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Distinctive single-channel properties of ?4?2-nicotinic acetylcholine receptor isoforms.

ABSTRACT: Central nervous system nicotinic acetylcholine receptors (nAChR) are predominantly of the ?4?2 subtype. Two isoforms exist, with high or low agonist sensitivity (HS-(?4?2)2?2- and LS-(?4?2)2?4-nAChR). Both isoforms exhibit similar macroscopic potency and efficacy values at low acetylcholine (ACh) concentrations, mediated by a common pair of high-affinity ?4(+)/(-)?2 subunit binding interfaces. However LS-(?4?2)2?4-nAChR also respond to higher concentrations of ACh, acting at a third ?4(+)/(-)?4 subunit interface. To probe isoform functional differences further, HS- and LS-?4?2-nAChR were expressed in Xenopus laevis oocytes and single-channel responses were assessed using cell-attached patch-clamp. In the presence of a low ACh concentration, both isoforms produce low-bursting function. HS-(?4?2)2?2-nAChR exhibit a single conductance state, whereas LS-(?4?2)2?4-nAChR display two distinctive conductance states. A higher ACh concentration did not preferentially recruit either conductance state, but did result in increased LS-(?4?2)2?4-nAChR bursting and reduced closed times. Introduction of an ?4(+)/(-)?4-interface loss-of-function ?4W182A mutation abolished these changes, confirming this site's role in mediating LS-(?4?2)2?4-nAChR responses. Small or large amplitude openings are highly-correlated within individual LS-(?4?2)2?4-nAChR bursts, suggesting that they arise from distinct intermediate states, each of which is stabilized by ?4(+)/(-)?4 site ACh binding. These findings are consistent with ?4(+)/(-)?4 subunit interface occupation resulting in allosteric potentiation of agonist actions at ?4(+)/(-)?2 subunit interfaces, rather than independent induction of high conductance channel openings.

SUBMITTER: Weltzin MM

PROVIDER: S-EPMC6405073 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Distinctive single-channel properties of α4β2-nicotinic acetylcholine receptor isoforms.

Weltzin Maegan M MM George Andrew A AA Lukas Ronald J RJ Whiteaker Paul P

PloS one 20190307 3

Central nervous system nicotinic acetylcholine receptors (nAChR) are predominantly of the α4β2 subtype. Two isoforms exist, with high or low agonist sensitivity (HS-(α4β2)2β2- and LS-(α4β2)2α4-nAChR). Both isoforms exhibit similar macroscopic potency and efficacy values at low acetylcholine (ACh) concentrations, mediated by a common pair of high-affinity α4(+)/(-)β2 subunit binding interfaces. However LS-(α4β2)2α4-nAChR also respond to higher concentrations of ACh, acting at a third α4(+)/(-)α4 ...[more]

PMID: 30845161

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Project description:The nicotinic acetylcholine receptor (nAChR) is a key molecule involved in the propagation of signals in the central nervous system and peripheral synapses. Although numerous computational and experimental studies have been performed on this receptor, the structural dynamics of the receptor underlying the gating mechanism is still unclear. To address the mechanical fundamentals of nAChR gating, both conventional molecular dynamics (CMD) and steered rotation molecular dynamics (SRMD) simulations have been conducted on the cryo-electron microscopy (cryo-EM) structure of nAChR embedded in a dipalmitoylphosphatidylcholine (DPPC) bilayer and water molecules. A 30-ns CMD simulation revealed a collective motion amongst C-loops, M1, and M2 helices. The inward movement of C-loops accompanying the shrinking of acetylcholine (ACh) binding pockets induced an inward and upward motion of the outer beta-sheet composed of beta9 and beta10 strands, which in turn causes M1 and M2 to undergo anticlockwise motions around the pore axis. Rotational motion of the entire receptor around the pore axis and twisting motions among extracellular (EC), transmembrane (TM), and intracellular MA domains were also detected by the CMD simulation. Moreover, M2 helices undergo a local twisting motion synthesized by their bending vibration and rotation. The hinge of either twisting motion or bending vibration is located at the middle of M2, possibly the gate of the receptor. A complementary twisting-to-open motion throughout the receptor was detected by a normal mode analysis (NMA). To mimic the pulsive action of ACh binding, nonequilibrium MD simulations were performed by using the SRMD method developed in one of our laboratories. The result confirmed all the motions derived from the CMD simulation and NMA. In addition, the SRMD simulation indicated that the channel may undergo an open-close (O <--> C) motion. The present MD simulations explore the structural dynamics of the receptor under its gating process and provide a new insight into the gating mechanism of nAChR at the atomic level.

Dataset Information

Distinctive single-channel properties of ?4?2-nicotinic acetylcholine receptor isoforms.

Publications

Distinctive single-channel properties of α4β2-nicotinic acetylcholine receptor isoforms.

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