How ATP inhibits the open K(ATP) channel

Area of Science:

• Biophysics
• Molecular Biology
• Ion Channel Physiology

Background:

• ATP-sensitive potassium (KATP) channels are crucial for cellular energy homeostasis.
• These channels comprise Kir6.2 pore-forming subunits and SUR1 regulatory subunits.
• ATP binding to Kir6.2 inhibits channel activity, with four potential binding sites.

Purpose of the Study:

• To elucidate the mechanism of ATP interaction with the open state of KATP channels.
• To determine the stoichiometry and kinetics of ATP binding to Kir6.2 subunits.
• To differentiate between proposed models of channel gating.

Main Methods:

• Single-channel kinetics analysis of concatenated Kir6.2 tetramers.
• Utilized mutated Kir6.2 subunits with impaired ATP-binding sites (0-4 mutations).
• Mathematical modeling (Monod-Wyman-Changeux, Hodgkin-Huxley) to fit kinetic data.

Main Results:

• The ATP-dependent decrease in mean burst duration aligns with a concerted gating model (Monod-Wyman-Changeux).
• Data rejects independent gating models (Hodgkin-Huxley, dimer).
• ATP binds to a single site on the open channel with a dissociation constant of 300 µM.

Conclusions:

• KATP channel closing is a single, concerted step involving all four subunits.
• ATP interaction with the open channel follows a simple binding mechanism at one site.
• This provides critical insight into the molecular mechanisms of KATP channel regulation.