1
|
Xu H, Van Remmen H. The SarcoEndoplasmic Reticulum Calcium ATPase (SERCA) pump: a potential target for intervention in aging and skeletal muscle pathologies. Skelet Muscle 2021; 11:25. [PMID: 34772465 PMCID: PMC8588740 DOI: 10.1186/s13395-021-00280-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 10/26/2021] [Indexed: 01/13/2023] Open
Abstract
As a key regulator of cellular calcium homeostasis, the Sarcoendoplasmic Reticulum Calcium ATPase (SERCA) pump acts to transport calcium ions from the cytosol back to the sarcoplasmic reticulum (SR) following muscle contraction. SERCA function is closely associated with muscle health and function, and SERCA activity is susceptible to muscle pathogenesis. For example, it has been well reported that pathological conditions associated with aging, neurodegeneration, and muscular dystrophy (MD) significantly depress SERCA function with the potential to impair intracellular calcium homeostasis and further contribute to muscle atrophy and weakness. As a result, targeting SERCA activity has attracted attention as a therapeutical method for the treatment of muscle pathologies. The interventions include activation of SERCA activity and genetic overexpression of SERCA. This review will focus on SERCA function and regulation mechanisms and describe how those mechanisms are affected under muscle pathological conditions including elevated oxidative stress induced by aging, muscle disease, or neuromuscular disorders. We also discuss the current progress and therapeutic approaches to targeting SERCA in vivo.
Collapse
Affiliation(s)
- Hongyang Xu
- Aging & Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, 73104, USA
| | - Holly Van Remmen
- Aging & Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, 73104, USA. .,Oklahoma City VA Medical Center, Oklahoma City, OK, USA. .,Department of Physiology, OUHSC, Oklahoma City, OK, USA.
| |
Collapse
|
2
|
Petrovich GD, Corradi GR, Pavan CH, Noli Truant S, Adamo HP. Highly exposed segment of the Spf1p P5A-ATPase near transmembrane M5 detected by limited proteolysis. PLoS One 2021; 16:e0245679. [PMID: 33507968 PMCID: PMC7842927 DOI: 10.1371/journal.pone.0245679] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2020] [Accepted: 01/05/2021] [Indexed: 11/20/2022] Open
Abstract
The yeast Spf1p protein is a primary transporter that belongs to group 5 of the large family of P-ATPases. Loss of Spf1p function produces ER stress with alterations of metal ion and sterol homeostasis and protein folding, glycosylation and membrane insertion. The amino acid sequence of Spf1p shows the characteristic P-ATPase domains A, N, and P and the transmembrane segments M1-M10. In addition, Spf1p exhibits unique structures at its N-terminus (N-T region), including two putative additional transmembrane domains, and a large insertion connecting the P domain with transmembrane segment M5 (D region). Here we used limited proteolysis to examine the structure of Spf1p. A short exposure of Spf1p to trypsin or proteinase K resulted in the cleavage at the N and C terminal regions of the protein and abrogated the formation of the catalytic phosphoenzyme and the ATPase activity. In contrast, limited proteolysis of Spf1p with chymotrypsin generated a large N-terminal fragment containing most of the M4-M5 cytosolic loop, and a minor fragment containing the C-terminal region. If lipids were present during chymotryptic proteolysis, phosphoenzyme formation and ATPase activity were preserved. ATP slowed Spf1p proteolysis without detectable changes of the generated fragments. The analysis of the proteolytic peptides by mass spectrometry and Edman degradation indicated that the preferential chymotryptic site was localized near the cytosolic end of M5. The susceptibility to proteolysis suggests an unexpected exposure of this region of Spf1p that may be an intrinsic feature of P5A-ATPases.
Collapse
Affiliation(s)
- Guido D. Petrovich
- Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Gerardo R. Corradi
- Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Carlos H. Pavan
- Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Sofia Noli Truant
- Facultad de Farmacia y Bioquímica, Cátedra de Inmunología and Instituto de Estudios de la Inmunidad Humoral Prof. Dr. Ricardo A. Margni (IDEHU), UBA-CONICET, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Hugo P. Adamo
- Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)-Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Universidad de Buenos Aires, Buenos Aires, Argentina
- * E-mail:
| |
Collapse
|
3
|
Engevik AC, Kaji I, Goldenring JR. The Physiology of the Gastric Parietal Cell. Physiol Rev 2020; 100:573-602. [PMID: 31670611 PMCID: PMC7327232 DOI: 10.1152/physrev.00016.2019] [Citation(s) in RCA: 97] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 10/10/2019] [Accepted: 10/13/2019] [Indexed: 12/11/2022] Open
Abstract
Parietal cells are responsible for gastric acid secretion, which aids in the digestion of food, absorption of minerals, and control of harmful bacteria. However, a fine balance of activators and inhibitors of parietal cell-mediated acid secretion is required to ensure proper digestion of food, while preventing damage to the gastric and duodenal mucosa. As a result, parietal cell secretion is highly regulated through numerous mechanisms including the vagus nerve, gastrin, histamine, ghrelin, somatostatin, glucagon-like peptide 1, and other agonists and antagonists. The tight regulation of parietal cells ensures the proper secretion of HCl. The H+-K+-ATPase enzyme expressed in parietal cells regulates the exchange of cytoplasmic H+ for extracellular K+. The H+ secreted into the gastric lumen by the H+-K+-ATPase combines with luminal Cl- to form gastric acid, HCl. Inhibition of the H+-K+-ATPase is the most efficacious method of preventing harmful gastric acid secretion. Proton pump inhibitors and potassium competitive acid blockers are widely used therapeutically to inhibit acid secretion. Stimulated delivery of the H+-K+-ATPase to the parietal cell apical surface requires the fusion of intracellular tubulovesicles with the overlying secretory canaliculus, a process that represents the most prominent example of apical membrane recycling. In addition to their unique ability to secrete gastric acid, parietal cells also play an important role in gastric mucosal homeostasis through the secretion of multiple growth factor molecules. The gastric parietal cell therefore plays multiple roles in gastric secretion and protection as well as coordination of physiological repair.
Collapse
Affiliation(s)
- Amy C Engevik
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| | - Izumi Kaji
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| | - James R Goldenring
- Departments of Surgery and of Cell and Developmental Biology and the Epithelial Biology Center, Vanderbilt University School of Medicine, Vanderbilt University Medical Center and the Nashville VA Medical Center, Nashville, Tennessee
| |
Collapse
|
4
|
Ortiz-Guerrero G, Amador-Muñoz D, Calderón-Ospina CA, López-Fuentes D, Nava Mesa MO. Proton Pump Inhibitors and Dementia: Physiopathological Mechanisms and Clinical Consequences. Neural Plast 2018; 2018:5257285. [PMID: 29755512 PMCID: PMC5883984 DOI: 10.1155/2018/5257285] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 02/14/2018] [Indexed: 12/11/2022] Open
Abstract
Alzheimer's disease (AD) is the most common type of dementia, mainly encompassing cognitive decline in subjects aged ≥65 years. Further, AD is characterized by selective synaptic and neuronal degeneration, vascular dysfunction, and two histopathological features: extracellular amyloid plaques composed of amyloid beta peptide (Aβ) and neurofibrillary tangles formed by hyperphosphorylated tau protein. Dementia and AD are chronic neurodegenerative conditions with a complex physiopathology involving both genetic and environmental factors. Recent clinical studies have shown that proton pump inhibitors (PPIs) are associated with risk of dementia, including AD. However, a recent case-control study reported decreased risk of dementia. PPIs are a widely indicated class of drugs for gastric acid-related disorders, although most older adult users are not treated for the correct indication. Although neurological side effects secondary to PPIs are rare, several preclinical reports indicate that PPIs might increase Aβ levels, interact with tau protein, and affect the neuronal microenvironment through several mechanisms. Considering the controversy between PPI use and dementia risk, as well as both cognitive and neuroprotective effects, the aim of this review is to examine the relationship between PPI use and brain effects from a neurobiological and clinical perspective.
Collapse
Affiliation(s)
- Gloria Ortiz-Guerrero
- Individualized Research Learner Program, Neuromuscular Research Division, University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | - Diana Amador-Muñoz
- Neuroscience (NEUROS) Research Group, School of Medicine and Health Sciences, Universidad del Rosario, Carrera 24 No. 63C–69, Bogotá 111221, Colombia
| | - Carlos Alberto Calderón-Ospina
- Unidad de Farmacología, School of Medicine and Health Sciences, Universidad del Rosario, Carrera 24 No. 63C–69, Bogotá 111221, Colombia
| | - Daniel López-Fuentes
- Medical Social Service, Hospital de San Francisco, Kra 8 No. 6A–121, Gacheta 251230, Colombia
| | - Mauricio Orlando Nava Mesa
- Neuroscience (NEUROS) Research Group, School of Medicine and Health Sciences, Universidad del Rosario, Carrera 24 No. 63C–69, Bogotá 111221, Colombia
| |
Collapse
|
5
|
Liu J, Lilly MN, Shapiro JI. Targeting Na/K-ATPase Signaling: A New Approach to Control Oxidative Stress. Curr Pharm Des 2018; 24:359-364. [PMID: 29318961 PMCID: PMC6052765 DOI: 10.2174/1381612824666180110101052] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2017] [Revised: 12/27/2017] [Accepted: 01/04/2017] [Indexed: 01/13/2023]
Abstract
Renal and cardiac function are greatly affected by chronic oxidative stress which can cause many pathophysiological states. The Na/K-ATPase is well-described as an ion pumping enzyme involved in maintaining cellular ion homeostasis; however, in the past two decades, extensive research has been done to understand the signaling function of the Na/K-ATPase and determine its role in physiological and pathophysiological states. Our lab has shown that the Na/K-ATPase signaling cascade can function as an amplifier of reactive oxygen species (ROS) which can be initiated by cardiotonic steroids or increases in ROS. Regulation of systemic oxidative stress by targeting Na/K-ATPase signaling mediated oxidant amplification improves 5/6th partial nephrectomy (PNx) mediated uremic cardiomyopathy, renal sodium handling, as well as ameliorates adipogenesis. This review will present this new concept of Na/K-ATPase signaling mediated oxidant amplification loop and its clinic implication.
Collapse
Affiliation(s)
- Jiang Liu
- Dept. of Biomedical Sciences, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV
| | - Megan N. Lilly
- Dept. of Biomedical Sciences, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV
| | - Joseph I. Shapiro
- Dept. of Medicine, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV
| |
Collapse
|
6
|
IP 3 receptor signaling and endothelial barrier function. Cell Mol Life Sci 2017; 74:4189-4207. [PMID: 28803370 DOI: 10.1007/s00018-017-2624-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 07/18/2017] [Accepted: 08/08/2017] [Indexed: 12/14/2022]
Abstract
The endothelium, a monolayer of endothelial cells lining vessel walls, maintains tissue-fluid homeostasis by restricting the passage of the plasma proteins and blood cells into the interstitium. The ion Ca2+, a ubiquitous secondary messenger, initiates signal transduction events in endothelial cells that is critical to control of vascular tone and endothelial permeability. The ion Ca2+ is stored inside the intracellular organelles and released into the cytosol in response to environmental cues. The inositol 1,4,5-trisphosphate (IP3) messenger facilitates Ca2+ release through IP3 receptors which are Ca2+-selective intracellular channels located within the membrane of the endoplasmic reticulum. Binding of IP3 to the IP3Rs initiates assembly of IP3R clusters, a key event responsible for amplification of Ca2+ signals in endothelial cells. This review discusses emerging concepts related to architecture and dynamics of IP3R clusters, and their specific role in propagation of Ca2+ signals in endothelial cells.
Collapse
|
7
|
Wang X, Liu J, Drummond CA, Shapiro JI. Sodium potassium adenosine triphosphatase (Na/K-ATPase) as a therapeutic target for uremic cardiomyopathy. Expert Opin Ther Targets 2017; 21:531-541. [PMID: 28338377 PMCID: PMC5590225 DOI: 10.1080/14728222.2017.1311864] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 03/23/2017] [Indexed: 12/30/2022]
Abstract
INTRODUCTION Clinically, patients with significant reductions in renal function present with cardiovascular dysfunction typically termed, uremic cardiomyopathy. It is a progressive series of cardiac pathophysiological changes, including left ventricular diastolic dysfunction and hypertrophy (LVH) which sometimes progress to left ventricular dilation (LVD) and systolic dysfunction in the setting of chronic kidney disease (CKD). Uremic cardiomyopathy is almost ubiquitous in patients afflicted with end stage renal disease (ESRD). Areas covered: This article reviews recent epidemiology, pathophysiology of uremic cardiomyopathy and provide a board overview of Na/K-ATPase research with detailed discussion on the mechanisms of Na/K-ATPase/Src/ROS amplification loop. We also present clinical and preclinical evidences as well as molecular mechanism of this amplification loop in the development of uremic cardiomyopathy. A potential therapeutic peptide that targets on this loop is discussed. Expert opinion: Current clinical treatment for uremic cardiomyopathy remains disappointing. Targeting the ROS amplification loop mediated by the Na/K-ATPase signaling function may provide a novel therapeutic target for uremic cardiomyopathy and related diseases. Additional studies of Na/K-ATPase and other strategies that regulate this loop will lead to new therapeutics.
Collapse
Affiliation(s)
- Xiaoliang Wang
- a Joan C Edwards School of Medicine at Marshall University , Huntington , WV , United States
- b University of Toledo College of Medicine and Life Sciences , Toledo , OH , United States
| | - Jiang Liu
- a Joan C Edwards School of Medicine at Marshall University , Huntington , WV , United States
| | - Christopher A Drummond
- b University of Toledo College of Medicine and Life Sciences , Toledo , OH , United States
| | - Joseph I Shapiro
- a Joan C Edwards School of Medicine at Marshall University , Huntington , WV , United States
| |
Collapse
|
8
|
Fan X, Xie J, Tian J. Reducing Cardiac Fibrosis: Na/K-ATPase Signaling Complex as a Novel Target. ACTA ACUST UNITED AC 2017; 6. [PMID: 29034264 DOI: 10.4172/2329-6607.1000204] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Cardiac fibrosis is a common pathological process in cardiac disease and may lead to heart failure. It can also cause sudden death even in those without cardiac symptoms. Tissue fibrosis can be categorized into two categories: replacement fibrosis (also called reparative fibrosis) and reactive fibrosis. In replacement fibrosis, infiltration of inflammatory cells and accumulation of Extracellular Matrix (ECM) proteins are the initial steps in forming scarlike fibrotic tissue after acute cardiac injury and cardiac cell necrosis. Reactive fibrosis can be formed in response to hormonal change and pressure or volume overload. Experimental studies in animals have identified important pathways such as the Renin-Angiotensin-Aldosterone System (RAAS) and the endothelin pathway that contribute to fibrosis formation. Despite the fact that clinical trials using RAAS inhibitors as therapies for reducing cardiac fibrosis and improving cardiac function have been promising, heart failure is still the leading cause of deaths in the United States. Intensive efforts have been made to find novel targets and to develop new treatments for cardiac fibrosis and heart failure in the past few decades. The Na/K-ATPase, a canonical ion transporter, has been shown to also function as a signal transducer and prolonged activation of Na/K-ATPase signaling has been found to promote the formation of cardiac fibrosis. Novel tools that block the activation of Na/K-ATPase signaling have been developed and have shown promise in reducing cardiac fibrosis. This review will discuss the recent development of novel molecular targets, focusing on the Na/K-ATPase signaling complex as a therapeutic target in treatment of cardiac fibrosis.
Collapse
Affiliation(s)
- X Fan
- Department of Medicine, Center for Hypertension and Personalized Medicine, University of Toledo, Ohio 43614, USA
| | - J Xie
- Department of Medicine, Center for Hypertension and Personalized Medicine, University of Toledo, Ohio 43614, USA
| | - J Tian
- Department of Medicine, Center for Hypertension and Personalized Medicine, University of Toledo, Ohio 43614, USA
| |
Collapse
|
9
|
Shattock MJ, Ottolia M, Bers DM, Blaustein MP, Boguslavskyi A, Bossuyt J, Bridge JHB, Chen-Izu Y, Clancy CE, Edwards A, Goldhaber J, Kaplan J, Lingrel JB, Pavlovic D, Philipson K, Sipido KR, Xie ZJ. Na+/Ca2+ exchange and Na+/K+-ATPase in the heart. J Physiol 2015; 593:1361-82. [PMID: 25772291 PMCID: PMC4376416 DOI: 10.1113/jphysiol.2014.282319] [Citation(s) in RCA: 141] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Accepted: 10/30/2014] [Indexed: 12/17/2022] Open
Abstract
This paper is the third in a series of reviews published in this issue resulting from the University of California Davis Cardiovascular Symposium 2014: Systems approach to understanding cardiac excitation–contraction coupling and arrhythmias: Na+ channel and Na+ transport. The goal of the symposium was to bring together experts in the field to discuss points of consensus and controversy on the topic of sodium in the heart. The present review focuses on cardiac Na+/Ca2+ exchange (NCX) and Na+/K+-ATPase (NKA). While the relevance of Ca2+ homeostasis in cardiac function has been extensively investigated, the role of Na+ regulation in shaping heart function is often overlooked. Small changes in the cytoplasmic Na+ content have multiple effects on the heart by influencing intracellular Ca2+ and pH levels thereby modulating heart contractility. Therefore it is essential for heart cells to maintain Na+ homeostasis. Among the proteins that accomplish this task are the Na+/Ca2+ exchanger (NCX) and the Na+/K+ pump (NKA). By transporting three Na+ ions into the cytoplasm in exchange for one Ca2+ moved out, NCX is one of the main Na+ influx mechanisms in cardiomyocytes. Acting in the opposite direction, NKA moves Na+ ions from the cytoplasm to the extracellular space against their gradient by utilizing the energy released from ATP hydrolysis. A fine balance between these two processes controls the net amount of intracellular Na+ and aberrations in either of these two systems can have a large impact on cardiac contractility. Due to the relevant role of these two proteins in Na+ homeostasis, the emphasis of this review is on recent developments regarding the cardiac Na+/Ca2+ exchanger (NCX1) and Na+/K+ pump and the controversies that still persist in the field.
Collapse
Affiliation(s)
- Michael J Shattock
- King's College London BHF Centre of Excellence, The Rayne Institute, St Thomas' Hospital, London, SE1 7EH, UK
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
10
|
Maggio N, Vlachos A. Synaptic plasticity at the interface of health and disease: New insights on the role of endoplasmic reticulum intracellular calcium stores. Neuroscience 2014; 281:135-46. [PMID: 25264032 DOI: 10.1016/j.neuroscience.2014.09.041] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 09/17/2014] [Accepted: 09/18/2014] [Indexed: 10/24/2022]
Abstract
Work from the past 40years has unraveled a wealth of information on the cellular and molecular mechanisms underlying synaptic plasticity and their relevance in physiological brain function. At the same time, it has been recognized that a broad range of neurological diseases may be accompanied by severe alterations in synaptic plasticity, i.e., 'maladaptive synaptic plasticity', which could initiate and sustain the remodeling of neuronal networks under pathological conditions. Nonetheless, our current knowledge on the specific contribution and interaction of distinct forms of synaptic plasticity (including metaplasticity and homeostatic plasticity) in the context of pathological brain states remains limited. This review focuses on recent experimental evidence, which highlights the fundamental role of endoplasmic reticulum-mediated Ca(2+) signals in modulating the duration, direction, extent and type of synaptic plasticity. We discuss the possibility that intracellular Ca(2+) stores may regulate synaptic plasticity and hence behavioral and cognitive functions at the interface between physiology and pathology.
Collapse
Affiliation(s)
- N Maggio
- Talpiot Medical Leadership Program, Department of Neurology, The Chaim Sheba Medical Center, 52621 Tel HaShomer, Israel
| | - A Vlachos
- Institute of Clinical Neuroanatomy, Neuroscience Center, Goethe-University Frankfurt, 60590 Frankfurt, Germany.
| |
Collapse
|
11
|
Na⁺/K⁺-ATPase E960 and phospholemman F28 are critical for their functional interaction. Proc Natl Acad Sci U S A 2012. [PMID: 23185013 DOI: 10.1073/pnas.1207866109] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Na(+)-K(+)-ATPase (NKA) establishes the transmembrane [Na(+)] gradient in cells. In heart, phospholemman (PLM) inhibits NKA activity by reducing its apparent Na(+) affinity, an effect that is relieved by PLM phosphorylation. The NKA crystal structure suggests regions of PLM-NKA interaction, but the sites important for functional effects in live cells are not known. We tested wild type (WT) and CFP-NKA-α1 point mutants (alanine substitution at F956, E960, L964, and F967) for fluorescence resonance energy transfer (FRET) with WT-PLM-YFP in HEK293 cells. NKA-PLM FRET was unaltered with F956A or F967A, reduced with L964A, and nearly abolished with E960A. Mutating the PLM site (F28A) identified by structural analysis to interact with E960-NKA also nearly abolished NKA-PLM FRET. In contrast, NKA-PLM coimmunoprecipitation was only slightly reduced by E960A-NKA or F28A-PLM mutants, consistent with an additional interaction site. FRET titrations indicate that the additional site has higher affinity than that between E960-NKA and F28-PLM. To test whether the FRET-preventing mutations also prevent PLM functional effects, we measured NKA-mediated Na(+)-transport in intact cells. For WT-NKA, PLM reduced apparent Na(+)-affinity of NKA and PLM phosphorylation reversed the effect. In contrast, for E960A-NKA the apparent Na(+)-affinity was unaltered by either PLM or forskolin-induced PLM phosphorylation. We conclude that E960 on NKA and F28 on PLM are critical for PLM effects on both NKA function and NKA-PLM FRET, but also there is at least one additional site that is critical for tethering PLM to NKA.
Collapse
|
12
|
Community-wide convergent evolution in insect adaptation to toxic cardenolides by substitutions in the Na,K-ATPase. Proc Natl Acad Sci U S A 2012; 109:13040-5. [PMID: 22826239 DOI: 10.1073/pnas.1202111109] [Citation(s) in RCA: 180] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The extent of convergent molecular evolution is largely unknown, yet is critical to understanding the genetics of adaptation. Target site insensitivity to cardenolides is a prime candidate for studying molecular convergence because herbivores in six orders of insects have specialized on these plant poisons, which gain their toxicity by blocking an essential transmembrane carrier, the sodium pump (Na,K-ATPase). We investigated gene sequences of the Na,K-ATPase α-subunit in 18 insects feeding on cardenolide-containing plants (spanning 15 genera and four orders) to screen for amino acid substitutions that might lower sensitivity to cardenolides. The replacement N122H that was previously shown to confer resistance in the monarch butterfly (Danaus plexippus) and Chrysochus leaf beetles was found in four additional species, Oncopeltus fasciatus and Lygaeus kalmii (Heteroptera, Lygaeidae), Labidomera clivicollis (Coleoptera, Chrysomelidae), and Liriomyza asclepiadis (Diptera, Agromyzidae). Thus, across 300 Myr of insect divergence, specialization on cardenolide-containing plants resulted in molecular convergence for an adaptation likely involved in coevolution. Our screen revealed a number of other substitutions connected to cardenolide binding in mammals. We confirmed that some of the particular substitutions provide resistance to cardenolides by introducing five distinct constructs of the Drosophila melanogaster gene into susceptible eucaryotic cells under an ouabain selection regime. These functional assays demonstrate that combined substitutions of Q(111) and N(122) are synergistic, with greater than twofold higher resistance than either substitution alone and >12-fold resistance over the wild type. Thus, even across deep phylogenetic branches, evolutionary degrees of freedom seem to be limited by physiological constraints, such that the same molecular substitutions confer adaptation.
Collapse
|
13
|
Haghighi K, Pritchard T, Bossuyt J, Waggoner JR, Yuan Q, Fan GC, Osinska H, Anjak A, Rubinstein J, Robbins J, Bers DM, Kranias EG. The human phospholamban Arg14-deletion mutant localizes to plasma membrane and interacts with the Na/K-ATPase. J Mol Cell Cardiol 2011; 52:773-82. [PMID: 22155237 DOI: 10.1016/j.yjmcc.2011.11.012] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Accepted: 11/20/2011] [Indexed: 12/18/2022]
Abstract
Depressed Ca-handling in cardiomyocytes is frequently attributed to impaired sarcoplasmic reticulum (SR) function in human and experimental heart failure. Phospholamban (PLN) is a key regulator of SR and cardiac function, and PLN mutations in humans have been associated with dilated cardiomyopathy (DCM). We previously reported the deletion of the highly conserved amino acid residue arginine 14 (nucleic acids 39, 40 and 41) in DCM patients. This basic amino acid is important in maintaining the upstream consensus sequence for PKA phosphorylation of Ser 16 in PLN. To assess the function of this mutant PLN, we introduced the PLN-R14Del in cardiac myocytes of the PLN null mouse. Transgenic lines expressing mutant PLN-R14Del at similar protein levels to wild types exhibited no inhibition of the initial rates of oxalate-facilitated SR Ca uptake compared to PLN-knockouts (PLN-KO). The contractile parameters and Ca-kinetics also remained highly stimulated in PLN-R14Del cardiomyocytes, similar to PLN-KO, and isoproterenol did not further stimulate these hyper-contractile basal parameters. Consistent with the lack of inhibition on SR Ca-transport and contractility, confocal microscopy indicated that the PLN-R14Del failed to co-localize with SERCA2a. Moreover, PLN-R14Del did not co-immunoprecipitate with SERCA2a (as did WT-PLN), but rather co-immunoprecipitated with the sarcolemmal Na/K-ATPase (NKA) and stimulated NKA activity. In addition, studies in HEK cells indicated significant fluorescence resonance energy transfer between PLN-R14Del-YFP and NKAα1-CFP, but not with the NKA regulator phospholemman. Despite the enhanced cardiac function in PLN-R14Del hearts (as in PLN-knockouts), there was cardiac hypertrophy (unlike PLN-KO) coupled with activation of Akt and the MAPK pathways. Thus, human PLN-R14Del is misrouted to the sarcolemma, in the absence of endogenous PLN, and alters NKA activity, leading to cardiac remodeling.
Collapse
Affiliation(s)
- Kobra Haghighi
- Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267-0575, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
14
|
Xu L, Wang Z, Xiong X, Gu X, Gao X, Gao X. Identification of a novel point mutation of mouse Atp2b2 induced by N-ethyl-N-nitrosourea mutagenesis. Exp Anim 2011; 60:71-8. [PMID: 21325754 DOI: 10.1538/expanim.60.71] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
N-ethyl-N-nitrosourea (ENU)-induced mutagenesis is an important approach in the study of gene function and the establishment of human disease models. Here we report an ENU-induced mutation, Elfin, as a mouse model with hearing loss. Homozygous mutants were deaf and displayed severe ataxia, while heterozygous mice had a significant hearing loss. Histological analysis of the inner ear revealed that Elfin had progressive degeneration of the organ of Corti, spiral ganglion cells and an absence of otoconia in the vestibular system. The new mutation was mapped to chromosome 6 between microsatellite markers D6Mit39 and D6Mit254, where the Ca(2+)-ATPase type 2 (Atp2b2) gene resides. Sequence analysis revealed a unique T-to-A transition mutation at amino acid 655 resulting in Ile-to-Asn substitution. These results for the Elfin mutant confirm the role of ATP2B2 in balance, hearing and formation of otoconia and suggest it may serve as a new model of human hereditary hearing loss.
Collapse
Affiliation(s)
- Lin Xu
- Department of Otolaryngology and Head & Neck Surgery, The Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing 210008, China
| | | | | | | | | | | |
Collapse
|
15
|
Einholm AP, Toustrup-Jensen MS, Holm R, Andersen JP, Vilsen B. The rapid-onset dystonia parkinsonism mutation D923N of the Na+, K+-ATPase alpha3 isoform disrupts Na+ interaction at the third Na+ site. J Biol Chem 2010; 285:26245-54. [PMID: 20576601 PMCID: PMC2924038 DOI: 10.1074/jbc.m110.123976] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Revised: 05/31/2010] [Indexed: 11/06/2022] Open
Abstract
Rapid-onset dystonia parkinsonism (RDP), a rare neurological disorder, is caused by mutation of the neuron-specific alpha3-isoform of Na(+), K(+)-ATPase. Here, we present the functional consequences of RDP mutation D923N. Relative to the wild type, the mutant exhibits a remarkable approximately 200-fold reduction of Na(+) affinity for activation of phosphorylation from ATP, reflecting a defective interaction of the E(1) form with intracellular Na(+). This is the largest effect on Na(+) affinity reported so far for any Na(+), K(+)-ATPase mutant. D923N also affects the interaction with extracellular Na(+) normally driving the E(1)P to E(2)P conformational transition backward. However, no impairment of K(+) binding was observed for D923N, leading to the conclusion that Asp(923) is specifically associated with the third Na(+) site that is selective toward Na(+). The crystal structure of the Na(+), K(+)-ATPase in E(2) form shows that Asp(923) is located in the cytoplasmic half of transmembrane helix M8 inside a putative transport channel, which is lined by residues from the transmembrane helices M5, M7, M8, and M10 and capped by the C terminus, recently found involved in recognition of the third Na(+) ion. Structural modeling of the E(1) form of Na(+), K(+)-ATPase based on the Ca(2+)-ATPase crystal structure is consistent with the hypothesis that Asp(923) contributes to a site binding the third Na(+) ion. These results in conjunction with our previous findings with other RDP mutants suggest that a selective defect in the handling of Na(+) may be a general feature of the RDP disorder.
Collapse
Affiliation(s)
- Anja Pernille Einholm
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Mads S. Toustrup-Jensen
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Rikke Holm
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Jens Peter Andersen
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Bente Vilsen
- From the Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Danish National Research Foundation, Department of Physiology and Biophysics, Aarhus University, DK-8000 Aarhus C, Denmark
| |
Collapse
|
16
|
Taub M, Springate JE, Cutuli F. Targeting of renal proximal tubule Na,K-ATPase by salt-inducible kinase. Biochem Biophys Res Commun 2010; 393:339-44. [PMID: 20152810 DOI: 10.1016/j.bbrc.2010.02.037] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Accepted: 02/06/2010] [Indexed: 11/20/2022]
Abstract
The renal proximal tubule (RPT) is a central locale for Na+ reabsorption, and blood pressure regulation. Na+ reabsorption in the RPT depends upon the Na,K-ATPase, which is controlled by a complex regulatory network, including Salt-Inducible Protein Kinase (SIK). SIKs are recently discovered members of the AMP-activated Protein Kinase (AMPK) family, which regulate salt homeostasis and metabolism in a number of tissues. In the RPT, SIK interacts with the Na,K-ATPase in the basolateral membrane (BM), regulating both the activity and level of Na,K-ATPase in the BM. Thus, Na,K-ATPase activity can be rapidly adjusted in response to changes in Na+ balance. Long-term changes in Na+ intake affect the state of SIK phosphorylation, and as a consequence the phosphorylation of TORCs, Transducers of Regulated CREB (cAMP Regulatory Element Binding Protein). Once phosphorylated, TORCs enter the nucleus, and activate transcription of the ATP1B1 gene encoding for the Na,K-ATPase beta subunit.
Collapse
Affiliation(s)
- Mary Taub
- Department of Biochemistry, University at Buffalo, 140 Farber Hall, 3435 Main Street, Buffalo, NY 14214, USA.
| | | | | |
Collapse
|
17
|
Liu J, Xie ZJ. The sodium pump and cardiotonic steroids-induced signal transduction protein kinases and calcium-signaling microdomain in regulation of transporter trafficking. Biochim Biophys Acta Mol Basis Dis 2010; 1802:1237-45. [PMID: 20144708 DOI: 10.1016/j.bbadis.2010.01.013] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 01/28/2010] [Accepted: 01/30/2010] [Indexed: 12/12/2022]
Abstract
The Na/K-ATPase was discovered as an energy transducing ion pump. A major difference between the Na/K-ATPase and other P-type ATPases is its ability to bind a group of chemicals called cardiotonic steroids (CTS). The plant-derived CTS such as digoxin are valuable drugs for the management of cardiac diseases, whereas ouabain and marinobufagenin (MBG) have been identified as a new class of endogenous hormones. Recent studies have demonstrated that the endogenous CTS are important regulators of renal Na(+) excretion and blood pressure. The Na/K-ATPase is not only an ion pump, but also an important receptor that can transduce the ligand-like effect of CTS on intracellular protein kinases and Ca(2+) signaling. Significantly, these CTS-provoked signaling events are capable of reducing the surface expression of apical NHE3 (Na/H exchanger isoform 3) and basolateral Na/K-ATPase in renal proximal tubular cells. These findings suggest that endogenous CTS may play an important role in regulation of tubular Na(+) excretion under physiological conditions; conversely, a defect at either the receptor level (Na/K-ATPase) or receptor-effector coupling would reduce the ability of renal proximal tubular cells to excrete Na(+), thus culminating/resulting in salt-sensitive hypertension.
Collapse
Affiliation(s)
- Jiang Liu
- Department of Medicine, University of Toledo College of Medicine, Toledo, OH, USA
| | | |
Collapse
|
18
|
Ivermectin is a nonselective inhibitor of mammalian P-type ATPases. Naunyn Schmiedebergs Arch Pharmacol 2009; 381:147-52. [PMID: 20041321 DOI: 10.1007/s00210-009-0483-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Accepted: 12/01/2009] [Indexed: 10/20/2022]
Abstract
Ivermectin is a large spectrum antiparasitic drug that is very safe at the doses actually used. However, as it is being studied for new applications that would require higher doses, we should pay attention to its effects at high concentrations. As micromolar concentrations of ivermectin have been reported to inhibit the sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA), we decided to investigate its putative inhibitory effect on other two important P-type ATPases, namely the Na(+) , K(+)-ATPase and H(+)/K(+)-ATPase. We first extended the data on SERCA, using preparations from rat enriched in SERCA1a (extensor digitorum longus) and 1b (heart) isoforms. Secondly, we tested the effect of ivermectin in two preparations of rat Na(+), K(+)-ATPase in order to appreciate its putative selectivity towards the alpha(1) isoform (kidney) and the alpha(2)/alpha(3) isoforms (brain), and in an H(+)/K(+)-ATPase preparation from rat stomach. Ivermectin inhibited all these ATPases with similar IC(50) values (6-17 microM). With respect to the inhibition of the Na(+), K(+)-ATPase, ivermectin acts by a mechanism different from the classical cardiac glycosides, based on selectivity towards the isoforms, sensibility to the antagonistic effect of K(+) and to ionic conditions favoring different conformations of the enzyme. We conclude that ivermectin is a nonselective inhibitor of three important mammalian P-type ATPases, which is indicative of putative important adverse effects if this drug were used at high doses. As a consequence, we propose that novel analogs of ivermectin should be developed and tested both for their parasitic activity and in vitro effects on P-type ATPases.
Collapse
|
19
|
DNA polymerase epsilon and delta proofreading suppress discrete mutator and cancer phenotypes in mice. Proc Natl Acad Sci U S A 2009; 106:17101-4. [PMID: 19805137 DOI: 10.1073/pnas.0907147106] [Citation(s) in RCA: 171] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Organisms require faithful DNA replication to avoid deleterious mutations. In yeast, replicative leading- and lagging-strand DNA polymerases (Pols epsilon and delta, respectively) have intrinsic proofreading exonucleases that cooperate with each other and mismatch repair to limit spontaneous mutation to less than 1 per genome per cell division. The relationship of these pathways in mammals and their functions in vivo are unknown. Here we show that mouse Pol epsilon and delta proofreading suppress discrete mutator and cancer phenotypes. We found that inactivation of Pol epsilon proofreading elevates base-substitution mutations and accelerates a unique spectrum of spontaneous cancers; the types of tumors are entirely different from those triggered by loss of Pol delta proofreading. Intercrosses of Pol epsilon-, Pol delta-, and mismatch repair-mutant mice show that Pol epsilon and delta proofreading act in parallel pathways to prevent spontaneous mutation and cancer. These findings distinguish Pol epsilon and delta functions in vivo and reveal tissue-specific requirements for DNA replication fidelity.
Collapse
|
20
|
Abstract
Deactivation of glutamatergic signaling in the brain is mediated by glutamate uptake into glia and neurons by glutamate transporters. Glutamate transporters are sodium-dependent proteins that putatively rely indirectly on Na,K-ATPases to generate ion gradients that drive transmitter uptake. Based on anatomical colocalization, mutual sodium dependency, and the inhibitory effects of the Na,K-ATPase inhibitor ouabain on glutamate transporter activity, we postulated that glutamate transporters are directly coupled to Na,K-ATPase and that Na,K-ATPase is an essential modulator of glutamate uptake. Na,K-ATPase was purified from rat cerebellum by tandem anion exchange and ouabain affinity chromatography, and the cohort of associated proteins was characterized by mass spectrometry. The alpha1-alpha 3 subunits of Na,K-ATPase were detected, as were the glutamate transporters GLAST and GLT-1, demonstrating that glutamate transporters copurify with Na,K-ATPases. The link between glutamate transporters and Na,K-ATPase was further established by coimmunoprecipitation and colocalization. Analysis of the regulation of glutamate transporter and Na,K-ATPase activities was assessed using [(3)H]D-aspartate, [(3)H]L-glutamate, and rubidium-86 uptake into synaptosomes and cultured astrocytes. In synaptosomes, ouabain produced a dose-dependent inhibition of glutamate transporter and Na,K-ATPase activities, whereas in astrocytes, ouabain showed a bimodal effect whereby glutamate transporter activity was stimulated at 1 microm ouabain and inhibited at higher concentrations. The effects of protein kinase inhibitors on [(3)H]D-aspartate uptake indicated the selective involvement of Src kinases, which are probably a component of the Na,K-ATPase/glutamate transporter complex. These findings demonstrate that glutamate transporters and Na,K-ATPases are part of the same macromolecular complexes and operate as a functional unit to regulate glutamatergic neurotransmission.
Collapse
|
21
|
Bamford M. 3 H+/K+ ATPase Inhibitors in the Treatment of Acid-Related Disorders. PROGRESS IN MEDICINAL CHEMISTRY 2009; 47:75-162. [DOI: 10.1016/s0079-6468(08)00203-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
|
22
|
Voss P, Engels M, Strosova M, Grune T, Horakova L. Protective effect of antioxidants against sarcoplasmic reticulum (SR) oxidation by Fenton reaction, however without prevention of Ca-pump activity. Toxicol In Vitro 2008; 22:1726-33. [PMID: 18692562 DOI: 10.1016/j.tiv.2008.07.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2008] [Revised: 04/18/2008] [Accepted: 07/16/2008] [Indexed: 01/09/2023]
Abstract
The Ca(2+)-ATPase of the sarcoplasmic reticulum (SERCA) of rabbit skeletal muscle was oxidized by Fe2+/H2O2/ascorbic acid (AA), a system which generates HO(.) radicals according to the Fenton reaction: (Fe2(+)+H2O2-->HO(.)+OH(-)+Fe(3+)) under conditions similar to the pathological state of inflammation. Under these conditions, when hydroxyl-radicals and/or ferryl-radicals are generated, a 50% decrease of the SERCA activity was observed, a significant decrease of SH groups and an increase of protein carbonyl groups and lipid peroxidation were identified. Two new bands, time dependent in density, appeared in the SERCA protein electrophoresis after incubation with the Fenton system (at approximately 50 and 75kDa), probably due to structural changes as supported also by trypsin digestion. Immunoblotting of DNPH derivatized protein bound carbonyls detected a time dependent increase after incubation of SERCA with the Fenton system. Trolox and the pyridoindole stobadine (50microM) protected SR against oxidation induced via the Fenton system by preventing SH group oxidation and lipid peroxidation. Pycnogenol((R)) and EGb761 (40microg/ml) protected SERCA in addition against protein bound carbonyl formation. In spite of the antioxidant effects, trolox and stobadine were not able to prevent a decrease in the SERCA Ca(2+)-ATPase activity. Pycnogenol and EGb761 even enhanced the decrease of the Ca(2+)-ATPase activity induced by the Fenton system, probably by secondary oxidative reactions.
Collapse
Affiliation(s)
- Peter Voss
- Research Institute for Environmental Medicine gGmbH at the Heinrich-Heine-University, Duesseldorf, Germany
| | | | | | | | | |
Collapse
|
23
|
Shin JM, Munson K, Vagin O, Sachs G. The gastric HK-ATPase: structure, function, and inhibition. Pflugers Arch 2008; 457:609-22. [PMID: 18536934 DOI: 10.1007/s00424-008-0495-4] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2008] [Revised: 03/07/2008] [Accepted: 03/11/2008] [Indexed: 02/06/2023]
Abstract
The gastric H,K-ATPase, a member of the P(2)-type ATPase family, is the integral membrane protein responsible for gastric acid secretion. It is an alpha,beta-heterodimeric enzyme that exchanges cytoplasmic hydronium with extracellular potassium. The catalytic alpha subunit has ten transmembrane segments with a cluster of intramembranal carboxylic amino acids located in the middle of the transmembrane segments TM4, TM5,TM6, and TM8. Comparison to the known structure of the SERCA pump, mutagenesis, and molecular modeling has identified these as constituents of the ion binding domain. The beta subunit has one transmembrane segment with N terminus in cytoplasmic region. The extracellular domain of the beta subunit contains six or seven N-linked glycosylation sites. N-glycosylation is important for the enzyme assembly, maturation, and sorting. The enzyme pumps acid by a series of conformational changes from an E(1) (ion site in) to an E(2) (ion site out) configuration following binding of MgATP and phosphorylation. Several experimental observations support the hypothesis that expulsion of the proton at 160 mM (pH 0.8) results from movement of lysine 791 into the ion binding site in the E(2)P configuration. Potassium access from the lumen depends on activation of a K and Cl conductance via a KCNQ1/KCNE2 complex and Clic6. K movement through the luminal channel in E(2)P is proposed to displace the lysine along with dephosphorylation to return the enzyme to the E(1) configuration. This enzyme is inhibited by the unique proton pump inhibitor class of drug, allowing therapy of acid-related diseases.
Collapse
Affiliation(s)
- Jai Moo Shin
- Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles and VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA
| | | | | | | |
Collapse
|
24
|
Roles of transmembrane segment M1 of Na+,K+-ATPase and Ca2-ATPase, the gatekeeper and the pivot. J Bioenerg Biomembr 2008; 39:357-66. [PMID: 18058007 DOI: 10.1007/s10863-007-9106-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
In this review we summarize mutagenesis work on the structure-function relationship of transmembrane segment M1 in the Na+,K+-ATPase and the sarco(endo)plasmic reticulum Ca2+-ATPase. The original hypothesis that charged residues in the N-terminal part of M1 interact with the transported cations can be rejected. On the other hand hydrophobic residues in the middle part of M1 turned out to play crucial roles in Ca2+ interaction/occlusion in Ca2+-ATPase and K+ interaction/occlusion in Na+,K+-ATPase. Leu65 of the Ca2+-ATPase and Leu99 of the Na+,K+-ATPase, located at homologous positions in M1, function as gate-locking residues that restrict the mobility of the side chain of the cation binding/gating residue of transmembrane segment M4, Glu309/Glu329. A pivot formed between a pair of a glycine and a bulky residue in M1 and M3 seems critical to the opening of the extracytoplasmic gate in both the Ca2+-ATPase and the Na+,K+-ATPase.
Collapse
|
25
|
Shin JM, Vagin O, Munson K, Kidd M, Modlin IM, Sachs G. Molecular mechanisms in therapy of acid-related diseases. Cell Mol Life Sci 2008; 65:264-81. [PMID: 17928953 PMCID: PMC3081136 DOI: 10.1007/s00018-007-7249-x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Inhibition of gastric acid secretion is the mainstay of the treatment of gastroesophageal reflux disease and peptic ulceration; therapies to inhibit acid are among the best-selling drugs worldwide. Highly effective agents targeting the histamine H2 receptor were first identified in the 1970s. These were followed by the development of irreversible inhibitors of the parietal cell hydrogen-potassium ATPase (the proton pump inhibitors) that inhibit acid secretion much more effectively. Reviewed here are the chemistry, biological targets and pharmacology of these drugs, with reference to their current and evolving clinical utilities. Future directions in the development of acid inhibitory drugs include modifications of current agents and the emergence of a novel class of agents, the acid pump antagonists.
Collapse
Affiliation(s)
- J. M. Shin
- Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California USA
- VA Greater Los Angeles Healthcare System, West LA Medical Center, 11301 Wilshire Boulevard, Building 113, Los Angeles, California 90073 USA
| | - O. Vagin
- Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California USA
- VA Greater Los Angeles Healthcare System, West LA Medical Center, 11301 Wilshire Boulevard, Building 113, Los Angeles, California 90073 USA
| | - K. Munson
- Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California USA
- VA Greater Los Angeles Healthcare System, West LA Medical Center, 11301 Wilshire Boulevard, Building 113, Los Angeles, California 90073 USA
| | - M. Kidd
- Department of Surgery, Yale University School of Medicine, TMP202, 333 Cedar Street, New Haven Connecticut, 06520-8062 USA
| | - I. M. Modlin
- Department of Surgery, Yale University School of Medicine, TMP202, 333 Cedar Street, New Haven Connecticut, 06520-8062 USA
| | - G. Sachs
- Department of Physiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California USA
- VA Greater Los Angeles Healthcare System, West LA Medical Center, 11301 Wilshire Boulevard, Building 113, Los Angeles, California 90073 USA
| |
Collapse
|
26
|
Regulation of sodium pump endocytosis by cardiotonic steroids: Molecular mechanisms and physiological implications. ACTA ACUST UNITED AC 2007; 14:171-81. [PMID: 17961998 DOI: 10.1016/j.pathophys.2007.09.008] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
We have previously shown that ouabain and other cardiotonic steroids interact with the plasmalemmal Na/K-ATPase and cause a time and dose dependent endocytosis of the Na/K-ATPase. This endocytosis is demonstrable using fluorescence imaging as well as conventional biochemical and biophysical cell separation methods. In proximal tubule cells, this process appears to regulate the density of basolateral Na/K-ATPase expression directly as well as indirectly modulate transepithelial sodium transport. Work with genetic manipulations, as well as pharmacological agents with cell culture models, have demonstrated that the cardiotonic steroid stimulated endocytosis of the plasmalemmal Na/K-ATPase requires caveolin and clathrin as well as the activation of c-Src, transactivation of the EGFR and activation of PI3K. Interestingly c-Src, EGFR and ERK1/2 all appear to be endocytosed along with the plasmalemmal Na/K-ATPase. These observations suggest a close analogy between a subset of plasmalemmal Na/K-ATPase and signaling companions with conventional receptor tyrosine kinases. While further studies are necessary to delineate the role of this endocytosis in the generation as well as the limit of signal transduction through the Na/K-ATPase signal cascade, we propose that it has an important role in the regulation of renal sodium handling as well as other important processes.
Collapse
|
27
|
Fonseca J, Kaya S. Temporal Analysis of Valence & Electrostatics in Ion-Motive Sodium Pump. JOURNAL OF COMPUTATIONAL ELECTRONICS 2007; 6:381-385. [PMID: 18769504 PMCID: PMC1858632 DOI: 10.1007/s10825-006-0141-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The present work establishes a unique framework for the simulation study of ion-motive pumps in general and the Na(+)/K(+)-ATPase, or sodium pump, in particular. We shall discuss the implications of electrostatic analysis, valence calculations, and protein cavity data, each carried over data extracted from molecular dynamics simulations, on the structure-function relationship of Na(+)/K(+)-ATPase. These diverse set of tools will be used to investigate atomic-level characteristics that remain undetermined such as ion binding and accessibility.
Collapse
Affiliation(s)
| | - S. Kaya
- e-mail: , fax: (740) 593-0007
| |
Collapse
|
28
|
Jayantha Gunaratne H, Vacquier VD. Sequence, annotation and developmental expression of the sea urchin Ca2+-ATPase family. Gene 2007; 397:67-75. [PMID: 17482382 DOI: 10.1016/j.gene.2007.04.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2007] [Revised: 04/07/2007] [Accepted: 04/07/2007] [Indexed: 11/30/2022]
Abstract
Whole genome sequence data permit the study of protein families regulating cellular homeostasis during development. Here we present a study of the sea urchin Ca(2+)-ATPases made possible by the Sea Urchin Genome Sequencing Project. This is of potential interest because adult sea urchins, their gametes and embryos live in the relatively high Ca(2+) concentration of 10 mM. Three Ca(2+)-ATPases regulate Ca(2+) levels in animal cells: plasma membrane Ca(2+)-ATPase (PMCA), sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA) and secretory pathway Ca(2+)-ATPase (SPCA). The primary structures of Sp-PMCA and Sp-SERCA in the sea urchin, Strongylocentrotus purpuratus (Sp), have been published. Here, we present the primary structure of Sp-SPCA, which is 912 amino acids and has 66% identity and 80% similarity to human SPCA1. Southern blots and genome analysis show that Sp-SPCA is a single copy gene. Each Sp Ca(2+)-ATPase is highly conserved when compared to its human ortholog, indicating that human and sea urchin share structurally similar energy driven Ca(2+) homeostasis mechanisms that have been maintained throughout the course of deuterostome evolution. Annotation using the assembled sea urchin genome reveals that Sp-SPCA, Sp-PMCA and Sp-SERCA have 23, 17 and 24 exons. RT-Q-PCR shows that transcripts of Sp-SPCA are at low levels compared to Sp-PMCA and Sp-SERCA. Gradual increases in Sp-PMCA and Sp-SERCA mRNA begin at the 18 hour hatched blastula stage and peak 4-5-fold higher by 25 h at the mid to late blastulae stage.
Collapse
Affiliation(s)
- H Jayantha Gunaratne
- Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0202, USA.
| | | |
Collapse
|
29
|
Guennoun-Lehmann S, Fonseca JE, Horisberger JD, Rakowski RF. Palytoxin acts on Na(+),K (+)-ATPase but not nongastric H(+),K (+)-ATPase. J Membr Biol 2007; 216:107-16. [PMID: 17639367 PMCID: PMC2396460 DOI: 10.1007/s00232-007-9040-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2007] [Accepted: 05/14/2007] [Indexed: 10/23/2022]
Abstract
Palytoxin (PTX) opens a pathway for ions to pass through Na,K-ATPase. We investigate here whether PTX also acts on nongastric H,K-ATPases. The following combinations of cRNA were expressed in Xenopus laevis oocytes: Bufo marinus bladder H,K-ATPase alpha(2)- and Na,K-ATPase beta(2)-subunits; Bufo Na,K-ATPase alpha(1)- and Na,K-ATPase beta(2)-subunits; and Bufo Na,K-ATPase beta(2)-subunit alone. The response to PTX was measured after blocking endogenous Xenopus Na,K-ATPase with 10 microM ouabain. Functional expression was confirmed by measuring (86)Rb uptake. PTX (5 nM: ) produced a large increase of membrane conductance in oocytes expressing Bufo Na,K-ATPase, but no significant increase occurred in oocytes expressing Bufo H,K-ATPase or in those injected with Bufo beta(2)-subunit alone. Expression of the following combinations of cDNA was investigated in HeLa cells: rat colonic H,K-ATPase alpha(1)-subunit and Na,K-ATPase beta(1)-subunit; rat Na,K-ATPase alpha(2)-subunit and Na,K-ATPase beta(2)-subunit; and rat Na,K-ATPase beta(1)- or Na,K-ATPase beta(2)-subunit alone. Measurement of increases in (86)Rb uptake confirmed that both rat Na,K and H,K pumps were functional in HeLa cells expressing rat colonic HKalpha(1)/NKbeta(1) and NKalpha(2)/NKbeta(2). Whole-cell patch-clamp measurements in HeLa cells expressing rat colonic HKalpha(1)/NKbeta(1) exposed to 100 nM PTX showed no significant increase of membrane current, and there was no membrane conductance increase in HeLa cells transfected with rat NKbeta(1)- or rat NKbeta(2)-subunit alone. However, in HeLa cells expressing rat NKalpha(2)/NKbeta(2), outward current was observed after pump activation by 20 mM K(+) and a large membrane conductance increase occurred after 100 nM PTX. We conclude that nongastric H,K-ATPases are not sensitive to PTX when expressed in these cells, whereas PTX does act on Na,K-ATPase.
Collapse
Affiliation(s)
| | - James E. Fonseca
- School of Electrical Engineering & Computer Science, Ohio University, Athens, OH 45701 USA
| | - Jean-Daniel Horisberger
- Dept. of Pharmacology and Toxicology of the University of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland
| | - Robert F. Rakowski
- Department of Biological Sciences, Ohio University, Athens, OH 45701 USA
| |
Collapse
|
30
|
Kiec-Wilk B, Dembinska-Kiec A, Olszanecka A, Bodzioch M, Schmitz G, Kawecka-Jaszcz K. A724A polymorphism of sarco(endo)plasmic reticulum Ca2+-ATPase 2 (SERCA2) in hypertensive patients. Clin Chem Lab Med 2007; 45:467-70. [PMID: 17439322 DOI: 10.1515/cclm.2007.092] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND Impaired function of calcium ion transporter sarco(endo)plasmic reticulum Ca2+-ATPase2 (SERCA2), encoded by ATP2A2 gene, was observed in hypertension. The aim of this study was to screen for mutations in the ATP2A2 gene, in hypertensive patients compared to healthy controls. METHODS The frequency of a novel mutation in exon 15 of ATP2A2, coding SERCA2, was studied in 107 hypertensive patients and a control group of 50 healthy volunteers. 24-h ambulatory blood-pressure monitoring (ABPM) was carried out. ATP2A2 genotyping was performed by denaturing HPLC and sequencing. RESULTS In exon 15 of the ATP2A2 gene, a novel c.2171G>A polymorphism was identified that does not change the amino acid sequence. The frequency of the A allele was significantly higher in normotensive controls than in hypertensive patients (p=0.017). GA genotype carriers demonstrated a tendency towards lower blood pressure values in the doctor's office (p=0.367 systolic, p=0.439 diastolic blood pressure) and measured by ABPM. CONCLUSIONS Our results suggest a protective role of the A724A (c.2171G>A) polymorphism of ATP2A2 in subjects without hypertension.
Collapse
Affiliation(s)
- Beata Kiec-Wilk
- Clinical Biochemistry Department, Medical College Jagiellonian University, Krakow, Poland.
| | | | | | | | | | | |
Collapse
|
31
|
Purhonen P, Thomsen K, Maunsbach AB, Hebert H. Association of renal Na,K-ATPase alpha-subunit with the beta- and gamma-subunits based on cryoelectron microscopy. J Membr Biol 2007; 214:139-46. [PMID: 17557166 DOI: 10.1007/s00232-006-0056-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2006] [Revised: 11/29/2006] [Indexed: 11/28/2022]
Abstract
Na,K-ATPase transports Na(+) and K(+) across cell membranes and consists of alpha- and beta-subunits. Na,K-ATPase also associates with small FXYD proteins that regulate the activity of the pump. We have used cryoelectron microscopy of two-dimensional crystals including data to 8 A resolution to determine the three-dimensional (3-D) structure of renal Na,K-ATPase containing FXYD2, the gamma-subunit. A homology model for the alpha-subunit was calculated from a Ca(2+)-ATPase structure and used to locate the additional beta- and gamma-subunits present in the 3-D map of Na,K-ATPase. Based on the 3-D map, the beta-subunit is located close to transmembrane helices M8 and M10 and the gamma-subunit is adjacent to helices M2 and M9 of the alpha-subunit.
Collapse
Affiliation(s)
- P Purhonen
- Department of Biosciences and Nutrition and School of Technology and Health, Karolinska Institutet, Royal Institute of Technology, S-141 57, Huddinge, Sweden
| | | | | | | |
Collapse
|
32
|
Teriete P, Franzin CM, Choi J, Marassi FM. Structure of the Na,K-ATPase regulatory protein FXYD1 in micelles. Biochemistry 2007; 46:6774-83. [PMID: 17511473 PMCID: PMC2527028 DOI: 10.1021/bi700391b] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
FXYD1 is a major regulatory subunit of the Na,K-ATPase and the principal substrate of hormone-regulated phosphorylation by c-AMP dependent protein kinases A and C in heart and skeletal muscle sarcolemma. It is a member of an evolutionarily conserved family of membrane proteins that regulate the function of the enzyme complex in a tissue-specific and physiological-state-specific manner. Here, we present the three-dimensional structure of FXYD1 determined in micelles by NMR spectroscopy. Structure determination was made possible by measuring residual dipolar couplings in weakly oriented micelle samples of the protein. This allowed us to obtain the relative orientations of the helical segments and information about the protein dynamics. The structural analysis was further facilitated by the inclusion of distance restraints, obtained from paramagnetic spin label relaxation enhancements, and by refinement with a micelle depth restraint, derived from paramagnetic Mn line broadening effects. The structure of FXYD1 provides the foundation for understanding its intra-membrane association with the Na,K-ATPase alpha subunit and suggests a mechanism whereby the phosphorylation of conserved Ser residues, by protein kinases A and C, could induce a conformational change in the cytoplasmic domain of the protein to modulate its interaction with the alpha subunit.
Collapse
Affiliation(s)
| | | | | | - Francesca M. Marassi
- *Address correspondence to: Francesca M. Marassi, The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037 USA, , Phone:858-795-5282, Fax: 858-713-6268
| |
Collapse
|
33
|
Li C, Geering K, Horisberger JD. The third sodium binding site of Na,K-ATPase is functionally linked to acidic pH-activated inward current. J Membr Biol 2007; 213:1-9. [PMID: 17347782 DOI: 10.1007/s00232-006-0035-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2006] [Accepted: 10/03/2006] [Indexed: 11/30/2022]
Abstract
Sodium- and potassium-activated adenosine triphosphatases (Na,K-ATPase) is the ubiquitous active transport system that maintains the Na(+) and K(+) gradients across the plasma membrane by exchanging three intracellular Na(+) ions against two extracellular K(+) ions. In addition to the two cation binding sites homologous to the calcium site of sarcoplasmic and endoplasmic reticulum calcium ATPase and which are alternatively occupied by Na(+) and K(+) ions, a third Na(+)-specific site is located close to transmembrane domains 5, 6 and 9, and mutations close to this site induce marked alterations of the voltage-dependent release of Na(+) to the extracellular side. In the absence of extracellular Na(+) and K(+), Na,K-ATPase carries an acidic pH-activated, ouabain-sensitive "leak" current. We investigated the relationship between the third Na(+) binding site and the pH-activated current. The decrease (in E961A, T814A and Y778F mutants) or the increase (in G813A mutant) of the voltage-dependent extracellular Na(+) affinity was paralleled by a decrease or an increase in the pH-activated current, respectively. Moreover, replacing E961 with oxygen-containing side chain residues such as glutamine or aspartate had little effect on the voltage-dependent affinity for extracellular Na(+) and produced only small effects on the pH-activated current. Our results suggest that extracellular protons and Na(+) ions share a high field access channel between the extracellular solution and the third Na(+) binding site.
Collapse
Affiliation(s)
- Ciming Li
- Department of Pharmacology and Toxicology, University of Lausanne, CH-1005 Lausanne, Switzerland
| | | | | |
Collapse
|
34
|
Artigas P, Gadsby DC. Ouabain affinity determining residues lie close to the Na/K pump ion pathway. Proc Natl Acad Sci U S A 2006; 103:12613-8. [PMID: 16894161 PMCID: PMC1567927 DOI: 10.1073/pnas.0602720103] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Na/K pump establishes essential ion concentration gradients across animal cell membranes. Cardiotonic steroids, such as ouabain, are specific inhibitors of the Na/K pump. We exploited the marine toxin, palytoxin, to probe both the ion translocation pathway through the Na/K pump and the site of its interaction with ouabain. Palytoxin uncouples the pump's gates, which normally open strictly alternately, thus allowing both gates to sometimes be open, so transforming the pump into an ion channel. Palytoxin therefore permits electrophysiological analysis of even a single Na/K pump. We used outside-out patch recording of Xenopus alpha1beta3 Na/K pumps, which were made ouabain-resistant by point mutation, after expressing them in Xenopus oocytes. Endogenous, ouabain-sensitive, Xenopus alpha1beta3 Na/K pumps were silenced by continuous exposure to ouabain. We found that side-chain charge of two residues at either end of the alpha subunit's first extracellular loop, known to make a major contribution to ouabain affinity, strongly influenced conductance of single palytoxin-bound pump-channels by an electrostatic mechanism. The effects were mimicked by modification of cysteines introduced at those two positions with variously charged methanethiosulfonate reagents. The consequences of these modifications demonstrate that both residues lie in a wide vestibule near the mouth of the pump's ion pathway. Bound ouabain protects the site with the strongest influence on conductance from methanethiosulfonate modification, while leaving the site with the weaker influence unprotected. The results suggest a method for mapping the footprint of bound cardiotonic steroid on the extracellular surface of the Na/K pump.
Collapse
Affiliation(s)
- Pablo Artigas
- Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10021
| | - David C. Gadsby
- Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10021
- *To whom correspondence should be addressed. E-mail:
| |
Collapse
|
35
|
Codina J, Liu J, Bleyer AJ, Penn RB, DuBose TD. Phosphorylation of S955 at the protein kinase A consensus promotes maturation of the alpha subunit of the colonic H+,K+ -ATPase. J Am Soc Nephrol 2006; 17:1833-40. [PMID: 16738016 DOI: 10.1681/asn.2006010032] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
All the alpha subunits of the Na+,K+ -ATPases and H+,K+ -ATPases have a protein kinase A (PKA) consensus sequence near or in the ninth transmembrane domain. The role of this domain in influencing alpha subunit synthesis/degradation, plasma membrane localization, and 86Rb+ uptake has not been established for the alpha subunit of the colonic H+,K+ -ATPase. This study examined the effect of mutating S955 (within the PKA consensus site of the alpha subunit of the colonic H+,K+ -ATPase [HKalpha2]) to alanine (S955/A) or aspartic acid (S955/D) on alpha subunit expression and function. The results demonstrate that a negatively charged amino acid at position 955 of HKalpha2 promotes higher expression levels of both whole-cell and plasma membrane-localized HKalpha2. Moreover, inhibition of PKA reduced expression of wild-type HKalpha2 and associated 86Rb+ uptake. Last, the activity of the HKalpha2 S955/A was rescued by treatment with 4-phenylbutyric acid, a compound that was shown previously to restore function to the cystic fibrosis transmembrane conductance regulator.
Collapse
Affiliation(s)
- Juan Codina
- Sections on Nephrology and Molecular Medicine, Department of Internal Medicine, Wake Forest University Health Sciences, Medical Center Boulevard, Winston-Salem, NC 27157, USA
| | | | | | | | | |
Collapse
|
36
|
Affiliation(s)
- Jai Moo Shin
- Department of Physiology and Medicine, University of California at Los Angeles, and VA Greater Los Angeles Healthcare System, Los Angeles, California 90073, USA
| | | |
Collapse
|
37
|
Pedemonte CH, Efendiev R, Bertorello AM. Inhibition of Na,K-ATPase by Dopamine in Proximal Tubule Epithelial Cells. Semin Nephrol 2005; 25:322-7. [PMID: 16139687 DOI: 10.1016/j.semnephrol.2005.03.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In the current report we review the results that lay grounds for the model of intracellular sodium-mediated dopamine-induced endocytosis of Na,K-ATPase. Under conditions of a high salt diet, dopamine activates PKCzeta, which phosphorylates NKA alpha1 Ser-18. The phosphorylation produces a conformational change of alpha1 NH2-terminus, which through interaction with other domains of alpha1 exposes PI3K- and AP-2-binding domains. PI3K bound to the NKA alpha1 induces the recruitment and activation of other proteins involved in endocytosis, and PI3K-generated 3-phosphoinositides affect the local cytoskeleton and modify the biophysical conditions of the membrane for development of clathrin-coated pits. Plasma membrane phosphorylated NKA is internalized to specialized intracellular compartments where the NKA will be dephosphorylated. The NKA internalization results in a reduced Na+ transport by proximal tubule epithelial cells.
Collapse
|
38
|
Dempski RE, Friedrich T, Bamberg E. The beta subunit of the Na+/K+-ATPase follows the conformational state of the holoenzyme. ACTA ACUST UNITED AC 2005; 125:505-20. [PMID: 15851504 PMCID: PMC2217500 DOI: 10.1085/jgp.200409186] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Na+/K+-ATPase is a ubiquitous plasma membrane ion pump that utilizes ATP hydrolysis to regulate the intracellular concentration of Na+ and K+. It is comprised of at least two subunits, a large catalytic alpha subunit that mediates ATP hydrolysis and ion transport, and an ancillary beta subunit that is required for proper trafficking of the holoenzyme. Although processes mediated by the alpha subunit have been extensively studied, little is known about the participation of the beta subunit in conformational changes of the enzyme. To elucidate the role of the beta subunit during ion transport, extracellular amino acids proximal to the transmembrane region of the sheep beta1 subunit were individually replaced for cysteines. This enabled sulfhydryl-specific labeling with the environmentally sensitive fluorescent dye tetramethylrhodamine-6-maleimide (TMRM) upon expression in Xenopus oocytes. Investigation by voltage-clamp fluorometry identified three reporter positions on the beta1 subunit that responded with fluorescence changes to alterations in ionic conditions and/or membrane potential. These experiments for the first time show real-time detection of conformational rearrangements of the Na+/K+-ATPase through a fluorophore-labeled beta subunit. Simultaneous recording of presteady-state or stationary currents together with fluorescence signals enabled correlation of the observed environmental changes of the beta subunit to certain reaction steps of the Na+/K+-ATPase, which involve changes in the occupancy of the two principle conformational states, E1P and E2P. From these experiments, evidence is provided that the beta1-S62C mutant can be directly used to monitor the conformational state of the enzyme, while the F64C mutant reveals a relaxation process that is triggered by sodium transport but evolves on a much slower time scale. Finally, shifts in voltage dependence and kinetics observed for mutant K65C show that this charged lysine residue, which is conserved in beta1 isoforms, directly influences the effective potential that determines voltage dependence of extracellular cation binding and release.
Collapse
Affiliation(s)
- Robert E Dempski
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | | | | |
Collapse
|
39
|
Einholm AP, Toustrup-Jensen M, Andersen JP, Vilsen B. Mutation of Gly-94 in transmembrane segment M1 of Na+,K+-ATPase interferes with Na+ and K+ binding in E2P conformation. Proc Natl Acad Sci U S A 2005; 102:11254-9. [PMID: 16049100 PMCID: PMC1183542 DOI: 10.1073/pnas.0501201102] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The importance of Gly-93 and Gly-94 in transmembrane segment M1 of the Na+,K+-ATPase for interaction with Na+ and K+ was demonstrated by functional analysis of mutants Gly-93-Ala and Gly-94-Ala. In the crystal structures of the Ca2+-ATPase, the corresponding residues, Asp-59 and Leu-60, are located exactly where M1 bends. Rapid kinetic measurements of K+-induced dephosphorylation allowed determination of the affinity of the E2P phosphoenzyme intermediate for K+. In Gly-94-Ala, the K+ affinity was reduced 9-fold, i.e., to the same extent as seen for mutation of the cation-binding residue Glu-329. Furthermore, Gly-94-Ala showed strongly reduced sensitivity of the E1P-E2P equilibrium to Na+, with accumulation of E2P even at 600 mM Na+, indicating that interaction of E2P with extracellular Na+ is impaired. On the contrary, in Gly-93-Ala, the affinity for K+ was slightly increased, and the E1P-E2P equilibrium was displaced in favor of E1P. In both mutants, the affinity of the cytoplasmically facing sites of E1 for Na+ was reduced, but this effect was relatively small compared with the effects seen for E2P in Gly-94-Ala. Comparison with Ca2+-ATPase mutagenesis data suggests that the role of M1 in binding of the transported ions is universal among P-type ATPases, despite the low sequence homology in this region. Structural modeling of Na+,K+-ATPase mutant Gly-94-Ala on the basis of the Ca2+-ATPase crystal structures indicates that the alanine side chain comes close to Ile-287 of M3, particularly in E2P, thus resulting in a steric clash that may explain the present observations.
Collapse
Affiliation(s)
- Anja Pernille Einholm
- Department of Physiology, Institute of Physiology and Biophysics, University of Aarhus, DK-8000 Aarhus C, Denmark
| | | | | | | |
Collapse
|
40
|
Segall L, Mezzetti A, Scanzano R, Gargus JJ, Purisima E, Blostein R. Alterations in the alpha2 isoform of Na,K-ATPase associated with familial hemiplegic migraine type 2. Proc Natl Acad Sci U S A 2005; 102:11106-11. [PMID: 16037212 PMCID: PMC1178013 DOI: 10.1073/pnas.0504323102] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A number of missense mutations in the Na,K-ATPase alpha2 catalytic subunit have been identified in familial hemiplegic migraine with aura. Two alleles (L764P and W887R) showed loss-of-function, whereas a third (T345A) is fully functional but with altered Na,K-ATPase kinetics. This study describes two additional mutants, R689Q and M731T, originally identified by Vanmolkot et al. [Vanmolkot, K. R., et al. (2003) Ann. Neurol. 54, 360-366], which we show here to also be functional and kinetically altered. Both mutants have reduced catalytic turnover and increased apparent affinity for extracellular K(+). For both R689Q and M731T, sensitivity to vanadate inhibition is decreased, suggesting that the steady-state E(1) <==> E(2) poise of the enzyme is shifted toward E(1). Whereas the K'(ATP) is not affected by the R689Q replacement, the M731T mutant has an increase in apparent affinity for ATP. Analysis of the structural changes effected by T345A, R689Q, and M731T mutations, based on homologous replacements in the known crystal structure of the sarcoplasmic reticulum Ca-ATPase, provides insights into the molecular bases for the kinetic alterations. It is suggested that the disease phenotype is the consequence of lowered molecular activity of the alpha2 pump isoform due to either decreased K(+) affinity (T345A) or catalytic turnover (R689Q and M731T), thus causing a delay in extracellular K(+) clearance and/or altered localized Ca(2+) handling/signaling secondary to reduced activity in colocalized Na(+)/Ca(2+) exchange.
Collapse
Affiliation(s)
- Laura Segall
- Departments of Biochemistry and Medicine, McGill University and Montreal General Hospital Research Institute, Montreal, Quebec, Canada H3G 1A4
| | | | | | | | | | | |
Collapse
|
41
|
Myari A, Hadjiliadis N, Fatemi N, Sarkar B. Copper(I) interaction with model peptides of WD6 and TM6 domains of Wilson ATPase: regulatory and mechanistic implications. J Inorg Biochem 2005; 98:1483-94. [PMID: 15337600 DOI: 10.1016/j.jinorgbio.2004.05.013] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2004] [Revised: 05/13/2004] [Accepted: 05/20/2004] [Indexed: 11/20/2022]
Abstract
With the aim to investigate the mechanism of Cu(I) transport by Wilson ATPase (ATP7B), we have studied the interaction of the peptides 2K10p (CH(3)CO-Lys-Gly-Met-Thr-Cys-Ala-Ser-Cys-Val-His-Asn-Lys-CONH(2)), and 2K8p (CH(3)CO-Lys-Leu-Cys-Ile-Ala-Cys-Pro-Cys-Ser-Lys-CONH(2)), part of the sixth metal binding domain (WD6) and the sixth transmembrane segment (TM6) of Wilson ATPase, respectively, by means of CD, NMR spectroscopy and homology modeling. In addition, the interaction of Cu(I) with the 2K8p mutants 1s (CH(3)CO-Lys-Leu-Ser-Ile-Ala-Cys-Pro-Cys-Ser-Lys-CONH(2)), 2s (CH(3)CO-Lys-Leu-Cys-Ile-Ala-Ser-Pro-Cys-Ser-Lys-CONH(2)) and 3s (CH(3)CO-Lys-Leu-Cys-Ile-Ala-Cys-Pro-Ser-Ser-Lys-CONH(2)), containing two cysteines in various positions, have been studied with the same methods, in order to understand the role of each cysteine in copper binding. Our studies show that the three cysteine thiolates present in the 2K8p peptide sequence act mainly as bridging ligands for Cu(I) binding, and dithiothreitol acts as an important ligand in Cu(I) ligation by 2K10p and the 2K8p mutants. Formation of oligomeric species has been evidenced for all peptides except 2s. Shift of the equilibrium between the various oligomeric species has been accomplished by reducing the Cu(I):peptide ratio. Significant shifts of proline protons upon interaction with Cu(I) have been observed for all proline containing peptides implying a possible role of proline in facilitating Cu(I) binding. These findings have been further discussed with respect to the molecular basis of copper trafficking and intermolecular interactions.
Collapse
Affiliation(s)
- Alexandra Myari
- Department of Chemistry, University of Ioannina, Ioannina 45110, Greece
| | | | | | | |
Collapse
|
42
|
Keenan SM, DeLisle RK, Welsh WJ, Paula S, Ball WJ. Elucidation of the Na+, K+-ATPase digitalis binding site. J Mol Graph Model 2005; 23:465-75. [PMID: 15886034 DOI: 10.1016/j.jmgm.2005.02.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2004] [Revised: 02/23/2005] [Accepted: 02/24/2005] [Indexed: 10/25/2022]
Abstract
Despite controversy over their use and the potential for toxic side effects, cardiac glycosides have remained an important clinical component for the treatment for congestive heart failure (CHF) and supraventricular arrhythmias since the effects of Digitalis purpurea were first described in 1785. While there is a wealth of information available with regard to the effects of these drugs on their pharmacological receptor, the Na(+), K(+)-ATPase, the exact molecular mechanism of digitalis binding and inhibition of the enzyme has remained elusive. In particular, the absence of structural knowledge about Na(+), K(+)-ATPase has thwarted the development of improved therapeutic agents with larger therapeutic indices via rational drug design approaches. Here, we propose a binding mode for digoxin and several analogues to the Na(+), K(+)-ATPase. A 3D-structural model of the extracellular loop regions of the catalytic alpha1-subunit of the digitalis-sensitive sheep Na(+), K(+)-ATPase was constructed from the crystal structure of an E(1)Ca(2+) conformation of the SERCA1a and a consensus orientation for digitalis binding was inferred from the in silico docking of a series of steroid-based cardiotonic compounds. Analyses of species-specific enzyme affinities for ouabain were also used to validate the model and, for the first time, propose a detailed model of the digitalis binding site.
Collapse
Affiliation(s)
- Susan M Keenan
- Department of Pharmacology, University of Medicine and Dentistry, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | | | | | | | | |
Collapse
|
43
|
Capendeguy O, Horisberger JD. The role of the third extracellular loop of the Na+,K+-ATPase alpha subunit in a luminal gating mechanism. J Physiol 2005; 565:207-18. [PMID: 15774534 PMCID: PMC1464502 DOI: 10.1113/jphysiol.2004.080218] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Na+,K+-ATPase is responsible for maintaining the cross-membrane Na+ and K+ gradients of animal cells. This P-type ATPase works via a complex transport cycle, during which it binds and occludes three intracellular Na+ ions and then two extracellular K+ ions, which it then releases on the other side of the membrane. The cation pathway through the protein, and the structures responsible for occluding cations inside the protein, have not yet been definitely identified. We used cysteine mutagenesis to explore the accessibility and the role of five conserved residues in the short third extracellular loop, between the fifth and the sixth transmembrane helices. The P801C and L802C mutants were not affected by extracellular sulfhydryl reagents. The presence of cysteine residues at three positions (G803C, T804C and V805C) conferred sensitivity to omeprazole, a known inhibitor of the gastric proton pump, and to [2-(trimethylammonium)-ethyl]methanethiosulphonate bromide (MTSET). The effects of omeprazole and MTSET were modulated by the presence of extracellular K+, indicating that the accessibility of these positions depended on the conformational state of the protein. MTSET binding to cysteine at position 803 partially inhibited the Na+,K+-pump function by decreasing its affinity towards extracellular K+, suggesting a restriction of the access of extracellular K+ ions to their binding sites. In contrast, MTSET binding to cysteine at position 805 partially inhibited the Na+,K+-pump function by reducing its maximum turnover rate, probably by slowing a rate-limiting conformational change. These residues occupy positions that are critical for either the cation pathway or the conformational modifications.
Collapse
Affiliation(s)
- Oihana Capendeguy
- Institut de Pharmacologie et de Toxicologie, Université de Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland
| | | |
Collapse
|
44
|
Abstract
The fluorescent styryl dye RH421 was used to identify and investigate electrogenic reaction steps of the H,K-ATPase pump cycle. Equilibrium titration experiments were performed with membrane vesicles isolated from hog gastric mucosa, and cytoplasmic and luminal binding of K(+) and H(+) ions was studied. It was found that the binding and release steps of both ion species in both principal conformations of the ion pump, E(1) and P-E(2), are electrogenic, whereas the conformation transitions do not contribute significantly to a charge movement within the membrane dielectric. This behavior is in agreement with the transport mechanism found for the Na,K-ATPase and the sarcoplasmic reticulum Ca-ATPase. The data were analyzed on the basis of the Post-Albers reaction cycle. For proton binding, two pK values were found in both conformations: 6.7 and </=4.5 in the E(1) conformation; 6.7 and </=2 in the P-E(2) conformation. The equilibrium dissociation constants for K(+) binding on the cytoplasmic side were 11 and 16 mM. The respective equilibrium dissociation constants on the luminal side were obtained via K(+) concentration dependence of the enzyme activity and determined to be 0.11 mM for both luminal binding sites.
Collapse
Affiliation(s)
- Anna Diller
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany
| | | | | | | |
Collapse
|
45
|
Kargacin GJ, Aschar-Sobbi R, Kargacin ME. Inhibition of SERCA2 Ca(2+)-ATPases by Cs(+). Pflugers Arch 2004; 449:356-63. [PMID: 15480749 DOI: 10.1007/s00424-004-1345-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2004] [Accepted: 09/06/2004] [Indexed: 10/26/2022]
Abstract
Replacement of K(+) with Cs(+) on the cytoplasmic side of the sarcoplasmic reticulum (SR) membrane reduces the maximum velocity (V(max)) of Ca(2+) uptake into the SR of saponin-permeabilized rat ventricular myocytes. To compare the sensitivity of the cardiac and smooth muscle/non-muscle forms of the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a and -2b respectively) to replacement of K(+) with Cs(+), SERCA2a and SERCA2b were expressed in HEK-293 cells. Ca(2+) uptake into HEK cell microsomes was inhibited by replacement of extravesicular K(+) with Cs(+) (V(max) of SERCA2a-mediated Ca(2+) uptake in CsCl was 80% of that in KCl; V(max) of SERCA2b-mediated uptake was 70% of that in KCl). The Ca(2+) sensitivity of uptake was decreased for both SERCA2a- and SERCA2b-mediated uptake and the Hill coefficients were increased in the presence of CsCl. The effects of Cs(+) on uptake were associated with direct inhibition of the ATPase activity of SERCA2a and SERCA2b. Our results indicate that cation binding sites are present in both SERCA2 isoforms, although the extent to which SERCA2b is inhibited by K(+) replacement is greater than that of SERCA2a or SERCA1. Consideration of these results and the recent molecular modeling work of others suggests that monovalent cations could interact with the Ca(2+) binding region of SERCA.
Collapse
Affiliation(s)
- Gary J Kargacin
- Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada.
| | | | | |
Collapse
|
46
|
de Carvalho Aguiar P, Sweadner KJ, Penniston JT, Zaremba J, Liu L, Caton M, Linazasoro G, Borg M, Tijssen MAJ, Bressman SB, Dobyns WB, Brashear A, Ozelius LJ. Mutations in the Na+/K+ -ATPase alpha3 gene ATP1A3 are associated with rapid-onset dystonia parkinsonism. Neuron 2004; 43:169-75. [PMID: 15260953 DOI: 10.1016/j.neuron.2004.06.028] [Citation(s) in RCA: 352] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2004] [Revised: 06/18/2004] [Accepted: 06/23/2004] [Indexed: 10/26/2022]
Abstract
Rapid-onset dystonia-parkinsonism (RDP, DYT12) is a distinctive autosomal-dominant movement disorder with variable expressivity and reduced penetrance characterized by abrupt onset of dystonia, usually accompanied by signs of parkinsonism. The sudden onset of symptoms over hours to a few weeks, often associated with physical or emotional stress, suggests a trigger initiating a nervous system insult resulting in permanent neurologic disability. We report the finding of six missense mutations in the gene for the Na+/K+ -ATPase alpha3 subunit (ATP1A3) in seven unrelated families with RDP. Functional studies and structural analysis of the protein suggest that these mutations impair enzyme activity or stability. This finding implicates the Na+/K+ pump, a crucial protein responsible for the electrochemical gradient across the cell membrane, in dystonia and parkinsonism.
Collapse
|
47
|
Pratap PR, Dediu O, Nienhaus GU. FTIR study of ATP-induced changes in Na+/K+-ATPase from duck supraorbital glands. Biophys J 2004; 85:3707-17. [PMID: 14645062 PMCID: PMC1303674 DOI: 10.1016/s0006-3495(03)74787-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The Na+/K+-ATPase uses energy from the hydrolysis of ATP to pump Na+ ions out of and K+ ions into the cell. ATP-induced conformational changes in the protein have been examined in the Na+/K+-ATPase isolated from duck supraorbital salt glands using Fourier transform infrared spectroscopy. Both standard transmission and attenuated total internal reflection sample geometries have been employed. Under transmission conditions, enzyme at 75 mg/ml was incubated with dimethoxybenzoin-caged ATP. ATP was released by flashing with a UV laser pulse at 355 nm, which resulted in a large change in the amide I band. The absorbance at 1659 cm(-1) decreased with a concomitant increase in the absorbance at 1620 cm(-1). These changes are consistent with a partial conversion of protein secondary structure from alpha-helix to beta-sheet. The changes were approximately 8% of the total absorbance, much larger than those seen with other P-type ATPases. Using attenuated total internal reflection Fourier transform infrared spectroscopy, the decrease in absorbance at approximately 1650 cm(-1) was titrated with ATP, and the titration midpoint K0.5 was determined under different ionic conditions. In the presence of metal ions (Na+, Na+ and K+, or Mg2+), K0.5 was on the order of a few microM. In the absence of these ions, K0.5 was an order of magnitude lower (0.1 microM), indicating a higher apparent affinity. This effect suggests that the equilibrium for the ATP-induced conformational changes is dependent on the presence of metal ions.
Collapse
Affiliation(s)
- Promod R Pratap
- Department of Physics and Astronomy, University of North Carolina at Greensboro, Greensboro, North Carolina 27402-6710, USA.
| | | | | |
Collapse
|
48
|
Artigas P, Gadsby DC. Large diameter of palytoxin-induced Na/K pump channels and modulation of palytoxin interaction by Na/K pump ligands. ACTA ACUST UNITED AC 2004; 123:357-76. [PMID: 15024043 PMCID: PMC2217460 DOI: 10.1085/jgp.200308964] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Palytoxin binds to Na/K pumps to generate nonselective cation channels whose pore likely comprises at least part of the pump's ion translocation pathway. We systematically analyzed palytoxin's interactions with native human Na/K pumps in outside-out patches from HEK293 cells over a broad range of ionic and nucleotide conditions, and with or without cardiotonic steroids. With 5 mM internal (pipette) [MgATP], palytoxin activated the conductance with an apparent affinity that was highest for Na+-containing (K+-free) external and internal solutions, lowest for K+-containing (Na+-free) external and internal solutions, and intermediate for the mixed external Na+/internal K+, and external K+/internal Na+ conditions; with Na+ solutions and MgATP, the mean dwell time of palytoxin on the Na/K pump was about one day. With Na+ solutions, the apparent affinity for palytoxin action was low after equilibration of patches with nucleotide-free pipette solution. That apparent affinity was increased in two phases as the equilibrating [MgATP] was raised over the submicromolar, and submillimolar, ranges, but was increased by pipette MgAMPPNP in a single phase, over the submillimolar range; the apparent affinity at saturating [MgAMPPNP] remained ∼30-fold lower than at saturating [MgATP]. After palytoxin washout, the conductance decay that reflects palytoxin unbinding was accelerated by cardiotonic steroid. When Na/K pumps were preincubated with cardiotonic steroid, subsequent activation of palytoxin-induced conductance was greatly slowed, even after washout of the cardiotonic steroid, but activation could still be accelerated by increasing palytoxin concentration. These results indicate that palytoxin and a cardiotonic steroid can simultaneously occupy the same Na/K pump, each destabilizing the other. The palytoxin-induced channels were permeable to several large organic cations, including N-methyl-d-glucamine+, suggesting that the narrowest section of the pore must be ∼7.5 Å wide. Enhanced understanding of palytoxin action now allows its use for examining the structures and mechanisms of the gates that occlude/deocclude transported ions during the normal Na/K pump cycle.
Collapse
Affiliation(s)
- Pablo Artigas
- Laboratory of Cardiac/Membrane Physiology, Rockefeller University, New York, NY 10021-6399, USA
| | | |
Collapse
|
49
|
Gumz ML, Duda D, McKenna R, Wingo CS, Cain BD. Molecular modeling of the rabbit colonic (HKalpha2a) H+, K+ ATPase. J Mol Model 2003; 9:283-9. [PMID: 12884085 DOI: 10.1007/s00894-003-0140-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2002] [Accepted: 05/13/2003] [Indexed: 11/27/2022]
Abstract
A model of the HKalpha2a subunit of the rabbit colonic H+, K+ ATPase has been generated using the crystal structure of the Ca(+2) ATPase as a template. A pairwise sequence alignment of the deduced primary sequences of the two proteins demonstrated that they share 29% amino acid sequence identity and 47% similarity. Using O (version 7) the model of HKalpha2a was constructed by interactively mutating, deleting, and inserting the amino acids that differed between the pairwise sequence alignment of the Ca(+2) ATPase and HKalpha2a. Insertions and deletions in the HKalpha2a sequence occur in apparent extra-membraneous loop regions. The HKalpha2a model was energy minimized and globally refined to a level comparable to that of the Ca(+2) ATPase structure using CNS. The charge distribution over the surface of HKalpha2a was evaluated in GRASP and possible secondary structure elements of HKalpha2a were visualized in BOBSCRIPT. Conservation and placement of residues that may be involved in ouabain binding by the H+, K+ ATPase were considered and a putative location for the beta subunit was postulated within the structure.
Collapse
Affiliation(s)
- Michelle L Gumz
- Department of Biochemistry and Molecular Biology, University of Florida, 1600 SW Archer Rd., Box 100245 JHMHSC, Gainesville, FL 32610, USA
| | | | | | | | | |
Collapse
|
50
|
Jorgensen PL, Hakansson KO, Karlish SJD. Structure and mechanism of Na,K-ATPase: functional sites and their interactions. Annu Rev Physiol 2003; 65:817-49. [PMID: 12524462 DOI: 10.1146/annurev.physiol.65.092101.142558] [Citation(s) in RCA: 384] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The cell membrane Na,K-ATPase is a member of the P-type family of active cation transport proteins. Recently the molecular structure of the related sarcoplasmic reticulum Ca-ATPase in an E1 conformation has been determined at 2.6 A resolution. Furthermore, theoretical models of the Ca-ATPase in E2 conformations are available. As a result of these developments, these structural data have allowed construction of homology models that address the central questions of mechanism of active cation transport by all P-type cation pumps. This review relates recent evidence on functional sites of Na,K-ATPase for the substrate (ATP), the essential cofactor (Mg(2+) ions), and the transported cations (Na(+) and K(+)) to the molecular structure. The essential elements of the Ca-ATPase structure, including 10 transmembrane helices and well-defined N, P, and A cytoplasmic domains, are common to all PII-type pumps such as Na,K-ATPase and H,K-ATPases. However, for Na,K-ATPase and H,K-ATPase, which consist of both alpha- and beta-subunits, there may be some detailed differences in regions of subunit interactions. Mutagenesis, proteolytic cleavage, and transition metal-catalyzed oxidative cleavages are providing much evidence about residues involved in binding of Na(+), K(+), ATP, and Mg(2+) ions and changes accompanying E1-E2 or E1-P-E2-P conformational transitions. We discuss this evidence in relation to N, P, and A cytoplasmic domain interactions, and long-range interactions between the active site and the Na(+) and K(+) sites in the transmembrane segments, for the different steps of the catalytic cycle.
Collapse
Affiliation(s)
- Peter L Jorgensen
- Biomembrane Center, August Krogh Institute, Copenhagen University, Universitetsparken 13, 2100 Copenhagen OE, Denmark.
| | | | | |
Collapse
|