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A stepwise mechanism for acetylcholine receptor channel gating


Muscle contraction is triggered by the opening of acetylcholine receptors at the vertebrate nerve–muscle synapse1,2,3,4. The M2 helix of this allosteric membrane protein lines the channel, and contains a ‘gate’ that regulates the flow of ions through the pore. We used single-molecule kinetic analysis to probe the transition state of the gating conformational change and estimate the relative timing of M2 motions in the α-subunit of the murine acetylcholine receptor5. This analysis produces a ‘Φ-value’ for a given residue that reflects its open-like versus closed-like character at the transition state. Here we show that most of the residues throughout the length of M2 have a Φ-value of 0.64 but that some near the middle have lower Φ-values of 0.52 or 0.31, suggesting that αM2 moves in three discrete steps. The core of the channel serves both as a gate that regulates ion flow and as a hub that directs the propagation of the gating isomerization through the membrane domain of the acetylcholine receptor.

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Figure 1: The location of αM2.
Figure 2: Φ -value analysis.
Figure 3: Distribution of Φ -values.
Figure 4: Map of Φ -values.

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We thank C. Grosman, P. Gottlieb and F. Sachs for discussions, and C. Nicolai, B. Steidl, M. Merritt and M. Teeling for technical assistance. This work was supported by the NIH.

Author Contributions All of the experiments and data analyses shown in Fig. 2 were performed by P.P. except for those for positions 4′ and 9′, which were performed by A.M.

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Correspondence to Anthony Auerbach.

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This file contains Supplementary Methods, Supplementary Tables 1-2, Supplementary Figures 1-2 with Legends and additional references. (PDF 298 kb)

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Purohit, P., Mitra, A. & Auerbach, A. A stepwise mechanism for acetylcholine receptor channel gating. Nature 446, 930–933 (2007).

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