Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 4, 9747AG, Groningen, The Netherlands.
Moscow Institute of Physics and Technology, Dolgoprudny, Russia.
Nat Commun. 2020 Feb 21;11(1):998. doi: 10.1038/s41467-020-14834-8.
Glutamate transporters are cation-coupled secondary active membrane transporters that clear the neurotransmitter L-glutamate from the synaptic cleft. These transporters are homotrimers, with each protomer functioning independently by an elevator-type mechanism, in which a mobile transport domain alternates between inward- and outward-oriented states. Using single-particle cryo-EM we have determined five structures of the glutamate transporter homologue Glt, a Na- L-aspartate symporter, embedded in lipid nanodiscs. Dependent on the substrate concentrations used, the protomers of the trimer adopt a variety of asymmetrical conformations, consistent with the independent movement. Six of the 15 resolved protomers are in a hitherto elusive state of the transport cycle in which the inward-facing transporters are loaded with Na ions. These structures explain how substrate-leakage is prevented - a strict requirement for coupled transport. The belt protein of the lipid nanodiscs bends around the inward oriented protomers, suggesting that membrane deformations occur during transport.
谷氨酸转运体是阳离子偶联的次级主动膜转运体，可清除突触间隙中的神经递质 L-谷氨酸。这些转运体是同源三聚体，每个亚基通过电梯式机制独立发挥作用，其中可移动的转运结构域在内向和外向状态之间交替。我们使用单颗粒 cryo-EM 技术确定了嵌入脂质纳米盘的谷氨酸转运体同源物 Glt（Na+-L-天冬氨酸共转运体）的五个结构。根据使用的底物浓度，三聚体的亚基采用多种不对称构象，与独立运动一致。在 15 个解析出的亚基中，有 6 个处于运输循环中迄今难以捉摸的状态，其中内向转运体被 Na 离子加载。这些结构解释了如何防止底物泄漏 - 这是偶联转运的严格要求。脂质纳米盘的带蛋白围绕内向的亚基弯曲，表明在转运过程中会发生膜变形。
