Mechanisms for ligand binding to GluR0 ion channels: Crystal structures of the glutamate and serine complexes and a closed Apo state
Mechanisms for ligand binding to GluR0 ion channels: Crystal structures of the glutamate and serine complexes and a closed Apo state
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DOI：
10.1006/jmbi.2001.4884
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发表时间：
2001-08-24
影响因子：
5.6
通讯作者：
Gouaux, E
中科院分区：
文献类型：
--
作者：
Mayer, ML;Olson, R;Gouaux, E
GluR0 的配体结合核心的高分辨率结构已通过 X 射线衍射解析，GluR0 是来自集胞藻 PCC 6803 的谷氨酸受体离子通道。 GluR0 结构揭示了与细菌周质结合蛋白和大鼠 GluR2 AMPA 亚型神经递质受体的同源性。配体结合位点由两个球状 α/β 结构域之间的裂缝形成。 L-谷氨酸以扩展构象结合，类似于谷氨酰胺结合蛋白 (GlnBP) 观察到的构象。然而，L-谷氨酸γ-羧基仅与结构域1中的Asn51相互作用，这不同于在GluR2和GlnBP中观察到的配体与结构域2残基的相互作用。为了解决中性氨基酸如何激活 GluR0 门控，我们解决了与 L-丝氨酸结合位点复合物的结构。这揭示了溶剂分子充当替代配体原子，使得丝氨酸 OH 基团与 Asn51 形成溶剂介导的氢键。无配体的闭裂构象的结构揭示了由溶剂分子介导的广泛的氢键网络。平衡离心分析揭示了 GluR0 配体结合核心的二聚化，解离常数为 0.8 μM。在晶体中，涉及结构域 1 中残基的对称二聚体沿着晶体学 2 倍轴出现，表明四聚体谷氨酸受体离子通道是由二聚体的二聚体组装而成的。我们认为配体诱导的构象变化导致离子通道打开，这是由于域 2 相对于二聚体界面的分离增加的结果。
High-resolution structures of the ligand binding core of GluR0, a glutamate receptor ion channel from Synechocystis PCC 6803, have been solved by X-ray diffraction. The GluR0 structures reveal homology with bacterial periplasmic binding proteins and the rat GluR2 AMPA subtype neurotransmitter receptor. The ligand binding site is formed by a cleft between two globular alpha/beta domains. L-Glutamate binds in an extended conformation, similar to that observed for glutamine binding protein (GlnBP). However, the L-glutamate gamma -carboxyl group interacts exclusively with Asn51 in domain 1, different from the interactions of ligand with domain 2 residues observed for GluR2 and GlnBP. To address how neutral amino acids activate GluR0 gating we solved the structure of the binding site complex with L-serine. This revealed solvent molecules acting as surrogate ligand atoms, such that the serine OH group makes solvent-mediated hydrogen bonds with Asn51. The structure of a ligand-free, closed-cleft conformation revealed an extensive hydrogen bond network mediated by solvent molecules. Equilibrium centrifugation analysis revealed dimerization of the GluR0 ligand binding core with a dissociation constant of 0.8 muM. In the crystal, a symmetrical dimer involving residues in domain 1 occurs along a crystallographic 2-fold axis and suggests that tetrameric glutamate receptor ion channels are assembled from dimers of dimers. We propose that ligand-induced conformational changes cause the ion channel to open as a result of an increase in domain 2 separation relative to the dimer interface.