Karlin A, Cox R N, Dipaola M, Holtzman E, Kao P N, Lobel P, Wang L, Yodh N
Ann N Y Acad Sci. 1986;463:53-69. doi: 10.1111/j.1749-6632.1986.tb21503.x.
The nicotinic acetylcholine receptor is a multisubunit, membrane-spanning protein that contains a gated, cation-conducting channel. Our approach to the understanding of the function of this receptor in molecular terms has been to locate its functionally significant sites in the sequences of its subunits and in its three-dimensional structure. In addition, we have tried to correlate transitions in the properties of these sites with functional transitions of the receptor. On binding acetylcholine, the nicotinic acetylcholine receptor enters at least two transient states, the open state and the rapid-onset desensitized state, and, in the continued presence of agonist, finally subsides into the slow-onset desensitized state. The transitions of the receptor between these various states are susceptible to regulation by acetylcholine and its congeners acting at one type of site and by a broad class of noncompetitive inhibitors (NCIs), including local anesthetics, acting at other sites. The chain composition of the receptor is alpha 2 beta gamma delta. The two acetylcholine binding sites are on the alpha chains, and two residues contributing to these sites, Cys-192 and Cys-193, have been identified. Furthermore, these adjacent Cys residues are cross-linked by a disulfide bond. In the quaternary structure of the receptor, the chains appear to be arranged in the order alpha gamma alpha beta delta around a central channel. Both the alpha and beta chains contribute to functionally significant NCI binding sites. The addition to receptor-rich membrane from Torpedo electric tissue of agonists (but not competitive antagonists) renders these NCI sites susceptible to photolabeling by the NCI quinacrine azide (QA). Furthermore, this susceptibility is transient, arising in milliseconds and subsiding in hundreds of milliseconds. These transiently susceptible sites are protected by other NCIs against photolabeling by QA. The time-course of the susceptibility and its dependence on agonist-concentration suggest that it might be the transient, rapid-onset desensitized state of the receptor that is most susceptible to photolabeling by QA.
烟碱型乙酰胆碱受体是一种多亚基跨膜蛋白，含有一个门控的阳离子传导通道。我们从分子层面理解该受体功能的方法是，在其亚基序列和三维结构中定位其功能重要位点。此外，我们试图将这些位点性质的转变与受体的功能转变联系起来。结合乙酰胆碱后，烟碱型乙酰胆碱受体至少进入两种瞬时状态，即开放状态和快速起效的脱敏状态，并且在激动剂持续存在的情况下，最终进入缓慢起效的脱敏状态。受体在这些不同状态之间的转变易受乙酰胆碱及其同系物作用于一种位点的调节，以及一大类非竞争性抑制剂（NCIs）（包括局部麻醉药）作用于其他位点的调节。受体的链组成是α2βγδ。两个乙酰胆碱结合位点在α链上，并且已经确定了对这些位点有贡献的两个残基，即半胱氨酸-192和半胱氨酸-193。此外，这些相邻的半胱氨酸残基通过二硫键交联。在受体的四级结构中，这些链似乎围绕着一个中央通道按αγ-αβδ的顺序排列。α链和β链都对功能重要的NCI结合位点有贡献。向来自电鳐电组织的富含受体的膜中添加激动剂（但不是竞争性拮抗剂）会使这些NCI位点易于被NCI叠氮喹吖因（QA）光标记。此外，这种易感性是瞬时的，在几毫秒内出现并在几百毫秒内消退。这些瞬时易感位点受到其他NCIs的保护，免受QA的光标记。易感性的时间进程及其对激动剂浓度的依赖性表明，最易被QA光标记的可能是受体的瞬时、快速起效的脱敏状态。
