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Schirripa Spagnolo C, Luin S. Impact of temporal resolution in single particle tracking analysis. DISCOVER NANO 2024; 19:87. [PMID: 38724858 PMCID: PMC11082114 DOI: 10.1186/s11671-024-04029-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2024] [Accepted: 04/29/2024] [Indexed: 05/12/2024]
Abstract
Temporal resolution is a key parameter in the observation of dynamic processes, as in the case of single molecules motions visualized in real time in two-dimensions by wide field (fluorescence) microscopy, but a systematic investigation of its effects in all the single particle tracking analysis steps is still lacking. Here we present tools to quantify its impact on the estimation of diffusivity and of its distribution using one of the most popular tracking software for biological applications on simulated data and movies. We found important shifts and different widths for diffusivity distributions, depending on the interplay of temporal sampling conditions with various parameters, such as simulated diffusivity, density of spots, signal-to-noise ratio, lengths of trajectories, and kind of boundaries in the simulation. We examined conditions starting from the ones of experiments on the fluorescently labelled receptor p75NTR, a relatively fast-diffusing membrane receptor (diffusivity around 0.5-1 µm2/s), visualized by TIRF microscopy on the basal membrane of living cells. From the analysis of the simulations, we identified the best conditions in cases similar to these ones; considering also the experiments, we could confirm a range of values of temporal resolution suitable for obtaining reliable diffusivity results. The procedure we present can be exploited in different single particle/molecule tracking applications to find an optimal temporal resolution.
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Affiliation(s)
| | - Stefano Luin
- NEST Laboratory, Scuola Normale Superiore, Piazza San Silvestro 12, 56127, Pisa, Italy.
- NEST Laboratory, Istituto Nanoscienze-CNR, Piazza San Silvestro 12, 56127, Pisa, Italy.
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2
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Smith JW, Carnevale LN, Das A, Chen Q. Electron videography of a lipid-protein tango. SCIENCE ADVANCES 2024; 10:eadk0217. [PMID: 38630809 PMCID: PMC11023515 DOI: 10.1126/sciadv.adk0217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Accepted: 03/15/2024] [Indexed: 04/19/2024]
Abstract
Biological phenomena, from enzymatic catalysis to synaptic transmission, originate in the structural transformations of biomolecules and biomolecular assemblies in liquid water. However, directly imaging these nanoscopic dynamics without probes or labels has been a fundamental methodological challenge. Here, we developed an approach for "electron videography"-combining liquid phase electron microscopy with molecular modeling-with which we filmed the nanoscale structural fluctuations of individual, suspended, and unlabeled membrane protein nanodiscs in liquid. Systematic comparisons with biochemical data and simulation indicate the graphene encapsulation involved can afford sufficiently reduced effects of the illuminating electron beam for these observations to yield quantitative fingerprints of nanoscale lipid-protein interactions. Our results suggest that lipid-protein interactions delineate dynamically modified membrane domains across unexpectedly long ranges. Moreover, they contribute to the molecular mechanics of the nanodisc as a whole in a manner specific to the protein within. Overall, this work illustrates an experimental approach to film, quantify, and understand biomolecular dynamics at the nanometer scale.
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Affiliation(s)
- John W. Smith
- Department of Materials Science and Engineering, University of Illinois Urbana–Champaign, Urbana, IL 61801, USA
| | - Lauren N. Carnevale
- Department of Biochemistry, University of Illinois Urbana–Champaign, Urbana, IL 61801, USA
| | - Aditi Das
- School of Chemistry and Biochemistry, Parker H. Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Qian Chen
- Department of Materials Science and Engineering, University of Illinois Urbana–Champaign, Urbana, IL 61801, USA
- Beckman Institute for Advanced Science and Technology, University of Illinois Urbana–Champaign, Urbana, IL 61801, USA
- Department of Chemistry, University of Illinois Urbana–Champaign, Urbana, IL 61801, USA
- Materials Research Laboratory, University of Illinois Urbana–Champaign, Urbana, IL 61801, USA
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3
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Szczepaniak F, Dehez F, Roux B. Configurational Sampling of All-Atom Solvated Membranes Using Hybrid Nonequilibrium Molecular Dynamics Monte Carlo Simulations. J Phys Chem Lett 2024; 15:3796-3804. [PMID: 38557030 DOI: 10.1021/acs.jpclett.4c00305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
All-atom simulations are a powerful approach to study the structure and dynamics of biological membranes. However, sampling the atomic configurations of inhomogeneous membranes can be challenging due to the slow lateral diffusion of the various constituents. To address this issue, a hybrid nonequilibrium molecular dynamics Monte Carlo (neMD/MC) simulation method is proposed in which randomly chosen lipid molecules are swapped to generate configurations that are subsequently accepted or rejected according to a Metropolis criterion based on the alchemical work for the attempted swap calculated via a short trajectory. A dual-topology framework constraining the common atoms of the exchanging molecules yields a good acceptance probability using switching trajectories as short as 10 ps. The performance of the hybrid neMD/MC algorithm and its ability to sample the distribution of lipids near a transmembrane helix carrying a net charge are illustrated for a binary mixture of charged and zwitterionic lipids.
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Affiliation(s)
- Florence Szczepaniak
- CNRS, LPCT, Université de Lorraine, F-54000 Nancy, France
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637,United States
| | - François Dehez
- CNRS, LPCT, Université de Lorraine, F-54000 Nancy, France
- Laboratoire International Associé Centre National de la Recherche Scientifique et University of Illinois at Urbana-Champaign, Université de Lorraine, LPCT, F-54000 Nancy, France
| | - Benoît Roux
- Department of Chemistry, University of Chicago, Chicago, Illinois 60637,United States
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4
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Investigation of Molecular Diffusion at Block Copolymer Thin Films Using Maximum Entropy Method-Based Fluorescence Correlation Spectroscopy and Single Molecule Tracking. J Fluoresc 2022; 32:1779-1787. [PMID: 35689743 DOI: 10.1007/s10895-022-02975-6] [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: 04/07/2022] [Accepted: 05/27/2022] [Indexed: 10/18/2022]
Abstract
Fluorescence correlation spectroscopy (FCS) has been widely used to investigate molecular diffusion behavior in various samples. The use of the maximum entropy method (MEM) for FCS data analysis provides a unique means to determine multiple distinct diffusion coefficients without a priori assumption of their number. Comparison of the MEM-based FCS method (MEM-FCS) with another method will reveal its utility and advantage as an analytical tool to investigate diffusion dynamics. Herein, we measured diffusion of fluorescent probes doped into nanostructured thin films using MEM-FCS, and validated the results with single molecule tracking (SMT) data. The efficacy of the MEM code employed was first demonstrated by analyzing simulated FCS data for systems incorporating one and two diffusion modes with broadly distributed diffusion coefficients. The MEM analysis accurately afforded the number of distinct diffusion modes and their mean diffusion coefficients. These results contrasted with those obtained by fitting the simulated data to conventional two-component and anomalous diffusion models, which yielded inaccurate estimates of the diffusion coefficients. Subsequently, the MEM analysis was applied to FCS data acquired from hydrophilic dye molecules incorporated into microphase-separated polystyrene-block-poly(ethylene oxide) (PS-b-PEO) thin films characterized under a water-saturated N2 atmosphere. The MEM analysis revealed distinct fast and slow diffusion components attributable to molecules diffusing on the film surface and inside the film, respectively. SMT studies of the same materials yielded trajectories for mobile molecules that appear to follow the curved PEO microdomains. Diffusion coefficients obtained from the SMT data were consistent with those obtained for the slow diffusion component detected by MEM-FCS. These results highlight the utility of MEM-FCS and SMT for gaining complementary information on molecular diffusion processes in heterogeneous material systems.
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5
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Huang SH, Huang BC, Chao L. Development of Cell Membrane Electrophoresis to Measure the Diffusivity of a Native Transmembrane Protein. Anal Chem 2022; 94:4531-4537. [PMID: 35230091 DOI: 10.1021/acs.analchem.2c00211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The lateral diffusion of transmembrane proteins in cell membranes is an important process that controls the dynamics and functions of the cell membrane. Several fluorescence-based techniques have been developed to study the diffusivities of transmembrane proteins. However, it is challenging to measure the diffusivity of a transmembrane protein with slow diffusion because of the photobleaching effect caused by long exposure times or multiple exposures to light. In this study, we developed a cell membrane electrophoresis platform to measure diffusivity. We deposited cell membrane vesicles derived from HeLa cells to form supported cell membrane patches. We demonstrated that the electrophoresis platform can be used to drive the movement of not only a lipid probe but also a native transmembrane protein, GLUT1. The movements were halted by the boundaries of the membrane patches and the concentration profiles reached steady states when the diffusion mass flux was balanced with the electrical mass flux. We used the Nernst-Planck equation as the mass balance equation to describe the steady concentration profiles and fitted these equations to our data to obtain the diffusivities. The obtained diffusivities were comparable to those obtained by fluorescence recovery after photobleaching, suggesting the validity of this new method of diffusivity measurement. Only a single snapshot is required for the diffusivity measurement, addressing the problems associated with photobleaching and allowing researchers to measure the diffusivity of transmembrane proteins with slow diffusion.
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Affiliation(s)
- Sin-Han Huang
- Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Bo-Chuan Huang
- Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Ling Chao
- Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
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6
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Unraveling the hidden temporal range of fast β 2-adrenergic receptor mobility by time-resolved fluorescence. Commun Biol 2022; 5:176. [PMID: 35228644 PMCID: PMC8885909 DOI: 10.1038/s42003-022-03106-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 02/02/2022] [Indexed: 12/29/2022] Open
Abstract
G-protein-coupled receptors (GPCRs) are hypothesized to possess molecular mobility over a wide temporal range. Until now the temporal range has not been fully accessible due to the crucially limited temporal range of available methods. This in turn, may lead relevant dynamic constants to remain masked. Here, we expand this dynamic range by combining fluorescent techniques using a spot confocal setup. We decipher mobility constants of β2-adrenergic receptor over a wide time range (nanosecond to second). Particularly, a translational mobility (10 µm²/s), one order of magnitude faster than membrane associated lateral mobility that explains membrane protein turnover and suggests a wider picture of the GPCR availability on the plasma membrane. And a so far elusive rotational mobility (1-200 µs) which depicts a previously overlooked dynamic component that, despite all complexity, behaves largely as predicted by the Saffman-Delbrück model. The mobility of the β2-adrenergic receptor, from the nanosecond to the second range, is revealed by combining several fluorescent spectroscopy techniques. These data also show a previously hidden mobility of this GPCR.
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7
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Uribe J, Traberg WC, Hama A, Druet V, Mohamed Z, Ooi A, Pappa AM, Huerta M, Inal S, Owens RM, Daniel S. Dual Mode Sensing of Binding and Blocking of Cancer Exosomes to Biomimetic Human Primary Stem Cell Surfaces. ACS Biomater Sci Eng 2021; 7:5585-5597. [PMID: 34802228 DOI: 10.1021/acsbiomaterials.1c01056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cancer-derived exosomes (cEXOs) facilitate transfer of information between tumor and human primary stromal cells, favoring cancer progression. Although the mechanisms used during this information exchange are still not completely understood, it is known that binding is the initial contact established between cEXOs and cells. Hence, studying binding and finding strategies to block it are of great therapeutic value. However, such studies are challenging for a variety of reasons, including the need for human primary cell culture, the difficulty in decoupling and isolating binding from internalization and cargo delivery, and the lack of techniques to detect these specific interactions. In this work, we created a supported biomimetic stem cell membrane incorporating membrane components from human primary adipose-derived stem cells (ADSCs). We formed the supported membrane on glass and on multielectrode arrays to offer the dual option of optical or electrical detection of cEXO binding to the membrane surface. Using our platform, we show that cEXOs bind to the stem cell membrane and that binding is blocked when an antibody to integrin β1, a component of ADSC surface, is exposed to the membrane surface prior to cEXOs. To test the biological outcome of blocking this interaction, we first confirm that adding cEXOs to cultured ADSCs leads to the upregulation of vascular endothelial growth factor, a measure of proangiogenic activity. Next, when ADSCs are first blocked with anti-integrin β1 and then exposed to cEXOs, the upregulation of proangiogenic activity and cell proliferation are significantly reduced. This biomimetic membrane platform is the first cell-free label-free in vitro platform for the recapitulation and study of cEXO binding to human primary stem cells with potential for therapeutic molecule screening as it is compatible with scale-up and multiplexing.
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Affiliation(s)
- Johana Uribe
- Meinig School of Biomedical Engineering, Cornell University, Ithaca, New York 14853-0001, United States
| | - Walther C Traberg
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB3 0AS, United Kingdom
| | - Adel Hama
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 3955, Kingdom of Saudi Arabia
| | - Victor Druet
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 3955, Kingdom of Saudi Arabia
| | - Zeinab Mohamed
- Meinig School of Biomedical Engineering, Cornell University, Ithaca, New York 14853-0001, United States
| | - Amanda Ooi
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 3955, Kingdom of Saudi Arabia
| | - Anna-Maria Pappa
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB3 0AS, United Kingdom.,Department of Biomedical Engineering, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates
| | - Miriam Huerta
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853-5201, United States
| | - Sahika Inal
- Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 3955, Kingdom of Saudi Arabia
| | - Róisín M Owens
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB3 0AS, United Kingdom
| | - Susan Daniel
- Meinig School of Biomedical Engineering, Cornell University, Ithaca, New York 14853-0001, United States.,School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853-5201, United States
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8
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Rose M, Kurylowicz M, Mahmood M, Winkel S, Moran-Mirabal JM, Fradin C. Direct Measurement of the Affinity between tBid and Bax in a Mitochondria-Like Membrane. Int J Mol Sci 2021; 22:8240. [PMID: 34361006 PMCID: PMC8348223 DOI: 10.3390/ijms22158240] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Revised: 07/19/2021] [Accepted: 07/22/2021] [Indexed: 01/05/2023] Open
Abstract
The execution step in apoptosis is the permeabilization of the outer mitochondrial membrane, controlled by Bcl-2 family proteins. The physical interactions between the different proteins in this family and their relative abundance literally determine the fate of the cells. These interactions, however, are difficult to quantify, as they occur in a lipid membrane and involve proteins with multiple conformations and stoichiometries which can exist both in soluble and membrane. Here we focus on the interaction between two core Bcl-2 family members, the executor pore-forming protein Bax and the truncated form of the activator protein Bid (tBid), which we imaged at the single particle level in a mitochondria-like planar supported lipid bilayer. We inferred the conformation of the proteins from their mobility, and detected their transient interactions using a novel single particle cross-correlation analysis. We show that both tBid and Bax have at least two different conformations at the membrane, and that their affinity for one another increases by one order of magnitude (with a 2D-KD decreasing from ≃1.6μm-2 to ≃0.1μm-2) when they pass from their loosely membrane-associated to their transmembrane form. We conclude by proposing an updated molecular model for the activation of Bax by tBid.
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Affiliation(s)
- Markus Rose
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
| | - Martin Kurylowicz
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
| | - Mohammad Mahmood
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
| | - Sheldon Winkel
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
| | - Jose M. Moran-Mirabal
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, ON L8S 4M1, Canada;
| | - Cécile Fradin
- Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada; (M.R.); (M.K.); (M.M.); (S.W.)
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON L8S 4K1, Canada
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9
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Single-particle tracking photoactivated localization microscopy of membrane proteins in living plant tissues. Nat Protoc 2021; 16:1600-1628. [PMID: 33627844 DOI: 10.1038/s41596-020-00471-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Accepted: 11/24/2020] [Indexed: 01/31/2023]
Abstract
Super-resolution microscopy techniques have pushed the limit of optical imaging to unprecedented spatial resolutions. However, one of the frontiers in nanoscopy is its application to intact living organisms. Here we describe the implementation and application of super-resolution single-particle tracking photoactivated localization microscopy (sptPALM) to probe single-molecule dynamics of membrane proteins in live roots of the model plant Arabidopsis thaliana. We first discuss the advantages and limitations of sptPALM for studying the diffusion properties of membrane proteins and compare this to fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS). We describe the technical details for handling and imaging the samples for sptPALM, with a particular emphasis on the specificity of imaging plant cells, such as their thick cell walls or high degree of autofluorescence. We then provide a practical guide from data collection to image analyses. In particular, we introduce our sptPALM_viewer software and describe how to install and use it for analyzing sptPALM experiments. Finally, we report an R statistical analysis pipeline to analyze and compare sptPALM experiments. Altogether, this protocol should enable plant researchers to perform sptPALM using a benchmarked reproducible protocol. Routinely, the procedure takes 3-4 h of imaging followed by 3-4 d of image processing and data analysis.
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10
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Membrane Homeostasis: The Role of Actin Cytoskeleton. J Indian Inst Sci 2021. [DOI: 10.1007/s41745-020-00217-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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11
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Otosu T, Yamaguchi S. Leaflet-specific Lipid Diffusion Revealed by Fluorescence Lifetime Correlation Analyses. CHEM LETT 2020. [DOI: 10.1246/cl.200539] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Takuhiro Otosu
- Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Shoichi Yamaguchi
- Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
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12
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Lateral diffusion of CD14 and TLR2 in macrophage plasma membrane assessed by raster image correlation spectroscopy and single particle tracking. Sci Rep 2020; 10:19375. [PMID: 33168941 PMCID: PMC7652837 DOI: 10.1038/s41598-020-76272-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 10/23/2020] [Indexed: 01/02/2023] Open
Abstract
The diffusion of membrane receptors is central to many biological processes, such as signal transduction, molecule translocation, and ion transport, among others; consequently, several advanced fluorescence microscopy techniques have been developed to measure membrane receptor mobility within live cells. The membrane-anchored receptor cluster of differentiation 14 (CD14) and the transmembrane toll-like receptor 2 (TLR2) are important receptors in the plasma membrane of macrophages that activate the intracellular signaling cascade in response to pathogenic stimuli. The aim of the present work was to compare the diffusion coefficients of CD14 and TLR2 on the apical and basal membranes of macrophages using two fluorescence-based methods: raster image correlation spectroscopy (RICS) and single particle tracking (SPT). In the basal membrane, the diffusion coefficients obtained from SPT and RICS were found to be comparable and revealed significantly faster diffusion of CD14 compared with TLR2. In addition, RICS showed that the diffusion of both receptors was significantly faster in the apical membrane than in the basal membrane, suggesting diffusion hindrance by the adhesion of the cells to the substrate. This finding highlights the importance of selecting the appropriate membrane (i.e., basal or apical) and corresponding method when measuring receptor diffusion in live cells. Accurately knowing the diffusion coefficient of two macrophage receptors involved in the response to pathogen insults will facilitate the study of changes that occur in signaling in these cells as a result of aging and disease.
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13
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Thompson CJ, Su Z, Vu VH, Wu Y, Leckband DE, Schwartz DK. Cadherin clusters stabilized by a combination of specific and nonspecific cis-interactions. eLife 2020; 9:e59035. [PMID: 32876051 PMCID: PMC7505656 DOI: 10.7554/elife.59035] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Accepted: 09/01/2020] [Indexed: 12/13/2022] Open
Abstract
We demonstrate a combined experimental and computational approach for the quantitative characterization of lateral interactions between membrane-associated proteins. In particular, weak, lateral (cis) interactions between E-cadherin extracellular domains tethered to supported lipid bilayers, were studied using a combination of dynamic single-molecule Förster Resonance Energy Transfer (FRET) and kinetic Monte Carlo (kMC) simulations. Cadherins are intercellular adhesion proteins that assemble into clusters at cell-cell contacts through cis- and trans- (adhesive) interactions. A detailed and quantitative understanding of cis-clustering has been hindered by a lack of experimental approaches capable of detecting and quantifying lateral interactions between proteins on membranes. Here single-molecule intermolecular FRET measurements of wild-type E-cadherin and cis-interaction mutants combined with simulations demonstrate that both nonspecific and specific cis-interactions contribute to lateral clustering on lipid bilayers. Moreover, the intermolecular binding and dissociation rate constants are quantitatively and independently determined, demonstrating an approach that is generalizable for other interacting proteins.
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Affiliation(s)
- Connor J Thompson
- Department of Chemical and Biological Engineering, University of Colorado BoulderBoulderUnited States
| | - Zhaoqian Su
- Department of Systems and Computational Biology, Albert Einstein College of MedicineBronxUnited States
| | - Vinh H Vu
- Department of Biochemistry and University of Illinois, Urbana-ChampaignUrbanaUnited States
| | - Yinghao Wu
- Department of Systems and Computational Biology, Albert Einstein College of MedicineBronxUnited States
| | - Deborah E Leckband
- Department of Biochemistry and University of Illinois, Urbana-ChampaignUrbanaUnited States
- Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana-ChampaignUrbanaUnited States
| | - Daniel K Schwartz
- Department of Chemical and Biological Engineering, University of Colorado BoulderBoulderUnited States
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14
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Bailey-Hytholt CM, Shen TL, Nie B, Tripathi A, Shukla A. Placental Trophoblast-Inspired Lipid Bilayers for Cell-Free Investigation of Molecular Interactions. ACS APPLIED MATERIALS & INTERFACES 2020; 12:31099-31111. [PMID: 32558532 DOI: 10.1021/acsami.0c06197] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The placenta plays a key role in regulating the maternal-fetal transport but it is a difficult organ to study due to a lack of existing in vitro models. Lipid bilayers inspired by the placenta can provide a facile new in vitro tool with promise for screening molecular transport across this important organ. Here we developed lipid bilayers that mimic the composition of human placental trophoblast cells at different times during the course of pregnancy. Mass spectrometry identified five major lipid classes (phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and sphingomyelin) present at varying concentrations in trophoblasts representative of the first and third trimesters and full-term placenta. We successfully developed supported and suspended lipid bilayers mimicking these trophoblast lipid compositions and then demonstrated the utility of these synthetic placenta models for investigating molecular interactions. Specifically, we investigated the interactions with di(2-ethylhexyl) phthalate (DEHP), a common plasticizer and environmental toxicant, and amphotericin B, a common yet toxic, antifungal therapeutic. Overall, we observed that DEHP adsorbs and potentially embeds itself within all placental lipid bilayers, with varying levels of interaction. For both amphotericin B and a liposomal formulation of amphotericin B, AmBisome, we noted lower levels of permeation in transport studies with bilayers and trophoblast cells compared with DEHP, likely driven by differences in size. AmBisome interacted less with both the supported and suspended placental lipid bilayers in comparison to amphotericin B, suggesting that drug delivery carriers can vary the impact of a pharmaceutical agent on these lipid structures. We found that the apparent permeability observed in suspended bilayers was approximately an order of magnitude less than those observed for trophoblast monolayers, which is typical of lipid bilayers. Ultimately, these placenta mimetic lipid bilayers can serve as a platform for the rapid initial screening of molecular interactions with the maternal-fetal interface to better inform future testing.
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Affiliation(s)
- Christina M Bailey-Hytholt
- School of Engineering, Center for Biomedical Engineering, Brown University, Providence, Rhode Island 02912, United States
| | - Tun-Li Shen
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Bonnee Nie
- Department of Biochemistry and Molecular Biology, Brown University, Providence, Rhode Island 02912, United States
| | - Anubhav Tripathi
- School of Engineering, Center for Biomedical Engineering, Brown University, Providence, Rhode Island 02912, United States
| | - Anita Shukla
- School of Engineering, Center for Biomedical Engineering, Brown University, Providence, Rhode Island 02912, United States
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15
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Robinson J, Berselli GB, Ryadnov MG, Keyes TE. Annexin V Drives Stabilization of Damaged Asymmetric Phospholipid Bilayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:5454-5465. [PMID: 32326703 DOI: 10.1021/acs.langmuir.0c00035] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Annexins are soluble membrane-binding proteins that associate in a calcium dependent manner with anionic phospholipids. They play roles in membrane organization, signaling and vesicle transport and in several disease states including thrombosis and inflammation. Annexin V is believed to be involved in membrane repair. Mediated through binding to phosphatidylserine exposed at damaged plasma membrane, the protein forms crystalline networks that seal or stabilize small membrane tears. Herein, we model this biochemical mechanism to simulate membrane healing at microcavity array supported, transversally asymmetric, lipid bilayers (MSLBs) comprising 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS). Varying annexin V concentration, lipid composition, and DOPS presence at each leaflet, fluorescence imaging and correlation spectroscopy confirmed that when DOPS was present at the external, annexin V, contacting leaflet, the protein assembled rapidly at the membrane interface to form a layer. From electrochemical impedance studies, the annexin layer decreased membrane capacitance while reducing resistance. With DOPS incorporated only at the lower (proximal) leaflet, no appreciable annexin assembly was observed over the first 21 h. This suggests that membrane asymmetry is preserved over this window and transversal diffusion of DOPS is slow. Intense laser light applied to the membrane, in which DOPS is initially isolated at the lower leaflet, was found to simulate membrane damage, stimulating the rapid assembly of annexin V at the membrane interface confirmed by fluorescence imaging, correlation spectroscopy, and electrochemical impedance measurements. The damage induced by light increased impedance and decreased membrane resistance. The resulting bilayer annexin V patched bilayer showed better temporal stability toward impedance changes when compared with that of the parent membrane. In summary, this simple model of annexin V assembly in a fluidic lipid membrane provides new insights into the assembly of annexins as well as an empirical basis for building patch-repair mechanisms into interfacial bilayer membrane assemblies.
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Affiliation(s)
- Jack Robinson
- School of Chemical Sciences and National Centre for Sensor Research, Dublin City University, Glasnevin, Dublin 9, Ireland
| | - Guilherme B Berselli
- School of Chemical Sciences and National Centre for Sensor Research, Dublin City University, Glasnevin, Dublin 9, Ireland
| | - Maxim G Ryadnov
- National Physical Laboratory, Hampton Road, Teddington TW110LW, United Kingdom
| | - Tia E Keyes
- School of Chemical Sciences and National Centre for Sensor Research, Dublin City University, Glasnevin, Dublin 9, Ireland
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16
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Verardo D, Agnarsson B, Zhdanov VP, Höök F, Linke H. Single-Molecule Detection with Lightguiding Nanowires: Determination of Protein Concentration and Diffusivity in Supported Lipid Bilayers. NANO LETTERS 2019; 19:6182-6191. [PMID: 31369284 DOI: 10.1021/acs.nanolett.9b02226] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Determining the surface concentration and diffusivity of cell-membrane-bound molecules is central to the understanding of numerous important biochemical processes taking place at cell membranes. Here we use the high aspect ratio and lightguiding properties of semiconductor nanowires (NWs) to detect the presence of single freely diffusing proteins bound to a lipid bilayer covering the NW surface. Simultaneous observation of light-emission dynamics of hundreds of individual NWs occurring on the time scale of only a few seconds is interpreted using analytical models and employed to determine both surface concentration and diffusivity of cholera toxin subunit B (CTxB) bound to GM1 gangliosides in supported lipid bilayer (SLB) at surface concentrations down to below one CTxB per μm2. In particular, a decrease in diffusivity was observed with increasing GM1 content in the SLB, suggesting increasing multivalent binding of CTxB to GM1. The lightguiding capability of the NWs makes the method compatible with conventional epifluorescence microscopy, and it is shown to work well for both photostable and photosensitive dyes. These features make the concept an interesting complement to existing techniques for studying the diffusivity of low-abundance cell-membrane-bound molecules, expanding the rapidly growing use of semiconductor NWs in various bioanalytical sensor applications and live cell studies.
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Affiliation(s)
- Damiano Verardo
- NanoLund and Solid State Physics , Lund University , 22100 Lund , Sweden
| | - Björn Agnarsson
- Department of Physics , Chalmers University of Technology , 41296 Göteborg , Sweden
| | - Vladimir P Zhdanov
- Department of Physics , Chalmers University of Technology , 41296 Göteborg , Sweden
- Boreskov Institute of Catalysis , Russian Academy of Sciences , Novosibirsk 630090 , Russia
| | - Fredrik Höök
- Department of Physics , Chalmers University of Technology , 41296 Göteborg , Sweden
| | - Heiner Linke
- NanoLund and Solid State Physics , Lund University , 22100 Lund , Sweden
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17
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Coker HLE, Cheetham MR, Kattnig DR, Wang YJ, Garcia-Manyes S, Wallace MI. Controlling Anomalous Diffusion in Lipid Membranes. Biophys J 2019; 116:1085-1094. [PMID: 30846364 DOI: 10.1016/j.bpj.2018.12.024] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 11/21/2018] [Accepted: 12/14/2018] [Indexed: 12/24/2022] Open
Abstract
Diffusion in cell membranes is not just simple two-dimensional Brownian motion but typically depends on the timescale of the observation. The physical origins of this anomalous subdiffusion are unresolved, and model systems capable of quantitative and reproducible control of membrane diffusion have been recognized as a key experimental bottleneck. Here, we control anomalous diffusion using supported lipid bilayers containing lipids derivatized with polyethylene glycol (PEG) headgroups. Bilayers with specific excluded area fractions are formed by control of PEG lipid mole fraction. These bilayers exhibit a switch in diffusive behavior, becoming anomalous as bilayer continuity is disrupted. Using a combination of single-molecule fluorescence and interferometric imaging, we measure the anomalous behavior in this model over four orders of magnitude in time. Diffusion in these bilayers is well described by a power-law dependence of the mean-square displacement with observation time. Anomaleity in this system can be tailored by simply controlling the mole fraction of PEG lipid, producing bilayers with diffusion parameters similar to those observed for anomalous diffusion in biological membranes.
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Affiliation(s)
- Helena L E Coker
- Department of Chemistry, King's College London, London, United Kingdom; Chemistry Research Laboratory, University of Oxford, Oxford, United Kingdom
| | - Matthew R Cheetham
- Department of Chemistry, King's College London, London, United Kingdom; Chemistry Research Laboratory, University of Oxford, Oxford, United Kingdom
| | - Daniel R Kattnig
- Living Systems Institute & Department of Physics, University of Exeter, Exeter, United Kingdom
| | - Yong J Wang
- Department of Physics, King's College London, London, United Kingdom
| | | | - Mark I Wallace
- Department of Chemistry, King's College London, London, United Kingdom.
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18
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Otosu T, Yamaguchi S. Quantifying the Diffusion of Lipids in the Proximal/Distal Leaflets of a Supported Lipid Bilayer by Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy. J Phys Chem B 2018; 122:10315-10319. [DOI: 10.1021/acs.jpcb.8b08614] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Takuhiro Otosu
- Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan
| | - Shoichi Yamaguchi
- Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan
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19
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Weatherill EE, Coker HLE, Cheetham MR, Wallace MI. Urea-mediated anomalous diffusion in supported lipid bilayers. Interface Focus 2018; 8:20180028. [PMID: 30443327 PMCID: PMC6227775 DOI: 10.1098/rsfs.2018.0028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/08/2018] [Indexed: 12/16/2022] Open
Abstract
Diffusion in biological membranes is seldom simply Brownian motion; instead, the rate of diffusion is dependent on the time scale of observation and so is often described as anomalous. In order to help better understand this phenomenon, model systems are needed where the anomalous diffusion of the lipid bilayer can be tuned and quantified. We recently demonstrated one such model by controlling the excluded area fraction in supported lipid bilayers (SLBs) through the incorporation of lipids derivatized with polyethylene glycol. Here, we extend this work, using urea to induce anomalous diffusion in SLBs. By tuning incubation time and urea concentration, we produce bilayers that exhibit anomalous behaviour on the same scale as that observed in biological membranes.
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Affiliation(s)
- E. E. Weatherill
- Department of Chemistry, Britannia House, King's College London, 7 Trinity Street, London SE1 1DB, UK
| | - H. L. E. Coker
- Department of Chemistry, Britannia House, King's College London, 7 Trinity Street, London SE1 1DB, UK
- Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, UK
| | - M. R. Cheetham
- Department of Chemistry, Britannia House, King's College London, 7 Trinity Street, London SE1 1DB, UK
- Cavendish Laboratory, Department of Physics, NanoPhotonics Centre, University of Cambridge, Cambridge CB3 0HE, UK
| | - M. I. Wallace
- Department of Chemistry, Britannia House, King's College London, 7 Trinity Street, London SE1 1DB, UK
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20
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Otosu T, Yamaguchi S. Total Internal Reflection Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy. J Phys Chem B 2018; 122:5758-5764. [DOI: 10.1021/acs.jpcb.8b01176] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Takuhiro Otosu
- Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan
| | - Shoichi Yamaguchi
- Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan
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21
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Harwardt MLIE, Dietz MS, Heilemann M, Wohland T. SPT and Imaging FCS Provide Complementary Information on the Dynamics of Plasma Membrane Molecules. Biophys J 2018; 114:2432-2443. [PMID: 29650369 PMCID: PMC6129459 DOI: 10.1016/j.bpj.2018.03.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 02/10/2018] [Accepted: 03/12/2018] [Indexed: 12/27/2022] Open
Abstract
The dynamics of biomolecules in the plasma membrane is of fundamental importance to understanding cellular processes. Cellular signaling often starts with extracellular ligand binding to a membrane receptor, which then transduces an intracellular signal. Ligand binding and receptor-complex activation often involve a complex rearrangement of proteins in the membrane, which results in changes in diffusion properties. Two widely used methods to characterize biomolecular diffusion are single-particle tracking (SPT) and imaging total internal reflection fluorescence correlation spectroscopy (ITIR-FCS). Here, we compare the results of recovered diffusion coefficients and mean-square displacements of the two methods by simulations of free, domain-confined, or meshwork diffusion. We introduce, to our knowledge, a new method for the determination of confinement radii from ITIR-FCS data. We further establish and demonstrate simultaneous SPT/ITIR-FCS for direct comparison within living cells. Finally, we compare the results obtained by SPT and ITIR-FCS for the receptor tyrosine kinase MET. Our results show that SPT and ITIR-FCS yield complementary information on diffusion properties of biomolecules in cell membranes.
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Affiliation(s)
- Marie-Lena I E Harwardt
- Institute of Physical and Theoretical Chemistry, Johann Wolfgang Goethe-University, Frankfurt, Germany
| | - Marina S Dietz
- Institute of Physical and Theoretical Chemistry, Johann Wolfgang Goethe-University, Frankfurt, Germany
| | - Mike Heilemann
- Institute of Physical and Theoretical Chemistry, Johann Wolfgang Goethe-University, Frankfurt, Germany.
| | - Thorsten Wohland
- Departments of Biological Sciences and Chemistry, Center for Bioimaging Sciences, National University of Singapore, Singapore, Singapore.
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22
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Schoch RL, Barel I, Brown FLH, Haran G. Lipid diffusion in the distal and proximal leaflets of supported lipid bilayer membranes studied by single particle tracking. J Chem Phys 2018; 148:123333. [DOI: 10.1063/1.5010341] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Affiliation(s)
- Rafael L. Schoch
- Department of Chemical and Biological Physics, Weizmann Institute of Science, P.O. Box 26, Rehovot 7610001, Israel
| | - Itay Barel
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106, USA
| | - Frank L. H. Brown
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106, USA
| | - Gilad Haran
- Department of Chemical and Biological Physics, Weizmann Institute of Science, P.O. Box 26, Rehovot 7610001, Israel
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23
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Bryce DA, Kitt JP, Harris JM. Confocal-Raman Microscopy Characterization of Supported Phospholipid Bilayers Deposited on the Interior Surfaces of Chromatographic Silica. J Am Chem Soc 2018; 140:4071-4078. [DOI: 10.1021/jacs.7b13777] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- David A. Bryce
- Department of Chemistry, University of Utah, 315 South 1400 East,Salt Lake City, Utah 84112-0850, United States
| | - Jay P. Kitt
- Department of Chemistry, University of Utah, 315 South 1400 East,Salt Lake City, Utah 84112-0850, United States
| | - Joel M. Harris
- Department of Chemistry, University of Utah, 315 South 1400 East,Salt Lake City, Utah 84112-0850, United States
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24
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Struntz P, Weiss M. The hitchhiker's guide to quantitative diffusion measurements. Phys Chem Chem Phys 2018; 20:28910-28919. [DOI: 10.1039/c8cp06158k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Quantitative comparison of three widely used techniques for diffusion measurements, implemented on a light sheet microscope.
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Affiliation(s)
- Philipp Struntz
- Experimental Physics I
- University of Bayreuth
- D-95447 Bayreuth
- Germany
| | - Matthias Weiss
- Experimental Physics I
- University of Bayreuth
- D-95447 Bayreuth
- Germany
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25
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Fradin C. On the importance of protein diffusion in biological systems: The example of the Bicoid morphogen gradient. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:1676-1686. [PMID: 28919007 DOI: 10.1016/j.bbapap.2017.09.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Revised: 08/16/2017] [Accepted: 09/05/2017] [Indexed: 10/18/2022]
Abstract
Morphogens are proteins that form concentration gradients in embryos and developing tissues, where they act as postal codes, providing cells with positional information and allowing them to behave accordingly. Bicoid was the first discovered morphogen, and remains one of the most studied. It regulates segmentation in flies, forming a striking exponential gradient along the anterior-posterior axis of early Drosophila embryos, and activating the transcription of multiple target genes in a concentration-dependent manner. In this review, the work done by us and by others to characterize the mobility of Bicoid in D. melanogaster embryos is presented. The central role played by the diffusion of Bicoid in both the establishment of the gradient and the activation of target genes is discussed, and placed in the context of the need for these processes to be all at once rapid, precise and robust. The Bicoid system, and morphogen gradients in general, remain amongst the most amazing examples of the coexistence, often observed in living systems, of small-scale disorder and large-scale spatial order. This article is part of a Special Issue entitled: Biophysics in Canada, edited by Lewis Kay, John Baenziger, Albert Berghuis and Peter Tieleman.
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Affiliation(s)
- Cécile Fradin
- Dept. of Physics and Astronomy, McMaster University, 1280 Main St W., Hamilton, ON L8S 4M1, Canada
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26
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Faller R. Molecular modeling of lipid probes and their influence on the membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2353-2361. [PMID: 26891817 DOI: 10.1016/j.bbamem.2016.02.014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2015] [Revised: 02/08/2016] [Accepted: 02/09/2016] [Indexed: 01/03/2023]
Abstract
In this review a number of Molecular Dynamics simulation studies are discussed which focus on the understanding of the behavior of lipid probes in biomembranes. Experiments often use specialized probe moieties or molecules to report on the behavior of a membrane and try to gain information on the membrane as a whole from the probe lipids as these probes are the only things an experiment sees. Probes can be used to make NMR, EPR and fluorescence accessible to the membrane and use fluorescent or spin-active moieties for this purpose. Clearly membranes with and without probes are not identical which makes it worthwhile to elucidate the differences between them with detailed atomistic simulations. In almost all cases these differences are confined to the local neighborhood of the probe molecules which are sparsely used and generally present as single molecules. In general, the behavior of the bulk membrane lipids can be qualitatively understood from the probes but in most cases their properties cannot be directly quantitatively deduced from the probe behavior. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- Roland Faller
- Department of Chemical Engineering & Materials Science, University of California-Davis, Davis, CA 95616, USA.
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27
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Effect of Cholesterol on the Structure of a Five-Component Mitochondria-Like Phospholipid Membrane. MEMBRANES 2015; 5:664-84. [PMID: 26529029 PMCID: PMC4704005 DOI: 10.3390/membranes5040664] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 10/16/2015] [Indexed: 12/23/2022]
Abstract
Cellular membranes have a complex phospholipid composition that varies greatly depending on the organism, cell type and function. In spite of this complexity, most structural data available for phospholipid bilayers concern model systems containing only one or two different phospholipids. Here, we examine the effect of cholesterol on the structure of a complex membrane reflecting the lipid composition of mitochondrial membranes, with five different types of headgroups (phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS) and cardiolipin (CL)) and a variety of hydrocarbon tails. This particular system was chosen because elevated cholesterol contents in mitochondrial membranes have been linked to a breaking down of Bax-mediated membrane permeabilization and resistance to cancer treatments. High resolution electron density profiles were determined by X-ray reflectivity, while the area per phospholipid chain, Apc, and the chain order parameter, SX-ray, were determined by wide-angle X-ray scattering (WAXS). We show that chain order increases upon the addition of cholesterol, resulting in both a thickening of the lipid bilayer and a reduction in the average surface area per phospholipid chain. This effect, well known as cholesterol’s condensation effect, is similar, but not as pronounced as for single-component phospholipid membranes. We conclude by discussing the relevance of these findings for the insertion of the pro-apoptotic protein Bax in mitochondrial membranes with elevated cholesterol content.
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