A structural model of agonist binding to the α3β4 neuronal nicotinic receptor

Abstract

1 (a3) 2 (b4) 3 is the most abundant type of neuronal nicotinic ACh receptor (nAChR) mediating cholinergic actions on the autonomic nervous system. Studies to refine or devise drugs selectively acting on (a3) 2 (b4) 3 receptors would benefit from a detailed description of the hitherto unclear agonist-binding domain. 2 The present study reports a three-dimensional model for the ligand-binding domain (LBD) of this receptor either in its unoccupied or agonist-bound conformation. The receptor model was based on the structure of the acetylcholine-binding protein (AChBP), and was obtained using molecular modelling techniques. 3 ACh, nicotine and cytisine (full agonists), muscarine (a selective agonist of muscarinic ACh receptors) and the allosteric modulator eserine were docked into the binding pockets of the receptor model. Simulated agonist -receptor complexes were compared with the agonist-binding complex of the AChBP, as well as of the (a4) 2 (b2) 3 type of nAChR, which is the commonest in the brain. 4 Agonist docking identified discrete amino-acid residues of the b subunits important for pharmacological selectivity of nAChRs. The predicted affinity of muscarine for the nAChR was low, suggesting the present model to be suitable for effective discrimination of nicotinic agonist binding versus nonselective cholinergic binding. Furthermore, the current model outlined a potential binding site for the allosteric modulator eserine, the site of action of which has remained elusive. 5 The present LBD model of the receptor in its free state provides a novel structural framework to interpret experimental observations and a useful template for future investigations to develop (a3) 2 (b4) 3 -selective ligands.

Design, synthesis and binding affinity of new nicotinic ligands

“…29 Rapid progress in the techniques developed for structural biology studies is expected to make the structure-based drug design approach possible; at present, the homology models based on the X-ray structures of Acetylcholine Binding Protein (AChBP), [30][31][32][33] representing only the extracellular part of the receptor which contains the ligand binding domain, have been used mainly to rationalize existing data. [34][35][36][37] Recently, models of the whole muscle-type 38 or α7 39 receptors, based on the cryo-electron microscopy data of the membrane domain collected on Torpedo Marmorata nAChRs, 40 have been developed, and hopefully they will overcome the limitations inherent to the previous models. To look for new ideas for the discovery of novel nicotinic ligands, we thought it interesting to apply the 3D database searching approach, 42 a method which was used, although with some differences, almost 20 years ago by Sheridan and Venkataraghavan.…”

Simvastatin Inhibits Catecholamine Secretion and Synthesis Induced by Acetylcholine via Blocking Na+and Ca2+Influx in Bovine Adrenal Medullary Cells

“…Among nAChRs, ␣3␤4 and ␣3␤4␣5 are expressed in adrenal medulla and autonomic neurons, and they have been found in the brain (Picciotto et al, 2001;Di Angelantonio et al, 2003). The agonist-binding site was located at the interface between ␣3 and ␤4 subunits, and was mostly composed of aromatic residues (Costa et al, 2003). A previous review (Léna and Changeux, 1993) proposed that noncompetitive blockers such as phencyclidine inhibit nAChRs at the area of interface between the nAChR protein and the membrane phospholipids.…”

Number and Locations of Agonist Binding Sites Required to Activate Homomeric Cys-Loop Receptors

“…First, residues contributing to the binding site are well known (Brejc et al, 2001;Sine, 2002). Among these residues, we chose to mutate Y190 from the principal face and W55 from the complementary face (O'Leary and White, 1992;Sine et al, 1994;Chen et al, 1995;Chiara et al, 1998;Costa et al, 2003); mutations of either residue alone or both residues together completely inhibit the response to agonist. Second, the single-channel current amplitudes span from undetectable with five LC subunits to 10 pA at Ϫ120 mV with five HC subunits, allowing distinction of channel opening episodes from receptors with different numbers of high-and low-conductance subunits.…”