1
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Dong F, Lojko P, Bazzone A, Bernhard F, Borodina I. Transporter function characterization via continuous-exchange cell-free synthesis and solid supported membrane-based electrophysiology. Bioelectrochemistry 2024; 159:108732. [PMID: 38810322 DOI: 10.1016/j.bioelechem.2024.108732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Revised: 05/02/2024] [Accepted: 05/13/2024] [Indexed: 05/31/2024]
Abstract
Functional characterization of transporters is impeded by the high cost and technical challenges of current transporter assays. Thus, in this work, we developed a new characterization workflow that combines cell-free protein synthesis (CFPS) and solid supported membrane-based electrophysiology (SSME). For this, membrane protein synthesis was accomplished in a continuous exchange cell-free system (CECF) in the presence of nanodiscs. The resulting transporters expressed in nanodiscs were incorporated into proteoliposomes and assayed in the presence of different substrates using the surface electrogenic event reader. As a proof of concept, we validated this workflow to express and characterize five diverse transporters: the drug/H+-coupled antiporters EmrE and SugE, the lactose permease LacY, the Na+/H+ antiporter NhaA from Escherichia coli, and the mitochondrial carrier AAC2 from Saccharomyces cerevisiae. For all transporters kinetic parameters, such as KM, IMAX, and pH dependency, were evaluated. This robust and expedite workflow (e.g., can be executed within only five workdays) offers a convenient direct functional assessment of transporter protein activity and has the ability to facilitate applications of transporters in medical and biotechnological research.
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Affiliation(s)
- Fang Dong
- The Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Denmark
| | - Pawel Lojko
- The Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Denmark
| | | | - Frank Bernhard
- Institute of Biophysical Chemistry, Centre for Biomolecular Magnetic Resonance, J.W. Goethe-University, Frankfurt am Main, Germany
| | - Irina Borodina
- The Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Denmark.
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2
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Hussein A, Zhang X, Stokes DL. Numerical model for electrogenic transport by the ATP-dependent potassium pump KdpFABC. BIOPHYSICAL REPORTS 2024; 4:100169. [PMID: 38950825 PMCID: PMC11304011 DOI: 10.1016/j.bpr.2024.100169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2024] [Revised: 06/15/2024] [Accepted: 06/28/2024] [Indexed: 07/03/2024]
Abstract
In vitro assays of ion transport are an essential tool for understanding molecular mechanisms associated with ATP-dependent pumps. Because ion transport is generally electrogenic, principles of electrophysiology are applicable, but conventional tools like patch-clamp are ineffective due to relatively low turnover rates of the pumps. Instead, assays have been developed to measure either voltage or current generated by transport activity of a population of molecules either in cell-derived membrane fragments or after reconstituting purified protein into proteoliposomes. In order to understand the nuances of these assays and to characterize effects of various operational parameters, we have developed a numerical model to simulate data produced by two relevant assays: fluorescence from voltage-sensitive dyes and current recorded by capacitive coupling on solid supported membranes. Parameters of the model, which has been implemented in Python, are described along with underlying principles of the computational algorithm. Experimental data from KdpFABC, a K+ pump associated with P-type ATPases, are presented, and model parameters have been adjusted to mimic these data. In addition, effects of key parameters such as nonselective leak conductance and turnover rate are demonstrated. Finally, simulated data are used to illustrate the effects of capacitive coupling on measured current and to compare alternative methods for quantification of raw data.
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Affiliation(s)
- Adel Hussein
- Department of Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| | - Xihui Zhang
- Department of Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| | - David L Stokes
- Department of Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York.
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3
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Gulati A, Kokane S, Perez-Boerema A, Alleva C, Meier PF, Matsuoka R, Drew D. Structure and mechanism of the K +/H + exchanger KefC. Nat Commun 2024; 15:4751. [PMID: 38834573 PMCID: PMC11150392 DOI: 10.1038/s41467-024-49082-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Accepted: 05/23/2024] [Indexed: 06/06/2024] Open
Abstract
Intracellular potassium (K+) homeostasis is fundamental to cell viability. In addition to channels, K+ levels are maintained by various ion transporters. One major family is the proton-driven K+ efflux transporters, which in gram-negative bacteria is important for detoxification and in plants is critical for efficient photosynthesis and growth. Despite their importance, the structure and molecular basis for K+-selectivity is poorly understood. Here, we report ~3.1 Å resolution cryo-EM structures of the Escherichia coli glutathione (GSH)-gated K+ efflux transporter KefC in complex with AMP, AMP/GSH and an ion-binding variant. KefC forms a homodimer similar to the inward-facing conformation of Na+/H+ antiporter NapA. By structural assignment of a coordinated K+ ion, MD simulations, and SSM-based electrophysiology, we demonstrate how ion-binding in KefC is adapted for binding a dehydrated K+ ion. KefC harbors C-terminal regulator of K+ conductance (RCK) domains, as present in some bacterial K+-ion channels. The domain-swapped helices in the RCK domains bind AMP and GSH and they inhibit transport by directly interacting with the ion-transporter module. Taken together, we propose that KefC is activated by detachment of the RCK domains and that ion selectivity exploits the biophysical properties likewise adapted by K+-ion-channels.
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Affiliation(s)
- Ashutosh Gulati
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Surabhi Kokane
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Annemarie Perez-Boerema
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Claudia Alleva
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Pascal F Meier
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Rei Matsuoka
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - David Drew
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden.
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4
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George A, Zuckerman DM. From Average Transient Transporter Currents to Microscopic Mechanism─A Bayesian Analysis. J Phys Chem B 2024; 128:1830-1842. [PMID: 38373358 DOI: 10.1021/acs.jpcb.3c07025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2024]
Abstract
Electrophysiology studies of secondary active transporters have revealed quantitative mechanistic insights over many decades of research. However, the emergence of new experimental and analytical approaches calls for investigation of the capabilities and limitations of the newer methods. We examine the ability of solid-supported membrane electrophysiology (SSME) to characterize discrete-state kinetic models with >10 rate constants. We use a Bayesian framework applied to synthetic data for three tasks: to quantify and check (i) the precision of parameter estimates under different assumptions, (ii) the ability of computation to guide the selection of experimental conditions, and (iii) the ability of our approach to distinguish among mechanisms based on SSME data. When the general mechanism, i.e., event order, is known in advance, we show that a subset of kinetic parameters can be "practically identified" within ∼1 order of magnitude, based on SSME current traces that visually appear to exhibit simple exponential behavior. This remains true even when accounting for systematic measurement bias and realistic uncertainties in experimental inputs (concentrations) are incorporated into the analysis. When experimental conditions are optimized or different experiments are combined, the number of practically identifiable parameters can be increased substantially. Some parameters remain intrinsically difficult to estimate through SSME data alone, suggesting that additional experiments are required to fully characterize parameters. We also demonstrate the ability to perform model selection and determine the order of events when that is not known in advance, comparing Bayesian and maximum-likelihood approaches. Finally, our studies elucidate good practices for the increasingly popular but subtly challenging Bayesian calculations for structural and systems biology.
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Affiliation(s)
- August George
- Department of Biomedical Engineering, Oregon Health and Science University, Portland, Oregon 97239, United States
| | - Daniel M Zuckerman
- Department of Biomedical Engineering, Oregon Health and Science University, Portland, Oregon 97239, United States
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5
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Colucci E, Anshari ZR, Patiño-Ruiz MF, Nemchinova M, Whittaker J, Slotboom DJ, Guskov A. Mutation in glutamate transporter homologue GltTk provides insights into pathologic mechanism of episodic ataxia 6. Nat Commun 2023; 14:1799. [PMID: 37002226 PMCID: PMC10066184 DOI: 10.1038/s41467-023-37503-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 03/20/2023] [Indexed: 04/03/2023] Open
Abstract
Episodic ataxias (EAs) are rare neurological conditions affecting the nervous system and typically leading to motor impairment. EA6 is linked to the mutation of a highly conserved proline into an arginine in the glutamate transporter EAAT1. In vitro studies showed that this mutation leads to a reduction in the substrates transport and an increase in the anion conductance. It was hypothesised that the structural basis of these opposed functional effects might be the straightening of transmembrane helix 5, which is kinked in the wild-type protein. In this study, we present the functional and structural implications of the mutation P208R in the archaeal homologue of glutamate transporters GltTk. We show that also in GltTk the P208R mutation leads to reduced aspartate transport activity and increased anion conductance, however a cryo-EM structure reveals that the kink is preserved. The arginine side chain of the mutant points towards the lipidic environment, where it may engage in interactions with the phospholipids, thereby potentially interfering with the transport cycle and contributing to stabilisation of an anion conducting state.
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Affiliation(s)
- Emanuela Colucci
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Zaid R Anshari
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Miyer F Patiño-Ruiz
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Mariia Nemchinova
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Jacob Whittaker
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands
| | - Dirk J Slotboom
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands.
| | - Albert Guskov
- Groningen Institute for Biomolecular Sciences and Biotechnology, University of Groningen, 9747AG, Groningen, the Netherlands.
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6
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Pommereau A, Licher T, Bärenz F. Solid-Supported Membrane (SSM)-Based Electrophysiology Assays Using Surface Electrogenic Event Reader Technology (SURFE²R) in Early Drug Discovery. Curr Protoc 2023; 3:e650. [PMID: 36912603 DOI: 10.1002/cpz1.650] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/14/2023]
Abstract
This article presents detailed descriptions of procedures and troubleshooting tips for solid-supported membrane (SSM)-based electrophysiology assays (SURFE²R) to measure electrogenic solute carrier transporter proteins (SLCs) and assess the effects of compounds that modulate their activity. SURFE²R allows the use of the standard 96-well format, making it an ideal platform for tertiary assays in a drug-discovery campaign. The assays are performed with cell-line-derived membrane fractions or proteoliposomes containing the transporter of interest. Three main protocols are described for the isolation of membrane fractions from cell culture and the generation of proteoliposomes containing the transporter of interest. Additionally, detailed protocols for SURFE²R single concentration and dose-response experiments are included to measure the potencies of test compounds in stimulating or inhibiting transporter function (EC50 or IC50 values, respectively) and kinetic functional assays to calculate apparent affinity (kM ) and maximal velocity (Vmax ) of substrate uptake. © 2023 Sanofi. Current Protocols published by Wiley Periodicals LLC. PROTOCOL GROUP 1: Sample preparation for SSM-based electrophysiology assays Support Protocol 1: Production of cell batches Support Protocol 2: Simple isolation of cell membranes Alternate Protocol 1: Isolation of cell membranes with sucrose gradient pre-purification Support Protocol 3: Production and isolation of liposomes Support Protocol 4: Preparation of sensor with isolated cell membranes Alternate Protocol 2: Preparation of sensor with isolated proteoliposomes PROTOCOL GROUP 2: Determination of assay parameters for SSM-based electrophysiology assay Support Protocol 5: Assay with stable buffer Alternate Protocol 3: Assay with ion gradient Support Protocol 6: Determination of membrane/liposome concentration Support Protocol 7: Determination of substrate dependency kM PROTOCOL GROUP 3: Determination of advanced assay parameters for SSM-based electrophysiology assays Support Protocol 8: Assessment of ion concentration dependency Support Protocol 9: Assessment of pH dependency Support Protocol 10: Assessment of DMSO dependency Support Protocol 11: Assessment of signal stability with multiple activations PROTOCOL GROUP 4: Compound testing through SSM-based electrophysiology assays using SURFE²R apparatus Support Protocol 12: Assessment of signal specificity of a published inhibitor or unknown compound(s) Support Protocol 13: Compound wash-out Support Protocol 14: Statistical analysis.
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Affiliation(s)
- Antje Pommereau
- Sanofi, Integrated Drug Discovery, Industriepark Hoechst, Frankfurt am Main, Germany
| | - Thomas Licher
- Sanofi, Integrated Drug Discovery, Industriepark Hoechst, Frankfurt am Main, Germany
| | - Felix Bärenz
- Sanofi, Integrated Drug Discovery, Industriepark Hoechst, Frankfurt am Main, Germany
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7
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Tadini-Buoninsegni F, Mikkelsen SA, Mogensen LS, Holm R, Molday RS, Andersen JP. Electrogenic reaction step and phospholipid translocation pathway of the mammalian P4-ATPase ATP8A2. FEBS Lett 2023; 597:495-503. [PMID: 35945663 DOI: 10.1002/1873-3468.14459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 07/21/2022] [Accepted: 07/25/2022] [Indexed: 11/09/2022]
Abstract
ATP8A2 is a mammalian P4-ATPase (flippase) that translocates the negatively charged lipid substrate phosphatidylserine from the exoplasmic leaflet to the cytoplasmic leaflet of cellular membranes. Using an electrophysiological method based on solid supported membranes, we investigated the electrogenicity of specific reaction steps of ATP8A2 and explored a potential phospholipid translocation pathway involving residues with positively charged side chains. Changes to the current signals caused by mutations show that the main electrogenic event occurs in connection with the release of the bound phosphatidylserine to the cytoplasmic leaflet and support the hypothesis that the phospholipid interacts with specific lysine and arginine residues near the cytoplasmic border of the lipid bilayer during the translocation and reorientation required for insertion into the cytoplasmic leaflet.
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Affiliation(s)
| | | | | | - Rikke Holm
- Department of Biomedicine, Aarhus University, Denmark
| | - Robert S Molday
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada.,Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, Canada
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8
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Current Methods to Unravel the Functional Properties of Lysosomal Ion Channels and Transporters. Cells 2022; 11:cells11060921. [PMID: 35326372 PMCID: PMC8946281 DOI: 10.3390/cells11060921] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Revised: 03/04/2022] [Accepted: 03/05/2022] [Indexed: 02/07/2023] Open
Abstract
A distinct set of channels and transporters regulates the ion fluxes across the lysosomal membrane. Malfunctioning of these transport proteins and the resulting ionic imbalance is involved in various human diseases, such as lysosomal storage disorders, cancer, as well as metabolic and neurodegenerative diseases. As a consequence, these proteins have stimulated strong interest for their suitability as possible drug targets. A detailed functional characterization of many lysosomal channels and transporters is lacking, mainly due to technical difficulties in applying the standard patch-clamp technique to these small intracellular compartments. In this review, we focus on current methods used to unravel the functional properties of lysosomal ion channels and transporters, stressing their advantages and disadvantages and evaluating their fields of applicability.
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9
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Bazzone A, Tesmer L, Kurt D, Kaback HR, Fendler K, Madej MG. Investigation of sugar binding kinetics of the E. coli sugar/H + symporter XylE using solid supported membrane-based electrophysiology. J Biol Chem 2021; 298:101505. [PMID: 34929170 PMCID: PMC8784342 DOI: 10.1016/j.jbc.2021.101505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 12/11/2021] [Accepted: 12/13/2021] [Indexed: 12/19/2022] Open
Abstract
Bacterial transporters are difficult to study using conventional electrophysiology because of their low transport rates and the small size of bacterial cells. Here, we applied solid-supported membrane–based electrophysiology to derive kinetic parameters of sugar translocation by the Escherichia coli xylose permease (XylE), including functionally relevant mutants. Many aspects of the fucose permease (FucP) and lactose permease (LacY) have also been investigated, which allow for more comprehensive conclusions regarding the mechanism of sugar translocation by transporters of the major facilitator superfamily. In all three of these symporters, we observed sugar binding and transport in real time to determine KM, Vmax, KD, and kobs values for different sugar substrates. KD and kobs values were attainable because of a conserved sugar-induced electrogenic conformational transition within these transporters. We also analyzed interactions between the residues in the available X-ray sugar/H+ symporter structures obtained with different bound sugars. We found that different sugars induce different conformational states, possibly correlating with different charge displacements in the electrophysiological assay upon sugar binding. Finally, we found that mutations in XylE altered the kinetics of glucose binding and transport, as Q175 and L297 are necessary for uncoupling H+ and d-glucose translocation. Based on the rates for the electrogenic conformational transition upon sugar binding (>300 s−1) and for sugar translocation (2 s−1 − 30 s−1 for different substrates), we propose a multiple-step mechanism and postulate an energy profile for sugar translocation. We also suggest a mechanism by which d-glucose can act as an inhibitor for XylE.
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Affiliation(s)
- Andre Bazzone
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry in Frankfurt/M, Germany
| | - Laura Tesmer
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry in Frankfurt/M, Germany
| | - Derya Kurt
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry in Frankfurt/M, Germany
| | - H Ronald Kaback
- University of California, Department of Physiology and Department of Microbiology, Immunology, Molecular Genetics, Molecular Biology Institute in Los Angeles CA, USA
| | - Klaus Fendler
- Max-Planck-Institute of Biophysics, Department of Biophysical Chemistry in Frankfurt/M, Germany
| | - M Gregor Madej
- Institute of Biophysics and Biophysical Chemistry, Department of Structural Biology, University of Regensburg, Universitätsstr. 31, 95053 Regensburg, Germany; Institute of Biophysics, Department of Structural Biology, Saarland University, Center of Human and Molecular Biology, Building 60, 66421 Homburg, Germany
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10
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Sordi G, Goti A, Young HS, Palchetti I, Tadini‐Buoninsegni F. Stimulation of Ca 2+ -ATPase Transport Activity by a Small-Molecule Drug. ChemMedChem 2021; 16:3293-3299. [PMID: 34297466 PMCID: PMC8571031 DOI: 10.1002/cmdc.202100350] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 07/19/2021] [Indexed: 11/11/2022]
Abstract
The sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA) hydrolyzes ATP to transport Ca2+ from the cytoplasm to the sarcoplasmic reticulum (SR) lumen, thereby inducing muscle relaxation. Dysfunctional SERCA has been related to various diseases. The identification of small-molecule drugs that can activate SERCA may offer a therapeutic approach to treat pathologies connected with SERCA malfunction. Herein, we propose a method to study the mechanism of interaction between SERCA and novel SERCA activators, i. e. CDN1163, using a solid supported membrane (SSM) biosensing approach. Native SR vesicles or reconstituted proteoliposomes containing SERCA were adsorbed on the SSM and activated by ATP concentration jumps. We observed that CDN1163 reversibly interacts with SERCA and enhances ATP-dependent Ca2+ translocation. The concentration dependence of the CDN1163 effect provided an EC50 =6.0±0.3 μM. CDN1163 was shown to act directly on SERCA and to exert its stimulatory effect under physiological Ca2+ concentrations. These results suggest that CDN1163 interaction with SERCA can promote a protein conformational state that favors Ca2+ release into the SR lumen.
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Affiliation(s)
- Giacomo Sordi
- Department of Chemistry “Ugo Schiff”University of FlorenceVia della Lastruccia 3–1350019Sesto FiorentinoItaly
- Present address: PQE Group50066 ReggelloFlorenceItaly
| | - Andrea Goti
- Department of Chemistry “Ugo Schiff”University of FlorenceVia della Lastruccia 3–1350019Sesto FiorentinoItaly
| | - Howard S. Young
- Department of BiochemistryUniversity of AlbertaEdmonton, AlbertaT6G 2H7Canada
| | - Ilaria Palchetti
- Department of Chemistry “Ugo Schiff”University of FlorenceVia della Lastruccia 3–1350019Sesto FiorentinoItaly
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11
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Expression, purification and characterization of human proton-coupled oligopeptide transporter 1 hPEPT1. Protein Expr Purif 2021; 190:105990. [PMID: 34637915 DOI: 10.1016/j.pep.2021.105990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 09/27/2021] [Accepted: 10/05/2021] [Indexed: 11/22/2022]
Abstract
The human peptide transporter hPEPT1 (SLC15A1) is responsible for uptake of dietary di- and tripeptides and a number of drugs from the small intestine by utilizing the proton electrochemical gradient, and hence an important target for peptide-like drug design and drug delivery. hPEPT1 belongs to the ubiquitous major facilitator superfamily that all contain a 12TM core structure, with global conformational changes occurring during the transport cycle. Several bacterial homologues of these transporters have been characterized, providing valuable insight into the transport mechanism of this family. Here we report the overexpression and purification of recombinant hPEPT1 in a detergent-solubilized state. Thermostability profiling of hPEPT1 at different pH values revealed that hPEPT1 is more stable at pH 6 as compared to pH 7 and 8. Micro-scale thermophoresis (MST) confirmed that the purified hPEPT1 was able to bind di- and tripeptides respectively. To assess the in-solution oligomeric state of hPEPT1, negative stain electron microscopy was performed, demonstrating a predominantly monomeric state.
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12
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Thomas NE, Feng W, Henzler-Wildman KA. A solid-supported membrane electrophysiology assay for efficient characterization of ion-coupled transport. J Biol Chem 2021; 297:101220. [PMID: 34562455 PMCID: PMC8517846 DOI: 10.1016/j.jbc.2021.101220] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 09/14/2021] [Accepted: 09/20/2021] [Indexed: 12/03/2022] Open
Abstract
Transport stoichiometry determination can provide great insight into the mechanism and function of ion-coupled transporters. Traditional reversal potential assays are a reliable, general method for determining the transport stoichiometry of ion-coupled transporters, but the time and material costs of this technique hinder investigations of transporter behavior under multiple experimental conditions. Solid-supported membrane electrophysiology (SSME) allows multiple recordings of liposomal or membrane samples adsorbed onto a sensor and is sensitive enough to detect transport currents from moderate-flux transporters that are inaccessible to traditional electrophysiology techniques. Here, we use SSME to develop a new method for measuring transport stoichiometry with greatly improved throughput. Using this technique, we were able to verify the recent report of a fixed 2:1 stoichiometry for the proton:guanidinium antiporter Gdx, reproduce the 1H+:2Cl- antiport stoichiometry of CLC-ec1, and confirm loose proton:nitrate coupling for CLC-ec1. Furthermore, we were able to demonstrate quantitative exchange of internal contents of liposomes adsorbed onto SSME sensors to allow multiple experimental conditions to be tested on a single sample. Our SSME method provides a fast, easy, general method for measuring transport stoichiometry, which will facilitate future mechanistic and functional studies of ion-coupled transporters.
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Affiliation(s)
- Nathan E Thomas
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Wei Feng
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California, USA
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13
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Andrei A, Di Renzo MA, Öztürk Y, Meisner A, Daum N, Frank F, Rauch J, Daldal F, Andrade SLA, Koch HG. The CopA2-Type P 1B-Type ATPase CcoI Serves as Central Hub for cbb 3-Type Cytochrome Oxidase Biogenesis. Front Microbiol 2021; 12:712465. [PMID: 34589071 PMCID: PMC8475189 DOI: 10.3389/fmicb.2021.712465] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 07/12/2021] [Indexed: 11/13/2022] Open
Abstract
Copper (Cu)-transporting P1B-type ATPases are ubiquitous metal transporters and crucial for maintaining Cu homeostasis in all domains of life. In bacteria, the P1B-type ATPase CopA is required for Cu-detoxification and exports excess Cu(I) in an ATP-dependent reaction from the cytosol into the periplasm. CopA is a member of the CopA1-type ATPase family and has been biochemically and structurally characterized in detail. In contrast, less is known about members of the CopA2-type ATPase family, which are predicted to transport Cu(I) into the periplasm for cuproprotein maturation. One example is CcoI, which is required for the maturation of cbb 3-type cytochrome oxidase (cbb 3-Cox) in different species. Here, we reconstituted purified CcoI of Rhodobacter capsulatus into liposomes and determined Cu transport using solid-supported membrane electrophysiology. The data demonstrate ATP-dependent Cu(I) translocation by CcoI, while no transport is observed in the presence of a non-hydrolysable ATP analog. CcoI contains two cytosolically exposed N-terminal metal binding sites (N-MBSs), which are both important, but not essential for Cu delivery to cbb 3-Cox. CcoI and cbb 3-Cox activity assays in the presence of different Cu concentrations suggest that the glutaredoxin-like N-MBS1 is primarily involved in regulating the ATPase activity of CcoI, while the CopZ-like N-MBS2 is involved in Cu(I) acquisition. The interaction of CcoI with periplasmic Cu chaperones was analyzed by genetically fusing CcoI to the chaperone SenC. The CcoI-SenC fusion protein was fully functional in vivo and sufficient to provide Cu for cbb 3-Cox maturation. In summary, our data demonstrate that CcoI provides the link between the cytosolic and periplasmic Cu chaperone networks during cbb 3-Cox assembly.
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Affiliation(s)
- Andreea Andrei
- Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.,Faculty of Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Maria Agostina Di Renzo
- Institute for Biochemistry, Faculty of Chemistry and Pharmacy, Albert-Ludwigs-University Freiburg, Freiburg, Germany.,Spemann Graduate School of Biology and Medicine (SGBM), University of Freiburg, Freiburg, Germany.,Faculty of Chemistry and Pharmacy, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Yavuz Öztürk
- Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Alexandra Meisner
- Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Noel Daum
- Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Fabian Frank
- Institute for Biochemistry, Faculty of Chemistry and Pharmacy, Albert-Ludwigs-University Freiburg, Freiburg, Germany
| | - Juna Rauch
- Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Fevzi Daldal
- Department of Biology, University of Pennsylvania, Philadelphia, PA, United States
| | - Susana L A Andrade
- Institute for Biochemistry, Faculty of Chemistry and Pharmacy, Albert-Ludwigs-University Freiburg, Freiburg, Germany
| | - Hans-Georg Koch
- Institut für Biochemie und Molekularbiologie, ZBMZ, Faculty of Medicine, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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14
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Dvorak V, Wiedmer T, Ingles-Prieto A, Altermatt P, Batoulis H, Bärenz F, Bender E, Digles D, Dürrenberger F, Heitman LH, IJzerman AP, Kell DB, Kickinger S, Körzö D, Leippe P, Licher T, Manolova V, Rizzetto R, Sassone F, Scarabottolo L, Schlessinger A, Schneider V, Sijben HJ, Steck AL, Sundström H, Tremolada S, Wilhelm M, Wright Muelas M, Zindel D, Steppan CM, Superti-Furga G. An Overview of Cell-Based Assay Platforms for the Solute Carrier Family of Transporters. Front Pharmacol 2021; 12:722889. [PMID: 34447313 PMCID: PMC8383457 DOI: 10.3389/fphar.2021.722889] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Accepted: 07/19/2021] [Indexed: 12/12/2022] Open
Abstract
The solute carrier (SLC) superfamily represents the biggest family of transporters with important roles in health and disease. Despite being attractive and druggable targets, the majority of SLCs remains understudied. One major hurdle in research on SLCs is the lack of tools, such as cell-based assays to investigate their biological role and for drug discovery. Another challenge is the disperse and anecdotal information on assay strategies that are suitable for SLCs. This review provides a comprehensive overview of state-of-the-art cellular assay technologies for SLC research and discusses relevant SLC characteristics enabling the choice of an optimal assay technology. The Innovative Medicines Initiative consortium RESOLUTE intends to accelerate research on SLCs by providing the scientific community with high-quality reagents, assay technologies and data sets, and to ultimately unlock SLCs for drug discovery.
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Affiliation(s)
- Vojtech Dvorak
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | - Tabea Wiedmer
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | - Alvaro Ingles-Prieto
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | | | - Helena Batoulis
- Drug Discovery Sciences–Lead Discovery, Bayer Pharmaceuticals, Wuppertal, Germany
| | - Felix Bärenz
- Sanofi-Aventis Deutschland GmbH, Frankfurt am Main, Germany
| | - Eckhard Bender
- Drug Discovery Sciences–Lead Discovery, Bayer Pharmaceuticals, Wuppertal, Germany
| | - Daniela Digles
- Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | | | - Laura H. Heitman
- Division of Drug Discovery and Safety, LACDR, Leiden University, Leiden, Netherlands
| | - Adriaan P. IJzerman
- Division of Drug Discovery and Safety, LACDR, Leiden University, Leiden, Netherlands
| | - Douglas B. Kell
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, United Kingdom
- Novo Nordisk Foundation Centre for Biosustainability, Technical University of Denmark, Kgs. Lyngby, Denmark
| | - Stefanie Kickinger
- Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | - Daniel Körzö
- Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | - Philipp Leippe
- Department of Chemical Biology, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Thomas Licher
- Sanofi-Aventis Deutschland GmbH, Frankfurt am Main, Germany
| | | | | | | | | | - Avner Schlessinger
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Vanessa Schneider
- Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | - Hubert J. Sijben
- Division of Drug Discovery and Safety, LACDR, Leiden University, Leiden, Netherlands
| | | | | | | | | | - Marina Wright Muelas
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Diana Zindel
- Drug Discovery Sciences–Lead Discovery, Bayer Pharmaceuticals, Wuppertal, Germany
| | - Claire M. Steppan
- Pfizer Worldwide Research, Development and Medical, Groton, MA, United States
| | - Giulio Superti-Furga
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
- Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
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15
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Current problems and future avenues in proteoliposome research. Biochem Soc Trans 2021; 48:1473-1492. [PMID: 32830854 DOI: 10.1042/bst20190966] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Revised: 07/10/2020] [Accepted: 07/14/2020] [Indexed: 12/11/2022]
Abstract
Membrane proteins (MPs) are the gatekeepers between different biological compartments separated by lipid bilayers. Being receptors, channels, transporters, or primary pumps, they fulfill a wide variety of cellular functions and their importance is reflected in the increasing number of drugs that target MPs. Functional studies of MPs within a native cellular context, however, is difficult due to the innate complexity of the densely packed membranes. Over the past decades, detergent-based extraction and purification of MPs and their reconstitution into lipid mimetic systems has been a very powerful tool to simplify the experimental system. In this review, we focus on proteoliposomes that have become an indispensable experimental system for enzymes with a vectorial function, including many of the here described energy transducing MPs. We first address long standing questions on the difficulty of successful reconstitution and controlled orientation of MPs into liposomes. A special emphasis is given on coreconstitution of several MPs into the same bilayer. Second, we discuss recent progress in the development of fluorescent dyes that offer sensitive detection with high temporal resolution. Finally, we briefly cover the use of giant unilamellar vesicles for the investigation of complex enzymatic cascades, a very promising experimental tool considering our increasing knowledge of the interplay of different cellular components.
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16
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Tadini-Buoninsegni F. Protein Adsorption on Solid Supported Membranes: Monitoring the Transport Activity of P-Type ATPases. Molecules 2020; 25:molecules25184167. [PMID: 32933017 PMCID: PMC7570688 DOI: 10.3390/molecules25184167] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 09/01/2020] [Accepted: 09/02/2020] [Indexed: 02/07/2023] Open
Abstract
P-type ATPases are a large family of membrane transporters that are found in all forms of life. These enzymes couple ATP hydrolysis to the transport of various ions or phospholipids across cellular membranes, thereby generating and maintaining crucial electrochemical potential gradients. P-type ATPases have been studied by a variety of methods that have provided a wealth of information about the structure, function, and regulation of this class of enzymes. Among the many techniques used to investigate P-type ATPases, the electrical method based on solid supported membranes (SSM) was employed to investigate the transport mechanism of various ion pumps. In particular, the SSM method allows the direct measurement of charge movements generated by the ATPase following adsorption of the membrane-bound enzyme on the SSM surface and chemical activation by a substrate concentration jump. This kind of measurement was useful to identify electrogenic partial reactions and localize ion translocation in the reaction cycle of the membrane transporter. In the present review, we discuss how the SSM method has contributed to investigate some key features of the transport mechanism of P-type ATPases, with a special focus on sarcoplasmic reticulum Ca2+-ATPase, mammalian Cu+-ATPases (ATP7A and ATP7B), and phospholipid flippase ATP8A2.
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17
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Seica AFS, Iancu CV, Pfeilschifter B, Madej MG, Choe JY, Hellwig P. Asp 22 drives the protonation state of the Staphylococcus epidermidis glucose/H + symporter. J Biol Chem 2020; 295:15253-15261. [PMID: 32859752 DOI: 10.1074/jbc.ra120.014069] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 08/26/2020] [Indexed: 12/24/2022] Open
Abstract
The Staphylococcus epidermidis glucose/H+ symporter (GlcPSe) is a membrane transporter highly specific for glucose and a homolog of the human glucose transporters (GLUT, SLC2 family). Most GLUTs and their bacterial counterparts differ in the transport mechanism, adopting uniport and sugar/H+ symport, respectively. Unlike other bacterial GLUT homologs (for example, XylE), GlcPSe has a loose H+/sugar coupling. Asp22 is part of the proton-binding site of GlcPSe and crucial for the glucose/H+ co-transport mechanism. To determine how pH variations affect the proton site and the transporter, we performed surface-enhanced IR absorption spectroscopy on the immobilized GlcPSe We found that Asp22 has a pKa of 8.5 ± 0.1, a value consistent with that determined previously for glucose transport, confirming the central role of this residue for the transport mechanism of GlcPSe A neutral replacement of the negatively charged Asp22 led to positive charge displacements over the entire pH range, suggesting that the polarity change of the WT reflects the protonation state of Asp22 We expected that the substitution of the residue Ile105 for a serine, located within hydrogen-bonding distance to Asp22, would change the microenvironment, but the pKa of Asp22 corresponded to that of the WT. A167E mutation, selected in analogy to the XylE, introduced an additional protonatable site and perturbed the protonation state of Asp22, with the latter now exhibiting a pKa of 6.4. These studies confirm that Asp22 is the proton-binding residue in GlcPSe and show that charged residues in its vicinity affect the pKa of glucose/H+ symport.
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Affiliation(s)
- Ana Filipa Santos Seica
- Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CMC, Université de Strasbourg CNRS, Strasbourg, France
| | - Cristina V Iancu
- Department of Chemistry, East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, North Carolina, USA
| | - Benedikt Pfeilschifter
- University of Regensburg, Institute of Biophysics and Physical Biochemistry, Regensburg, Germany
| | - M Gregor Madej
- University of Regensburg, Institute of Biophysics and Physical Biochemistry, Regensburg, Germany
| | - Jun-Yong Choe
- Department of Chemistry, East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, North Carolina, USA; Department of Biochemistry and Molecular Biology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, USA.
| | - Petra Hellwig
- Laboratoire de Bioélectrochimie et Spectroscopie, UMR 7140, CMC, Université de Strasbourg CNRS, Strasbourg, France
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18
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Tadini-Buoninsegni F, Palchetti I. Label-Free Bioelectrochemical Methods for Evaluation of Anticancer Drug Effects at a Molecular Level. SENSORS 2020; 20:s20071812. [PMID: 32218227 PMCID: PMC7181070 DOI: 10.3390/s20071812] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Revised: 03/19/2020] [Accepted: 03/21/2020] [Indexed: 02/06/2023]
Abstract
Cancer is a multifactorial family of diseases that is still a leading cause of death worldwide. More than 100 different types of cancer affecting over 60 human organs are known. Chemotherapy plays a central role for treating cancer. The development of new anticancer drugs or new uses for existing drugs is an exciting and increasing research area. This is particularly important since drug resistance and side effects can limit the efficacy of the chemotherapy. Thus, there is a need for multiplexed, cost-effective, rapid, and novel screening methods that can help to elucidate the mechanism of the action of anticancer drugs and the identification of novel drug candidates. This review focuses on different label-free bioelectrochemical approaches, in particular, impedance-based methods, the solid supported membranes technique, and the DNA-based electrochemical sensor, that can be used to evaluate the effects of anticancer drugs on nucleic acids, membrane transporters, and living cells. Some relevant examples of anticancer drug interactions are presented which demonstrate the usefulness of such methods for the characterization of the mechanism of action of anticancer drugs that are targeted against various biomolecules.
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Affiliation(s)
| | - Ilaria Palchetti
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino, Italy
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19
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Abstract
Here, we present a protocol for the functional characterization of the H+-coupled human peptide transporter PepT1 and sufficient notes to transfer the protocol to the Na+-coupled sugar transporter SGLT1, the organic cation transporter OCT2, the Na+/Ca2+ exchanger NCX, and the neuronal glutamate transporter EAAT3.The assay was developed for the commercially available SURFE2R N1 instrument (Nanion Technologies GmbH) which applies solid supported membrane (SSM)-based electrophysiology. This technique is widely used for the functional characterization of membrane transporters with more than 100 different transporters characterized so far. The technique is cost-effective, easy to use, and capable of high-throughput measurements.SSM-based electrophysiology utilizes SSM-coated gold sensors to physically adsorb membrane vesicles containing the protein of interest. A fast solution exchange provides the substrate and activates transport. For the measurement of PepT1 activity, we applied a peptide concentration jump to activate H+/peptide symport. Proton influx charges the sensor. A capacitive current is measured reflecting the transport activity of PepT1 . Multiple measurements on the same sensor allow for comparison of transport activity under different conditions. Here, we determine EC50 for PepT1-mediated glycylglycine transport and perform an inhibition experiment using the specific peptide inhibitor Lys[Z(NO2)]-Val.
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20
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Mutation of two key aspartate residues alters stoichiometry of the NhaB Na +/H + exchanger from Klebsiella pneumoniae. Sci Rep 2019; 9:15390. [PMID: 31659210 PMCID: PMC6817889 DOI: 10.1038/s41598-019-51887-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2019] [Accepted: 10/08/2019] [Indexed: 12/02/2022] Open
Abstract
Bacterial NhaB Na+/H+ exchangers belonging to the Ion Transporter superfamily are poorly characterized in contrast to Na+/H+ exchangers of the Cation Proton Antiporter superfamily which have NhaA from Escherichia coli as a prominent member. For a more detailed understanding of the intricacies of the exchanger’s transport mechanism, mutational studies are essential. Therefore, we mutated two protonatable residues present in the putative transmembrane region of NhaB from Klebsiella pneumoniae (KpNhaB), which could serve as substrate binding sites, Asp146 and Asp404, to either glutamate or alanine and analyzed transport function and stability of the mutants using electrophysiological and fluorimetric techniques. While mutation of either Asp residue to Glu only had slight to moderate effects on the transport activity of the exchanger, the mutations D404A and D146A, in particular, had more profound effects on the transport function. Furthermore, a double mutant, D146A/D404A, exhibited a remarkable behavior at alkaline pH, where recorded electrical currents changed polarity, showing steady-state transport with a stoichiometry of H+:Na+ < 1, as opposed to the H+:Na+ > 1 stoichiometry of the WT. Thus, we showed that Asp146 and Asp404 are part of the substrate binding site(s) of KpNhaB and engineered a Na+/H+ exchanger with a variable stoichiometry.
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21
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Mikušević V, Schrecker M, Kolesova N, Patiño-Ruiz M, Fendler K, Hänelt I. A channel profile report of the unusual K + channel KtrB. J Gen Physiol 2019; 151:1357-1368. [PMID: 31624134 PMCID: PMC6888753 DOI: 10.1085/jgp.201912384] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Revised: 09/03/2019] [Accepted: 09/27/2019] [Indexed: 11/20/2022] Open
Abstract
KtrAB is a key player in bacterial K+ uptake required for K+ homeostasis and osmoadaptation. The system is unique in structure and function. It consists of the K+-translocating channel subunit KtrB, which forms a dimer in the membrane, and the soluble regulatory subunit KtrA, which attaches to the cytoplasmic side of the dimer as an octameric ring conferring Na+ and ATP dependency to the system. Unlike most K+ channels, KtrB lacks the highly conserved T(X)GYG selectivity filter sequence. Instead, only a single glycine residue is found in each pore loop, which raises the question of how selective the ion channel is. Here, we characterized the KtrB subunit from the Gram-negative pathogen Vibrio alginolyticus by isothermal titration calorimetry, solid-supported membrane-based electrophysiology, whole-cell K+ uptake, and ACMA-based transport assays. We found that, despite its simple selectivity filter, KtrB selectively binds K+ with micromolar affinity. Rb+ and Cs+ bind with millimolar affinities. However, only K+ and the poorly binding Na+ are efficiently translocated, based on size exclusion by the gating loop. Importantly, the physiologically required K+ over Na+ selectivity is provided by the channel's high affinity for potassium, which interestingly results from the presence of the sodium ions themselves. In the presence of the KtrA subunit, sodium ions further decrease the Michaelis-Menten constant for K+ uptake from milli- to micromolar concentrations and increase the Vmax, suggesting that Na+ also facilitates channel gating. In conclusion, high binding affinity and facilitated K+ gating allow KtrAB to function as a selective K+ channel.
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Affiliation(s)
- Vedrana Mikušević
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt, Germany
| | - Marina Schrecker
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt, Germany
| | - Natalie Kolesova
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt, Germany
| | - Miyer Patiño-Ruiz
- Department of Biophysical Chemistry, Max Planck Institute for Biophysics, Frankfurt, Germany
| | - Klaus Fendler
- Department of Biophysical Chemistry, Max Planck Institute for Biophysics, Frankfurt, Germany
| | - Inga Hänelt
- Institute of Biochemistry, Goethe University Frankfurt, Frankfurt, Germany
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22
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Phosphatidylserine flipping by the P4-ATPase ATP8A2 is electrogenic. Proc Natl Acad Sci U S A 2019; 116:16332-16337. [PMID: 31371510 DOI: 10.1073/pnas.1910211116] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Phospholipid flippases (P4-ATPases) utilize ATP to translocate specific phospholipids from the exoplasmic leaflet to the cytoplasmic leaflet of biological membranes, thus generating and maintaining transmembrane lipid asymmetry essential for a variety of cellular processes. P4-ATPases belong to the P-type ATPase protein family, which also encompasses the ion transporting P2-ATPases: Ca2+-ATPase, Na+,K+-ATPase, and H+,K+-ATPase. In comparison with the P2-ATPases, understanding of P4-ATPases is still very limited. The electrogenicity of P4-ATPases has not been explored, and it is not known whether lipid transfer between membrane bilayer leaflets can lead to displacement of charge across the membrane. A related question is whether P4-ATPases countertransport ions or other substrates in the opposite direction, similar to the P2-ATPases. Using an electrophysiological method based on solid supported membranes, we observed the generation of a transient electrical current by the mammalian P4-ATPase ATP8A2 in the presence of ATP and the negatively charged lipid substrate phosphatidylserine, whereas only a diminutive current was generated with the lipid substrate phosphatidylethanolamine, which carries no or little charge under the conditions of the measurement. The current transient seen with phosphatidylserine was abolished by the mutation E198Q, which blocks dephosphorylation. Likewise, mutation I364M, which causes the neurological disorder cerebellar ataxia, mental retardation, and disequilibrium (CAMRQ) syndrome, strongly interfered with the electrogenic lipid translocation. It is concluded that the electrogenicity is associated with a step in the ATPase reaction cycle directly involved in translocation of the lipid. These measurements also showed that no charged substrate is being countertransported, thereby distinguishing the P4-ATPase from P2-ATPases.
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23
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Mirandela GD, Tamburrino G, Hoskisson PA, Zachariae U, Javelle A. The lipid environment determines the activity of the Escherichia coli ammonium transporter AmtB. FASEB J 2019; 33:1989-1999. [PMID: 30211659 PMCID: PMC6338640 DOI: 10.1096/fj.201800782r] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Accepted: 08/14/2018] [Indexed: 12/22/2022]
Abstract
The movement of ammonium across biologic membranes is a fundamental process in all living organisms and is mediated by the ubiquitous ammonium transporter/methylammonium permease/rhesus protein (Amt/Mep/Rh) family of transporters. Recent structural analysis and coupled mass spectrometry studies have shown that the Escherichia coli ammonium transporter AmtB specifically binds 1-palmitoyl-2-oleoyl phosphatidylglycerol (POPG). Upon POPG binding, several residues of AmtB undergo a small conformational change, which stabilizes the protein against unfolding. However, no studies have so far been conducted, to our knowledge, to explore whether POPG binding to AmtB has functional consequences. Here, we used an in vitro experimental assay with purified components, together with molecular dynamics simulations, to characterize the relation between POPG binding and AmtB activity. We show that the AmtB activity is electrogenic. Our results indicate that the activity, at the molecular level, of Amt in archaebacteria and eubacteria may differ. We also show that POPG is an important cofactor for AmtB activity and that, in the absence of POPG, AmtB cannot complete the full translocation cycle. Furthermore, our simulations reveal previously undiscovered POPG binding sites on the intracellular side of the lipid bilayer between the AmtB subunits. Possible molecular mechanisms explaining the functional role of POPG are discussed.-Mirandela, G. D., Tamburrino, G., Hoskisson, P. A., Zachariae, U., Javelle, A. The lipid environment determines the activity of the Escherichia coli ammonium transporter AmtB.
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Affiliation(s)
- Gaëtan Dias Mirandela
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Giulia Tamburrino
- Computational Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
- Physics, School of Science and Engineering, University of Dundee, Dundee, United Kingdom
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
| | - Ulrich Zachariae
- Computational Biology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
- Physics, School of Science and Engineering, University of Dundee, Dundee, United Kingdom
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom
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24
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Patiño-Ruiz M, Dwivedi M, Călinescu O, Karabel M, Padan E, Fendler K. Replacement of Lys-300 with a glutamine in the NhaA Na +/H + antiporter of Escherichia coli yields a functional electrogenic transporter. J Biol Chem 2019; 294:246-256. [PMID: 30409911 PMCID: PMC6322889 DOI: 10.1074/jbc.ra118.004903] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 11/06/2018] [Indexed: 01/28/2023] Open
Abstract
Much of the research on Na+/H+ exchange has been done in prokaryotic models, mainly on the NhaA Na+/H+-exchanger from Escherichia coli (EcNhaA). Two conserved aspartate residues, Asp-163 and Asp-164, are essential for transport and are candidates for possible binding sites for the two H+ that are exchanged for one Na+ to make the overall transport process electrogenic. More recently, a proposed mechanism of transport for EcNhaA has suggested direct binding of one of the transported H+ to the conserved Lys-300 residue, a salt bridge partner of Asp-163. This contention is supported by a study reporting that substitution of the equivalent residue, Lys-305, of a related Na+/H+ antiporter, NapA from Thermus thermophilus, renders the transporter electroneutral. In this work, we sought to establish whether the Lys-300 residue and its partner Asp-163 are essential for the electrogenicity of EcNhaA. To that end, we replaced Lys-300 with Gln, either alone or together with the simultaneous substitution of Asp-163 with Asn, and characterized these transporter variants in electrophysiological experiments combined with H+ transport measurements and stability analysis. We found that K300Q EcNhaA can still support electrogenic Na+/H+ antiport in EcNhaA, but has reduced thermal stability. A parallel electrophysiological investigation of the K305Q variant of TtNapA revealed that it is also electrogenic. Furthermore, replacement of both salt bridge partners in the ion-binding site of EcNhaA produced an electrogenic variant (D163N/K300Q). Our findings indicate that alternative mechanisms sustain EcNhaA activity in the absence of canonical ion-binding residues and that the conserved lysines confer structural stability.
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Affiliation(s)
- Miyer Patiño-Ruiz
- Max-Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Manish Dwivedi
- Institute of Life Sciences, Hebrew University of Jerusalem, 91904 Jerusalem, Israel
| | - Octavian Călinescu
- Max-Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany; Department of Biophysics, "Carol Davila" University of Medicine and Pharmacy, 050474 Bucharest, Romania
| | - Mehmet Karabel
- Max-Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Etana Padan
- Institute of Life Sciences, Hebrew University of Jerusalem, 91904 Jerusalem, Israel
| | - Klaus Fendler
- Max-Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany.
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25
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Sacconi A, Tadini-Buoninsegni F, Tiribilli B, Margheri G. A Comparative Study of Phosphatidylcholine versus Phosphatidylserine-Based Solid Supported Membranes for the Preparation of Liposome-Rich Interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:12183-12190. [PMID: 30217106 DOI: 10.1021/acs.langmuir.8b02397] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Solid supported membranes (SSMs) are usually formed by an hybrid octadecanethiol/phosphatidylcholine (PC) bilayer supported by a gold electrode. Recently, it was shown that phosphatidylserine (PS) in place of PC can promote a more effective accumulation of lipid vesicles on the SSM surface when Ca2+ and Mg2+ ions are present in the external environment. Here we performed a detailed comparative study of the vesicle adsorption process onto PC- and PS-SSMs by employing surface plasmon resonance (SPR), electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM). SPR analysis has demonstrated a higher affinity of the PS-SSM surface for the phospholipid vesicles. Both SPR and EIS measurements suggest that adsorption of lipid vesicles on the PC-SSM tends to a saturating value, whereas a continuous and progressive vesicle adsorption occurs on the PS-SSM surface following subsequent liposome additions. AFM analysis pointed out a systematic flattening of the adsorbed vesicles on the PS-SSM surface. We interpreted our results as due to the strong coordinating action of the high amount of divalent cations accumulated at the negatively charged PS-SSM surface, whereas a lower amount of cations is present on the dipolar PC-SSM surface, which can therefore adsorb only a limited number of vesicles.
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Affiliation(s)
- Alessio Sacconi
- Department of Chemistry "Ugo Schiff" , University of Florence , Via della Lastruccia 3-13 , 50019 Sesto Fiorentino , Italy
| | - Francesco Tadini-Buoninsegni
- Department of Chemistry "Ugo Schiff" , University of Florence , Via della Lastruccia 3-13 , 50019 Sesto Fiorentino , Italy
| | - Bruno Tiribilli
- Institute for Complex Systems , National Research Council , Via Madonna del Piano 10 , 50019 Sesto Fiorentino , Italy
| | - Giancarlo Margheri
- Institute for Complex Systems , National Research Council , Via Madonna del Piano 10 , 50019 Sesto Fiorentino , Italy
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26
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Niessen K, Seeger T, Rappenglück S, Wein T, Höfner G, Wanner K, Thiermann H, Worek F. In vitro pharmacological characterization of the bispyridinium non-oxime compound MB327 and its 2- and 3-regioisomers. Toxicol Lett 2018; 293:190-197. [DOI: 10.1016/j.toxlet.2017.10.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 09/29/2017] [Accepted: 10/08/2017] [Indexed: 11/27/2022]
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Shabeeb D, Najafi M, Hasanzadeh G, Hadian MR, Musa AE, Shirazi A. Electrophysiological measurements of diabetic peripheral neuropathy: A systematic review. Diabetes Metab Syndr 2018; 12:591-600. [PMID: 29610062 DOI: 10.1016/j.dsx.2018.03.026] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Accepted: 03/26/2018] [Indexed: 12/27/2022]
Abstract
INTRODUCTION Peripheral neuropathy is one of the main complications of diabetes mellitus. One of the features of diabetic nerve damage is abnormality of sensory and motor nerve conduction study. An electrophysiological examination can be reproduced and is also a non-invasive approach in the assessment of peripheral nerve function. Population-based and clinical studies have been conducted to validate the sensitivity of these methods. When the diagnosis was based on clinical electrophysiological examination, abnormalities were observed in all patients. METHOD In this research, using a review design, we reviewed the issue of clinical electrophysiological examination of diabetic peripheral neuropathy in articles from 2008 to 2017. For this purpose, PubMed, Scopus and Embase databases of journals were used for searching articles. RESULTS/FINDINGS The researchers indicated that diabetes (both types) is a very disturbing health issue in the modern world and should be given serious attention. Based on conducted studies, it was demonstrated that there are different procedures for prevention and treatment of diabetes-related health problems such as diabetic polyneuropathy (DPN). The first objective quantitative indication of the peripheral neuropathy is abnormality of sensory and motor nerve conduction tests. Electrophysiology is accurate, reliable and sensitive. It can be reproduced and also is a noninvasive approach in the assessment of peripheral nerve function. CONCLUSION The methodological review has found that the best method for quantitative indication of the peripheral neuropathy compared with all other methods is clinical electrophysiological examination. For best results, standard protocols such as temperature control and equipment calibration are recommended.
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Affiliation(s)
- Dheyauldeen Shabeeb
- Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Science, International Campus, Tehran, Iran; Department of Physiology, College of Medicine, University of Misan, Iraq; Electrophysiology Research Center, Neuroscience Institute, Tehran University of Medical Science, Tehran, Iran
| | - Masoud Najafi
- Radiology and Nuclear Medicine Department, School of Paramedical Sciences, Kermanshah University of Medical Science, Kermanshah, Iran
| | - Gholamreza Hasanzadeh
- Department of Anatomy, School of Medicine, Tehran University of Medical Science, Tehran, Iran
| | - Mohammed Reza Hadian
- Brain and Spinal Injury Repair Research Center, Tehran University of Medical Science, Tehran, Iran
| | - Ahmed Eleojio Musa
- Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Science, International Campus, Tehran, Iran; Research Center for Molecular and Cellular Imaging, Tehran University of Medical Science, Tehran, Iran
| | - Alireza Shirazi
- Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Science, International Campus, Tehran, Iran; Electrophysiology Research Center, Neuroscience Institute, Tehran University of Medical Science, Tehran, Iran.
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Diederichs T, Nguyen QH, Urban M, Tampé R, Tornow M. Transparent Nanopore Cavity Arrays Enable Highly Parallelized Optical Studies of Single Membrane Proteins on Chip. NANO LETTERS 2018; 18:3901-3910. [PMID: 29741381 DOI: 10.1021/acs.nanolett.8b01252] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Membrane proteins involved in transport processes are key targets for pharmaceutical research and industry. Despite continuous improvements and new developments in the field of electrical readouts for the analysis of transport kinetics, a well-suited methodology for high-throughput characterization of single transporters with nonionic substrates and slow turnover rates is still lacking. Here, we report on a novel architecture of silicon chips with embedded nanopore microcavities, based on a silicon-on-insulator technology for high-throughput optical readouts. Arrays containing more than 14 000 inverted-pyramidal cavities of 50 femtoliter volumes and 80 nm circular pore openings were constructed via high-resolution electron-beam lithography in combination with reactive ion etching and anisotropic wet etching. These cavities feature both, an optically transparent bottom and top cap. Atomic force microscopy analysis reveals an overall extremely smooth chip surface, particularly in the vicinity of the nanopores, which exhibits well-defined edges. Our unprecedented transparent chip design provides parallel and independent fluorescent readout of both cavities and buffer reservoir for unbiased single-transporter recordings. Spreading of large unilamellar vesicles with efficiencies up to 96% created nanopore-supported lipid bilayers, which are stable for more than 1 day. A high lipid mobility in the supported membrane was determined by fluorescent recovery after photobleaching. Flux kinetics of α-hemolysin were characterized at single-pore resolution with a rate constant of 0.96 ± 0.06 × 10-3 s-1. Here, we deliver an ideal chip platform for pharmaceutical research, which features high parallelism and throughput, synergistically combined with single-transporter resolution.
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Affiliation(s)
- Tim Diederichs
- Institute of Biochemistry, Biocenter , Goethe University Frankfurt , Max-von-Laue-Str. 9 , 60438 Frankfurt/M. , Germany
| | - Quoc Hung Nguyen
- Molecular Electronics , Technical University of Munich , Theresienstrasse 90 , 80333 Munich , Germany
| | - Michael Urban
- Institute of Biochemistry, Biocenter , Goethe University Frankfurt , Max-von-Laue-Str. 9 , 60438 Frankfurt/M. , Germany
| | - Robert Tampé
- Institute of Biochemistry, Biocenter , Goethe University Frankfurt , Max-von-Laue-Str. 9 , 60438 Frankfurt/M. , Germany
- Cluster of Excellence Frankfurt (CEF) Macromolecular Complexes ; Goethe University Frankfurt , Max-von-Laue-Strasse 9 , 60438 Frankfurt/M. , Germany
| | - Marc Tornow
- Molecular Electronics , Technical University of Munich , Theresienstrasse 90 , 80333 Munich , Germany
- Fraunhofer Research Institution for Microsystems and Solid State Technologies (EMFT) , Hansastrasse 27d , 80686 Munich , Germany
- Center for NanoScience (CeNS) , Ludwig-Maximilians-University , Geschwister-Scholl Platz 1 , 80539 Munich , Germany
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Tadini-Buoninsegni F, Sordi G, Smeazzetto S, Natile G, Arnesano F. Effect of cisplatin on the transport activity of P II-type ATPases. Metallomics 2018. [PMID: 28636017 DOI: 10.1039/c7mt00100b] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Cisplatin (cis-diamminedichlorido-Pt(ii)) is extensively used as a chemotherapeutic agent against various types of tumors. However, cisplatin administration causes serious side effects, including nephrotoxicity, ototoxicity and neurotoxicity. It has been shown that cisplatin can interact with P-type ATPases, e.g., Cu+-ATPases (ATP7A and ATP7B) and Na+,K+-ATPase. Cisplatin-induced inhibition of Na+,K+-ATPase has been related to the nephrotoxic effect of the drug. To investigate the inhibitory effects of cisplatin on the pumping activity of PII-type ATPases, electrical measurements were performed on sarcoplasmic reticulum Ca2+-ATPase (SERCA) and Na+,K+-ATPase embedded in vesicles/membrane fragments adsorbed on a solid-supported membrane. We found that cisplatin inhibits SERCA and Na+,K+-ATPase only when administered without a physiological reducing agent (GSH); in contrast, inhibition was also observed in the case of Cu+-ATPases in the presence of 1 mM GSH. Our results indicate that cisplatin is a much stronger inhibitor of SERCA (with an IC50 value of 1.3 μM) than of Na+,K+-ATPase (with an IC50 value of 11.1 μM); moreover, cisplatin inhibition of Na+,K+-ATPase is reversible, whereas it is irreversible in the case of SERCA. In the absence of a physiological substrate, while Cu+-ATPases are able to translocate cisplatin, SERCA and Na+,K+-ATPase do not perform ATP-dependent cisplatin displacement.
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30
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Tadini-Buoninsegni F, Smeazzetto S, Gualdani R, Moncelli MR. Drug Interactions With the Ca 2+-ATPase From Sarco(Endo)Plasmic Reticulum (SERCA). Front Mol Biosci 2018; 5:36. [PMID: 29696147 PMCID: PMC5904271 DOI: 10.3389/fmolb.2018.00036] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Accepted: 03/26/2018] [Indexed: 11/13/2022] Open
Abstract
The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is an intracellular membrane transporter that utilizes the free energy provided by ATP hydrolysis for active transport of Ca2+ ions from the cytoplasm to the lumen of sarco(endo)plasmic reticulum. SERCA plays a fundamental role for cell calcium homeostasis and signaling in muscle cells and also in cells of other tissues. Because of its prominent role in many physiological processes, SERCA dysfunction is associated to diseases displaying various degrees of severity. SERCA transport activity can be inhibited by a variety of compounds with different chemical structures. Specific SERCA inhibitors were identified which have been instrumental in studies of the SERCA catalytic and transport mechanism. It has been proposed that SERCA inhibition may represent a novel therapeutic strategy to cure certain diseases by targeting SERCA activity in pathogens, parasites and cancer cells. Recently, novel small molecules have been developed that are able to stimulate SERCA activity. Such SERCA activators may also offer an innovative and promising therapeutic approach to treat diseases, such as heart failure, diabetes and metabolic disorders. In the present review the effects of pharmacologically relevant compounds on SERCA transport activity are presented. In particular, we will discuss the interaction of SERCA with specific inhibitors and activators that are potential therapeutic agents for different diseases.
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Affiliation(s)
| | - Serena Smeazzetto
- Department of Chemistry "Ugo Schiff," University of Florence, Florence, Italy
| | - Roberta Gualdani
- Laboratory of Cell Physiology, Institute of Neuroscience, Université Catholique de Louvain, Louvain-la-Neuve, Belgium
| | - Maria Rosa Moncelli
- Department of Chemistry "Ugo Schiff," University of Florence, Florence, Italy
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31
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Pflüger T, Hernández CF, Lewe P, Frank F, Mertens H, Svergun D, Baumstark MW, Lunin VY, Jetten MSM, Andrade SLA. Signaling ammonium across membranes through an ammonium sensor histidine kinase. Nat Commun 2018; 9:164. [PMID: 29323112 PMCID: PMC5764959 DOI: 10.1038/s41467-017-02637-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 12/15/2017] [Indexed: 01/07/2023] Open
Abstract
Sensing and uptake of external ammonium is essential for anaerobic ammonium-oxidizing (anammox) bacteria, and is typically the domain of the ubiquitous Amt/Rh ammonium transporters. Here, we report on the structure and function of an ammonium sensor/transducer from the anammox bacterium "Candidatus Kuenenia stuttgartiensis" that combines a membrane-integral ammonium transporter domain with a fused histidine kinase. It contains a high-affinity ammonium binding site not present in assimilatory Amt proteins. The levels of phosphorylated histidine in the kinase are coupled to the presence of ammonium, as conformational changes during signal recognition by the Amt module are transduced internally to modulate the kinase activity. The structural analysis of this ammonium sensor by X-ray crystallography and small-angle X-ray-scattering reveals a flexible, bipartite system that recruits a large uptake transporter as a sensory module and modulates its functionality to achieve a mechanistic coupling to a kinase domain in order to trigger downstream signaling events.
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Affiliation(s)
- Tobias Pflüger
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany
| | - Camila F Hernández
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany
| | - Philipp Lewe
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany
| | - Fabian Frank
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany
| | - Haydyn Mertens
- European Molecular Biology Laboratory, Hamburg Unit, EMBL c/o DESY, Notkestr. 85, Hamburg, D-22603, Germany
| | - Dmitri Svergun
- European Molecular Biology Laboratory, Hamburg Unit, EMBL c/o DESY, Notkestr. 85, Hamburg, D-22603, Germany
| | - Manfred W Baumstark
- Center for Medicine, Institute for Exercise and Occupational Medicine, Medical Center, University of Freiburg, Hugstetterstr. 55, Freiburg, 79106, Germany.,Faculty of Medicine, University of Freiburg, Freiburg, 79106, Germany
| | - Vladimir Y Lunin
- Institute of Mathematical Problems of Biology RAS, Keldysh Institute of Applied Mathematics of Russian Academy of Sciences, Vitkevicha str. 1, Pushchino, 142290, Russia
| | - Mike S M Jetten
- Department of Microbiology, Radboud University, Institute for Water and Wetland Research, Heyendaalseweg 135, Nijmegen, NL-6525 AJ, The Netherlands
| | - Susana L A Andrade
- Institute for Biochemistry, University of Freiburg, Albertstr. 21, Freiburg, 79104, Germany. .,BIOSS Centre for Biological Signalling Studies, University of Freiburg, Schänzlestr. 1, Freiburg, 79104, Germany.
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32
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Bazzone A, Zabadne AJ, Salisowski A, Madej MG, Fendler K. A Loose Relationship: Incomplete H +/Sugar Coupling in the MFS Sugar Transporter GlcP. Biophys J 2018; 113:2736-2749. [PMID: 29262366 PMCID: PMC5770559 DOI: 10.1016/j.bpj.2017.09.038] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2017] [Revised: 09/11/2017] [Accepted: 09/29/2017] [Indexed: 11/26/2022] Open
Abstract
The glucose transporter from Staphylococcus epidermidis, GlcPSe, is a homolog of the human GLUT sugar transporters of the major facilitator superfamily. Together with the xylose transporter from Escherichia coli, XylEEc, the other prominent prokaryotic GLUT homolog, GlcPSe, is equipped with a conserved proton-binding site arguing for an electrogenic transport mode. However, the electrophysiological analysis of GlcPSe presented here reveals important differences between the two GLUT homologs. GlcPSe, unlike XylEEc, does not perform steady-state electrogenic transport at symmetrical pH conditions. Furthermore, when a pH gradient is applied, partially uncoupled transport modes can be generated. In contrast to other bacterial sugar transporters analyzed so far, in GlcPSe sugar binding, translocation and release are also accomplished by the deprotonated transporter. Based on these experimental results, we conclude that coupling of sugar and H+ transport is incomplete in GlcPSe. To verify the viability of the observed partially coupled GlcPSe transport modes, we propose a universal eight-state kinetic model in which any degree of coupling is realized and H+/sugar symport represents only a specific instance. Furthermore, using sequence comparison with strictly coupled XylEEc and similar sugar transporters, we identify an additional charged residue that may be essential for effective H+/sugar symport.
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Affiliation(s)
- Andre Bazzone
- Max Planck Institute of Biophysics, Frankfurt/Main, Germany
| | | | | | - M Gregor Madej
- Max Planck Institute of Biophysics, Frankfurt/Main, Germany
| | - Klaus Fendler
- Max Planck Institute of Biophysics, Frankfurt/Main, Germany.
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33
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Schlesinger R. Do It Fast: Immediate Functional Testing of Membrane Pumps Expressed into Nanodiscs. Biophys J 2017; 113:1177-1178. [PMID: 28867509 DOI: 10.1016/j.bpj.2017.08.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 08/14/2017] [Indexed: 12/13/2022] Open
Affiliation(s)
- Ramona Schlesinger
- Department of Physics, Genetic Biophysics, Freie Universität Berlin, Berlin, Germany.
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34
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Abstract
Functional characterization of transport proteins using conventional electrophysiology can be challenging, especially for low turnover transporters or transporters from bacteria and intracellular compartments. Solid-supported membrane (SSM)-based electrophysiology is a sensitive and cell-free assay technique for the characterization of electrogenic membrane proteins. Purified proteins reconstituted into proteoliposomes or membrane vesicles from cell culture or native tissues are adsorbed to the sensor holding an SSM. A substrate or a ligand is applied via rapid solution exchange. The electrogenic transporter activity charges the sensor, which is recorded as a transient current. The high stability of the SSM allows cumulative measurements on the same sensor using different experimental conditions. This allows the determination of kinetic properties including EC50, IC50, Km, KD, and rate constants of electrogenic reactions. About 100 different transporters have been measured so far using this technique, among them symporters, exchangers, uniporters, ATP-, redox-, and light-driven ion pumps, as well as receptors and ion channels. Different instruments apply this technique: the laboratory setups use a closed flow-through arrangement, while the commercially available SURFE2R N1 resembles a pipetting robot. For drug screening purposes high-throughput systems, such as the SURFE2R 96SE enable the simultaneous measurement of up to 96 sensors.
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Affiliation(s)
- Andre Bazzone
- Max Planck Institute of Biophysics, Frankfurt/Main, Germany; Nanion Technologies GmbH, Munich, Germany
| | | | - Klaus Fendler
- Max Planck Institute of Biophysics, Frankfurt/Main, Germany.
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35
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Călinescu O, Dwivedi M, Patiño-Ruiz M, Padan E, Fendler K. Lysine 300 is essential for stability but not for electrogenic transport of the Escherichia coli NhaA Na +/H + antiporter. J Biol Chem 2017; 292:7932-7941. [PMID: 28330875 PMCID: PMC5427271 DOI: 10.1074/jbc.m117.778175] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 03/09/2017] [Indexed: 11/06/2022] Open
Abstract
Na+/H+ antiporters are located in the cytoplasmic and intracellular membranes and play crucial roles in regulating intracellular pH, Na+, and volume. The NhaA antiporter of Escherichia coli is the best studied member of the Na+/H+ exchanger family and a model system for all related Na+/H+ exchangers, including eukaryotic representatives. Several amino acid residues are important for the transport activity of NhaA, including Lys-300, a residue that has recently been proposed to carry one of the two H+ ions that NhaA exchanges for one Na+ ion during one transport cycle. Here, we sought to characterize the effects of mutating Lys-300 of NhaA to amino acid residues containing side chains of different polarity and length (i.e. Ala, Arg, Cys, His, Glu, and Leu) on transporter stability and function. Salt resistance assays, acridine-orange fluorescence dequenching, solid supported membrane-based electrophysiology, and differential scanning fluorometry were used to characterize Na+ and H+ transport, charge translocation, and thermal stability of the different variants. These studies revealed that NhaA could still perform electrogenic Na+/H+ exchange even in the absence of a protonatable residue at the Lys-300 position. However, all mutants displayed lower thermal stability and reduced ion transport activity compared with the wild-type enzyme, indicating the critical importance of Lys-300 for optimal NhaA structural stability and function. On the basis of these experimental data, we propose a tentative mechanism integrating the functional and structural role of Lys-300.
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Affiliation(s)
- Octavian Călinescu
- From the Max-Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
- the "Carol Davila" University of Medicine and Pharmacy, 050474 Bucharest, Romania, and
| | - Manish Dwivedi
- the Institute of Life Sciences, Hebrew University of Jerusalem, 91904 Jerusalem, Israel
| | - Miyer Patiño-Ruiz
- From the Max-Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Etana Padan
- the Institute of Life Sciences, Hebrew University of Jerusalem, 91904 Jerusalem, Israel
| | - Klaus Fendler
- From the Max-Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany,
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36
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Zhou W, Burke PJ. Versatile Bottom-Up Synthesis of Tethered Bilayer Lipid Membranes on Nanoelectronic Biosensor Devices. ACS APPLIED MATERIALS & INTERFACES 2017; 9:14618-14632. [PMID: 28387499 PMCID: PMC6373873 DOI: 10.1021/acsami.7b00268] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Interfacing nanoelectronic devices with cell membranes can enable multiplexed detection of fundamental biological processes (such as signal transduction, electrophysiology, and import/export control) even down to the single ion channel level, which can lead to a variety of applications in pharmacology and clinical diagnosis. Therefore, it is necessary to understand and control the chemical and electrical interface between the device and the lipid bilayer membrane. Here, we develop a simple bottom-up approach to assemble tethered bilayer lipid membranes (tBLMs) on silicon wafers and glass slides, using a covalent tether attachment chemistry based on silane functionalization, followed by step-by-step stacking of two other functional molecular building blocks (oligo-poly(ethylene glycol) (PEG) and lipid). A standard vesicle fusion process was used to complete the bilayer formation. The monolayer synthetic scheme includes three well-established chemical reactions: self-assembly, epoxy-amine reaction, and EDC/NHS cross-linking reaction. All three reactions are facile and simple and can be easily implemented in many research labs, on the basis of common, commercially available precursors using mild reaction conditions. The oligo-PEG acts as the hydrophilic spacer, a key role in the formation of a homogeneous bilayer membrane. To explore the broad applicability of this approach, we have further demonstrated the formation of tBLMs on three common classes of (nano)electronic biosensor devices: indium-tin oxide-coated glass, silicon nanoribbon devices, and high-density single-walled carbon nanotubes (SWNT) networks on glass. More importantly, we incorporated alemethicin into tBLMs and realized the real-time recording of single ion channel activity with high sensitivity and high temporal resolution using the tBLMs/SWNT network transistor hybrid platform. This approach can provide a covalently bonded lipid coating on the oxide layer of nanoelectronic devices, which will enable a variety of applications in the emerging field of nanoelectronic interfaces to electrophysiology.
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Affiliation(s)
- Weiwei Zhou
- Integrated Nanosystems Research Facility, Department of Electrical Engineering and Computer Science, University of California at Irvine, Irvine, California 92697, United States
| | - Peter J. Burke
- Integrated Nanosystems Research Facility, Department of Electrical Engineering and Computer Science, University of California at Irvine, Irvine, California 92697, United States
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From Gene to Function: Cell-Free Electrophysiological and Optical Analysis of Ion Pumps in Nanodiscs. Biophys J 2017; 113:1331-1341. [PMID: 28450130 DOI: 10.1016/j.bpj.2017.03.026] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 03/14/2017] [Accepted: 03/27/2017] [Indexed: 12/15/2022] Open
Abstract
Nanodiscs that hold a lipid bilayer surrounded by a boundary of scaffold proteins have emerged as a powerful tool for membrane protein solubilization and analysis. By combining nanodiscs and cell-free expression technologies, even completely detergent-free membrane protein characterization protocols can be designed. Nanodiscs are compatible with various techniques, and due to their bilayer environment and increased stability, they are often superior to detergent micelles or liposomes for membrane protein solubilization. However, transport assays in nanodiscs have not been conducted so far, due to limitations of the two-dimensional nature of nanodisc membranes that offers no compartmentalization. Here, we study Krokinobacter eikastus rhodopsin-2 (KR2), a microbial light-driven sodium or proton pump, with noncovalent mass-spectrometric, electrophysiological, and flash photolysis measurements after its cotranslational insertion into nanodiscs. We demonstrate the feasibility of adsorbing nanodiscs containing KR2 to an artificial bilayer. This allows us to record light-induced capacitive currents that reflect KR2's ion transport activity. The solid-supported membrane assay with nanodisc samples provides reliable control over the ionic condition and information of the relative ion activity of this promiscuous pump. Our strategy is complemented with flash photolysis data, where the lifetimes of different photointermediates were determined at different ionic conditions. The advantage of using identical samples to three complementary approaches allows for a comprehensive comparability. The cell-free synthesis in combination with nanodiscs provides a defined hydrophobic lipid environment minimizing the detergent dependence often seen in assays with membrane proteins. KR2 is a promising tool for optogenetics, thus directed engineering to modify ion selectivity can be highly beneficial. Our approach, using the fast generation of functional ion pumps incorporated into nanodiscs and their subsequent analysis by several biophysical techniques, can serve as a versatile screening and engineering platform. This may open new avenues for the study of ion pumps and similar electrogenic targets.
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Apostolou T, Moschopoulou G, Kolotourou E, Kintzios S. Assessment of in vitro dopamine-neuroblastoma cell interactions with a bioelectric biosensor: perspective for a novel in vitro functional assay for dopamine agonist/antagonist activity. Talanta 2017; 170:69-73. [PMID: 28501215 DOI: 10.1016/j.talanta.2017.03.098] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2017] [Revised: 03/27/2017] [Accepted: 03/30/2017] [Indexed: 10/19/2022]
Abstract
Current receptor-binding assays for dopamine do not measure the in vitro whole cellular response against dopamine or potential agonist/antagonist molecules. We herewith report the development of a novel functional assay concept for studying the in vitro interaction of the neurotransmitter dopamine with neural cells bearing dopamine receptors. The concept is based on the ultra-rapid measurement of changes in the electric properties of cultured N2a mouse neuroblastoma cells (corresponding to cumulative changes of the cell membrane potential). A close relationship between cumulative cell membrane potential and dopamine concentration was observed. Membrane depolarization was observed at nanomolar dopamine concentrations, while hyperpolarization was associated with micromolar ones. Treatment with the dopamine D2-receptor antagonist eticlopride resulted to a concentration-dependent membrane depolarization. Treatment with sodium chloride caused considerable weakening of the dopamine-associated hyperpolarization effect. The observed bioelectric response to dopamine was highly inversely correlated with the pattern of dopamine release-uptake balance by N2a cells, as determined with cyclic voltammetry. The bioelectric approach was also used to evaluate the dopaminergic activity of chaste tree (Vitex agnus-castus) extracts. The novel assay concept offers promising perspectives for the development of advanced companion diagnostics system for the high throughput, fast functional characterization of neurotransmitter agonists and antagonists.
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Affiliation(s)
- Theofylaktos Apostolou
- Laboratory of Cell Technology, Faculty of Biotechnology, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece
| | - Georgia Moschopoulou
- Laboratory of Cell Technology, Faculty of Biotechnology, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece.
| | - Evdokia Kolotourou
- Laboratory of Cell Technology, Faculty of Biotechnology, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece
| | - Spyridon Kintzios
- Laboratory of Cell Technology, Faculty of Biotechnology, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece
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Choudhary P, Armstrong EJ, Jorgensen CC, Piotrowski M, Barthmes M, Torella R, Johnston SE, Maruyama Y, Janiszewski JS, Storer RI, Skerratt SE, Benn CL. Discovery of Compounds that Positively Modulate the High Affinity Choline Transporter. Front Mol Neurosci 2017; 10:40. [PMID: 28289374 PMCID: PMC5326799 DOI: 10.3389/fnmol.2017.00040] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 02/03/2017] [Indexed: 01/09/2023] Open
Abstract
Cholinergic hypofunction is associated with decreased attention and cognitive deficits in the central nervous system in addition to compromised motor function. Consequently, stimulation of cholinergic neurotransmission is a rational therapeutic approach for the potential treatment of a variety of neurological conditions. High affinity choline uptake (HACU) into acetylcholine (ACh)-synthesizing neurons is critically mediated by the sodium- and pH-dependent high-affinity choline transporter (CHT, encoded by the SLC5A7 gene). This transporter is comparatively well-characterized but otherwise unexplored as a potential drug target. We therefore sought to identify small molecules that would enable testing of the hypothesis that positive modulation of CHT mediated transport would enhance activity-dependent cholinergic signaling. We utilized existing and novel screening techniques for their ability to reveal both positive and negative modulation of CHT using literature tools. A screening campaign was initiated with a bespoke compound library comprising both the Pfizer Chemogenomic Library (CGL) of 2,753 molecules designed specifically to help enable the elucidation of new mechanisms in phenotypic screens and 887 compounds from a virtual screening campaign to select molecules with field-based similarities to reported negative and positive allosteric modulators. We identified a number of previously unknown active and structurally distinct molecules that could be used as tools to further explore CHT biology or as a starting point for further medicinal chemistry.
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Affiliation(s)
| | | | | | | | | | | | | | - Yuya Maruyama
- Central Research Laboratory, Kissei Pharmaceutical Co., Ltd. Nagano, Japan
| | | | - R Ian Storer
- Pfizer, Worldwide Medicinal Chemistry Cambridge, UK
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40
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Tadini-Buoninsegni F, Smeazzetto S. Mechanisms of charge transfer in human copper ATPases ATP7A and ATP7B. IUBMB Life 2017; 69:218-225. [PMID: 28164426 DOI: 10.1002/iub.1603] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Accepted: 12/26/2016] [Indexed: 12/30/2022]
Abstract
ATP7A and ATP7B are Cu+ -transporting ATPases of subclass IB and play a fundamental role in intracellular copper homeostasis. ATP7A/B transfer Cu+ ions across the membrane from delivery to acceptor proteins without establishing a free Cu+ gradient. Transfer of copper across the membrane is coupled to ATP hydrolysis. Current measurements on solid supported membranes (SSM) were performed to investigate the mechanism of copper-related charge transfer across ATP7A and ATP7B. SSM measurements demonstrated that electrogenic copper displacement occurs within ATP7A/B following addition of ATP and formation of the phosphorylated intermediate. Comparison of the time constants for cation displacement in ATP7A/B and sarcoplasmic reticulum Ca2+ -ATPase is consistent with the slower phosphoenzyme formation in copper ATPases. Moreover, ATP-dependent copper transfer in ATP7A/B is not affected by varying the pH, suggesting that net proton counter-transport may not occur in copper ATPases. Platinum anticancer drugs activate ATP7A/B and are subjected to ATP-dependent vectorial displacement with a mechanism analogous to that of copper. © 2016 IUBMB Life, 69(4):218-225, 2017.
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Affiliation(s)
| | - Serena Smeazzetto
- Department of Chemistry "Ugo Schiff,", University of Florence, Sesto Fiorentino, Italy
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41
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Călinescu O, Linder M, Wöhlert D, Yildiz Ö, Kühlbrandt W, Fendler K. Electrogenic Cation Binding in the Electroneutral Na+/H+ Antiporter of Pyrococcus abyssi. J Biol Chem 2016; 291:26786-26793. [PMID: 27821589 PMCID: PMC5207186 DOI: 10.1074/jbc.m116.761080] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Revised: 11/02/2016] [Indexed: 01/04/2023] Open
Abstract
Na+/H+ antiporters in the CPA1 branch of the cation proton antiporter family drive the electroneutral exchange of H+ against Na+ ions and ensure pH homeostasis in eukaryotic and prokaryotic organisms. Although their transport cycle is overall electroneutral, specific partial reactions are electrogenic. Here, we present an electrophysiological study of the PaNhaP Na+/H+ antiporter from Pyrococcus abyssi reconstituted into liposomes. Positive transient currents were recorded upon addition of Na+ to PaNhaP proteoliposomes, indicating a reaction where positive charge is rapidly displaced into the proteoliposomes with a rate constant of k >200 s-1 We attribute the recorded currents to an electrogenic reaction that includes Na+ binding and possibly occlusion. Subsequently, positive charge is transported out of the cell associated with H+ binding, so that the overall reaction is electroneutral. We show that the differences in pH profile and Na+ affinity of PaNhaP and the related MjNhaP1 from Methanocaldococcus jannaschii can be attributed to an additional negatively charged glutamate residue in PaNhaP. The results are discussed in the context of the physiological function of PaNhaP and other microbial Na+/H+ exchangers. We propose that both, electroneutral and electrogenic Na+/H+ antiporters, represent a carefully tuned self-regulatory system, which drives the cytoplasmic pH back to neutral after any deviation.
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Affiliation(s)
- Octavian Călinescu
- From the Departments of Biological Chemistry and.,the Department of Biophysics, "Carol Davila" University of Medicine and Pharmacy, 050474 Bucharest, Romania
| | - Mark Linder
- From the Departments of Biological Chemistry and.,Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany and
| | - David Wöhlert
- Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany and
| | - Özkan Yildiz
- Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany and
| | - Werner Kühlbrandt
- Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany and
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Siebels I, Dröse S. Charge translocation by mitochondrial NADH:ubiquinone oxidoreductase (complex I) from Yarrowia lipolytica measured on solid-supported membranes. Biochem Biophys Res Commun 2016; 479:277-282. [PMID: 27639643 DOI: 10.1016/j.bbrc.2016.09.059] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 09/12/2016] [Indexed: 11/17/2022]
Abstract
The charge translocation by purified reconstituted mitochondrial complex I from the obligate aerobic yeast Yarrowia lipolytica was investigated after adsorption of proteoliposomes to solid-supported membranes. In presence of n-decylubiquinone (DBQ), pulses of NADH provided by rapid solution exchange induced charge transfer reflecting steady-state pumping activity of the reconstituted enzyme. The signal amplitude increased with time, indicating 'deactive→active' transition of the Yarrowia complex I. Furthermore, an increase of the membrane-conductivity after addition of 5-(N-ethyl-N-isopropyl)amiloride (EIPA) was detected which questiones the use of EIPA as an inhibitor of the Na+/H+-antiporter-like subunits of complex I. This investigation shows that electrical measurements on solid-supported membranes are a suitable method to analyze transport events and 'active/deactive' transition of mitochondrial complex I.
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Affiliation(s)
- Ilka Siebels
- Molecular Bioenergetics Group, Medical School, Johann Wolfgang Goethe-University, 60590, Frankfurt am Main, Germany; Goethe University Frankfurt, Institute of Organic Chemistry and Chemical Biology, Buchmann Institute for Molecular Life Sciences, Protein Reaction Control Group, Max-von-Laue-Str. 15, 60438, Frankfurt am Main, Germany
| | - Stefan Dröse
- Molecular Bioenergetics Group, Medical School, Johann Wolfgang Goethe-University, 60590, Frankfurt am Main, Germany; Department of Anesthesiology, Intensive-Care Medicine and Pain Therapy, University Hospital Frankfurt, 60590, Frankfurt am Main, Germany.
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43
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Bazzone A, Madej MG, Kaback HR, Fendler K. pH Regulation of Electrogenic Sugar/H+ Symport in MFS Sugar Permeases. PLoS One 2016; 11:e0156392. [PMID: 27227677 PMCID: PMC4882079 DOI: 10.1371/journal.pone.0156392] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Accepted: 05/15/2016] [Indexed: 01/27/2023] Open
Abstract
Bacterial sugar symporters in the Major Facilitator Superfamily (MFS) use the H+ (and in a few cases Na+) electrochemical gradients to achieve active transport of sugar into the cell. Because a number of structures of MFS sugar symporters have been solved recently, molecular insight into the transport mechanism is possible from detailed functional analysis. We present here a comparative electrophysiological study of the lactose permease (LacY), the fucose permease (FucP) and the xylose permease (XylE), which reveals common mechanistic principles and differences. In all three symporters energetically downhill electrogenic sugar/H+ symport is observed. Comparison of the pH dependence of symport at symmetrical pH exhibits broad bell-shaped pH profiles extending over 3 to 6 pH units and a decrease at extremely alkaline pH ≥ 9.4 and at acidic to neutral pH = 4.6-7.5. The pH dependence can be described by an acidic to neutral apparent pK (pKapp) and an alkaline pKapp. Experimental evidence suggests that the alkaline pKapp is due to H+ depletion at the protonation site, while the acidic pKapp is due to inhibition of deprotonation. Since previous studies suggest that a single carboxyl group in LacY (Glu325) may be the only side chain directly involved in H+ translocation and a carboxyl side chain with similar properties has been identified in FucP (Asp46) and XylE (Asp27), the present results imply that the pK of this residue is switched during H+/sugar symport in all three symporters.
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Affiliation(s)
- Andre Bazzone
- Department of Biophysical Chemistry, Max-Planck-Institute of Biophysics, Frankfurt/M, Germany
| | - M. Gregor Madej
- Department of Biophysical Chemistry, Max-Planck-Institute of Biophysics, Frankfurt/M, Germany
- Departments of Physiology and Microbiology, Immunology, and Molecular Genetics, Molecular Biology Institute, University of California Los Angeles, Los Angeles, California, United States of America
| | - H. Ronald Kaback
- Departments of Physiology and Microbiology, Immunology, and Molecular Genetics, Molecular Biology Institute, University of California Los Angeles, Los Angeles, California, United States of America
| | - Klaus Fendler
- Department of Biophysical Chemistry, Max-Planck-Institute of Biophysics, Frankfurt/M, Germany
- * E-mail:
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44
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Srinivasan L, Baars TL, Fendler K, Michel H. Functional characterization of solute carrier (SLC) 26/sulfate permease (SulP) proteins in membrane mimetic systems. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:698-705. [DOI: 10.1016/j.bbamem.2016.01.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2015] [Revised: 12/17/2015] [Accepted: 01/12/2016] [Indexed: 11/25/2022]
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45
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Niessen K, Muschik S, Langguth F, Rappenglück S, Seeger T, Thiermann H, Worek F. Functional analysis of Torpedo californica nicotinic acetylcholine receptors in multiple activation states by SSM-based electrophysiology. Toxicol Lett 2016; 247:1-10. [DOI: 10.1016/j.toxlet.2016.02.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Revised: 01/27/2016] [Accepted: 02/02/2016] [Indexed: 01/21/2023]
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46
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Tadini-Buoninsegni F, Bartolommei G. Electrophysiological Measurements on Solid Supported Membranes. Methods Mol Biol 2016; 1377:293-303. [PMID: 26695041 DOI: 10.1007/978-1-4939-3179-8_26] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The solid supported membrane (SSM) represents a convenient model system for a biological membrane with the advantage of being mechanically so stable that solutions can be rapidly exchanged at the surface. The SSM consists of a hybrid alkanethiol-phospholipid bilayer supported by a gold electrode. Proteoliposomes, membrane vesicles, or membrane fragments containing the transport protein of interest are adsorbed on the SSM surface and are subjected to a rapid substrate concentration jump. The substrate concentration jump activates the protein and the charge displacement concomitant with its transport activity is recorded as a current transient. Since this technique is well suited for the functional characterization of electrogenic membrane transporters, it is expected to become a promising platform technology for drug screening and development.
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Affiliation(s)
| | - Gianluca Bartolommei
- Department of Chemistry "Ugo Schiff", University of Florence, 50019, Sesto Fiorentino, Italy
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47
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Sodium-Proton (Na+/H+) Antiporters: Properties and Roles in Health and Disease. Met Ions Life Sci 2016; 16:391-458. [DOI: 10.1007/978-3-319-21756-7_12] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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48
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Tadini-Buoninsegni F, Moncelli MR, Peruzzi N, Ninham BW, Dei L, Nostro PL. Hofmeister effect of anions on calcium translocation by sarcoplasmic reticulum Ca(2+)-ATPase. Sci Rep 2015; 5:14282. [PMID: 26435197 PMCID: PMC4593048 DOI: 10.1038/srep14282] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Accepted: 07/24/2015] [Indexed: 11/18/2022] Open
Abstract
The occurrence of Hofmeister (specific ion) effects in various membrane-related physiological processes is well documented. For example the effect of anions on the transport activity of the ion pump Na+, K+-ATPase has been investigated. Here we report on specific anion effects on the ATP-dependent Ca2+ translocation by the sarcoplasmic reticulum Ca2+-ATPase (SERCA). Current measurements following ATP concentration jumps on SERCA-containing vesicles adsorbed on solid supported membranes were carried out in the presence of different potassium salts. We found that monovalent anions strongly interfere with ATP-induced Ca2+ translocation by SERCA, according to their increasing chaotropicity in the Hofmeister series. On the contrary, a significant increase in Ca2+ translocation was observed in the presence of sulphate. We suggest that the anions can affect the conformational transition between the phosphorylated intermediates E1P and E2P of the SERCA cycle. In particular, the stabilization of the E1P conformation by chaotropic anions seems to be related to their adsorption at the enzyme/water and/or at the membrane/water interface, while the more kosmotropic species affect SERCA conformation and functionality by modifying the hydration layers of the enzyme.
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Affiliation(s)
| | - Maria Rosa Moncelli
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
| | - Niccolò Peruzzi
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.,CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
| | - Barry W Ninham
- Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australia 0200
| | - Luigi Dei
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.,CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
| | - Pierandrea Lo Nostro
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.,CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
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49
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Rycovska-Blume A, Lü W, Andrade S, Fendler K, Einsle O. Structural and Functional Studies of NirC from Salmonella typhimurium. Methods Enzymol 2015; 556:475-97. [PMID: 25857796 DOI: 10.1016/bs.mie.2014.12.034] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/15/2023]
Abstract
NirC is a pentameric transport system for monovalent anions that is expressed in the context of assimilatory nitrite reductase NirBD in a wide variety of enterobacterial species. A NirC pentamer contains individual pores in each protomer that mediate the passage of at least the nitrite [Formula: see text] and nitrate [Formula: see text] anions. As a member of the formate/nitrite transporter family of membrane transport proteins, NirC shares a range of structural and functional features with the formate channel FocA and the hydrosulfide channel AsrD (HSC). NirC from the enteropathogen Salmonella typhimurium has been studied by X-ray crystallography, proton uptake assays, and different electrophysiological techniques, and the picture that has emerged shows a fast and versatile transport system for nitrite that doubles as a defense system during the enteric life of the bacterium. Structural and functional assays are described, which shed light on the transport mechanism of this important molecular machine.
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Affiliation(s)
- Adriana Rycovska-Blume
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
| | - Wei Lü
- Institute for Biochemistry, Albert-Ludwigs-University Freiburg, Freiburg im Breisgau, Germany
| | - Susana Andrade
- Institute for Biochemistry, Albert-Ludwigs-University Freiburg, Freiburg im Breisgau, Germany; BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, Freiburg im Breisgau, Germany
| | - Klaus Fendler
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Oliver Einsle
- Institute for Biochemistry, Albert-Ludwigs-University Freiburg, Freiburg im Breisgau, Germany; BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, Freiburg im Breisgau, Germany
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50
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Perez C, Faust B, Mehdipour AR, Francesconi KA, Forrest LR, Ziegler C. Substrate-bound outward-open state of the betaine transporter BetP provides insights into Na+ coupling. Nat Commun 2014; 5:4231. [PMID: 25023443 DOI: 10.1038/ncomms5231] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Accepted: 05/28/2014] [Indexed: 12/26/2022] Open
Abstract
The Na(+)-coupled betaine symporter BetP shares a highly conserved fold with other sequence unrelated secondary transporters, for example, with neurotransmitter symporters. Recently, we obtained atomic structures of BetP in distinct conformational states, which elucidated parts of its alternating-access mechanism. Here, we report a structure of BetP in a new outward-open state in complex with an anomalous scattering substrate, adding a fundamental piece to an unprecedented set of structural snapshots for a secondary transporter. In combination with molecular dynamics simulations these structural data highlight important features of the sequential formation of the substrate and sodium-binding sites, in which coordinating water molecules play a crucial role. We observe a strictly interdependent binding of betaine and sodium ions during the coupling process. All three sites undergo progressive reshaping and dehydration during the alternating-access cycle, with the most optimal coordination of all substrates found in the closed state.
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Affiliation(s)
- Camilo Perez
- 1] Structural Biology Department, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2] [3]
| | - Belinda Faust
- 1] Structural Biology Department, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2] [3]
| | - Ahmad Reza Mehdipour
- 1] Computational Structural Biology Group, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2]
| | - Kevin A Francesconi
- Institute of Chemistry-Analytical Chemistry, University of Graz, Graz 8010, Austria
| | - Lucy R Forrest
- 1] Computational Structural Biology Group, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2]
| | - Christine Ziegler
- 1] Structural Biology Department, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2] Institute of Biophysics and Biophysical Chemistry, University of Regensburg, Regensburg 95053, Germany
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