Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA.
J Neurosci. 2010 Feb 17;30(7):2728-40. doi: 10.1523/JNEUROSCI.5146-09.2010.
Subunit assembly governs regulation of AMPA receptor (AMPA-R) synaptic delivery and determines biophysical parameters of the ion channel. However, little is known about the molecular pathways of this process. Here, we present single-particle EM three-dimensional structures of dimeric biosynthetic intermediates of the GluA2 subunit of AMPA-Rs. Consistent with the structures of intact tetramers, the N-terminal domains of the biosynthetic intermediates form dimers. Transmembrane domains also dimerize despite the two ligand-binding domains (LBDs) being separated. A significant difference was detected between the dimeric structures of the wild type and the L504Y mutant, a point mutation that blocks receptor trafficking and desensitization. In contrast to the wild type, whose LBD is separated, the LBD of the L504Y mutant was detected as a single density. Our results provide direct structural evidence that separation of the LBD within the intact dimeric subunits is critical for efficient tetramerization in the endoplasmic reticulum and further trafficking of AMPA-Rs. The contribution of stargazin on the subunit assembly of AMPA-R was examined. Our data suggest that stargazin affects AMPA-R trafficking at a later stage of receptor maturation.
亚基组装控制 AMPA 受体 (AMPA-R) 突触传递的调节，并决定离子通道的生物物理参数。然而，对于这个过程的分子途径知之甚少。在这里，我们呈现了 AMPA-R 的 GluA2 亚基的生物合成中间体的单颗粒 EM 三维结构。与完整四聚体的结构一致，生物合成中间体的 N 端结构域形成二聚体。尽管两个配体结合域 (LBD) 分离，但跨膜结构域也二聚化。在野生型和阻止受体运输和脱敏的 L504Y 突变体的二聚体结构之间检测到显著差异。与野生型的 LBD 分离不同，L504Y 突变体的 LBD 被检测为单一密度。我们的结果提供了直接的结构证据，表明完整二聚体亚基内 LBD 的分离对于内质网中有效四聚体化和 AMPA-R 的进一步运输至关重要。我们还研究了星状蛋白对 AMPA-R 亚基组装的贡献。我们的数据表明，星状蛋白在受体成熟的后期阶段影响 AMPA-R 的运输。
