Wöhlert David, Kühlbrandt Werner, Yildiz Ozkan
Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
Elife. 2014 Nov 26;3:e03579. doi: 10.7554/eLife.03579.
Sodium/proton antiporters maintain intracellular pH and sodium levels. Detailed structures of antiporters with bound substrate ions are essential for understanding how they work. We have resolved the substrate ion in the dimeric, electroneutral sodium/proton antiporter PaNhaP from Pyrococcus abyssi at 3.2 Å, and have determined its structure in two different conformations at pH 8 and pH 4. The ion is coordinated by three acidic sidechains, a water molecule, a serine and a main-chain carbonyl in the unwound stretch of trans-membrane helix 5 at the deepest point of a negatively charged cytoplasmic funnel. A second narrow polar channel may facilitate proton uptake from the cytoplasm. Transport activity of PaNhaP is cooperative at pH 6 but not at pH 5. Cooperativity is due to pH-dependent allosteric coupling of protomers through two histidines at the dimer interface. Combined with comprehensive transport studies, the structures of PaNhaP offer unique new insights into the transport mechanism of sodium/proton antiporters.
钠/质子反向转运体维持细胞内pH值和钠水平。结合底物离子的反向转运体的详细结构对于理解其工作原理至关重要。我们已解析了来自深渊嗜热栖热菌的二聚体、电中性钠/质子反向转运体PaNhaP中底物离子的结构，分辨率为3.2 Å，并确定了其在pH 8和pH 4时的两种不同构象。该离子由三个酸性侧链、一个水分子、一个丝氨酸以及跨膜螺旋5在带负电荷的细胞质漏斗最深处展开部分的一个主链羰基配位。第二个狭窄的极性通道可能有助于从细胞质中摄取质子。PaNhaP的转运活性在pH 6时具有协同性，但在pH 5时没有。协同性是由于通过二聚体界面处的两个组氨酸，原聚体之间存在pH依赖性的变构偶联。结合全面的转运研究，PaNhaP的结构为钠/质子反向转运体的转运机制提供了独特的新见解。
