Refined structure of the nicotinic acetylcholine receptor at 4 Å resolution
Refined structure of the nicotinic acetylcholine receptor at 4 Å resolution
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DOI：
10.1016/j.jmb.2004.12.031
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发表时间：
2005-03-04
影响因子：
5.6
通讯作者：
Unwin, N
中科院分区：
文献类型：
--
作者：
Unwin, N
我们提出了一个精细模型的膜相关电鳐乙酰胆碱（ACh）受体在4埃分辨率。从螺旋管的342个电子图像中获得了改进的实验密度图，并通过标准晶体学方法将对应于单个分子的密度放入人工晶胞中后，得到了R因子为36.7%（无R因子为37.9%）的精细结构。沿沿着螺旋层线的实验和计算的相位之间的协议被用来监测在细化的进展，并给出一个独立的测量的准确性。原子模型允许详细描述整个受体的封闭通道的形式，包括配体结合和细胞内的结构域，这还没有以前被解释在化学水平。我们确认，两个配体结合的α亚基具有不同的扩展构象从其他三个亚基在封闭通道，并确定几个相互作用的两对亚基接口，并在α亚基，这可能是负责其“扭曲”的结构。α亚基的乙酰胆碱配位氨基酸侧链在闭合通道中相距很远，表明激活后发生了局部重排，涉及结合乙酰胆碱分子周围的环B和C的闭合。的α亚基的结构与具有配体存在的乙酰胆碱BP的结构的比较，表明如何本地化重排克服的扭曲，并启动与开放的通道的旋转运动。通道的两个前庭都是强负电性的，在膜孔的任一入口处提供阳离子稳定环境。进入细胞内侧的孔进一步受到窄的侧窗的影响，这将被预期以静电方式筛选出错误电荷和大小的离子。(C)2004爱思唯尔有限公司保留所有权利。
We present a refined model of the membrane-associated Torpedo acetylcholine (ACh) receptor at 4Angstrom resolution. An improved experimental density map was obtained from 342 electron images of helical tubes, and the refined structure was derived to an R-factor of 36.7% (R-free 37.9%) by standard crystallographic methods, after placing the densities corresponding to a single molecule into an artificial unit cell. The agreement between experimental and calculated phases along the helical layer-lines was used to monitor progress in the refinement and to give an independent measure of the accuracy. The atomic model allowed a detailed description of the whole receptor in the closed-channel form, including the ligand-binding and intracellular domains, which have not previously been interpreted at a chemical level. We confirm that the two ligand-binding alpha subunits have a different extended conformation from the three other subunits in the closed channel, and identify several interactions on both pairs of subunit interfaces, and within the alpha subunits, which may be responsible for their "distorted" structures. The ACh-coordinating amino acid side-chains of the alpha subunits are far apart in the closed channel, indicating that a localised rearrangement, involving closure of loops B and C around the bound ACh molecule, occurs upon activation. A comparison of the structure of the alpha subunit with that of AChBP having ligand present, suggests how the localised rearrangement overcomes the distortions and initiates the rotational movements associated with opening of the channel. Both vestibules of the channel are strongly electronegative, providing a cation-stabilising environment at either entrance of the membrane pore. Access to the pore on the intracellular side is further influenced by narrow lateral windows, which would be expected to screen out electrostatically ions of the wrong charge and size. (C) 2004 Elsevier Ltd. All rights reserved.