Lateral mobility in membranes as detected by fluorescence recovery after photobleaching

Abstract

The evaluation of lateral diffusion coefficients of membrane components by the technique of fluorescence recovery after photobleaching (FRAP) is often complicated by uncertainties in the values of the intensities F(O), immediately after bleaching, and F(infinity), after full recovery. These uncertainties arise from instrumental settling time immediately after bleaching and from cell, tissue, microscope, or laser beam movements at the long times required to measure F(infinity). We have developed a method for precise analysis of FRAP data that minimizes these problems. The method is based on the observation that a plot of the reciprocal function R(tau) = F(infinity)/[F(infinity)-F(tau)] is linear over a large time range when (a) the laser beam has a Gaussian profile, (b) recovery involves a single diffusion coefficient, and (c) there is no membrane flow. Moreover, the ratio of intercept to slope of the linear plot is equal to tau 1/2, the time required for the bleached fluorescence to rise to 50% of the full recovery value, F(infinity). The lateral diffusion coefficient D is related to tau 1/2 by tau 1/2 = beta w2/4D where beta is a defined parameter and w is the effective radius of the focused laser beam. These results are shown to indicate that the recovery of fluorescence F(tau) can be represented over a large range of percent bleach, and recovery time tau by the relatively simple expression F(tau) = [ F(o) + F(infinity) (tau/tau 1/2)]/[1 + tau/tau 1/2)]. FRAP data can therefore be easily evaluated by a nonlinear regression analysis with this equation or by a linear fit to the reciprocal function R(tau). It is shown that any error in F(infinity) can be easily detected in a plot of R(tau) vs. tau which deviates significantly from a straight line when F(infinity) is in error by as little as 5%. A scheme for evaluating D by linear analysis is presented. It is also shown that the linear reciprocal plot provides a simple method for detecting flow or multiple diffusion coefficients and for establishing conditions (data precision, differences in multiple diffusion coefficients, magnitude of flow rate compared to lateral diffusion) under which flow or multiple diffusion coefficients can be detected. These aspects are discussed in some detail.

Early sorting of inner nuclear membrane proteins is conserved

“…The area was scanned every 3 sec for 5 min. Lateral mobility was determined by using the method described (20). The data were analyzed with GraphPad (San Diego, CA) Instat 3 by using a t test (95% confidence interval).…”

Lateral Diffusion, Function, and Expression of the Slow Channel Congenital Myasthenia Syndrome αC418W Nicotinic Receptor Mutation with Changes in Lipid Raft Components

“…where F(t) is the normalized fluorescence recovery; ROI (1) is the fluorescence intensity of the bleached region at time t; ROI(2) is the fluorescence intensity of the reference region at time t; and ROI (3) is the fluorescence intensity at the extracellular background at time t. Fluorescence recovery kinetics was determined by exponential fitting of the corrected data (37)(38)(39)(40),…”

Diffusion of α-Chymotrypsin in Solution-Crowded Media. A Fluorescence Recovery after Photobleaching Study

“…In crowded media, typically in vivo and in a great number of in vitro processes, the existence of different macromolecular species, proteins, nucleic acids, organelles, etc., hinders the diffusion process. In these cases, equation 1 must be generalized for situations of anomalous diffusion [52][53][54][55][56][57][58] as:…”