A tyrosine substitution in the cavity wall of a k channel induces an inverted inactivation.
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 +60 mV the channel inactivated with two distinct rates (tau(1) = 20 ms, tau(2) = 400 ms). 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 -40 mV inactivates the channel with a time constant of 500 ms. Negative voltage steps do not cause the channel to recover from this inactivated state (tau >> 10 min), whereas positive voltage steps quickly do (tau = 2 ms at +60 mV). The experimental findings can be explained by a simple branched kinetic model with two inactivation pathways from the open state.
Klement
Göran
G
The Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
Nilsson
Johanna
J
Arhem
Peter
P
Elinder
Fredrik
F
D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D015640:Ion Channel Gating / Q000502:physiology*; D008954:Models, Biological; D008956:Models, Chemical; D008958:Models, Molecular; D009865:Oocytes / Q000502:physiology*; D016062:Porosity; D011487:Protein Conformation; D014443:Tyrosine / Q000737:chemistry*; D014982:Xenopus laevis
D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D014443:Tyrosine