Jung Sukkyeong, Kokane Surabhi, Li Hang, Iwata So, Nomura Norimichi, Drew David
Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, 171-65 Stockholm, Sweden.
Graduate School of Medicine, Kyoto University, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
Int J Mol Sci. 2025 Apr 29;26(9):4221. doi: 10.3390/ijms26094221.
The sodium/proton exchanger NHA2, also known as SLC9B2, is important for insulin secretion, renal blood pressure regulation, and electrolyte retention. Recent structures of bison NHA2 has revealed its unique 14-transmembrane helix architecture, which is different from SLC9A/NHE members made up from 13-TM helices. Sodium/proton exchangers are functional homodimers, and the additional N-terminal helix in NHA2 was found to alter homodimer assembly. Here, we present the cryo-electron microscopy structures of apo human NHA2 in complex with a Fab fragment and also with the inhibitor phloretin bound at 2.8 and 2.9 Å resolution, respectively. We show how phosphatidic acid (PA) lipids bind to the homodimer interface of NHA2 on the extracellular side, which we propose has a regulatory role linked to cell volume regulation. The ion binding site of human NHA2 has a salt bridge interaction between the ion binding aspartate D278 and R432, an interaction previously broken in the bison NHA2 structure, and these differences suggest a possible ion coupling mechanism. Lastly, the human NHA2 structure in complex with phloretin offers a template for structure-guided drug design, potentially leading to the development of more selective and potent NHA2 inhibitors.
钠/质子交换体NHA2，也被称为SLC9B2，对胰岛素分泌、肾血压调节和电解质潴留很重要。最近美洲野牛NHA2的结构揭示了其独特的14跨膜螺旋结构，这与由13个跨膜螺旋组成的SLC9A/NHE成员不同。钠/质子交换体是功能性同二聚体，并且发现NHA2中额外的N端螺旋会改变同二聚体组装。在这里，我们分别展示了与Fab片段复合以及与抑制剂根皮素结合的脱辅基人类NHA2的冷冻电子显微镜结构，分辨率分别为2.8 Å和2.9 Å。我们展示了磷脂酸（PA）脂质如何在细胞外侧结合到NHA2的同二聚体界面，我们认为这与细胞体积调节相关联，具有调节作用。人类NHA2的离子结合位点在离子结合天冬氨酸D278和R432之间存在盐桥相互作用，这种相互作用在美洲野牛NHA2结构中之前被破坏，这些差异提示了一种可能的离子偶联机制。最后，与根皮素复合的人类NHA2结构为结构导向药物设计提供了一个模板，可能会导致开发出更具选择性和强效的NHA2抑制剂。
