Nicotine and Carbamylcholine Binding to Nicotinic Acetylcholine Receptors as Studied in AChBP Crystal Structures

Abstract

Nicotinic acetylcholine receptors are prototypes for the pharmaceutically important family of pentameric ligand-gated ion channels. Here we present atomic resolution structures of nicotine and carbamylcholine binding to AChBP, a water-soluble homolog of the ligand binding domain of nicotinic receptors and their family members, GABAA, GABAC, 5HT3 serotonin, and glycine receptors. Ligand binding is driven by enthalpy and is accompanied by conformational changes in the ligand binding site. Residues in the binding site contract around the ligand, with the largest movement in the C loop. As expected, the binding is characterized by substantial aromatic and hydrophobic contributions, but additionally there are close contacts between protein oxygens and positively charged groups in the ligands. The higher affinity of nicotine is due to a main chain hydrogen bond with the B loop and a closer packing of the aromatic groups. These structures will be useful tools for the development of new drugs involving nicotinic acetylcholine receptor-associated diseases.

Insight in nAChR subtype selectivity from AChBP crystal structures

“…AChBPs from Lymnaea stagnalis [17], Bulinus truncatus [18] and Aplysia californica [19] share only a 20-24% sequence identity with nAChRs ( Figure 1a) but display a striking structural resemblance with the Torpedo nAChR or mouse α1 nAChR protomer (Figure 1b). Nicotinic ligand binding to these AChBPs was assayed through different methods such as radioligand ( 125 I-αBungarotoxin) displacement, surface plasmon resonance [20][21][22], isothermal titration calorimetry [18] or intrinsic fluorescence quenching [19], and all the AChBPs were found to display a pharmacological profile close to that of the homopentameric α 7 nAChR [18,23].…”

“…A c c e p t e d M a n u s c r i p t 8 interactions in the stabilization of the nicotinic ligand cation [36,37]. Structures of AChBP complexes with these small agonists indeed reveal that the tertiary nitrogen of nicotine and epibatidine or the quaternary nitrogen of carbamylcholine interact with the negative charge generated by the π electrons from the side chains of the residues making up the aromatic cage [23,38]. Polar nitrogens can also contribute to ligand stabilization in the binding pocket through a hydrogen bond with the main chain carbonyl group of the conserved tryptophan from the B loop.…”

“…Polar nitrogens can also contribute to ligand stabilization in the binding pocket through a hydrogen bond with the main chain carbonyl group of the conserved tryptophan from the B loop. The nicotine-bound X-ray structure of AChBP [23] clearly shows that the carbonyl group of LsAChBP W143 is involved in a hydrogen bond with the nitrogen from the nicotine pyrrolidine moiety. This carbonyl group is stabilized by a hydrogen bond between the NH group from the peptide bond between residues 143 and 144 and the negatively charged D85 side chain.…”

A therapeutic vaccine for nicotine dependence: preclinical efficacy, and phase I safety and immunogenicity

“…Whilst nicotine and acetylcholine are structurally dissimilar, nicotine exerts its action by binding to the acetylcholine-binding pocket of nicotinic acetylcholine receptors [20]. Crossreactivity of the anti-nicotine antibodies to acetylcholine was measured by attempting to inhibit binding of tritium-labeled (-)-nicotine with acetylcholine ( Fig.…”

Structure-guided drug design: Conferring selectivity among neuronal nicotinic receptor and acetylcholine-binding protein subtypes

“…Several structures of agonist (epibatidine, nicotine, lobeline, carbamylcholine) and antagonist (α-conotoxin, methyllycaconitine, α-bungarotoxin) bound to AChBP have been reported [6,[9][10][11][12], and other structures have been resolved at high resolution or are under study. Hence, one now has a fairly comprehensive perspective on structures of the AChBP complexes.…”