Probing for and Quantifying Agonist Hydrogen Bonds in α6β2 Nicotinic Acetylcholine Receptors

Biochemistry. 2017 Apr 4;56(13):1836-1840. doi: 10.1021/acs.biochem.7b00213. Epub 2017 Mar 21.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Acetylcholine / chemistry*
  • Acetylcholine / pharmacology
  • Animals
  • Gene Expression
  • Hydrogen Bonding
  • Mutagenesis, Site-Directed
  • Mutation
  • Nicotine / analogs & derivatives*
  • Nicotine / chemistry
  • Nicotine / pharmacology
  • Nicotinic Agonists / chemistry*
  • Nicotinic Agonists / pharmacology
  • Patch-Clamp Techniques
  • Protein Binding
  • Rats
  • Receptors, Nicotinic / chemistry*
  • Receptors, Nicotinic / genetics
  • Receptors, Nicotinic / metabolism
  • Thermodynamics
  • Tryptophan / chemistry
  • Tryptophan / metabolism
  • Xenopus laevis

Substances

  • Nicotinic Agonists
  • Receptors, Nicotinic
  • alpha6beta2 nicotinic acetylcholine receptor
  • N'-methylnicotinium
  • Nicotine
  • Tryptophan
  • Acetylcholine