Probing for and Quantifying Agonist Hydrogen Bonds in α6β2 Nicotinic Acetylcholine Receptors
作者:Michael R. Post、Henry A. Lester、Dennis A. Dougherty
DOI:10.1021/acs.biochem.7b00213
日期:2017.4.4
Designing subtype-selective agonists for neuronal nicotinic acetylcholine receptors is a challenging and significant goal aided by intricate knowledge of each subtype’s binding patterns. We previously reported that in α6β2 receptors, acetylcholine makes a functional cation−π interaction with Trp149, but nicotine and TC299423 do not, suggesting a distinctive binding site. This work explores hydrogen binding at the backbone carbonyl associated with α6β2 Trp149. Substituting residue i + 1, Thr150, with its α-hydroxy analogue (Tah) attenuates the carbonyl’s hydrogen bond accepting ability. At α6(T150Tah)β2, nicotine shows a 24-fold loss of function, TC299423 shows a modest loss, and acetylcholine shows no effect. Nicotine was further analyzed via a double-mutant cycle analysis utilizing N′-methylnicotinium, which indicated a hydrogen bond in α6β2 with a ΔΔG of 2.6 kcal/mol. Thus, even though nicotine does not make the conserved cation−π interaction with Trp149, it still makes a functional hydrogen bond to its associated backbone carbonyl.
设计对神经烟碱型乙酰胆碱受体的亚型选择性激动剂是一个具有挑战性和重要意义的目标,这有赖于对各亚型结合模式精细知识的辅助。我们之前报道,在α6β2受体中,乙酰胆碱与Trp149发生了功能性的阳离子−π相互作用,而尼古丁和TC299423则没有,这表明存在一个独特的结合位点。这项工作探索了与α6β2受体中Trp149相关的骨架羰基上的氢键作用。将残基i + 1,即Thr150,替换为其α-羟基类似物(Tah)会削弱羰基的氢键接受能力。在α6(T150Tah)β2受体中,尼古丁显示出24倍的功能丧失,TC299423显示出适度损失,而乙酰胆碱则无影响。通过利用N′-甲基尼古丁离子进行的二重突变环分析进一步分析了尼古丁,结果表明在α6β2中存在一个氢键,其ΔΔG为2.6 kcal/mol。因此,尽管尼古丁没有与Trp149形成保守的阳离子−π相互作用,但它仍能与其相关的骨架羰基形成功能性的氢键。