Adenylate kinase phosphotransfer communicates cellular energetic signals to ATP-sensitive potassium channels

Abstract

Transduction of energetic signals into membrane electrical events governs vital cellular functions, ranging from hormone secretion and cytoprotection to appetite control and hair growth. Central to the regulation of such diverse cellular processes are the metabolism sensing ATP-sensitive K ؉ (KATP) channels. However, the mechanism that communicates metabolic signals and integrates cellular energetics with K ATP channel-dependent membrane excitability remains elusive. Here, we identify that the response of KATP channels to metabolic challenge is regulated by adenylate kinase phosphotransfer. Adenylate kinase associates with the KATP channel complex, anchoring cellular phosphotransfer networks and facilitating delivery of mitochondrial signals to the membrane environment. Deletion of the adenylate kinase gene compromised nucleotide exchange at the channel site and impeded communication between mitochondria and K ATP channels, rendering cellular metabolic sensing defective. Assigning a signal processing role to adenylate kinase identifies a phosphorelay mechanism essential for efficient coupling of cellular energetics with K ATP channels and associated functions. D elivery of metabolic signals to intracellular compartments is a critical determinant of cellular homeostasis. In particular, efficient communication between cellular energetics and membrane metabolic sensors is required for regulation of cell excitability and associated functions (1, 2). Plasmalemmal ATPsensitive K ϩ (K ATP ) channels, formed by the Kir6.2 potassium channel and the sulfonylurea receptor (SUR), are unique nucleotide sensors that adjust membrane potential in response to intracellular metabolic oscillations (2-5). Transition of the SUR subunit from the ATP to the ADP-liganded state promotes K ϩ permeation through Kir6.2 and defines K ATP channel activity (5-7). However, the mechanism that facilitates nucleotide exchange in the K ATP channel environment and promotes coupling of membrane electrical events with cellular metabolic pathways remains unknown.Cellular phosphotransfer reactions catalyze nucleotide exchange facilitating communication between sites of ATP generation and ATP utilization (8-11). In this way, the phosphotransfer enzyme adenylate kinase (AK) amplifies metabolic signals and promotes intracellular phosphoryl transfer by catalyzing the reaction ATP ϩ AMP 7 2ADP (12, 13). Adenylate kinase has a distinct signaling role in setting the cellular response to stress through activation of AMP-dependent processes (12-15). Deletion of the major AK isoform (AK1) results in disturbed muscle energetic economy and decreased tolerance to metabolic stress (14, 15). Mutations in AK compromise nucleotide export from mitochondria (16), as well as the function of ATP-binding cassette transporters (17). Conversely, stimulation of AK phosphotransfer promotes nucleotide-dependent membrane functions (18,19). However, the actual significance of AK phosphotransfer in communicating energetic signals to membrane metabolic sensors, such as the K ATP cha...

ATP-sensitive K channel channel/enzyme multimer: Metabolic gating in the heart

“…Structural and functional interactions of K ATP channel proteins with the phosphotransfer enzymes, adenylate kinase (AK: 2ADP ↔ ATP + AMP) and creatine kinase (CK: ADP + CrP ↔ ATP + Cr), are assured by the wide distribution of these enzymes in distinct cellular compartments, including membranes, and their physical association with K ATP channel sub-units [8,15,91]. Creatine phosphate, the substrate for creatine kinase, facilitates ATP-induced K ATP channel inhibition, a regulation absent in knockout mice lacking the creatine kinase gene M-CK [15].…”

“…Creatine phosphate, the substrate for creatine kinase, facilitates ATP-induced K ATP channel inhibition, a regulation absent in knockout mice lacking the creatine kinase gene M-CK [15]. Analogously, AMP, the substrate for adenylate kinase, antagonizes ATP-induced K ATP channel closure, an effect lost in cardiomyocytes from mice lacking the adenylate kinase AK1 gene [8]. Thus, phosphotransfer reactions regulate K ATP channels providing a mechanism for coupling channel behavior with the cellular energetic state.…”

“…Theoretical and experimental analysis of cooperative interaction between the two prototypic phosphotransfer enzymes, creatine kinase (CK) and adenylate kinase (AK) systems, in a compartmentalized cellular environment reveals unique properties of these enzymes in transmission of energetic signals to sarcolemmal K ATP channels [8,15,16]. Specifically, signal transmission from the cytosol to the submembrane compartment is limited due to restricted diffusion of nucleotides, creatine (Cr) and creatine phosphate (CrP).…”

“…Under severe metabolic challenge, provided that a local regenerating system maintains submembrane ATP levels (i.e. glycolysis or an external source of ATP), bulk AK catalysis could elevate AMP flux into the submembrane compartment and promote the generation of submembrane ADP (ATP + AMP → 2~ADP) facilitating K ATP channel opening [8,16]. Thus, energetic signals generated in the cytosol are processed by CK and AK systems that are capable of synchronizing K ATP channel function with changes in the cellular energetic state (Fig.…”

“…Physical association of the Kir6.2 and SUR2A isoforms generates cardiac K ATP channels that are expressed in high density at the sarcolemma [5,6]. By virtue of their integration with cellular energetic networks and their ability to decode metabolic signals, K ATP channels set membrane excitability to match demand for homeostatic maintenance [7][8][9][10][11]. Recent progress in the understanding of K ATP channel structure and function has been founded on the dissection of channel subunit properties, mapping of channel coupling with cellular energetics and definition of the metabolic sensing role in both healthy and diseased cells.…”