title: Mutations of the S4-S5 linker alter activation properties of HERG potassium channels expressed in Xenopus oocytes.
abstract: 1. The structural basis for the activation gate of voltage-dependent K+ channels is not known, but indirect evidence has implicated the S4-S5 linker, the cytoplasmic region between the fourth and fifth transmembrane domains of the channel subunit. We have studied the effects of mutations in the S4-S5 linker of HERG (human ether-á-go-go-related gene), a human delayed rectifier K+ channel, in Xenopus oocytes. 2. Mutation of acidic residues (D540, E544) in the S4-S5 linker of HERG channels to neutral (Ala) or basic (Lys) residues accelerated the rate of channel deactivation. Most mutations greatly accelerated the rate of activation. However, E544K HERG channels activated more slowly than wild-type HERG channels. 3. Mutation of residues in the S4-S5 linker had little or no effect on fast inactivation, consistent with independence of HERG channel activation and inactivation 4. In response to large hyperpolarizations, D540K HERG channels can reopen into a state that is distinct from the normal depolarization-induced open state. It is proposed that substitution of a negatively charged Asp with the positively charged Lys disrupts a subunit interaction that normally stabilizes the channel in a closed state at negative transmembrane potentials. 5. The results indicate that the S4-S5 linker is a crucial component of the activation gate of HERG channels.
authors.affiliation: Eccles Program in Human Molecular Biology and Genetics, Division of Cardiology, Department of Medicine, University of Utah, Salt Lake City,UT 84112, USA.mike.sanguinetti@hci.utah.edu
authors.forename: M C
authors.initials: MC
authors.lastname: Sanguinetti
authors.forename: Q P
authors.initials: QP
authors.lastname: Xu
mesh_terms: D000818:Animals; D001711:Biotransformation / Q000502:physiology; D027682:Cation Transport Proteins; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D004558:Electric Stimulation; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D016254:Mutagenesis, Insertional; D009154:Mutation / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D014982:Xenopus laevis
chemical_list: D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; C072312:ERG protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG