无法生长。我们分析了大肠杆菌内膜中NhaS1至NhaS6的Na+外流驱动的H+摄取活性。生物分级分离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（PM）。光合作用活性的测量表明，NhaS2促进ATP的产生以及电子从质体醌（PQ）到P700的传递。细胞外和细胞质中pH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在高光处理下可防止光抑制。这些结果表明，由NhaS1和NhaS2介导的H+转运在调节细胞内pH和维持光合电子传递中起作用。
