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Flatt S, Busiello DM, Zamuner S, De Los Rios P. ABC transporters are billion-year-old Maxwell Demons. COMMUNICATIONS PHYSICS 2023; 6:205. [PMID: 38665399 PMCID: PMC11041718 DOI: 10.1038/s42005-023-01320-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 07/26/2023] [Indexed: 04/28/2024]
Abstract
ATP-Binding Cassette (ABC) transporters are a broad family of biological machines, found in most prokaryotic and eukaryotic cells, performing the crucial import or export of substrates through both plasma and organellar membranes, and maintaining a steady concentration gradient driven by ATP hydrolysis. Building upon the present biophysical and biochemical characterization of ABC transporters, we propose here a model whose solution reveals that these machines are an exact molecular realization of the autonomous Maxwell Demon, a century-old abstract device that uses an energy source to drive systems away from thermodynamic equilibrium. In particular, the Maxwell Demon does not perform any direct mechanical work on the system, but simply selects which spontaneous processes to allow and which ones to forbid based on information that it collects and processes. In its autonomous version, the measurement device is embedded in the system itself. In the molecular model introduced here, the different operations that characterize Maxwell Demons (measurement, feedback, resetting) are features that emerge from the biochemical and structural properties of ABC transporters, revealing the crucial role of allostery to process information. Our framework allows us to develop an explicit bridge between the molecular-level description and the higher-level language of information theory for ABC transporters.
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Affiliation(s)
- Solange Flatt
- Institute of Physics, School of Basic Sciences, École Polytechnique Fédérale de Lausanne—EPFL, Lausanne, 1015 Switzerland
| | - Daniel Maria Busiello
- Institute of Physics, School of Basic Sciences, École Polytechnique Fédérale de Lausanne—EPFL, Lausanne, 1015 Switzerland
- Max Planck Institute for the Physics of Complex Systems, Dresden, 01187 Germany
| | - Stefano Zamuner
- Institute of Physics, School of Basic Sciences, École Polytechnique Fédérale de Lausanne—EPFL, Lausanne, 1015 Switzerland
| | - Paolo De Los Rios
- Institute of Physics, School of Basic Sciences, École Polytechnique Fédérale de Lausanne—EPFL, Lausanne, 1015 Switzerland
- Institute of Bioengineering, School of Life Sciences, École Polytechnique Fédérale de Lausanne—EPFL, Lausanne, 1015 Switzerland
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2
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De Vocht T, Buyck C, Deferm N, Qi B, Van Brantegem P, van Vlijmen H, Snoeys J, Hoeben E, Vermeulen A, Annaert P. Identification of novel inhibitors of rat Mrp3. Eur J Pharm Sci 2021; 162:105813. [PMID: 33753214 DOI: 10.1016/j.ejps.2021.105813] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 02/18/2021] [Accepted: 03/16/2021] [Indexed: 10/21/2022]
Abstract
Multidrug resistance-associated protein (MRP; ABCC gene family) mediated efflux transport plays an important role in the systemic and tissue exposure profiles of many drugs and their metabolites, and also of endogenous compounds like bile acids and bilirubin conjugates. However, potent and isoform-selective inhibitors of the MRP subfamily are currently lacking. Therefore, the purpose of the present work was to identify novel rat Mrp3 inhibitors. Using 5(6)-carboxy-2',7'-dichlorofluorescein diacetate (CDFDA) as a model-(pro)substrate for Mrp3 in an oil-spin assay with primary rat hepatocytes, the extent of inhibition of CDF efflux was determined for 1584 compounds, yielding 59 hits (excluding the reference inhibitor) that were identified as new Mrp3 inhibitors. A naive Bayesian prediction model was constructed in Pipeline Pilot to elucidate physicochemical and structural features of compounds causing Mrp3 inhibition. The final Bayesian model generated common physicochemical properties of Mrp3 inhibitors. For instance, more than half of the hits contain a phenolic structure. The identified compounds have an AlogP between 2 and 4.5, between 5 to 8 hydrogen bond acceptor atoms, a molecular weight between 260 and 400, and 2 or more aromatic rings. Compared to the depleted dataset (i.e. 90% remaining compounds), the Mrp3 hit rate in the enriched set was 7.5-fold higher (i.e. 17.2% versus 2.3%). Several hits from this first screening approach were confirmed in an additional study using Mrp3 transfected inside-out membrane vesicles. In conclusion, several new and potent inhibitors of Mrp3 mediated efflux were identified in an optimized in vitro rat hepatocyte assay and confirmed using Mrp3 transfected inside-out membrane vesicles. A final naive Bayesian model was developed in an iterative way to reveal common physicochemical and structural features for Mrp3 inhibitors. The final Bayesian model will enable in silico screening of larger libraries and in vitro identification of more potent Mrp3 inhibitors.
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Affiliation(s)
- Tom De Vocht
- Drug Delivery and Disposition, KU Leuven Department of Pharmaceutical and Pharmacological Sciences, Campus Gasthuisberg, O&N2, Herestraat 49 box 921, B-3000 Leuven, Belgium
| | - Christophe Buyck
- Discovery Sciences, Janssen Research & Development, a division of Janssen Pharmaceutica N.V., Turnhoutseweg 30, B-2340 Beerse, Belgium
| | - Neel Deferm
- Drug Delivery and Disposition, KU Leuven Department of Pharmaceutical and Pharmacological Sciences, Campus Gasthuisberg, O&N2, Herestraat 49 box 921, B-3000 Leuven, Belgium
| | - Bing Qi
- Drug Delivery and Disposition, KU Leuven Department of Pharmaceutical and Pharmacological Sciences, Campus Gasthuisberg, O&N2, Herestraat 49 box 921, B-3000 Leuven, Belgium
| | - Pieter Van Brantegem
- Drug Delivery and Disposition, KU Leuven Department of Pharmaceutical and Pharmacological Sciences, Campus Gasthuisberg, O&N2, Herestraat 49 box 921, B-3000 Leuven, Belgium
| | - Herman van Vlijmen
- Discovery Sciences, Janssen Research & Development, a division of Janssen Pharmaceutica N.V., Turnhoutseweg 30, B-2340 Beerse, Belgium
| | - Jan Snoeys
- Drug Metabolism and Pharmacokinetics, Janssen Research & Development, a division of Janssen Pharmaceutica N.V., Turnhoutseweg 30, B-2340 Beerse, Belgium
| | - Eef Hoeben
- Quantitative Sciences, Janssen Research and Development, a division of Janssen Pharmaceutica N.V., Turnhoutseweg 30, B-2340 Beerse, Belgium; BioNotus GCV, Wetenschapspark Universiteit Antwerpen, Galileilaan 15, B-2845 Niel, Belgium
| | - An Vermeulen
- Quantitative Sciences, Janssen Research and Development, a division of Janssen Pharmaceutica N.V., Turnhoutseweg 30, B-2340 Beerse, Belgium
| | - Pieter Annaert
- Drug Delivery and Disposition, KU Leuven Department of Pharmaceutical and Pharmacological Sciences, Campus Gasthuisberg, O&N2, Herestraat 49 box 921, B-3000 Leuven, Belgium; BioNotus GCV, Wetenschapspark Universiteit Antwerpen, Galileilaan 15, B-2845 Niel, Belgium.
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3
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Tátrai P, Krajcsi P. Prediction of Drug-Induced Hyperbilirubinemia by In Vitro Testing. Pharmaceutics 2020; 12:pharmaceutics12080755. [PMID: 32796590 PMCID: PMC7465333 DOI: 10.3390/pharmaceutics12080755] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Revised: 07/28/2020] [Accepted: 08/07/2020] [Indexed: 12/23/2022] Open
Abstract
Bilirubin, the end product of heme catabolism, is produced continuously in the body and may reach toxic levels if accumulates in the serum and tissues; therefore, a highly efficient mechanism evolved for its disposition. Normally, unconjugated bilirubin enters hepatocytes through the uptake transporters organic anion transporting polypeptide (OATP) 1B1 and 1B3, undergoes glucuronidation by the Phase II enzyme UDP glucuronosyltransferase 1A1 (UGT1A1), and conjugated forms are excreted into the bile by the canalicular export pump multidrug resistance protein 2 (MRP2). Any remaining conjugated bilirubin is transported back to the blood by MRP3 and passed on for uptake and excretion by downstream hepatocytes or the kidney. The bile salt export pump BSEP as the main motor of bile flow is indirectly involved in bilirubin disposition. Genetic mutations and xenobiotics that interfere with this machinery may impede bilirubin disposition and cause hyperbilirubinemia. Several pharmaceutical compounds are known to cause hyperbilirubinemia via inhibition of OATP1Bs, UGT1A1, or BSEP. Herein we briefly review the in vitro prediction methods that serve to identify drugs with a potential to induce hyperbilirubinemia. In vitro assays can be deployed early in drug development and may help to minimize late-stage attrition. Based on current evidence, drugs that behave as mono- or multispecific inhibitors of OATP1B1, UGT1A1, and BSEP in vitro are at risk of causing clinically significant hyperbilirubinemia. By integrating inhibition data from in vitro assays, drug serum concentrations, and clinical reports of hyperbilirubinemia, predictor cut-off values have been established and are provisionally suggested in this review. Further validation of in vitro readouts to clinical outcomes is expected to enhance the predictive power of these assays.
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Affiliation(s)
- Péter Tátrai
- Solvo Biotechnology, Science Park, Building B1, 4-20 Irinyi József utca, H-1117 Budapest, Hungary;
| | - Péter Krajcsi
- Solvo Biotechnology, Science Park, Building B1, 4-20 Irinyi József utca, H-1117 Budapest, Hungary;
- Faculty of Health Sciences, Semmelweis University, H-1085 Budapest, Hungary
- Faculty of Information Technology and Bionics, Péter Pázmány Catholic University, H-1083 Budapest, Hungary
- Correspondence:
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Bock C, Zollmann T, Lindt KA, Tampé R, Abele R. Peptide translocation by the lysosomal ABC transporter TAPL is regulated by coupling efficiency and activation energy. Sci Rep 2019; 9:11884. [PMID: 31417173 PMCID: PMC6695453 DOI: 10.1038/s41598-019-48343-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Accepted: 07/25/2019] [Indexed: 11/15/2022] Open
Abstract
The lysosomal polypeptide transporter TAPL belongs to the superfamily of ATP-binding cassette transporters. TAPL forms a homodimeric transport complex, which translocates oligo- and polypeptides into the lumen of lysosomes driven by ATP hydrolysis. Although the structure and the function of ABC transporters were intensively studied in the past, details about the single steps of the transport cycle are still elusive. Therefore, we analyzed the coupling of peptide binding, transport and ATP hydrolysis for different substrate sizes. Although longer and shorter peptides bind with the same affinity and are transported with identical Km values, they differ significantly in their transport rates. This difference can be attributed to a higher activation energy for the longer peptide. TAPL shows a basal ATPase activity, which is inhibited in the presence of longer peptides. Uncoupling between ATP hydrolysis and peptide transport increases with peptide length. Remarkably, also the type of nucleotide determines the uncoupling. While GTP is hydrolyzed as good as ATP, peptide transport is significantly reduced. In conclusion, TAPL does not differentiate between transport substrates in the binding process but during the following steps in the transport cycle, whereas, on the other hand, not only the coupling efficiency but also the activation energy varies depending on the size of peptide substrate.
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Affiliation(s)
- Christoph Bock
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue Str. 9, 60438, Frankfurt am Main, Germany
| | - Tina Zollmann
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue Str. 9, 60438, Frankfurt am Main, Germany
| | - Katharina-Astrid Lindt
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue Str. 9, 60438, Frankfurt am Main, Germany
| | - Robert Tampé
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue Str. 9, 60438, Frankfurt am Main, Germany
| | - Rupert Abele
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue Str. 9, 60438, Frankfurt am Main, Germany.
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Sjöstedt N, Salminen TA, Kidron H. Endogenous, cholesterol-activated ATP-dependent transport in membrane vesicles from Spodoptera frugiperda cells. Eur J Pharm Sci 2019; 137:104963. [PMID: 31226387 DOI: 10.1016/j.ejps.2019.104963] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Revised: 06/04/2019] [Accepted: 06/17/2019] [Indexed: 12/19/2022]
Abstract
Transport proteins of the ATP-binding cassette (ABC) family are found in all kingdoms of life. In humans, several ABC efflux transporters play a role in drug disposition and excretion. Therefore, in vitro methods have been developed to characterize the substrate and inhibitor properties of drugs with respect to these transporters. In the vesicular transport assay, transport is studied using inverted membrane vesicles produced from transporter overexpressing cell lines of both mammalian and insect origin. Insect cell expression systems benefit from a higher expression compared to background, but are not as well characterized as their mammalian counterparts regarding endogenous transport. Therefore, the contribution of this transport in the assay might be underappreciated. In this study, endogenous transport in membrane vesicles from Spodoptera frugiperda -derived Sf9 cells was characterized using four typical substrates of human ABC transporters: 5(6)-carboxy-2,'7'-dichlorofluorescein (CDCF), estradiol-17β-glucuronide, estrone sulfate and N-methyl-quinidine. Significant ATP-dependent transport was observed for three of the substrates with cholesterol-loading of the vesicles, which is sometimes used to improve the activity of human transporters expressed in Sf9 cells. The highest effect of cholesterol was on CDCF transport, and this transport in the cholesterol-loaded Sf9 vesicles was time and concentration dependent with a Km of 8.06 ± 1.11 μM. The observed CDCF transport was inhibited by known inhibitors of human ABCC transporters, but not by ABCB1 and ABCG2 inhibitors verapamil and Ko143, respectively. Two candidate genes for ABCC-type transporters in the S. frugiperda genome (SfABCC2 and SfABCC3) were identified based on sequence analysis as a hypothesis to explain the observed endogenous ABCC-type transport in Sf9 vesicles. Although further studies are needed to verify the role of SfABCC2 and SfABCC3 in Sf9 vesicles, the findings of this study highlight the need to carefully characterize background transport in Sf9 derived membrane vesicles to avoid false positive substrate findings for human ABC transporters studied with this overexpression system.
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Affiliation(s)
- Noora Sjöstedt
- Drug Research Program, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
| | - Tiina A Salminen
- Structural Bioinformatics Laboratory, Biochemistry, Faculty of Science and Engineering, Åbo Akademi University, Turku, Finland
| | - Heidi Kidron
- Drug Research Program, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
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Abstract
The transport of specific molecules across lipid membranes is an essential function of all living organisms. The processes are usually mediated by specific transporters. One of the largest transporter families is the ATP-binding cassette (ABC) family. More than 40 ABC transporters have been identified in human, which are divided into 7 subfamilies (ABCA to ABCG) based on their gene structure, amino acid sequence, domain organization, and phylogenetic analysis. Of them, at least 11 ABC transporters including P-glycoprotein (P-GP/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2) are involved in multidrug resistance (MDR) development. These ABC transporters are expressed in various tissues such as the liver, intestine, kidney, and brain, playing important roles in absorption, distribution, and excretion of drugs. Some ABC transporters are also involved in diverse cellular processes such as maintenance of osmotic homeostasis, antigen processing, cell division, immunity, cholesterol, and lipid trafficking. Several human diseases such as cystic fibrosis, sitosterolemia, Tangier disease, intrahepatic cholestasis, and retinal degeneration are associated with mutations in corresponding transporters. This chapter will describe function and expression of several ABC transporters (such as P-GP, BCRP, and MRPs), their substrates and inhibitors, as well as their clinical significance.
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Affiliation(s)
- Xiaodong Liu
- China Pharmaceutical University, Nanjing, China.
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7
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Dolberg AM, Reichl S. Activity of Multidrug Resistance-Associated Proteins 1-5 (MRP1-5) in the RPMI 2650 Cell Line and Explants of Human Nasal Turbinate. Mol Pharm 2017; 14:1577-1590. [PMID: 28291371 DOI: 10.1021/acs.molpharmaceut.6b00838] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The profound influence of ATP-binding cassette (ABC) transporters on the disposition of numerous drugs has led to increased interest in characterizing their expression profiles in various epithelial and endothelial barriers. The present work examined the presence and functional activity of five ABC efflux proteins, i.e., MRP 1-5, in freshly isolated human nasal epithelial cells and two in vitro models based on the human RPMI 2650 cell line. To evaluate the expression patterns of MRP1, MRP2, MRP3, MRP4, and MRP5 at the mRNA and protein levels in the ex vivo model and the differently cultured RPMI 2650 cells, reverse transcriptase polymerase chain reaction (RT-PCR), Western blot analysis, and indirect immunofluorescence staining were used. The functionality of the MRP transporters in the three models was assessed using efflux experiments and accumulation assays with the respective substrates and inhibitors. The mRNA and protein expression of all selected ABC transporters was detected in excised human nasal mucosa as well as in the corresponding cell culture models. Moreover, the functional expression of the MRP transport proteins was demonstrated in the three models for the first time. Therefore, the potential impact of multidrug resistance-associated proteins 1-5 on drug disposition after intranasal administration may be taken into consideration for future developments. The specimens of human nasal turbinate exhibited slightly lower efflux capacities of MRP1, MRP3, and MRP5 in relation to the submerged and ALI-cultured RPMI 2650 cells, but showed a promising comparability to both in vitro models concerning the activity of MRP2 and MRP4. In this regard, the different RPMI 2650 cell culture models will be able to provide useful experimental data in the preclinical phase to estimate the interaction of particular efflux transporters with drug candidates for nasal application.
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Affiliation(s)
- Anne M Dolberg
- Institut für Pharmazeutische Technologie, Technische Universität Braunschweig , Braunschweig 38106, Germany
| | - Stephan Reichl
- Institut für Pharmazeutische Technologie, Technische Universität Braunschweig , Braunschweig 38106, Germany.,Zentrum für Pharmaverfahrenstechnik, Technische Universität Braunschweig , Braunschweig 38106, Germany
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8
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Tebben L, Mück-Lichtenfeld C, Fernández G, Grimme S, Studer A. From Additivity to Cooperativity in Chemistry: Can Cooperativity Be Measured? Chemistry 2016; 23:5864-5873. [DOI: 10.1002/chem.201604651] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Indexed: 11/12/2022]
Affiliation(s)
- Ludger Tebben
- Organisch-Chemisches Institut; Westfälische Wilhelms Universität Münster; Corrensstraße 40 48149 Münster Germany
| | - Christian Mück-Lichtenfeld
- Organisch-Chemisches Institut; Westfälische Wilhelms Universität Münster; Corrensstraße 40 48149 Münster Germany
- Center for Multiscale Theory and Computation; Westfälische Wilhelms-Universität Münster; Corrensstraße 40 48149 Münster Germany
| | - Gustavo Fernández
- Organisch-Chemisches Institut; Westfälische Wilhelms Universität Münster; Corrensstraße 40 48149 Münster Germany
| | - Stefan Grimme
- Mulliken Center for Theoretical Chemistry; Institut für Physikalische und Theoretische Chemie; Universität Bonn; Beringstraße 4 53115 Bonn Germany
| | - Armido Studer
- Organisch-Chemisches Institut; Westfälische Wilhelms Universität Münster; Corrensstraße 40 48149 Münster Germany
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9
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Single liposome analysis of peptide translocation by the ABC transporter TAPL. Proc Natl Acad Sci U S A 2015; 112:2046-51. [PMID: 25646430 DOI: 10.1073/pnas.1418100112] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
ATP-binding cassette (ABC) transporters use ATP to drive solute transport across biological membranes. Members of this superfamily have crucial roles in cell physiology, and some of the transporters are linked to severe diseases. However, understanding of the transport mechanism, especially of human ABC exporters, is scarce. We reconstituted the human lysosomal polypeptide ABC transporter TAPL, expressed in Pichia pastoris, into lipid vesicles (liposomes) and performed explicit transport measurements. We analyzed solute transport at the single liposome level by monitoring the coincident fluorescence of solutes and proteoliposomes in the focal volume of a confocal microscope. We determined a turnover number of eight peptides per minute, which is two orders of magnitude higher than previously estimated from macroscopic measurements. Moreover, we show that TAPL translocates peptides against a large concentration gradient. Maximal filling is not limited by an electrochemical gradient but by trans-inhibition. Countertransport and reversibility studies demonstrate that peptide translocation is a strictly unidirectional process. Altogether, these data are included in a refined model of solute transport by ABC exporters.
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Drücker P, Gerke V, Galla HJ. Importance of phospholipid bilayer integrity in the analysis of protein-lipid interactions. Biochem Biophys Res Commun 2014; 453:143-7. [PMID: 25264195 DOI: 10.1016/j.bbrc.2014.09.079] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Accepted: 09/18/2014] [Indexed: 11/29/2022]
Abstract
The integrity of supported phospholipid bilayer membranes is of crucial importance for the investigation of lipid-protein interactions. Therefore we recorded the formation of supported membranes on SiO2 and mica by quartz crystal microbalance and controlled the integrity by atomic force microscopy. This study aims to analyze how membrane defects affect protein-lipid interactions. The experiments focused on a lipid mixture of POPC/DOPC/Chol/POPS/PI(4,5)P2 (37:20:20:20:3) and the binding of the peripheral membrane associated protein annexin A2. We found that formation of a continuous undisturbed bilayer is an indispensable precondition for a reliable determination and quantification of lipid-protein-interactions. If membrane defects were present, protein adsorption causes membrane disruption and lipid detachment on a support thus leading to false determination of binding constants. Our results obtained for PI(4,5)P2 and cholesterol containing supported membranes yield new knowledge to construct functional surfaces that may cover nanoporous substrates, form free standing membranes or may be used for lab-on-a-chip applications.
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Affiliation(s)
- Patrick Drücker
- Institute of Biochemistry, University of Münster, Wilhelm-Klemm-Str. 2, D-48149 Münster, Germany
| | - Volker Gerke
- Institute of Medical Biochemistry, ZMBE, University of Münster, Von-Esmarch-Str. 56, D-48149 Münster, Germany
| | - Hans-Joachim Galla
- Institute of Biochemistry, University of Münster, Wilhelm-Klemm-Str. 2, D-48149 Münster, Germany.
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11
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Abstract
AbstractABC transporters comprise a large, diverse, and ubiquitous superfamily of membrane active transporters. Their core architecture is a dimer of dimers, comprising two transmembrane (TM) domains that bind substrate, and two ATP-binding cassettes, which use the cell's energy currency to couple substrate translocation to ATP hydrolysis. Despite the availability of over a dozen resolved structures and a wealth of biochemical and biophysical data, this field is bedeviled by controversy and long-standing mechanistic questions remain unresolved. The prevailing paradigm for the ABC transport mechanism is the Switch Model, in which the ATP-binding cassettes dimerize upon binding two ATP molecules, and thence dissociate upon sequential ATP hydrolysis. This cycle of nucleotide-binding domain (NBD) dimerization and dissociation is coupled to a switch between inward- or outward facing conformations of a single TM channel; this alternating access enables substrate binding on one face of the membrane and its release at the other. Notwithstanding widespread acceptance of the Switch Model, there is substantial evidence that the NBDs do not separate very much, if at all, and thus physical separation of the ATP cassettes observed in crystallographic structures may be an artefact. An alternative Constant Contact Model has been proposed, in which ATP hydrolysis occurs alternately at the two ATP-binding sites, with one of the sites remaining closed and containing occluded nucleotide at all times. In this model, the cassettes remain in contact and the active sites swing open in an alternately seesawing motion. Whilst the concept of NBD association/dissociation in the Switch Model is naturally compatible with a single alternating-access channel, the asymmetric functioning proposed by the Constant Contact model suggests an alternating or reciprocating function in the TMDs. Here, a new model for the function of ABC transporters is proposed in which the sequence of ATP binding, hydrolysis, and product release in each active site is directly coupled to the analogous sequence of substrate binding, translocation and release in one of two functionally separate substrate translocation pathways. Each translocation pathway functions 180° out of phase. A wide and diverse selection of data for both ABC importers and exporters is examined, and the ability of the Switch and Reciprocating Models to explain the data is compared and contrasted. This analysis shows that not only can the Reciprocating Model readily explain the data; it also suggests straightforward explanations for the function of a number of atypical ABC transporters. This study represents the most coherent and complete attempt at an all-encompassing scheme to explain how these important proteins work, one that is consistent with sound biochemical and biophysical evidence.
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12
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Structure and mechanism of ATP-dependent phospholipid transporters. Biochim Biophys Acta Gen Subj 2014; 1850:461-75. [PMID: 24746984 DOI: 10.1016/j.bbagen.2014.04.008] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2014] [Revised: 04/04/2014] [Accepted: 04/07/2014] [Indexed: 01/09/2023]
Abstract
BACKGROUND ATP-binding cassette (ABC) transporters and P4-ATPases are two large and seemingly unrelated families of primary active pumps involved in moving phospholipids from one leaflet of a biological membrane to the other. SCOPE OF REVIEW This review aims to identify common mechanistic features in the way phospholipid flipping is carried out by two evolutionarily unrelated families of transporters. MAJOR CONCLUSIONS Both protein families hydrolyze ATP, although they employ different mechanisms to use it, and have a comparable size with twelve transmembrane segments in the functional unit. Further, despite differences in overall architecture, both appear to operate by an alternating access mechanism and during transport they might allow access of phospholipids to the internal part of the transmembrane domain. The latter feature is obvious for ABC transporters, but phospholipids and other hydrophobic molecules have also been found embedded in P-type ATPase crystal structures. Taken together, in two diverse groups of pumps, nature appears to have evolved quite similar ways of flipping phospholipids. GENERAL SIGNIFICANCE Our understanding of the structural basis for phospholipid flipping is still limited but it seems plausible that a general mechanism for phospholipid flipping exists in nature. This article is part of a Special Issue entitled Structural biochemistry and biophysics of membrane proteins.
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13
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Isoproterenol effects evaluated in heart slices of human and rat in comparison to rat heart in vivo. Toxicol Appl Pharmacol 2014; 274:302-12. [DOI: 10.1016/j.taap.2013.11.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Revised: 10/04/2013] [Accepted: 11/15/2013] [Indexed: 11/22/2022]
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14
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Seelheim P, Galla HJ. Tethered proteoliposomes containing human ABC transporter MRP3: new perspectives for biosensor application based on transmembrane proteins. Biochem Biophys Res Commun 2013; 431:519-23. [PMID: 23321307 DOI: 10.1016/j.bbrc.2013.01.026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Accepted: 01/07/2013] [Indexed: 11/25/2022]
Abstract
While transmembrane proteins and transporters comprise one of the largest protein families, their use in biosensors like biochips or lab-on-a-chip devices has so far been limited by their demanding requirements of a stable and compartmentalized lipid environment. A possible remedy lies in the tethering of proteoliposomes containing the reconstituted transmembrane protein to the biosensoric surface. As a proof of concept, we reconstituted the human ABC transporter MRP3 into biotinylated proteoliposomes and tethered those to a gold surface coated with streptavidin on a biotinylated self-assembled thiol monolayer. The tethering process was investigated by quartz crystal microbalance with dissipation monitoring. The final assembly of tethered proteoliposomes exhibited biological activity in terms of drug-stimulated ATP hydrolysis and substrate translocation. The presented facile immobilization approach can be easily extended to other transmembrane proteins as it does not require any modification of the protein and will open up transmembrane proteins for future application in biosensors.
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Affiliation(s)
- Patrick Seelheim
- Institute for Biochemistry/International Graduate School of Chemistry, University of Muenster, Wilhelm-Klemm-Str. 2, 48149 Muenster, Germany
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