Neurotransmitter:sodium symporters (NSS), targets of antidepressants and psychostimulants, clear neurotransmitters from the synaptic cleft through sodium (Na⁺)-coupled transport. Substrate and Na⁺ are thought to be transported from the extracellular to intracellular space through an alternating access mechanism by coordinated conformational rearrangements in the symporter that alternately expose the binding sites to each side of the membrane. However, the mechanism by which the binding of ligands coordinates conformational changes occurring on opposite sides of the membrane is not well understood. Here, we report the use of single-molecule fluorescence resonance energy transfer (smFRET) techniques to image transitions between distinct conformational states on both the extracellular and intracellular sides of the prokaryotic NSS LeuT, including partially open intermediates associated with transport activity. The nature and functional context of these hitherto unidentified intermediate states shed new light on the allosteric mechanism that couples substrate and Na⁺ symport by the NSS family through conformational dynamics.

中文翻译：

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LeuT 的部分开放的向内中间构象与 Na+ 释放和底物运输相关。

^{神经递质：钠同向转运蛋白（NSS），抗抑郁药和精神兴奋剂的靶标，通过钠（Na +} ）耦合转运从突触间隙清除神经递质。底物和 Na ⁺被认为是通过交替进入机制从细胞外转运到细胞内空间，通过同向转运蛋白中协调的构象重排，交替地将结合位点暴露于膜的每一侧。然而，配体结合协调膜相对侧发生的构象变化的机制尚不清楚。在这里，我们报告了使用单分子荧光共振能量转移（smFRET）技术对原核 NSS LeuT 细胞外和细胞内两侧不同构象状态之间的转变进行成像，包括与转运活性相关的部分开放中间体。这些迄今为止尚未识别的中间态的性质和功能背景为 NSS 家族通过构象动力学耦合底物和 Na ⁺同构机制提供了新的线索。