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Frain KM, Dedic E, Nel L, Bohush A, Olesen E, Thaysen K, Wüstner D, Stokes DL, Pedersen BP. Conformational changes in the Niemann-Pick type C1 protein NCR1 drive sterol translocation. Proc Natl Acad Sci U S A 2024; 121:e2315575121. [PMID: 38568972 PMCID: PMC11009665 DOI: 10.1073/pnas.2315575121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Accepted: 02/22/2024] [Indexed: 04/05/2024] Open
Abstract
The membrane protein Niemann-Pick type C1 (NPC1, named NCR1 in yeast) is central to sterol homeostasis in eukaryotes. Saccharomyces cerevisiae NCR1 is localized to the vacuolar membrane, where it is suggested to carry sterols across the protective glycocalyx and deposit them into the vacuolar membrane. However, documentation of a vacuolar glycocalyx in fungi is lacking, and the mechanism for sterol translocation has remained unclear. Here, we provide evidence supporting the presence of a glycocalyx in isolated S. cerevisiae vacuoles and report four cryo-EM structures of NCR1 in two distinct conformations, named tense and relaxed. These two conformations illustrate the movement of sterols through a tunnel formed by the luminal domains, thus bypassing the barrier presented by the glycocalyx. Based on these structures and on comparison with other members of the Resistance-Nodulation-Division (RND) superfamily, we propose a transport model that links changes in the luminal domains with a cycle of protonation and deprotonation within the transmembrane region of the protein. Our model suggests that NPC proteins work by a generalized RND mechanism where the proton motive force drives conformational changes in the transmembrane domains that are allosterically coupled to luminal/extracellular domains to promote sterol transport.
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Affiliation(s)
- Kelly M. Frain
- Department of Molecular Biology and Genetics, Aarhus University, AarhusC 8000, Denmark
| | - Emil Dedic
- Department of Molecular Biology and Genetics, Aarhus University, AarhusC 8000, Denmark
| | - Lynette Nel
- Department of Molecular Biology and Genetics, Aarhus University, AarhusC 8000, Denmark
| | - Anastasiia Bohush
- Department of Molecular Biology and Genetics, Aarhus University, AarhusC 8000, Denmark
- Department of Molecular Biology and Genetics, Aarhus Institute of Advanced Studies, Aarhus University, AarhusC 8000, Denmark
| | - Esben Olesen
- Department of Molecular Biology and Genetics, Aarhus University, AarhusC 8000, Denmark
| | - Katja Thaysen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, OdenseM 5230, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, OdenseM 5230, Denmark
| | - David L. Stokes
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY10016
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2
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Wüstner D, Egebjerg JM, Lauritsen L. Dynamic Mode Decomposition of Multiphoton and Stimulated Emission Depletion Microscopy Data for Analysis of Fluorescent Probes in Cellular Membranes. Sensors (Basel) 2024; 24:2096. [PMID: 38610307 PMCID: PMC11013970 DOI: 10.3390/s24072096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2024] [Revised: 03/14/2024] [Accepted: 03/21/2024] [Indexed: 04/14/2024]
Abstract
An analysis of the membrane organization and intracellular trafficking of lipids often relies on multiphoton (MP) and super-resolution microscopy of fluorescent lipid probes. A disadvantage of particularly intrinsically fluorescent lipid probes, such as the cholesterol and ergosterol analogue, dehydroergosterol (DHE), is their low MP absorption cross-section, resulting in a low signal-to-noise ratio (SNR) in live-cell imaging. Stimulated emission depletion (STED) microscopy of membrane probes like Nile Red enables one to resolve membrane features beyond the diffraction limit but exposes the sample to a lot of excitation light and suffers from a low SNR and photobleaching. Here, dynamic mode decomposition (DMD) and its variant, higher-order DMD (HoDMD), are applied to efficiently reconstruct and denoise the MP and STED microscopy data of lipid probes, allowing for an improved visualization of the membranes in cells. HoDMD also allows us to decompose and reconstruct two-photon polarimetry images of TopFluor-cholesterol in model and cellular membranes. Finally, DMD is shown to not only reconstruct and denoise 3D-STED image stacks of Nile Red-labeled cells but also to predict unseen image frames, thereby allowing for interpolation images along the optical axis. This important feature of DMD can be used to reduce the number of image acquisitions, thereby minimizing the light exposure of biological samples without compromising image quality. Thus, DMD as a computational tool enables gentler live-cell imaging of fluorescent probes in cellular membranes by MP and STED microscopy.
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Affiliation(s)
- Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark; (J.M.E.); (L.L.)
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Kuhns S, Juhl AD, Anvarian Z, Wüstner D, Pedersen LB, Andersen JS. Endogenous Tagging of Ciliary Genes in Human RPE1 Cells for Live-Cell Imaging. Methods Mol Biol 2024; 2725:147-166. [PMID: 37856023 DOI: 10.1007/978-1-0716-3507-0_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2023]
Abstract
CRISPR-mediated endogenous tagging of genes provides unique possibilities to explore the function and dynamic subcellular localization of proteins in living cells. Here, we describe experimental strategies for endogenous PCR-tagging of ciliary genes in human RPE1 cells and how image acquisition and analysis of the expressed fluorescently tagged proteins can be utilized to study the dynamic ciliary processes of intraflagellar transport and vesicular trafficking.
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Affiliation(s)
- Stefanie Kuhns
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Zeinab Anvarian
- Department of Biology, University of Copenhagen, Copenhagen Ø, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Lotte B Pedersen
- Department of Biology, University of Copenhagen, Copenhagen Ø, Denmark
| | - Jens S Andersen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark.
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Wüstner D, Dupont Juhl A, Egebjerg JM, Werner S, McNally J, Schneider G. Kinetic modelling of sterol transport between plasma membrane and endo-lysosomes based on quantitative fluorescence and X-ray imaging data. Front Cell Dev Biol 2023; 11:1144936. [PMID: 38020900 PMCID: PMC10644255 DOI: 10.3389/fcell.2023.1144936] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2023] [Accepted: 10/20/2023] [Indexed: 12/01/2023] Open
Abstract
Niemann Pick type C1 and C2 (NPC1 and NPC2) are two sterol-binding proteins which, together, orchestrate cholesterol transport through late endosomes and lysosomes (LE/LYSs). NPC2 can facilitate sterol exchange between model membranes severalfold, but how this is connected to its function in cells is poorly understood. Using fluorescent analogs of cholesterol and quantitative fluorescence microscopy, we have recently measured the transport kinetics of sterol between plasma membrane (PM), recycling endosomes (REs) and LE/LYSs in control and NPC2 deficient fibroblasts. Here, we use kinetic modeling of this data to determine rate constants for sterol transport between intracellular compartments. Our model predicts that sterol is trapped in intraluminal vesicles (ILVs) of LE/LYSs in the absence of NPC2, causing delayed sterol export from LE/LYSs in NPC2 deficient fibroblasts. Using soft X-ray tomography, we confirm, that LE/LYSs of NPC2 deficient cells but not of control cells contain enlarged, carbon-rich intraluminal vesicular structures, supporting our model prediction of lipid accumulation in ILVs. By including sterol export via exocytosis of ILVs as exosomes and by release of vesicles-ectosomes-from the PM, we can reconcile measured sterol efflux kinetics and show that both pathways can be reciprocally regulated by the intraluminal sterol transfer activity of NPC2 inside LE/LYSs. Our results thereby connect the in vitro function of NPC2 as sterol transfer protein between membranes with its in vivo function.
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Affiliation(s)
- Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Jacob Marcus Egebjerg
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Stephan Werner
- Department of X-Ray Microscopy, Helmholtz-Zentrum Berlin, Berlin, Germany
| | - James McNally
- Department of X-Ray Microscopy, Helmholtz-Zentrum Berlin, Berlin, Germany
| | - Gerd Schneider
- Department of X-Ray Microscopy, Helmholtz-Zentrum Berlin, Berlin, Germany
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5
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Egebjerg JM, Szomek M, Thaysen K, Juhl AD, Kozakijevic S, Werner S, Pratsch C, Schneider G, Kapishnikov S, Ekman A, Röttger R, Wüstner D. Automated quantification of vacuole fusion and lipophagy in Saccharomyces cerevisiae from fluorescence and cryo-soft X-ray microscopy data using deep learning. Autophagy 2023:1-21. [PMID: 37908116 DOI: 10.1080/15548627.2023.2270378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Accepted: 10/02/2023] [Indexed: 11/02/2023] Open
Abstract
During starvation in the yeast Saccharomyces cerevisiae vacuolar vesicles fuse and lipid droplets (LDs) can become internalized into the vacuole in an autophagic process named lipophagy. There is a lack of tools to quantitatively assess starvation-induced vacuole fusion and lipophagy in intact cells with high resolution and throughput. Here, we combine soft X-ray tomography (SXT) with fluorescence microscopy and use a deep-learning computational approach to visualize and quantify these processes in yeast. We focus on yeast homologs of mammalian NPC1 (NPC intracellular cholesterol transporter 1; Ncr1 in yeast) and NPC2 proteins, whose dysfunction leads to Niemann Pick type C (NPC) disease in humans. We developed a convolutional neural network (CNN) model which classifies fully fused versus partially fused vacuoles based on fluorescence images of stained cells. This CNN, named Deep Yeast Fusion Network (DYFNet), revealed that cells lacking Ncr1 (ncr1∆ cells) or Npc2 (npc2∆ cells) have a reduced capacity for vacuole fusion. Using a second CNN model, we implemented a pipeline named LipoSeg to perform automated instance segmentation of LDs and vacuoles from high-resolution reconstructions of X-ray tomograms. From that, we obtained 3D renderings of LDs inside and outside of the vacuole in a fully automated manner and additionally measured droplet volume, number, and distribution. We find that ncr1∆ and npc2∆ cells could ingest LDs into vacuoles normally but showed compromised degradation of LDs and accumulation of lipid vesicles inside vacuoles. Our new method is versatile and allows for analysis of vacuole fusion, droplet size and lipophagy in intact cells.Abbreviations: BODIPY493/503: 4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-Indacene; BPS: bathophenanthrolinedisulfonic acid disodium salt hydrate; CNN: convolutional neural network; DHE; dehydroergosterol; npc2∆, yeast deficient in Npc2; DSC, Dice similarity coefficient; EM, electron microscopy; EVs, extracellular vesicles; FIB-SEM, focused ion beam milling-scanning electron microscopy; FM 4-64, N-(3-triethylammoniumpropyl)-4-(6-[4-{diethylamino} phenyl] hexatrienyl)-pyridinium dibromide; LDs, lipid droplets; Ncr1, yeast homolog of human NPC1 protein; ncr1∆, yeast deficient in Ncr1; NPC, Niemann Pick type C; NPC2, Niemann Pick type C homolog; OD600, optical density at 600 nm; ReLU, rectifier linear unit; PPV, positive predictive value; NPV, negative predictive value; MCC, Matthews correlation coefficient; SXT, soft X-ray tomography; UV, ultraviolet; YPD, yeast extract peptone dextrose.
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Affiliation(s)
- Jacob Marcus Egebjerg
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
- Department of Mathematics and Computer Science, University of Southern Denmark, Odense M, Denmark
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Katja Thaysen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Suzana Kozakijevic
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Stephan Werner
- Department of X‑Ray Microscopy, Helmholtz-Zentrum Berlin, Germany and Humboldt-Universität zu Berlin, Institut für Physik, Berlin, Germany
| | - Christoph Pratsch
- Department of X‑Ray Microscopy, Helmholtz-Zentrum Berlin, Germany and Humboldt-Universität zu Berlin, Institut für Physik, Berlin, Germany
| | - Gerd Schneider
- Department of X‑Ray Microscopy, Helmholtz-Zentrum Berlin, Germany and Humboldt-Universität zu Berlin, Institut für Physik, Berlin, Germany
| | - Sergey Kapishnikov
- SiriusXT, 9A Holly Ave. Stillorgan Industrial Park, Blackrock, Co, Dublin, Ireland
| | - Axel Ekman
- Department of Biological and Environmental Science and Nanoscience Centre, University of Jyväskylä, Jyväskylä, Finland
| | - Richard Röttger
- Department of Mathematics and Computer Science, University of Southern Denmark, Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
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6
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Akkerman V, Scheidt HA, Reinholdt P, Bashawat M, Szomek M, Lehmann M, Wessig P, Covey DF, Kongsted J, Müller P, Wüstner D. Natamycin interferes with ergosterol-dependent lipid phases in model membranes. BBA Adv 2023; 4:100102. [PMID: 37691996 PMCID: PMC10482743 DOI: 10.1016/j.bbadva.2023.100102] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/12/2023] Open
Abstract
Natamycin is an antifungal polyene macrolide that is used as a food preservative but also to treat fungal keratitis and other yeast infections. In contrast to other polyene antimycotics, natamycin does not form ion pores in the plasma membrane, but its mode of action is poorly understood. Using nuclear magnetic resonance (NMR) spectroscopy of deuterated sterols, we find that natamycin slows the mobility of ergosterol and cholesterol in liquid-ordered (Lo) membranes to a similar extent. This is supported by molecular dynamics (MD) simulations, which additionally reveal a strong impact of natamycin dimers on sterol dynamics and water permeability. Interference with sterol-dependent lipid packing is also reflected in a natamycin-mediated increase in membrane accessibility for dithionite, particularly in bilayers containing ergosterol. NMR experiments with deuterated sphingomyelin (SM) in sterol-containing membranes reveal that natamycin reduces phase separation and increases lipid exchange in bilayers with ergosterol. In ternary lipid mixtures containing monounsaturated phosphatidylcholine, saturated SM, and either ergosterol or cholesterol, natamycin interferes with phase separation into Lo and liquid-disordered (Ld) domains, as shown by NMR spectroscopy. Employing the intrinsic fluorescence of natamycin in ultraviolet-sensitive microscopy, we can visualize the binding of natamycin to giant unilamellar vesicles (GUVs) and find that it has the highest affinity for the Lo phase in GUVs containing ergosterol. Our results suggest that natamycin specifically interacts with the sterol-induced ordered phase, in which it disrupts lipid packing and increases solvent accessibility. This property is particularly pronounced in ergosterol containing membranes, which could underlie the selective antifungal activity of natamycin.
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Affiliation(s)
- Vibeke Akkerman
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230, Odense M, Denmark
| | - Holger A. Scheidt
- Institute for Medical Physics and Biophysics, Leipzig University, Härtelstr. 16-18, D-04107, Leipzig, Germany
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230, Odense M, Denmark
| | - Mohammad Bashawat
- Department of Biology, Humboldt University Berlin, Invalidenstr. 43, D-10115, Berlin, Germany
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230, Odense M, Denmark
| | - Max Lehmann
- Institute for Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476, Potsdam, Germany
| | - Pablo Wessig
- Institute for Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476, Potsdam, Germany
| | - Douglas F. Covey
- Department of Developmental Biology, Washington University, St. Louis, MO, 63110, USA
- Taylor Family Institute for Innovative Psychiatric Research, St. Louis, Missouri, USA
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230, Odense M, Denmark
| | - Peter Müller
- Department of Biology, Humboldt University Berlin, Invalidenstr. 43, D-10115, Berlin, Germany
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230, Odense M, Denmark
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7
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Juhl AD, Kozakijevic S, Willms T, Egebjerg JM, Szomek M, Thaysen K, Pratsch C, Werner S, Schneider G, Müller P, Wüstner D. Direct Observation of Uptake and Dissolution of Cholesterol Crystals by Macrophages Using Combined Fluorescence and X-ray Microscopy. Microsc Microanal 2023; 29:1158-1159. [PMID: 37613485 DOI: 10.1093/micmic/ozad067.592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Affiliation(s)
- Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Suzana Kozakijevic
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Tido Willms
- Department of Biology, Humboldt University Berlin, Berlin, Germany
| | - Jacob M Egebjerg
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Katja Thaysen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Christoph Pratsch
- Department of X-Ray Microscopy, Helmholtz-Zentrum Berlin, Berlin, Germany
| | - Stephan Werner
- Department of X-Ray Microscopy, Helmholtz-Zentrum Berlin, Berlin, Germany
| | - Gerd Schneider
- Department of X-Ray Microscopy, Helmholtz-Zentrum Berlin, Berlin, Germany
| | - Peter Müller
- Department of Biology, Humboldt University Berlin, Berlin, Germany
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
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8
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Wagh K, Stavreva DA, Jensen RAM, Paakinaho V, Fettweis G, Schiltz RL, Wüstner D, Mandrup S, Presman DM, Upadhyaya A, Hager GL. Dynamic switching of transcriptional regulators between two distinct low-mobility chromatin states. Sci Adv 2023; 9:eade1122. [PMID: 37315128 PMCID: PMC10954219 DOI: 10.1126/sciadv.ade1122] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Accepted: 05/10/2023] [Indexed: 06/16/2023]
Abstract
How chromatin dynamics relate to transcriptional activity remains poorly understood. Using single-molecule tracking, coupled with machine learning, we show that histone H2B and multiple chromatin-bound transcriptional regulators display two distinct low-mobility states. Ligand activation results in a marked increase in the propensity of steroid receptors to bind in the lowest-mobility state. Mutational analysis revealed that interactions with chromatin in the lowest-mobility state require an intact DNA binding domain and oligomerization domains. These states are not spatially separated as previously believed, but individual H2B and bound-TF molecules can dynamically switch between them on time scales of seconds. Single bound-TF molecules with different mobilities exhibit different dwell time distributions, suggesting that the mobility of TFs is intimately coupled with their binding dynamics. Together, our results identify two unique and distinct low-mobility states that appear to represent common pathways for transcription activation in mammalian cells.
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Affiliation(s)
- Kaustubh Wagh
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Department of Physics, University of Maryland, College Park, MD 20742, USA
| | - Diana A. Stavreva
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Rikke A. M. Jensen
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Ville Paakinaho
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Institute of Biomedicine, University of Eastern Finland, Kuopio, P.O. Box 1627, 70211 Kuopio, Finland
| | - Gregory Fettweis
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - R. Louis Schiltz
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Susanne Mandrup
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Diego M. Presman
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE), CONICET-Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Buenos Aires C1428EGA, Argentina
| | - Arpita Upadhyaya
- Department of Physics, University of Maryland, College Park, MD 20742, USA
- Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
| | - Gordon L. Hager
- Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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9
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Szomek M, Reinholdt P, Walther HL, Scheidt HA, Müller P, Obermaier S, Poolman B, Kongsted J, Wüstner D. Natamycin sequesters ergosterol and interferes with substrate transport by the lysine transporter Lyp1 from yeast. Biochim Biophys Acta Biomembr 2022; 1864:184012. [PMID: 35914570 DOI: 10.1016/j.bbamem.2022.184012] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Revised: 06/30/2022] [Accepted: 07/21/2022] [Indexed: 06/15/2023]
Abstract
Natamycin is a polyene macrolide, widely employed to treat fungal keratitis and other yeast infections as well as to protect food products against fungal molds. In contrast to other polyene macrolides, such as nystatin or amphotericin B, natamycin does not form pores in yeast membranes, and its mode of action is not well understood. Here, we have employed a variety of spectroscopic methods, computational modeling, and membrane reconstitution to study the molecular interactions of natamycin underlying its antifungal activity. We find that natamycin forms aggregates in an aqueous solution with strongly altered optical properties compared to monomeric natamycin. Interaction of natamycin with model membranes results in a concentration-dependent fluorescence increase which is more pronounced for ergosterol- compared to cholesterol-containing membranes up to 20 mol% sterol. Evidence for formation of specific ergosterol-natamycin complexes in the bilayer is provided. Using nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy, we find that natamycin sequesters sterols, thereby interfering with their well-known ability to order acyl chains in lipid bilayers. This effect is more pronounced for membranes containing the sterol of fungi, ergosterol, compared to those containing mammalian cholesterol. Natamycin interferes with ergosterol-dependent transport of lysine by the yeast transporter Lyp1, which we propose to be due to the sequestering of ergosterol, a mechanism that also affects other plasma membrane proteins. Our results provide a mechanistic explanation for the selective antifungal activity of natamycin, which can set the stage for rational design of novel polyenes in the future.
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Affiliation(s)
- Maria Szomek
- Department of Biochemistry and Molecular Biology, PhyLife, Physical Life Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Hanna-Loisa Walther
- Department of Biochemistry and Molecular Biology, PhyLife, Physical Life Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Holger A Scheidt
- Institute for Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, 04107 Leipzig, Germany
| | - Peter Müller
- Department of Biology, Humboldt University Berlin, Invalidenstr. 43, 10115 Berlin, Germany
| | - Sebastian Obermaier
- Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 Groningen, the Netherlands
| | - Bert Poolman
- Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 Groningen, the Netherlands
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, PhyLife, Physical Life Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark.
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10
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Wüstner D. Image segmentation and separation of spectrally similar dyes in fluorescence microscopy by dynamic mode decomposition of photobleaching kinetics. BMC Bioinformatics 2022; 23:334. [PMID: 35962314 PMCID: PMC9373304 DOI: 10.1186/s12859-022-04881-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Accepted: 08/03/2022] [Indexed: 12/03/2022] Open
Abstract
Background Image segmentation in fluorescence microscopy is often based on spectral separation of fluorescent probes (color-based segmentation) or on significant intensity differences in individual image regions (intensity-based segmentation). These approaches fail, if dye fluorescence shows large spectral overlap with other employed probes or with strong cellular autofluorescence. Results Here, a novel model-free approach is presented which determines bleaching characteristics based on dynamic mode decomposition (DMD) and uses the inferred photobleaching kinetics to distinguish different probes or dye molecules from autofluorescence. DMD is a data-driven computational method for detecting and quantifying dynamic events in complex spatiotemporal data. Here, DMD is first used on synthetic image data and thereafter used to determine photobleaching characteristics of a fluorescent sterol probe, dehydroergosterol (DHE), compared to that of cellular autofluorescence in the nematode Caenorhabditis elegans. It is shown that decomposition of those dynamic modes allows for separating probe from autofluorescence without invoking a particular model for the bleaching process. In a second application, DMD of dye-specific photobleaching is used to separate two green-fluorescent dyes, an NBD-tagged sphingolipid and Alexa488-transferrin, thereby assigning them to different cellular compartments. Conclusions Data-based decomposition of dynamic modes can be employed to analyze spatially varying photobleaching of fluorescent probes in cells and tissues for spatial and temporal image segmentation, discrimination of probe from autofluorescence and image denoising. The new method should find wide application in analysis of dynamic fluorescence imaging data. Supplementary Information The online version contains supplementary material available at 10.1186/s12859-022-04881-x.
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Affiliation(s)
- Daniel Wüstner
- Department of Biochemistry and Molecular Biology and Physics of Life Sciences (PhyLife) Center, University of Southern Denmark, Campusvej 55, DK-5230, Odense, Denmark.
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11
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Juhl AD, Anvarian Z, Kuhns S, Berges J, Andersen JS, Wüstner D, Pedersen LB. Transient accumulation and bidirectional movement of KIF13B in primary cilia. J Cell Sci 2022; 136:275012. [DOI: 10.1242/jcs.259257] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 04/01/2022] [Indexed: 10/18/2022] Open
Abstract
Primary cilia are microtubule-based sensory organelles whose assembly and function rely on the conserved bidirectional intraflagellar transport (IFT) system, which is powered by anterograde kinesin-2 and retrograde cytoplasmic dynein 2 motors. Nematodes additionally employ a cell type-specific kinesin-3 motor, KLP-6, which moves within cilia independently of IFT and regulates ciliary content and function. Here we provide evidence that a KLP-6 homolog, KIF13B, undergoes bursts of bidirectional movement within primary cilia of cultured immortalized human retinal pigment epithelial (hTERT-RPE1) cells. Anterograde and retrograde intraciliary velocities of KIF13B were similar to those of IFT (IFT172-eGFP), but intraciliary movement of KIF13B required its own motor domain and appeared to be cell-type specific. Our work provides the first demonstration of motor-driven, intraciliary movement by a vertebrate kinesin other than kinesin-2 motors.
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Affiliation(s)
- Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Zeinab Anvarian
- Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark
| | - Stefanie Kuhns
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Julia Berges
- Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark
- Department of Biomedicine, Facultad Ciencias Experimentales, Universidad Francisco de Vitoria, Ctra. Pozuelo-Majadahonda Km. 1.800, 28223 Pozuelo de Alarcón (Madrid), Spain
| | - Jens S. Andersen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Lotte B. Pedersen
- Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark
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12
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Abstract
Cholesterol is an essential molecule in cellular membranes, but too much cholesterol can be toxic. Therefore, mammalian cells have developed complex mechanisms to remove excess cholesterol. In this review article, we discuss what is known about such efflux pathways including a discussion of reverse cholesterol transport and formation of high-density lipoprotein, the function of ABC transporters and other sterol efflux proteins, and we highlight their role in human diseases. Attention is paid to the biophysical principles governing efflux of sterols from cells. We also discuss recent evidence for cholesterol efflux by the release of exosomes, microvesicles, and migrasomes. The role of the endo-lysosomal network, lipophagy, and selected lysosomal transporters, such as Niemann Pick type C proteins in cholesterol export from cells is elucidated. Since oxysterols are important regulators of cellular cholesterol efflux, their formation, trafficking, and secretion are described briefly. In addition to discussing results obtained with traditional biochemical methods, focus is on studies that use established and novel bioimaging approaches to obtain insight into cholesterol efflux pathways, including fluorescence and electron microscopy, atomic force microscopy, X-ray tomography as well as mass spectrometry imaging.
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Affiliation(s)
- Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, PhyLife, Physical Life Sciences, University of Southern Denmark, Odense, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, PhyLife, Physical Life Sciences, University of Southern Denmark, Odense, Denmark
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13
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Reinholdt P, Joensen LE, Petersen D, Szomek M, Mularski A, Simonsen AC, Kongsted J, Wüstner D. Photophysical and Structural Characterization of Intrinsically Fluorescent Sterol Aggregates. J Phys Chem B 2021; 125:5838-5852. [PMID: 34061522 DOI: 10.1021/acs.jpcb.1c00628] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Self-association of cholesterol into aggregates and crystals is a hallmark of developing atherosclerosis. Intrinsically fluorescent sterols, such as dehydroergosterol (DHE), can be used to study sterol aggregation by fluorescence spectroscopy and microscopy, but a thorough understanding of DHE's photophysical and structural properties in the aggregated state is missing. Here, we show that DHE forms submicron fluorescent aggregates when evaporated from an ethanol solution. Using atomic force microscopy, we find that DHE, like cholesterol, forms compact oblate-shape aggregates of <100 nm in diameter. DHE's fluorescence is lowered in the aggregate compared to the monomeric form, and characteristic spectral changes accompany the aggregation process. Electronic structure calculations of DHE dimers in water indicate that Frenkel-type exciton coupling contributes to the lowered DHE fluorescence in the aggregates. Using molecular dynamics (MD) simulations, we show that DHE forms compact aggregates on the nanosecond scale and with strong intermolecular attraction, in which a broad range of orientations, and therefore electronic couplings, will take place. Tight packing of DHE in aggregates also lowers the apparent absorption cross section, further reducing the molecular brightness of the aggregates. Our results pave the way for systematic solubility studies of intrinsically fluorescent analogues of biologically relevant sterols.
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Affiliation(s)
- Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Lütje E Joensen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Daniel Petersen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Anna Mularski
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Adam Cohen Simonsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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14
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Juhl AD, Heegaard CW, Werner S, Schneider G, Krishnan K, Covey DF, Wüstner D. Quantitative imaging of membrane contact sites for sterol transfer between endo-lysosomes and mitochondria in living cells. Sci Rep 2021; 11:8927. [PMID: 33903617 PMCID: PMC8076251 DOI: 10.1038/s41598-021-87876-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Accepted: 03/31/2021] [Indexed: 01/25/2023] Open
Abstract
Mitochondria receive cholesterol from late endosomes and lysosomes (LE/LYSs) or from the plasma membrane for production of oxysterols and steroid hormones. This process depends on the endo-lysosomal sterol transfer protein Niemann Pick C2 (NPC2). Using the intrinsically fluorescent cholesterol analog, cholestatrienol, we directly observe sterol transport to mitochondria in fibroblasts upon treating NPC2 deficient human fibroblasts with NPC2 protein. Soft X-ray tomography reveals the ultrastructure of mitochondria and discloses close contact to endosome-like organelles. Using fluorescence microscopy, we localize endo-lysosomes containing NPC2 relative to mitochondria based on the Euclidian distance transform and use statistical inference to show that about 30% of such LE/LYSs are in contact to mitochondria in human fibroblasts. Using Markov Chain Monte Carlo image simulations, we show that interaction between both organelle types, a defining feature of membrane contact sites (MCSs) can give rise to the observed spatial organelle distribution. We devise a protocol to determine the surface fraction of endo-lysosomes in contact with mitochondria and show that this fraction does not depend on functional NPC1 or NPC2 proteins. Finally, we localize MCSs between LE/LYSs containing NPC2 and mitochondria in time-lapse image sequences and show that they either form transiently or remain stable for tens of seconds. Lasting MCSs between endo-lysosomes containing NPC2 and mitochondria move by slow anomalous sub-diffusion, providing location and time for sterol transport between both organelles. Our quantitative imaging strategy will be of high value for characterizing the dynamics and function of MCSs between various organelles in living cells.
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Affiliation(s)
- Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark
| | - Christian W Heegaard
- Department of Molecular Biology and Genetics, University of Aarhus, 8000, Aarhus C, Denmark
| | - Stephan Werner
- Department of X-Ray Microscopy, Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489, Berlin, Germany
| | - Gerd Schneider
- Department of X-Ray Microscopy, Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489, Berlin, Germany
| | - Kathiresan Krishnan
- Department of Developmental Biology, Washington University, St. Louis, MO, 63110, USA
| | - Douglas F Covey
- Department of Developmental Biology, Washington University, St. Louis, MO, 63110, USA
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark.
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15
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Hornum M, Mulberg MW, Szomek M, Reinholdt P, Brewer JR, Wüstner D, Kongsted J, Nielsen P. Substituted 9-Diethylaminobenzo[ a]phenoxazin-5-ones (Nile Red Analogues): Synthesis and Photophysical Properties. J Org Chem 2021; 86:1471-1488. [PMID: 33370098 DOI: 10.1021/acs.joc.0c02346] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Nile Red is a benzo[a]phenoxazone dye containing a diethylamino substituent at the 9-position. In recent years, it has become a popular histological stain for cellular membranes and lipid droplets due to its unrivaled fluorescent properties in lipophilic environments. This makes it an attractive lead for chemical decoration to tweak its attributes and optimize it for more specialized microscopy techniques, e.g., fluorescence lifetime imaging or two-photon excited fluorescence microscopy, to which Nile Red has never been optimized. Herein, we present synthesis approaches to a series of monosubstituted Nile Red derivatives (9-diethylbenzo[a]phenoxazin-5-ones) starting from 1-naphthols or 1,3-naphthalenediols. The solvatochromic responsiveness of these fluorophores is reported with focus on how the substituents affect the absorption and emission spectra, luminosity, fluorescence lifetimes, and two-photon absorptivity. Several of the analogues emerge as strong candidates for reporting the polarity of their local environment. Specifically, the one- and two-photon excited fluorescence of Nile Red turns out to be very responsive to substitution, and the spectroscopic features can be finely tuned by judiciously introducing substituents of distinct electronic character at specific positions. This new toolkit of 9-diethylbenzo[a]phenoxazine-5-ones constitutes a step toward the next generation of optical molecular probes for advancing the understanding of lipid structures and cellular processes.
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16
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Juhl AD, Lund FW, Jensen MLV, Szomek M, Heegaard CW, Guttmann P, Werner S, McNally J, Schneider G, Kapishnikov S, Wüstner D. Niemann Pick C2 protein enables cholesterol transfer from endo-lysosomes to the plasma membrane for efflux by shedding of extracellular vesicles. Chem Phys Lipids 2021; 235:105047. [PMID: 33422548 DOI: 10.1016/j.chemphyslip.2020.105047] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Accepted: 12/28/2020] [Indexed: 10/22/2022]
Abstract
The Niemann-Pick C2 protein (NPC2) is a sterol transfer protein in the lumen of late endosomes and lysosomes (LE/LYSs). Absence of functional NPC2 leads to endo-lysosomal buildup of cholesterol and other lipids. How NPC2's known capacity to transport cholesterol between model membranes is linked to its function in living cells is not known. Using quantitative live-cell imaging combined with modeling of the efflux kinetics, we show that NPC2-deficient human fibroblasts can export the cholesterol analog dehydroergosterol (DHE) from LE/LYSs. Internalized NPC2 accelerated sterol efflux extensively, accompanied by reallocation of LE/LYSs containing fluorescent NPC2 and DHE to the cell periphery. Using quantitative fluorescence loss in photobleaching of TopFluor-cholesterol (TF-Chol), we estimate a residence time for a rapidly exchanging sterol pool in LE/LYSs localized in close proximity to the plasma membrane (PM), of less than one min and observed non-vesicular sterol exchange between LE/LYSs and the PM. Excess sterol was released from the PM by shedding of cholesterol-rich vesicles. The ultrastructure of such vesicles was analyzed by combined fluorescence and cryo soft X-ray tomography (SXT), revealing that they can contain lysosomal cargo and intraluminal vesicles. Treating cells with apoprotein A1 and with nuclear receptor liver X-receptor (LXR) agonists to upregulate expression of ABC transporters enhanced cholesterol efflux from the PM, at least partly by accelerating vesicle release. We conclude that NPC2 inside LE/LYSs facilitates non-vesicular sterol exchange with the PM for subsequent sterol efflux to acceptor proteins and for shedding of sterol-rich vesicles from the cell surface.
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Affiliation(s)
- Alice Dupont Juhl
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230, Odense M, Denmark
| | - Frederik W Lund
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230, Odense M, Denmark
| | - Maria Louise V Jensen
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230, Odense M, Denmark
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230, Odense M, Denmark
| | - Christian W Heegaard
- Department of Molecular Biology and Genetics, University of Aarhus, DK-8000, Aarhus C, Denmark
| | - Peter Guttmann
- Department X-Ray Microscopy, Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489, Berlin, Germany
| | - Stephan Werner
- Department X-Ray Microscopy, Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489, Berlin, Germany
| | - James McNally
- Department X-Ray Microscopy, Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489, Berlin, Germany
| | - Gerd Schneider
- Department X-Ray Microscopy, Helmholtz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489, Berlin, Germany
| | - Sergey Kapishnikov
- Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230, Odense M, Denmark.
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17
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Work EM, Ferraudi G, Kiefer L, Liu G, Grigalunas M, Bhardwaj A, Kaur R, Dempsey JM, Wüstner D, Helquist P, Wiest O. Design, Synthesis, and Evaluation of a Luminescent Cholesterol Mimic. J Org Chem 2020; 86:1612-1621. [PMID: 33369429 DOI: 10.1021/acs.joc.0c02460] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The development of new chemical tools with improved properties is essential to chemical and cell biology. Of particular interest is the development of mimics of small molecules with important cellular function that allow the direct observation of their trafficking in a cell. To this end, a novel 15-azasterol has been designed and synthesized as a luminescent cholesterol mimic for the monitoring of cholesterol trafficking. The brightness of this probe, which is ∼32-times greater than the widely used dehydroergosterol probe, is combined with resistance to photobleaching in solution and in human fibroblasts and an exceptionally large Stokes-like shift of ∼150-200 nm. The photophysical properties of the probe have been studied experimentally and computationally, suggesting an intersystem crossing to the triplet excited state with subsequent phosphorescent decay. Molecular dynamics simulations show a similar binding mode of cholesterol and the azasterol probe to NPC proteins, demonstrating the structural similarity of the probe to cholesterol.
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Affiliation(s)
- Emily M Work
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46566, United States
| | - Guillermo Ferraudi
- Radiation Research Laboratory, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Luke Kiefer
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46566, United States
| | - Gang Liu
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46566, United States
| | - Michael Grigalunas
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46566, United States
| | - Atul Bhardwaj
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46566, United States
| | - Rasmin Kaur
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Janel M Dempsey
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46566, United States
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Paul Helquist
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46566, United States
| | - Olaf Wiest
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46566, United States
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18
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Szomek M, Reinholdt P, Petersen D, Caci A, Kongsted J, Wüstner D. Direct observation of nystatin binding to the plasma membrane of living cells. Biochim Biophys Acta Biomembr 2020; 1863:183528. [PMID: 33279513 DOI: 10.1016/j.bbamem.2020.183528] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 11/24/2020] [Accepted: 11/30/2020] [Indexed: 01/04/2023]
Abstract
Nystatin is an antifungal polyene macrolide which is widely applied to treat yeast infections. Nystatin has also been used as a laboratory tool to inhibit endocytic processes in mammalian cells. The interaction of nystatin with model membranes has been studied thoroughly by various spectroscopic methods, making use of its weak fluorescence in the ultraviolet (UV). Studying its interaction with cells would require direct imaging, which, so far, required attachment of a fluorophore to nystatin. Using UV-sensitive microscopy, we show here how to visualize the interaction of nystatin with the plasma membrane (PM) directly. We find that nystatin forms micron-sized aggregates in buffer, and molecular dynamics simulations confirm that nystatin rapidly self-assembles into aggregates in aqueous solution. Using UV-sensitive microscopy, we find that large nystatin aggregates adhere to the surface of Chinese Hamster Ovarian (CHO) cells, causing slow spreading of nystatin fluorescence into the PM. Binding of nystatin to CHO cells does not interfere with cellular uptake or lateral membrane diffusion of the cholesterol analogue TopFluor-cholesterol (TF-Chol). Nystatin binds extensively to the PM of yeast cells as inferred from a strong UV signal in this membrane. Loading a yeast mutant unable to synthesize ergosterol with cholesterol gave much less nystatin membrane staining compared to loading such cells with ergosterol. These results explain the selective fungicidal effect of nystatin by differential interaction of nystatin with yeast membranes containing ergosterol compared to the mammalian cholesterol. Our combined experimental and computational approach provides a toolset for future design of new polyene macrolides.
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Affiliation(s)
- Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Daniel Petersen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Atenisa Caci
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej55, DK-5230 Odense M, Denmark.
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19
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Moesgaard L, Petersen D, Szomek M, Reinholdt P, Winkler MBL, Frain KM, Müller P, Pedersen BP, Kongsted J, Wüstner D. Mechanistic Insight into Lipid Binding to Yeast Niemann Pick Type C2 Protein. Biochemistry 2020; 59:4407-4420. [PMID: 33141558 DOI: 10.1021/acs.biochem.0c00574] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Niemann Pick type C2 (NPC2) is a small sterol binding protein in the lumen of late endosomes and lysosomes. We showed recently that the yeast homologue of NPC2 together with its binding partner NCR1 mediates integration of ergosterol, the main sterol in yeast, into the vacuolar membrane. Here, we study the binding specificity and the molecular details of lipid binding to yeast NPC2. We find that NPC2 binds fluorescence- and spin-labeled analogues of phosphatidylcholine (PC), phosphatidylserine, phosphatidylinositol (PI), and sphingomyelin. Spectroscopic experiments show that NPC2 binds lipid monomers in solution but can also interact with lipid analogues in membranes. We further identify ergosterol, PC, and PI as endogenous NPC2 ligands. Using molecular dynamics simulations, we show that NPC2's binding pocket can adapt to the ligand shape and closes around bound ergosterol. Hydrophobic interactions stabilize the binding of ergosterol, but binding of phospholipids is additionally stabilized by electrostatic interactions at the mouth of the binding site. Our work identifies key residues that are important in stabilizing the binding of a phospholipid to yeast NPC2, thereby rationalizing future mutagenesis studies. Our results suggest that yeast NPC2 functions as a general "lipid solubilizer" and binds a variety of amphiphilic lipid ligands, possibly to prevent lipid micelle formation inside the vacuole.
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Affiliation(s)
- Laust Moesgaard
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Daniel Petersen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Mikael B L Winkler
- Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10, Aarhus C 8000, Denmark
| | - Kelly May Frain
- Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10, Aarhus C 8000, Denmark
| | - Peter Müller
- Department of Biology, Humboldt University Berlin, Unter den Linden 6, 10099 Berlin, Germany
| | - Bjørn Panyella Pedersen
- Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10, Aarhus C 8000, Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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20
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Szomek M, Moesgaard L, Reinholdt P, Haarhøj Hald SB, Petersen D, Krishnan K, Covey DF, Kongsted J, Wüstner D. Membrane organization and intracellular transport of a fluorescent analogue of 27-hydroxycholesterol. Chem Phys Lipids 2020; 233:105004. [PMID: 33137329 DOI: 10.1016/j.chemphyslip.2020.105004] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2020] [Revised: 09/29/2020] [Accepted: 10/24/2020] [Indexed: 11/30/2022]
Abstract
Oxysterols are cholesterol metabolites with multiple functions in controlling cellular homeostasis. In particular, 27-hydroxycholesterol (27-OH-Chol) has been shown to regulate a variety of physiological functions, but little is known about its uptake, intracellular trafficking, and efflux from cells. This is largely due to a lack of suitable analogs of 27-OH-Chol, which mimic this oxysterol closely. Here, we present the intrinsically fluorescent 27-hydroxy-cholestatrienol (27-OH-CTL), which differs from 27-OH-Chol only by having two additional double bonds in the steroid ring system. Based on molecular dynamics (MD) simulations, we show that 27-OH-CTL possesses almost identical membrane properties compared to 27-OH-Chol. By comparative imaging of 27-OH-CTL and of the cholesterol analogue cholestatrienol (CTL) in living cells, we assess the impact of a single hydroxy group on sterol trafficking. We find that human fibroblasts take up more CTL than 27-OH-CTL, but efflux the oxysterol analogue more efficiently. For both sterols, efflux includes shedding of vesicles from the plasma membrane. Intracellular, 27-OH-CTL accumulates primarily in lipid droplets (LDs), while CTL is mostly found in endosomes and lysosomes. Using fluorescence recovery after photobleaching (FRAP), we find for both sterols a rapidly exchanging pool, which moves orders of magnitude faster than sterol containing vesicles and LDs. In summary, by applying a new fluorescent derivative of 27-OH-Chol we demonstrate that human cells can distinguish sterols based on a single hydroxy group in the side chain, resulting in different transport itineraries, dynamics, and efflux kinetics. Both intrinsically fluorescent cholesterol and oxysterol analogues show rapid non-vesicular transport in human fibroblasts.
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Affiliation(s)
- Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Laust Moesgaard
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Sophia Bell Haarhøj Hald
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Daniel Petersen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Kathiresan Krishnan
- Department of Developmental Biology, Washington University, St. Louis, MO 63110, USA
| | - Douglas F Covey
- Department of Developmental Biology, Washington University, St. Louis, MO 63110, USA
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
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21
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Dubey V, Bozorg B, Wüstner D, Khandelia H. Cholesterol binding to the sterol-sensing region of Niemann Pick C1 protein confines dynamics of its N-terminal domain. PLoS Comput Biol 2020; 16:e1007554. [PMID: 33021976 PMCID: PMC7537887 DOI: 10.1371/journal.pcbi.1007554] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Accepted: 07/02/2020] [Indexed: 12/12/2022] Open
Abstract
Lysosomal accumulation of cholesterol is a hallmark of Niemann Pick type C (NPC) disease caused by mutations primarily in the lysosomal membrane protein NPC1. NPC1 contains a transmembrane sterol-sensing domain (SSD), which is supposed to regulate protein activity upon cholesterol binding, but the mechanisms underlying this process are poorly understood. Using atomistic simulations, we show that in the absence of cholesterol in the SSD, the luminal domains of NPC1 are highly dynamic, resulting in the disengagement of the NTD from the rest of the protein. The disengaged NPC1 adopts a flexed conformation that approaches the lipid bilayer, and could represent a conformational state primed to receive a sterol molecule from the soluble lysosomal cholesterol carrier NPC2. The binding of cholesterol to the SSD of NPC1 allosterically suppresses the conformational dynamics of the luminal domains resulting in an upright NTD conformation. The presence of an additional 20% cholesterol in the membrane has negligible impact on this process. The additional presence of an NTD-bound cholesterol suppresses the flexing of the NTD. We propose that cholesterol acts as an allosteric effector, and the modulation of NTD dynamics by the SSD-bound cholesterol constitutes an allosteric feedback mechanism in NPC1 that controls cholesterol abundance in the lysosomal membrane. Cholesterol is absorbed from LDL particles in esterified form, and is broken down to free cholesterol in the lysosomes of cells, from where cholesterol must be transported to other cellular compartments such as the plasma membrane. The Niemann Pick type C (NPC) diseases arise from deficient cholesterol transport and result from mutations in the cholesterol transport protein NPC1. Using computer simulations, we show that cholesterol, when bound to one part of NPC1, can control the structural transitions of an 8-nm distant, different part of NPC1 protein called the N-terminal domain (NTD). Such long-range control of protein conformations (allostery), controls a wide range of cellular functions mediated by proteins. Fundamental molecular insights into the function of the NPC1 protein can potentially lead to better pharmaceutical interventions for the NPC diseases.
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Affiliation(s)
- Vikas Dubey
- PhyLife Physical Life Sciences, Department of Physics Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
- Department of Physics Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
| | - Behruz Bozorg
- PhyLife Physical Life Sciences, Department of Physics Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
- Department of Physics Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
| | - Daniel Wüstner
- PhyLife Physical Life Sciences, Department of Physics Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
| | - Himanshu Khandelia
- PhyLife Physical Life Sciences, Department of Physics Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
- Department of Physics Chemistry, and Pharmacy, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
- MEMPHYS: Center for Biomembrane Physics, Odense M, Denmark
- * E-mail:
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22
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Moesgaard L, Reinholdt P, Wüstner D, Kongsted J. Modeling the Sterol-Binding Domain of Aster-A Provides Insight into Its Multiligand Specificity. J Chem Inf Model 2020; 60:2268-2281. [PMID: 32233488 DOI: 10.1021/acs.jcim.0c00086] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Intracellular transport of cholesterol and related sterols relies to a large degree on nonvesicular mechanisms, which are only partly understood at the molecular level. Aster proteins belonging to the Lam family of sterol transfer proteins have recently been identified as important catalysts of nonvesicular sterol exchange between the plasma membrane (PM) and endoplasmic reticulum (ER). Here, we used a range of computational tools to study the molecular mechanisms underlying sterol binding as well as multisterol ligand specificity of Aster-A. Our study focused primarily on gaining atomistic insight into the bound ligand-protein complex and was, on this basis, performed in the absence of any membrane. Molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) calculations provide a rationale for the experimentally found ranking of binding affinities of various sterols to Aster-A. In particular, the polarity of the sterols and the length of their alkyl chain could be identified as being critical determinants of ligand affinity. A Gibbs free energy decomposition identified a charged residue, Glu444, at the base of the binding pose as an important control point for sterol binding. Removing its net charge via protonation was found to cause significant changes to the environment surrounding this residue. In addition, the protonation of Glu444 was found to be paralleled by a large redistribution of molecular flexibility in the Aster domain. This finding was supplemented by multiple branched adaptive steered molecular dynamics (MB-ASMD) simulations by which we defined a possible molecular path for sterol release and demonstrated the importance of Glu444 in this process.
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Affiliation(s)
- Laust Moesgaard
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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23
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Hornum M, Reinholdt P, Zaręba JK, Jensen BB, Wüstner D, Samoć M, Nielsen P, Kongsted J. One- and two-photon solvatochromism of the fluorescent dye Nile Red and its CF3, F and Br-substituted analogues. Photochem Photobiol Sci 2020; 19:1382-1391. [DOI: 10.1039/d0pp00076k] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Nile Red is a valuable fluorescent dye for studying lipophilic environments. This study presents how solvent polarity and decoration with simple electron-withdrawing substituents influence its absorption, fluorescence and two-photon cross-section.
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Affiliation(s)
- Mick Hornum
- Department of Physics
- Chemistry and Pharmacy
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
| | - Peter Reinholdt
- Department of Physics
- Chemistry and Pharmacy
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
| | - Jan K. Zaręba
- Advanced Materials Engineering and Modelling Group
- Wrocław University of Science and Technology
- 50-370 Wrocław
- Poland
| | - Brian B. Jensen
- Department of Biochemistry and Molecular Biology
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
| | - Marek Samoć
- Advanced Materials Engineering and Modelling Group
- Wrocław University of Science and Technology
- 50-370 Wrocław
- Poland
| | - Poul Nielsen
- Department of Physics
- Chemistry and Pharmacy
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
| | - Jacob Kongsted
- Department of Physics
- Chemistry and Pharmacy
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
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24
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Poongavanam V, Kongsted J, Wüstner D. Computational Modeling Explains the Multi Sterol Ligand Specificity of the N-Terminal Domain of Niemann-Pick C1-Like 1 Protein. ACS Omega 2019; 4:20894-20904. [PMID: 31867479 PMCID: PMC6921270 DOI: 10.1021/acsomega.9b01668] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Accepted: 10/18/2019] [Indexed: 06/10/2023]
Abstract
Niemann-Pick C1 like 1 (NPC1L1) is a sterol transporter expressed in the apical membrane of enterocytes and hepatocytes. NPC1L1 resembles the lysosomal NPC1 protein including an N-terminal domain (NTD), which binds a variety of sterols. The molecular mechanisms underlying this multiligand specificity of the NTD of NPC1L1 (NPC1L1-NTD) are not known. On the basis of the crystal structure of NPC1L1-NTD, we have investigated the structural details of protein-sterol interactions using molecular mechanics Poisson Boltzmann surface area calculations here. We found a good agreement between experimental and calculated binding affinities with similar ranking of various sterol ligands. We defined hydrogen bonding of sterol ligands via the 3'-β-hydroxy group inside the binding pose as instrumental in stabilizing the interaction. A leucine residue (LEU213) at the mouth of the binding pocket transiently opens to allow for the access of sterol into the binding pose. Our calculations also predict that NPC1L1-NTD binds polyene sterols, such as dehydroergosterol or cholestatrienol with high affinity, which validates their use in future experiments as close intrinsically fluorescent cholesterol analogs. A free energy decomposition and computational mutation analysis revealed that the binding of various sterols to NPC1L1-NTD depends critically on specific amino acid residues within the binding pocket. Some of these residues were previously detected as being relevant for intestinal cholesterol absorption. We show that clinically known mutations in the NPC1L1-NTD associated with lowered risk of coronary heart disease result in strongly reduced binding energies, providing a molecular explanation for the clinical phenotype.
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Affiliation(s)
- Vasanthanathan Poongavanam
- Department of Physics, Chemistry and Pharmacy and Department of Biochemistry and
Molecular Biology, University of Southern
Denmark, DK-5230 Odense M, Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy and Department of Biochemistry and
Molecular Biology, University of Southern
Denmark, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Physics, Chemistry and Pharmacy and Department of Biochemistry and
Molecular Biology, University of Southern
Denmark, DK-5230 Odense M, Denmark
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25
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Winkler MBL, Kidmose RT, Szomek M, Thaysen K, Rawson S, Muench SP, Wüstner D, Pedersen BP. Structural Insight into Eukaryotic Sterol Transport through Niemann-Pick Type C Proteins. Cell 2019; 179:485-497.e18. [PMID: 31543266 DOI: 10.1016/j.cell.2019.08.038] [Citation(s) in RCA: 86] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 07/05/2019] [Accepted: 08/21/2019] [Indexed: 12/24/2022]
Abstract
Niemann-Pick type C (NPC) proteins are essential for sterol homeostasis, believed to drive sterol integration into the lysosomal membrane before redistribution to other cellular membranes. Here, using a combination of crystallography, cryo-electron microscopy, and biochemical and in vivo studies on the Saccharomyces cerevisiae NPC system (NCR1 and NPC2), we present a framework for sterol membrane integration. Sterols are transferred between hydrophobic pockets of vacuolar NPC2 and membrane-protein NCR1. NCR1 has its N-terminal domain (NTD) positioned to deliver a sterol to a tunnel connecting NTD to the luminal membrane leaflet 50 Å away. A sterol is caught inside this tunnel during transport, and a proton-relay network of charged residues in the transmembrane region is linked to this tunnel supporting a proton-driven transport mechanism. We propose a model for sterol integration that clarifies the role of NPC proteins in this essential eukaryotic pathway and that rationalizes mutations in patients with Niemann-Pick disease type C.
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Affiliation(s)
- Mikael B L Winkler
- Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10, Aarhus C 8000, Denmark
| | - Rune T Kidmose
- Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10, Aarhus C 8000, Denmark
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M 5230, Denmark
| | - Katja Thaysen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M 5230, Denmark
| | - Shaun Rawson
- School of Biomedical Sciences and The Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Stephen P Muench
- School of Biomedical Sciences and The Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M 5230, Denmark
| | - Bjørn Panyella Pedersen
- Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10, Aarhus C 8000, Denmark; Aarhus Institute of Advanced Studies, Aarhus University, Høegh-Guldbergs Gade 6B, Aarhus C 8000, Denmark.
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26
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Petersen D, Reinholdt P, Szomek M, Hansen SK, Poongavanam V, Dupont A, Heegaard CW, Krishnan K, Fujiwara H, Covey DF, Ory DS, Kongsted J, Wüstner D. Binding and intracellular transport of 25-hydroxycholesterol by Niemann-Pick C2 protein. Biochim Biophys Acta Biomembr 2019; 1862:183063. [PMID: 31521631 DOI: 10.1016/j.bbamem.2019.183063] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2019] [Revised: 08/26/2019] [Accepted: 09/09/2019] [Indexed: 12/16/2022]
Abstract
Side-chain oxidized cholesterol derivatives, like 25-hydroxycholesterol (25-OH-Chol) are important regulators of cellular cholesterol homeostasis. How transport of oxysterols through the endo-lysosomal pathway contributes to their biological function is not clear. The Niemann-Pick C2 protein (NPC2) is a small lysosomal sterol transfer protein required for export of cholesterol from late endosomes and lysosomes (LE/LYSs). Here, we show that 25-hydroxy-cholestatrienol, (25-OH-CTL), an intrinsically fluorescent analogue of 25-OH-Chol, becomes trapped in LE/LYSs of NPC2-deficient fibroblasts, but can efflux from the cells even in the absence of NPC2 upon removal of the sterol source. Fluorescence recovery after photobleaching (FRAP) of 25-OH-CTL in endo-lysosomes was rapid and extensive and only partially dependent on NPC2 function. Using quenching of NPC2's intrinsic fluorescence, we show that 25-OH-Chol and 25-OH-CTL can bind to NPC2 though with lower affinity compared to cholesterol and its fluorescent analogues, cholestatrienol (CTL) and dehydroergosterol (DHE). This is confirmed by calculations of binding energies which additionally show that 25-OH-CTL can bind in two orientations to NPC2, in stark contrast to cholesterol and its analogues. We conclude that NPC2's affinity for all sterols is energetically favored over their self-aggregation in the lysosomal lumen. Lysosomal export of 25-OH-Chol is not strictly dependent on the NPC2 protein.
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Affiliation(s)
- Daniel Petersen
- Department of Biochemistry and Molecular Biology, DK-5230 Odense M, Denmark
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy, DK-5230 Odense M, Denmark
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, DK-5230 Odense M, Denmark
| | | | | | - Alice Dupont
- Department of Biochemistry and Molecular Biology, DK-5230 Odense M, Denmark
| | - Christian W Heegaard
- Department of Molecular Biology and Genetics, University of Aarhus, DK-8000 Aarhus, C, Denmark
| | - Kathiresan Krishnan
- Department of Developmental Biology, Washington University, St. Louis, MO 63110, USA
| | - Hideji Fujiwara
- Department of Developmental Biology, Washington University, St. Louis, MO 63110, USA
| | - Douglas F Covey
- Department of Developmental Biology, Washington University, St. Louis, MO 63110, USA; Taylor Family Institute for Innovative Psychiatric Research, Washington University, St. Louis, MO 63110, USA
| | - Daniel S Ory
- Department of Medicine, Washington University, St. Louis, MO 63110, USA
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, DK-5230 Odense M, Denmark.
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27
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Reinholdt P, Wind S, Wüstner D, Kongsted J. Computational Characterization of a Cholesterol-Based Molecular Rotor in Lipid Membranes. J Phys Chem B 2019; 123:7313-7326. [PMID: 31381343 DOI: 10.1021/acs.jpcb.9b04967] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Biophysical properties of cellular membranes critically depend on their content of cholesterol and its interaction with various other lipid species. Cholesterol-dependent friction at the nanoscale can be studied with molecular rotors, whose quantum yield depends on rotational dynamics of functional groups during their excited state lifetime. Here, we present a detailed computational analysis of a phenyl-BODIPY-linked cholesterol based molecular rotor in direct comparison with the well-known TopFluor-cholesterol. We describe a new parametrization strategy of force field parameters for the BODIPY moiety and carry out extensive molecular dynamics simulations of the probe in membranes in the absence or presence of cholesterol. Our study quantifies the extent of membrane perturbation by these probes, analyzes their tilting resistance in the bilayer and derives dynamic properties directly related to the rotor propensity. We show that phenyl-BODIPY-cholesterol bears potential as a cholesterol-dependent molecular rotor to report about microviscosity of sterol-containing model and cell membranes.
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Affiliation(s)
- Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy , University of Southern Denmark , Campusvej 55 , DK-5230 Odense M , Denmark
| | - Signe Wind
- Department of Physics, Chemistry and Pharmacy , University of Southern Denmark , Campusvej 55 , DK-5230 Odense M , Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology , University of Southern Denmark , Campusvej 55 , DK-5230 Odense M , Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy , University of Southern Denmark , Campusvej 55 , DK-5230 Odense M , Denmark
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28
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Bonvicini A, Reinholdt P, Tognetti V, Joubert L, Wüstner D, Kongsted J. Rational design of novel fluorescent analogues of cholesterol: a “step-by-step” computational study. Phys Chem Chem Phys 2019; 21:15487-15503. [DOI: 10.1039/c9cp01902b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
State-of-the-art quantum chemical and molecular dynamics simulations are used as guidelines in design of novel fluorescent analogues of cholesterol.
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Affiliation(s)
- Andrea Bonvicini
- Normandy Univ. COBRA UMR 6014 & FR 3038
- Université de Rouen
- INSA Rouen
- CNRS
- 76821 Mont Saint Aignan
| | - Peter Reinholdt
- Department of Physics, Chemistry and Pharmacy
- University of Southern Denmark
- Odense M
- Denmark
| | - Vincent Tognetti
- Normandy Univ. COBRA UMR 6014 & FR 3038
- Université de Rouen
- INSA Rouen
- CNRS
- 76821 Mont Saint Aignan
| | - Laurent Joubert
- Normandy Univ. COBRA UMR 6014 & FR 3038
- Université de Rouen
- INSA Rouen
- CNRS
- 76821 Mont Saint Aignan
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology
- University of Southern Denmark
- DK-5230 Odense
- Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy
- University of Southern Denmark
- Odense M
- Denmark
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29
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Stendevad J, Hornum M, Wüstner D, Kongsted J. Photophysical investigation of two emissive nucleosides exhibiting gigantic stokes shifts. Photochem Photobiol Sci 2019; 18:1858-1865. [DOI: 10.1039/c9pp00172g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present discovery of two highly emissive nucleoside analogs with gigantic Stokes shifts and use in silico methods for rationalizing their striking fluorescent properties.
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Affiliation(s)
- Julie Stendevad
- Department of Physics
- Chemistry and Pharmacy
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
| | - Mick Hornum
- Department of Physics
- Chemistry and Pharmacy
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
| | - Jacob Kongsted
- Department of Physics
- Chemistry and Pharmacy
- University of Southern Denmark
- DK-5230 Odense M
- Denmark
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30
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Hansen CV, Schroll HJ, Wüstner D. A discontinuous Galerkin model for fluorescence loss in photobleaching of intracellular polyglutamine protein aggregates. BMC Biophys 2018; 11:7. [PMID: 30519460 PMCID: PMC6264036 DOI: 10.1186/s13628-018-0046-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/22/2018] [Accepted: 10/30/2018] [Indexed: 12/03/2022]
Abstract
Background Intracellular phase separation and aggregation of proteins with extended poly-glutamine (polyQ) stretches are hallmarks of various age-associated neurodegenerative diseases. Progress in our understanding of such processes heavily relies on quantitative fluorescence imaging of suitably tagged proteins. Fluorescence loss in photobleaching (FLIP) is particularly well-suited to study the dynamics of protein aggregation in cellular models of Chorea Huntington and other polyQ diseases, as FLIP gives access to the full spatio-temporal profile of intensity changes in the cell geometry. In contrast to other methods, also dim aggregates become visible during time evolution of fluorescence loss in cellular compartments. However, methods for computational analysis of FLIP data are sparse, and transport models for estimation of transport and diffusion parameters from experimental FLIP sequences are missing. Results In this paper, we present a computational method for analysis of FLIP imaging experiments of intracellular polyglutamine protein aggregates also called inclusion bodies (IBs). By this method, we can determine the diffusion constant and nuclear membrane transport coefficients of polyQ proteins as well as the exchange rates between aggregates and the cytoplasm. Our method is based on a reaction-diffusion multi-compartment model defined on a mesh obtained by segmentation of the cell images from the FLIP sequence. The discontinuous Galerkin (DG) method is used for numerical implementation of our model in FEniCS, which greatly reduces the computing time. The method is applied to representative experimental FLIP sequences, and consistent estimates of all transport parameters are obtained. Conclusions By directly estimating the transport parameters from live-cell image sequences using our new computational FLIP approach surprisingly fast exchange dynamics of mutant Huntingtin between cytoplasm and dim IBs could be revealed. This is likely relevant also for other polyQ diseases. Thus, our method allows for quantifying protein dynamics at different stages of the protein aggregation process in cellular models of neurodegeneration. Electronic supplementary material The online version of this article (10.1186/s13628-018-0046-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Christian V Hansen
- 1Department of Mathematics and Computer Science, University of Southern Denmark, Campusvej 55, Odense M, 5230 Denmark
| | - Hans J Schroll
- 1Department of Mathematics and Computer Science, University of Southern Denmark, Campusvej 55, Odense M, 5230 Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, Campusvej 55, Odense M, 5230 Denmark
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31
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Berzina Z, Solanko LM, Mehadi AS, Jensen MLV, Lund FW, Modzel M, Szomek M, Solanko KA, Dupont A, Nielsen GK, Heegaard CW, Ejsing CS, Wüstner D. Niemann-Pick C2 protein regulates sterol transport between plasma membrane and late endosomes in human fibroblasts. Chem Phys Lipids 2018; 213:48-61. [PMID: 29580834 DOI: 10.1016/j.chemphyslip.2018.03.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 03/13/2018] [Accepted: 03/15/2018] [Indexed: 11/28/2022]
Abstract
Niemann-Pick disease type C2 is a lipid storage disorder in which mutations in the NPC2 protein cause accumulation of lipoprotein-derived cholesterol in late endosomes and lysosomes (LE/LYSs). Whether cholesterol delivered by other means to NPC2 deficient cells also accumulates in LE/LYSs is currently unknown. We show that the close cholesterol analog dehydroergosterol (DHE), when delivered to the plasma membrane (PM) accumulates in LE/LYSs of human fibroblasts lacking functional NPC2. We measured two different time scales of sterol diffusion; while DHE rich LE/LYSs moved by slow anomalous diffusion in disease cells (D ∼ 4.6∙10-4 μm2/sec; α∼0.76), a small pool of sterol could exchange rapidly with D ∼ 3 μm2/s between LE/LYSs, as shown by fluorescence recovery after photobleaching (FRAP). By quantitative lipid mass spectrometry we found that esterification of 13C-labeled cholesterol but not of DHE is reduced 10-fold in disease fibroblasts compared to control cells. Internalized NPC2 rescued the sterol storage phenotype and strongly expanded the dynamic sterol pool seen in FRAP experiments. Together, our study shows that cholesterol esterification and trafficking of sterols between the PM and LE/LYSs depends on a functional NPC2 protein. NPC2 likely acts inside LE/LYSs from where it increases non-vesicular sterol exchange with other organelles.
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Affiliation(s)
- Zane Berzina
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Lukasz M Solanko
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark; Orphazyme ApS, Ole Maales Vej 3, 2200 Copenhagen N, Denmark
| | - Ahmed S Mehadi
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Maria Louise V Jensen
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Frederik W Lund
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Maciej Modzel
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Maria Szomek
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Katarzyna A Solanko
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Alice Dupont
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Gitte Krogh Nielsen
- Department of Molecular Biology and Genetics, University of Aarhus, DK-8000 Aarhus C, Denmark
| | - Christian W Heegaard
- Department of Molecular Biology and Genetics, University of Aarhus, DK-8000 Aarhus C, Denmark
| | - Christer S Ejsing
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, VILLUM Center for Bioanalytical Sciences, University of Southern Denmark, DK-5230 Odense M, Denmark.
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Modzel M, Solanko KA, Szomek M, Hansen SK, Dupont A, Nåbo LJ, Kongsted J, Wüstner D. Live-cell imaging of new polyene sterols for improved analysis of intracellular cholesterol transport. J Microsc 2018. [PMID: 29516493 DOI: 10.1111/jmi.12691] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Analysis of intracellular cholesterol transport by fluorescence microscopy requires suitable fluorescent analogues of cholesterol. Most existing cholesterol analogues contain lipophilic dyes which can compromise the sterol properties in membranes. An alternative strategy is to introduce additional double bonds into the sterol ring system resulting in intrinsic fluorescence, while at the same time keeping the cholesterol-like properties of the analogues. Existing polyene sterols, such as dehydroergosterol (DHE) or cholestatrienol (CTL), however, contain only three double bonds and suffer from low brightness, significant photobleaching and excitation/emission in the ultraviolet region. Thus, special equipment is required to image such sterols. Here, we describe synthesis, characterization and intracellular imaging of new polyene sterols containing four conjugated double bonds in the sterol ring system. We show that such analogues have red-shifted excitation and emission by ∼20 nm compared to DHE or CTL. The red shift was even more pronounced when preventing keto-enol tautomer equilibration by protecting the 3'-hydroxy group with acetate. We show that the latter analogue can be imaged on a conventional wide field microscope with a DAPI/filipin filter cube. The new polyene sterols show reduced photobleaching compared to DHE or CTL allowing for improved deconvolution microscopy of sterol containing cellular membranes.
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Affiliation(s)
- M Modzel
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense, Denmark
| | - K A Solanko
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense, Denmark
| | - M Szomek
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense, Denmark
| | - S K Hansen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense, Denmark
| | - A Dupont
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense, Denmark
| | - L J Nåbo
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense, Denmark
| | - J Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, DK-5230 Odense, Denmark
| | - D Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense, Denmark
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Solanko LM, Sullivan DP, Sere YY, Szomek M, Lunding A, Solanko KA, Pizovic A, Stanchev LD, Pomorski TG, Menon AK, Wüstner D. Ergosterol is mainly located in the cytoplasmic leaflet of the yeast plasma membrane. Traffic 2018; 19:198-214. [DOI: 10.1111/tra.12545] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 12/22/2017] [Accepted: 12/22/2017] [Indexed: 12/20/2022]
Affiliation(s)
- Lukasz M. Solanko
- Department of Biochemistry and Molecular BiologyUniversity of Southern Denmark Odense M Denmark
| | - David P. Sullivan
- Department of BiochemistryWeill Cornell Medical College New York, New York
| | - Yves Y. Sere
- Department of BiochemistryWeill Cornell Medical College New York, New York
| | - Maria Szomek
- Department of Biochemistry and Molecular BiologyUniversity of Southern Denmark Odense M Denmark
| | - Anita Lunding
- Department of Biochemistry and Molecular BiologyUniversity of Southern Denmark Odense M Denmark
| | - Katarzyna A. Solanko
- Department of Biochemistry and Molecular BiologyUniversity of Southern Denmark Odense M Denmark
| | - Azra Pizovic
- Department of Biochemistry and Molecular BiologyUniversity of Southern Denmark Odense M Denmark
| | - Lyubomir D. Stanchev
- Department of Plant and Environmental SciencesUniversity of Copenhagen Frederiksberg C Denmark
- Department of Molecular BiochemistryRuhr‐University Bochum Bochum Germany
| | - Thomas Günther Pomorski
- Department of Plant and Environmental SciencesUniversity of Copenhagen Frederiksberg C Denmark
- Department of Molecular BiochemistryRuhr‐University Bochum Bochum Germany
| | - Anant K. Menon
- Department of BiochemistryWeill Cornell Medical College New York, New York
| | - Daniel Wüstner
- Department of Biochemistry and Molecular BiologyUniversity of Southern Denmark Odense M Denmark
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Abstract
Cellular cholesterol homeostasis relies on precise control of the sterol content of organelle membranes. Obtaining insight into cholesterol trafficking pathways and kinetics by live-cell imaging relies on two conditions. First, one needs to develop suitable analogs that resemble cholesterol as closely as possible with respect to their biophysical and biochemical properties. Second, the cholesterol analogs should have good fluorescence properties. This interferes, however, often with the first requirement, such that the imaging instrumentation must be optimized to collect photons from suboptimal fluorophores, but good cholesterol mimics, such as the intrinsically fluorescent sterols, cholestatrienol (CTL) or dehydroergosterol (DHE). CTL differs from cholesterol only in having two additional double bonds in the ring system, which is why it is slightly fluorescent in the ultraviolet (UV). In the first part of this protocol, we describe how to synthesize and image CTL in living cells relative to caveolin, a structural component of caveolae. In the second part, we explain in detail how to perform time-lapse experiments of commercially available BODIPY-tagged cholesterol (TopFluor-cholesterol®; TF-Chol) in comparison to DHE. Finally, using two-photon time-lapse imaging data of TF-Chol, we demonstrate how to use our imaging toolbox SpatTrack for tracking sterol rich vesicles in living cells over time.
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Affiliation(s)
- Maciej Modzel
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M, 5230, Denmark
| | - Frederik W Lund
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M, 5230, Denmark.,Department of Biochemistry, Weill Medical College of Cornell University, New York, NY, 10065, USA
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M, 5230, Denmark.
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Nåbo LJ, Olsen JMH, Holmgaard List N, Solanko LM, Wüstner D, Kongsted J. Embedding beyond electrostatics—The role of wave function confinement. J Chem Phys 2016; 145:104102. [DOI: 10.1063/1.4962367] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
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Affiliation(s)
- Vasanthanathan Poongavanam
- Department of Physics, Chemistry
and Pharmacy and †Department of Biochemistry and
Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry
and Pharmacy and †Department of Biochemistry and
Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
| | - Daniel Wüstner
- Department of Physics, Chemistry
and Pharmacy and †Department of Biochemistry and
Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark
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Solanko KA, Modzel M, Solanko LM, Wüstner D. Fluorescent Sterols and Cholesteryl Esters as Probes for Intracellular Cholesterol Transport. Lipid Insights 2016; 8:95-114. [PMID: 27330304 PMCID: PMC4902042 DOI: 10.4137/lpi.s31617] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Revised: 04/04/2016] [Accepted: 04/07/2016] [Indexed: 12/20/2022] Open
Abstract
Cholesterol transport between cellular organelles comprised vesicular trafficking and nonvesicular exchange; these processes are often studied by quantitative fluorescence microscopy. A major challenge for using this approach is producing analogs of cholesterol with suitable brightness and structural and chemical properties comparable with those of cholesterol. This review surveys currently used fluorescent sterols with respect to their behavior in model membranes, their photophysical properties, as well as their transport and metabolism in cells. In the first part, several intrinsically fluorescent sterols, such as dehydroergosterol or cholestatrienol, are discussed. These polyene sterols (P-sterols) contain three conjugated double bonds in the steroid ring system, giving them slight fluorescence in ultraviolet light. We discuss the properties of P-sterols relative to cholesterol, outline their chemical synthesis, and explain how to image them in living cells and organisms. In particular, we show that P-sterol esters inserted into low-density lipoprotein can be tracked in the fibroblasts of Niemann–Pick disease using high-resolution deconvolution microscopy. We also describe fluorophore-tagged cholesterol probes, such as BODIPY-, NBD-, Dansyl-, or Pyrene-tagged cholesterol, and eventual esters of these analogs. Finally, we survey the latest developments in the synthesis and use of alkyne cholesterol analogs to be labeled with fluorophores by click chemistry and discuss the potential of all approaches for future applications.
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Affiliation(s)
- Katarzyna A Solanko
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Maciej Modzel
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Lukasz M Solanko
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
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Wüstner D, Lund FW, Röhrl C, Stangl H. Potential of BODIPY-cholesterol for analysis of cholesterol transport and diffusion in living cells. Chem Phys Lipids 2016; 194:12-28. [DOI: 10.1016/j.chemphyslip.2015.08.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Revised: 08/07/2015] [Accepted: 08/12/2015] [Indexed: 01/04/2023]
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Sezgin E, Can FB, Schneider F, Clausen MP, Galiani S, Stanly TA, Waithe D, Colaco A, Honigmann A, Wüstner D, Platt F, Eggeling C. A comparative study on fluorescent cholesterol analogs as versatile cellular reporters. J Lipid Res 2015; 57:299-309. [PMID: 26701325 DOI: 10.1194/jlr.m065326] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Indexed: 12/12/2022] Open
Abstract
Cholesterol (Chol) is a crucial component of cellular membranes, but knowledge of its intracellular dynamics is scarce. Thus, it is of utmost interest to develop tools for visualization of Chol organization and dynamics in cells and tissues. For this purpose, many studies make use of fluorescently labeled Chol analogs. Unfortunately, the introduction of the label may influence the characteristics of the analog, such as its localization, interaction, and trafficking in cells; hence, it is important to get knowledge of such bias. In this report, we compared different fluorescent lipid analogs for their performance in cellular assays: 1) plasma membrane incorporation, specifically the preference for more ordered membrane environments in phase-separated giant unilamellar vesicles and giant plasma membrane vesicles; 2) cellular trafficking, specifically subcellular localization in Niemann-Pick type C disease cells; and 3) applicability in fluorescence correlation spectroscopy (FCS)-based and super-resolution stimulated emission depletion-FCS-based measurements of membrane diffusion dynamics. The analogs exhibited strong differences, with some indicating positive performance in the membrane-based experiments and others in the intracellular trafficking assay. However, none showed positive performance in all assays. Our results constitute a concise guide for the careful use of fluorescent Chol analogs in visualizing cellular Chol dynamics.
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Affiliation(s)
- Erdinc Sezgin
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, OX39DS Oxford, United Kingdom
| | - Fatma Betul Can
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, OX39DS Oxford, United Kingdom
| | - Falk Schneider
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, OX39DS Oxford, United Kingdom
| | - Mathias P Clausen
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, OX39DS Oxford, United Kingdom MEMPHYS-Center for Biomembrane Physics, Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark, 5230 Odense M, Denmark
| | - Silvia Galiani
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, OX39DS Oxford, United Kingdom
| | - Tess A Stanly
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, OX39DS Oxford, United Kingdom
| | - Dominic Waithe
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, OX39DS Oxford, United Kingdom
| | - Alexandria Colaco
- Department of Pharmacology, University of Oxford, OX13QT Oxford, United Kingdom
| | - Alf Honigmann
- Max Planck Institute of Cell Biology and Genetics, 01307 Dresden, Germany
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, 5230 Odense M, Denmark
| | - Frances Platt
- Department of Pharmacology, University of Oxford, OX13QT Oxford, United Kingdom
| | - Christian Eggeling
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, OX39DS Oxford, United Kingdom
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Nåbo LJ, List NH, Witzke S, Wüstner D, Khandelia H, Kongsted J. Design of new fluorescent cholesterol and ergosterol analogs: Insights from theory. Biochimica et Biophysica Acta (BBA) - Biomembranes 2015; 1848:2188-99. [DOI: 10.1016/j.bbamem.2015.04.018] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Revised: 04/24/2015] [Accepted: 04/29/2015] [Indexed: 12/23/2022]
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Wüstner D, Solanko K. How cholesterol interacts with proteins and lipids during its intracellular transport. Biochimica et Biophysica Acta (BBA) - Biomembranes 2015; 1848:1908-26. [DOI: 10.1016/j.bbamem.2015.05.010] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2015] [Revised: 04/14/2015] [Accepted: 05/13/2015] [Indexed: 12/13/2022]
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Lund FW, Jensen MLV, Christensen T, Nielsen GK, Heegaard CW, Wüstner D. SpatTrack: An Imaging Toolbox for Analysis of Vesicle Motility and Distribution in Living Cells. Traffic 2014; 15:1406-29. [DOI: 10.1111/tra.12228] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Revised: 09/16/2014] [Accepted: 09/17/2014] [Indexed: 01/01/2023]
Affiliation(s)
- Frederik W. Lund
- Department of Biochemistry and Molecular Biology; University of Southern Denmark; DK-5230 Odense M Denmark
- Department of Biochemistry; Weill Medical College of Cornell University; York Ave. 1300 10065 NY USA
| | - Maria Louise V. Jensen
- Department of Biochemistry and Molecular Biology; University of Southern Denmark; DK-5230 Odense M Denmark
| | - Tanja Christensen
- Department of Biochemistry and Molecular Biology; University of Southern Denmark; DK-5230 Odense M Denmark
| | - Gitte K. Nielsen
- Department of Biomedicine; University of Aarhus; DK-8000 Aarhus C. Denmark
| | - Christian W. Heegaard
- Department of Molecular Biology and Genetics; University of Aarhus; DK-8000 Aarhus C. Denmark
| | - Daniel Wüstner
- Department of Biochemistry and Molecular Biology; University of Southern Denmark; DK-5230 Odense M Denmark
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Wüstner D, Christensen T, Solanko LM, Sage D. Photobleaching kinetics and time-integrated emission of fluorescent probes in cellular membranes. Molecules 2014; 19:11096-130. [PMID: 25076144 PMCID: PMC6271172 DOI: 10.3390/molecules190811096] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 07/04/2014] [Accepted: 07/10/2014] [Indexed: 12/02/2022] Open
Abstract
Since the pioneering work of Hirschfeld, it is known that time-integrated emission (TiEm) of a fluorophore is independent of fluorescence quantum yield and illumination intensity. Practical implementation of this important result for determining exact probe distribution in living cells is often hampered by the presence of autofluorescence. Using kinetic modelling of photobleaching combined with pixel-wise bleach rate fitting of decay models with an updated plugin to the ImageJ program, it is shown that the TiEm of a fluorophore in living cells can be determined exactly from the product of bleaching amplitude and time constant. This applies to mono-exponential bleaching from the first excited singlet and/or triplet state and to multi-exponential combinations of such processes. The TiEm can be used to correct for illumination shading and background autofluorescence without the need for fluorescent test layers or separate imaging of non-stained cells. We apply the method to simulated images and to images of cells, whose membranes were labelled with fluorescent sterols and sphingolipids. Our bleaching model can be extended to include a probability density function (PDF) of intrinsic bleach rate constants with a memory kernel. This approach results in a time-dependent bleach rate coefficient and is exemplified for fluorescent sterols in restricted intracellular environments, like lipid droplets. We show that for small deviations from the classical exponential bleaching, the TiEm of decay functions with rate coefficients remains largely independent of fluorescence lifetime and illumination, and thereby represents a faithful measure of probe distribution.
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Affiliation(s)
- Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark.
| | - Tanja Christensen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark.
| | - Lukasz M Solanko
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark.
| | - Daniel Sage
- Biomedical Imaging Group, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
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Eriksen JJ, Solanko LM, Nåbo LJ, Wüstner D, Sauer SP, Kongsted J. The Second-Order Polarization Propagator Approximation (SOPPA) method coupled to the polarizable continuum model. COMPUT THEOR CHEM 2014. [DOI: 10.1016/j.comptc.2014.02.034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Pourmousa M, Róg T, Mikkeli R, Vattulainen L, Solanko LM, Wüstner D, List NH, Kongsted J, Karttunen M. Dehydroergosterol as an Analogue for Cholesterol: Why It Mimics Cholesterol So Well—or Does It? J Phys Chem B 2014; 118:7345-57. [DOI: 10.1021/jp406883k] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Mohsen Pourmousa
- Department
of Physics, Tampere University of Technology, Korkeakoulunkatu 3, 33720 Tampere, Finland
| | - Tomasz Róg
- Department
of Physics, Tampere University of Technology, Korkeakoulunkatu 3, 33720 Tampere, Finland
| | - Risto Mikkeli
- Department
of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto, Finland
| | - llpo Vattulainen
- Department
of Physics, Tampere University of Technology, Korkeakoulunkatu 3, 33720 Tampere, Finland
- MEMPHYS−Center
of Biomembrane Physics, Physics Department, University of Southern Denmark, Odense, Denmark
| | | | | | | | | | - Mikko Karttunen
- Department
of Chemistry and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo N2L 3G1, Ontario, Canada
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Solanko LM, Honigmann A, Midtiby HS, Lund FW, Brewer JR, Dekaris V, Bittman R, Eggeling C, Wüstner D. Membrane orientation and lateral diffusion of BODIPY-cholesterol as a function of probe structure. Biophys J 2014; 105:2082-92. [PMID: 24209853 DOI: 10.1016/j.bpj.2013.09.031] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Revised: 08/26/2013] [Accepted: 09/16/2013] [Indexed: 11/29/2022] Open
Abstract
Cholesterol tagged with the BODIPY fluorophore via the central difluoroboron moiety of the dye (B-Chol) is a promising probe for studying intracellular cholesterol dynamics. We synthesized a new BODIPY-cholesterol probe (B-P-Chol) with the fluorophore attached via one of its pyrrole rings to carbon-24 of cholesterol (B-P-Chol). Using two-photon fluorescence polarimetry in giant unilamellar vesicles and in the plasma membrane (PM) of living intact and actin-disrupted cells, we show that the BODIPY-groups in B-Chol and B-P-Chol are oriented perpendicular and almost parallel to the bilayer normal, respectively. B-Chol is in all three membrane systems much stronger oriented than B-P-Chol. Interestingly, we found that the lateral diffusion in the PM was two times slower for B-Chol than for B-P-Chol, although we found no difference in lateral diffusion in model membranes. Stimulated emission depletion microscopy, performed for the first time, to our knowledge, with fluorescent sterols, revealed that the difference in lateral diffusion of the BODIPY-cholesterol probes was not caused by anomalous subdiffusion, because diffusion of both analogs in the PM was free but not hindered. Our combined measurements show that the position and orientation of the BODIPY moiety in cholesterol analogs have a severe influence on lateral diffusion specifically in the PM of living cells.
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Affiliation(s)
- Lukasz M Solanko
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
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47
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Abstract
Biological membranes are complex assemblies of many different molecules of which analysis demands a variety of experimental and computational approaches. In this article, we explain challenges and advantages of atomistic Monte Carlo (MC) simulation of lipid membranes. We provide an introduction into the various move sets that are implemented in current MC methods for efficient conformational sampling of lipids and other molecules. In the second part, we demonstrate for a concrete example, how an atomistic local-move set can be implemented for MC simulations of phospholipid monomers and bilayer patches. We use our recently devised chain breakage/closure (CBC) local move set in the bond-/torsion angle space with the constant-bond-length approximation (CBLA) for the phospholipid dipalmitoylphosphatidylcholine (DPPC). We demonstrate rapid conformational equilibration for a single DPPC molecule, as assessed by calculation of molecular energies and entropies. We also show transition from a crystalline-like to a fluid DPPC bilayer by the CBC local-move MC method, as indicated by the electron density profile, head group orientation, area per lipid, and whole-lipid displacements. We discuss the potential of local-move MC methods in combination with molecular dynamics simulations, for example, for studying multi-component lipid membranes containing cholesterol.
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Affiliation(s)
- Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M DK-5230, Denmark.
| | - Heinz Sklenar
- Theoretical Biophysics Group, Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin D-13125, Germany.
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48
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Wüstner D, Solanko LM, Lund FW, Sage D, Schroll HJ, Lomholt MA. Quantitative fluorescence loss in photobleaching for analysis of protein transport and aggregation. BMC Bioinformatics 2012; 13:296. [PMID: 23148417 PMCID: PMC3557157 DOI: 10.1186/1471-2105-13-296] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2012] [Accepted: 10/31/2012] [Indexed: 12/23/2022] Open
Abstract
Background Fluorescence loss in photobleaching (FLIP) is a widely used imaging technique, which provides information about protein dynamics in various cellular regions. In FLIP, a small cellular region is repeatedly illuminated by an intense laser pulse, while images are taken with reduced laser power with a time lag between the bleaches. Despite its popularity, tools are lacking for quantitative analysis of FLIP experiments. Typically, the user defines regions of interest (ROIs) for further analysis which is subjective and does not allow for comparing different cells and experimental settings. Results We present two complementary methods to detect and quantify protein transport and aggregation in living cells from FLIP image series. In the first approach, a stretched exponential (StrExp) function is fitted to fluorescence loss (FL) inside and outside the bleached region. We show by reaction–diffusion simulations, that the StrExp function can describe both, binding/barrier–limited and diffusion-limited FL kinetics. By pixel-wise regression of that function to FL kinetics of enhanced green fluorescent protein (eGFP), we determined in a user-unbiased manner from which cellular regions eGFP can be replenished in the bleached area. Spatial variation in the parameters calculated from the StrExp function allow for detecting diffusion barriers for eGFP in the nucleus and cytoplasm of living cells. Polyglutamine (polyQ) disease proteins like mutant huntingtin (mtHtt) can form large aggregates called inclusion bodies (IB’s). The second method combines single particle tracking with multi-compartment modelling of FL kinetics in moving IB’s to determine exchange rates of eGFP-tagged mtHtt protein (eGFP-mtHtt) between aggregates and the cytoplasm. This method is self-calibrating since it relates the FL inside and outside the bleached regions. It makes it therefore possible to compare release kinetics of eGFP-mtHtt between different cells and experiments. Conclusions We present two complementary methods for quantitative analysis of FLIP experiments in living cells. They provide spatial maps of exchange dynamics and absolute binding parameters of fluorescent molecules to moving intracellular entities, respectively. Our methods should be of great value for quantitative studies of intracellular transport.
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Affiliation(s)
- Daniel Wüstner
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M, DK-5230, Denmark.
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49
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Lund FW, Lomholt MA, Solanko LM, Bittman R, Wüstner D. Two-photon time-lapse microscopy of BODIPY-cholesterol reveals anomalous sterol diffusion in chinese hamster ovary cells. BMC Biophys 2012; 5:20. [PMID: 23078907 PMCID: PMC3532368 DOI: 10.1186/2046-1682-5-20] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Accepted: 09/19/2012] [Indexed: 01/08/2023]
Abstract
Background Cholesterol is an important membrane component, but our knowledge about its transport in cells is sparse. Previous imaging studies using dehydroergosterol (DHE), an intrinsically fluorescent sterol from yeast, have established that vesicular and non-vesicular transport modes contribute to sterol trafficking from the plasma membrane. Significant photobleaching, however, limits the possibilities for in-depth analysis of sterol dynamics using DHE. Co-trafficking studies with DHE and the recently introduced fluorescent cholesterol analog BODIPY-cholesterol (BChol) suggested that the latter probe has utility for prolonged live-cell imaging of sterol transport. Results We found that BChol is very photostable under two-photon (2P)-excitation allowing the acquisition of several hundred frames without significant photobleaching. Therefore, long-term tracking and diffusion measurements are possible. Two-photon temporal image correlation spectroscopy (2P-TICS) provided evidence for spatially heterogeneous diffusion constants of BChol varying over two orders of magnitude from the cell interior towards the plasma membrane, where D ~ 1.3 μm2/s. Number and brightness (N&B) analysis together with stochastic simulations suggest that transient partitioning of BChol into convoluted membranes slows local sterol diffusion. We observed sterol endocytosis as well as fusion and fission of sterol-containing endocytic vesicles. The mobility of endocytic vesicles, as studied by particle tracking, is well described by a model for anomalous subdiffusion on short time scales with an anomalous exponent α ~ 0.63 and an anomalous diffusion constant of Dα = 1.95 x 10-3 μm2/sα. On a longer time scale (t > ~5 s), a transition to superdiffusion consistent with slow directed transport with an average velocity of v ~ 6 x 10-3 μm/s was observed. We present an analytical model that bridges the two regimes and fit this model to vesicle trajectories from control cells and cells with disrupted microtubule or actin filaments. Both treatments reduced the anomalous diffusion constant and the velocity by ~40-50%. Conclusions The mobility of sterol-containing vesicles on the short time scale could reflect dynamic rearrangements of the cytoskeleton, while directed transport of sterol vesicles occurs likely along both, microtubules and actin filaments. Spatially varying anomalous diffusion could contribute to fine-tuning and local regulation of intracellular sterol transport.
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Affiliation(s)
- Frederik W Lund
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, Odense M, DK-5230, Denmark.
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Abstract
Cholesterol plays an important role in determining the biophysical properties of biological membranes, and its concentration is tightly controlled by homeostatic processes. The intracellular transport of cholesterol among organelles is a key part of the homeostatic mechanism, but sterol transport processes are not well understood. Fluorescence microscopy is a valuable tool for studying intracellular transport processes, but this method can be challenging for lipid molecules because addition of a fluorophore may alter the properties of the molecule greatly. We discuss the use of fluorescent molecules that can bind to cholesterol to reveal its distribution in cells. We also discuss the use of intrinsically fluorescent sterols that closely mimic cholesterol, as well as some minimally modified fluorophore-labeled sterols. Methods for imaging these sterols by conventional fluorescence microscopy and by multiphoton microscopy are described. Some label-free methods for imaging cholesterol itself are also discussed briefly.
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