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

2012 ◽  
Vol 140 (2) ◽  
pp. 175-187 ◽  
Author(s):  
Emily B. Pratt ◽  
Qing Zhou ◽  
Joel W. Gay ◽  
Show-Ling Shyng
Keyword(s):  
Cell Metabolism ◽  
Katp Channels ◽  
Dynamic Parameter ◽  
Sulfonylurea Receptor ◽  
Wild Type ◽  
Membrane Excitability ◽  
Close Proximity ◽  
Secretion Inhibition ◽  
Sulfonylurea Receptor 1 ◽  
Hallmark Feature

The ATP-sensitive potassium (KATP) channel consisting of the inward rectifier Kir6.2 and SUR1 (sulfonylurea receptor 1) couples cell metabolism to membrane excitability and regulates insulin secretion. Inhibition by intracellular ATP is a hallmark feature of the channel. ATP sensitivity is conferred by Kir6.2 but enhanced by SUR1. The mechanism by which SUR1 increases channel ATP sensitivity is not understood. In this study, we report molecular interactions between SUR1 and Kir6.2 that markedly alter channel ATP sensitivity. Channels bearing an E203K mutation in SUR1 and a Q52E in Kir6.2 exhibit ATP sensitivity ∼100-fold higher than wild-type channels. Cross-linking of E203C in SUR1 and Q52C in Kir6.2 locks the channel in a closed state and is reversible by reducing agents, demonstrating close proximity of the two residues. Our results reveal that ATP sensitivity in KATP channels is a dynamic parameter dictated by interactions between SUR1 and Kir6.2.

scholarly journals Differential mechanisms of Cantú syndrome–associated gain of function mutations in the ABCC9 (SUR2) subunit of the KATP channel

2015 ◽  
Vol 146 (6) ◽  
pp. 527-540 ◽  
Author(s):  
Paige E. Cooper ◽  
Monica Sala-Rabanal ◽  
Sun Joo Lee ◽  
Colin G. Nichols
Keyword(s):  
Cell Metabolism ◽  
Katp Channels ◽  
Sulfonylurea Receptor ◽  
Membrane Excitability ◽  
Gain Of Function ◽  
Equivalent Position ◽  
Functional Consequences ◽  
Atp Inhibition ◽  
Patch Clamp Electrophysiology ◽  
Inwardly Rectifying

Cantú syndrome (CS) is a rare disease characterized by congenital hypertrichosis, distinct facial features, osteochondrodysplasia, and cardiac defects. Recent genetic analysis has revealed that the majority of CS patients carry a missense mutation in ABCC9, which codes for the sulfonylurea receptor SUR2. SUR2 subunits couple with Kir6.x, inwardly rectifying potassium pore-forming subunits, to form adenosine triphosphate (ATP)-sensitive potassium (KATP) channels, which link cell metabolism to membrane excitability in a variety of tissues including vascular smooth muscle, skeletal muscle, and the heart. The functional consequences of multiple uncharacterized CS mutations remain unclear. Here, we have focused on determining the functional consequences of three documented human CS-associated ABCC9 mutations: human P432L, A478V, and C1043Y. The mutations were engineered in the equivalent position in rat SUR2A (P429L, A475V, and C1039Y), and each was coexpressed with mouse Kir6.2. Using macroscopic rubidium (86Rb+) efflux assays, we show that KATP channels formed with P429L, A475V, or C1039Y mutants enhance KATP activity compared with wild-type (WT) channels. We used inside-out patch-clamp electrophysiology to measure channel sensitivity to ATP inhibition and to MgADP activation. For P429L and A475V mutants, sensitivity to ATP inhibition was comparable to WT channels, but activation by MgADP was significantly greater. C1039Y-dependent channels were significantly less sensitive to inhibition by ATP or by glibenclamide, but MgADP activation was comparable to WT. The results indicate that these three CS mutations all lead to overactive KATP channels, but at least two mechanisms underlie the observed gain of function: decreased ATP inhibition and enhanced MgADP activation.

scholarly journals Identification of a Familial Hyperinsulinism-causing Mutation in the Sulfonylurea Receptor 1 That Prevents Normal Trafficking and Function of KATP Channels

2002 ◽  
Vol 277 (19) ◽  
pp. 17139-17146 ◽  
Author(s):  
Grit Taschenberger ◽  
Adam Mougey ◽  
Shu Shen ◽  
Linda B. Lester ◽  
Stephen LaFranchi ◽  
...  
Keyword(s):  
Katp Channels ◽  
Sulfonylurea Receptor ◽  
Sulfonylurea Receptor 1 ◽  
And Function

scholarly journals Stabilization of the Activity of ATP-sensitive Potassium Channels by Ion Pairs Formed between Adjacent Kir6.2 Subunits

2003 ◽  
Vol 122 (2) ◽  
pp. 225-237 ◽  
Author(s):  
Yu-Wen Lin ◽  
Taiping Jia ◽  
Anne M. Weinsoft ◽  
Show-Ling Shyng
Keyword(s):  
Disulfide Bond ◽  
Bond Formation ◽  
Ion Pairs ◽  
Katp Channels ◽  
Ion Pair ◽  
Disulfide Bond Formation ◽  
Sulfonylurea Receptor ◽  
Close Proximity ◽  
Arginine Residues ◽  
Equivalent Residue

ATP-sensitive potassium (KATP) channels are formed by the coassembly of four Kir6.2 subunits and four sulfonylurea receptor subunits (SUR). The cytoplasmic domains of Kir6.2 mediate channel gating by ATP, which closes the channel, and membrane phosphoinositides, which stabilize the open channel. Little is known, however, about the tertiary or quaternary structures of the domains that are responsible for these interactions. Here, we report that an ion pair between glutamate 229 and arginine 314 in the intracellular COOH terminus of Kir6.2 is critical for maintaining channel activity. Mutation of either residue to alanine induces inactivation, whereas charge reversal at positions 229 and 314 (E229R/R314E) abolishes inactivation and restores the wild-type channel phenotype. The close proximity of these two residues is demonstrated by disulfide bond formation between cysteine residues introduced at the two positions (E229C/R314C); disulfide bond formation abolishes inactivation and stabilizes the current. Using Kir6.2 tandem dimer constructs, we provide evidence that the ion pair likely forms by residues from two adjacent Kir6.2 subunits. We propose that the E229/R314 intersubunit ion pairs may contribute to a structural framework that facilitates the ability of other positively charged residues to interact with membrane phosphoinositides. Glutamate and arginine residues are found at homologous positions in many inward rectifier subunits, including the G-protein–activated inwardly rectifying potassium channel (GIRK), whose cytoplasmic domain structure has recently been solved. In the GIRK structure, the E229- and R314-corresponding residues are oriented in opposite directions in a single subunit such that in the tetramer model, the E229 equivalent residue from one subunit is in close proximity of the R314 equivalent residue from the adjacent subunit. The structure lends support to our findings in Kir6.2, and raises the possibility that a homologous ion pair may be involved in the gating of GIRKs.

Arrhythmia susceptibility and premature death in transgenic mice overexpressing both SUR1 and Kir6.2[ΔN30,K185Q] in the heart

2007 ◽  
Vol 293 (1) ◽  
pp. H836-H845 ◽  
Author(s):  
Thomas P. Flagg ◽  
Brian Patton ◽  
Ricard Masia ◽  
Carrie Mansfield ◽  
Anatoli N. Lopatin ◽  
...  
Keyword(s):  
Transcriptional Control ◽  
Premature Death ◽  
Sulfonylurea Receptor ◽  
Wild Type ◽  
Membrane Excitability ◽  
Β Cell ◽  
Isolated Hearts ◽  
High Level ◽  
Conscious Animals

Sarcolemmal ATP-sensitive potassium (KATP) channels are activated after pathological depletion of intracellular ATP, unlike their pancreatic β-cell counterparts, which dynamically regulate membrane excitability in response to changes in blood glucose. We recently engineered a series of transgenic (TG) mice overexpressing an ATP-insensitive inward rectifying K+ channel protein (Kir)6.2 mutant (Kir6.2[ΔN30,K185Q]) or the accessory sulfonylurea receptor (SUR)2A (FLAG-SUR2A) or SUR1 (FLAG-SUR1) subunits of the KATP channel, under transcriptional control of the α-myosin heavy chain promoter. In the present study, we generated double transgenic (DTG) animals overexpressing both Kir6.2[ΔN30,K185Q] and FLAG-SUR1 or FLAG-SUR2A and examined the effects on cardiac excitability in vivo. No animals expressing both FLAG-SUR1 and Kir6.2[ΔN30,K185Q] transgenes at a high level were obtained. DTG mice expressing one transgene at a high level and the other at a lower level are born, but they die prematurely. Electrocardiographic analysis of both anesthetized and conscious animals revealed a constellation of arrhythmias in DTG animals, but not in wild-type or single TG littermates. The proarrhythmic effect of the transgene combination is intrinsic to the myocardium, since it persists in isolated hearts. Importantly, this effect is specific for SUR1-expressing DTG animals: DTG animals expressing both Kir6.2[ΔN30,K185Q] and FLAG-SUR2A at high levels exhibit neither impaired survival nor increased arrhythmia frequency, even with both subunits expressed at high levels. In demonstrating the profound arrhythmic consequences of KATP channels comprised of SUR1 and Kir6.2[ΔN30,K185Q] in the myocardium specifically, the results highlight the critical differential activation of SUR1 versus SUR2A, and indicate that expression of hyperactive KATP in the heart is likely to be proarrhythmic.

scholarly journals Noble Gas Xenon Is a Novel Adenosine Triphosphate-sensitive Potassium Channel Opener

2010 ◽  
Vol 112 (3) ◽  
pp. 623-630 ◽  
Author(s):  
Carsten Bantel ◽  
Mervyn Maze ◽  
Stefan Trapp
Keyword(s):  
Blood Brain Barrier ◽  
Adenosine Triphosphate ◽  
Katp Channel ◽  
Katp Channels ◽  
Brain Barrier ◽  
Hek293 Cells ◽  
Sulfonylurea Receptor ◽  
Channel Opener ◽  
Blood Brain ◽  
Sulfonylurea Receptor 1

Background Adenosine triphosphate-sensitive potassium (KATP) channels in brain are involved in neuroprotective mechanisms. Pharmacologic activation of these channels is seen as beneficial, but clinical exploitation by using classic K channel openers is hampered by their inability to cross the blood-brain barrier. This is different with the inhalational anesthetic xenon, which recently has been suggested to activate KATP channels; it partitions freely into the brain. Methods To evaluate the type and mechanism of interaction of xenon with neuronal-type KATP channels, these channels, consisting of Kir6.2 pore-forming subunits and sulfonylurea receptor-1 regulatory subunits, were expressed in HEK293 cells and whole cell, and excised patch-clamp recordings were performed. Results Xenon, in contrast to classic KATP channel openers, acted directly on the Kir6.2 subunit of the channel. It had no effect on the closely related, adenosine triphosphate (ATP)-regulated Kir1.1 channel and failed to activate an ATP-insensitive mutant version of Kir6.2. Furthermore, concentration-inhibition curves for ATP obtained from inside-out patches in the absence or presence of 80% xenon revealed that xenon reduced the sensitivity of the KATP channel to ATP. This was reflected in an approximately fourfold shift of the concentration causing half-maximal inhibition (IC50) from 26 +/- 4 to 96 +/- 6 microm. Conclusions Xenon represents a novel KATP channel opener that increases KATP currents independently of the sulfonylurea receptor-1 subunit by reducing ATP inhibition of the channel. Through this action and by its ability to readily partition across the blood-brain barrier, xenon has considerable potential in clinical settings of neuronal injury, including stroke.

scholarly journals ATP binding without hydrolysis switches sulfonylurea receptor 1 (SUR1) to outward-facing conformations that activate KATP channels

2018 ◽  
Vol 294 (10) ◽  
pp. 3707-3719 ◽  
Author(s):  
Jelena Sikimic ◽  
Timothy S. McMillen ◽  
Cita Bleile ◽  
Frank Dastvan ◽  
Ulrich Quast ◽  
...  
Keyword(s):  
Katp Channels ◽  
Atp Binding ◽  
Sulfonylurea Receptor ◽  
Sulfonylurea Receptor 1

scholarly journals Muscle KATP Channels: Recent Insights to Energy Sensing and Myoprotection

2010 ◽  
Vol 90 (3) ◽  
pp. 799-829 ◽  
Author(s):  
Thomas P. Flagg ◽  
Decha Enkvetchakul ◽  
Joseph C. Koster ◽  
Colin G. Nichols
Keyword(s):  
Cell Metabolism ◽  
Katp Channels ◽  
Sulfonylurea Receptor ◽  
Channel Activity ◽  
Tissue Specific ◽  
Fiber Damage ◽  
Cellular Energetics ◽  
Muscle Types ◽  
Energy Sensing ◽  
The Cost

ATP-sensitive potassium (KATP) channels are present in the surface and internal membranes of cardiac, skeletal, and smooth muscle cells and provide a unique feedback between muscle cell metabolism and electrical activity. In so doing, they can play an important role in the control of contractility, particularly when cellular energetics are compromised, protecting the tissue against calcium overload and fiber damage, but the cost of this protection may be enhanced arrhythmic activity. Generated as complexes of Kir6.1 or Kir6.2 pore-forming subunits with regulatory sulfonylurea receptor subunits, SUR1 or SUR2, the differential assembly of KATP channels in different tissues gives rise to tissue-specific physiological and pharmacological regulation, and hence to the tissue-specific pharmacological control of contractility. The last 10 years have provided insights into the regulation and role of muscle KATP channels, in large part driven by studies of mice in which the protein determinants of channel activity have been deleted or modified. As yet, few human diseases have been correlated with altered muscle KATP activity, but genetically modified animals give important insights to likely pathological roles of aberrant channel activity in different muscle types.

scholarly journals Cryo-electron microscopy structures and progress toward a dynamic understanding of KATP channels

2018 ◽  
Vol 150 (5) ◽  
pp. 653-669 ◽  
Author(s):  
Michael C. Puljung
Keyword(s):  
Electron Microscopy ◽  
Ligand Binding ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Cell Metabolism ◽  
Katp Channels ◽  
K Channel ◽  
Sulfonylurea Receptor ◽  
Binding Domains ◽  
Cryo Electron Microscopy

Adenosine triphosphate (ATP)–sensitive K+ (KATP) channels are molecular sensors of cell metabolism. These hetero-octameric channels, comprising four inward rectifier K+ channel subunits (Kir6.1 or Kir6.2) and four sulfonylurea receptor (SUR1 or SUR2A/B) subunits, detect metabolic changes via three classes of intracellular adenine nucleotide (ATP/ADP) binding site. One site, located on the Kir subunit, causes inhibition of the channel when ATP or ADP is bound. The other two sites, located on the SUR subunit, excite the channel when bound to Mg nucleotides. In pancreatic β cells, an increase in extracellular glucose causes a change in oxidative metabolism and thus turnover of adenine nucleotides in the cytoplasm. This leads to the closure of KATP channels, which depolarizes the plasma membrane and permits Ca2+ influx and insulin secretion. Many of the molecular details regarding the assembly of the KATP complex, and how changes in nucleotide concentrations affect gating, have recently been uncovered by several single-particle cryo-electron microscopy structures of the pancreatic KATP channel (Kir6.2/SUR1) at near-atomic resolution. Here, the author discusses the detailed picture of excitatory and inhibitory ligand binding to KATP that these structures present and suggests a possible mechanism by which channel activation may proceed from the ligand-binding domains of SUR to the channel pore.

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