Interactions between 2′-fluoro-(carbamoylpyridinyl)deschloroepibatidine analogues and acetylcholine-binding protein inform on potent antagonist activity against nicotinic receptors

Abstract

Low-nanomolar binding constants were recorded for a series of six 2′-fluoro-(carbamoylpyridinyl)deschloroepibatidine analogues with acetylcholine-binding protein (AChBP). The crystal structures of three complexes with AChBP reveal details of molecular recognition in the orthosteric binding site and imply how the other three ligands bind. Comparisons exploiting AChBP as a surrogate for α4β2 and α7 nicotinic acetylcholine receptors (nAChRs) suggest that the key interactions are conserved. The ligands interact with the same residues as the archetypal nAChR agonist nicotine yet display greater affinity, thereby rationalizing their in vivo activity as potent antagonists of nicotine-induced antinociception. An oxyanion-binding site is formed on the periphery of the AChBP orthosteric site by Lys42, Asp94, Glu170 and Glu210. These residues are highly conserved in the human α4, β2 and α7 nAChR sequences. However, specific sequence differences are discussed that could contribute to nAChR subtype selectivity and in addition may represent a point of allosteric modulation. The ability to engage with this peripheral site may explain, in part, the function of a subset of ligands to act as agonists of α7 nAChR.

Delineating the activity of the potent nicotinic acetylcholine receptor agonists (+)-anatoxin-a and (−)-hosieine-A

“…The (+)anatoxin-a carbonyl accepts a hydrogen bond from a water molecule that in turn participates in hydrogen bonds to the main-chain amide of Ile135 and the carbonyl of Ile123. This hydration feature is common to other structures, for example AChBP-nicotine complexes (Sauguet et al, 2015;Shahsavar et al, 2016;Bueno et al, 2022). The (+)-anatoxin-a O atom occupies almost exactly the same position as the pyridine N atom of the agonist nicotine, representing an overlap of two hydrogen-bond acceptors in the orthosteric site.…”

“…Tyr72 may contribute to cation-interactions. In some complexes between AcAChBP and tertiary amines, for example epibatidine derivatives (Bueno et al, 2022), the hydroxyl group of Tyr110 forms a hydrogen bond to the amine. In the (+)-anatoxin-a complex the separation (over 4 A ˚) and orientation of the functional groups precludes such an interaction.…”