Single molecule studies of molecular diffusion in cellular membranes: Determining membrane structure

Abstract

Since the advent of single particle/molecule microscopies, researchers have applied these techniques to understanding the fluid membranes of cells. By observing diffusion of membrane proteins and lipids in live cell membranes of eukaryotic cells, it has been found that membranes contain a mosaic of fluid compartments. Such structure may be instrumental in understanding key characteristics of the membrane. Recent single molecule observations on prokaryotic cell membranes will also be discussed. © 2007 Wiley Periodicals, Inc. Biopolymers 87: 95–101, 2007.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com

LFA-1 dynamics on the membrane of leukocytes : a single dye tracing study

“…In the third model simple viscous resistance to membrane protein motion might slow diffusion on the micro scale. The diffusion barrier and transient binding models predict a strong dependence between the diffusant size and its diffusion constant and are therefore inconsistent with our data [205,231]. On the other hand, our data on the overall LFA-1 population is in favor of the viscous resistance model, since it is predicting a weak dependence between the size of the diffusant and its diffusion constant D, as is shown below.…”

“…A weak dependence between aggregate size and its lateral diffusion constant in the membrane has been found before on live cells [205]. However, others found a much stronger dependence between the diffusant size and its diffusion constant [247,231]. These different results show that the relation between diffusant size and its diffusion constant are highly context dependent, c.q., their interactions with-, and binding to the micro-and nano-environment determine the observed relationship.…”

“…The mobility of objects in biological membranes has been studied in multiple theoretical and experimental studies [205,135,231]. Kucik et al [205] classified the different models explaining the mobility of a diffusing object in a membrane in three categories.…”

“…This observation suggests that only extended LFA-1 in GPI-AP "hotspots" is truly interacting with cytoskeleton related proteins, while the inactive majority of LFA-1 merely experiences increased viscous drag. Trapping of transmembrane receptors in highly viscous membrane areas has been observed before in other systems [135,231] and enhancement of reaction rates between proteins trapped in nanodomains has been modeled [243]. However, this hypothesis has not been validated for LFA-1 and needs further investigation.…”

Single-molecule diffusion in freely suspended smectic films

“…Single-molecule tracking has been applied to biological membranes [11,12] and recently to liquid crystal films on solid substrates [13][14][15]. As fluorescent dye we use Nile red, dissolved in the liquid crystal samples at concentrations around 10 −8 mol/L (about 3 × 10 −7 wt %).…”