FRAP to Characterize Molecular Diffusion and Interaction in Various Membrane Environments

PLoS One. 2016 Jul 7;11(7):e0158457. doi: 10.1371/journal.pone.0158457. eCollection 2016.

Abstract

Fluorescence recovery after photobleaching (FRAP) is a standard method used to study the dynamics of lipids and proteins in artificial and cellular membrane systems. The advent of confocal microscopy two decades ago has made quantitative FRAP easily available to most laboratories. Usually, a single bleaching pattern/area is used and the corresponding recovery time is assumed to directly provide a diffusion coefficient, although this is only true in the case of unrestricted Brownian motion. Here, we propose some general guidelines to perform FRAP experiments under a confocal microscope with different bleaching patterns and area, allowing the experimentalist to establish whether the molecules undergo Brownian motion (free diffusion) or whether they have restricted or directed movements. Using in silico simulations of FRAP measurements, we further indicate the data acquisition criteria that have to be verified in order to obtain accurate values for the diffusion coefficient and to be able to distinguish between different diffusive species. Using this approach, we compare the behavior of lipids in three different membrane platforms (supported lipid bilayers, giant liposomes and sponge phases), and we demonstrate that FRAP measurements are consistent with results obtained using other techniques such as Fluorescence Correlation Spectroscopy (FCS) or Single Particle Tracking (SPT). Finally, we apply this method to show that the presence of the synaptic protein Munc18-1 inhibits the interaction between the synaptic vesicle SNARE protein, VAMP2, and its partner from the plasma membrane, Syn1A.

MeSH terms

  • Animals
  • Cell Membrane / physiology*
  • Cytoplasm / chemistry
  • Diffusion
  • Fluorescence Recovery After Photobleaching*
  • Lipid Bilayers / chemistry
  • Lipids / chemistry
  • Membranes, Artificial
  • Mice
  • Microscopy, Confocal
  • Munc18 Proteins / chemistry
  • Rats
  • Reproducibility of Results
  • Synapsins / chemistry
  • Vesicle-Associated Membrane Protein 2 / chemistry

Substances

  • Lipid Bilayers
  • Lipids
  • Membranes, Artificial
  • Munc18 Proteins
  • Stxbp1 protein, rat
  • Synapsins
  • Vesicle-Associated Membrane Protein 2
  • vesicle-associated membrane protein 2, mouse

Grants and funding

This work was supported by the ANR @RATION SynBioExo to J.E.R.; by the ANR Blanc ANR-12-BSV5- 0002 to F.P.; by the ANR Blanc ANR-12-BSV8-0010-ASSEMBLY to W.U.; by the ANR Jeunes Chercheurs ANR-09-JCJC-0062-01 and the AFM Trampoline 16799 to D.T.; V.A. is supported by funds from the PhD Program “Frontières du Vivant (FdV) – Cursus Bettencourt”. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Rong Yang worked in James Rothman's lab at Columbia University as a post-doctoral research scientist from January 2005 to October 2006. Any research work performed by this author during this period was funded by James Rothman’s lab. None of the work related to this manuscript was funded by Rong Yang’s current employer, Adimab, LLC. This current employer did not play any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.