1
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Voce N, Stevenson P. Experimentally Probing the Effect of Confinement Geometry on Lipid Diffusion. J Phys Chem B 2024; 128:4404-4413. [PMID: 38574293 PMCID: PMC11089508 DOI: 10.1021/acs.jpcb.3c07388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 03/18/2024] [Accepted: 03/19/2024] [Indexed: 04/06/2024]
Abstract
The lateral mobility of molecules within the cell membrane is ultimately governed by the local environment of the membrane. Confined regions induced by membrane structures, such as protein aggregates or the actin meshwork, occur over a wide range of length scales and can impede or steer the diffusion of membrane components. However, a detailed picture of the origins and nature of these confinement effects remains elusive. Here, we prepare model lipid systems on substrates patterned with confined domains of varying geometries constructed with different materials to explore the influences of physical boundary conditions and specific molecular interactions on diffusion. We demonstrate a platform that is capable of significantly altering and steering the long-range diffusion of lipids by using simple oxide deposition approaches, enabling us to systematically explore how confinement size and shape impact diffusion over multiple length scales. While we find that a "boundary condition" description of the system captures underlying trends in some cases, we are also able to directly compare our systems to analytical models, revealing the unexpected breakdown of several approximate solutions. Our results highlight the importance of considering the length scale dependence when discussing properties such as diffusion.
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Affiliation(s)
- Nicole Voce
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, United States
| | - Paul Stevenson
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, United States
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2
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Quantifying postsynaptic receptor dynamics: insights into synaptic function. Nat Rev Neurosci 2023; 24:4-22. [PMID: 36352031 DOI: 10.1038/s41583-022-00647-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/28/2022] [Indexed: 11/11/2022]
Abstract
The molecular composition of presynaptic and postsynaptic neuronal terminals is dynamic, and yet long-term stabilizations in postsynaptic responses are necessary for synaptic development and long-term plasticity. The need to reconcile these concepts is further complicated by learning- and memory-related plastic changes in the molecular make-up of synapses. Advances in single-particle tracking mean that we can now quantify the number and diffusive properties of specific synaptic molecules, while statistical thermodynamics provides a framework to analyse these molecular fluctuations. In this Review, we discuss the use of these approaches to gain quantitative descriptions of the processes underlying the turnover, long-term stability and plasticity of postsynaptic receptors and show how these can help us to understand the balance between local molecular turnover and synaptic structural identity and integrity.
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3
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Asaro RJ, Zhu Q, MacDonald IC. Tethering, evagination, and vesiculation via cell-cell interactions in microvascular flow. Biomech Model Mechanobiol 2020; 20:31-53. [PMID: 32656697 DOI: 10.1007/s10237-020-01366-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Accepted: 06/25/2020] [Indexed: 12/13/2022]
Abstract
Vesiculation is a ubiquitous process undergone by most cell types and serves a variety of vital cell functions; vesiculation from erythrocytes, in particular, is a well-known example and constitutes a self-protection mechanism against premature clearance, inter alia. Herein, we explore a paradigm that red blood cell derived vesicles may form within the microvascular, in intense shear flow, where cells become adhered to either other cells or the extracellular matrix, by forming tethers or an evagination. Adherence may be enhanced, or caused, by diseased states or chemical anomalies as are discussed herein. The mechanisms for such processes are detailed via numerical simulations that are patterned directly from video-recorded cell microflow within the splenic venous sinus (MacDonald et al. 1987), as included, e.g., as Supplementary Material. The mechanisms uncovered highlight the necessity of accounting for remodeling of the erythrocyte's membrane skeleton and, specifically, for the time scales associated with that process that is an integral part of cell deformation. In this way, the analysis provides pointed, and vital, insights into the notion of what the, often used phrase, cell deformability actually entails in a more holistic manner. The analysis also details what data are required to make further quantitative descriptions possible and suggests experimental pathways for acquiring such.
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Affiliation(s)
- Robert J Asaro
- Department of Structural Engineering, University of California, San Diego, CA, USA.
| | - Qiang Zhu
- Department of Structural Engineering, University of California, San Diego, CA, USA
| | - Ian C MacDonald
- Department of Medical Biophysics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
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4
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Asaro RJ, Zhu Q. Vital erythrocyte phenomena: what can theory, modeling, and simulation offer? Biomech Model Mechanobiol 2020; 19:1361-1388. [DOI: 10.1007/s10237-020-01302-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Accepted: 01/22/2020] [Indexed: 12/14/2022]
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5
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Polanowski P, Sikorski A. Molecular transport in systems containing binding obstacles. SOFT MATTER 2019; 15:10045-10054. [PMID: 31769460 DOI: 10.1039/c9sm01876j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We studied the movement of particles in crowded environments by means of extensive Monte Carlo simulations. The dynamic lattice liquid model was employed for this purpose. It is based on the cooperative movement concept and allows the study of systems at high densities. The cooperative model of molecular transport is assumed: the motion of all moving particles is highly correlated. The model is supposed to mimic lateral motion in a membrane and therefore the system is two-dimensional with moving objects and traps placed on a triangular lattice. In our study the interaction (binding) of traps with moving particles was assumed. The conditions in which subdiffusive motion appeared in the system were analysed. The influence of the strength of binding on the dynamic percolation threshold was also shown. The differences in the dynamics compared to systems with impenetrable obstacles and with systems without correlation in motion were presented and discussed. It was shown that in the case of correlated motion the influence of deep traps is similar to that of impenetrable obstacles. If the traps are shallow a recovery to normal diffusion was observed for longer time periods.
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Affiliation(s)
- Piotr Polanowski
- Department of Molecular Physics, Łódź University of Technology, 90-924 Łódź, Poland
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6
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Sokolov Y, Diamant H. Permeability of immobile rings of membrane inclusions to in-plane flow. J Chem Phys 2019; 150:154901. [DOI: 10.1063/1.5086865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Yulia Sokolov
- Raymond and Beverly Sackler School of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Haim Diamant
- Raymond and Beverly Sackler School of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
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7
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Polanowski P, Sikorski A. Motion in a crowded environment: the influence of obstacles’ size and shape and model of transport. J Mol Model 2019; 25:84. [PMID: 30826982 DOI: 10.1007/s00894-019-3968-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Accepted: 02/08/2019] [Indexed: 10/27/2022]
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8
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Sumi T, Okumoto A, Goto H, Sekino H. Numerical calculation on a two-step subdiffusion behavior of lateral protein movement in plasma membranes. Phys Rev E 2018; 96:042410. [PMID: 29347488 DOI: 10.1103/physreve.96.042410] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Indexed: 11/06/2022]
Abstract
A two-step subdiffusion behavior of lateral movement of transmembrane proteins in plasma membranes has been observed by using single-molecule experiments. A nested double-compartment model where large compartments are divided into several smaller ones has been proposed in order to explain this observation. These compartments are considered to be delimited by membrane-skeleton "fences" and membrane-protein "pickets" bound to the fences. We perform numerical simulations of a master equation using a simple two-dimensional lattice model to investigate the heterogeneous diffusion dynamics behavior of transmembrane proteins within plasma membranes. We show that the experimentally observed two-step subdiffusion process can be described using fence and picket models combined with decreased local diffusivity of transmembrane proteins in the vicinity of the pickets. This allows us to explain the two-step subdiffusion behavior without explicitly introducing nested double compartments.
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Affiliation(s)
- Tomonari Sumi
- Research Institute for Interdisciplinary Science and Department of Chemistry, Faculty of Science, Okayama University, 3-1-1 Tsushima-Naka, Kita-ku, Okayama 700-8530, Japan
| | - Atsushi Okumoto
- Department of Computer Science and Engineering, Graduate School of Engineering, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580, Japan
| | - Hitoshi Goto
- Department of Computer Science and Engineering, Graduate School of Engineering, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580, Japan
| | - Hideo Sekino
- Department of Computer Science and Engineering, Graduate School of Engineering, Toyohashi University of Technology, Tempaku-cho, Toyohashi 441-8580, Japan.,Institute for Advanced Computational Science, Stony Brook University, Stony Brook, New York 11794, USA
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9
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Li X, Li H, Chang HY, Lykotrafitis G, Em Karniadakis G. Computational Biomechanics of Human Red Blood Cells in Hematological Disorders. J Biomech Eng 2017; 139:2580906. [PMID: 27814430 DOI: 10.1115/1.4035120] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Indexed: 02/02/2023]
Abstract
We review recent advances in multiscale modeling of the biomechanical characteristics of red blood cells (RBCs) in hematological diseases, and their relevance to the structure and dynamics of defective RBCs. We highlight examples of successful simulations of blood disorders including malaria and other hereditary disorders, such as sickle-cell anemia, spherocytosis, and elliptocytosis.
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Affiliation(s)
- Xuejin Li
- Division of Applied Mathematics, Brown University, Providence, RI 02912 e-mail:
| | - He Li
- Division of Applied Mathematics, Brown University, Providence, RI 02912
| | - Hung-Yu Chang
- Division of Applied Mathematics, Brown University, Providence, RI 02912
| | - George Lykotrafitis
- Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269;Department of Biomedical Engineering, University of Connecticut, Storrs, CT 06269
| | - George Em Karniadakis
- Fellow ASME Division of Applied Mathematics, Brown University, Providence, RI 02912 e-mail:
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10
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Bressloff PC, Karamched BR, Lawley SD, Levien E. Diffusive transport in the presence of stochastically gated absorption. Phys Rev E 2017; 96:022102. [PMID: 28950455 DOI: 10.1103/physreve.96.022102] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2017] [Indexed: 11/07/2022]
Abstract
We analyze a population of Brownian particles moving in a spatially uniform environment with stochastically gated absorption. The state of the environment at time t is represented by a discrete stochastic variable k(t)∈{0,1} such that the rate of absorption is γ[1-k(t)], with γ a positive constant. The variable k(t) evolves according to a two-state Markov chain. We focus on how stochastic gating affects the attenuation of particle absorption with distance from a localized source in a one-dimensional domain. In the static case (no gating), the steady-state attenuation is given by an exponential with length constant sqrt[D/γ], where D is the diffusivity. We show that gating leads to slower, nonexponential attenuation. We also explore statistical correlations between particles due to the fact that they all diffuse in the same switching environment. Such correlations can be determined in terms of moments of the solution to a corresponding stochastic Fokker-Planck equation.
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Affiliation(s)
- Paul C Bressloff
- Department of Mathematics, University of Utah, 155 South 1400 East, Salt Lake City, Utah 84112, USA
| | - Bhargav R Karamched
- Department of Mathematics, University of Utah, 155 South 1400 East, Salt Lake City, Utah 84112, USA
| | - Sean D Lawley
- Department of Mathematics, University of Utah, 155 South 1400 East, Salt Lake City, Utah 84112, USA
| | - Ethan Levien
- Department of Mathematics, University of Utah, 155 South 1400 East, Salt Lake City, Utah 84112, USA
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11
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Vasilyeva NA, Murzina GB, Kireev II, Pivovarov AS. Influence of Membrane Receptor Lateral Diffusion on the Short-Term Depression of Acetylcholine-Induced Current in Helix Neurons. Cell Mol Neurobiol 2017; 37:1443-1455. [PMID: 28236056 DOI: 10.1007/s10571-017-0475-3] [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: 12/09/2016] [Accepted: 02/16/2017] [Indexed: 11/29/2022]
Abstract
We have studied how various drugs increasing the rate of nicotinic acetylcholine receptors (nAChRs) lateral diffusion affect the depression of ACh-induced current in land snail Helix lucorum neurons responsible for defensive behavior. The acetylcholine (ACh) iontophoretic application protocol imitated the behavioral habituation protocol for the intact animal. We found that the drugs decreasing cholesterol level in cell membranes as methyl-β-cyclodextrin 1 mM and Ro 48-8071 2 µM, and polyclonal antibodies to actin-binding proteins as spectrin 5 µg/ml and merlin 2.5 µg/ml have changed the dynamic of ACh-current depression. The nAChRs lateral diffusion coefficient was obtained by fluorescence recovery after photobleaching. A curve fitting model specially created for analysis of short-term choline sensitivity depression in snail neurons helped us evaluate separately the contribution of nAChRs lateral diffusion, their endocytosis and exocytosis to observed effects during electrophysiological experiments. Taken together, we hypothesize that nAChRs lateral diffusion plays an important role in the cellular correlate of habituation in land snail Helix lucorum neurons.
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Affiliation(s)
- Natalia A Vasilyeva
- Department of Higher Nervous Activity, Lomonosov Moscow State University, Leninskie Gory, 1, building 12, Moscow, Russia, 119234.,Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Butlerova, 5a, Moscow, Russia, 117485
| | - Galina B Murzina
- Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Butlerova, 5a, Moscow, Russia, 117485
| | - Igor I Kireev
- A.N.Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 1, building 40, Moscow, Russia, 119234
| | - Arkady S Pivovarov
- Department of Higher Nervous Activity, Lomonosov Moscow State University, Leninskie Gory, 1, building 12, Moscow, Russia, 119234.
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12
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Sapp K, Maibaum L. Suppressing membrane height fluctuations leads to a membrane-mediated interaction among proteins. Phys Rev E 2016; 94:052414. [PMID: 27967200 PMCID: PMC5376292 DOI: 10.1103/physreve.94.052414] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Indexed: 01/27/2023]
Abstract
Membrane-induced interactions can play a significant role in the spatial distribution of membrane-bound proteins. We develop a model that combines a continuum description of lipid bilayers with a discrete particle model of proteins to probe the emerging structure of the combined membrane-protein system. Our model takes into account the membrane's elastic behavior, the steric repulsion between proteins, and the quenching of membrane shape fluctuations due to the presence of the proteins. We employ coupled Langevin equations to describe the dynamics of the system. We show that coupling to the membrane induces an attractive interaction among proteins, which may contribute to the clustering of proteins in biological membranes. We investigate the lateral protein diffusion and find that it is reduced due to transient fluctuations in membrane shape.
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Affiliation(s)
- Kayla Sapp
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
| | - Lutz Maibaum
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
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13
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Koldsø H, Reddy T, Fowler PW, Duncan AL, Sansom MSP. Membrane Compartmentalization Reducing the Mobility of Lipids and Proteins within a Model Plasma Membrane. J Phys Chem B 2016; 120:8873-81. [PMID: 27483109 DOI: 10.1021/acs.jpcb.6b05846] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The cytoskeleton underlying cell membranes may influence the dynamic organization of proteins and lipids within the bilayer by immobilizing certain transmembrane (TM) proteins and forming corrals within the membrane. Here, we present coarse-grained resolution simulations of a biologically realistic membrane model of asymmetrically organized lipids and TM proteins. We determine the effects of a model of cytoskeletal immobilization of selected membrane proteins using long time scale coarse-grained molecular dynamics simulations. By introducing compartments with varying degrees of restraints within the membrane models, we are able to reveal how compartmentalization caused by cytoskeletal immobilization leads to reduced and anomalous diffusional mobility of both proteins and lipids. This in turn results in a reduced rate of protein dimerization within the membrane and of hopping of membrane proteins between compartments. These simulations provide a molecular realization of hierarchical models often invoked to explain single-molecule imaging studies of membrane proteins.
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Affiliation(s)
- Heidi Koldsø
- Department of Biochemistry, University of Oxford , South Parks Road, OX1 3QU Oxford, United Kingdom
| | - Tyler Reddy
- Department of Biochemistry, University of Oxford , South Parks Road, OX1 3QU Oxford, United Kingdom
| | - Philip W Fowler
- Department of Biochemistry, University of Oxford , South Parks Road, OX1 3QU Oxford, United Kingdom
| | - Anna L Duncan
- Department of Biochemistry, University of Oxford , South Parks Road, OX1 3QU Oxford, United Kingdom
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford , South Parks Road, OX1 3QU Oxford, United Kingdom
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14
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Creep and stress relaxation of human red cell membrane. Biomech Model Mechanobiol 2016; 16:239-247. [PMID: 27514540 DOI: 10.1007/s10237-016-0813-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2016] [Accepted: 08/02/2016] [Indexed: 11/27/2022]
Abstract
In contrast to most mechanical properties of the red cell, experimental information on stress relaxation (SR) of the membrane skeleton is scarce. On the other hand, many postulates or assumptions as to the value of the characteristic time of SR [Formula: see text] can be found in the literature. Here, an experiment is presented that allows measurement of [Formula: see text] up to values of about 10 h. The membrane skeleton was deformed passively by changing the spontaneous curvature of the bilayer thus transforming the natively biconcave red cells into echinocytes. This shape and the concomitant deformation of the skeleton were kept up to 4 h by incubation at 37 ℃. During this period, no plastic deformation (creep) was observed. After the incubation, the spontaneous curvature was returned to normal. The resulting shape was smooth showing no remnants of the echinocytic shape. Both observations indicate [Formula: see text] 10 h. This result is in gross disagreement to postulates or assumptions existing in the literature.
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15
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Polanowski P, Sikorski A. Simulation of Molecular Transport in Systems Containing Mobile Obstacles. J Phys Chem B 2016; 120:7529-37. [PMID: 27387448 DOI: 10.1021/acs.jpcb.6b02682] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In this paper, we investigate the movement of molecules in crowded environments with obstacles undergoing Brownian motion by means of extensive Monte Carlo simulations. Our investigations were performed using the dynamic lattice liquid model, which was based on the cooperative movement concept and allowed to mimic systems at high densities where the motion of all elements (obstacles as well as moving particles) were highly correlated. The crowded environments are modeled on a two-dimensional triangular lattice containing obstacles (particles whose mobility was significantly reduced) moving by a Brownian motion. The subdiffusive motion of both elements in the system was analyzed. It was shown that the percolation transition does not exist in such systems in spite of the cooperative character of the particles' motion. The reduction of the obstacle mobility leads to the longer caging of liquid particles by mobile obstacles.
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Affiliation(s)
- Piotr Polanowski
- Department of Molecular Physics, Technical University of Łódź , 90-924 Łódź, Poland
| | - Andrzej Sikorski
- Department of Chemistry, University of Warsaw , Pasteura 1, 02-093 Warsaw, Poland
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16
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Li H, Zhang Y, Ha V, Lykotrafitis G. Modeling of band-3 protein diffusion in the normal and defective red blood cell membrane. SOFT MATTER 2016; 12:3643-3653. [PMID: 26977476 DOI: 10.1039/c4sm02201g] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We employ a two-component red blood cell (RBC) membrane model to simulate lateral diffusion of band-3 proteins in the normal RBC and in the RBC with defective membrane proteins. The defects reduce the connectivity between the lipid bilayer and the membrane skeleton (vertical connectivity), or the connectivity of the membrane skeleton itself (horizontal connectivity), and are associated with the blood disorders of hereditary spherocytosis (HS) and hereditary elliptocytosis (HE) respectively. Initially, we demonstrate that the cytoskeleton limits band-3 lateral mobility by measuring the band-3 macroscopic diffusion coefficients in the normal RBC membrane and in a lipid bilayer without the cytoskeleton. Then, we study band-3 diffusion in the defective RBC membrane and quantify the relation between band-3 diffusion coefficients and percentage of protein defects in HE RBCs. In addition, we illustrate that at low spectrin network connectivity (horizontal connectivity) band-3 subdiffusion can be approximated as anomalous diffusion, while at high horizontal connectivity band-3 diffusion is characterized as confined diffusion. Our simulations show that the band-3 anomalous diffusion exponent depends on the percentage of protein defects in the membrane cytoskeleton. We also confirm that the introduction of attraction between the lipid bilayer and the spectrin network reduces band-3 diffusion, but we show that this reduction is lower than predicted by the percolation theory. Furthermore, we predict that the attractive force between the spectrin filament and the lipid bilayer is at least 20 times smaller than the binding forces at band-3 and glycophorin C, the two major membrane binding sites. Finally, we explore diffusion of band-3 particles in the RBC membrane with defects related to vertical connectivity. We demonstrate that in this case band-3 diffusion can be approximated as confined diffusion for all attraction levels between the spectrin network and the lipid bilayer. By comparing the diffusion coefficients measured in horizontal vs. vertical defects, we conclude that band-3 mobility is primarily controlled by the horizontal connectivity.
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Affiliation(s)
- He Li
- Division of Applied Mathematics, Brown University, Providence, RI 02912, USA
| | - Yihao Zhang
- Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, Unit 3139, Storrs, CT 06269-3139, USA.
| | - Vi Ha
- Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, Unit 3139, Storrs, CT 06269-3139, USA.
| | - George Lykotrafitis
- Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, Unit 3139, Storrs, CT 06269-3139, USA. and Department of Biomedical Engineering, University of Connecticut, Storrs, CT 06269, USA
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17
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Jeon H, Cho HW, Kim J, Sung BJ. Non-Gaussian rotational diffusion in heterogeneous media. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:042105. [PMID: 25375436 DOI: 10.1103/physreve.90.042105] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Indexed: 06/04/2023]
Abstract
We employ a simple model for rotational diffusivity DR of dumbbells in porous media in order to study spatially heterogeneous and non-Gaussian dynamics at Fickian time scales. We obtain the distribution P(DR) of DR's of single dumbbells for both ergodic and nonergodic systems. When a pore percolating network disappears beyond the pore percolation transition and the rotational dynamics becomes nonergodic, each single dumbbell undergoes Gaussian rotational dynamics but with different DR, which depends solely on the local pore structure. We also construct a map of heterogeneous dynamic regions and illustrate that such seemingly Fickian but non-Gaussian dynamics could be understood as the linear combination of the Gaussian rotational displacement distribution functions of each dumbbell. With a percolating pore network, the rotational dynamics becomes ergodic, and P(DR) is a δ function at the average value of DR.
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Affiliation(s)
- Heejin Jeon
- Department of Chemistry, Sogang University, Seoul 121-742, Republic of Korea
| | - Hyun Woo Cho
- Department of Chemistry, Sogang University, Seoul 121-742, Republic of Korea
| | - Jeongmin Kim
- Department of Chemistry, Sogang University, Seoul 121-742, Republic of Korea
| | - Bong June Sung
- Department of Chemistry, Sogang University, Seoul 121-742, Republic of Korea
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18
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Polanowski P, Sikorski A. Simulation of diffusion in a crowded environment. SOFT MATTER 2014; 10:3597-3607. [PMID: 24663121 DOI: 10.1039/c3sm52861h] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We performed extensive and systematic simulation studies of two-dimensional fluid motion in a complex crowded environment. In contrast to other studies we focused on cooperative phenomena that occurred if the motion of particles takes place in a dense crowded system, which can be considered as a crude model of a cellular membrane. Our main goal was to answer the following question: how do the fluid molecules move in an environment with a complex structure, taking into account the fact that motions of fluid molecules are highly correlated. The dynamic lattice liquid (DLL) model, which can work at the highest fluid density, was employed. Within the frame of the DLL model we considered cooperative motion of fluid particles in an environment that contained static obstacles. The dynamic properties of the system as a function of the concentration of obstacles were studied. The subdiffusive motion of particles was found in the crowded system. The influence of hydrodynamics on the motion was investigated via analysis of the displacement in closed cooperative loops. The simulation and the analysis emphasize the influence of the movement correlation between moving particles and obstacles.
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Affiliation(s)
- Piotr Polanowski
- Department of Molecular Physics, Technical University of Łódź, 90-924 Łódź, Poland
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19
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Chinnapen DJF, Hsieh WT, te Welscher YM, Saslowsky DE, Kaoutzani L, Brandsma E, D'Auria L, Park H, Wagner JS, Drake KR, Kang M, Benjamin T, Ullman MD, Costello CE, Kenworthy AK, Baumgart T, Massol RH, Lencer WI. Lipid sorting by ceramide structure from plasma membrane to ER for the cholera toxin receptor ganglioside GM1. Dev Cell 2013; 23:573-86. [PMID: 22975326 DOI: 10.1016/j.devcel.2012.08.002] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Revised: 04/06/2012] [Accepted: 08/04/2012] [Indexed: 01/26/2023]
Abstract
The glycosphingolipid GM1 binds cholera toxin (CT) on host cells and carries it retrograde from the plasma membrane (PM) through endosomes, the trans-Golgi (TGN), and the endoplasmic reticulum (ER) to induce toxicity. To elucidate how a membrane lipid can specify trafficking in these pathways, we synthesized GM1 isoforms with alternate ceramide domains and imaged their trafficking in live cells. Only GM1 with unsaturated acyl chains sorted efficiently from PM to TGN and ER. Toxin binding, which effectively crosslinks GM1 lipids, was dispensable, but membrane cholesterol and the lipid raft-associated proteins actin and flotillin were required. The results implicate a protein-dependent mechanism of lipid sorting by ceramide structure and provide a molecular explanation for the diversity and specificity of retrograde trafficking by CT in host cells.
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Affiliation(s)
- Daniel J-F Chinnapen
- Division of Gastroenterology, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA
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20
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Sagle LB, Ruvuna LK, Bingham JM, Liu C, Cremer PS, Van Duyne RP. Single plasmonic nanoparticle tracking studies of solid supported bilayers with ganglioside lipids. J Am Chem Soc 2012; 134:15832-9. [PMID: 22938041 PMCID: PMC3526348 DOI: 10.1021/ja3054095] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Single-particle tracking experiments were carried out with gold nanoparticle-labeled solid supported lipid bilayers (SLBs) containing increasing concentrations of ganglioside (GM(1)). The negatively charged nanoparticles electrostatically associate with a small percentage of positively charged lipids (ethyl phosphatidylcholine) in the bilayers. The samples containing no GM(1) show random diffusion in 92% of the particles examined with a diffusion constant of 4.3(±4.5) × 10(-9) cm(2)/s. In contrast, samples containing 14% GM(1) showed a mixture of particles displaying both random and confined diffusion, with the majority of particles, 62%, showing confined diffusion. Control experiments support the notion that the nanoparticles are not associating with the GM(1) moieties but instead most likely confined to regions in between the GM(1) clusters. Analysis of the root-mean-squared displacement plots for all of the data reveals decreasing trends in the confined diffusion constant and diameter of the confining region versus increasing GM(1) concentration. In addition, a linearly decreasing trend is observed for the percentage of randomly diffusing particles versus GM(1) concentration, which offers a simple, direct way to measure the percolation threshold for this system, which has not previously been measured. The percolation threshold is found to be 22% GM(1) and the confining diameter at the percolation threshold only ∼50 nm.
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Affiliation(s)
- Laura B. Sagle
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, United Sates
| | - Laura K. Ruvuna
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, United Sates
| | - Julia M. Bingham
- Department of Chemistry, Saint Xavier University, 3700 West 103 Street, Chicago, IL 60655, United Sates
| | - Chunming Liu
- Department of Chemistry, Texas A&M University, 3255 TAMU College Station, TX 77843, United Sates
| | - Paul S. Cremer
- Department of Chemistry, Texas A&M University, 3255 TAMU College Station, TX 77843, United Sates
| | - Richard P. Van Duyne
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, United Sates
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21
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Wallace R. Neural membrane signaling platforms. Int J Mol Sci 2010; 11:2421-42. [PMID: 20640161 PMCID: PMC2904925 DOI: 10.3390/ijms11062421] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2010] [Revised: 06/03/2010] [Accepted: 06/09/2010] [Indexed: 11/16/2022] Open
Abstract
Throughout much of the history of biology, the cell membrane was functionally defined as a semi-permeable barrier separating aqueous compartments, and an anchoring site for proteins. Little attention was devoted to its possible regulatory role in intracellular molecular processes and neuron electrical signaling. This article reviews the history of membrane studies and the current state of the art. Emphasis is placed on natural and artificial membrane studies of electric field effects on molecular organization, especially as these may relate to impulse propagation in neurons. Implications of these studies for new designs in artificial intelligence are briefly examined.
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Affiliation(s)
- Ron Wallace
- Department of Anthropology, University of Central Florida, Box 25000, Orlando, FL, 32816, USA; E-Mail: ; Tel.: +1-407-823-2227
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22
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Das R, Cairo CW, Coombs D. A hidden Markov model for single particle tracks quantifies dynamic interactions between LFA-1 and the actin cytoskeleton. PLoS Comput Biol 2009; 5:e1000556. [PMID: 19893741 PMCID: PMC2768823 DOI: 10.1371/journal.pcbi.1000556] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2009] [Accepted: 10/06/2009] [Indexed: 12/17/2022] Open
Abstract
The extraction of hidden information from complex trajectories is a continuing problem in single-particle and single-molecule experiments. Particle trajectories are the result of multiple phenomena, and new methods for revealing changes in molecular processes are needed. We have developed a practical technique that is capable of identifying multiple states of diffusion within experimental trajectories. We model single particle tracks for a membrane-associated protein interacting with a homogeneously distributed binding partner and show that, with certain simplifying assumptions, particle trajectories can be regarded as the outcome of a two-state hidden Markov model. Using simulated trajectories, we demonstrate that this model can be used to identify the key biophysical parameters for such a system, namely the diffusion coefficients of the underlying states, and the rates of transition between them. We use a stochastic optimization scheme to compute maximum likelihood estimates of these parameters. We have applied this analysis to single-particle trajectories of the integrin receptor lymphocyte function-associated antigen-1 (LFA-1) on live T cells. Our analysis reveals that the diffusion of LFA-1 is indeed approximately two-state, and is characterized by large changes in cytoskeletal interactions upon cellular activation.
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Affiliation(s)
- Raibatak Das
- Department of Mathematics and Institute of Applied Mathematics, University of British Columbia, Vancouver, British Columbia, Canada.
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23
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Bressloff PC, Earnshaw BA. A dynamic corral model of receptor trafficking at a synapse. Biophys J 2009; 96:1786-802. [PMID: 19254538 DOI: 10.1016/j.bpj.2008.12.3889] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2008] [Accepted: 12/01/2008] [Indexed: 11/29/2022] Open
Abstract
The postsynaptic density (PSD) is a cytoskeletal specialization within the postsynaptic membrane of a neuron that helps to concentrate and organize neurotransmitter receptors at a chemical synapse. The total number of receptors within the PSD, which is a major factor in determining the physiological strength or weight of a synapse, fluctuates due to the surface diffusion of receptors into and out of the PSD, and the interactions of receptors with scaffolding proteins and cytoskeletal elements within the PSD. In this article, we present a stochastic model of protein receptor trafficking at the PSD that takes into account these various processes. The PSD is treated as a stochastically gated corral, which contributes a source of extrinsic or environmental noise that supplements the intrinsic noise arising from small receptor numbers. Using a combination of stochastic analysis and Monte Carlo simulations, we determine the time-dependent variation in the mean and variance of synaptic receptor numbers for a variety of initial conditions that simulate fluorescence recovery after photobleaching experiments, and indicate how such data might be used to infer certain properties of the PSD.
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Affiliation(s)
- Paul C Bressloff
- Department of Mathematics, University of Utah, Salt Lake City, Utah, USA.
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24
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Auth T, Gov NS. Diffusion in a fluid membrane with a flexible cortical cytoskeleton. Biophys J 2009; 96:818-30. [PMID: 19186123 DOI: 10.1016/j.bpj.2008.10.038] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2008] [Accepted: 10/15/2008] [Indexed: 10/21/2022] Open
Abstract
We calculate the influence of a flexible network of long-chain proteins, which is anchored to a fluid membrane, on protein diffusion in this membrane. This is a model for the cortical cytoskeleton and the lipid bilayer of the red blood cell, which we apply to predict the influence of the cytoskeleton on the diffusion coefficient of a mobile band 3 protein. Using the pressure field that the cytoskeleton exerts on the membrane, from the steric repulsion between the diffusing protein and the cytoskeletal filaments, we define a potential landscape for the diffusion within the bilayer. We study the changes to the diffusion coefficient on removal of one type of anchor proteins, e.g., in several hemolytic anemias, as well as for isotropic and anisotropic stretching of the cytoskeleton. We predict an overall increase of the diffusion for a smaller number of anchor proteins and increased diffusion for anisotropic stretching in the direction of the stretch, because of the decrease in the spatial frequency as well as in the height of the potential barriers.
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Affiliation(s)
- Thorsten Auth
- Department of Materials and Interfaces, The Weizmann Institute of Science, Rehovot, Israel; Institute for Solid State Research, Research Centre Jülich, Jülich, Germany.
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25
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Affiliation(s)
- Frank L.H. Brown
- Department of Chemistry and Biochemistry and Department of Physics, University of California, Santa Barbara, California 93106;
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26
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Müller DJ, Wu N, Palczewski K. Vertebrate membrane proteins: structure, function, and insights from biophysical approaches. Pharmacol Rev 2008; 60:43-78. [PMID: 18321962 DOI: 10.1124/pr.107.07111] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Membrane proteins are key targets for pharmacological intervention because they are vital for cellular function. Here, we analyze recent progress made in the understanding of the structure and function of membrane proteins with a focus on rhodopsin and development of atomic force microscopy techniques to study biological membranes. Membrane proteins are compartmentalized to carry out extra- and intracellular processes. Biological membranes are densely populated with membrane proteins that occupy approximately 50% of their volume. In most cases membranes contain lipid rafts, protein patches, or paracrystalline formations that lack the higher-order symmetry that would allow them to be characterized by diffraction methods. Despite many technical difficulties, several crystal structures of membrane proteins that illustrate their internal structural organization have been determined. Moreover, high-resolution atomic force microscopy, near-field scanning optical microscopy, and other lower resolution techniques have been used to investigate these structures. Single-molecule force spectroscopy tracks interactions that stabilize membrane proteins and those that switch their functional state; this spectroscopy can be applied to locate a ligand-binding site. Recent development of this technique also reveals the energy landscape of a membrane protein, defining its folding, reaction pathways, and kinetics. Future development and application of novel approaches during the coming years should provide even greater insights to the understanding of biological membrane organization and function.
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Affiliation(s)
- Daniel J Müller
- Biotechnology Center, University of Technology, Dresden, Germany
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27
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ZWEYER M, TROIAN B, SPREAFICO V, PRATO S. SNOM on cell thin sections: observation of Jurkat and MDAMB453 cells. J Microsc 2008; 229:440-6. [DOI: 10.1111/j.1365-2818.2008.01925.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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28
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Yeung C, Shtrahman M, Wu XL. Stick-and-diffuse and caged diffusion: a comparison of two models of synaptic vesicle dynamics. Biophys J 2007; 92:2271-80. [PMID: 17218458 PMCID: PMC1864819 DOI: 10.1529/biophysj.106.081794] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2006] [Accepted: 11/27/2006] [Indexed: 11/18/2022] Open
Abstract
Two models were recently proposed to enable us to understand the dynamics of synaptic vesicles in hippocampal neurons. In the caged diffusion model, the vesicles diffuse in small circular cages located randomly in the bouton, while in the stick-and-diffuse model the vesicles bind and release from a cellular cytomatrix. In this article, we obtain analytic expressions for the fluorescence correlation spectroscopy (FCS) autocorrelation function for the two models and test their predictions against our earlier FCS measurements of the vesicle dynamics. We find that the stick-and-diffuse model agrees much better with the experiment. We find also that, due to the slow dynamics of the vesicles, the finite experimental integration time has an important effect on the FCS autocorrelation function and demonstrate its effect for the different models. The two models of the dynamics are also relevant to other cellular environments where mobile species undergo slow diffusionlike motion in restricted spaces or bind and release from a stationary substrate.
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Affiliation(s)
- Chuck Yeung
- School of Science, Pennsylvania State University at Erie, The Behrend College, Erie, Pennsylvania, USA.
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29
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Jin S, Verkman AS. Single particle tracking of complex diffusion in membranes: simulation and detection of barrier, raft, and interaction phenomena. J Phys Chem B 2007; 111:3625-32. [PMID: 17388520 DOI: 10.1021/jp067187m] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Single particle tracking is being used increasingly to follow the motion of membrane-associated receptors and lipids. Anomalous and complex diffusive behaviors are generally found in cell membranes. We developed computational algorithms to simulate particle trajectories and to detect complex diffusive behaviors in two dimensions, including confined and convective diffusion, intramembrane barrier and raft phenomena, and interparticle interactions. Little useful information regarding barrier, raft, and interaction effects were provided by standard computational procedures for identification of anomalous diffusion, including analysis of mean squared displacement, distributions of diffusion rates and range, and time evolution of particle position. New algorithms were developed and optimized to detect complex diffusive behaviors from simulated single particle trajectories. A barrier detection algorithm was developed on the basis of spatial averaging of particle positions in trajectories. A raft detection algorithm utilized spatially resolved diffusion coefficients and particle density functions. An interaction algorithm utilized interparticle distance distributions. The algorithms developed here are applicable to identify biologically important diffusive phenomena in cell membranes.
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Affiliation(s)
- Songwan Jin
- Departments of Medicine and Physiology, Cardiovascular Research Institute, University of California, San Francisco, California 94143-0521, USA
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30
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Wallace R. Neural membrane microdomains as computational systems: Toward molecular modeling in the study of neural disease. Biosystems 2006; 87:20-30. [PMID: 16650927 DOI: 10.1016/j.biosystems.2006.02.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2005] [Revised: 12/02/2005] [Accepted: 02/28/2006] [Indexed: 11/23/2022]
Abstract
Several studies indicate that the lipid biological membrane contains discrete regions known as rafts or microdomains. These structures range in size from approximately 50 to 70nm to nearly a mum and play important roles in cell signaling. In the neuron, computational models suggest that transiently polarized microdomain ethenes may regulate ion-channel dynamics and control impulse propagation. Thus the microdomain is nominated as the fundamental unit of nervous system signaling. Based on this model, the article proposes a first-approximation design for a supported-membrane device which would mimic microdomain properties. The basic architecture would consist of an electrically addressable biotemplated nanowire crossing an artificial membrane corralled in a vertical carbon nanofiber barrier. Advantages and disadvantages of model components are discussed at length. It is proposed that artificial devices of this type would be medically useful in simulating membrane states correlated with neural disease. This possibility is examined with reference to the A-current potassium channel, implicated in epilepsy.
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Affiliation(s)
- Ron Wallace
- Department of Sociology and Anthropology, University of Central Florida, Box 25000, Orlando, FL 32816, USA.
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31
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Brannigan G, Lin LCL, Brown FLH. Implicit solvent simulation models for biomembranes. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2005; 35:104-24. [PMID: 16187129 DOI: 10.1007/s00249-005-0013-y] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2005] [Revised: 08/03/2005] [Accepted: 08/12/2005] [Indexed: 11/25/2022]
Abstract
Fully atomic simulation strategies are infeasible for the study of many processes of interest to membrane biology, biophysics and biochemistry. We review various coarse-grained simulation methodologies with special emphasis on methods and models that do not require the explicit simulation of water. Examples from our own research demonstrate that such models have potential for simulating a variety of biologically relevant phenomena at the membrane surface.
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Affiliation(s)
- Grace Brannigan
- Department of Physics and Astronomy, University of California, Santa Barbara, CA 93106-9530, USA
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32
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Lin LCL, Brown FLH. Dynamic simulations of membranes with cytoskeletal interactions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 72:011910. [PMID: 16090004 DOI: 10.1103/physreve.72.011910] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2005] [Indexed: 05/03/2023]
Abstract
We describe a simulation algorithm for the dynamics of elastic membrane sheets over long length and time scales. Our model includes implicit hydrodynamic coupling between membrane and surrounding solvent and allows for arbitrary external forces acting on the membrane surface. In particular, the methodology is well suited to studying membranes in interaction with cytoskeletal filaments. We present results for the thermal undulations of a lipid bilayer attached to a regular network of spectrin filaments as a model for the red blood cell membrane. The dynamic fluctuations of the bilayer over the spectrin network are quantified and used to predict the macroscopic diffusion constant of band 3 on the surface of the red blood cell. We find that thermal undulations likely play a role in the mobility of band 3 in the plane of the erythrocyte membrane.
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Affiliation(s)
- Lawrence C-L Lin
- Department of Physics, University of California, Santa Barbara, 93106, USA
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33
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Lin LCL, Brown FLH. Brownian dynamics in Fourier space: membrane simulations over long length and time scales. PHYSICAL REVIEW LETTERS 2004; 93:256001. [PMID: 15697914 DOI: 10.1103/physrevlett.93.256001] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2004] [Indexed: 05/15/2023]
Abstract
A simulation algorithm for elastic membrane sheets is presented. Overdamped stochastic dynamics including hydrodynamic coupling to surrounding solvent and arbitrary external forces are generated by employing Fourier modes of the sheet as the primary dynamic variables. Simulations over the micron length scale and second time scale are easily achieved. The dynamics of a lipid bilayer attached to an underlying network of cytoskeletal filaments is used to estimate the diffusion constant of membrane-bound proteins on the surface of the red blood cell.
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Affiliation(s)
- Lawrence C-L Lin
- Department of Physics, University of California, Santa Barbara, California 93106-9530, USA
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34
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Gordy C, Mishra S, Rodgers W. Visualization of antigen presentation by actin-mediated targeting of glycolipid-enriched membrane domains to the immune synapse of B cell APCs. THE JOURNAL OF IMMUNOLOGY 2004; 172:2030-8. [PMID: 14764667 DOI: 10.4049/jimmunol.172.4.2030] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Glycolipid-enriched membrane (GEM) domains, or lipid rafts, function in signaling in immune cells, but their properties during Ag presentation are less clear. To address this question, GEM domains were studied using fluorescence cell imaging of mouse CH27 B cells presenting Ag to D10 T cells. Our experiments showed that APCs were enriched with GEM domains in the immune synapse, and this occurred in an actin-dependent manner. This enrichment was specific to GEM domains, because a marker for non-GEM regions of the membrane was excluded from the immune synapse. Furthermore, fluorescence photobleaching experiments showed that protein in the immune synapse was dynamic and rapidly exchanged with that in other compartments of CH27 cells. To identify the signals for targeting GEM domains to the immune synapse in APCs, capping of the domains was measured in cells after cross-linking surface molecules. This showed that co-cross-linking CD48 with MHC class II was required for efficient capping and intracellular signaling. Capping of GEM domains by co-cross-linking CD48 and MHC class II occurred with co-capping of filamentous actin, and both domain capping and T cell-CH27 cell conjugation were inhibited by pretreating CH27 cells with latrunculin B. Furthermore, disruption of the actin cytoskeleton of the CH27 cells also inhibited formation of a mature immune synapse in those T cells that did conjugate to APCs. Thus, Ag presentation and efficient T cell stimulation occur by an actin-dependent targeting of GEM domains in the APC to the site of T cell engagement.
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Affiliation(s)
- Claire Gordy
- Molecular Immunogenetics Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
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35
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Lin LCL, Brown FLH. Dynamics of pinned membranes with application to protein diffusion on the surface of red blood cells. Biophys J 2004; 86:764-80. [PMID: 14747313 PMCID: PMC1303925 DOI: 10.1016/s0006-3495(04)74153-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2003] [Accepted: 10/16/2003] [Indexed: 10/21/2022] Open
Abstract
We present a theoretical treatment and simulation algorithm for the dynamics of Helfrich elastic membrane surfaces in the presence of general harmonic perturbations and hydrodynamic coupling to the surrounding solvent. In the limit of localized and strong interactions, this harmonic model can be used to pin the membrane to intracellular/intercellular structures. We consider the case of pinning to the cytoskeleton and use such a model to estimate the macroscopic diffusion constant for band 3 protein on the surface of human erythrocytes. Comparison to experimental results suggests that thermal undulations of the membrane surface should play a significant role in protein mobility on the red blood cell.
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Affiliation(s)
- Lawrence C-L Lin
- Department of Physics, University of California, Santa Barbara, California 93106-9510, USA
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36
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Barsegov V, Shapir Y, Mukamel S. One-dimensional transport with dynamic disorder. PHYSICAL REVIEW E 2003; 68:011101. [PMID: 12935121 DOI: 10.1103/physreve.68.011101] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2003] [Indexed: 11/07/2022]
Abstract
We study the mean quenching time distribution and its moments in a one-dimensional N-site donor-bridge-acceptor system where all sites are coupled to a two-state jump bath for arbitrary disorder and an arbitrary ratio kappa identical with <k>/R of the bath jump rate R and the average hopping rate <k>. When kappaN approximately 1, the quenching time distribution has long power-law tails even when the waiting times are exponentially distributed. These disappear for kappaN<<1 where the hopping rate self-averages on the bath relaxation time scale. In the absence of disorder or for small kappa, the mean quenching time scales linearly with N. Otherwise, we observe a power law, approximately N1+gamma, with a crossover to linear scaling (gamma=0) for large N. Distributions of particle position, its second moment, velocity and diffusion coefficient are computed in the infinite N limit. For times longer than R-1, the dynamic disorder self-averages and the average position, velocity, and diffusion coefficient scale linearly in time.
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Affiliation(s)
- Valeri Barsegov
- Department of Chemistry, University of Rochester, Rochester, New York 14627-0216, USA
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37
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Jordan S, Rodgers W. T cell glycolipid-enriched membrane domains are constitutively assembled as membrane patches that translocate to immune synapses. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2003; 171:78-87. [PMID: 12816985 DOI: 10.4049/jimmunol.171.1.78] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In T cells, glycolipid-enriched membrane (GEM) domains, or lipid rafts, are assembled into immune synapses in response to Ag presentation. However, the properties of T cell GEM domains in the absence of stimulatory signals, such as their size and distribution in the plasma membrane, are less clear. To address this question, we used confocal microscopy to measure GEM domains in unstimulated T cells expressing a GEM-targeted green fluorescent protein molecule. Our experiments showed that the GEM domains were assembled into membrane patches that were micrometers in size, as evidenced by a specific enrichment of GEM-associated molecules and resistance of the patches to extraction by Triton X-100. However, treatment of cells with latrunculin B disrupted the patching of the GEM domains and their resistance to Triton X-100. Similarly, the patches were coenriched with F-actin, and actin occurred in the detergent-resistant GEM fraction of T cells. Live-cell imaging showed that the patches were mobile and underwent translocation in the plasma membrane to immune synapses in stimulated T cells. Targeting of GEM domains to immune synapses was found to be actin-dependent, and required phosphatidylinositol 3-kinase activity and myosin motor proteins. We conclude from our results that T cell GEM domains are constitutively assembled by the actin cytoskeleton into micrometer-sized membrane patches, and that GEM domains and the GEM-enriched patches can function as a vehicle for targeting molecules to immune synapses.
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Affiliation(s)
- Stephen Jordan
- Molecular Immunogenetics Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
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38
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Brown FLH. Regulation of protein mobility via thermal membrane undulations. Biophys J 2003; 84:842-53. [PMID: 12547768 PMCID: PMC1302664 DOI: 10.1016/s0006-3495(03)74903-0] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2002] [Accepted: 10/16/2002] [Indexed: 11/22/2022] Open
Abstract
The in-plane diffusivelike motion of membrane bound proteins on the surface of cells is considered. We suggest, on the basis of theoretical arguments and simulation, that thermally excited undulations of the lipid bilayer may serve as a mechanism for proteins to hop between adjacent regions on the cell surface separated by barriers composed of internal cellular structure (e.g., the cytoskeleton). We specifically investigate the mobility of band 3 dimer on the surface of red blood cells where the spectrin cytoskeletal meshwork defines a series of "corrals" on the cell surface known to hinder protein motion. Previous models of this system have postulated that the cytoskeleton must deform to allow passage of membrane bound proteins out of these corral regions and have ignored fluctuations of the bilayer. Our model provides a complementary mechanism and we posit that the mobility of real proteins in real cells is likely the result of several mechanisms acting in parallel.
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Affiliation(s)
- Frank L H Brown
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510, USA
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39
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Peran M, Hicks BW, Peterson NL, Hooper H, Salas R. Lateral mobility and anchoring of recombinant GABAA receptors depend on subunit composition. CELL MOTILITY AND THE CYTOSKELETON 2001; 50:89-100. [PMID: 11746674 DOI: 10.1002/cm.1043] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The clustering of type A gamma-aminobutyric acid receptors (GABA(A)R) at discrete and functionally significant domains on the nerve cell surface is an important determinant in the integration of synaptic inputs. To discern the role that the subunits of the GABA(A)R play in determining the receptor's cell surface topography and mobility, the alpha1, beta1, beta3, and gamma2s subunits were transfected into COS7, HEK293, and PC12 cells and the distribution and cell surface mobility of these recombinant receptors were examined. Our results show that alpha1 subunits are retained in the endoplasmic reticulum while beta1 and beta3 subunits are sorted to the plasma membrane where they form clusters. Co-expression and co-assembly of alpha1 and beta3 subunits result in the rescue of intracellular alpha1 subunits, which are transported as alphabeta subunit complexes to the cell surface where they formed clusters. Fluorescence photobleach recovery and single particle tracking of recombinant receptors show that, despite clustering, beta3 subunit homooligomers are mobile within a cell surface domain. Inclusion of alpha1 in beta3 or beta3gamma2s complexes, however, dramatically reduces the receptor's lateral mobility in COS 7 and PC12 cells and anchors GABA(A)Rs on the cell surface, suggesting the formation of a direct link to a component of the cytoskeleton. The mobility of recombinant receptors that include the alpha1 subunit mirrors the mobility of GABA(A)Rs on cell bodies and dendrites of cortical and spinal cord neurons. The results suggest that incorporation of alpha1 subunits give rise to a population of GABA(A)Rs that are immobilized on the cell surface.
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Affiliation(s)
- M Peran
- Departamento de Bioquimica, Facultad de Medicina, Universidad de Malaga, Malaga, Spain
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