A Role for Cholesterol as a Structural Effector of the Nicotinic Acetylcholine Receptor

Fernández‐Ballester, Gregorio; Castresana, José; Fernández, Asia M.; Arrondo, José‐Luis R.; Ferragut, José A.; González-Ros, José M.

doi:10.1021/bi00179a035

Cited by 72 publications

(63 citation statements)

References 46 publications

(82 reference statements)

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“…The functional requirement of the nAChR for neutral and anionic lipids has been attributed to the binding of each lipid to distinct sites at or near the protein-lipid interface with distinct effects on the gross secondary structure of the nAChR (3, 8 -11). Others have reported more dramatic alterations in the content of both ␣-helix and ␤-sheet, with increasing levels of Chol in reconstituted neutral lipid depleted soybean asolectin membranes (12). In contrast, a recent Fourier transform infrared (FTIR) and hydrogen/deuterium exchange study was unable to detect any definitive lipid-dependent alterations in nAChR secondary structure, suggesting that both neutral and anionic lipids modulate nAChR function through subtle, but as yet unidentified changes in nAChR structure (13).…”

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confidence: 92%

“…McNamee and co-workers (10,11) proposed that the rigid sterol ring of Chol may intercalate into the grooves of ␣-helices stabilizing transmembrane ␣-helical secondary structures, whereas the negatively charged head group of anionic lipids may form electrostatic interactions with extra membranous regions of the nAChR leading to the stabilization of ␤-sheet. Others have reported more dramatic alterations in the content of both ␣-helix and ␤-sheet with increasing levels of Chol in reconstituted neutral lipid-depleted soybean asolectin membranes (12).…”

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confidence: 99%

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Structural Effects of Neutral and Anionic Lipids on the Nicotinic Acetylcholine Receptor

Ryan

Demers

Chew

et al. 1996

Journal of Biological Chemistry

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The effects of both neutral and anionic lipids on the structure of the nicotinic acetylcholine receptor (nAChR) have been probed using infrared difference spectroscopy. The difference between infrared spectra of the nAChR recorded using the attenuated total reflectance technique in the presence and absence of the neurotransmitter analog, carbamylcholine, exhibits a complex pattern of positive and negative bands that provides a spectral map of the structural changes that occur in the nAChR upon ligand binding and subsequent desensitization. This spectral map is essentially identical in difference spectra recorded from native, native alkaline-extracted, and affinity-purified nAChR reconstituted into either soybean asolectin or egg phosphatidylcholine membranes containing both neutral and anionic lipids. This result suggests both a similar structure of the nAChR and a similar resting to desensitized conformational change in each membrane environment. In contrast, difference spectra recorded from the nAChR reconstituted into egg phosphatidylcholine membranes lacking neutral and/or anionic lipids all exhibit an essentially identical pattern of band intensity variations, which is similar to the pattern of variations observed in difference spectra recorded in the continuous presence of the desensitizing local anesthetic, dibucaine. The difference spectra suggest that the main effect of both neutral and anionic lipids in a reconstituted egg phosphatidylcholine membrane is to help stabilize the nAChR in a resting conformation. In the absence of neutral and/or anionic lipids, the nAChR is converted into an alternate conformation that appears to be analogous to the local anesthetic-induced desensitized state. Significantly, the proportion of receptors found in the resting versus the putative desensitized state appears to be dependent upon the final lipid composition of the reconstituted membrane. A lipid-dependent modulation of the equilibrium between a channel-active resting and channel-inactive desensitized state may account for the modulations of nAChR activity that are observed in different lipid membranes.

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confidence: 92%

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confidence: 99%

Structural Effects of Neutral and Anionic Lipids on the Nicotinic Acetylcholine Receptor

Ryan

Demers

Chew

et al. 1996

Journal of Biological Chemistry

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“…The studies by Gonzalez-Ros and co-workers (Castresana et al, 1992;Fernandez-Ballester et al, 1994), on the influence of cholesterol on the structure and stability of the nicotinic acetyl- (Cortijo et al, 1982). choline receptor deserve a mention here although the main subject of this review is rather the opposite, i.e.…”

Section: Membrane Lipid Perturbation By Intrinsic Proteinsmentioning

confidence: 99%

Infrared studies of protein-induced perturbation of lipids in lipoproteins and membranes

Arrondo

Goñi

1998

Chemistry and Physics of Lipids

118

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The paper reviews the main recent publications concerning infrared (IR) spectroscopy as applied to the study of lipid-protein interactions in model and cell membranes, lipoproteins, and related systems (e.g. lung surfactant). The review focuses mainly on transmission IR. Based on the available data, a number of general conclusions are presented on the perturbations caused by proteins on either the hydrocarbon chains, the polar headgroups or the interface region. Lipid-protein interactions in native cell membranes do not reveal significant differences from what is observed in semisynthetic model systems.

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“…Indirect mechanisms are those in which a cholesterol-induced change in fluid or elastic properties of the lipid bilayer modulates the protein behavior. Although early studies (6,7) indicated that current flow through the channel is insensitive to bilayer fluid properties, more recent studies (8,9) have proposed that this result depends on the choice of order parameters. The direct mechanism requires cholesterol binding to the nAChR and effecting structural and/or dynamic changes.…”

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Embedded cholesterol in the nicotinic acetylcholine receptor

Brannigan

Hénin

Law

et al. 2008

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

150

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The nicotinic acetylcholine receptor (nAChR) is a cation-selective channel central to both neuronal and muscular processes and is considered the prototype for ligand-gated ion channels, motivating a structural determination effort that spanned several decades [Unwin N (2005) Refined structure of the nicotinic acetylcholine receptor at 4 Å resolution. J Mol Biol 346:967-989]. Purified nAChR must be reconstituted in a mixture containing cholesterol to function. Proposed modes of interaction between cholesterol and the protein range from specific binding to indirect membranemediated mechanisms. However, the underlying cause of nAChR sensitivity to cholesterol remains controversial, in part because the vast majority of functional studies were conducted before a medium resolution structure was reported. We show that the nAChR contains internal sites capable of containing cholesterol, whose occupation stabilizes the protein structure. We detect sites at the protein-lipid interface as conventionally predicted from functional data, as well as deeply buried sites that are not usually considered. Molecular dynamics simulations reveal that occupation of both superficial and deeply buried sites most effectively preserves the experimental structure; the structure collapses in the absence of bound cholesterol. In particular, we find that bound cholesterol directly supports contacts between the agonist-binding domain and the pore that are thought to be essential for activation of the receptor. These results likely apply to those other ion channels within the Cys-loop superfamily that depend on cholesterol, such as the GABA receptor.protein-lipid interaction ͉ ligand-gated ion channel ͉ cys loop receptor C ritical for memory and cognition, the nAChR is implicated in neurological disorders (1), addiction (2, 3), and the mechanism of anesthetics (4). Early efforts to reconstitute the nAChR noted that cholesterol as well as charged lipids (such as phosphatidic acid) are required for proper function (5). Proposed mechanisms for the role of cholesterol in nAChR function fall into two general types: indirect and direct. Indirect mechanisms are those in which a cholesterol-induced change in fluid or elastic properties of the lipid bilayer modulates the protein behavior. Although early studies (6, 7) indicated that current flow through the channel is insensitive to bilayer fluid properties, more recent studies (8, 9) have proposed that this result depends on the choice of order parameters. The direct mechanism requires cholesterol binding to the nAChR and effecting structural and/or dynamic changes. Proponents of this theory have determined that (i) cholesterol molecules in proximity to the protein exchange very slowly with the bulk lipid bilayer (10) (electron spin resonance difference spectroscopy); (ii) cholesterol accesses sites on the protein that cannot be occupied by phospholipids (11) (fluorescence quenching); and (iii) some cholesterol bound to the nAChR interacts with the phospholipids in the surrounding bilayer (12) (substit...

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A Role for Cholesterol as a Structural Effector of the Nicotinic Acetylcholine Receptor

Cited by 72 publications

References 46 publications

Structural Effects of Neutral and Anionic Lipids on the Nicotinic Acetylcholine Receptor

Structural Effects of Neutral and Anionic Lipids on the Nicotinic Acetylcholine Receptor

Infrared studies of protein-induced perturbation of lipids in lipoproteins and membranes

Embedded cholesterol in the nicotinic acetylcholine receptor

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