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Related Concept Videos

Protein Diffusion in the Membrane01:24

Protein Diffusion in the Membrane

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Proteins show rotational as well as lateral diffusion across the membrane. The lateral diffusion of proteins was confirmed through the cell fusion experiment where mouse and human cells were fused, resulting in hybrid cells. When the human and mouse cells fused, the specific membrane proteins on human and mouse cells were marked with the red and green-fluorescent markers, respectively. Initially, the red and green fluorescence was located on the respective hemisphere of the cell. As time...
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Different fluorescence-based techniques are used to study the protein dynamics in living cells. These techniques include FRAP, FRET, and PET.
Fluorescent recovery after photobleaching (FRAP) is a fluorescent-protein-based detection technique used to quantify protein movement rates within the cell. This method exposes a small portion of the cell to an intense laser beam. The laser beam causes permanent photobleaching of the fluorophore-tagged proteins in the exposed region. As the bleached...
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Membrane fluidity is explained by the fluid mosaic model of the cell membrane, which describes the plasma membrane structure as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character.
Mosaic nature of the membrane
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Cell membranes are composed of phospholipids, proteins, and carbohydrates loosely attached to one another through chemical interactions. Molecules are generally able to move about in the plane of the membrane, giving the membrane its flexible nature called fluidity. Two other features of the membrane contribute to membrane fluidity: the chemical structure of the phospholipids and the presence of cholesterol in the membrane.
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Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
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Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
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From Fast Fluorescence Imaging to Molecular Diffusion Law on Live Cell Membranes in a Commercial Microscope
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FRAP to Characterize Molecular Diffusion and Interaction in Various Membrane Environments.

Frédéric Pincet1,2, Vladimir Adrien1,3, Rong Yang4

  • 1Laboratoire de Physique Statistique, Ecole Normale Supérieure, CNRS UMR 8550, Université Pierre et Marie Curie, Sorbonne Universités, Paris, France.

Plos One
|July 9, 2016
PubMed
Summary

This study provides guidelines for accurate Fluorescence Recovery After Photobleaching (FRAP) experiments to analyze molecular diffusion in membranes. It demonstrates how FRAP can reveal restricted movement and protein interactions, such as Munc18-1 inhibiting VAMP2-Syn1A binding.

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Area of Science:

  • Membrane biophysics
  • Confocal microscopy techniques
  • Protein-lipid interactions

Background:

  • Fluorescence Recovery After Photobleaching (FRAP) is a key technique for studying molecular dynamics in membranes.
  • Standard FRAP analysis assumes unrestricted Brownian motion, which may not always be accurate.
  • Confocal microscopy has democratized quantitative FRAP, necessitating refined methodologies.

Purpose of the Study:

  • To establish general guidelines for performing FRAP experiments with varied bleaching patterns and areas.
  • To enable differentiation between free diffusion, restricted movement, and directed motion of molecules.
  • To validate the proposed FRAP methodology using in silico simulations and comparison with other techniques.

Main Methods:

  • Development of FRAP experimental guidelines using diverse bleaching patterns and areas.
  • In silico simulations to determine optimal data acquisition criteria for accurate diffusion coefficients.
  • Comparative analysis of lipid diffusion across supported lipid bilayers, giant liposomes, and sponge phases.
  • Application of FRAP to investigate the effect of Munc18-1 on VAMP2-Syn1A interactions.

Main Results:

  • Proposed FRAP guidelines allow discrimination between different types of molecular motion.
  • In silico simulations confirm criteria for accurate diffusion coefficient determination.
  • FRAP results for lipids in various membrane platforms align with Fluorescence Correlation Spectroscopy (FCS) and Single Particle Tracking (SPT) data.
  • Munc18-1 was shown to inhibit the interaction between VAMP2 and Syn1A.

Conclusions:

  • Refined FRAP protocols enhance the study of molecular dynamics in biological membranes.
  • The method accurately distinguishes between free and restricted diffusion, providing insights into membrane organization.
  • FRAP is a reliable technique for studying protein-lipid interactions, exemplified by the Munc18-1/VAMP2/Syn1A system.