[3H]Epibatidine Photolabels Non-equivalent Amino Acids in the Agonist Binding Site of Torpedo and α4β2 Nicotinic Acetylcholine Receptors

Abstract

Nicotinic acetylcholine receptor (nAChR) agonists, such as epibatidine and its molecular derivatives, are potential therapeutic agents for a variety of neurological disorders. In order to identify determinants for subtype-selective agonist binding, it is important to determine whether an agonist binds in a common orientation in different nAChR subtypes. To compare the mode of binding of epibatidine in a muscle and a neuronal nAChR, we photolabeled Torpedo ␣ 2 ␤␥␦ and expressed human ␣4␤2

Identification of novel α7 nicotinic receptor ligands by in silico screening against the crystal structure of a chimeric α7 receptor ligand binding domain

“…Furthermore, no formation of hydrogen bonds between the ligand and protein binding site is observed. It is noted that in a recent study by Srivastava et al in which photolabeling of the human α4β2 nAChR with azidoepibatidine was combined with docking experiments in a α4β2 homology model, evidence for two distinct binding orientations of epibatine was obtained 25 . Interestingly, the proposed binding poses of epibatidine resemble the two docking poses that we obtained for compound 4 .…”

A Structural and Mutagenic Blueprint for Molecular Recognition of Strychnine and d-Tubocurarine by Different Cys-Loop Receptors

“…This adds a new level of diversity among CLRs, whose heterogeneity is known to arise from homomeric and heteromeric assemblies of α- and non-α subunits with different pharmacological properties. Multiple orientations of the same ligand in binding sites of the same AChBP molecule revealed in our work may be present in complexes with true CLRs [38] .…”

Photolabeling a Nicotinic Acetylcholine Receptor (nAChR) with an (α4)3(β2)2 nAChR-Selective Positive Allosteric Modulator

“…Photoaffinity labeling identifies amino acid residues within the protein structure that are in direct contact with a bound drug and differentiates them from amino acids not contributing to the binding site but important for drug action, which can be identified by mutational analyses. Even though CMPI bound with .30-fold higher affinity in the Torpedo nAChR ion channel than in the transmitter binding sites, 55 in the g subunit, suggests that CMPI binds preferentially to the ACh binding site at the a-g interface, as is seen for d-tubocurarine, the classic muscle-type nAChR competitive antagonist, which photolabels the same amino acids in the ACh binding site as CMPI (Chiara and Cohen, 1997;Chiara et al, 1999 (Chiara and Cohen, 1997;Nirthanan et al, 2005;Srivastava et al, 2009 (Hamouda et al, 2013(Hamouda et al, , 2015 , which indicates that CMPI does not bind to the dFBr/ physostigmine/galanthamine allosteric sites in the ECD at the a/g subunit interface near the entry of the ACh binding site or in the vestibule of the ion channel.…”