Glutamate is the most abundant excitatory neurotransmitter in the central nervous system, therefore its precise control is vital for maintaining normal brain function and preventing excitotoxicity1. Removal of extracellular glutamate is achieved by plasma membrane-bound transporters, which couple glutamate transport to sodium, potassium and pH gradients using an elevator mechanism2-5. Glutamate transporters also conduct chloride ions via a channel-like process that is thermodynamically uncoupled from transport6-8. However, the molecular mechanisms that allow these dual-function transporters to carry out two seemingly contradictory roles are unknown. Here we report the cryo-electron microscopy structure of a glutamate transporter homologue in an open-channel state, revealing an aqueous cavity that is formed during the transport cycle. Using functional studies and molecular dynamics simulations, we show that this cavity is an aqueous-accessible chloride permeation pathway gated by two hydrophobic regions, and is conserved across mammalian and archaeal glutamate transporters. Our findings provide insight into the mechanism by which glutamate transporters support their dual function and add a crucial piece of information to aid mapping of the complete transport cycle shared by the SLC1A transporter family.

中文翻译：

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谷氨酸转运蛋白包含带有两个疏水门的保守氯离子通道

谷氨酸是中枢神经系统中最丰富的兴奋性神经递质，因此其精确控制对于维持正常的脑功能和预防兴奋性毒性至关重要。胞外谷氨酸的去除是通过质膜结合的转运蛋白实现的，该转运蛋白利用升降机机理将谷氨酸的转运耦合到钠，钾和pH梯度2-5。谷氨酸转运蛋白还通过类似通道的过程传导氯离子，该过程在热力学上与转运6-8脱钩。但是，使这些双功能转运蛋白发挥两个看似矛盾的作用的分子机制尚不清楚。在这里我们报告谷氨酸转运蛋白同系物在开放通道状态下的低温电子显微镜结构，揭示了在运输周期中形成的水​​腔。使用功能研究和分子动力学模拟，我们显示该腔是由两个疏水区域控制的水可及的氯离子渗透途径，在哺乳动物和古细菌谷氨酸转运蛋白中是保守的。我们的发现提供了对谷氨酸转运蛋白支持其双重功能并添加关键信息以帮助绘制SLC1A转运蛋白家族共享的完整转运周期的机制的深入了解。