title: 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.
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Iva
authors.initials: I
authors.lastname: Bruhova
authors.forename: Boris S
authors.initials: BS
authors.lastname: Zhorov
mesh_terms: D000818:Animals; D001665:Binding Sites; D002104:Cadmium / Q000737:chemistry* / Q000378:metabolism; D003198:Computer Simulation; D015640:Ion Channel Gating; D008024:Ligands; D008954:Models, Biological; D008956:Models, Chemical; D008958:Models, Molecular; D016062:Porosity; D015221:Potassium Channels / Q000737:chemistry* / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated / Q000737:chemistry* / Q000502:physiology; D011485:Protein Binding; D011487:Protein Conformation; D051637:Shaker Superfamily of Potassium Channels; D013329:Structure-Activity Relationship
chemical_list: D008024:Ligands; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051637:Shaker Superfamily of Potassium Channels; D002104:Cadmium