The nicotinic receptor ligand binding domain

Sine, Steven M.

doi:10.1002/neu.10139

Cited by 162 publications

(156 citation statements)

References 108 publications

(117 reference statements)

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“…This soluble acetylcholine binding protein (AChBP) was more amenable to x-ray crystallography because of the natural lack of a membrane spanning domain and therefore it was solved at higher resolution (2.7 Å). AChBP has up to 23% sequence identity with the LBD of the complete receptors, and it is most similar to that in the human ␣7 (h␣7) subunit (21,22). AChBP structure has subsequently been solved with ligands bound [Protein Data Bank ID codes 1UV6 (carbamylcholine), 1UW6 (nicotine), and 1UX2 (Hepes)] (23).…”

mentioning

confidence: 99%

A gating mechanism proposed from a simulation of a human α7 nicotinic acetylcholine receptor

Law

Henchman

McCammon

2005

Proc. Natl. Acad. Sci. U.S.A.

134

142

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The nicotinic acetylcholine receptor is a well characterized ligandgated ion channel, yet a proper description of the mechanisms involved in gating, opening, closing, ligand binding, and desensitization does not exist. Until recently, atomic-resolution structural information on the protein was limited, but with the production of the x-ray crystal structure of the Lymnea stagnalis acetylcholine binding protein and the EM image of the transmembrane domain of the torpedo electric ray nicotinic channel, we were provided with a window to examine the mechanism by which this channel operates. A 15-ns all-atom simulation of a homology model of the homomeric human ␣7 form of the receptor was conducted in a solvated palmitoyl-2-oleoyl-sn-glycerol-phosphatidylcholine bilayer and examined in detail. The receptor was unliganded. The structure undergoes a twist-to-close motion that correlates movements of the C loop in the ligand binding domain, via the ␤10-strand that connects the two, with the 10°rotation and inward movement of two nonadjacent subunits. The Cys loop appears to act as a stator around which the ␣-helical transmembrane domain can pivot and rotate relative to the rigid ␤-sheet binding domain. The M2-M3 loop may have a role in controlling the extent or kinetics of these relative movements. All of this motion, along with essential dynamics analysis, is suggestive of the direction of larger motions involved in gating of the channel.T he nicotinic acetylcholine receptor is one of the best-studied ligand-gated ion channels (LGICs) (1). It has been found to have a role in a wide range of pathological conditions and diseases including epilepsy (2), schizophrenia (3), Alzheimer's (4), Parkinson's (5), neuromuscular diseases (6), inflammation (7), nicotine addiction (8), and addiction to other drugs such as alcohol (9) and cocaine (10), as well as a role in anesthetic action (11). The nicotinic acetylcholine receptor is a member of a superfamily of pentameric receptors that include the serotonin (excitory), GABA, and glycine (inhibitory) receptors that are all involved in the transmission and modification of electrical signals in excitory cells. The family is known as the Cys-loop LGIC family, because of a conserved pair of linked cysteines in the N-terminal domain of the receptor (12). Within the superfamily, an array of different nicotinic receptor subunits exists (13,14), making different subunit assemblies possible, for different roles, in different cell types. In all of these receptors, the ligand binds at the interface between the ␣ and other subunits of the ligand binding domain (LBD). This event begins a chain reaction of conformational changes within the receptor that transmits the message of ligand binding to the transmembrane domain (TMD), which then opens to allow the passage of ions through the channel. Although the genetics, kinetics, electrophysiology, and many topological aspects are well characterized for the nicotinic receptor (15, 16), the exact nature of the structural rearrangments involved in activ...

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mentioning

confidence: 99%

A gating mechanism proposed from a simulation of a human α7 nicotinic acetylcholine receptor

Law

Henchman

McCammon

2005

Proc. Natl. Acad. Sci. U.S.A.

134

142

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“…The superfamily of pentameric ligand-gated ion channels activated by acetylcholine (ACh), 1 ␥-aminobutyric acid, glycine, and serotonin mediate rapid synaptic transmission throughout the nervous system. Their strategic position in the pathway of information flow makes them strategic loci for disease processes as well as logical targets for drugs used clinically.…”

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confidence: 99%

Curariform Antagonists Bind in Different Orientations to Acetylcholine-binding Protein

Gao

Bern

Little

et al. 2003

Journal of Biological Chemistry

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Acetylcholine-binding protein (AChBP) recently emerged as a prototype for relating structure to function of the ligand binding domain of nicotinic acetylcholine receptors (AChRs). To understand interactions of competitive antagonists at the atomic structural level, we studied binding of the curare derivatives d-tubocurarine (d-TC) and metocurine to AChBP using computational methods, mutagenesis, and ligand binding measurements. To account for protein flexibility, we used a 2-ns molecular dynamics simulation of AChBP to generate multiple snapshots of the equilibrated dynamic structure to which optimal docking orientations were determined. Our results predict a predominant docking orientation for both d-TC and metocurine, but unexpectedly, the bound orientations differ fundamentally for each ligand. At one subunit interface of AChBP, the side chain of Tyr-89 closely approaches a positively charged nitrogen in d-TC but is farther away from the equivalent nitrogen in metocurine, whereas, at the opposing interface, side chains of Trp-53 and Gln-55 closely approach the metocurine scaffold but not that of d-TC. The different orientations correspond to ϳ170°rotation and ϳ30°d egree tilt of the curare scaffold within the binding pocket. Mutagenesis of binding site residues in AChBP, combined with measurements of ligand binding, confirms the different docking orientations. Thus structurally similar ligands can adopt distinct orientations at receptor binding sites, posing challenges for interpreting structure-activity relationships for many drugs.The superfamily of pentameric ligand-gated ion channels activated by acetylcholine (ACh), 1 ␥-aminobutyric acid, glycine, and serotonin mediate rapid synaptic transmission throughout the nervous system. Their strategic position in the pathway of information flow makes them strategic loci for disease processes as well as logical targets for drugs used clinically. The synaptic protrusion of these channels contains a ligand binding domain, which harbors structural components specialized for binding agonists and competitive antagonists. The ligand binding domain is formed at interfaces between subunits where conserved aromatic and hydrophobic residues are clustered (1-3). In the nicotinic receptor found at the motor endplate, the alpha subunit forms one face of the ligand binding domain, whereas a non-alpha subunit, gamma, delta or epsilon, forms the other face. Studies of subunit chimeras and site-directed mutations have pinpointed key residues critical for stabilizing bound agonists and antagonists. In particular, residues on both alpha and non-alpha subunits are critical for binding competitive antagonists of the curare family, suggesting that these antagonists prevent ACh binding by bridging the subunit interface (4).The potential for understanding ligand binding at the atomic structural level recently arose with the discovery of acetylcholine-binding protein (AChBP) (5), a soluble protein homologous to the ligand binding domains of pentameric ligand-gated ion channels. Moreover, ...

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“…Given that the residue 153 has been shown to be involved in agonist binding, it is probable that the mutation may affect the affinity ratio of closed and open state and that these changes are more significant for levamisole than for ACh. The mutated amino acids form part of two different binding loops, B (␣Asp-152, ␣Gly-153, and ␣Ser-154) and C (␣-ins191), which contain residues directly contributing to the ACh binding pocket in ␣ subunits (30,31). Although , and Cys-193 form a barrier to entry and escape of agonist (30,31), a proline insertion in position 191 does not introduce changes in the activation by levamisole of the AChR.…”

Section: Achrs By Levamisolementioning

confidence: 99%

“…The mutated amino acids form part of two different binding loops, B (␣Asp-152, ␣Gly-153, and ␣Ser-154) and C (␣-ins191), which contain residues directly contributing to the ACh binding pocket in ␣ subunits (30,31). Although , and Cys-193 form a barrier to entry and escape of agonist (30,31), a proline insertion in position 191 does not introduce changes in the activation by levamisole of the AChR. This observation is consistent with the lack of effects reported previously (32) for mutations of other nearby residues.…”

Section: Achrs By Levamisolementioning

confidence: 99%

Molecular Basis of the Differential Sensitivity of Nematode and Mammalian Muscle to the Anthelmintic Agent Levamisole

Rayes

Rosa

Bartos

et al. 2004

Journal of Biological Chemistry

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Levamisole is an anthelmintic agent that exerts its therapeutic effect by acting as a full agonist of the nicotinic receptor (AChR) of nematode muscle. Its action at the mammalian muscle AChR has not been elucidated to date despite its wide use as an anthelmintic in humans and cattle. By single channel and macroscopic current recordings, we investigated the interaction of levamisole with the mammalian muscle AChR. Levamisole activates mammalian AChRs. However, single channel openings are briefer than those activated by acetylcholine (ACh) and do not appear in clusters at high concentrations. The peak current induced by levamisole is about 3% that activated by ACh. Thus, the anthelmintic acts as a weak agonist of the mammalian AChR. Levamisole also produces open channel blockade of the AChR. The apparent affinity for block (190 M at ؊70 mV) is similar to that of the nematode AChR, suggesting that differences in channel activation kinetics govern the different sensitivity of nematode and mammalian muscle to anthelmintics. To identify the structural basis of this different sensitivity, we performed mutagenesis targeting residues in the ␣ subunit that differ between vertebrates and nematodes. The replacement of the conserved ␣Gly-153 with the homologous glutamic acid of nematode AChR significantly increases the efficacy of levamisole to activate channels. Channel activity takes place in clusters having two different kinetic modes. The kinetics of the high open probability mode are almost identical when the agonist is ACh or levamisole. It is concluded that ␣Gly-153 is involved in the low efficacy of levamisole to activate mammalian muscle AChRs.At the neuromuscular junction, acetylcholine (ACh) 1 mediates fast neurotransmission by activating nicotinic receptors (AChRs). AChRs in nematode muscle are targets for anthelmintic chemotherapy. Levamisole and pyrantel are two widely used anthelmintic drugs. By binding to the AChR they lead to a depolarization of the somatic muscle of nematodes. The efficacy of these drugs is based on their ability to act as full agonists of AChRs in nematodes (1). Contractility and membrane potential measurements have shown that the nematode axial muscle is 10 -100 times more sensitive to the acute action of pyrantel and levamisole than the rat muscle (2). The molecular bases of this selectivity have not been yet elucidated. The kinetics of activation of nematode AChRs by levamisole has been studied in several preparations from parasite muscle (1, 3), but its action on mammalian muscle AChRs has not been described to date. The effects of levamisole on human neuronal ␣ 3 ␤ 2 and ␣ 3 ␤ 4 AChRs have been studied recently (4) with the voltage clamp method. It was shown that levamisole behaves as a weak partial agonist, an allosteric modulator, and an open channel blocker of neuronal AChRs (4).ACh is responsible for neuromuscular transmission in nematodes (1). In Caenorhabditis elegans muscle, levamisoleactivated AChRs are composed of the unc-38 subunit, which encodes an ␣ subunit, and lev-1 and...

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The nicotinic receptor ligand binding domain

Cited by 162 publications

References 108 publications

A gating mechanism proposed from a simulation of a human α7 nicotinic acetylcholine receptor

A gating mechanism proposed from a simulation of a human α7 nicotinic acetylcholine receptor

Curariform Antagonists Bind in Different Orientations to Acetylcholine-binding Protein

Molecular Basis of the Differential Sensitivity of Nematode and Mammalian Muscle to the Anthelmintic Agent Levamisole

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