# Residue 39 of Kir6.2 drives a difference in ATP sensitivity in human and canine beta-cell KATP channels

## TL;DR

This study shows that a single amino acid difference at position 39 in the Kir6.2 subunit causes human and canine beta-cell KATP channels to respond differently to ATP.

## Contribution

The study identifies residue 39 in Kir6.2 as the key determinant of species-specific ATP sensitivity in KATP channels.

## Key findings

- Canine KATP channels show reduced ATP sensitivity compared to human channels.
- Swapping residue 39 between human and canine Kir6.2 alters ATP sensitivity accordingly.
- MgADP sensitivity remains unaffected by the species-specific residue variation.

## Abstract

ATP-sensitive potassium (KATP) channels link beta-cell metabolism to electrical activity. By modulating the beta-cell membrane potential, they finely regulate glucose-stimulated insulin secretion. KATP channels are hetero-octameric complexes composed of four pore-forming subunits (Kir6.2, encoded by KCNJ11) and four regulatory subunits (SUR1, encoded by ABCC8). A multi-species alignment of the KCNJ11 gene revealed that, although the sequence is highly conserved, residue 39 varies among different mammals. Previous studies have shown that this residue plays a critical role in regulating KATP channel activity and its mutation results in neonatal diabetes in humans. We therefore explored whether the canine and human KATP channel show different ATP sensitivities as a result of their sequence variation. We used patch-clamp electrophysiology to investigate species variation in the ATP sensitivity of the KATP channel. Functional studies showed that canine KATP channels exhibit reduced ATP sensitivity compared to human channels. However, stimulation by MgADP was unaffected. We next compared the ATP sensitivity of hybrid channels (human Kir6.2 with canine SUR1, and vice versa), as well as KATP channels in which residue 39 was swapped between human and canine Kir6.2. In each case, ATP sensitivity was mainly determined by the identity of the residue at position 39. Our study suggests that the ATP sensitivity of the pancreatic KATP channel differs between human and dog. This suggests that the beta-cell membrane potential and potentially insulin release may be fine-tuned differently across species.

Diagram depicting glucose metabolism in beta-cells and the role of K_ATP channels. It illustrates glucose entering the cell, triggering ATP/ADP metabolic cascades, which influence K_ATP and L-type Ca^2+ channels, resulting in insulin release. Below, a 3D structural model of two Kir6.2 pore forming subunits highlights residue 39 and its involvement in the binding sites of PIP2 and ATP. The bottom section has three graphs comparing the effects of ATP on channel activity, labeled cK_ATP, hKir6.2+cSUR1, and h/K39N, with I/I_C plotted against ATP concentration. The model is derived from PDB: 8TI1 using PyMol software.