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Schirripa Spagnolo C, Moscardini A, Amodeo R, Beltram F, Luin S. Quantitative determination of fluorescence labeling implemented in cell cultures. BMC Biol 2023; 21:190. [PMID: 37697318 PMCID: PMC10496409 DOI: 10.1186/s12915-023-01685-0] [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: 11/29/2022] [Accepted: 08/18/2023] [Indexed: 09/13/2023] Open
Abstract
BACKGROUND Labeling efficiency is a crucial parameter in fluorescence applications, especially when studying biomolecular interactions. Current approaches for estimating the yield of fluorescent labeling have critical drawbacks that usually lead them to be inaccurate or not quantitative. RESULTS We present a method to quantify fluorescent-labeling efficiency that addresses the critical issues marring existing approaches. The method operates in the same conditions of the target experiments by exploiting a ratiometric evaluation with two fluorophores used in sequential reactions. We show the ability of the protocol to extract reliable quantification for different fluorescent probes, reagents concentrations, and reaction timing and to optimize labeling performance. As paradigm, we consider the labeling of the membrane-receptor TrkA through 4'-phosphopantetheinyl transferase Sfp in living cells, visualizing the results by TIRF microscopy. This investigation allows us to find conditions for demanding single and multi-color single-molecule studies requiring high degrees of labeling. CONCLUSIONS The developed method allows the quantitative determination and the optimization of staining efficiency in any labeling strategy based on stable reactions.
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Affiliation(s)
| | - Aldo Moscardini
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127, Pisa, Italy
| | - Rosy Amodeo
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127, Pisa, Italy
- Present address: Department of Biomedical Sciences, Humanitas University, Via Rita Levi Montalcini 4, Pieve Emanuele, 20072, Milan, Italy
| | - Fabio Beltram
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127, Pisa, Italy
- NEST Laboratory, Istituto Nanoscienze-CNR, Piazza San Silvestro 12, 56127, Pisa, Italy
| | - Stefano Luin
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127, Pisa, Italy.
- NEST Laboratory, Istituto Nanoscienze-CNR, Piazza San Silvestro 12, 56127, Pisa, Italy.
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2
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Veit S, Paweletz LC, Günther Pomorski T. Determination of membrane protein orientation upon liposomal reconstitution down to the single vesicle level. Biol Chem 2023; 404:647-661. [PMID: 36857289 DOI: 10.1515/hsz-2022-0325] [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: 11/10/2022] [Accepted: 02/07/2023] [Indexed: 03/02/2023]
Abstract
Reconstitution of membrane proteins into liposomal membranes represents a key technique in enabling functional analysis under well-defined conditions. In this review, we provide a brief introduction to selected methods that have been developed to determine membrane protein orientation after reconstitution in liposomes, including approaches based on proteolytic digestion with proteases, site-specific labeling, fluorescence quenching and activity assays. In addition, we briefly highlight new strategies based on single vesicle analysis to address the problem of sample heterogeneity.
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Affiliation(s)
- Sarina Veit
- Department of Molecular Biochemistry , Faculty of Chemistry and Biochemistry , NC 7/174, Ruhr University Bochum, Universitätsstraße 150, D-44780 Bochum, Germany
| | - Laura Charlotte Paweletz
- Department of Molecular Biochemistry , Faculty of Chemistry and Biochemistry , NC 7/174, Ruhr University Bochum, Universitätsstraße 150, D-44780 Bochum, Germany
| | - Thomas Günther Pomorski
- Department of Molecular Biochemistry , Faculty of Chemistry and Biochemistry , NC 7/174, Ruhr University Bochum, Universitätsstraße 150, D-44780 Bochum, Germany
- Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark
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Mathiassen PPM, Pomorski TG. A Fluorescence-based Assay for Measuring Phospholipid Scramblase Activity in Giant Unilamellar Vesicles. Bio Protoc 2022; 12:e4366. [PMID: 35434199 PMCID: PMC8983165 DOI: 10.21769/bioprotoc.4366] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2022] [Revised: 11/09/2021] [Accepted: 03/01/2022] [Indexed: 07/28/2023] Open
Abstract
Transbilayer movement of phospholipids in biological membranes is mediated by a diverse set of lipid transporters. Among them are scramblases that facilitate rapid bi-directional movement of lipids without metabolic energy input. In this protocol, we describe the incorporation of phospholipid scramblases into giant unilamellar vesicles (GUVs) formed from scramblase-containing large unilamellar vesicles by electroformation. We also describe how to analyze their activity using membrane-impermeant sodium dithionite, to bleach symmetrically incorporated fluorescent ATTO488-conjugated phospholipids. The fluorescence-based readout allows single vesicle tracking for a large number of settled/immobilized GUVs, and provides a well-defined experimental setup to directly characterize these lipid transporters at the molecular level. Graphic abstract: Giant unilamellar vesicles (GUVs) are formed by electroformation from large unilamellar vesicles (LUVs) containing phospholipid scramblases (purple) and trace amounts of a fluorescent lipid reporter (green). The scramblase activity is analyzed by a fluorescence-based assay of single GUVs, using the membrane-impermeant quencher dithionite. Sizes not to scale. Modified from Mathiassen et al. (2021).
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Affiliation(s)
- Patricia P. M. Mathiassen
- Department of Molecular Biochemistry, Faculty of Chemistry and Biochemistry, Ruhr University Bochum, 44780, Bochum, Germany
| | - Thomas Günther Pomorski
- Department of Molecular Biochemistry, Faculty of Chemistry and Biochemistry, Ruhr University Bochum, 44780, Bochum, Germany
- Department of Plant and Environmental Sciences, University of Copenhagen, 1871, Frederiksberg C, Denmark
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4
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Endoplasmic reticulum phospholipid scramblase activity revealed after protein reconstitution into giant unilamellar vesicles containing a photostable lipid reporter. Sci Rep 2021; 11:14364. [PMID: 34257324 PMCID: PMC8277826 DOI: 10.1038/s41598-021-93664-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Accepted: 06/28/2021] [Indexed: 02/04/2023] Open
Abstract
Transbilayer movement of phospholipids in biological membranes is mediated by a diverse set of lipid transporters. Among them are scramblases that facilitate a rapid bi-directional movement of lipids without metabolic energy input. Here, we established a new fluorescence microscopy-based assay for detecting phospholipid scramblase activity of membrane proteins upon their reconstitution into giant unilamellar vesicles formed from proteoliposomes by electroformation. The assay is based on chemical bleaching of fluorescence of a photostable ATTO-dye labeled phospholipid with the membrane-impermeant reductant sodium dithionite. We demonstrate that this new methodology is suitable for the study of the scramblase activity of the yeast endoplasmic reticulum at single vesicle level.
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5
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The Groovy TMEM16 Family: Molecular Mechanisms of Lipid Scrambling and Ion Conduction. J Mol Biol 2021; 433:166941. [PMID: 33741412 DOI: 10.1016/j.jmb.2021.166941] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 03/09/2021] [Accepted: 03/09/2021] [Indexed: 12/28/2022]
Abstract
The TMEM16 family of membrane proteins displays a remarkable functional dichotomy - while some family members function as Ca2+-activated anion channels, the majority of characterized TMEM16 homologs are Ca2+-activated lipid scramblases, which catalyze the exchange of phospholipids between the two membrane leaflets. Furthermore, some TMEM16 scramblases can also function as channels. Due to their involvement in important physiological processes, the family has been actively studied ever since their molecular identity was unraveled. In this review, we will summarize the recent advances in the field and how they influenced our view of TMEM16 family function and evolution. Structural, functional and computational studies reveal how relatively small rearrangements in the permeation pathway are responsible for the observed functional duality: while TMEM16 scramblases can adopt both ion- and lipid conductive conformations, TMEM16 channels can only populate the former. Recent data further provides the molecular details of a stepwise activation mechanism, which is initiated by Ca2+ binding and modulated by various cellular factors, including lipids. TMEM16 function and the surrounding membrane properties are inextricably intertwined, with the protein inducing bilayer deformations associated with scrambling, while the surrounding lipids modulate TMEM16 conformation and activity.
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6
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Reconstitution of Proteoliposomes for Phospholipid Scrambling and Nonselective Channel Assays. Methods Mol Biol 2020; 2127:207-225. [PMID: 32112325 DOI: 10.1007/978-1-0716-0373-4_15] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Phospholipid scramblases catalyze the rapid trans-bilayer movement of lipids down their concentration gradients. This process is essential for numerous cellular signaling functions including cell fusion, blood coagulation, and apoptosis. The importance of scramblases is highlighted by the number of human diseases caused by mutations in these proteins. Because of their indispensable function, it is essential to understand and characterize the molecular function of phospholipid scramblases. Powerful tools to measure lipid transport in cells are available. However, these approaches provide limited mechanistic insights into the molecular bases of scrambling. Here we describe in detail an in vitro phospholipid scramblase assay and the accompanying analysis which allows for determination of the macroscopic rate constants associated with phospholipid scrambling. Notably, members of the TMEM16 family of scramblases also function as nonselective ion channels. To better understand the physiological relevance of this channel function as well as its relationship to the scrambling activity of the TMEM16s we also describe in detail an in vitro flux assay to measure nonselective channel activity. Together, these two assays can be used to investigate the dual activities of the TMEM16 scramblases/nonselective channels.
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7
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Chandra G, Defour A, Mamchoui K, Pandey K, Mishra S, Mouly V, Sreetama S, Mahad Ahmad M, Mahjneh I, Morizono H, Pattabiraman N, Menon AK, Jaiswal JK. Dysregulated calcium homeostasis prevents plasma membrane repair in Anoctamin 5/TMEM16E-deficient patient muscle cells. Cell Death Discov 2019; 5:118. [PMID: 31341644 PMCID: PMC6639303 DOI: 10.1038/s41420-019-0197-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 06/10/2019] [Accepted: 06/13/2019] [Indexed: 01/30/2023] Open
Abstract
Autosomal recessive mutations in Anoctamin 5 (ANO5/TMEM16E), a member of the transmembrane 16 (TMEM16) family of Ca2+-activated ion channels and phospholipid scramblases, cause adult-onset muscular dystrophies (limb girdle muscular dystrophy 2L (LGMD2L) and Miyoshi Muscular Dystrophy (MMD3). However, the molecular role of ANO5 is unclear and ANO5 knockout mouse models show conflicting requirements of ANO5 in muscle. To study the role of ANO5 in human muscle cells we generated a myoblast line from a MMD3-patient carrying the c.2272C>T mutation, which we find causes the mutant protein to be degraded. The patient myoblasts exhibit normal myogenesis, but are compromised in their plasma membrane repair (PMR) ability. The repair deficit is linked to the poor ability of the endoplasmic reticulum (ER) to clear cytosolic Ca2+ increase caused by focal plasma membrane injury. Expression of wild-type ANO5 or pharmacological prevention of injury-triggered cytosolic Ca2+ overload enable injured patient muscle cells to repair. A homology model of ANO5 shows that several of the known LGMD2L/MMD3 patient mutations line the transmembrane region of the protein implicated in its channel activity. These results point to a role of cytosolic Ca2+ homeostasis in PMR, indicate a role for ANO5 in ER-mediated cytosolic Ca2+ uptake and identify normalization of cytosolic Ca2+ homeostasis as a potential therapeutic approach to treat muscular dystrophies caused by ANO5 deficit.
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Affiliation(s)
- Goutam Chandra
- 1Center of Genetic Medicine Research, Children's National Health System, 111 Michigan Avenue, NW, Washington, DC 20010 USA
| | - Aurelia Defour
- 1Center of Genetic Medicine Research, Children's National Health System, 111 Michigan Avenue, NW, Washington, DC 20010 USA.,7Present Address: Aix Marseille Université, UMR_S 910, Génétique Médicale et Génomique Fonctionnelle, 13385 Marseille, France
| | - Kamel Mamchoui
- 2Center for Research in Myology, Sorbonne Universités, UPMC Université Paris 06, INSERM UMRS974, 47 Boulevard de l'hôpital, 75013 Paris, France
| | - Kalpana Pandey
- 3Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065 USA
| | - Soumya Mishra
- 1Center of Genetic Medicine Research, Children's National Health System, 111 Michigan Avenue, NW, Washington, DC 20010 USA
| | - Vincent Mouly
- 2Center for Research in Myology, Sorbonne Universités, UPMC Université Paris 06, INSERM UMRS974, 47 Boulevard de l'hôpital, 75013 Paris, France
| | - SenChandra Sreetama
- 1Center of Genetic Medicine Research, Children's National Health System, 111 Michigan Avenue, NW, Washington, DC 20010 USA
| | - Mohammad Mahad Ahmad
- 1Center of Genetic Medicine Research, Children's National Health System, 111 Michigan Avenue, NW, Washington, DC 20010 USA
| | - Ibrahim Mahjneh
- 4Department of Neurology, MRC Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland
| | - Hiroki Morizono
- 1Center of Genetic Medicine Research, Children's National Health System, 111 Michigan Avenue, NW, Washington, DC 20010 USA.,5Department of Genomics and Precision Medicine, George Washington University, Washington, DC 20037 USA
| | | | - Anant K Menon
- 3Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065 USA
| | - Jyoti K Jaiswal
- 1Center of Genetic Medicine Research, Children's National Health System, 111 Michigan Avenue, NW, Washington, DC 20010 USA.,5Department of Genomics and Precision Medicine, George Washington University, Washington, DC 20037 USA
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Exterkate M, Driessen AJM. Synthetic Minimal Cell: Self-Reproduction of the Boundary Layer. ACS OMEGA 2019; 4:5293-5303. [PMID: 30949617 PMCID: PMC6443216 DOI: 10.1021/acsomega.8b02955] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Accepted: 03/01/2019] [Indexed: 05/09/2023]
Abstract
A critical aspect in the bottom-up construction of a synthetic minimal cell is to develop an entity that is capable of self-reproduction. A key role in this process is the expansion and division of the boundary layer that surrounds the compartment, a process in which content loss has to be avoided and the barrier function maintained. Here, we describe the latest developments regarding self-reproduction of a boundary layer with a focus on the growth and division of phospholipid-based membranes in the context of a synthetic minimal cell.
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Affiliation(s)
- Marten Exterkate
- Department of Molecular Microbiology,
Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 7, 9747
AG Groningen, The Netherlands
| | - Arnold J. M. Driessen
- Department of Molecular Microbiology,
Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 7, 9747
AG Groningen, The Netherlands
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