Potassium channel opening: a subtle two-step.
Voltage-gated K(+) channels undergo a voltage-dependent conductance change that plays a key role in modulating cellular excitability. While the Open state is captured in crystal structures of Kv1.2 and a chimeric Kv1.2/Kv2.1 channel, the Close state and the mechanism of this transition are still a subject of debate. Here, we propose a model based on mutagenesis combined with measurements of both ionic and gating currents which is consistent with the idea that the Open state is the default state, the energy of the electric field being used to keep the channel closed. Our model incorporates an 'Activated state' where the bulk of sensor movement is completed without channel opening. The model accounts for the well characterized electrophysiology of the 'V2' and 'ILT' mutations in Shaker, where sensor movement and channel opening occur over distinct voltage ranges. Moreover, the model proposes relatively small protein rearrangements in going from the Activated to the Open state, consistent with the rapid transitions observed in single channel records of Shaker type channels at zero millivolts.
Upadhyay
Sanjeev K
SK
National Centre for Biological Sciences, Tata Institute of Fundamental Research, UAS-GKVK Campus, Bangalore 560065, Karnataka, India.
Nagarajan
P
P
Mathew
M K
MK
D000595:Amino Acid Sequence; D000818:Animals; D003460:Crystallization; D005260:Female; D015640:Ion Channel Gating / Q000502:physiology*; D051663:Kv1.2 Potassium Channel / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D014982:Xenopus laevis
D051663:Kv1.2 Potassium Channel