Engineered interaction between SUR1 and Kir6.2 that enhances ATP sensitivity in KATP channels

Area of Science:

• Ion channel biophysics
• Molecular pharmacology
• Cellular physiology

Background:

• ATP-sensitive potassium (KATP) channels, composed of Kir6.2 and SUR1, link cellular metabolism to membrane excitability and regulate insulin secretion.
• Intracellular ATP inhibits KATP channel activity, a key regulatory feature.
• While Kir6.2 confers ATP sensitivity, SUR1 enhances it, but the underlying mechanism remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanism by which SUR1 enhances the ATP sensitivity of KATP channels.
• To investigate the direct interactions between SUR1 and Kir6.2 subunits.

Main Methods:

• Site-directed mutagenesis to introduce specific mutations (E203K in SUR1, Q52E in Kir6.2).
• Functional characterization of mutant KATP channels to assess ATP sensitivity.
• Site-directed cysteine mutagenesis and chemical cross-linking (E203C in SUR1, Q52C in Kir6.2) to probe residue proximity.

Main Results:

• Mutations E203K in SUR1 and Q52E in Kir6.2 resulted in KATP channels with approximately 100-fold increased ATP sensitivity compared to wild-type.
• Cross-linking of cysteine residues at positions E203 in SUR1 and Q52 in Kir6.2 locked the channel in a closed state.
• The cross-linked state was reversible by reducing agents, confirming close proximity of these residues.

Conclusions:

• Direct molecular interactions between SUR1 and Kir6.2 subunits are critical for modulating KATP channel ATP sensitivity.
• The specific residues E203 in SUR1 and Q52 in Kir6.2 are in close proximity and play a key role in regulating channel gating.
• KATP channel ATP sensitivity is a dynamic parameter influenced by the interplay between SUR1 and Kir6.2.