Ordered and disordered phases coexist in plasma membrane vesicles of RBL-2H3 mast cells. An ESR study |
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Authors: | Ge Mingtao Gidwani Arun Brown H Alex Holowka David Baird Barbara Freed Jack H |
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Institution: | Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, USA. |
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Abstract: | Four chain spin labels and a spin-labeled cholestane were used to study the dynamic structure of plasma membrane vesicles (PMV) prepared from RBL-2H3 mast cells at temperatures ranging from 22 degrees C to 45 degrees C. Analysis shows that the spectra from most labels consist of two components. The abundant spectral components exhibit substantial ordering that is intermediate between that of a liquid-ordered (Lo) phase, and that of a liquid-crystalline (Lc) phase as represented by model membranes. Also, rotational diffusion rates of the spin labels are comparable to those in the Lo phase. In contrast, the ordering for the less abundant components is much lower. These results indicate that a Lo-like region or phase (the abundant component) and an Lc-like region or phase (the less abundant component) coexist in the PMV. In contrast, membranes reconstituted from extracted lipids exhibit the more ordered phase only. This suggests that membrane-associated proteins are important for the coexistence of Lo-like and Lc-like regions in the plasma membrane. In addition, binding of the myristoylated protein, ARF6 to PMV, leads to a new spectral component for a headgroup lipid spin label that indicates the formation of plasma membrane defects by this low molecular weight GTPase. |
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Keywords: | GPI glycosylphosphatidylinositol Chol cholesterol CSL 3β-doxyl-5α-cholestane DRM detergent resistant membranes DPPC 1 2-dipalmitoylphosphatidylcholine DPPTC 1 2-dipalmitoylphospho(TEMPO) choline TEMPO 2 2 6 6-tetramethyl-piperidine-1-oxy myr-ARF6 myristolyated ADP ribosylation factor 6 NLLS nonlinear least-squares PIP2 phosphatidylinositol 4 5-biphosphate POPC 1-palmitoyl-2-oleoyl-phosphatidylcholine SM sphingomyelin |
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