He Xue-Yan, Li Yan-Jun, Kalyanaraman Chakrapani, Qiu Li-Li, Chen Chen, Xiao Qi, Liu Wen-Xue, Zhang Wei, Yang Jian-Jun, Chen Guiquan, Jacobson Matthew P, Shi Yun Stone
State Key Laboratory of Pharmaceutical Biotechnology and MOE Key Laboratory of Model Animal for Disease Study, Model Animal Research Center, Nanjing University, Nanjing 210061 China;
Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158;
Proc Natl Acad Sci U S A. 2016 Sep 20;113(38):E5645-54. doi: 10.1073/pnas.1524358113. Epub 2016 Sep 6.
AMPA-type glutamate receptors (AMPARs) mediate fast excitatory neurotransmission and predominantly assemble as heterotetramers in the brain. Recently, the crystal structures of homotetrameric GluA2 demonstrated that AMPARs are assembled with two pairs of conformationally distinct subunits, in a dimer of dimers formation. However, the structure of heteromeric AMPARs remains unclear. Guided by the GluA2 structure, we performed cysteine mutant cross-linking experiments in full-length GluA1/A2, aiming to draw the heteromeric AMPAR architecture. We found that the amino-terminal domains determine the first level of heterodimer formation. When the dimers further assemble into tetramers, GluA1 and GluA2 subunits have preferred positions, possessing a 1-2-1-2 spatial assembly. By swapping the critical sequences, we surprisingly found that the spatial assembly pattern is controlled by the excisable signal peptides. Replacements with an unrelated GluK2 signal peptide demonstrated that GluA1 signal peptide plays a critical role in determining the spatial priority. Our study thus uncovers the spatial assembly of an important type of glutamate receptors in the brain and reveals a novel function of signal peptides.
AMPA 型谷氨酸受体（AMPARs）介导快速兴奋性神经传递，且在大脑中主要组装为异源四聚体。最近，同型四聚体 GluA2 的晶体结构表明，AMPARs 是以两对构象不同的亚基组装而成，形成二聚体的二聚体结构。然而，异源 AMPARs 的结构仍不清楚。在 GluA2 结构的指导下，我们对全长 GluA1/A2 进行了半胱氨酸突变体交联实验，旨在描绘异源 AMPAR 的结构。我们发现氨基末端结构域决定了异源二聚体形成的第一层次。当二聚体进一步组装成四聚体时，GluA1 和 GluA2 亚基具有优先位置，呈现 1-2-1-2 的空间组装方式。通过交换关键序列，我们惊奇地发现空间组装模式受可切除信号肽的控制。用无关的 GluK2 信号肽进行替换表明，GluA1 信号肽在确定空间优先级方面起关键作用。因此，我们的研究揭示了大脑中一类重要谷氨酸受体的空间组装，并揭示了信号肽的新功能。
