The two major nicotinic acetylcholine receptors (nAChRs) in the brain are the α4β2 and α7 subtypes. A "methyl scan" of the pyrrolidinium ring was used to detect differences in nicotine's interactions with these two receptors. Each methylnicotine was investigated using voltage-clamp and radioligand binding techniques. Methylation at each ring carbon elicited unique changes in nicotine's receptor interactions. Replacing the 1'-N-methyl with an ethyl group or adding a second 1'-N-methyl group significantly reduced interaction with α4β2 but not α7 receptors. The 2'-methylation uniquely enhanced binding and agonist potency at α7 receptors. Although 3'- and 5'-trans-methylations were much better tolerated by α7 receptors than α4β2 receptors, 4'-methylation decreased potency and efficacy at α7 receptors much more than at α4β2 receptors. Whereas cis-5'-methylnicotine lacked agonist activity and displayed a low affinity at both receptors, trans-5'-methylnicotine retained considerable α7 receptor activity. Differences between the two 5'-methylated analogs of the potent pyridyl oxymethylene-bridged nicotine analog A84543 were consistent with what was found for the 5'-methylnicotines. Computer docking of the methylnicotines to the Lymnaea acetylcholine binding protein crystal structure containing two persistent waters predicted most of the changes in receptor affinity that were observed with methylation, particularly the lower affinities of the cis-methylnicotines. The much smaller effects of 1'-, 3'-, and 5'-methylations and the greater effects of 2'- and 4'-methylations on nicotine α7 nAChR interaction might be exploited for the design of new drugs based on the nicotine scaffold. SIGNIFICANCE STATEMENT: Using a comprehensive "methyl scan" approach, we show that the orthosteric binding sites for acetylcholine and nicotine in the two major brain nicotinic acetylcholine receptors interact differently with the pyrrolidinium ring of nicotine, and we suggest reasons for the higher affinity of nicotine for the heteromeric receptor. Potential sites for nicotine structure modification were identified that may be useful in the design of new drugs targeting these receptors.

中文翻译：

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尼古丁吡咯烷鎓环的甲基扫描揭示了其与α7和α4β2烟碱乙酰胆碱受体相互作用的显着差异。

脑中的两个主要烟碱型乙酰胆碱受体（nAChRs）是α4β2和α7亚型。使用吡咯烷鎓环的“甲基扫描”来检测尼古丁与这两个受体相互作用的差异。使用电压钳和放射性配体结合技术研究了每种甲基烟碱。每个环碳上的甲基化引起尼古丁受体相互作用的独特变化。用乙基取代1'-N-甲基或添加第二个1'-N-甲基可显着降低与α4β2的相互作用，但不能降低与α7受体的相互作用。2'-甲基化独特地增强了对α7受体的结合和激动剂效力。尽管α7受体比α4β2受体对3'-和5'-反甲基的耐受性更好，但4' -甲基化作用在α7受体上的效力和功效比在α4β2受体上更大。顺式5'-甲基烟碱缺乏激动剂活性，并且对两种受体均显示低亲和力，而反式5'-甲基烟碱则保留了相当大的α7受体活性。强大的吡啶基甲醛亚甲基烟碱类似物A84543的两个5'-甲基化类似物之间的差异与5'-甲基烟碱的发现一致。甲基烟碱与包含两个持续水的Lymnaea乙酰胆碱结合蛋白晶体结构的计算机对接预测了甲基化所观察到的大多数受体亲和力变化，特别是顺式甲基烟碱的亲和力较低。1'-，3'-和5'-甲基化的作用小得多，而2' 尼古丁α7nAChR相互作用上的-和4'-甲基化可能被用于设计基于尼古丁支架的新药。意义声明：使用全面的“甲基扫描”方法，我们显示了两种主要脑型烟碱型乙酰胆碱受体中乙酰胆碱和尼古丁的正构结合位点与尼古丁的吡咯烷鎓环相互作用不同，并且我们提出了尼古丁亲和力更高的原因为异聚受体。确定了尼古丁结构修饰的潜在位点，这些位点可能对设计靶向这些受体的新药物有用。我们表明，在两个主要的大脑烟碱型乙酰胆碱受体中，乙酰胆碱和尼古丁的正构结合位点与尼古丁的吡咯烷鎓环相互作用不同，并且我们提出了尼古丁对异聚受体更高亲和力的原因。确定了尼古丁结构修饰的潜在位点，这些位点可能对设计靶向这些受体的新药物有用。我们表明，在两个主要的大脑烟碱型乙酰胆碱受体中，乙酰胆碱和尼古丁的正构结合位点与尼古丁的吡咯烷鎓环相互作用不同，并且我们提出了尼古丁对异聚受体更高亲和力的原因。确定了尼古丁结构修饰的潜在位点，这些位点可能对设计靶向这些受体的新药物有用。