Structure of an open K ATP channel reveals tandem PIP 2 binding sites mediating the Kir6.2 and SUR1 regulatory interface

Cholesterol Concentration in Cell Membranes and its Impact on Receptor-Ligand Interaction: A Computational Study of ATP-Sensitive Potassium Channels and ATP Binding

This work describes a computer study that looks at how different amounts of cholesterol (0%, 25%, and 50%) in cell membranes change the relationship between ATP and the KATP channel. This could explain why pancreatic beta-cells secrete insulin differently. We use computer simulations of molecular dynamics, calculations of binding free energy, and an integrated oscillator model to look at the electrical activity of beta-cells. There is a need for this kind of multiscale approach right now because cholesterol plays a part in metabolic syndrome and early type 2 diabetes. Our results showed that the increase in cholesterol concentration in the cell membrane affects the electrostatic interactions between ATP and the KATP channel, especially with charged residues in the binding site. Cholesterol can influence the properties of a membrane, including its local charge distribution near the channel. This affects the electrostatic environment around the ATP-binding site, increasing  the affinity of ATP for the channel as our results indicated from 0 to 25 and 50% cholesterol (- 141 to - 113 kJ/mol, respectively). Simulating this change in the affinity to ATP of the KATP channels in a model of the electrical activity of the pancreatic beta-cell indicates that even a minimal increase could produce hyperinsulism. The study answers an important research question about how the structure of the membrane affects the function of KATP and, in turn, insulin releases a common feature of metabolic syndrome and early stages of type 2 diabetes.

Dynamic duo: Kir6 and SUR in KATP channel structure and function

KATP channels are ligand-gated potassium channels that couple cellular energetics with membrane potential to regulate cell activity. Each channel is an eight subunit complex comprising four central pore-forming Kir6 inward rectifier potassium channel subunits surrounded by four regulatory subunits known as the sulfonylurea receptor, SUR, which confer homeostatic metabolic control of KATP gating. SUR is an ATP binding cassette (ABC) protein family homolog that lacks membrane transport activity but is essential for KATP expression and function. For more than four decades, understanding the structure-function relationship of Kir6 and SUR has remained a central objective of clinical significance. Here, we review progress in correlating the wealth of functional data in the literature with recent KATP cryoEM structures.

Non-radioactive Rb+ Efflux Assay for Screening KATP Channel Modulators

ATP-sensitive potassium (KATP) channels function as metabolic sensors that link cell membrane excitability to the cellular energy status by controlling potassium ion (K+) flow across the cell membrane according to intracellular ATP and ADP concentrations. As such, KATP channels influence a broad spectrum of physiological processes, including insulin secretion and cardiovascular functions. KATP channels are hetero-octamers, consisting of four inward rectifier potassium channel subunits, Kir6.1 or Kir6.2, and four sulfonylurea receptors (SURs), SUR1, SUR2A, or SUR2B. Different Kir6 and SUR isoforms assemble into KATP channel subtypes with distinct tissue distributions and physiological functions. Mutations in the genes encoding KATP channel subunits underlie various human diseases. Targeted treatment for these diseases requires subtype-specific KATP channel modulators. Rubidium ions (Rb+) also pass through KATP channels, and Rb+ efflux assays can be used to assess KATP channel function and activity. Flame atomic absorption spectroscopy (Flame-AAS) combined with microsampling can measure Rb+ in small volume, which provides an efficient tool to screen for compounds that alter KATP channel activity in Rb+ efflux assays. In this chapter, we describe a detailed protocol for Rb+ efflux assays designed to identify new KATP channel modulators with potential therapeutic utilities.