Verdon Grégory, Oh SeCheol, Serio Ryan N, Boudker Olga
Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States
Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States.
Elife. 2014 May 19;3:e02283. doi: 10.7554/eLife.02283.
Membrane transporters that clear the neurotransmitter glutamate from synapses are driven by symport of sodium ions and counter-transport of a potassium ion. Previous crystal structures of a homologous archaeal sodium and aspartate symporter showed that a dedicated transport domain carries the substrate and ions across the membrane. Here, we report new crystal structures of this homologue in ligand-free and ions-only bound outward- and inward-facing conformations. We show that after ligand release, the apo transport domain adopts a compact and occluded conformation that can traverse the membrane, completing the transport cycle. Sodium binding primes the transport domain to accept its substrate and triggers extracellular gate opening, which prevents inward domain translocation until substrate binding takes place. Furthermore, we describe a new cation-binding site ideally suited to bind a counter-transported ion. We suggest that potassium binding at this site stabilizes the translocation-competent conformation of the unloaded transport domain in mammalian homologues.DOI: http://dx.doi.org/10.7554/eLife.02283.001.
从突触清除神经递质谷氨酸的膜转运蛋白由钠离子同向转运和钾离子反向转运驱动。同源古菌钠和天冬氨酸同向转运体的先前晶体结构表明，一个专门的转运结构域携带底物和离子穿过膜。在这里，我们报告了该同源物在无配体和仅结合离子的外向和内向构象下的新晶体结构。我们表明，在配体释放后，脱辅基转运结构域采用紧凑且封闭的构象，该构象可以穿过膜，完成转运循环。钠结合使转运结构域准备好接受其底物并触发细胞外门打开，这会阻止结构域向内转运，直到底物结合发生。此外，我们描述了一个非常适合结合反向转运离子的新阳离子结合位点。我们认为，该位点的钾结合稳定了哺乳动物同源物中卸载的转运结构域的易位能力构象。DOI: http://dx.doi.org/10.7554/eLife.02283.001 。
