Coupling of agonist binding to channel gating in an ACh-binding protein linked to an ion channel

Bouzat, Cecilia; Gumilar, Fernanda; Spitzmaul, Guillermo Federico; Wang, Hailong; Rayes, Diego; Hansen, Scott B.; Taylor, Palmer; Sine, Steven M.

doi:10.1038/nature02753

Cited by 256 publications

(298 citation statements)

References 27 publications

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“…First, although a common activation mechanism is shared by cationic and anionic LGICs, fine structural complementarity at the interface region is likely to be a general rule for optimal allosteric coupling, as already suggested by chimeras made from the acetylcholine-binding protein (AChBP) and the 5HT 3 receptor (18,32). Indeed, for GlyR coupling, fast gating is mediated by only two nonconserved amino acid residues from the Cys-loop whereas for ␣7 nAChR fast coupling occurs through at most five nonconserved residues from the 2-3L region.…”

Section: Discussionmentioning

confidence: 99%

Molecular tuning of fast gating in pentameric ligand-gated ion channels

Grütter

Carvalho

Dufresne

et al. 2005

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

109

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Neurotransmitters such as acetylcholine (ACh) and glycine mediate fast synaptic neurotransmission by activating pentameric ligandgated ion channels (LGICs). These receptors are allosteric transmembrane proteins that rapidly convert chemical messages into electrical signals. Neurotransmitters activate LGICs by interacting with an extracellular agonist-binding domain (ECD), triggering a tertiary͞quaternary conformational change in the protein that results in the fast opening of an ion pore domain (IPD). However, the molecular mechanism that determines the fast opening of LGICs remains elusive. Here, we show by combining whole-cell and single-channel recordings of recombinant chimeras between the ECD of ␣7 nicotinic receptor (nAChR) and the IPD of the glycine receptor (GlyR) that only two GlyR amino acid residues of loop 7 (Cys-loop) from the ECD and at most five ␣7 nAChR amino acid residues of the M2-M3 loop (2-3L) from the IPD control the fast activation rates of the ␣7͞Gly chimera and WT GlyR. Mutual interactions of these residues at a critical pivot point between the agonist-binding site and the ion channel fine-tune the intrinsic opening and closing rates of the receptor through stabilization of the transition state of activation. These data provide a structural basis for the fast opening of pentameric LGICs.allosteric proteins ͉ chimeric receptor ͉ Cys-loop receptor ͉ transition state P entameric ligand-gated ion channels (LGICs), such as the cationic nicotinic acetylcholine receptor (nAChR) and the anionic glycine receptor (GlyR), mediate fast excitatory or inhibitory chemical neurotransmission between neurons (1-6). A unique feature of these receptors is that they activate the ion channel, a process known as gating, in less than a ms. For nicotinic receptors, a detailed single-channel analysis has recently established a speed limit for the opening of the ion channel in the s time range (7). Perturbations of this rapid transmission pathway by natural mutants lead to severe diseases such as congenital myasthenic syndromes (8), hereditary hyperekplexia (9), or epileptic disorders (10).Pentameric LGICs, or Cys-loop receptors, are composed of five homologous subunits, sharing a common structural organization, arranged (pseudo)symmetrically around the central ion pore (1, 2). All subunits are made of two distinct topological domains: the extracellular (ECD) and the ion pore domains (IPD). First, the ECD is folded into a twisted ␤-sandwich core, as revealed by x-ray crystallographic studies of the mollusk acetylcholine-binding protein (AChBP), a soluble pentameric protein homologous to the extracellular domain of LGICs (11-14). Second, electron microscopy images of Torpedo nAChR at 4-Å resolution revealed that the four transmembrane segments (M1 to M4) of the IPD are folded into ␣-helices joined by linking loops of variable lengths (15). By combining these structural data, we built a 3D model of the full ␣7 nAChR (16). In this model, the coupling zone located at the interface between the two domains is framed by f...

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Section: Discussionmentioning

confidence: 99%

Molecular tuning of fast gating in pentameric ligand-gated ion channels

Grütter

Carvalho

Dufresne

et al. 2005

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

109

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“…The key coupling region in this allosteric network is in the interface between amino-terminal binding domain and transmembrane gating domain for each subunit. A study using a chimeric receptor with AChBP and channel domains of 5HT 3 R revealed that the coupling interface requires matching of three loops (loop 2, loop 7, and loop 9) from the amino-terminal domain and one loop (M2-M3 linker) from the transmembrane domain for the receptor to be functional [43] . Additionally, a region in pre-M1 and the beginning of M1 that covalently links the amino-terminal domain to the transmembrane domain, is also important in channel gating ( Figure 4C) [44] .…”

Section: Functional Domains Of the Cys-loop Receptorsmentioning

confidence: 99%

“…Coupling between amino-terminal domain and the gating machinery As mentioned above, coupling between binding and gating domains requires matching of three loops (loop 2, loop 7/cys-loop, and loop 9/loop F) from the amino-terminal domain and one loop (M2-M3 linker) from the transmembrane domain [43] and pre-M1 and the beginning of M1 [44] . Since M2-M3 linker is not conserved across the entire cys-loop receptor family, detailed coupling residues could vary depending on subfamilies, although the general mechanism is likely to be conserved.…”

Section: Activation Mechanismmentioning

confidence: 99%

Allosteric activation mechanism of the cys-loop receptors

et al. 2009

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Binding of a neurotransmitter to its ionotropic receptor opens a distantly located ion channel, a process termed allosteric activation. Here we review recent advances in the molecular mechanism by which the cys-loop receptors are activated with emphasis on the best studied nicotinic acetylcholine receptors (nAChRs). With a combination of affinity labeling, mutagenesis, electrophysiology, kinetic modeling, electron microscopy (EM), and crystal structure analysis, the allosteric activation mechanism is emerging. Specifically, the binding domain and gating domain are interconnected by an allosteric activation network. Agonist binding induces conformational changes, resulting in the rotation of a β sheet of aminoterminal domain and outward movement of loop 2, loop F, and cys-loop, which are coupled to the M2-M3 linker to pull the channel to open. However, there are still some controversies about the movement of the channel-lining domain M2. Nine angstrom resolution EM structure of a nAChR imaged in the open state suggests that channel opening is the result of rotation of the M2 domain. In contrast, recent crystal structures of bacterial homologues of the cys-loop receptor family in apparently open state have implied an M2 tilting model with pore dilation and quaternary twist of the whole pentameric receptor. An elegant study of the nAChR using protonation scanning of M2 domain supports a similar pore dilation activation mechanism with minimal rotation of M2. This remains to be validated with other approaches including high resolution structure determination of the mammalian cys-loop receptors in the open state.

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“…3a). Given that the Cys-loop plays a central role at the interface between the two domains (Lummis et al 2005;Bouzat et al 2004), specific interactions between post-M4 and the Cys-loop may be essential for coupling agonist-binding to channel gating. Lipids could influence nAChR function by modulating post-M4 interactions with the Cys-loop.…”

Section: The M4 Lipid-sensor Modelmentioning

confidence: 99%

Molecular mechanisms of acetylcholine receptor–lipid interactions: from model membranes to human biology

Baenziger

daCosta

2012

Biophys Rev

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Lipids are potent modulators of the Torpedo nicotinic acetylcholine receptor. Lipids influence nicotinic receptor function by allosteric mechanisms, stabilizing varying proportions of pre-existing resting, open, desensitized, and uncoupled conformations. Recent structures reveal that lipids could alter function by modulating transmembrane α-helix/α-helix packing, which in turn could alter the conformation of the allosteric interface that links the agonist-binding and transmembrane pore domains-this interface is essential in the coupling of agonist binding to channel gating. We discuss potential mechanisms by which lipids stabilize different conformational states in the context of the hypothesis that lipid-nicotinic receptor interactions modulate receptor function at biological synapses.

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Coupling of agonist binding to channel gating in an ACh-binding protein linked to an ion channel

Cited by 256 publications

References 27 publications

Molecular tuning of fast gating in pentameric ligand-gated ion channels

Molecular tuning of fast gating in pentameric ligand-gated ion channels

Allosteric activation mechanism of the cys-loop receptors

Molecular mechanisms of acetylcholine receptor–lipid interactions: from model membranes to human biology

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