"ไขมันแพรุ่น" (Simons และแวน Meer, 1988 Simons และ Sampaio, 2011)This model (Figure 1A) is based on biophysical, microscopy, and biochemical studies. It proposes that, at any given time, approximately 35% of all membrane proteins are localized into membrane domains termed lipid rafts (Levental et al., 2010). The remaining proteins (65%) are randomly distributed and can move “freely” in accordance with the original fluid mosaic model by Singer and Nicolson (1972). The current view is that lipid rafts are dynamic nanoscale assemblies enriched for sterols and sphingolipids. Lipid rafts can be stabilized and enlarged through specific lipid–lipid, lipid–protein, and protein–protein interactions. Specifically interactions with cellular scaffolds, such as the actin cytoskeleton, have been shown to stabilize and enlarge lipid rafts (Viola and Gupta, 2007). Post-translational modifications (e.g., GPI-anchors or palmitoylation) can localize proteins into lipid rafts. A wide range of dimensions for lipid rafts have been reported using a variety of techniques, e.g., ~10 nm by fluorescence resonance energy transfer (FRET; Goswami et al., 2008); 12–24 nm (Prior and Hancock, 2012), 30–700 nm (Lillemeier et al., 2006), and 100–150 nm (Cambi et al., 2006) by electron microscopy; < 20 nm by stimulated emission depletion (STED) microscopy (Eggeling et al., 2009); 100–200 nm by pair-correlation photo-activated localization microscopy (PALM; Sengupta et al., 2011); <120 nm variable spot size fluorescence correlation spectroscopy (FCS; Lenne et al., 2006). The same variability has been seen for the life-time of lipid rafts spanning from milliseconds (Eggeling et al., 2009) to seconds (Brameshuber et al., 2010), and minutes if stabilized through coalescence as seen for T cell microcluster (MC; Bunnell et al., 2002; Campi et al., 2005). The broad range of dimensions and life-times might be due to differences in detection methods or the existence of different lipid raft types (Kenworthy, 2002; Zacharias et al., 2002; Wilson et al., 2004).
การแปล กรุณารอสักครู่..