The Net Orientation of Nicotinic Receptor Transmembrane α-Helices in the Resting and Desensitized States

Hill, D. G.; Baenziger, John E.

doi:10.1529/biophysj.106.082693

Cited by 10 publications

(9 citation statements)

References 38 publications

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“…1-6). These bands are absent in the difference between two spectra of the nAChR recorded both in the absence of ligand (data not shown, but see Hill and Baenziger, 2006). They are also absent in control Carb difference spectra recorded from nAChR membranes that have been pretreated with the competitive antagonist ␣-bungarotoxin (Baenziger et al, 1993).…”

Section: Ftir Spectroscopy As a Tool For Monitoring Localmentioning

confidence: 83%

“…Previous studies have shown that these difference bands reflect a change in both the orientation and hydrogen bonding of a region(s) of the polypeptide backbone that is (are) highly accessible to aqueous solvent (Baenziger and Chew, 1997;Hill and Baenziger, 2006). Given both the relatively large changes in structure that occur upon ligand binding to the binding site "C-loop" and the relative solvent accessibility of this region of the polypeptide backbone, it was suggested previously that the vibrational changes that result from the closing of the C-loop around Carb upon transition from the unliganded resting to the liganded desensitized state may dominate the spectral features observed in the amide I and II regions of the Carb difference spectrum (Hill and Baenziger, 2006). Regardless, these noted bands serve as markers of the ability of the nAChR to undergo the resting to desensitized conformational transition (Ryan et al, 1996).…”

Section: Ftir Spectroscopy As a Tool For Monitoring Localmentioning

confidence: 99%

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Lipid Composition Alters Drug Action at the Nicotinic Acetylcholine Receptor

Baenziger

Ryan²,

Goodreid³

et al. 2007

Mol Pharmacol

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We tested the hypothesis that membrane lipid composition influences drug action at membrane proteins by studying local anesthetic action at the nicotinic acetylcholine receptor (nAChR). Infrared difference spectra show that concentrations of tetracaine consistent with binding to the ion channel (Ͻ50 M) stabilize a resting-like state when the nAChR is reconstituted into phosphatidylcholine membranes containing the anionic lipid, phosphatidic acid, but have no effect on the nAChR reconstituted into membranes lacking phosphatidic acid, either in the presence or absence of cholesterol. Concentrations of tetracaine above 200 M lead to neurotransmitter site binding in all membranes. In the presence of phosphatidic acid, cholesterol, or both, neurotransmitter site binding leads to the formation of quaternary amine-aromatic interactions between tetracaine and binding site tyrosine/tryptophan residues and the stabilization of a desensitized state. One interpretation suggested by lipid partitioning studies is that phosphatidic acid enhances tetracaine action at the channel pore by increasing the partitioning of tetracaine into the lipid bilayer, thereby enhancing access to the transmembrane pore. However, subtle membrane-dependent variations in the vibrations of tyrosine and tryptophan residues, and agonist analog binding studies indicate that the structures of the agonist-bound neurotransmitter sites of the nAChR in membranes lacking both phosphatidic acid and cholesterol differ from the structures of the agonist-desensitized neurotransmitter sites in the presence of both lipids. Lipid action at the nAChR thus involves more than a simple modulation of the equilibrium between resting and desensitized states.

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Section: Ftir Spectroscopy As a Tool For Monitoring Localmentioning

confidence: 83%

Section: Ftir Spectroscopy As a Tool For Monitoring Localmentioning

confidence: 99%

Lipid Composition Alters Drug Action at the Nicotinic Acetylcholine Receptor

Baenziger

Ryan²,

Goodreid³

et al. 2007

Mol Pharmacol

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“…Desensitization of the Cys-loop receptor family has been well characterized kinetically. It involves dramatic increase in binding affinity to agonists (12,13) and closure of the ion conducting pathway (9) with little structural change in transmembrane domain (14). It is an intrinsic property of the receptors (15).…”

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confidence: 99%

Desensitization of α7 Nicotinic Receptor Is Governed by Coupling Strength Relative to Gate Tightness

Zhang

Xue

Whiteaker

et al. 2011

Journal of Biological Chemistry

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Binding of a neurotransmitter to its membrane receptor opens an integral ion conducting pore. However, prolonged exposure to the neurotransmitter drives the receptor to a refractory state termed desensitization, which plays an important role in shaping synaptic transmission. Despite intensive research in the past, the structural mechanism of desensitization is still elusive. Using mutagenesis and voltage clamp in an oocyte expression system, we provide several lines of evidence supporting a novel hypothesis that uncoupling between binding and gating machinery is the underlying mechanism for ␣7 nicotinic receptor (nAChR) desensitization. First, the decrease in gate tightness was highly correlated to the reduced desensitization. Second, nonfunctional mutants in three important coupling loops (loop 2, loop 7, and the M2-M3 linker) could be rescued by a gating mutant. Furthermore, the decrease in coupling strength in these rescued coupling loop mutants reversed the gating effect on desensitization. Finally, coupling between M1 and hinge region of the M2-M3 linker also influenced the receptor desensitization. Thus, the uncoupling between N-terminal domain and transmembrane domain, governed by the balance of coupling strength and gate tightness, underlies the mechanism of desensitization for the ␣7 nAChR.The Cys-loop receptor family of ligand-gated ion channels are allosteric proteins (1-4). Binding of neurotransmitter to the receptor binding site located in the N-terminal domain induces conformational changes (5), which propagate to the transmembrane domain (M1-M4) 3 through the interface between these two domains to open the gate, which is formed by M2 domains (see Fig. 1A). Coupling through this interface is mainly mediated by noncovalent interactions between loops 2 and 7 (Cysloop) from N-terminal domain and M2-M3 linker from the transmembrane domain (see Fig. 1B) (6, 7). In addition, pre-M1 and M1 is the only covalent linkage between N-terminal domain and transmembrane domain, which also play a role in controlling channel gating (7). However, agonist binding does not guarantee channel opening. With prolonged exposure to neurotransmitters, most receptors are driven to a refractory state, termed desensitization (8). At the single channel level, desensitization appears as long-lasting nonconducting states (9). Desensitization is a widespread phenomenon in most ligand-gated ion channels. It plays an important role in shaping synaptic transmission (10, 11). Desensitization of the Cys-loop receptor family has been well characterized kinetically. It involves dramatic increase in binding affinity to agonists (12, 13) and closure of the ion conducting pathway (9) with little structural change in transmembrane domain (14). It is an intrinsic property of the receptors (15).Previous studies have identified numerous factors that can influence desensitization. For example, desensitization is dependent on agonists (16) and receptor subtypes (17, 18). Mutations of a residue in the binding pocket (19) or between two binding loops...

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“…Both difference spectra are the average of 20 1,000-scan difference spectra, each recorded at 22.5°C and at a resolution of 8 cm −1 (adapted from [11]). [61] and changes in α-helical orientation upon desensitization using polarization and H-D exchange have been demonstrated [117]. In addition, nAChR has been studied using transmittance FTIR difference spectroscopy using a "caged" carbamylcholine [102].…”

Section: Atr-ftir Differences Of Nicotinic Acetylcholine Receptormentioning

confidence: 99%

The early development and application of FTIR difference spectroscopy to membrane proteins: A personal perspective

Rothschild

2016

BSI

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Abstract. Membrane proteins facilitate some of the most important cellular processes including energy conversion, ion transport and signal transduction. While conventional infrared absorption provides information about membrane protein secondary structure, a major challenge is to develop a dynamic picture of the functioning of membrane proteins at the molecular level. The introduction of FTIR difference spectroscopy around 1980 to study structural changes in membrane proteins along with a number of associated techniques including protein isotope labeling, site-directed mutagenesis, polarization dichroism, attenuated total reflection and time-resolved spectroscopy have led to significant progress towards this goal. It is now possible to routinely detect conformational changes of individual amino acid residues, backbone peptides, binding ligands, chromophores and even internal water molecules under physiological conditions with time-resolution down to nanoseconds. The advent of ultrafast pulsed-IR lasers has pushed this time-resolution down to femtoseconds. The early development of FTIR difference spectroscopy as applied to membrane proteins with special focus on bacteriorhodopsin is reviewed from a personal perspective.

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The Net Orientation of Nicotinic Receptor Transmembrane α-Helices in the Resting and Desensitized States

Cited by 10 publications

References 38 publications

Lipid Composition Alters Drug Action at the Nicotinic Acetylcholine Receptor

Lipid Composition Alters Drug Action at the Nicotinic Acetylcholine Receptor

Desensitization of α7 Nicotinic Receptor Is Governed by Coupling Strength Relative to Gate Tightness

The early development and application of FTIR difference spectroscopy to membrane proteins: A personal perspective

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