Cholesterol depletion induces solid-like regions in the plasma membrane

¹ Stanford University
² Stanford Univeristy

^* To whom correspondence should be addressed. E-mail: snishimu{at}stanford.edu.

Submitted on July 11, 2005
Revised on August 17, 2005
Accepted on 14 October 2005

	Abstract

Glycosylphosphatidylinositol (GPI)-linked and transmembrane MHC class II I-Ek proteins, as well as Tritc-DHPE, are used as probes to determine the effect of varying the cholesterol concentration on the organization of the plasma membrane at temperatures in the range of 22 - 42°C. Cholesterol depletion caused a decrease in the diffusion coefficients for the MHC II proteins and the slow fraction of the Tritc-DHPE population. At 37°C, reduction of the total cell cholesterol concentration results in a smaller suppression of the translational diffusion for I-Ek proteins than was observed in an earlier work at 22°C. At 37°C, the diffusion of both I-Ek proteins is Brownian (0.9< -parameter < 1.1). More than 99% of the protein population diffuses homogeneously when imaged at 65 frames per second. When the temperature is raised from 22 to 42°C, a break is seen at ~35°C in the Arrhenius plots. Cytoskeletal effects appear to be minimal. These results are consistent with our previously described model of solid-like domain formation in the plasma membrane.

Key Words: Cholesterol, GPI-linked and native I-Ek, Lateral Diffusion, Lipid Microdomains, Plasma Membrane, Single-molecule epifluorescence microscopy

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