NMDA Receptors with Locked Glutamate-Binding Clefts Open with High Efficacy
NMDA Receptors with Locked Glutamate-Binding Clefts Open with High Efficacy
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DOI：
10.1523/jneurosci.3337-10.2010
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发表时间：
2010-09-15
影响因子：
5.3
通讯作者：
Popescu, Gabriela K.
中科院分区：
文献类型：
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作者：
Kussius, Cassandra L.;Popescu, Gabriela K.
谷氨酸门控通道介导基本的大脑过程，但神经递质控制通道激活的机制还不完全清楚。结构研究表明，激动剂具有桥接两个灵活的细胞外叶之间的鸿沟的关键作用，并巩固了激动剂诱导的裂缝闭合驱动进一步异构化，最终打开通道的观点。在谷氨酸受体家族中，NMDA敏感性通道的独特之处在于，它们需要甘氨酸和谷氨酸分别与GluN1和GluN2亚基上的同源区域结合，然后通道才能打开。为了研究从激动剂结合和解离中分离的门控反应，我们表征了单个NMDA受体的动力学机制，其配体结合裂缝通过跨叶设计的二硫桥锁定关闭。我们发现，锁定GluN1结构域对受体活性没有明显的影响，而锁定GluN2A结构域增加通道活性，而不减少可分辨的动力学状态的数量。基于这些结果，我们认为，谷氨酸，而不是甘氨酸激活NMDA受体次最大的功效。低谷氨酸功效可能代表神经递质维持对受体动力学的控制的机制，尽管与甘氨酸共享激活任务。
Glutamate-gated channels mediate fundamental brain processes, yet the mechanisms by which the neurotransmitter controls channel activation are incompletely understood. Structural studies revealed that the agonist has the critical role of bridging the divide between two flexible extracellular lobes and solidified the view that agonist-induced cleft-closure drives further isomerizations, which eventually open the channel. Within the glutamate receptor family, NMDA-sensitive channels are unique in their requirement that both glycine and glutamate bind to homologous regions on GluN1 and GluN2 subunits, respectively, before the channel can open. To study the gating reaction in separation from agonist binding and dissociation, we characterized the kinetic mechanism of individual NMDA receptors whose ligand-binding clefts were locked shut by disulfide bridges engineered across lobes. We found that locking GluN1 domains had no observable consequences on receptor activity, whereas locking GluN2A domains increased channel activity without reducing the number of resolvable kinetic states. Based on these results, we suggest that glutamate but not glycine activates NMDA receptors with submaximal efficacy. Low glutamate efficacy may represent a mechanism by which the neurotransmitter maintains control over receptor kinetics despite sharing with glycine the task of activation.