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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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Santner P, Martins JMDS, Laursen JS, Behrendt L, Riber L, Olsen CA, Arkin IT, Winther JR, Willemoës M, Lindorff-Larsen K. A Robust Proton Flux (pHlux) Assay for Studying the Function and Inhibition of the Influenza A M2 Proton Channel. Biochemistry 2018; 57:5949-5956. [PMID: 30230312 DOI: 10.1021/acs.biochem.8b00721] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The M2 protein is an important target for drugs in the fight against the influenza virus. Because of the emergence of resistance against antivirals directed toward the M2 proton channel, the search for new drugs against resistant M2 variants is of high importance. Robust and sensitive assays for testing potential drug compounds on different M2 variants are valuable tools in this search for new inhibitors. In this work, we describe a fluorescence sensor-based assay, which we termed "pHlux", that measures proton conduction through M2 when synthesized from an expression vector in Escherichia coli. The assay was compared to a previously established bacterial potassium ion transport complementation assay, and the results were compared to simulations obtained from analysis of a computational model of M2 and its interaction with inhibitor molecules. The inhibition of M2 was measured for five different inhibitors, including Rimantadine, Amantadine, and spiro type compounds, and the drug resistance of the M2 mutant variants (swine flu, V27A, and S31N) was confirmed. We demonstrate that the pHlux assay is robust and highly sensitive and shows potential for high-throughput screening.
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Affiliation(s)
- Paul Santner
- Department of Biology, Section for Biomolecular Sciences, Linderstrøm-Lang Centre for Protein Science , University of Copenhagen , Ole Maaloes Vej 5 , 2200 Copenhagen N, Denmark
| | - João Miguel da Silva Martins
- Department of Biology, Section for Biomolecular Sciences, Linderstrøm-Lang Centre for Protein Science , University of Copenhagen , Ole Maaloes Vej 5 , 2200 Copenhagen N, Denmark
| | - Jonas S Laursen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences , University of Copenhagen , Universitetsparken 2 , 2100 Copenhagen , Denmark
| | - Lars Behrendt
- Department of Biology, Section for Biomolecular Sciences, Linderstrøm-Lang Centre for Protein Science , University of Copenhagen , Ole Maaloes Vej 5 , 2200 Copenhagen N, Denmark
| | - Leise Riber
- Department of Biology, Section for Microbiology , University of Copenhagen , Ole Maaloes Vej 5 , 2200 Copenhagen N, Denmark
| | - Christian A Olsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences , University of Copenhagen , Universitetsparken 2 , 2100 Copenhagen , Denmark.,Center for Biopharmaceuticals, Faculty of Health and Medical Sciences , University of Copenhagen , Universitetsparken 2 , 2100 Copenhagen , Denmark
| | - Isaiah T Arkin
- Department of Biological Chemistry , The Hebrew University of Jerusalem , Edmond J. Safra Campus, Givat-Ram , Jerusalem 91904 , Israel
| | - Jakob R Winther
- Department of Biology, Section for Biomolecular Sciences, Linderstrøm-Lang Centre for Protein Science , University of Copenhagen , Ole Maaloes Vej 5 , 2200 Copenhagen N, Denmark
| | - Martin Willemoës
- Department of Biology, Section for Biomolecular Sciences, Linderstrøm-Lang Centre for Protein Science , University of Copenhagen , Ole Maaloes Vej 5 , 2200 Copenhagen N, Denmark
| | - Kresten Lindorff-Larsen
- Department of Biology, Section for Biomolecular Sciences, Linderstrøm-Lang Centre for Protein Science , University of Copenhagen , Ole Maaloes Vej 5 , 2200 Copenhagen N, Denmark
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3
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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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4
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Taube R, Alhadeff R, Assa D, Krugliak M, Arkin IT. Bacteria-based analysis of HIV-1 Vpu channel activity. PLoS One 2014; 9:e105387. [PMID: 25272035 PMCID: PMC4182682 DOI: 10.1371/journal.pone.0105387] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2014] [Accepted: 07/21/2014] [Indexed: 02/04/2023] Open
Abstract
HIV-1 Vpu is a small, single-span membrane protein with two attributed functions that increase the virus' pathogenicity: degradation of CD4 and inactivation of BST-2. Vpu has also been shown to posses ion channel activity, yet no correlation has been found between this attribute and Vpu's role in viral release. In order to gain further insight into the channel activity of Vpu we devised two bacteria-based assays that can examine this function in detail. In the first assay Vpu was over-expressed, such that it was deleterious to bacterial growth due to membrane permeabilization. In the second and more sensitive assay, the channel was expressed at low levels in K+ transport deficient bacteria. Consequently, Vpu expression enabled the bacteria to grow at otherwise non permissive low K+ concentrations. Hence, Vpu had the opposite impact on bacterial growth in the two assays: detrimental in the former and beneficial in the latter. Furthermore, we show that channel blockers also behave reciprocally in the two assays, promoting growth in the first assay and hindering it in the second assay. Taken together, we investigated Vpu's channel activity in a rapid and quantitative approach that is amenable to high-throughput screening, in search of novel blockers.
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Affiliation(s)
- Robert Taube
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmund J. Safra Campus, Jerusalem, Israel
- Institue of Biology, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Raphael Alhadeff
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmund J. Safra Campus, Jerusalem, Israel
| | - Dror Assa
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmund J. Safra Campus, Jerusalem, Israel
| | - Miriam Krugliak
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmund J. Safra Campus, Jerusalem, Israel
| | - Isaiah T. Arkin
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Edmund J. Safra Campus, Jerusalem, Israel
- * E-mail:
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Sacconi A, Moncelli MR, Margheri G, Tadini-Buoninsegni F. Enhanced adsorption of Ca-ATPase containing vesicles on a negatively charged solid-supported-membrane for the investigation of membrane transporters. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:13883-13889. [PMID: 24131452 DOI: 10.1021/la4034386] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A convenient model system for a biological membrane is a solid-supported membrane (SSM), which consists of a gold-supported alkanethiol|phospholipid bilayer. In combination with a concentration jump method, SSMs have been used for the investigation of several membrane transporters. Vesicles incorporating sarcoplasmic reticulum Ca-ATPase (SERCA) were adsorbed on a negatively charged SSM (octadecanethiol|phosphatidylserine bilayer). The current signal generated by the adsorbed vesicles following an ATP concentration jump was compared to that produced by SERCA-containing vesicles adsorbed on a conventional SSM (octadecanethiol|phosphatidylcholine bilayer). A significantly higher current amplitude was recorded on the serine-based SSM. The adsorption of SERCA-incorporating vesicles on the SSM was then characterized by surface plasmon resonance (SPR). The SPR measurements clearly indicate that in the presence of Ca(2+) and Mg(2+), the amount of adsorbed vesicles on the serine-based SSM is about twice that obtained using the conventional SSM, thereby demonstrating that the higher current amplitude recorded on the negatively charged SSM is correlated with a greater quantity of adsorbed vesicles. The enhanced adsorption of membrane vesicles on the PS-based SSM may be useful to study membrane preparations with a low concentration of transport protein generating small current signals, as in the case of various recombinantly expressed proteins.
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Affiliation(s)
- Alessio Sacconi
- Department of Chemistry "Ugo Schiff", University of Florence , via della Lastruccia 3, 50019 Sesto Fiorentino, Italy
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Beyleveld G, White KM, Ayllon J, Shaw ML. New-generation screening assays for the detection of anti-influenza compounds targeting viral and host functions. Antiviral Res 2013; 100:120-32. [PMID: 23933115 DOI: 10.1016/j.antiviral.2013.07.018] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Revised: 07/23/2013] [Accepted: 07/26/2013] [Indexed: 01/08/2023]
Abstract
Current options for influenza antiviral therapy are limited to the neuraminidase inhibitors, and knowledge that high levels of oseltamivir resistance have been seen among previously circulating H1N1 viruses increases the urgency to find new influenza therapeutics. To feed this pipeline, assays that are appropriate for use in high-throughput screens are being developed and are discussed in this review. Particular emphasis is placed on cell-based assays that capture both inhibitors of viral functions as well as the host functions that facilitate optimal influenza virus replication. Success in this area has been fueled by a greater understanding of the genome structure of influenza viruses and the ability to generate replication-competent recombinant viruses that carry a reporter gene, allowing for easy monitoring of viral infection in a high-throughput setting. This article forms part of a symposium in Antiviral Research on "Treatment of influenza: targeting the virus or the host."
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Affiliation(s)
- Grant Beyleveld
- Department of Microbiology and Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
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Wang J, Ma C, Wang J, Jo H, Canturk B, Fiorin G, Pinto LH, Lamb RA, Klein ML, DeGrado WF. Discovery of novel dual inhibitors of the wild-type and the most prevalent drug-resistant mutant, S31N, of the M2 proton channel from influenza A virus. J Med Chem 2013; 56:2804-12. [PMID: 23437766 DOI: 10.1021/jm301538e] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Anti-influenza drugs, amantadine and rimantadine, targeting the M2 channel from influenza A virus are no longer effective because of widespread drug resistance. S31N is the predominant and amantadine-resistant M2 mutant, present in almost all of the circulating influenza A strains as well as in the pandemic 2009 H1N1 and the highly pathogenic H5N1 flu strains. Thus, there is an urgent need to develop second-generation M2 inhibitors targeting the S31N mutant. However, the S31N mutant presents a huge challenge to drug discovery, and it has been considered undruggable for several decades. Using structural information, classical medicinal chemistry approaches, and M2-specific biological testing, we discovered benzyl-substituted amantadine derivatives with activity against both S31N and WT, among which 4-(adamantan-1-ylaminomethyl)-benzene-1,3-diol (44) is the most potent dual inhibitor. These inhibitors demonstrate that S31N is a druggable target and provide a new starting point to design novel M2 inhibitors that address the problem of drug-resistant influenza A infections.
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Affiliation(s)
- Jizhou Wang
- Influmedix Inc, 170 North Radnor-Chester Road, Suite 300, Radnor, Pennsylvania 19087, United States
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Balgi AD, Wang J, Cheng DYH, Ma C, Pfeifer TA, Shimizu Y, Anderson HJ, Pinto LH, Lamb RA, DeGrado WF, Roberge M. Inhibitors of the influenza A virus M2 proton channel discovered using a high-throughput yeast growth restoration assay. PLoS One 2013; 8:e55271. [PMID: 23383318 PMCID: PMC3562233 DOI: 10.1371/journal.pone.0055271] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Accepted: 12/22/2012] [Indexed: 11/18/2022] Open
Abstract
The M2 proton channel of the influenza A virus is the target of the anti-influenza drugs amantadine and rimantadine. The effectiveness of these drugs has been dramatically limited by the rapid spread of drug resistant mutations, mainly at sites S31N, V27A and L26F in the pore of the channel. Despite progress in designing inhibitors of V27A and L26F M2, there are currently no drugs targeting these mutated channels in clinical trials. Progress in developing new drugs has been hampered by the lack of a robust assay with sufficient throughput for discovery of new active chemotypes among chemical libraries and sufficient sensitivity to provide the SAR data essential for their improvement and development as drugs. In this study we adapted a yeast growth restoration assay, in which expression of the M2 channel inhibits yeast growth and exposure to an M2 channel inhibitor restores growth, into a robust and sensitive high-throughput screen for M2 channel inhibitors. A screen of over 250,000 pure chemicals and semi-purified fractions from natural extracts identified 21 active compounds comprising amantadine, rimantadine, 13 related adamantanes and 6 non-adamantanes. Of the non-adamantanes, hexamethylene amiloride and a triazine derivative represented new M2 inhibitory chemotypes that also showed antiviral activity in a plaque reduction assay. Of particular interest is the fact that the triazine derivative was not sufficiently potent for detection as an inhibitor in the traditional two electrode voltage clamp assay for M2 channel activity, but its discovery in the yeast assay led to testing of analogues of which one was as potent as amantadine.
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Affiliation(s)
- Aruna D. Balgi
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jun Wang
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, United States of America
| | - Daphne Y. H. Cheng
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Chunlong Ma
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois, United States of America
| | - Tom A. Pfeifer
- The Centre for Drug Research and Development, Vancouver, British Columbia, Canada
| | - Yoko Shimizu
- The Centre for Drug Research and Development, Vancouver, British Columbia, Canada
| | - Hilary J. Anderson
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Lawrence H. Pinto
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois, United States of America
| | - Robert A. Lamb
- Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois, United States of America
- Howard Hughes Medical Institute, Northwestern University, Evanston, Illinois, United States of America
| | - William F. DeGrado
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, United States of America
| | - Michel Roberge
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada
- The Centre for Drug Research and Development, Vancouver, British Columbia, Canada
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9
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Shadiac N, Nagarajan Y, Waters S, Hrmova M. Close allies in membrane protein research: Cell-free synthesis and nanotechnology. Mol Membr Biol 2013; 30:229-45. [DOI: 10.3109/09687688.2012.762125] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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10
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Assaying the proton transport and regulation of UCP1 using solid supported membranes. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2012; 41:675-9. [PMID: 22847775 DOI: 10.1007/s00249-012-0844-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Revised: 07/02/2012] [Accepted: 07/10/2012] [Indexed: 10/28/2022]
Abstract
The uncoupling protein 1 (UCP1) is a mitochondrial protein that carries protons across the inner mitochondrial membrane. It has an important role in non-shivering thermogenesis, and recent evidence suggests its role in human adult metabolism. Using rapid solution exchange on solid supported membranes, we succeeded in measuring electrical currents generated by the transport activity of UCP1. The protein was purified from mouse brown adipose tissue, reconstituted in liposomes and absorbed on solid supported membranes. A fast pH jump activated the ion transport, and electrical signals could be recorded. The currents were characterized by a fast rise and a slow decay, were stable over time, inhibited by purine nucleotides and activated by fatty acids. This new assay permits direct observation of UCP1 activity in controlled cell-free conditions, and opens up new possibilities for UCP1 functional characterization and drug screening because of its robustness and its potential for automation.
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Resistance characteristics of influenza to amino-adamantyls. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:547-53. [DOI: 10.1016/j.bbamem.2010.06.018] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Revised: 06/14/2010] [Accepted: 06/18/2010] [Indexed: 12/17/2022]
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12
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Inayat S, Zhao Y, Cantrell DR, Dikin D, Pinto LH, Troy JB. A novel way to go whole-cell in patch-clamp experiments. IEEE Trans Biomed Eng 2010; 57. [PMID: 20595080 DOI: 10.1109/tbme.2010.2055055] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
With a conventional patch-clamp electrode, an Ag/AgCl wire sits stationary inside the pipette. To move from the gigaseal cell-attached configuration to whole-cell recording, suction is applied inside the pipette. We have designed and developed a novel Pushpen patch-clamp electrode, in which a W wire insulated and wound with Ag/AgCl wire can move linearly inside the pipette. The W wire has a conical tip, which can protrude from the pipette tip like a push pen, a procedure we call the Pushpen Operation. We use the Pushpen operation to impale the cell membrane in cell-attached configuration to go whole-cell without disruption of the gigaseal. We successfully recorded whole-cell currents from chinese hamster ovarian cells expressing influenza A virus protein A/M2, after obtaining whole-cell configuration with the Pushpen operation. This novel method of achieving whole-cell configuration may have a higher success rate than is the case with the conventional patch clamp technique.
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