Chasing the open-state structure of pentameric ligand-gated ion channels.
Chasing the open-state structure of pentameric ligand-gated ion channels.
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DOI：
10.1085/jgp.201711803
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发表时间：
2017-12-04
期刊：
影响因子：
--
通讯作者：
Grosman C
中科院分区：
文献类型：
--
作者：
Gonzalez-Gutierrez G;Wang Y;Cymes GD;Tajkhorshid E;Grosman C
五聚体配体门控离子通道家族的成员已经结晶成不同的构象，其中包括跨膜孔惊人宽的构象。Gonzalez-Gutierrez等人的研究表明，动物成员的明渠构象更类似于窄孔模型。近二十年来，离子通道的结构表征取得了显著的进展。然而，将定义良好的功能状态明确地分配给所获得的结构模型是一项挑战。以烟碱受体通道超家族（也称为五聚体配体门控离子通道[plgic]）为例，在分辨率高于4.0 Å的结构基础上，提出了两种不同类型的开放通道构象模型。在跨膜孔水平上，来自Gloeobacter violaceus的质子门控pLGIC （GLIC）和无脊椎动物谷氨酸门控Cl -通道（GluCl）的开放状态模型非常相似，但甘氨酸受体（GlyR）的开放状态模型要宽得多。事实上，在这两类模型中，离子渗透轴与孔最窄处（位置- 2 '）的Cα原子之间的平均距离相差约2 Å，当涉及到理解离子传导和电荷选择性的物理化学基础时，这是一个很大的差异。在这里，我们利用了面向孔隙位置9 '的突变的极端开放通道稳定效应。我们发现I9'A突变减缓了GLIC进入脱敏状态的速度，以至于在pH值为4.5的溶液在细胞外侧应用几分钟后，宏观电流仅略有衰减。我们结晶（在pH 4.5下）两个携带该突变的GLIC变体，并将其结构解析为3.12 Å和3.36 Å。此外，我们使用不同的开放通道结构模型进行了离子渗透和微毒素阻滞的全原子分子动力学模拟。基于这些结果，我们倾向于这样一种观点，即来自动物的plgic的开放通道结构更接近于窄通道模型（GLIC和GluCl），而不是GlyR。
Members of the pentameric ligand-gated ion channel family have been crystallized in different conformations, including one in which the transmembrane pore is surprisingly wide. Gonzalez-Gutierrez et al. show that the open-channel conformation of animal members is more similar to the models with narrow pores. Remarkable advances have been made toward the structural characterization of ion channels in the last two decades. However, the unambiguous assignment of well-defined functional states to the obtained structural models has proved challenging. In the case of the superfamily of nicotinic-receptor channels (also referred to as pentameric ligand-gated ion channels [pLGICs]), for example, two different types of model of the open-channel conformation have been proposed on the basis of structures solved to resolutions better than 4.0 Å. At the level of the transmembrane pore, the open-state models of the proton-gated pLGIC from Gloeobacter violaceus (GLIC) and the invertebrate glutamate-gated Cl– channel (GluCl) are very similar to each other, but that of the glycine receptor (GlyR) is considerably wider. Indeed, the mean distances between the axis of ion permeation and the Cα atoms at the narrowest constriction of the pore (position −2′) differ by ∼2 Å in these two classes of model, a large difference when it comes to understanding the physicochemical bases of ion conduction and charge selectivity. Here, we take advantage of the extreme open-channel stabilizing effect of mutations at pore-facing position 9′. We find that the I9′A mutation slows down entry into desensitization of GLIC to the extent that macroscopic currents decay only slightly by the end of pH 4.5 solution applications to the extracellular side for several minutes. We crystallize (at pH 4.5) two variants of GLIC carrying this mutation and solve their structures to resolutions of 3.12 Å and 3.36 Å. Furthermore, we perform all-atom molecular dynamics simulations of ion permeation and picrotoxinin block, using the different open-channel structural models. On the basis of these results, we favor the notion that the open-channel structure of pLGICs from animals is much closer to that of the narrow models (of GLIC and GluCl) than it is to that of the GlyR.
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