Sirrieh Rita E, MacLean David M, Jayaraman Vasanthi
From the Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, Texas 77030.
From the Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, Texas 77030
J Biol Chem. 2015 May 15;290(20):12812-20. doi: 10.1074/jbc.M115.649723. Epub 2015 Mar 31.
The N-methyl-d-aspartate (NMDA) subtype of the ionotropic glutamate receptors is the primary mediator of calcium-permeable excitatory neurotransmission in the central nervous system. Subunit composition and binding of allosteric modulators to the amino-terminal domain determine the open probability of the channel. By using luminescence resonance energy transfer with functional receptors expressed in CHO cells, we show that the cleft of the amino-terminal domain of the GluN2B subunit, which has a lower channel open probability, is on average more closed than the GluN2A subunit, which has a higher open probability. Furthermore, the GluN1 amino-terminal domain adopts a more open conformation when coassembled with GluN2A than with GluN2B. Binding of spermine, an allosteric potentiator, opens the amino-terminal domain cleft of both the GluN2B subunit and the adjacent GluN1 subunit. These studies provide direct structural evidence that the inherent conformations of the amino-terminal domains vary based on the subunit and match the reported open probabilities for the receptor.
离子型谷氨酸受体的N-甲基-D-天冬氨酸（NMDA）亚型是中枢神经系统中钙通透性兴奋性神经传递的主要介质。亚基组成以及变构调节剂与氨基末端结构域的结合决定了通道的开放概率。通过对CHO细胞中表达的功能性受体使用荧光共振能量转移技术，我们发现通道开放概率较低的GluN2B亚基的氨基末端结构域裂隙平均比通道开放概率较高的GluN2A亚基的裂隙闭合程度更高。此外，与GluN2B共同组装时相比，GluN1氨基末端结构域与GluN2A共同组装时会采用更开放的构象。变构增强剂精胺的结合会打开GluN2B亚基和相邻GluN1亚基的氨基末端结构域裂隙。这些研究提供了直接的结构证据，表明氨基末端结构域的固有构象因亚基而异，并且与报道的受体开放概率相匹配。
