Mechanism of C-type inactivation in the hERG potassium channel

Figures

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  Fig. 1. Asymmetrical constricted conformation of the selectivity filter. (A to C) The C2 model based on an average structure (cyan) symmetrized by swapping between two opposite subunits shown from the top view is overlaid with the cryo-EM structure (red) (A), two side views highlighting different pairs of subunits with ion-binding sites marked (B and C). (D to G) 2D-PMF of the hERG and KcsA channels reveals local free energy basins corresponding to a general asymmetrically constricted conformation. The horizontal and vertical reaction coordinates, respectively, represent the cross-subunit distance between the Cα atoms of glycine (G626 in hERG or G77 in KcsA) of diagonally opposed subunits A and C (r1), and B and D (r2). Results for WT KcsA (F) and KcsAD-ala77 (G) from a similar PMF calculation were previously reported (18).

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  Fig. 2. Impacts of multiple mutations in hERG channel. (A) Computational and experimental measurements for WT and mutants. Left: 1D-PMFs along the constriction coordinate r (via integration of the 2D PMF). Middle: Representative currents in electrophysiological recordings for mutants and WT (in 10-mV increments). Right: Side view of representative conformations. (B) Sequence alignment among hERG, Shaker, and KcsA channels for the residues in or close to the selectivity filter (left) and the triple-pulse protocol to measure the inactivation of hERG channel (right).

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  Fig. 3. Comparison of the free energy landscape for the hERG, KcsA, and Shaker channels. The opening of the intracellular gate was selected to be almost the same for all these channels (16 to 18 Å). In the 2D-PMFs, the horizontal reaction coordinate r describes the constriction of the selectivity filter (defined as the average cross-diagonal distance between the Cα atoms of the central glycine equivalent to G77 in KcsA). The vertical reaction coordinate z indicates the position of the external K+ ion along the pore relative to its center of the selectivity filter. The bottom panel shows the integrated 1D-PMFs along r. The PMF for WT KcsA from a similar calculation was reported previously (18). The PMF for Shaker was calculated using a model based on the x-ray structure (PDB ID: 2R9R) of the Kv1.2/Kv2.1 chimera channel (57).