Pokharna Aditya, Stockwell Imogen, Ivica Josip, Singh Bishal, Schwab Johannes, Vega-Gutiérrez Carlos, Herguedas Beatriz, Cais Ondrej, Krieger James M, Greger Ingo H
Neurobiology Division, Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, UK.
Department of Genomic Medicine, University of Texas MD Anderson Cancer Center, Houston, TX, USA.
Nature. 2025 Jul 1. doi: 10.1038/s41586-025-09325-z.
AMPA-type glutamate receptors (AMPARs) mediate the majority of excitatory neurotransmission in the brain. Assembled from combinations of four core subunits, GluA1-4 and around 20 auxiliary subunits, their molecular diversity tunes information transfer and storage in a brain-circuit-specific manner. GluA3, a subtype strongly associated with disease, functions as both a fast-transmitting Ca-permeable AMPAR at sensory synapses, and as a Ca-impermeable receptor at cortical synapses. Here we present cryo-electron microscopy structures of the Ca-permeable GluA3 homomer, which substantially diverges from other AMPARs. The GluA3 extracellular domain tiers (N-terminal domain (NTD) and ligand-binding domain (LBD)) are closely coupled throughout gating states, creating interfaces that impact signalling and contain human disease-associated mutations. Central to this architecture is a stacking interaction between two arginine residues (Arg163) in the NTD dimer interface, trapping a unique NTD dimer conformation that enables close contacts with the LBD. Rupture of the Arg163 stack not only alters the structure and dynamics of the GluA3 extracellular region, but also increases receptor trafficking and the expression of GluA3 heteromers at the synapse. We further show that a mammalian-specific GluA3 trafficking checkpoint determines the conformational stability of the LBD tier. Thus, specific design features define communication and biogenesis of GluA3, offering a framework to examine this disease-associated glutamate receptor.
AMPA 型谷氨酸受体（AMPARs）介导大脑中大部分兴奋性神经传递。它们由四个核心亚基（GluA1 - 4）和大约 20 个辅助亚基组合而成，其分子多样性以脑回路特异性方式调节信息传递和存储。GluA3 是一种与疾病密切相关的亚型，在感觉突触处作为快速传递的钙通透 AMPAR 发挥作用，而在皮质突触处作为钙不通透受体发挥作用。在此，我们展示了钙通透型 GluA3 同聚体的冷冻电子显微镜结构，该结构与其他 AMPARs 有很大差异。GluA3 的细胞外结构域层级（N 端结构域（NTD）和配体结合结构域（LBD））在整个门控状态下紧密耦合，形成影响信号传导且包含人类疾病相关突变的界面。这种结构的核心是 NTD 二聚体界面中两个精氨酸残基（Arg163）之间的堆积相互作用，捕获了一种独特的 NTD 二聚体构象，使其能够与 LBD 紧密接触。Arg163 堆积的破坏不仅改变了 GluA3 细胞外区域的结构和动力学，还增加了受体运输以及 GluA3 异聚体在突触处的表达。我们进一步表明，一个哺乳动物特有的 GluA3 运输检查点决定了 LBD 层级的构象稳定性。因此，特定的设计特征定义了 GluA3 的通讯和生物发生，为研究这种与疾病相关的谷氨酸受体提供了一个框架。
