KvAP-Based Model of the Pore Region of Shaker Potassium Channel Is Consistent with Cadmium- and Ligand-Binding Experiments

Abstract

Potassium channels play fundamental roles in excitable cells. X-ray structures of bacterial potassium channels show that the pore-lining inner helices obstruct the cytoplasmic entrance to the closed channel KcsA, but diverge in widely open channels MthK and KvAP, suggesting a gating-hinge role for a conserved Gly in the inner helix. A different location of the gating hinge and a narrower open pore were proposed for voltage-gated Shaker potassium channels that have the Pro-473-Val-Pro motif. Two major observations back the proposal: cadmium ions lock mutant Val-476-Cys in the open state by bridging Cys-476 and His-486 in adjacent helices, and cadmium blocks the locked-open double mutant Val-474-Cys/Val-476-Cys by binding to Cys-474 residues. Here we used molecular modeling to show that the open Shaker should be as wide as KvAP to accommodate an open-channel blocker, correolide. We further built KvAP-, MthK-, and KcsA-based models of the Shaker mutants and Monte-Carlo-minimized them with constraints Cys-476-Cd(2+)-His-486. The latter were consistent with the KvAP-based model, causing a small-bend N-terminal to the Pro-473-Val-Pro motif. The constraints significantly distorted the MthK-based structure, making it similar to KvAP. The KcsA structure resisted the constraints. Two Cd(2+) ions easily block the locked-open KvAP-based model at Cys-474 residues, whereas constraining a single cadmium ion to four Cys-474 caused large conformational changes and electrostatic imbalance. Although mutual disposition of the voltage-sensor and pore domains in the KvAP x-ray structure is currently disputed, our results suggest that the pore-region domain retains a nativelike conformation in the crystal.

Interaction of d-Tubocurarine with Potassium Channels: Molecular Modeling and Ligand Binding

“…The predicted characteristics are consistent with the later published structure of Kv1.2 (Long et al, 2005a). The model of Bruhova and Zhorov (2005) also explained the paraxial fact that large correolide and small Cd 2ϩ ions block the inner vestibule of the open Kv1.3 at the same level of the pore. The MthK-based model of the Shaker channel was found inconsistent with the distance constraints of Webster et al (2004).…”

“…Based on their studies of Cd 2ϩ action on the Shaker channel mutants, Webster et al (2004) derived valuable distance constraints between the inner helix residues in positions i22, i24, and i34. Bruhova and Zhorov (2005) used these distance constraints to build the KvAP-based model of the Shaker channel, which predicted a smooth bend at the Pro-Val-Pro motif and the pore width of ϳ10 Å. The predicted characteristics are consistent with the later published structure of Kv1.2 (Long et al, 2005a).…”

The Receptor Site and Mechanism of Action of Sodium Channel Blocker Insecticides

“…Therefore, the Na v Ms x-ray structure, which lacks the S4-S5 linkers, appears suitable for computational docking of SCBIs. We used MCM to move C ␣ atoms of Na v Ab/K v 1.2-based model to positions of respective atoms in the Na v Ms x-ray structure as described elsewhere (30). In the obtained model, positions of the S4-S5 helices are similar to those in the Na v Ab/K v 1.2-based model.…”

Chromanol 293B Binding in KCNQ1 (Kv7.1) Channels Involves Electrostatic Interactions with a Potassium Ion in the Selectivity Filter

“…It is noteworthy that nearby conservative exchanges F335Y, A336T, S338T, and F339Y also caused a significant reduction of 293B sensitivity. However, we believe that these ex- The outer helices were aligned according to Bruhova and Zhorov (2005). 293B-sensing residues in the pore loop and inner helices of KCNQ1 are underlined.…”