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Originally published as Biophys J. BioFAST on August 19, 2005.
doi:10.1529/biophysj.105.068783
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Biophysical Journal 89:3071-3078 (2005)
© 2005 The Biophysical Society

Plasticity of Acetylcholine Receptor Gating Motions via Rate-Energy Relationships

Ananya Mitra, Richard Tascione, Anthony Auerbach and Stuart Licht

Center for Single Molecule Biophysics and the Department of Physiology and Biophysics, The State University of New York, Buffalo, New York

Correspondence: Address reprint requests to S. Licht, Tel.: 617-452-3525; E-mail: lichts{at}mit.edu.

Like other protein conformational changes, ion channel gating requires the protein to achieve a high-energy transition-state structure. It is not known whether ion channel gating takes place on a broad energy landscape on which many alternative transition state structures are accessible, or on a narrow energy landscape where only a few transition-state structures are possible. To address this question, we measured how rate-equilibrium free energy relationships (REFERs) for di-liganded and unliganded acetylcholine receptor gating vary as a function of the gating equilibrium constant. A large slope for the REFER plot indicates an openlike transition state, whereas a small slope indicates a closedlike transition state. Due to this relationship between REFERs and transition-state structure, the sensitivity of the REFER slope to mutation-induced energetic perturbations allows estimation of the breadth of the energy landscape underlying gating. The relatively large sensitivity of di-liganded REFER slopes to energetic perturbations suggests that the motions underlying di-liganded gating take place on a broad, shallow energy landscape where many alternative transition-state structures are accessible.




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