https://www.phys.ens.fr/IMG/pdf/precisionthompson.pdf

Precise nanometer localization analysis for individual fluorescent probes

Measurements of trajectories of individual proteins or lipids in the plasma membrane of cells show a variety of types of motion. Brownian motion is observed, but many of the particles undergo non-Brownian motion, including directed motion, confined motion, and anomalous diffusion. The variety of motion leads to significant effects on the kinetics of reactions among membrane-bound species and requires a revision of existing views of membrane structure and dynamics.

SINGLE-PARTICLE TRACKING: Applications to Membrane Dynamics

Lateral heterogeneities in the classical fluid-mosaic model of cell membranes are now envisaged as domains or 'rafts' that are enriched in (glyco)sphingolipids, cholesterol, specific membrane proteins and glycosylphosphatidylinositol (GPI)-anchored proteins These rafts dictate the sorting of associated proteins and/or provide sites for assembling cytoplasmic signalling molecules However, there is no direct evidence that rafts exist in living cells We have now measured the extent of energy transfer between isoforms of the folate receptor bound to a fluorescent analogue of folic acid, in terms of the dependence of fluorescence polarization on fluorophore densities in membranes We find that the extent of energy transfer for the GPI-anchored folate-receptor isoform is density-independent, which is characteristic of organization in sub-pixel-sized domains at the surface of living cells; however, the extent of energy transfer for the transmembrane-anchored folate-receptor isoform was density-dependent, which is consistent with a random distribution These domains are likely to be less than 70 nm in diameter and are disrupted by removal of cellular cholesterol These results indicate that lipid-linked proteins are organized in cholesterol-dependent submicron-sized domains Our methodology offers a new way of monitoring nanometre-scale association between molecules in living cells

GPI-anchored proteins are organized in submicron domains at the cell surface

https://www.seas.upenn.edu/%7Edischer/pdfs/Cell_on_Gel-BJ.pdf

Substrate Compliance versus Ligand Density in Cell on Gel Responses

Lipid rafts bringing order to chaos

https://science.sciencemag.org/content/sci/268/5216/1441.full.pdf

Revisiting the fluid mosaic model of membranes.

Glycosylphosphatidylinositol (GPI)-anchored proteins participate in many cell surface functions; however, the molecular associations of these lipid-linked proteins within the plasma membrane are not well understood. Recent biochemical analyses of detergent insoluble membrane fractions have suggested that GPI-anchored proteins may be associated with glycosphingolipid (GSL)-enriched domains that also contain cholesterol and signaling molecules such as Src family kinases and, in some cases, caveolae. The movements of two components of the putative GSL-enriched domains, Thy-1, a GPI-anchored protein, and GM1, a GSL, were followed with single particle tracking on C3H 10T1/2 cell surfaces and categorized into four modes of lateral transport, fast diffusion, slow anomalous diffusion, diffusion confined to 325−370 nm diameter regions, and a fraction of molecules that was essentially stationary on the 6.6 s time scale. Longer observations (60 s) showed that Thy-1 and GM1 are transiently confined for 7−9 s to regio...

Rudolf Simson

Papers

Revisiting the fluid mosaic model of membranes.

Transient confinement of a glycosylphosphatidylinositol-anchored protein in the plasma membrane

Detection of temporary lateral confinement of membrane proteins using single-particle tracking analysis

Membrane Bending Modulus and Adhesion Energy of Wild-Type and Mutant Cells of Dictyostelium Lacking Talin or Cortexillins

Structural mosaicism on the submicron scale in the plasma membrane.