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Energy and structure of the M2 helix in acetylcholine receptor-channel gating.

ABSTRACT: We studied single-channel currents from neuromuscular acetylcholine receptor-channels with mutations in the pore-lining, M2 helix of the epsilon-subunit. Three parameters were quantified: 1), the diliganded gating equilibrium constant (E(2)), which reflects the energy difference between C(losed) and O(pen) conformations; 2), the correlation between the opening rate constant and E(2) on a log-log scale (Phi), which illuminates the energy character of the residue (C- versus O-like) within the C<-->O isomerization process; and 3), the open-channel current amplitude (i(0)), which reports whether a mutation alters the energetics of ion permeation. The largest E(2) changes were observed in the cytoplasmic half of epsilonM2 (5', 9', 12', 13', and 16'), with smaller changes apparent for residues > or =17'. Phi was approximately 0.54 for most epsilonM2 residues, but was approximately 0.32 at the positions that had largest E(2) changes. An arginine substitution reduced i(0) significantly at six positions, with the magnitude of the reduction increasing, 16'-->2'. The measurements suggest that the 9', 12', and 13' residues experience large and late free-energy changes in the channel-opening process. We speculate that in the gating isomerization the pore-facing residues >6' and <16' experience multiple energy perturbations associated with changes in protein structure and, perhaps, hydration.

SUBMITTER: Jha A

PROVIDER: S-EPMC2712209 | biostudies-literature | 2009 May

REPOSITORIES: biostudies-literature

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Energy and structure of the M2 helix in acetylcholine receptor-channel gating.

Jha Archana A Purohit Prasad P Auerbach Anthony A

Biophysical journal 20090501 10

We studied single-channel currents from neuromuscular acetylcholine receptor-channels with mutations in the pore-lining, M2 helix of the epsilon-subunit. Three parameters were quantified: 1), the diliganded gating equilibrium constant (E(2)), which reflects the energy difference between C(losed) and O(pen) conformations; 2), the correlation between the opening rate constant and E(2) on a log-log scale (Phi), which illuminates the energy character of the residue (C- versus O-like) within the C<-- ...[more]

PMID: 19450479

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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

Energy and structure of the M2 helix in acetylcholine receptor-channel gating.

Publications

Energy and structure of the M2 helix in acetylcholine receptor-channel gating.

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