Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, 37077 Göttingen, Germany.
Institute for Integrative Neuroanatomy, Charité, Medical University of Berlin, 10115 Berlin, Germany.
Cell Rep. 2018 Apr 10;23(2):535-545. doi: 10.1016/j.celrep.2018.03.055.
Vesicular glutamate transporters (VGLUTs) fill synaptic vesicles with glutamate and are thus essential for glutamatergic neurotransmission. However, VGLUTs were originally discovered as members of a transporter subfamily specific for inorganic phosphate (P). It is still unclear how VGLUTs accommodate glutamate transport coupled to an electrochemical proton gradient ΔμH with inversely directed P transport coupled to the Na gradient and the membrane potential. Using both functional reconstitution and heterologous expression, we show that VGLUT transports glutamate and P using a single substrate binding site but different coupling to cation gradients. When facing the cytoplasm, both ions are transported into synaptic vesicles in a ΔμH-dependent fashion, with glutamate preferred over P. When facing the extracellular space, P is transported in a Na-coupled manner, with glutamate competing for binding but at lower affinity. We conclude that VGLUTs have dual functions in both vesicle transmitter loading and P homeostasis within glutamatergic neurons.
囊泡谷氨酸转运体（VGLUTs）将谷氨酸填充到突触小泡中，因此对于谷氨酸能神经传递至关重要。然而，VGLUTs 最初被发现是无机磷酸盐（P）特异性转运体亚家族的成员。目前尚不清楚 VGLUTs 如何适应与电化学质子梯度 ΔμH 偶联的谷氨酸转运，而与 Na 梯度和膜电位偶联的 P 转运则相反。通过功能重建和异源表达，我们表明 VGLUT 使用单个底物结合位点但与阳离子梯度的不同偶联来转运谷氨酸和 P。当面对细胞质时，两种离子都以 ΔμH 依赖的方式被转运到突触小泡中，谷氨酸优先于 P。当面对细胞外空间时，P 以 Na 偶联的方式被转运，而谷氨酸竞争结合，但亲和力较低。我们得出结论，VGLUTs 在囊泡递质加载和谷氨酸能神经元内 P 稳态方面具有双重功能。
