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Conformational Dynamics of the M3 Transmembrane Helix during Acetylcholine Receptor Channel Gating

Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York

Correspondence: Address reprint requests to Anthony Auerbach, E-mail: auerbach{at}buffalo.edu.

Muscle acetylcholine receptors are synaptic ion channels that "gate" between closed- and open-channel conformations. We used -value analysis to probe the transition state of the diliganded gating reaction with regard to residues in the M3, membrane-spanning helix of the muscle acetylcholine receptor -subunit. (a fraction between 1 and 0) parameterizes the extent to which a mutation changes the opening versus the closing rate constant and, for a linear reaction mechanism, the higher the -value, the "earlier" the gating motion. In the upper half of M3 the gating motions of all five tested residues were temporally correlated ( 0.30) and serve to link structural changes occurring at the middle of the M2, pore-lining helix with those occurring at the interface of the extracellular and transmembrane domains. M3 belongs to a complex and diverse set of synchronously moving parts that change structure relatively late in the channel-opening process. The propagation of the gating Brownian conformational cascade has a complex spatial distribution in the transmembrane domain.

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