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Trujillo J, Khan AS, Adhikari DP, Stoneman MR, Chacko JV, Eliceiri KW, Raicu V. Implementation of FRET Spectrometry Using Temporally Resolved Fluorescence: A Feasibility Study. Int J Mol Sci 2024; 25:4706. [PMID: 38731924 PMCID: PMC11083457 DOI: 10.3390/ijms25094706] [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: 03/30/2024] [Revised: 04/21/2024] [Accepted: 04/22/2024] [Indexed: 05/13/2024] Open
Abstract
Förster resonance energy transfer (FRET) spectrometry is a method for determining the quaternary structure of protein oligomers from distributions of FRET efficiencies that are drawn from pixels of fluorescence images of cells expressing the proteins of interest. FRET spectrometry protocols currently rely on obtaining spectrally resolved fluorescence data from intensity-based experiments. Another imaging method, fluorescence lifetime imaging microscopy (FLIM), is a widely used alternative to compute FRET efficiencies for each pixel in an image from the reduction of the fluorescence lifetime of the donors caused by FRET. In FLIM studies of oligomers with different proportions of donors and acceptors, the donor lifetimes may be obtained by fitting the temporally resolved fluorescence decay data with a predetermined number of exponential decay curves. However, this requires knowledge of the number and the relative arrangement of the fluorescent proteins in the sample, which is precisely the goal of FRET spectrometry, thus creating a conundrum that has prevented users of FLIM instruments from performing FRET spectrometry. Here, we describe an attempt to implement FRET spectrometry on temporally resolved fluorescence microscopes by using an integration-based method of computing the FRET efficiency from fluorescence decay curves. This method, which we dubbed time-integrated FRET (or tiFRET), was tested on oligomeric fluorescent protein constructs expressed in the cytoplasm of living cells. The present results show that tiFRET is a promising way of implementing FRET spectrometry and suggest potential instrument adjustments for increasing accuracy and resolution in this kind of study.
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Affiliation(s)
- Justin Trujillo
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA; (J.T.); (A.S.K.); (D.P.A.); (M.R.S.)
| | - Aliyah S. Khan
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA; (J.T.); (A.S.K.); (D.P.A.); (M.R.S.)
| | - Dhruba P. Adhikari
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA; (J.T.); (A.S.K.); (D.P.A.); (M.R.S.)
| | - Michael R. Stoneman
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA; (J.T.); (A.S.K.); (D.P.A.); (M.R.S.)
| | - Jenu V. Chacko
- Center for Quantitative Cell Imaging, University of Wisconsin-Madison, Madison, WI 53705, USA; (J.V.C.); (K.W.E.)
| | - Kevin W. Eliceiri
- Center for Quantitative Cell Imaging, University of Wisconsin-Madison, Madison, WI 53705, USA; (J.V.C.); (K.W.E.)
- Departments of Biomedical Engineering and Medical Physics, University of Wisconsin-Madison, Madison, WI 53705, USA
- Morgridge Institute for Research, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Valerica Raicu
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA; (J.T.); (A.S.K.); (D.P.A.); (M.R.S.)
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Killeen TD, Rahman S, Badu DN, Biener G, Stoneman MR, Raicu V. Fluorescence Intensity Fluctuation Analysis of Protein Oligomerization in Cell Membranes. Curr Protoc 2022; 2:e384. [PMID: 35312215 DOI: 10.1002/cpz1.384] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Fluorescence fluctuation spectroscopy (FFS) encompasses a bevy of techniques that involve analyzing fluorescence intensity fluctuations occurring due to fluorescently labeled molecules diffusing in and out of a microscope's focal region. Statistical analysis of these fluctuations may reveal the oligomerization (i.e., association) state of said molecules. We have recently developed a new FFS-based method, termed Two-Dimensional Fluorescence Intensity Fluctuation (2D FIF) spectrometry, which provides quantitative information on the size and stability of protein oligomers as a function of receptor concentration. This article describes protocols for employing FIF spectrometry to quantify the oligomerization of a membrane protein of interest, with specific instructions regarding cell preparation, image acquisition, and analysis of images given in detail. Application of the FIF Spectrometry Suite, a software package designed for applying FIF analysis on fluorescence images, is emphasized in the protocol. Also discussed in detail is the identification, removal, and/or analysis of inhomogeneous regions of the membrane that appear as bright spots. The 2D FIF approach is particularly suited to assess the effects of agonists and antagonists on the oligomeric size of membrane receptors of interest. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Preparation of live cells expressing protein constructs Basic Protocol 2: Image acquisition and noise correction Basic Protocol 3: Drawing and segmenting regions of interest Basic Protocol 4: Calculating the molecular brightness and concentration of individual image segments Basic Protocol 5: Combining data subsets using a manual procedure (Optional) Alternate Protocol 1: Combining data subsets using the advanced FIF spectrometry suite (Optional; alternative to Basic Protocol 5) Basic Protocol 6: Performing meta-analysis of brightness spectrograms Alternate Protocol 2: Performing meta-analysis of brightness spectrograms (alternative to Basic Protocol 6) Basic Protocol 7: Spot extraction and analysis using a manual procedure or by writing a program (Optional) Alternate Protocol 3: Automated spot extraction and analysis (Optional; alternative to Protocol 7) Support Protocol: Monomeric brightness determination.
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Affiliation(s)
- Tom D Killeen
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Sadia Rahman
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Dammar N Badu
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Gabriel Biener
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Michael R Stoneman
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Valerică Raicu
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.,Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
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Adhikari DP, Biener G, Stoneman MR, Badu DN, Paprocki JD, Eis A, Park PSH, Popa I, Raicu V. Comparative photophysical properties of some widely used fluorescent proteins under two-photon excitation conditions. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2021; 262:120133. [PMID: 34243141 DOI: 10.1016/j.saa.2021.120133] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 06/17/2021] [Accepted: 06/28/2021] [Indexed: 06/13/2023]
Abstract
Understanding the photophysical properties of fluorescent proteins (FPs), such as emission and absorption spectra, molecular brightness, photostability, and photo-switching, is critical to the development of criteria for their selection as tags for fluorescent-based biological applications. While two-photon excitation imaging techniques have steadily gained popularity - due to comparatively deeper penetration depth, reduced out-of-focus photobleaching, and wide separation between emission spectra and two-photon excitation spectra -, most studies reporting on the photophysical properties of FPs tend to remain focused on single-photon excitation. Here, we report our investigation of the photophysical properties of several commonly used fluorescent proteins using two-photon microscopy with spectral resolution in both excitation and emission. Our measurements indicate that not only the excitation (and sometimes emission) spectra of FPs may be markedly different between single-photon and two-photon excitation, but also their relative brightness and their photo-stability. A good understanding of the photophysical properties of FPs under two-photon excitation is essential for choosing the right tag(s) for a desired experiment.
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Affiliation(s)
- Dhruba P Adhikari
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Gabriel Biener
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | | | - Dammar N Badu
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Joel D Paprocki
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Annie Eis
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Paul S-H Park
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Ionel Popa
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA
| | - Valerică Raicu
- Department of Physics, University of Wisconsin-Milwaukee, WI 53211, USA; Department of Biological Sciences, University of Wisconsin-Milwaukee, WI 53211, USA.
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Biener G, Stoneman MR, Raicu V. Fluorescence intensity fluctuation analysis of receptor oligomerization in membrane domains. Biophys J 2021; 120:3028-3039. [PMID: 34214533 DOI: 10.1016/j.bpj.2021.06.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 06/02/2021] [Accepted: 06/11/2021] [Indexed: 11/26/2022] Open
Abstract
Fluorescence micrographs of the plasma membrane of cells expressing fluorescently labeled G protein-coupled receptors (GPCRs) often exhibit small clusters of pixels (or puncta) with intensities that are higher than those of the surrounding pixels. Although studies of GPCR interactions in uniform membrane areas abound, understanding the details of the GPCR interactions within such puncta as well as the nature of the membrane formations underlying the puncta is hampered by the lack of adequate experimental techniques. Here, we introduce an enhancement of a recently developed method termed fluorescence intensity fluctuation spectrometry, which permits analysis of protein-protein interactions within the puncta in live cell membranes. We applied the novel fluorescence intensity fluctuation data analysis protocol to previously published data from cells expressing human secretin receptors and determined that the oligomer size increases with receptor concentration and duration of treatment with cognate ligand, not only within uniform regions of the membrane (in agreement with previous publications) but also within the puncta. In addition, we found that the number density and fractional area of the puncta increased after treatment with ligand. This method could be applied for probing the evolution in the time of the chain of events that begins with ligand binding and continues with coated pits formation and receptor internalization for other GPCRs and, indeed, other membrane receptors in living cells.
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Affiliation(s)
- Gabriel Biener
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Michael R Stoneman
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin
| | - Valerică Raicu
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin; Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin.
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Trujillo J, Raicu V. Real time monitoring of the evolution of an epidemic regarded as a physical relaxation process. PHYSICS LETTERS. A 2021; 388:127074. [PMID: 33299265 PMCID: PMC7713574 DOI: 10.1016/j.physleta.2020.127074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Revised: 11/21/2020] [Accepted: 11/29/2020] [Indexed: 06/12/2023]
Abstract
The emergence of an epidemic evokes the need to monitor its spread and assess and validate any mitigation measures enacted by governments and administrative bodies in real time. We present here a method based on previous models of relaxation in fractal structures to observe and quantify this spread and the response of affected populations and governing bodies, and apply it to COVID-19 as a case study. This method provides means to simultaneously track in real time quantities such as the mortality and the recovery rates as well as the number of new infections caused by an infected person. With sufficient data, this method enables thorough monitoring and assessment of an epidemic without ad-hoc assumptions regarding the evolution of the pandemic in the future.
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Affiliation(s)
- Justin Trujillo
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA
| | - Valerică Raicu
- Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA
- Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA
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Paprocki J, Biener G, Stoneman M, Raicu V. In-Cell Detection of Conformational Substates of a G Protein-Coupled Receptor Quaternary Structure: Modulation of Substate Probability by Cognate Ligand Binding. J Phys Chem B 2020; 124:10062-10076. [DOI: 10.1021/acs.jpcb.0c06081] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Joel Paprocki
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
| | - Gabriel Biener
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
| | - Michael Stoneman
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
| | - Valerică Raicu
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
- Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, United States
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Stoneman MR, Biener G, Raicu V. Proposal for simultaneous analysis of fluorescence intensity fluctuations and resonance energy transfer (IFRET) measurements. Methods Appl Fluoresc 2020; 8:035011. [DOI: 10.1088/2050-6120/ab9b68] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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