Regulatory Aspects of Membrane Microdomain (Raft) Dynamics in Live Cells
Most vertebrate cells display a considerable microheterogeneity in their plasma membranes, often termed microdomain structure. Some of these microdomains are enriched in glycosphingolipids and cholesterol and are resistant to solubilization with nonionic detergents; they are therefore called detergent-insoluble-glycolipid enriched membrane (DIG) or glycosphingolipid enriched membrane (GEM). These domains, also called “lipid rafts” (Simons and Ikonen, 1997), may form at the plasma membrane (PM) upon external stimuli or may be present in a preassembled form upon vesicular traffic to and fusion with the PM (Simons and Ikonen, 1997; Brown and Rose, 1992). We consider lipid rafts as transient molecular associations between lipid and protein components of the PM, providing a dynamic patchiness and local order in the fluid mosaic membrane (Edidin, 2001). Although the microdomain concept is widely accepted, and the existence of rafts has been confirmed by many lines of experimental evidence (e.g., biochemical data on detergent resistance, resolving membrane patchiness by high-resolution fluorescence and electron microscopies, tracking by videomicroscopy the lipid and protein motions in the membrane, etc.), some basic questions about the microdomains still remain open or highly controversial.
KeywordsLipid Raft Fluorescence Resonance Energy Transfer Model Membrane Fluorescence Correlation Spectroscopy Immunological Synapse
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