Action of nicotine and analogs on acetylcholine receptors having mutations of transmitter-binding site residue G153 (original) (raw)
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Activation of muscle nicotinic acetylcholine receptor channels by nicotinic and muscarinic agonists
British Journal of Pharmacology, 1999
The dose-response parameters of recombinant mouse adult neuromuscular acetylcholine receptor channels (nAChR) activated by carbamylcholine, nicotine, muscarine and oxotremorine were measured. Rate constants for agonist association and dissociation, and channel opening and closing, were estimated from single-channel kinetic analysis. 2 The dissociation equilibrium constants were (mM): ACh (0.16)5oxotremorine M (0.6)5carbamylcholine (0.8)5nicotine (2.6). 3 The gating equilibrium constants (opening/closing) were: ACh (45)4carbamylcholine (5.1)4oxotremorine M (0.6)4nicotine (0.5)4muscarine (0.15). 4 Rat neuronal a 4 b 2 nAChR can be activated by all of the agonists. However, detailed kinetic analysis was impossible because the recordings lacked clusters representing the activity of a single receptor complex. Thus, the number of channels in the patch was unknown and the activation rate constants could not be determined. 5 Considering both receptor anity and agonist ecacy, muscarine and oxotremorine are signi®cant agonists of muscle-type nAChR. The results are discussed in terms of structure-function relationships at the nAChR transmitter binding site.
ACS Chemical Biology, 2012
The nicotinic acetylcholine receptors (nAChRs) are a family of closely related but pharmacologically distinct neurotransmitter-gated ion channels. They are therapeutic targets for a wide range of neurological disorders, and a key issue in drug development is selective targeting among the greater than 20 subtypes of nAChRs that are known. The present work evaluates a proposed hydrogen bonding interaction involving a residue known as the "loop B glycine" that distinguishes receptors that are highly responsive to ACh and nicotine from those that are much less so. We have performed structure-function studies on the loop B site, including unnatural amino acid mutagenesis, in three different nAChR subtypes and found that the correlation between agonist potency and this residue is strong. Low potency receptor subtypes have a glycine at this key site, and mutation to a residue with a side chain converts a low potency receptor to a high potency receptor. Innately high potency receptors have a lysine at the loop B site and show a decrease in potency for the reverse mutation (i.e. introducing a glycine). This residue lies outside of the agonist binding site, and studies of other residues at the agonist binding site show that the details of how changes at the loop B glycine site impact agonist potency vary for differing receptor subtypes. This suggests a model in which the loop B residue influences the global shape of the agonist binding site rather than modulating any specific interaction.
Aaps Journal, 2009
The acronym SePhaChARNS, for "selective pharmacological chaperoning of acetylcholine receptor number and stoichiometry," is introduced. We hypothesize that SePhaChARNS underlies classical observations that chronic exposure to nicotine causes "upregulation" of nicotinic receptors (nAChRs). If the hypothesis is proven, (1) SePhaChARNS is the molecular mechanism of the first step in neuroadaptation to chronic nicotine; and (2) nicotine addiction is partially a disease of excessive chaperoning. The chaperone is a pharmacological one, nicotine; and the chaperoned molecules are α4β2* nAChRs. SePhaChARNS may also underlie two inadvertent therapeutic effects of tobacco use:
Biophysical Journal, 1995
Affinity labeling and mutagenesis studies have demonstrated that the conserved tyrosine Y190 of the acetylcholine receptor (AChR) a-subunit is a key determinant of the agonist binding site. Here we describe the binding and gating kinetics of embryonic mouse AChRs with mutations at Y190. In Y1 90F the dissociation constant for ACh binding to closed channels was reduced-35-fold at the first binding site and only-2-fold at the second site. At both binding sites the association and dissociation rate constants were decreased by the mutation. Compared with wildtype AChRs, doublyliganded aYl 90F receptors open 400 times more slowly but close only 2 times more rapidly. Considering the overall activation reaction (vacant-closed to fully occupied-open), there is an increase of-6.4 kcal/mol caused by the Y-to-F mutation, of which at least 2.1 and 0.3 kcal/mol comes from altered agonist binding to the first and second binding sites, respectively. The closing rate constant of aYl 90F receptors was the same with ACh, carbamoylcholine, or tetramethylammonium as the agonist. This rate constant was-3 times faster in ACh-activated S, W, and T mutants. The equilibrium dissociation constant for channel block by ACh was-2-fold lower in aYl 90F receptors compared with in wildtype receptors, suggesting that there are changes in the pore region of the receptor as a consequence of the mutation. The activation reaction is discussed with regard to energy provided by agonist-receptor binding contacts, and by the intrinsic folding energy of the receptor.
The influence of ␣ and  subunits on the properties of nicotineinduced activation and desensitization of neuronal nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus oocytes was examined. Receptors containing ␣4 subunits were more sensitive to activation by nicotine than ␣3-containing receptors. At low concentrations of nicotine, nAChRs containing 2 subunits reached near-maximal desensitization more rapidly than 4-containing receptors. The concentration of nicotine producing half-maximal desensitization was influenced by the particular ␣ subunit expressed; similar to results for activation, ␣4-containing receptors were more sensitive to desensitizing levels of nicotine than ␣3-containing receptors. The ␣ subunit also influenced the rate of recovery from desensitization; this rate was approximately inversely proportional to the apparent nicotine affinity for the desensitized state. The homomeric ␣7 receptor showed the lowest sensitivity to nicotine for both activation and desensitization; ␣7 nAChRs also demonstrated the fastest desensitization kinetics. These subunitdependent properties remained in the presence of external calcium, although subtle, receptor subtype-specific effects on both the apparent affinities for activation and desensitization and the desensitization kinetics were noted. These data imply that the subunit composition of various nAChRs determines the degree to which receptors are desensitized and/or activated by tobacco-related levels of nicotine. The subtype-specific balance between receptor activation and desensitization should be considered important when the cellular and behavioral actions of nicotine are interpreted.
The Nicotinic Acetylcholine Receptor, A Model of Ligand-Gated Ion Channels
The Jerusalem Symposia on Quantum Chemistry and Biochemistry, 1992
Acetylcholine (ACh) was one of the first neurotransmitters to be discovered and is one of the most important in the central nervous system (CNS) and peripheral nervous system (PNS). ACh is produced by the enzyme choline acetyltransferase and its actions are mediated through two types of acetylcholine receptors (AChRs) -the G protein-coupled muscarinic AChRs and the nicotinic AChRs (nAChRs).
Molecular Pharmacology, 2004
Although the muscle-type and homomeric ␣7-type nicotinic acetylcholine receptors (nAChRs) share many structural features and bind ␣-bungarotoxin with high affinity, several important functional and pharmacological properties distinguish these two major nAChR subtypes. We have shown previously that amino acid sequence in the second transmembrane (TM) domain of the  subunit is critical for pharmacological distinction between muscle type and heteromeric neuronal (e.g., ganglionic) nAChRs. We tested the hypothesis that homologous substitution of amino acid sequence from the muscle 1 subunit into the ␣7 subunit would confer specific properties of muscle-type receptors to mutant ␣7 nAChRs. In this study, we show that a single amino acid substitution at the ␣7 TM2 6Ј
The effective opening of nicotinic acetylcholine receptors with single agonist binding sites
2011
Modern understanding of synaptic ion channels began with the isolation (Karlin and Cowburn, 1973) and subsequent cloning of nicotinic acetylcholine (ACh) receptors (nAChRs) (Numa et al., 1983). Based on the presence of primary binding site elements, including a pair of vicinal cysteines, 10 different nAChR subunits have been identified in vertebrates as subunits (1-10). Non- subunits, which demonstrably contain the required elements for forming the complementary surface of an agonist binding site, are , , and in muscle-type receptors and 2 and 4 in neuronal receptors. The nAChR ligand binding domain is formed by the interface of two protein subunits; the primary surface is formed by an subunit, which contains several other key elements in addition to the adjacent cysteines of a subdomain identified as the C-loop (Sine, 2002). The distinction between and non- subunits relates to a key dichotomy in several of the subfamilies of Cys-loop receptors between types that function as pentamers of an identical subunit (homomeric receptors) and those that require both and non- subunits in each penta-Correspondence to Roger L.