A Tyrosine Substitution in the Cavity Wall of a K Channel Induces an Inverted Inactivation

• Published in: Biophysical journal 2008-04, Vol.94 (8), p.3014-3022
• Main Authors: Klement, Göran, Nilsson, Johanna, Århem, Peter, Elinder, Fredrik
• Format: Article
• Language: English
• Subjects: Activation; Amino Acid Substitution; Amino acids; Animals; Cells, Cultured; Channels; Channels, Receptors, and Electrical Signaling; Computer Simulation; Electric potential; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels - chemistry; Ether-A-Go-Go Potassium Channels - metabolism; Ether-A-Go-Go Potassium Channels - ultrastructure; Genes; Holes; Inactivation; Ion Channel Gating - physiology; Ions; Kinetics; MEDICIN; Medicin och hälsovetenskap; MEDICINE; Models, Biological; Models, Chemical; Models, Molecular; Mutation; Oocytes - physiology; Porosity; Protein Conformation; Tyrosine; Tyrosine - chemistry; Voltage; Walls; Xenopus laevis
• ISSN: 0006-3495; 1542-0086; 1542-0086
• DOI: 10.1529/biophysj.107.119842

Ion permeation and gating kinetics of voltage-gated K channels critically depend on the amino-acid composition of the cavity wall. Residue 470 in the Shaker K channel is an isoleucine, making the cavity volume in a closed channel insufficiently large for a hydrated K+ ion. In the cardiac human ether-a-go-go-related gene channel, which exhibits slow activation and fast inactivation, the corresponding residue is tyrosine. To explore the role of a tyrosine at this position in the Shaker channel, we studied I470Y. The activation became slower, and the inactivation faster and more complex. At +60mV the channel inactivated with two distinct rates (τ1=20ms, τ2=400ms). Experiments with tetraethylammonium and high K+ concentrations suggest that the slower component was of the P/C-type. In addition, an inactivation component with inverted voltage dependence was introduced. A step to −40mV inactivates the channel with a time constant of 500ms. Negative voltage steps do not cause the channel to recover from this inactivated state (τ≫10min), whereas positive voltage steps quickly do (τ=2ms at +60mV). The experimental findings can be explained by a simple branched kinetic model with two inactivation pathways from the open state.