Abstract

K⁺ channels conduct and regulate K⁺ flux across the cell membrane. Several crystal structures and biophysical studies of tetrameric ion channels have revealed many of the structural details of ion selectivity and gating. A narrow pore lined with four arrays of carbonyl groups is responsible for ion selectivity, whereas a conformational change of the four inner transmembrane helices (TM2) is involved in gating. We used NMR to examine full-length KcsA, a prototypical K⁺ channel, in its open, closed and intermediate states. These studies reveal that at least two conformational states exist both in the selectivity filter and near the C-terminal ends of the TM2 helices. In the ion-conducting open state, we observed rapid structural exchange between two conformations of the filter, presumably of low and high K⁺ affinity, respectively. Such measurements of millisecond-timescale dynamics reveal the basis for simultaneous ion selection and gating.

1. Structural Biology Laboratory, The Salk Institute, La Jolla, California 92037, USA.
2. Laboratory of Physical Chemistry, Swiss Institute of Technology (ETH) Zurich, CH-8093 Switzerland.
3. These authors contributed equally to this work.

Correspondence to: Senyon Choe¹ e-mail: choe@salk.edu

Correspondence to: Roland Riek^1,2 e-mail: riek@salk.edu

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