Dynamics in the plasma membrane: how to combine fluidity and order
TL;DR: The basic concepts of Brownian diffusion and lipid domain formation in model membranes are summarized and the development of ideas and tools in this field are tracked, outlining key results obtained on the dynamic processes at work in membrane structure and assembly.
Abstract: Cell membranes are fascinating supramolecular aggregates that not only form a barrier between compartments but also harbor many chemical reactions essential to the existence and functioning of a cell. Here, it is proposed to review the molecular dynamics and mosaic organization of the plasma membrane, which are thought to have important functional implications. We will first summarize the basic concepts of Brownian diffusion and lipid domain formation in model membranes and then track the development of ideas and tools in this field, outlining key results obtained on the dynamic processes at work in membrane structure and assembly. We will focus in particular on findings made using fluorescent labeling and imaging procedures to record these dynamic processes. We will also discuss a few examples showing the impact of lateral diffusion on cell signal transduction, and outline some future methodological challenges which must be met before we can answer some of the questions arising in this field of research.
Citations
More filters
18 Nov 2009
TL;DR: This paper aims to demonstrate the efforts towards in-situ applicability of EMMARM, as to provide real-time information about concrete mechanical properties such as E-modulus and compressive strength.
Abstract: OF DISSERTATION Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY ENGINEERING The University of New Mexico Albuquerque, New Mexico
28 citations
TL;DR: Four different specific membrane markers are used to test the lateral organization, the differences between the inner and outer membrane leaflet, and the influence of the cytoskeleton of up to five different cell lines, and clear differences of the FCS diffusion law and EArr for the different probes in dependence of their localization are shown.
28 citations
TL;DR: It is demonstrated by analysis of the structure and dynamics of the vesicles that the impact of aescin strongly depends on the lipid state and below Tm the membrane becomes fluidized and softer, above Tm solidified and stiffer compared to a DMPC membrane without additive at similar conditions.
Abstract: Vesicle shape and bilayer parameters are studied by small-angle X-ray (SAXS) and small-angle neutron (SANS) scattering in the presence of the saponin aescin. We confirm successful incorporation of aescin molecules by analysis of the radii of gyration RG and study furthermore the impact of aescin incorporation on bilayer thickness parameters from the neutron and X-ray perspective. Additionally, the bending elasticity (κ) of these 1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicle bilayers is studied in the presence of aescin. Neutron spin-echo spectroscopy (NSE) allows to detect subtle changes in the dynamics and κ of lipid membranes. Changes of κ are detectable at temperatures below and above the main phase transition temperature Tm of the lipid. The impact of aescin is much more significant below Tm. It has been found that below Tm the addition of aescin to the vesicles decreases the value of κ and softens the bilayer. Above Tm the value of κ increases with increasing aescin content and the bilayer becomes more rigid. Altogether, we demonstrate by analysis of the structure and dynamics of the vesicles that the impact of aescin strongly depends on the lipid state. Below Tm the membrane becomes fluidized and softer, above Tm solidified and stiffer compared to a DMPC membrane without additive at similar conditions.
28 citations
TL;DR: Folate/AuNRs can be as effective and promising nanomaterials for photothermal therapy of folate receptor bearing tumor.
Abstract: Photothermal cancer therapy, as a prospective approach for local cancer treatment, is attracting increasing interests. In this paper, gold nanorods were conjugated with folate (folate/AuNRs), and their photothermal effects on hepatocellular carcinoma cell line (HepG2) using MTT assay, flow cytometry, as well as on the cellular morphology, cytoskeleton, cell surface adhesion, and stiffness detected at subcellular level by an atomic force microscope (AFM) were investigated. The results indicated that near-infrared laser-induced hyperthermia of folate/AuNRs could break the cell membrane integrity and homeostasis and then lead to the depolymerization of cytoskeleton and influx of intracellular Ca2+. Thus, folate/AuNRs can be as effective and promising nanomaterials for photothermal therapy of folate receptor bearing tumor.
27 citations
Cites background from "Dynamics in the plasma membrane: ho..."
...In cells, the membrane forms a barrier between the cell and the external environment and acts as the exchange interface between the inside and outside of the cell (Marguet et al. 2006)....
[...]
TL;DR: In this article, the lateral diffusion of a protein interacting with the curvature of the membrane is considered and it is shown that curvature coupling substantially enhances the diffusion coefficient, and the correlation of the forces acting on the particle indicates that the diffusion inclusion tries to follow favorable positions on the membrane such that forces along the trajectory are on average smaller than they would be for random particle positions.
Abstract: We consider the lateral diffusion of a protein interacting with the curvature of the membrane. The interaction energy is minimized if the particle is at a membrane position with a certain curvature that agrees with the spontaneous curvature of the particle. We employ stochastic simulations that take into account both the thermal fluctuations of the membrane and the diffusive behavior of the particle. In this study, we neglect the influence of the particle on the membrane dynamics, thus the membrane dynamics agrees with that of a freely fluctuating membrane. Overall, we find that this curvature coupling substantially enhances the diffusion coefficient. We compare the ratio of the projected or measured diffusion coefficient and the free intramembrane diffusion coefficient, which is a parameter of the simulations, with analytical results that rely on several approximations. We find that the simulations always lead to a somewhat smaller diffusion coefficient than that from our analytical approach. A detailed study of the correlations of the forces acting on the particle indicates that the diffusing inclusion tries to follow favorable positions on the membrane such that forces along the trajectory are on average smaller than they would be for random particle positions.
27 citations
References
More filters
TL;DR: Results strongly indicate that the bivalent antibodies produce an aggregation of the surface immunoglobulin molecules in the plane of the membrane, which can occur only if the immunoglOBulin molecules are free to diffuse in the membrane.
Abstract: A fluid mosaic model is presented for the gross organization and structure of the proteins and lipids of biological membranes. The model is consistent with the restrictions imposed by thermodynamics. In this model, the proteins that are integral to the membrane are a heterogeneous set of globular molecules, each arranged in an amphipathic structure, that is, with the ionic and highly polar groups protruding from the membrane into the aqueous phase, and the nonpolar groups largely buried in the hydrophobic interior of the membrane. These globular molecules are partially embedded in a matrix of phospholipid. The bulk of the phospholipid is organized as a discontinuous, fluid bilayer, although a small fraction of the lipid may interact specifically with the membrane proteins. The fluid mosaic structure is therefore formally analogous to a two-dimensional oriented solution of integral proteins (or lipoproteins) in the viscous phospholipid bilayer solvent. Recent experiments with a wide variety of techniqes and several different membrane systems are described, all of which abet consistent with, and add much detail to, the fluid mosaic model. It therefore seems appropriate to suggest possible mechanisms for various membrane functions and membrane-mediated phenomena in the light of the model. As examples, experimentally testable mechanisms are suggested for cell surface changes in malignant transformation, and for cooperative effects exhibited in the interactions of membranes with some specific ligands. Note added in proof: Since this article was written, we have obtained electron microscopic evidence (69) that the concanavalin A binding sites on the membranes of SV40 virus-transformed mouse fibroblasts (3T3 cells) are more clustered than the sites on the membranes of normal cells, as predicted by the hypothesis represented in Fig. 7B. T-here has also appeared a study by Taylor et al. (70) showing the remarkable effects produced on lymphocytes by the addition of antibodies directed to their surface immunoglobulin molecules. The antibodies induce a redistribution and pinocytosis of these surface immunoglobulins, so that within about 30 minutes at 37 degrees C the surface immunoglobulins are completely swept out of the membrane. These effects do not occur, however, if the bivalent antibodies are replaced by their univalent Fab fragments or if the antibody experiments are carried out at 0 degrees C instead of 37 degrees C. These and related results strongly indicate that the bivalent antibodies produce an aggregation of the surface immunoglobulin molecules in the plane of the membrane, which can occur only if the immunoglobulin molecules are free to diffuse in the membrane. This aggregation then appears to trigger off the pinocytosis of the membrane components by some unknown mechanism. Such membrane transformations may be of crucial importance in the induction of an antibody response to an antigen, as well as iv other processes of cell differentiation.
7,790 citations
TL;DR: The new generations of qdots have far-reaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.
Abstract: Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biological applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biology. Recent examples of their experimental use include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes in live animals by near-infrared emission during surgery. The new generations of qdots have farreaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.
7,499 citations
"Dynamics in the plasma membrane: ho..." refers background in this paper
...The use of fluorescent quantum dots is emerging as a promising alternative to classical fluorescent tags (GFPs and organic fluorophores) (Michalet et al, 2005)....
[...]
...…quantum yields, large molar extinction coefficients, size-dependent tunable emission and high photostability) make them appeal- &2006 European Molecular Biology Organization The EMBO Journal VOL 25 | NO 15 | 2006 3449 ing candidate tags for use with SDT (Dahan et al, 2003; Michalet et al, 2005)....
[...]
TL;DR: This review looks at current methods for preparing QD bioconjugates as well as presenting an overview of applications, and concludes that the potential of QDs in biology has just begun to be realized and new avenues will arise as the ability to manipulate these materials improves.
Abstract: One of the fastest moving and most exciting interfaces of nanotechnology is the use of quantum dots (QDs) in biology. The unique optical properties of QDs make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations, in which traditional fluorescent labels based on organic molecules fall short of providing long-term stability and simultaneous detection of multiple signals. The ability to make QDs water soluble and target them to specific biomolecules has led to promising applications in cellular labelling, deep-tissue imaging, assay labelling and as efficient fluorescence resonance energy transfer donors. Despite recent progress, much work still needs to be done to achieve reproducible and robust surface functionalization and develop flexible bioconjugation techniques. In this review, we look at current methods for preparing QD bioconjugates as well as presenting an overview of applications. The potential of QDs in biology has just begun to be realized and new avenues will arise as our ability to manipulate these materials improves.
5,875 citations
"Dynamics in the plasma membrane: ho..." refers background in this paper
...However, there is still a need to improve the functionalization of QD surfaces, the flexibility for bioconjugations and single irreversible molecular associations between individually tracked molecules (Medintz et al, 2005)....
[...]
Book•
01 Jan 1983
TL;DR: This book is a lucid, straightforward introduction to the concepts and techniques of statistical physics that students of biology, biochemistry, and biophysics must know.
Abstract: This book is a lucid, straightforward introduction to the concepts and techniques of statistical physics that students of biology, biochemistry, and biophysics must know. It provides a sound basis for understanding random motions of molecules, subcellular particles, or cells, or of processes that depend on such motion or are markedly affected by it. Readers do not need to understand thermodynamics in order to acquire a knowledge of the physics involved in diffusion, sedimentation, electrophoresis, chromatography, and cell motility--subjects that become lively and immediate when the author discusses them in terms of random walks of individual particles.
3,041 citations
"Dynamics in the plasma membrane: ho..." refers background in this paper
...Brownian motion is a principle that applies to all biological systems (Berg, 1983): as the result of thermal agitation processes, molecules are constantly on the move, colliding with each other and bouncing back and forth (Figure 1)....
[...]
...…plasma membrane dynamics Brownian motion, diffusion and membrane organization Brownian motion is a principle that applies to all biological systems (Berg, 1983): as the result of thermal agitation processes, molecules are constantly on the move, colliding with each other and bouncing back and…...
[...]
TL;DR: A unified characterization of the best available FPs provides a useful guide in narrowing down the options for biological imaging tools.
Abstract: The recent explosion in the diversity of available fluorescent proteins (FPs) promises a wide variety of new tools for biological imaging. With no unified standard for assessing these tools, however, a researcher is faced with difficult questions. Which FPs are best for general use? Which are the brightest? What additional factors determine which are best for a given experiment? Although in many cases, a trial-and-error approach may still be necessary in determining the answers to these questions, a unified characterization of the best available FPs provides a useful guide in narrowing down the options.
2,933 citations
"Dynamics in the plasma membrane: ho..." refers background in this paper
...As the cDNA encoding the GFP was characterized, a wide variety of monomeric fluorescent proteins have provided attractive potential candidates for monitoring dynamic processes in which different molecular species are simultaneously involved (for a review, see Shaner et al, 2005)....
[...]