Conformational plasticity of NaK2K and TREK2 potassium channel selectivity filters.

The K channel selectivity filter (SF) is defined by TxGYG amino acid sequences that generate four identical K binding sites (S1-S4). Only two sites (S3, S4) are present in the non-selective bacterial NaK channel, but a four-site K-selective SF is obtained by mutating the wild-type TVGDGN SF sequence to a canonical K channel TVGYGD sequence (NaK2K mutant). Using single molecule FRET (smFRET), we show that the SF of NaK2K, but not of non-selective NaK, is ion-dependent, with the constricted SF configuration stabilized in high K conditions.

Studying Structural Dynamics of Potassium Channels by Single-Molecule FRET.

Single-molecule FRET (smFRET) can visualize conformational dynamics of individual ion channels in lipid bilayers of defined composition. Dynamic and distance measurements from smFRET, combined with single channel recordings, can provide previously unattainable direct mechanistic insights into ion channel function and modulation. smFRET measurements require site-specific fluorophore labeling between two distinct sites, which is a major challenge for multimeric ion channels.

Role of protein dynamics in ion selectivity and allosteric coupling in the NaK channel.

Flux-dependent inactivation that arises from functional coupling between the inner gate and the selectivity filter is widespread in ion channels. The structural basis of this coupling has only been well characterized in KcsA. Here we present NMR data demonstrating structural and dynamic coupling between the selectivity filter and intracellular constriction point in the bacterial nonselective cation channel, NaK.