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Puljung M, Vedovato N, Usher S, Ashcroft F. Activation mechanism of ATP-sensitive K + channels explored with real-time nucleotide binding. eLife 2019; 8:41103. [PMID: 30789344 PMCID: PMC6400584 DOI: 10.7554/elife.41103] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 02/14/2019] [Indexed: 01/15/2023] Open
Abstract
The response of ATP-sensitive K+ channels (KATP) to cellular metabolism is coordinated by three classes of nucleotide binding site (NBS). We used a novel approach involving labeling of intact channels in a native, membrane environment with a non-canonical fluorescent amino acid and measurement (using FRET with fluorescent nucleotides) of steady-state and time-resolved nucleotide binding to dissect the role of NBS2 of the accessory SUR1 subunit of KATP in channel gating. Binding to NBS2 was Mg2+-independent, but Mg2+ was required to trigger a conformational change in SUR1. Mutation of a lysine (K1384A) in NBS2 that coordinates bound nucleotides increased the EC50 for trinitrophenyl-ADP binding to NBS2, but only in the presence of Mg2+, indicating that this mutation disrupts the ligand-induced conformational change. Comparison of nucleotide-binding with ionic currents suggests a model in which each nucleotide binding event to NBS2 of SUR1 is independent and promotes KATP activation by the same amount.
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Affiliation(s)
- Michael Puljung
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Natascia Vedovato
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Samuel Usher
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
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Puljung MC. Cryo-electron microscopy structures and progress toward a dynamic understanding of K ATP channels. J Gen Physiol 2018; 150:653-669. [PMID: 29685928 PMCID: PMC5940251 DOI: 10.1085/jgp.201711978] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 03/26/2018] [Indexed: 12/11/2022] Open
Abstract
Puljung reviews recent cryo-EM KATP channel structures and proposes a mechanism by which ligand binding results in channel opening. Adenosine triphosphate (ATP)–sensitive K+ (KATP) channels are molecular sensors of cell metabolism. These hetero-octameric channels, comprising four inward rectifier K+ channel subunits (Kir6.1 or Kir6.2) and four sulfonylurea receptor (SUR1 or SUR2A/B) subunits, detect metabolic changes via three classes of intracellular adenine nucleotide (ATP/ADP) binding site. One site, located on the Kir subunit, causes inhibition of the channel when ATP or ADP is bound. The other two sites, located on the SUR subunit, excite the channel when bound to Mg nucleotides. In pancreatic β cells, an increase in extracellular glucose causes a change in oxidative metabolism and thus turnover of adenine nucleotides in the cytoplasm. This leads to the closure of KATP channels, which depolarizes the plasma membrane and permits Ca2+ influx and insulin secretion. Many of the molecular details regarding the assembly of the KATP complex, and how changes in nucleotide concentrations affect gating, have recently been uncovered by several single-particle cryo-electron microscopy structures of the pancreatic KATP channel (Kir6.2/SUR1) at near-atomic resolution. Here, the author discusses the detailed picture of excitatory and inhibitory ligand binding to KATP that these structures present and suggests a possible mechanism by which channel activation may proceed from the ligand-binding domains of SUR to the channel pore.
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Affiliation(s)
- Michael C Puljung
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, England, UK
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Zhao J, Beyrakhova K, Liu Y, Alvarez CP, Bueler SA, Xu L, Xu C, Boniecki MT, Kanelis V, Luo ZQ, Cygler M, Rubinstein JL. Molecular basis for the binding and modulation of V-ATPase by a bacterial effector protein. PLoS Pathog 2017; 13:e1006394. [PMID: 28570695 PMCID: PMC5469503 DOI: 10.1371/journal.ppat.1006394] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Revised: 06/13/2017] [Accepted: 05/01/2017] [Indexed: 12/16/2022] Open
Abstract
Intracellular pathogenic bacteria evade the immune response by replicating within host cells. Legionella pneumophila, the causative agent of Legionnaires’ Disease, makes use of numerous effector proteins to construct a niche supportive of its replication within phagocytic cells. The L. pneumophila effector SidK was identified in a screen for proteins that reduce the activity of the proton pumping vacuolar-type ATPases (V-ATPases) when expressed in the yeast Saccharomyces cerevisae. SidK is secreted by L. pneumophila in the early stages of infection and by binding to and inhibiting the V-ATPase, SidK reduces phagosomal acidification and promotes survival of the bacterium inside macrophages. We determined crystal structures of the N-terminal region of SidK at 2.3 Å resolution and used single particle electron cryomicroscopy (cryo-EM) to determine structures of V-ATPase:SidK complexes at ~6.8 Å resolution. SidK is a flexible and elongated protein composed of an α-helical region that interacts with subunit A of the V-ATPase and a second region of unknown function that is flexibly-tethered to the first. SidK binds V-ATPase strongly by interacting via two α-helical bundles at its N terminus with subunit A. In vitro activity assays show that SidK does not inhibit the V-ATPase completely, but reduces its activity by ~40%, consistent with the partial V-ATPase deficiency phenotype its expression causes in yeast. The cryo-EM analysis shows that SidK reduces the flexibility of the A-subunit that is in the ‘open’ conformation. Fluorescence experiments indicate that SidK binding decreases the affinity of V-ATPase for a fluorescent analogue of ATP. Together, these results reveal the structural basis for the fine-tuning of V-ATPase activity by SidK. V-ATPase-driven acidification of lysosomes in phagocytic cells activates enzymes important for killing of phagocytized pathogens. Successful pathogens can subvert host defenses by secreting effectors that target V-ATPases to inhibit lysosomal acidification or lysosomal fusion with other cell compartments. This study reveals the structure of the V-ATPase:SidK complex, an assembly formed from the interaction of host and pathogen proteins involved in the infection of phagocytic white blood cells by Legionella pneumophila. The structure and activity of the V-ATPase is altered upon SidK binding, providing insight into the infection strategy used by L. pneumophila and possibly other intravacuolar pathogens.
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Affiliation(s)
- Jianhua Zhao
- The Hospital for Sick Children Research Institute, Toronto, Ontario, Canada
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - Ksenia Beyrakhova
- Department of Biochemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Yao Liu
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana, United States of America
| | - Claudia P. Alvarez
- Department of Chemistry, University of Toronto, Toronto, Ontario, Canada
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada
| | | | - Li Xu
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana, United States of America
| | - Caishuang Xu
- Department of Biochemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Michal T. Boniecki
- Department of Biochemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Voula Kanelis
- Department of Chemistry, University of Toronto, Toronto, Ontario, Canada
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Zhao-Qing Luo
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana, United States of America
| | - Miroslaw Cygler
- Department of Biochemistry, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- * E-mail: (JLR); (MC)
| | - John L. Rubinstein
- The Hospital for Sick Children Research Institute, Toronto, Ontario, Canada
- Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
- * E-mail: (JLR); (MC)
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Alvarez CP, Stagljar M, Muhandiram DR, Kanelis V. Hyperinsulinism-Causing Mutations Cause Multiple Molecular Defects in SUR1 NBD1. Biochemistry 2017; 56:2400-2416. [PMID: 28346775 DOI: 10.1021/acs.biochem.6b00681] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The sulfonylurea receptor 1 (SUR1) protein forms the regulatory subunit in ATP sensitive K+ (KATP) channels in the pancreas. SUR proteins are members of the ATP binding cassette (ABC) superfamily of proteins. Binding and hydrolysis of MgATP at the SUR nucleotide binding domains (NBDs) lead to channel opening. Pancreatic KATP channels play an important role in insulin secretion. SUR1 mutations that result in increased levels of channel opening ultimately inhibit insulin secretion and lead to neonatal diabetes. In contrast, SUR1 mutations that disrupt trafficking and/or decrease gating of KATP channels cause congenital hyperinsulinism, where oversecretion of insulin occurs even in the presence of low glucose levels. Here, we present data on the effects of specific congenital hyperinsulinism-causing mutations (G716V, R842G, and K890T) located in different regions of the first nucleotide binding domain (NBD1). Nuclear magnetic resonance (NMR) and fluorescence data indicate that the K890T mutation affects residues throughout NBD1, including residues that bind MgATP, NBD2, and coupling helices. The mutations also decrease the MgATP binding affinity of NBD1. Size exclusion and NMR data indicate that the G716V and R842G mutations cause aggregation of NBD1 in vitro, possibly because of destabilization of the domain. These data describe structural characterization of SUR1 NBD1 and shed light on the underlying molecular basis of mutations that cause congenital hyperinsulinism.
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Affiliation(s)
- Claudia P Alvarez
- Department of Chemical and Physical Sciences, University of Toronto Mississauga , 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6.,Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
| | - Marijana Stagljar
- Department of Chemical and Physical Sciences, University of Toronto Mississauga , 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6.,Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.,Department of Cell and Systems Biology, University of Toronto , 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5
| | - D Ranjith Muhandiram
- Department of Molecular Genetics, University of Toronto , 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
| | - Voula Kanelis
- Department of Chemical and Physical Sciences, University of Toronto Mississauga , 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6.,Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.,Department of Cell and Systems Biology, University of Toronto , 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5
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de Araujo ED, Alvarez CP, López-Alonso JP, Sooklal CR, Stagljar M, Kanelis V. Phosphorylation-dependent changes in nucleotide binding, conformation, and dynamics of the first nucleotide binding domain (NBD1) of the sulfonylurea receptor 2B (SUR2B). J Biol Chem 2015. [PMID: 26198630 DOI: 10.1074/jbc.m114.636233] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The sulfonylurea receptor 2B (SUR2B) forms the regulatory subunit of ATP-sensitive potassium (KATP) channels in vascular smooth muscle. Phosphorylation of the SUR2B nucleotide binding domains (NBD1 and NBD2) by protein kinase A results in increased channel open probability. Here, we investigate the effects of phosphorylation on the structure and nucleotide binding properties of NBD1. Phosphorylation sites in SUR2B NBD1 are located in an N-terminal tail that is disordered. Nuclear magnetic resonance (NMR) data indicate that phosphorylation of the N-terminal tail affects multiple residues in NBD1, including residues in the NBD2-binding site, and results in altered conformation and dynamics of NBD1. NMR spectra of NBD1 lacking the N-terminal tail, NBD1-ΔN, suggest that phosphorylation disrupts interactions of the N-terminal tail with the core of NBD1, a model supported by dynamic light scattering. Increased nucleotide binding of phosphorylated NBD1 and NBD1-ΔN, compared with non-phosphorylated NBD1, suggests that by disrupting the interaction of the NBD core with the N-terminal tail, phosphorylation also exposes the MgATP-binding site on NBD1. These data provide insights into the molecular basis by which phosphorylation of SUR2B NBD1 activates KATP channels.
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Affiliation(s)
- Elvin D de Araujo
- From the Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario L5L 1C6, the Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, and
| | - Claudia P Alvarez
- From the Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario L5L 1C6, the Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, and
| | - Jorge P López-Alonso
- From the Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario L5L 1C6, the Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, and the Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada
| | - Clarissa R Sooklal
- From the Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario L5L 1C6, the Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, and
| | - Marijana Stagljar
- From the Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario L5L 1C6, the Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, and the Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada
| | - Voula Kanelis
- From the Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario L5L 1C6, the Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, and the Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada
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de Araujo ED, Kanelis V. Successful development and use of a thermodynamic stability screen for optimizing the yield of nucleotide binding domains. Protein Expr Purif 2014; 103:38-47. [PMID: 25153533 DOI: 10.1016/j.pep.2014.08.006] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Revised: 08/08/2014] [Accepted: 08/09/2014] [Indexed: 01/09/2023]
Abstract
ATP sensitive potassium (KATP) channels consist of four copies of a pore-forming inward rectifying potassium channel (Kir6.1 or Kir6.2) and four copies of a sulfonylurea receptor (SUR1, SUR2A, or SUR2B). SUR proteins are members of the ATP-binding cassette superfamily of proteins. Binding of ATP to the Kir6.x subunit mediates channel inhibition, whereas MgATP binding and hydrolysis at the SUR NBDs results in channel opening. Mutations in SUR1 and SUR2A NBDs cause diseases of insulin secretion and cardiac disorders, respectively, underlying the importance of studying the NBDs. Although purification of SUR2A NBD1 in a soluble form is possible, the lack of long-term sample stability of the protein in a concentrated form has precluded detailed studies of the protein aimed at gaining a molecular-level understanding of how SUR mutations cause disease. Here we use a convenient and cost-effective thermodynamic screening method to probe stabilizing conditions for SUR2A NBD1. Results from the screen are used to alter the purification protocol to allow for significantly increased yields of the purified protein. In addition, the screen provides strategies for long-term storage of NBD1 and generating NBD1 samples at high concentrations suitable for NMR studies. NMR spectra of NBD1 with MgAMP-PNP are of higher quality compared to using MgATP, indicating that MgAMP-PNP be used as the ligand in future NMR studies. The screen presented here can be expanded to using different additives and can be employed to enhance purification yields, sample life times, and storage of other low stability nucleotide binding domains, such as GTPases.
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Affiliation(s)
- Elvin D de Araujo
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada; Department of Chemical and Physical Sciences, University of Toronto Mississauga, 3359 Mississauga Rd., Mississauga, Ontario L5L 1C6, Canada
| | - Voula Kanelis
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada; Department of Chemical and Physical Sciences, University of Toronto Mississauga, 3359 Mississauga Rd., Mississauga, Ontario L5L 1C6, Canada; Department of Cell and Systems Biology, University of Toronto, 25 Harbord St., Toronto, Ontario M5S 3G5, Canada.
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