Differences Between Ion Binding to eag and HERG voltage sensors Contribute to Differential Regulation of Activation and Deactivation Gating

• Published in: Channels (Austin, Tex.) Vol. 1; no. 6; pp. 429 - 437
• Main Authors: Lin, Meng-chin, Papazian, Diane
• Format: Journal Article
• Language: English
• Published: United States Taylor & Francis 01.11.2007
• Subjects: Amino Acid Sequence; Animals; Binding; Binding Sites; Biology; Bioscience; Calcium; Cancer; Cations; Cell; Cycle; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels - chemistry; Ether-A-Go-Go Potassium Channels - metabolism; Ions - chemistry; Kinetics; Landes; Magnesium - chemistry; Molecular Sequence Data; Oocytes - metabolism; Organogenesis; Potassium Channels, Voltage-Gated - chemistry; Protein Binding; Proteins; Sequence Homology, Amino Acid; Xenopus
• ISSN: 1933-6950; 1933-6969
• DOI: 10.4161/chan.1.6.5760

HERG (KCNH2) and ether-à-go-go (eag) (KCNH1) are members of the same subfamily of voltage-gated K+ channels. In eag, voltage-dependent activation is significantly slowed by extracellular divalent cations. To exert this effect, ions bind to a site located between transmembrane segments S2 and S3 in the voltage sensor domain where they interact with acidic residues that are conserved only among members of the eag subfamily. In HERG channels, extracellular divalent ions significantly accelerate deactivation. To investigate the ion-binding site in HERG, acidic residues in S2 and S3 were neutralized singly or in pairs to alanine, and the functional effects of extracellular Mg2+ were characterized in Xenopus oocytes. To modulate deactivation kinetics in HERG, divalent cations interact with eag subfamily-specific acidic residues (D460 and D509) and also with an acidic residue in S2 (D456) that is widely conserved in the voltage-gated channel superfamily. In contrast, the analogous widely-conserved residue does not contribute to the ion-binding site that modulates activation kinetics in eag. We propose that structural differences between the ion-binding sites in the eag and HERG voltage sensors contribute to the differential regulation of activation and deactivation gating in these channels. A previously proposed model for S4 conformational changes during voltage-dependent activation can account for the differential regulation of gating seen in eag and HERG.