1
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Nüesch MF, Pietrek L, Holmstrom ED, Nettels D, von Roten V, Kronenberg-Tenga R, Medalia O, Hummer G, Schuler B. Nanosecond chain dynamics of single-stranded nucleic acids. Nat Commun 2024; 15:6010. [PMID: 39019880 PMCID: PMC11255343 DOI: 10.1038/s41467-024-50092-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Accepted: 07/01/2024] [Indexed: 07/19/2024] Open
Abstract
The conformational dynamics of single-stranded nucleic acids are fundamental for nucleic acid folding and function. However, their elementary chain dynamics have been difficult to resolve experimentally. Here we employ a combination of single-molecule Förster resonance energy transfer, nanosecond fluorescence correlation spectroscopy, and nanophotonic enhancement to determine the conformational ensembles and rapid chain dynamics of short single-stranded nucleic acids in solution. To interpret the experimental results in terms of end-to-end distance dynamics, we utilize the hierarchical chain growth approach, simple polymer models, and refinement with Bayesian inference to generate structural ensembles that closely align with the experimental data. The resulting chain reconfiguration times are exceedingly rapid, in the 10-ns range. Solvent viscosity-dependent measurements indicate that these dynamics of single-stranded nucleic acids exhibit negligible internal friction and are thus dominated by solvent friction. Our results provide a detailed view of the conformational distributions and rapid dynamics of single-stranded nucleic acids.
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Affiliation(s)
- Mark F Nüesch
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Lisa Pietrek
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Max-von-Laue-Straße 3, 60438, Frankfurt am Main, Germany
| | - Erik D Holmstrom
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
- Department of Chemistry, University of Kansas, Lawrence, KS, USA.
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS, USA.
| | - Daniel Nettels
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Valentin von Roten
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Rafael Kronenberg-Tenga
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Ohad Medalia
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Gerhard Hummer
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Max-von-Laue-Straße 3, 60438, Frankfurt am Main, Germany.
- Institute for Biophysics, Goethe University Frankfurt, 60438, Frankfurt am Main, Germany.
| | - Benjamin Schuler
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
- Department of Physics, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
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2
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Okamoto K, Sako Y. Two Closed Conformations of CRAF Require the 14-3-3 Binding Motifs and Cysteine-Rich Domain to be Intact in Live Cells. J Mol Biol 2023; 435:167989. [PMID: 36736888 DOI: 10.1016/j.jmb.2023.167989] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 01/20/2023] [Accepted: 01/26/2023] [Indexed: 02/04/2023]
Abstract
The protein rapidly accelerated fibrosarcoma (RAF) is a kinase downstream of the membrane protein RAS in the cellular signal transduction system. In the structure of RAF, the N- and C-terminus domains are connected with a flexible linker. The open/close dynamics and dimerization of RAF are thought to regulate its activity, although the details of these conformations are unknown, especially in live cells. In this work, we used alternating laser excitation to measure cytosolic CRAF in live HeLa cells and obtained single-molecule Förster resonance energy transfer (smFRET) distributions of the structural states. We compared the results for wild-type (WT)-CRAF before and after epidermal growth factor (EGF) stimulation, with mutations of the 14-3-3 binding sites and cysteine-rich domain, and an N-terminus truncation. The smFRET distributions of full-length CRAFs were analyzed by global fitting with three beta distributions. Our results suggested that a 14-3-3 dimer bound to two sites on a single CRAF molecule and induced the formation of the autoinhibitory closed conformation. There were two closed conformations, which the majority of WT-CRAF adopted. These two conformations showed different responsiveness to EGF stimulation.
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Affiliation(s)
- Kenji Okamoto
- Cellular Informatics Laboratory, Cluster for Pioneering Research, RIKEN, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan.
| | - Yasushi Sako
- Cellular Informatics Laboratory, Cluster for Pioneering Research, RIKEN, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan.
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3
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Harris PD, Lerner E. Identification and quantification of within-burst dynamics in singly labeled single-molecule fluorescence lifetime experiments. BIOPHYSICAL REPORTS 2022; 2. [PMID: 36204594 PMCID: PMC9534301 DOI: 10.1016/j.bpr.2022.100071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Single-molecule spectroscopy has revolutionized molecular biophysics and provided means to probe how structural moieties within biomolecules spatially reorganize at different timescales. There are several single-molecule methodologies that probe local structural dynamics in the vicinity of a single dye-labeled residue, which rely on fluorescence lifetimes as readout. Nevertheless, an analytical framework to quantify dynamics in such single-molecule single dye fluorescence bursts, at timescales of microseconds to milliseconds, has not yet been demonstrated. Here, we suggest an analytical framework for identifying and quantifying within-burst lifetime-based dynamics, such as conformational dynamics recorded in single-molecule photo-isomerization-related fluorescence enhancement. After testing the capabilities of the analysis on simulations, we proceed to exhibit within-burst millisecond local structural dynamics in the unbound α-synuclein monomer. The analytical framework provided in this work paves the way for extracting a full picture of the energy landscape for the coordinate probed by fluorescence lifetime-based single-molecule measurements.
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Affiliation(s)
- Paul David Harris
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, Faculty of Mathematics & Science, The Edmond J. Safra Campus, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
| | - Eitan Lerner
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, Faculty of Mathematics & Science, The Edmond J. Safra Campus, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel.,The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel
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4
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Kaeokhamloed N, Legeay S, Roger E. FRET as the tool for in vivo nanomedicine tracking. J Control Release 2022; 349:156-173. [PMID: 35779657 DOI: 10.1016/j.jconrel.2022.06.048] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Revised: 06/20/2022] [Accepted: 06/25/2022] [Indexed: 11/29/2022]
Abstract
Advanced drug delivery system utilizing a nanocarrier is the major application of nanotechnology on pharmacotherapeutics. However, despite the promising benefits and a leading trend in pharmaceutical research, nanomedicine development suffers from a poor clinical translation problem as only a handful of nanomedicine products reach the market yearly. The conventional pharmacokinetic study generally focuses only on monitoring the level of a free drug but ignores the nanocarrier's role in pharmacokinetics. One hurdle is that it is difficult to directly track intact nanocarriers in vivo to explore their pharmacokinetics. Although several imaging techniques such as radiolabeling, nuclear imaging, fluorescence imaging, etc., have been developed over the past few years, currently, one method that can successfully track the intact nanocarriers in vivo directly is by Förster resonance energy transfer (FRET). This review summarizes the application of FRET as the in vivo nanoparticle tracker for studying the in vivo pharmacokinetics of the organic nanocarriers and gives elaborative details on the techniques utilized.
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Affiliation(s)
| | - Samuel Legeay
- MINT, INSERM U1066, CNRS 6021, SFR-ICAT, University of Angers, 49333 Angers, France
| | - Emilie Roger
- MINT, INSERM U1066, CNRS 6021, SFR-ICAT, University of Angers, 49333 Angers, France.
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5
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Yukhnovets O, Höfig H, Bustorff N, Katranidis A, Fitter J. Impact of Molecule Concentration, Diffusion Rates and Surface Passivation on Single-Molecule Fluorescence Studies in Solution. Biomolecules 2022; 12:468. [PMID: 35327660 PMCID: PMC8946791 DOI: 10.3390/biom12030468] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Revised: 03/09/2022] [Accepted: 03/16/2022] [Indexed: 12/04/2022] Open
Abstract
For single-molecule studies in solution, very small concentrations of dye-labelled molecules are employed in order to achieve single-molecule sensitivity. In typical studies with confocal microscopes, often concentrations in the pico-molar regime are required. For various applications that make use of single-molecule Förster resonance energy transfer (smFRET) or two-color coincidence detection (TCCD), the molecule concentration must be set explicitly to targeted values and furthermore needs to be stable over a period of several hours. As a consequence, specific demands must be imposed on the surface passivation of the cover slides during the measurements. The aim of having only one molecule in the detection volume at the time is not only affected by the absolute molecule concentration, but also by the rate of diffusion. Therefore, we discuss approaches to control and to measure absolute molecule concentrations. Furthermore, we introduce an approach to calculate the probability of chance coincidence events and demonstrate that measurements with challenging smFRET samples require a strict limit of maximal sample concentrations in order to produce meaningful results.
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Affiliation(s)
- Olessya Yukhnovets
- AG Biophysik, I. Physikalisches Institut (IA), RWTH Aachen University, 52074 Aachen, Germany;
| | - Henning Höfig
- AG Biophysik, I. Physikalisches Institut (IA), RWTH Aachen University, 52074 Aachen, Germany;
| | - Nuno Bustorff
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C-3), Institute of Biological Information Processing IBI-6, Forschungszentrum Jülich, 52425 Jülich, Germany; (N.B.); (A.K.)
| | - Alexandros Katranidis
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C-3), Institute of Biological Information Processing IBI-6, Forschungszentrum Jülich, 52425 Jülich, Germany; (N.B.); (A.K.)
| | - Jörg Fitter
- AG Biophysik, I. Physikalisches Institut (IA), RWTH Aachen University, 52074 Aachen, Germany;
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C-3), Institute of Biological Information Processing IBI-6, Forschungszentrum Jülich, 52425 Jülich, Germany; (N.B.); (A.K.)
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6
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Biocompatible surface functionalization architecture for a diamond quantum sensor. Proc Natl Acad Sci U S A 2022; 119:2114186119. [PMID: 35193961 PMCID: PMC8872777 DOI: 10.1073/pnas.2114186119] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/16/2022] [Indexed: 01/02/2023] Open
Abstract
Diamond-based quantum sensing enables nanoscale measurements of biological systems with unprecedented sensitivity. Potential applications of this emerging technology range from the investigation of fundamental biological processes to the development of next-generation medical diagnostics devices. One of the main challenges faced by bioquantum sensing is the need to interface quantum sensors with biological target systems. Specifically, such an interface needs to maintain the highly fragile quantum states of our sensor and at the same time be able to fish intact biomolecules out of solution and immobilize them on our quantum sensor surface. Our work overcomes these challenges by combining tools from quantum engineering, single-molecule biophysics, and material processing. Quantum metrology enables some of the most precise measurements. In the life sciences, diamond-based quantum sensing has led to a new class of biophysical sensors and diagnostic devices that are being investigated as a platform for cancer screening and ultrasensitive immunoassays. However, a broader application in the life sciences based on nanoscale NMR spectroscopy has been hampered by the need to interface highly sensitive quantum bit (qubit) sensors with their biological targets. Here, we demonstrate an approach that combines quantum engineering with single-molecule biophysics to immobilize individual proteins and DNA molecules on the surface of a bulk diamond crystal that hosts coherent nitrogen vacancy qubit sensors. Our thin (sub–5 nm) functionalization architecture provides precise control over the biomolecule adsorption density and results in near-surface qubit coherence approaching 100 μs. The developed architecture remains chemically stable under physiological conditions for over 5 d, making our technique compatible with most biophysical and biomedical applications.
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7
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Harris PD, Narducci A, Gebhardt C, Cordes T, Weiss S, Lerner E. Multi-parameter photon-by-photon hidden Markov modeling. Nat Commun 2022; 13:1000. [PMID: 35194038 PMCID: PMC8863987 DOI: 10.1038/s41467-022-28632-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 02/03/2022] [Indexed: 02/06/2023] Open
Abstract
Single molecule Förster resonance energy transfer (smFRET) is a unique biophysical approach for studying conformational dynamics in biomacromolecules. Photon-by-photon hidden Markov modeling (H2MM) is an analysis tool that can quantify FRET dynamics of single biomolecules, even if they occur on the sub-millisecond timescale. However, dye photophysical transitions intertwined with FRET dynamics may cause artifacts. Here, we introduce multi-parameter H2MM (mpH2MM), which assists in identifying FRET dynamics based on simultaneous observation of multiple experimentally-derived parameters. We show the importance of using mpH2MM to decouple FRET dynamics caused by conformational changes from photophysical transitions in confocal-based smFRET measurements of a DNA hairpin, the maltose binding protein, MalE, and the type-III secretion system effector, YopO, from Yersinia species, all exhibiting conformational dynamics ranging from the sub-second to microsecond timescales. Overall, we show that using mpH2MM facilitates the identification and quantification of biomolecular sub-populations and their origin.
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Affiliation(s)
- Paul David Harris
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, Faculty of Mathematics & Science, The Edmond J. Safra Campus, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel.
| | - Alessandra Narducci
- Physical and Synthetic Biology. Faculty of Biology, Ludwig-Maximilians-Universität München, Großhadernerstr. 2-4, 82152, Planegg-Martinsried, Germany
| | - Christian Gebhardt
- Physical and Synthetic Biology. Faculty of Biology, Ludwig-Maximilians-Universität München, Großhadernerstr. 2-4, 82152, Planegg-Martinsried, Germany
| | - Thorben Cordes
- Physical and Synthetic Biology. Faculty of Biology, Ludwig-Maximilians-Universität München, Großhadernerstr. 2-4, 82152, Planegg-Martinsried, Germany
| | - Shimon Weiss
- Department of Chemistry and Biochemistry, and Department of Physiology, University of California, Los Angeles, CA, USA
- CaliforniaNanoSystems Institute, University of California, Los Angeles, CA, USA
| | - Eitan Lerner
- Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, Faculty of Mathematics & Science, The Edmond J. Safra Campus, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel.
- The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel.
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8
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Yadav R, Widom JR, Chauvier A, Walter NG. An anionic ligand snap-locks a long-range interaction in a magnesium-folded riboswitch. Nat Commun 2022; 13:207. [PMID: 35017489 PMCID: PMC8752731 DOI: 10.1038/s41467-021-27827-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2021] [Accepted: 12/02/2021] [Indexed: 01/22/2023] Open
Abstract
The archetypical transcriptional crcB fluoride riboswitch from Bacillus cereus is an intricately structured non-coding RNA element enhancing gene expression in response to toxic levels of fluoride. Here, we used single molecule FRET to uncover three dynamically interconverting conformations appearing along the transcription process: two distinct undocked states and one pseudoknotted docked state. We find that the fluoride anion specifically snap-locks the magnesium-induced, dynamically docked state. The long-range, nesting, single base pair A40-U48 acts as the main linchpin, rather than the multiple base pairs comprising the pseudoknot. We observe that the proximally paused RNA polymerase further fine-tunes the free energy to promote riboswitch docking. Finally, we show that fluoride binding at short transcript lengths is an early step toward partitioning folding into the docked conformation. These results reveal how the anionic fluoride ion cooperates with the magnesium-associated RNA to govern regulation of downstream genes needed for fluoride detoxification of the cell.
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Affiliation(s)
- Rajeev Yadav
- Single Molecule Analysis Group, Department of Chemistry and Center for RNA Biomedicine, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Physics and Astronomy, Michigan State University, East Lansing, MI, 48824, USA
| | - Julia R Widom
- Single Molecule Analysis Group, Department of Chemistry and Center for RNA Biomedicine, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Chemistry and Biochemistry, University of Oregon, Eugene, OR, 97403, USA
| | - Adrien Chauvier
- Single Molecule Analysis Group, Department of Chemistry and Center for RNA Biomedicine, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Nils G Walter
- Single Molecule Analysis Group, Department of Chemistry and Center for RNA Biomedicine, University of Michigan, Ann Arbor, MI, 48109, USA.
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9
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Gopich IV, Chung HS. Theory and Analysis of Single-Molecule FRET Experiments. Methods Mol Biol 2022; 2376:247-282. [PMID: 34845614 DOI: 10.1007/978-1-0716-1716-8_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Inter-dye distances and conformational dynamics can be studied using single-molecule FRET measurements. We consider two approaches to analyze sequences of photons with recorded photon colors and arrival times. The first approach is based on FRET efficiency histograms obtained from binned photon sequences. The experimental histograms are compared with the theoretical histograms obtained using the joint distribution of acceptor and donor photons or the Gaussian approximation. In the second approach, a photon sequence is analyzed without binning. The parameters of a model describing conformational dynamics are found by maximizing the appropriate likelihood function. The first approach is simpler, while the second one is more accurate, especially when the population of species is small and transition rates are fast. The likelihood-based analysis as well as the recoloring method has the advantage that diffusion of molecules through the laser focus can be rigorously handled.
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Affiliation(s)
- Irina V Gopich
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA.
| | - Hoi Sung Chung
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
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10
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Basak S, Sakia N, Dougherty L, Guo Z, Wu F, Mindlin F, Lary JW, Cole JL, Ding F, Bowen ME. Probing Interdomain Linkers and Protein Supertertiary Structure In Vitro and in Live Cells with Fluorescent Protein Resonance Energy Transfer. J Mol Biol 2021; 433:166793. [PMID: 33388290 DOI: 10.1016/j.jmb.2020.166793] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 12/03/2020] [Accepted: 12/21/2020] [Indexed: 12/23/2022]
Abstract
Many proteins are composed of independently-folded domains connected by flexible linkers. The primary sequence and length of such linkers can set the effective concentration for the tethered domains, which impacts rates of association and enzyme activity. The length of such linkers can be sensitive to environmental conditions, which raises questions as to how studies in dilute buffer relate to the highly-crowded cellular environment. To examine the role of linkers in domain separation, we measured Fluorescent Protein-Fluorescence Resonance Energy Transfer (FP-FRET) for a series of tandem FPs that varied in the length of their interdomain linkers. We used discrete molecular dynamics to map the underlying conformational distribution, which revealed intramolecular contact states that we confirmed with single molecule FRET. Simulations found that attached FPs increased linker length and slowed conformational dynamics relative to the bare linkers. This makes the CLYs poor sensors of inherent linker properties. However, we also showed that FP-FRET in CLYs was sensitive to solvent quality and macromolecular crowding making them potent environmental sensors. Finally, we targeted the same proteins to the plasma membrane of living mammalian cells to measure FP-FRET in cellulo. The measured FP-FRET when tethered to the plasma membrane was the same as that in dilute buffer. While caveats remain regarding photophysics, this suggests that the supertertiary conformational ensemble of these CLY proteins may not be affected by this specific cellular environment.
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Affiliation(s)
- Sujit Basak
- Department of Physiology & Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA
| | - Nabanita Sakia
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978, USA
| | - Laura Dougherty
- Department of Physiology & Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA
| | - Zhuojun Guo
- Department of Physiology & Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA
| | - Fang Wu
- Department of Physiology & Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA
| | - Frank Mindlin
- Department of Physiology & Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA
| | - Jeffrey W Lary
- National Analytical Ultracentrifugation Facility, University of Connecticut, Storrs, CT 06269, USA
| | - James L Cole
- National Analytical Ultracentrifugation Facility, University of Connecticut, Storrs, CT 06269, USA; Department of Molecular and Cell Biology, and Department of Chemistry, University of Connecticut, Storrs, CT 06269, USA
| | - Feng Ding
- Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978, USA
| | - Mark E Bowen
- Department of Physiology & Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, USA.
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11
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QuanTI-FRET: a framework for quantitative FRET measurements in living cells. Sci Rep 2020; 10:6504. [PMID: 32300110 PMCID: PMC7162988 DOI: 10.1038/s41598-020-62924-w] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Accepted: 03/17/2020] [Indexed: 12/15/2022] Open
Abstract
Förster Resonance Energy Transfer (FRET) allows for the visualization of nanometer-scale distances and distance changes. This sensitivity is regularly achieved in single-molecule experiments in vitro but is still challenging in biological materials. Despite many efforts, quantitative FRET in living samples is either restricted to specific instruments or limited by the complexity of the required analysis. With the recent development and expanding utilization of FRET-based biosensors, it becomes essential to allow biologists to produce quantitative results that can directly be compared. Here, we present a new calibration and analysis method allowing for quantitative FRET imaging in living cells with a simple fluorescence microscope. Aside from the spectral crosstalk corrections, two additional correction factors were defined from photophysical equations, describing the relative differences in excitation and detection efficiencies. The calibration is achieved in a single step, which renders the Quantitative Three-Image FRET (QuanTI-FRET) method extremely robust. The only requirement is a sample of known stoichiometry donor:acceptor, which is naturally the case for intramolecular FRET constructs. We show that QuanTI-FRET gives absolute FRET values, independent of the instrument or the expression level. Through the calculation of the stoichiometry, we assess the quality of the data thus making QuanTI-FRET usable confidently by non-specialists.
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12
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In-cell single-molecule FRET measurements reveal three conformational state changes in RAF protein. Biochim Biophys Acta Gen Subj 2019; 1864:129358. [PMID: 31071411 DOI: 10.1016/j.bbagen.2019.04.022] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2018] [Revised: 04/26/2019] [Accepted: 04/30/2019] [Indexed: 12/19/2022]
Abstract
BACKGROUND The structures of proteins are intimately related to their functions. Significant efforts have been dedicated to the structural investigation of proteins, mainly those of purified proteins in in vitro environments. Proteins function in living cells and thus protein structures must be regulated by interactions with various molecules, some of which participate in reaction networks, depending on the states, conditions, or actions of the cell. Therefore, it is very important to understand the structural behavior of proteins in living cells. METHODS Single-molecule Förster resonance energy transfer (smFRET) measurements were conducted using the alternative laser excitation (ALEX) technique. smFRET distributions of cytosolic Rapidly Accelerated Fibrosarcoma (RAF) proteins in living HeLa cells were obtained with exclusion of the negative effects of photobleached fluorophores and incompletely labeled proteins on smFRET. RESULTS smFRET histograms of wildtype (wt) RAF in live cells exhibited two major peaks, whereas that of the S621A mutant, which has been thought to have an expanded structure, was almost single-peaked. A population shift involving the peaks for wt RAF was detected upon epidermal growth factor stimulation. Spontaneous transitions between the conformational states corresponding to the two peaks were also detected using the FRET-two-channel kernel-based density distribution estimator method in comparison to static double-stranded DNA samples. CONCLUSIONS Cytosolic CRAF has at least three conformational states; in addition to the closed and open forms, the fully-open form was distinctly specified. Based on the results, we propose a speculative structural model for CRAF. GENERAL SIGNIFICANCE Structural distribution and changes to proteins in live cells as a result of intracellular interactions were successfully identified. smFRET using ALEX is applicable to any other cytosolic proteins.
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13
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Okamoto K, Sako Y. Single-Molecule Förster Resonance Energy Transfer Measurement Reveals the Dynamic Partially Ordered Structure of the Epidermal Growth Factor Receptor C-Tail Domain. J Phys Chem B 2019; 123:571-581. [PMID: 30571124 DOI: 10.1021/acs.jpcb.8b10066] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Intrinsically disordered proteins (IDPs) or regions (IDRs) are thought to exhibit unique functionalities without forming ordered structures. However, these molecular mechanisms are not easily elucidated, partly because of the difficultly of measuring structural information. In this study, we applied the alternative laser excitation (ALEX) method and circular dichroism (CD) spectroscopy to investigate the structure of the C-terminal tail (CTT) domain of the human epidermal growth factor receptor (EGFR). The single-molecule distributions of Förster resonance energy transfer (FRET) obtained by ALEX under solution conditions modified by the addition of potassium chloride (KCl), urea, or guanidinium chloride (GdmCl) allowed us to separately examine the influences of charge interactions and secondary structure formation. The CD spectrum analyses indicated the types of included secondary structure. The results suggested that the structure of the CTT is influenced by secondary structure formation, which is a principally antiparallel β-sheet, rather than by charge interactions and that phosphorylation of the major Grb2-binding sites partially denatures that secondary structure. Our findings suggest that the EGFR CTT might regulate ligand binding kinetics by local β-sheet formation or by the disruption associated with phosphorylation states.
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Affiliation(s)
- Kenji Okamoto
- Cellular Informatics Laboratory , RIKEN , 2-1 Hirosawa , Wako , Saitama 351-0198 Japan
| | - Yasushi Sako
- Cellular Informatics Laboratory , RIKEN , 2-1 Hirosawa , Wako , Saitama 351-0198 Japan
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14
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Ingargiola A, Segal M, Gulinatti A, Rech I, Labanca I, Maccagnani P, Ghioni M, Weiss S, Michalet X. 48-spot single-molecule FRET setup with periodic acceptor excitation. J Chem Phys 2018; 148:123304. [PMID: 29604810 DOI: 10.1063/1.5000742] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Single-molecule Förster resonance energy transfer (smFRET) allows measuring distances between donor and acceptor fluorophores on the 3-10 nm range. Solution-based smFRET allows measurement of binding-unbinding events or conformational changes of dye-labeled biomolecules without ensemble averaging and free from surface perturbations. When employing dual (or multi) laser excitation, smFRET allows resolving the number of fluorescent labels on each molecule, greatly enhancing the ability to study heterogeneous samples. A major drawback to solution-based smFRET is the low throughput, which renders repetitive measurements expensive and hinders the ability to study kinetic phenomena in real-time. Here we demonstrate a high-throughput smFRET system that multiplexes acquisition by using 48 excitation spots and two 48-pixel single-photon avalanche diode array detectors. The system employs two excitation lasers allowing separation of species with one or two active fluorophores. The performance of the system is demonstrated on a set of doubly labeled double-stranded DNA oligonucleotides with different distances between donor and acceptor dyes along the DNA duplex. We show that the acquisition time for accurate subpopulation identification is reduced from several minutes to seconds, opening the way to high-throughput screening applications and real-time kinetics studies of enzymatic reactions such as DNA transcription by bacterial RNA polymerase.
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Affiliation(s)
- Antonino Ingargiola
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA
| | - Maya Segal
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA
| | - Angelo Gulinatti
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Ivan Rech
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Ivan Labanca
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Piera Maccagnani
- Istituto per la Microelettronica e Microsistemi, IMM-CNR, Bologna, Italy
| | - Massimo Ghioni
- Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Shimon Weiss
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA
| | - Xavier Michalet
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA
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15
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Qu S, Liu C, Liu Q, Wu W, Du B, Wang J. Solvent effect on FRET spectroscopic ruler. J Chem Phys 2018; 148:123331. [PMID: 29604875 DOI: 10.1063/1.5004205] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
A discrepancy has emerged in recent years between single-molecule Förster resonance energy transfer (smFRET) measurements and small angle X-ray scattering (SAXS) or small angle neutron scattering experiments in the study of unfolded or intrinsically disordered proteins in denaturing solutions. Despite significant advances that have been made in identifying various factors which may have contributed to the manifestation of the so-called smFRET-SAXS discrepancy, no consensus has been reached so far on its original source or eventual resolution. In this study, we investigate this problem from the perspective of the solvent effect on FRET spectroscopic ruler (SEFSR), a generic term we use to describe various solvent-dependent factors affecting the accuracy of the FRET experimental method that is known as a "spectroscopic ruler." Some factors belonging to SEFSR, such as direct dye-solvent interaction and labeling configuration, seem to have not received due attention regarding their significance in contributing to the discrepancy. We identify SEFSR by measuring a rigid segment of a double-stranded DNA in various solutions using the smFRET method and evaluate its relative importance in smFRET experiments by measuring segments of a single-stranded DNA and polyethylene glycol (PEG) in solutions. We find that SEFSR can produce non-negligible FRET-inferred interdye distance changes in various solutions, with an intensity following the Hofmeister series in ionic solutions and dependent on labeling configurations. SEFSR is found to be significant in GuHCl and urea solutions, which can fully cover the apparent expansion signal of dye-labeled PEG. Our findings suggest that SEFSR may have played an important role in contributing to the smFRET-SAXS discrepancy.
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Affiliation(s)
- Songyuan Qu
- College of Physics, Jilin University, Changchun, Jilin 130012, People's Republic of China
| | - Chuanbo Liu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
| | - Qiong Liu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
| | - Wei Wu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
| | - Baoji Du
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
| | - Jin Wang
- College of Physics, Jilin University, Changchun, Jilin 130012, People's Republic of China
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16
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Zarrabi N, Schluesche P, Meisterernst M, Börsch M, Lamb DC. Analyzing the Dynamics of Single TBP-DNA-NC2 Complexes Using Hidden Markov Models. Biophys J 2018; 115:2310-2326. [PMID: 30527334 DOI: 10.1016/j.bpj.2018.11.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Revised: 11/12/2018] [Accepted: 11/12/2018] [Indexed: 10/27/2022] Open
Abstract
Single-pair Förster resonance energy transfer (spFRET) has become an important tool for investigating conformational dynamics in biological systems. To extract dynamic information from the spFRET traces measured with total internal reflection fluorescence microscopy, we extended the hidden Markov model (HMM) approach. In our extended HMM analysis, we incorporated the photon-shot noise from camera-based systems into the HMM. Thus, the variance in Förster resonance energy transfer (FRET) efficiency of the various states, which is typically a fitted parameter, is explicitly included in the analysis estimated from the number of detected photons. It is also possible to include an additional broadening of the FRET state, which would then only reflect the inherent flexibility of the dynamic biological systems. This approach is useful when comparing the dynamics of individual molecules for which the total intensities vary significantly. We used spFRET with the extended HMM analysis to investigate the dynamics of TATA-box-binding protein (TBP) on promoter DNA in the presence of negative cofactor 2 (NC2). We compared the dynamics of two promoters as well as DNAs of different length and labeling location. For the adenovirus major late promoter, four FRET states were observed; three states correspond to different conformations of the DNA in the TBP-DNA-NC2 complex and a four-state model in which the complex has shifted along the DNA. The HMM analysis revealed that the states are connected via a linear, four-well model. For the H2B promoter, more complex dynamics were observed. By clustering the FRET states detected with the HMM analysis, we could compare the general dynamics observed for the two promoter sequences. We observed that the dynamics from a stretched DNA conformation to a bent conformation for the two promoters were similar, whereas the bent conformation of the TBP-DNA-NC2 complex for the H2B promoter is approximately three times more stable than for the adenovirus major late promoter.
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Affiliation(s)
- Nawid Zarrabi
- Physikalisches Institut, University of Stuttgart, Stuttgart, Baden-Württemberg, Germany; Single-Molecule Microscopy Group, Jena University Hospital, Jena, Thuringia, Germany
| | - Peter Schluesche
- Department Chemie, Center for Nano Science, Center for Integrated Protein Science, and Nanosystems Initiative München, Ludwig-Maximilians-Universität Munich, Munich, Bavaria, Germany
| | - Michael Meisterernst
- GSF-National Research Center for Environment and Health, Gene Expression, Munich, Bavaria, Germany; Institute of Molecular Tumor Biology, Faculty of Medicine, University of Muenster, Muenster, North Rhine-Westphalia, Germany
| | - Michael Börsch
- Physikalisches Institut, University of Stuttgart, Stuttgart, Baden-Württemberg, Germany; Single-Molecule Microscopy Group, Jena University Hospital, Jena, Thuringia, Germany
| | - Don C Lamb
- Department Chemie, Center for Nano Science, Center for Integrated Protein Science, and Nanosystems Initiative München, Ludwig-Maximilians-Universität Munich, Munich, Bavaria, Germany.
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17
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Schrangl L, Göhring J, Schütz GJ. Kinetic analysis of single molecule FRET transitions without trajectories. J Chem Phys 2018; 148:123328. [DOI: 10.1063/1.5006038] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Lukas Schrangl
- Institute of Applied Physics, TU Wien, Wiedner Hauptstraße 8–10, 1040 Wien, Vienna, Austria
| | - Janett Göhring
- Institute for Hygiene and Applied Immunology, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Lazarettgasse 19, 1090 Wien, Vienna, Austria
| | - Gerhard J. Schütz
- Institute of Applied Physics, TU Wien, Wiedner Hauptstraße 8–10, 1040 Wien, Vienna, Austria
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18
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Single-molecule fluorescence-based analysis of protein conformation, interaction, and oligomerization in cellular systems. Biophys Rev 2017; 10:317-326. [PMID: 29243093 PMCID: PMC5899725 DOI: 10.1007/s12551-017-0366-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Accepted: 11/19/2017] [Indexed: 12/23/2022] Open
Abstract
Single-molecule imaging (SMI) of proteins in operation has a history of intensive investigations over 20 years and is now widely used in various fields of biology and biotechnology. We review the recent advances in SMI of fluorescently-tagged proteins in structural biology, focusing on technical applicability of SMI to the measurements in living cells. Basic technologies and recent applications of SMI in structural biology are introduced. Distinct from other methods in structural biology, SMI directly observes single molecules and single-molecule events one-by-one, thus, explicitly analyzing the distribution of protein structures and the history of protein dynamics. It also allows one to detect single events of protein interaction. One unique feature of SMI is that it is applicable in complicated and heterogeneous environments, including living cells. The numbers, location, movements, interaction, oligomerization, and conformation of single-protein molecules have been determined using SMI in cellular systems.
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19
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Cheng HK, Yeung MCL, Yam VWW. Molecular Engineering of Platinum(II) Terpyridine Complexes with Tetraphenylethylene-Modified Alkynyl Ligands: Supramolecular Assembly via Pt···Pt and/or π-π Stacking Interactions and the Formation of Various Superstructures. ACS APPLIED MATERIALS & INTERFACES 2017; 9:36220-36228. [PMID: 28991427 DOI: 10.1021/acsami.7b11807] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A series of platinum(II) terpyridine complexes with tetraphenylethylene-modified alkynyl ligands has been designed and synthesized. The introduction of the tetraphenylethylene motif has led to aggregation-induced emission (AIE) properties, which upon self-assembly led to the formation of metal-metal-to-ligand charge transfer (MMLCT) behavior stabilized by Pt···Pt and/or π-π interactions. Tuning the steric bulk or hydrophilicity through molecular engineering of the platinum(II) complexes has been found to alter their spectroscopic properties and result in interesting superstructures (including nanorods, nanospheres, nanowires, and nanoleaves) in the self-assembly process. The eye-catching color and emission changes upon varying the solvent compositions may have potential applications in chemosensing materials for the detection of microenvironment changes. Furthermore, the importance of the directional Pt···Pt and/or π-π interactions on the construction of distinctive superstructures has also been examined by UV-vis absorption and emission spectroscopy and transmission electron microscopy. This work represents the interplay of both inter- and intramolecular interactions as well as the energies of the two different chromophoric/luminophoric systems that may open up a new route for the development of platinum(II)-AIE hybrids as functional materials.
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Affiliation(s)
- Heung-Kiu Cheng
- Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee (Hong Kong)), and Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, P. R. China
| | - Margaret Ching-Lam Yeung
- Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee (Hong Kong)), and Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, P. R. China
| | - Vivian Wing-Wah Yam
- Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee (Hong Kong)), and Department of Chemistry, The University of Hong Kong , Pokfulam Road, Hong Kong, P. R. China
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20
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Ingargiola A, Lerner E, Chung S, Panzeri F, Gulinatti A, Rech I, Ghioni M, Weiss S, Michalet X. Multispot single-molecule FRET: High-throughput analysis of freely diffusing molecules. PLoS One 2017; 12:e0175766. [PMID: 28419142 PMCID: PMC5395192 DOI: 10.1371/journal.pone.0175766] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 03/30/2017] [Indexed: 12/03/2022] Open
Abstract
We describe an 8-spot confocal setup for high-throughput smFRET assays and illustrate its performance with two characteristic experiments. First, measurements on a series of freely diffusing doubly-labeled dsDNA samples allow us to demonstrate that data acquired in multiple spots in parallel can be properly corrected and result in measured sample characteristics consistent with those obtained with a standard single-spot setup. We then take advantage of the higher throughput provided by parallel acquisition to address an outstanding question about the kinetics of the initial steps of bacterial RNA transcription. Our real-time kinetic analysis of promoter escape by bacterial RNA polymerase confirms results obtained by a more indirect route, shedding additional light on the initial steps of transcription. Finally, we discuss the advantages of our multispot setup, while pointing potential limitations of the current single laser excitation design, as well as analysis challenges and their solutions.
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Affiliation(s)
- Antonino Ingargiola
- Department of Chemistry & Biochemistry, UCLA, Los Angeles, CA, United States of America
- * E-mail: (AI); (XM)
| | - Eitan Lerner
- Department of Chemistry & Biochemistry, UCLA, Los Angeles, CA, United States of America
| | - SangYoon Chung
- Department of Chemistry & Biochemistry, UCLA, Los Angeles, CA, United States of America
| | - Francesco Panzeri
- Dipartimento di Elettronica, Informazione e Bioingeneria, Politecnico di Milano, Milan, Italy
| | - Angelo Gulinatti
- Dipartimento di Elettronica, Informazione e Bioingeneria, Politecnico di Milano, Milan, Italy
| | - Ivan Rech
- Dipartimento di Elettronica, Informazione e Bioingeneria, Politecnico di Milano, Milan, Italy
| | - Massimo Ghioni
- Dipartimento di Elettronica, Informazione e Bioingeneria, Politecnico di Milano, Milan, Italy
| | - Shimon Weiss
- Department of Chemistry & Biochemistry, UCLA, Los Angeles, CA, United States of America
| | - Xavier Michalet
- Department of Chemistry & Biochemistry, UCLA, Los Angeles, CA, United States of America
- * E-mail: (AI); (XM)
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21
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Okamoto K, Sako Y. Recent advances in FRET for the study of protein interactions and dynamics. Curr Opin Struct Biol 2017; 46:16-23. [PMID: 29800904 DOI: 10.1016/j.sbi.2017.03.010] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Revised: 02/20/2017] [Accepted: 03/20/2017] [Indexed: 11/20/2022]
Abstract
Förster/fluorescence resonance energy transfer (FRET) has been extensively used to detect the binding state or conformation of biomolecules. In the past few decades, various in vitro and in vivo applications of FRET measurement have been developed, including FRET probes, in-cell measurements, single-molecule measurements, and combination with computer simulation. In this review, we describe recent advances in FRET methods for examining biomolecular interactions and dynamics: (i) phasor plot analysis for quantitative analysis of protein interactions, (ii) single-molecule FRET measurement for detecting conformational dynamics in live cells, and (iii) data assimilation using molecular dynamics simulation to evaluate conformation of the whole protein.
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Affiliation(s)
- Kenji Okamoto
- Cellular Informatics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
| | - Yasushi Sako
- Cellular Informatics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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22
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Benke S, Nettels D, Hofmann H, Schuler B. Quantifying kinetics from time series of single-molecule Förster resonance energy transfer efficiency histograms. NANOTECHNOLOGY 2017; 28:114002. [PMID: 28103588 DOI: 10.1088/1361-6528/aa5abd] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Single-molecule fluorescence spectroscopy is a powerful approach for probing biomolecular structure and dynamics, including protein folding. For the investigation of nonequilibrium kinetics, Förster resonance energy transfer combined with confocal multiparameter detection has proven particularly versatile, owing to the large number of observables and the broad range of accessible timescales, especially in combination with rapid microfluidic mixing. However, a comprehensive kinetic analysis of the resulting time series of transfer efficiency histograms and complementary observables can be challenging owing to the complexity of the data. Here we present and compare three different methods for the analysis of such kinetic data: singular value decomposition, multivariate curve resolution with alternating least square fitting, and model-based peak fitting, where an explicit model of both the transfer efficiency histogram of each species and the kinetic mechanism of the process is employed. While each of these methods has its merits for specific applications, we conclude that model-based peak fitting is most suitable for a quantitative analysis and comparison of kinetic mechanisms.
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Affiliation(s)
- Stephan Benke
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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23
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Gidi Y, Götte M, Cosa G. Conformational Changes Spanning Angstroms to Nanometers via a Combined Protein-Induced Fluorescence Enhancement-Förster Resonance Energy Transfer Method. J Phys Chem B 2017; 121:2039-2048. [PMID: 28177636 DOI: 10.1021/acs.jpcb.6b11495] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Förster resonance energy transfer (FRET)-based single-molecule techniques have revolutionized our understanding of conformational dynamics in biomolecular systems. Recently, a new single-molecule technique based on protein-induced fluorescence enhancement (PIFE) has aided studies in which minimal (<3 nm) displacements occur. Concerns have been raised regarding whether donor fluorophore intensity (and correspondingly fluorescence quantum yield Φf) fluctuations, intrinsic to PIFE methods, may adversely affect FRET studies when retrieving the donor-acceptor dye distance. Here, we initially show through revisions of Förster's original equation that distances may be calculated in FRET experiments regardless of protein-induced intensity (and Φf) fluctuations occurring in the donor fluorophore. We additionally demonstrate by an analysis of the recorded emission intensity and competing decay pathways that PIFE and FRET methods may be conveniently combined, providing parallel complementary information in a single experiment. Single-molecule studies conducted with Cy3- and ATTO647N-labeled RNA structures and the HCV-NS5B polymerase protein undergoing binding dynamics along the RNA backbone provide a case study to validate the results. The analysis behind the proposed method enables for PIFE and FRET changes to be disentangled when both FRET and PIFE fluctuate over time following protein arrival and, for example, sliding. A new method, intensity-FRET, is thus proposed to monitor conformational changes spanning from angstroms to nanometers.
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Affiliation(s)
- Yasser Gidi
- Department of Chemistry and Center for Self-Assembled Chemical Structures (CSACS-CRMAA), McGill University , 801 Sherbrooke Street West, Montreal, Quebec, Canada H3A 0B8
| | - Matthias Götte
- Department of Biochemistry and Department of Medical Microbiology and Immunology, University of Alberta , 6020K Katz Group Centre, Edmonton, Alberta, Canada T6G 2E1
| | - Gonzalo Cosa
- Department of Chemistry and Center for Self-Assembled Chemical Structures (CSACS-CRMAA), McGill University , 801 Sherbrooke Street West, Montreal, Quebec, Canada H3A 0B8
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24
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Chen Y, Shen K, Shan SO, Kou SC. Analyzing Single-Molecule Protein Transportation Experiments via Hierarchical Hidden Markov Models. J Am Stat Assoc 2016; 111:951-966. [PMID: 28943680 PMCID: PMC5606165 DOI: 10.1080/01621459.2016.1140050] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 12/01/2015] [Indexed: 01/10/2023]
Abstract
To maintain proper cellular functions, over 50% of proteins encoded in the genome need to be transported to cellular membranes. The molecular mechanism behind such a process, often referred to as protein targeting, is not well understood. Single-molecule experiments are designed to unveil the detailed mechanisms and reveal the functions of different molecular machineries involved in the process. The experimental data consist of hundreds of stochastic time traces from the fluorescence recordings of the experimental system. We introduce a Bayesian hierarchical model on top of hidden Markov models (HMMs) to analyze these data and use the statistical results to answer the biological questions. In addition to resolving the biological puzzles and delineating the regulating roles of different molecular complexes, our statistical results enable us to propose a more detailed mechanism for the late stages of the protein targeting process.
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Affiliation(s)
- Yang Chen
- Ph.D. candidate, Department of Statistics, Harvard University, Cambridge, MA 02138
| | - Kuang Shen
- Pfizer fellow of the Life Sciences Research Foundation, Whitehead Institute for Biomedical Research, Cambridge, MA 02142
| | - Shu-Ou Shan
- Professor, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125
| | - S C Kou
- Professor, Department of Statistics, Harvard University, Cambridge, MA 02138
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25
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Ingargiola A, Laurence T, Boutelle R, Weiss S, Michalet X. Photon-HDF5: An Open File Format for Timestamp-Based Single-Molecule Fluorescence Experiments. Biophys J 2016; 110:26-33. [PMID: 26745406 DOI: 10.1016/j.bpj.2015.11.013] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Revised: 11/04/2015] [Accepted: 11/10/2015] [Indexed: 10/22/2022] Open
Abstract
We introduce Photon-HDF5, an open and efficient file format to simplify exchange and long-term accessibility of data from single-molecule fluorescence experiments based on photon-counting detectors such as single-photon avalanche diode, photomultiplier tube, or arrays of such detectors. The format is based on HDF5, a widely used platform- and language-independent hierarchical file format for which user-friendly viewers are available. Photon-HDF5 can store raw photon data (timestamp, channel number, etc.) from any acquisition hardware, but also setup and sample description, information on provenance, authorship and other metadata, and is flexible enough to include any kind of custom data. The format specifications are hosted on a public website, which is open to contributions by the biophysics community. As an initial resource, the website provides code examples to read Photon-HDF5 files in several programming languages and a reference Python library (phconvert), to create new Photon-HDF5 files and convert several existing file formats into Photon-HDF5. To encourage adoption by the academic and commercial communities, all software is released under the MIT open source license.
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Affiliation(s)
- Antonino Ingargiola
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California.
| | - Ted Laurence
- Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California
| | - Robert Boutelle
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California
| | - Shimon Weiss
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California
| | - Xavier Michalet
- Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California
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26
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Ingargiola A, Lerner E, Chung S, Weiss S, Michalet X. FRETBursts: An Open Source Toolkit for Analysis of Freely-Diffusing Single-Molecule FRET. PLoS One 2016; 11:e0160716. [PMID: 27532626 PMCID: PMC4988647 DOI: 10.1371/journal.pone.0160716] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 07/22/2016] [Indexed: 12/04/2022] Open
Abstract
Single-molecule Förster Resonance Energy Transfer (smFRET) allows probing intermolecular interactions and conformational changes in biomacromolecules, and represents an invaluable tool for studying cellular processes at the molecular scale. smFRET experiments can detect the distance between two fluorescent labels (donor and acceptor) in the 3-10 nm range. In the commonly employed confocal geometry, molecules are free to diffuse in solution. When a molecule traverses the excitation volume, it emits a burst of photons, which can be detected by single-photon avalanche diode (SPAD) detectors. The intensities of donor and acceptor fluorescence can then be related to the distance between the two fluorophores. While recent years have seen a growing number of contributions proposing improvements or new techniques in smFRET data analysis, rarely have those publications been accompanied by software implementation. In particular, despite the widespread application of smFRET, no complete software package for smFRET burst analysis is freely available to date. In this paper, we introduce FRETBursts, an open source software for analysis of freely-diffusing smFRET data. FRETBursts allows executing all the fundamental steps of smFRET bursts analysis using state-of-the-art as well as novel techniques, while providing an open, robust and well-documented implementation. Therefore, FRETBursts represents an ideal platform for comparison and development of new methods in burst analysis. We employ modern software engineering principles in order to minimize bugs and facilitate long-term maintainability. Furthermore, we place a strong focus on reproducibility by relying on Jupyter notebooks for FRETBursts execution. Notebooks are executable documents capturing all the steps of the analysis (including data files, input parameters, and results) and can be easily shared to replicate complete smFRET analyzes. Notebooks allow beginners to execute complex workflows and advanced users to customize the analysis for their own needs. By bundling analysis description, code and results in a single document, FRETBursts allows to seamless share analysis workflows and results, encourages reproducibility and facilitates collaboration among researchers in the single-molecule community.
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Affiliation(s)
- Antonino Ingargiola
- Dept. Chemistry and Biochemistry, Univ. of California Los Angeles, Los Angeles, CA, United States of America
- * E-mail:
| | - Eitan Lerner
- Dept. Chemistry and Biochemistry, Univ. of California Los Angeles, Los Angeles, CA, United States of America
| | - SangYoon Chung
- Dept. Chemistry and Biochemistry, Univ. of California Los Angeles, Los Angeles, CA, United States of America
| | - Shimon Weiss
- Dept. Chemistry and Biochemistry, Univ. of California Los Angeles, Los Angeles, CA, United States of America
| | - Xavier Michalet
- Dept. Chemistry and Biochemistry, Univ. of California Los Angeles, Los Angeles, CA, United States of America
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27
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Choi UB, Zhao M, Zhang Y, Lai Y, Brunger AT. Complexin induces a conformational change at the membrane-proximal C-terminal end of the SNARE complex. eLife 2016; 5. [PMID: 27253060 PMCID: PMC4927292 DOI: 10.7554/elife.16886] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 06/01/2016] [Indexed: 01/14/2023] Open
Abstract
Complexin regulates spontaneous and activates Ca2+-triggered neurotransmitter release, yet the molecular mechanisms are still unclear. Here we performed single molecule fluorescence resonance energy transfer experiments and uncovered two conformations of complexin-1 bound to the ternary SNARE complex. In the cis conformation, complexin-1 induces a conformational change at the membrane-proximal C-terminal end of the ternary SNARE complex that specifically depends on the N-terminal, accessory, and central domains of complexin-1. The complexin-1 induced conformation of the ternary SNARE complex may be related to a conformation that is juxtaposing the synaptic vesicle and plasma membranes. In the trans conformation, complexin-1 can simultaneously interact with a ternary SNARE complex via the central domain and a binary SNARE complex consisting of syntaxin-1A and SNAP-25A via the accessory domain. The cis conformation may be involved in activation of synchronous neurotransmitter release, whereas both conformations may be involved in regulating spontaneous release. DOI:http://dx.doi.org/10.7554/eLife.16886.001 Nerve cells communicate via electrical signals that travel at high speeds. However, these signals cannot pass across the gaps – called synapses – that separate one nerve cell from the next. Instead, signals pass between nerve cells via molecules called neurotransmitters that are released from the membrane of the first cell and recognized by receptors in the membrane of the next. Prior to being released, neurotransmitters are packaged inside bubble-like structures called vesicles. The synaptic vesicles must fuse with the cell membrane in order to release their contents into the synaptic cleft. Proteins called SNAREs work together with other proteins to allow this membrane fusion to occur rapidly after the electrical signal arrives. Complexin is a synaptic protein that binds tightly to a complex of SNARE proteins to regulate membrane fusion. This protein activates the quick release of neurotransmitters, which is triggered by an increase in calcium ions as the electrical signal reachess the synapse. Complexin also regulates a different type of neurotransmitter release, which is known as “spontaneous release”. The complexin protein is made up of different regions, each of which is required for one or more of the protein’s activities. However, it is not clear how these regions, or domains, interact with SNAREs and other proteins to enable complexin to perform these roles. Choi et al. have now investigated whether the different activities of mammalian complexin are related to the structure that it adopts when it interacts with the SNARE complex. Complexes of SNARE proteins were assembled with one of the SNARE proteins tethered to a surface for imaging. Next, a light-based imaging technique called single molecule Förster resonance energy transfer (or FRET) was used to monitor how complexin interacts with the SNARE complex. This technique allows individual proteins that have been labeled with fluorescent markers to be followed under a microscope and can show how they interact in real-time. Using this approach, Choi et al. showed that complexin could adopt two different shapes or conformations when it binds to the SNARE complex. In one, complexin interacted closely with the SNARE complex so that it made part of the complex change shape. In the other, complexin was able to bridge two SNARE complexes. Complexin can therefore interact with SNARE complexes in different ways by using different regions of the protein. These findings provide insight into how complexin may regulate membrane fusion via the SNARE complex. In the future, single molecule FRET could be used to study other proteins found at synapses and understand the other steps that regulate the release of neurotransmitters. DOI:http://dx.doi.org/10.7554/eLife.16886.002
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Affiliation(s)
- Ucheor B Choi
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Neurology and Neurological Sciences, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Structural Biology, Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Minglei Zhao
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Neurology and Neurological Sciences, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Structural Biology, Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Yunxiang Zhang
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Neurology and Neurological Sciences, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Structural Biology, Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Ying Lai
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Neurology and Neurological Sciences, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Structural Biology, Howard Hughes Medical Institute, Stanford University, Stanford, United States
| | - Axel T Brunger
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Neurology and Neurological Sciences, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Photon Science, Howard Hughes Medical Institute, Stanford University, Stanford, United States.,Department of Structural Biology, Howard Hughes Medical Institute, Stanford University, Stanford, United States
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28
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Characterizing 3D RNA structure by single molecule FRET. Methods 2016; 103:57-67. [PMID: 26853327 DOI: 10.1016/j.ymeth.2016.02.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Revised: 02/02/2016] [Accepted: 02/03/2016] [Indexed: 12/26/2022] Open
Abstract
The importance of elucidating the three dimensional structures of RNA molecules is becoming increasingly clear. However, traditional protein structural techniques such as NMR and X-ray crystallography have several important drawbacks when probing long RNA molecules. Single molecule Förster resonance energy transfer (smFRET) has emerged as a useful alternative as it allows native sequences to be probed in physiological conditions and allows multiple conformations to be probed simultaneously. This review serves to describe the method of generating a three dimensional RNA structure from smFRET data from the biochemical probing of the secondary structure to the computational refinement of the final model.
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29
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Vieweger M, Holmstrom ED, Nesbitt DJ. Single-Molecule FRET Reveals Three Conformations for the TLS Domain of Brome Mosaic Virus Genome. Biophys J 2015; 109:2625-2636. [PMID: 26682819 PMCID: PMC4699858 DOI: 10.1016/j.bpj.2015.10.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Revised: 10/01/2015] [Accepted: 10/07/2015] [Indexed: 12/28/2022] Open
Abstract
Metabolite-dependent conformational switching in RNA riboswitches is now widely accepted as a critical regulatory mechanism for gene expression in bacterial systems. More recently, similar gene regulation mechanisms have been found to be important for viral systems as well. One of the most abundant and best-studied systems is the tRNA-like structure (TLS) domain, which has been found to occur in many plant viruses spread across numerous genera. In this work, folding dynamics for the TLS domain of Brome Mosaic Virus have been investigated using single-molecule fluorescence resonance energy transfer techniques. In particular, burst fluorescence methods are exploited to observe metal-ion ([M(n+)])-induced folding in freely diffusing RNA constructs resembling the minimal TLS element of brome mosaic virus RNA3. The results of these experiments reveal a complex equilibrium of at least three distinct populations. A stepwise, or consecutive, thermodynamic model for TLS folding is developed, which is in good agreement with the [M(n+)]-dependent evolution of conformational populations and existing structural information in the literature. Specifically, this folding pathway explains the metal-ion dependent formation of a functional TLS domain from unfolded RNAs via two consecutive steps: 1) hybridization of a long-range stem interaction, followed by 2) formation of a 3'-terminal pseudoknot. These two conformational transitions are well described by stepwise dissociation constants for [Mg(2+)] (K1 = 328 ± 30 μM and K2 = 1092 ± 183 μM) and [Na(+)] (K1 = 74 ± 6 mM and K2 = 243 ± 52 mM)-induced folding. The proposed thermodynamic model is further supported by inhibition studies of the long-range stem interaction using a complementary DNA oligomer, which effectively shifts the dynamic equilibrium toward the unfolded conformation. Implications of this multistep conformational folding mechanism are discussed with regard to regulation of virus replication.
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Affiliation(s)
- Mario Vieweger
- Joint Institute for Laboratory Astrophysics, University of Colorado and National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado
| | - Erik D Holmstrom
- Joint Institute for Laboratory Astrophysics, University of Colorado and National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado
| | - David J Nesbitt
- Joint Institute for Laboratory Astrophysics, University of Colorado and National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado.
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30
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Gopich IV. Accuracy of maximum likelihood estimates of a two-state model in single-molecule FRET. J Chem Phys 2015; 142:034110. [PMID: 25612692 DOI: 10.1063/1.4904381] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Photon sequences from single-molecule Förster resonance energy transfer (FRET) experiments can be analyzed using a maximum likelihood method. Parameters of the underlying kinetic model (FRET efficiencies of the states and transition rates between conformational states) are obtained by maximizing the appropriate likelihood function. In addition, the errors (uncertainties) of the extracted parameters can be obtained from the curvature of the likelihood function at the maximum. We study the standard deviations of the parameters of a two-state model obtained from photon sequences with recorded colors and arrival times. The standard deviations can be obtained analytically in a special case when the FRET efficiencies of the states are 0 and 1 and in the limiting cases of fast and slow conformational dynamics. These results are compared with the results of numerical simulations. The accuracy and, therefore, the ability to predict model parameters depend on how fast the transition rates are compared to the photon count rate. In the limit of slow transitions, the key parameters that determine the accuracy are the number of transitions between the states and the number of independent photon sequences. In the fast transition limit, the accuracy is determined by the small fraction of photons that are correlated with their neighbors. The relative standard deviation of the relaxation rate has a "chevron" shape as a function of the transition rate in the log-log scale. The location of the minimum of this function dramatically depends on how well the FRET efficiencies of the states are separated.
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Affiliation(s)
- Irina V Gopich
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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31
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Buning R, Kropff W, Martens K, van Noort J. spFRET reveals changes in nucleosome breathing by neighboring nucleosomes. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:064103. [PMID: 25564102 DOI: 10.1088/0953-8984/27/6/064103] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Chromatin, the structure in which DNA is compacted in eukaryotic cells, plays a key role in regulating DNA accessibility. FRET experiments on single nucleosomes, the basic units in chromatin, have revealed a dynamic nucleosome where spontaneous DNA unwrapping from the ends provides access to the nucleosomal DNA. Here we investigated how this DNA breathing is affected by extension of the linker DNA and by the presence of a neighboring nucleosome. We found that both electrostatic interactions between the entering and exiting linker DNA and nucleosome-nucleosome interactions increase unwrapping. Interactions between neighboring nucleosomes are more likely in dinucleosomes spaced by 55 bp of linker DNA than in dinucleosomes spaced by 50 bp of linker DNA. Such increased unwrapping may not only increase the accessibility of nucleosomal DNA in chromatin fibers, it may also be key to folding of nucleosomes into higher order structures.
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Affiliation(s)
- Ruth Buning
- Huygens-Kamerlingh Onnes Laboratory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
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32
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Gust A, Zander A, Gietl A, Holzmeister P, Schulz S, Lalkens B, Tinnefeld P, Grohmann D. A starting point for fluorescence-based single-molecule measurements in biomolecular research. Molecules 2014; 19:15824-65. [PMID: 25271426 PMCID: PMC6271140 DOI: 10.3390/molecules191015824] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 09/17/2014] [Accepted: 09/17/2014] [Indexed: 01/24/2023] Open
Abstract
Single-molecule fluorescence techniques are ideally suited to provide information about the structure-function-dynamics relationship of a biomolecule as static and dynamic heterogeneity can be easily detected. However, what type of single-molecule fluorescence technique is suited for which kind of biological question and what are the obstacles on the way to a successful single-molecule microscopy experiment? In this review, we provide practical insights into fluorescence-based single-molecule experiments aiming for scientists who wish to take their experiments to the single-molecule level. We especially focus on fluorescence resonance energy transfer (FRET) experiments as these are a widely employed tool for the investigation of biomolecular mechanisms. We will guide the reader through the most critical steps that determine the success and quality of diffusion-based confocal and immobilization-based total internal reflection fluorescence microscopy. We discuss the specific chemical and photophysical requirements that make fluorescent dyes suitable for single-molecule fluorescence experiments. Most importantly, we review recently emerged photoprotection systems as well as passivation and immobilization strategies that enable the observation of fluorescently labeled molecules under biocompatible conditions. Moreover, we discuss how the optical single-molecule toolkit has been extended in recent years to capture the physiological complexity of a cell making it even more relevant for biological research.
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Affiliation(s)
- Alexander Gust
- Physikalische und Theoretische Chemie - NanoBioSciences, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, Braunschweig 38106, Germany
| | - Adrian Zander
- Physikalische und Theoretische Chemie - NanoBioSciences, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, Braunschweig 38106, Germany
| | - Andreas Gietl
- Physikalische und Theoretische Chemie - NanoBioSciences, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, Braunschweig 38106, Germany
| | - Phil Holzmeister
- Physikalische und Theoretische Chemie - NanoBioSciences, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, Braunschweig 38106, Germany
| | - Sarah Schulz
- Physikalische und Theoretische Chemie - NanoBioSciences, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, Braunschweig 38106, Germany
| | - Birka Lalkens
- Physikalische und Theoretische Chemie - NanoBioSciences, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, Braunschweig 38106, Germany
| | - Philip Tinnefeld
- Physikalische und Theoretische Chemie - NanoBioSciences, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, Braunschweig 38106, Germany
| | - Dina Grohmann
- Physikalische und Theoretische Chemie - NanoBioSciences, Technische Universität Braunschweig, Hans-Sommer-Strasse 10, Braunschweig 38106, Germany.
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33
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Maillot S, Carvalho A, Vola JP, Boudier C, Mély Y, Haacke S, Léonard J. Out-of-equilibrium biomolecular interactions monitored by picosecond fluorescence in microfluidic droplets. LAB ON A CHIP 2014; 14:1767-1774. [PMID: 24683603 DOI: 10.1039/c3lc51283e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We developed a new experimental approach combining Time-Resolved Fluorescence (TRF) spectroscopy and Droplet Microfluidics (DμF) to investigate the relaxation dynamics of structurally heterogeneous biomolecular systems. Here DμF was used to produce with minimal material consumption an out-of-equilibrium, fluorescently labeled biomolecular complex by rapid mixing within the droplets. TRF detection was implemented with a streak camera to monitor the time evolution of the structural heterogeneity of the complex along its relaxation towards equilibrium while it propagates inside the microfluidic channel. The approach was validated by investigating the fluorescence decay kinetics of a model interacting system of bovine serum albumin and Patent Blue V. Fluorescence decay kinetics are acquired with very good signal-to-noise ratio and allow for global, multicomponent fluorescence decay analysis, evidencing heterogeneous structural relaxation over several 100 ms.
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Affiliation(s)
- Sacha Maillot
- Institut de Physique et Chimie des Matériaux de Strasbourg & Labex NIE, Université de Strasbourg, CNRS UMR 7504, F-67034 Strasbourg Cedex 2, France.
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34
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Liu L, Werner M, Gershenson A. Collapse of a long axis: single-molecule Förster resonance energy transfer and serpin equilibrium unfolding. Biochemistry 2014; 53:2903-14. [PMID: 24749911 PMCID: PMC4020580 DOI: 10.1021/bi401622n] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Revised: 03/17/2014] [Indexed: 01/25/2023]
Abstract
The energy required for mechanical inhibition of target proteases is stored in the native structure of inhibitory serpins and accessed by serpin structural remodeling. The overall serpin fold is ellipsoidal with one long and two short axes. Most of the structural remodeling required for function occurs along the long axis, while expansion of the short axes is associated with misfolded, inactive forms. This suggests that ellipticity, as typified by the long axis, may be important for both function and folding. Placement of donor and acceptor fluorophores approximately along the long axis or one of the short axes allows single-pair Förster resonance energy transfer (spFRET) to report on both unfolding transitions and the time-averaged shape of different conformations. Equilibrium unfolding and refolding studies of the well-characterized inhibitory serpin α1-antitrypsin reveal that the long axis collapses in the folding intermediates while the monitored short axis expands. These energetically distinct intermediates are thus more spherical than the native state. Our spFRET studies agree with other equilibrium unfolding studies that found that the region around one of the β strands, s5A, which helps define the long axis and must move for functionally required loop insertion, unfolds at low denaturant concentrations. This supports a connection between functionally important structural lability and unfolding in the inhibitory serpins.
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Affiliation(s)
- Lu Liu
- Department
of Chemistry, Brandeis University, Waltham, Massachusetts 02453, United States
| | - Michael Werner
- Department
of Chemistry, Brandeis University, Waltham, Massachusetts 02453, United States
| | - Anne Gershenson
- Department
of Biochemistry and Molecular Biology, University
of Massachusetts Amherst, Amherst, Massachusetts 01003, United States
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35
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König SLB, Hadzic M, Fiorini E, Börner R, Kowerko D, Blanckenhorn WU, Sigel RKO. BOBA FRET: bootstrap-based analysis of single-molecule FRET data. PLoS One 2013; 8:e84157. [PMID: 24386343 PMCID: PMC3873958 DOI: 10.1371/journal.pone.0084157] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 11/12/2013] [Indexed: 01/18/2023] Open
Abstract
Time-binned single-molecule Förster resonance energy transfer (smFRET) experiments with surface-tethered nucleic acids or proteins permit to follow folding and catalysis of single molecules in real-time. Due to the intrinsically low signal-to-noise ratio (SNR) in smFRET time traces, research over the past years has focused on the development of new methods to extract discrete states (conformations) from noisy data. However, limited observation time typically leads to pronounced cross-sample variability, i.e., single molecules display differences in the relative population of states and the corresponding conversion rates. Quantification of cross-sample variability is necessary to perform statistical testing in order to assess whether changes observed in response to an experimental parameter (metal ion concentration, the presence of a ligand, etc.) are significant. However, such hypothesis testing has been disregarded to date, precluding robust biological interpretation. Here, we address this problem by a bootstrap-based approach to estimate the experimental variability. Simulated time traces are presented to assess the robustness of the algorithm in conjunction with approaches commonly used in thermodynamic and kinetic analysis of time-binned smFRET data. Furthermore, a pair of functionally important sequences derived from the self-cleaving group II intron Sc.ai5γ (d3'EBS1*/IBS1*) is used as a model system. Through statistical hypothesis testing, divalent metal ions are shown to have a statistically significant effect on both thermodynamic and kinetic aspects of their interaction. The Matlab source code used for analysis (bootstrap-based analysis of smFRET data, BOBA FRET), as well as a graphical user interface, is available via http://www.aci.uzh.ch/rna/.
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Affiliation(s)
- Sebastian L. B. König
- Institute of Inorganic Chemistry, University of Zurich, Zurich, Switzerland
- * E-mail: (RKOS); (SLBK)
| | - Mélodie Hadzic
- Institute of Inorganic Chemistry, University of Zurich, Zurich, Switzerland
| | - Erica Fiorini
- Institute of Inorganic Chemistry, University of Zurich, Zurich, Switzerland
| | - Richard Börner
- Institute of Inorganic Chemistry, University of Zurich, Zurich, Switzerland
| | - Danny Kowerko
- Institute of Inorganic Chemistry, University of Zurich, Zurich, Switzerland
| | - Wolf U. Blanckenhorn
- Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
| | - Roland K. O. Sigel
- Institute of Inorganic Chemistry, University of Zurich, Zurich, Switzerland
- * E-mail: (RKOS); (SLBK)
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36
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Techen A, Czapla S, Möllnitz K, Budach D, Wessig P, Kumke MU. Synthesis and Spectroscopic Characterization of Fluorophore-Labeled Oligospiroketal Rods. Helv Chim Acta 2013. [DOI: 10.1002/hlca.201200616] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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37
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Single molecule FRET data analysis procedures for FRET efficiency determination: Probing the conformations of nucleic acid structures. Methods 2013; 64:36-42. [DOI: 10.1016/j.ymeth.2013.04.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Revised: 04/02/2013] [Accepted: 04/03/2013] [Indexed: 11/23/2022] Open
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38
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Oikawa H, Suzuki Y, Saito M, Kamagata K, Arai M, Takahashi S. Microsecond dynamics of an unfolded protein by a line confocal tracking of single molecule fluorescence. Sci Rep 2013; 3:2151. [PMID: 23827883 PMCID: PMC3701896 DOI: 10.1038/srep02151] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Accepted: 06/20/2013] [Indexed: 02/03/2023] Open
Abstract
We present a new method for high speed tracking of fluorescence time series from single proteins. The method uses a fast sample flow and a modified confocal microscopy, line confocal microscopy, and achieves the time resolution of less than 20 μs. The obtained time series from the B domain of protein A labeled with donor and acceptor fluorophores suggest conformational heterogeneity and dynamic fluctuations in the unfolded state.
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Affiliation(s)
- Hiroyuki Oikawa
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba, Sendai, Miyagi 980-8577, Japan
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39
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DeVore MS, Gull SF, Johnson CK. Reconstruction of Calmodulin Single-Molecule FRET States, Dye-Interactions, and CaMKII Peptide Binding by MultiNest and Classic Maximum Entropy. Chem Phys 2013; 422:10.1016/j.chemphys.2012.11.018. [PMID: 24223465 PMCID: PMC3819237 DOI: 10.1016/j.chemphys.2012.11.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We analyze single molecule FRET burst measurements using Bayesian nested sampling. The MultiNest algorithm produces accurate FRET efficiency distributions from single-molecule data. FRET efficiency distributions recovered by MultiNest and classic maximum entropy are compared for simulated data and for calmodulin labeled at residues 44 and 117. MultiNest compares favorably with maximum entropy analysis for simulated data, judged by the Bayesian evidence. FRET efficiency distributions recovered for calmodulin labeled with two different FRET dye pairs depended on the dye pair and changed upon Ca2+ binding. We also looked at the FRET efficiency distributions of calmodulin bound to the calcium/calmodulin dependent protein kinase II (CaMKII) binding domain. For both dye pairs, the FRET efficiency distribution collapsed to a single peak in the case of calmodulin bound to the CaMKII peptide. These measurements strongly suggest that consideration of dye-protein interactions is crucial in forming an accurate picture of protein conformations from FRET data.
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Affiliation(s)
- Matthew S. DeVore
- Department of Chemistry, University of Kansas, Lawrence, Kansas, 66045, United States
| | - Stephen F. Gull
- Astrophysics Group, Department of Physics, Cambridge University, Cambridge CB3 0HE, United Kingdom
| | - Carey K. Johnson
- Department of Chemistry, University of Kansas, Lawrence, Kansas, 66045, United States
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40
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Zarrabi N, Ernst S, Verhalen B, Wilkens S, Börsch M. Analyzing conformational dynamics of single P-glycoprotein transporters by Förster resonance energy transfer using hidden Markov models. Methods 2013; 66:168-79. [PMID: 23891547 DOI: 10.1016/j.ymeth.2013.07.026] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Revised: 07/04/2013] [Accepted: 07/16/2013] [Indexed: 12/15/2022] Open
Abstract
Single-molecule Förster resonance energy (smFRET) transfer has become a powerful tool for observing conformational dynamics of biological macromolecules. Analyzing smFRET time trajectories allows to identify the state transitions occuring on reaction pathways of molecular machines. Previously, we have developed a smFRET approach to monitor movements of the two nucleotide binding domains (NBDs) of P-glycoprotein (Pgp) during ATP hydrolysis driven drug transport in solution. One limitation of this initial work was that single-molecule photon bursts were analyzed by visual inspection with manual assignment of individual FRET levels. Here a fully automated analysis of Pgp smFRET data using hidden Markov models (HMM) for transitions up to 9 conformational states is applied. We propose new estimators for HMMs to integrate the information of fluctuating intensities in confocal smFRET measurements of freely diffusing lipid bilayer bound membrane proteins in solution. HMM analysis strongly supports that under conditions of steady state turnover, conformational states with short NBD distances and short dwell times are more populated compared to conditions without nucleotide or transport substrate present.
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Affiliation(s)
- Nawid Zarrabi
- Single-Molecule Microscopy Group, Jena University Hospital, Friedrich Schiller University Jena, 07743 Jena, Germany; 3rd Institute of Physics, University of Stuttgart, 70550 Stuttgart, Germany
| | - Stefan Ernst
- Single-Molecule Microscopy Group, Jena University Hospital, Friedrich Schiller University Jena, 07743 Jena, Germany
| | - Brandy Verhalen
- Department of Biochemistry & Molecular Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA
| | - Stephan Wilkens
- Department of Biochemistry & Molecular Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA
| | - Michael Börsch
- Single-Molecule Microscopy Group, Jena University Hospital, Friedrich Schiller University Jena, 07743 Jena, Germany; 3rd Institute of Physics, University of Stuttgart, 70550 Stuttgart, Germany.
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41
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Goodson KA, Wang Z, Haeusler AR, Kahn JD, English DS. LacI-DNA-IPTG loops: equilibria among conformations by single-molecule FRET. J Phys Chem B 2013; 117:4713-22. [PMID: 23406418 DOI: 10.1021/jp308930c] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The E. coli Lac repressor (LacI) tetramer binds simultaneously to a promoter-proximal DNA binding site (operator) and an auxiliary operator, resulting in a DNA loop, which increases repression efficiency. Induction of the lac operon by allolactose reduces the affinity of LacI for DNA, but induction does not completely prevent looping in vivo. Our previous work on the conformations of LacI loops used a hyperstable model DNA construct, 9C14, that contains a sequence directed bend flanked by operators. Single-molecule fluorescence resonance energy transfer (SM-FRET) on a dual fluorophore-labeled LacI-9C14 loop showed that it adopts a single, stable, high-FRET V-shaped LacI conformation. Ligand-induced changes in loop geometry can affect loop stability, and the current work assesses loop population distributions for LacI-9C14 complexes containing the synthetic inducer IPTG. SM-FRET confirms that the high-FRET LacI-9C14 loop is only partially destabilized by saturating IPTG. LacI titration experiments and FRET fluctuation analysis suggest that the addition of IPTG induces loop conformational dynamics and re-equilibration between loop population distributions that include a mixture of looped states that do not exhibit high-efficiency FRET. The results show that repression by looping even at saturating IPTG should be considered in models for regulation of the operon. We propose that persistent DNA loops near the operator function biologically to accelerate rerepression upon exhaustion of inducer.
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Affiliation(s)
- Kathy A Goodson
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
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Okamoto K, Sako Y. Variational Bayes analysis of a photon-based hidden Markov model for single-molecule FRET trajectories. Biophys J 2013; 103:1315-24. [PMID: 22995504 DOI: 10.1016/j.bpj.2012.07.047] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 07/27/2012] [Accepted: 07/30/2012] [Indexed: 11/29/2022] Open
Abstract
Single-molecule fluorescence resonance energy transfer (smFRET) measurement is a powerful technique for investigating dynamics of biomolecules, for which various efforts have been made to overcome significant stochastic noise. Time stamp (TS) measurement has been employed experimentally to enrich information within the signals, while data analyses such as the hidden Markov model (HMM) have been successfully applied to recover the trajectories of molecular state transitions from time-binned photon counting signals or images. In this article, we introduce the HMM for TS-FRET signals, employing the variational Bayes (VB) inference to solve the model, and demonstrate the application of VB-HMM-TS-FRET to simulated TS-FRET data. The same analysis using VB-HMM is conducted for other models and the previously reported change point detection scheme. The performance is compared to other analysis methods or data types and we show that our VB-HMM-TS-FRET analysis can achieve the best performance and results in the highest time resolution. Finally, an smFRET experiment was conducted to observe spontaneous branch migration of Holliday-junction DNA. VB-HMM-TS-FRET was successfully applied to reconstruct the state transition trajectory with the number of states consistent with the nucleotide sequence. The results suggest that a single migration process frequently involves rearrangement of multiple basepairs.
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Affiliation(s)
- Kenji Okamoto
- Advanced Science Institute, RIKEN, Wako, Saitama, Japan.
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Fluorescence study of drug-carrier interactions in CTAB/PBS buffer model systems. J Colloid Interface Sci 2012; 377:251-61. [PMID: 22520209 DOI: 10.1016/j.jcis.2012.03.063] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Revised: 03/21/2012] [Accepted: 03/22/2012] [Indexed: 11/22/2022]
Abstract
The well-known cationic surfactant hexadecyltrimethylammonium bromide (CTAB) was used as a model carrier to study drug-carrier interactions with fluorescence probes (5-hexadecanoylaminofluorescein (HAF) and 2,10-bis-(3-aminopropyloxy)dibenzo[a,j]perylene-8,16-dione (NIR 628) by applying ensemble as well as single molecule fluorescence techniques. The impact of the probes on the micelle parameters (critical micelle concentration, average aggregation number, hydrodynamic radius) was investigated under physiological conditions. In the presence of additional electrolytes, such as buffer, the critical micelle concentration decreased by a factor of about 10. In contrast, no influence of the probes on the critical micelle concentration and on average aggregation number was observed. The results show that HAF does not affect the characteristics of CTAB micelles. Analyzing fluorescence correlation spectroscopy data and time-resolved anisotropy decays in terms of the "two-step" in combination with the "wobbling-in-cone" model, it was proven that HAF and NIR 628 are differently associated with the micelles. Based on ensemble and single molecule fluorescence experiments, intra- and intermicellar energy transfer process between the two dyes were probed and characterized.
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Abstract
We consider the analysis of a class of experiments in which the number of photons in consecutive time intervals is recorded. Sequence of photon counts or, alternatively, of FRET efficiencies can be studied using likelihood-based methods. For a kinetic model of the conformational dynamics and state-dependent Poisson photon statistics, the formalism to calculate the exact likelihood that this model describes such sequences of photons or FRET efficiencies is developed. Explicit analytic expressions for the likelihood function for a two-state kinetic model are provided. The important special case when conformational dynamics are so slow that at most a single transition occurs in a time bin is considered. By making a series of approximations, we eventually recover the likelihood function used in hidden Markov models. In this way, not only is insight gained into the range of validity of this procedure, but also an improved likelihood function can be obtained.
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Affiliation(s)
- Irina V Gopich
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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Yim SW, Kim T, Laurence TA, Partono S, Kim D, Kim Y, Weiss S, Reitmair A. Four-color alternating-laser excitation single-molecule fluorescence spectroscopy for next-generation biodetection assays. Clin Chem 2012; 58:707-16. [PMID: 22266381 DOI: 10.1373/clinchem.2011.176958] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND Single-molecule detection (SMD) technologies are well suited for clinical diagnostic applications by offering the prospect of minimizing precious patient sample requirements while maximizing clinical information content. Not yet available, however, is a universal SMD-based platform technology that permits multiplexed detection of both nucleic acid and protein targets and that is suitable for automation and integration into the clinical laboratory work flow. METHODS We have used a sensitive, specific, quantitative, and cost-effective homogeneous SMD method that has high single-well multiplexing potential and uses alternating-laser excitation (ALEX) fluorescence-aided molecule sorting extended to 4 colors (4c-ALEX). Recognition molecules are tagged with different-color fluorescence dyes, and coincident confocal detection of ≥2 colors constitutes a positive target-detection event. The virtual exclusion of the majority of sources of background noise eliminates washing steps. Sorting molecules with multidimensional probe stoichiometries (S) and single-molecule fluorescence resonance energy transfer efficiencies (E) allows differentiation of numerous targets simultaneously. RESULTS We show detection, differentiation, and quantification-in a single well-of (a) 25 different fluorescently labeled DNAs; (b) 8 bacterial genetic markers, including 3 antibiotic drug-resistance determinants found in 11 septicemia-causing Staphylococcus and Enterococcus strains; and (c) 6 tumor markers present in blood. CONCLUSIONS The results demonstrate assay utility for clinical molecular diagnostic applications by means of multiplexed detection of nucleic acids and proteins and suggest potential uses for early diagnosis of cancer and infectious and other diseases, as well as for personalized medicine. Future integration of additional technology components to minimize preanalytical sample manipulation while maximizing throughput should allow development of a user-friendly ("sample in, answer out") point-of-care platform for next-generation medical diagnostic tests that offer considerable savings in costs and patient sample.
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Affiliation(s)
- Seok W Yim
- Nesher Technologies, Inc., Los Angeles, CA 90057, USA
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Kelly D, Dillingham M, Hudson A, Wiesner K. A new method for inferring hidden markov models from noisy time sequences. PLoS One 2012; 7:e29703. [PMID: 22247783 PMCID: PMC3256161 DOI: 10.1371/journal.pone.0029703] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2011] [Accepted: 12/02/2011] [Indexed: 02/05/2023] Open
Abstract
We present a new method for inferring hidden Markov models from noisy time sequences without the necessity of assuming a model architecture, thus allowing for the detection of degenerate states. This is based on the statistical prediction techniques developed by Crutchfield et al. and generates so called causal state models, equivalent in structure to hidden Markov models. The new method is applicable to any continuous data which clusters around discrete values and exhibits multiple transitions between these values such as tethered particle motion data or Fluorescence Resonance Energy Transfer (FRET) spectra. The algorithms developed have been shown to perform well on simulated data, demonstrating the ability to recover the model used to generate the data under high noise, sparse data conditions and the ability to infer the existence of degenerate states. They have also been applied to new experimental FRET data of Holliday Junction dynamics, extracting the expected two state model and providing values for the transition rates in good agreement with previous results and with results obtained using existing maximum likelihood based methods. The method differs markedly from previous Markov-model reconstructions in being able to uncover truly hidden states.
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Affiliation(s)
- David Kelly
- School of Mathematics, University of Bristol, Bristol, United Kingdom.
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Andreou AZ, Klostermeier D. Conformational changes of DEAD-box helicases monitored by single molecule fluorescence resonance energy transfer. Methods Enzymol 2012; 511:75-109. [PMID: 22713316 DOI: 10.1016/b978-0-12-396546-2.00004-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
DEAD-box proteins catalyze the ATP-dependent unwinding of RNA duplexes. The common unit of these enzymes is a helicase core of two flexibly linked RecA domains. ATP binding and phosphate release control opening and closing of the cleft in the helicase core. This movement coordinates RNA-binding and ATPase activity and is thus central to the function of DEAD-box helicases. In most DEAD box proteins, the helicase core is flanked by ancillary N-and C-terminal domains. Here, we describe single molecule fluorescence resonance energy transfer (smFRET) approaches to directly monitor conformational changes associated with opening and closing of the helicase core. We further outline smFRET strategies to determine the orientation of flanking N- and C-terminal domains of DEAD-box helicases and to assess the effects of regulatory proteins on DEAD-box helicase conformation.
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Okamoto K, Terazima M. Quantitative Analysis of Single-Molecule FRET Signals and its Application to Telomere DNA. SINGLE-MOLECULE BIOPHYSICS 2011. [DOI: 10.1002/9781118131374.ch3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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50
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Zhi Z, Liu P, Wang P, Huang Y, Zhao XS. Domain-Specific Folding Kinetics of Staphylococcal Nuclease Observed through Single-Molecule FRET in a Microfluidic Mixer. Chemphyschem 2011; 12:3515-8. [DOI: 10.1002/cphc.201100652] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 10/17/2011] [Indexed: 11/07/2022]
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