Single-channel behavior of heteromeric α1β glycine receptors:: An attempt to detect a conformational change before the channel opens
Single-channel behavior of heteromeric α1β glycine receptors:: An attempt to detect a conformational change before the channel opens
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DOI：
10.1523/jneurosci.3424-04.2004
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发表时间：
2004-12-01
影响因子：
5.3
通讯作者：
Sivilotti, LG
中科院分区：
文献类型：
--
作者：
Burzomato, V;Beato, M;Sivilotti, LG
α 1 - β异聚体受体可能是成人甘氨酸受体的主要突触形式。通过拟合四种甘氨酸浓度（10-1000 muM）下大鼠α 1 β受体在人胚胎肾293细胞中表达的单通道记录，研究了它们的激活机制。通过比较实验停留时间分布、开闭相关性和浓度-开概率（Popen）曲线与模型的预测，评估每种机制及其拟合速率常数的充分性。只有当该机制具有三个甘氨酸结合位点，允许部分和完全配体开口，并预测存在开闭相关性时，才能获得良好的描述。该数据的一个重要特征是，在通道打开之前，随着更多的甘氨酸分子结合，结合亲和力增加。对这种正结合协同性的一种解释是，结合位点相互作用，每个位点感知其他位点的连接状态。另一种新颖的解释是，激动剂结合稳定了由与通道打开分离并先于通道打开的构象变化（“翻转”）产生的高亲和力受体形式。“交互”方案和翻转方案都很好地描述了我们的数据，但后者的自由参数较少，最重要的是它提供了一种亲和性增加的机制。区分这两种机制对于我们理解烟碱超家族激活的结构动力学和理解这些受体的突变非常重要。
The alpha1beta heteromeric receptors are likely to be the predominant synaptic form of glycine receptors in the adult. Their activation mechanism was investigated by fitting putative mechanisms to single-channel recordings obtained at four glycine concentrations (10-1000 muM) from rat alpha1beta receptors, expressed in human embryonic kidney 293 cells. The adequacy of each mechanism, with its fitted rate constants, was assessed by comparing experimental dwell time distributions, open-shut correlations, and the concentration-open probability (Popen) curve with the predictions of the model. A good description was obtained only if the mechanism had three glycine binding sites, allowed both partially and fully liganded openings, and predicted the presence of open-shut correlations. A strong feature of the data was the appearance of an increase in binding affinity as more glycine molecules bind, before the channel opens. One interpretation of this positive binding cooperativity is that binding sites interact, each site sensing the state of ligation of the others. An alternative, and novel, explanation is that agonist binding stabilizes a higher affinity form of the receptor that is produced by a conformational change ("flip") that is separate from, and precedes, channel opening. Both the "interaction" scheme and the flip scheme describe our data well, but the latter has fewer free parameters and above all it offers a mechanism for the affinity increase. Distinguishing between the two mechanisms will be important for our understanding of the structural dynamics of activation in the nicotinic superfamily and is important for our understanding of mutations in these receptors.