title: Probing for and Quantifying Agonist Hydrogen Bonds in α6β2 Nicotinic Acetylcholine Receptors.
abstract: 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.
authors.affiliation: Division of Chemistry and Chemical Engineering and ‡Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Post
authors.affiliation: Division of Chemistry and Chemical Engineering and ‡Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Henry A
authors.initials: HA
authors.lastname: Lester
authors.affiliation: Division of Chemistry and Chemical Engineering and ‡Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Dennis A
authors.identifier: 0000-0003-1464-2461
authors.initials: DA
authors.lastname: Dougherty
mesh_terms: D000109:Acetylcholine / Q000737:chemistry* / Q000494:pharmacology; D000818:Animals; D015870:Gene Expression; D006860:Hydrogen Bonding; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009538:Nicotine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000737:chemistry* / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D051381:Rats; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; C559463:alpha6beta2 nicotinic acetylcholine receptor; C070297:N'-methylnicotinium; D009538:Nicotine; D014364:Tryptophan; D000109:Acetylcholine