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DiynePC powder was suspendedin Milli-Q water by freezing in liquid nitrogen and thawing at 60C (fivecycles). the functional roles of lipid rafts in biological membranes including retinal disk membranes. == Intro == Heterogeneous distributions of lipids and proteins in the cell membrane are profoundly affecting the membrane functions. Lipid rafts enriched with saturated phospholipids, cholesterol, and some types of proteins are believed to regulate a wide range of cellular functions, including cell signaling and proliferation, and are associated with diseases such as cancer and diabetes (1, 2, 3). The functional roles of 3,5-Diiodothyropropionic acid lipid rafts in the signal transduction of G protein-coupled receptors (GPCRs), the largest super family of human genome and the most important target of currently available drugs, are attaining heightened attention (4, 5, 6). The interactions between GPCR and rafts are reported to affect the dimer formation of GPCR and receptor signaling (7). However , the regulatory roles of lipid rafts on GPCRs functions are still poorly understood, partially owing to the lack of the methodology to quantitatively evaluate the affinity of membrane proteins to lipid raft (raftophilicity). The photoreceptor rhodopsin (Rh) is a GPCR that has been most extensively studied. Upon absorbing a photon, Rh undergoes conformational changes to metarhodopsin II (Rh), which can activate the G protein transducin (Gt). Although Rh is thought to have a low affinity to lipid raft as the other intrinsic membrane proteins (2), Rh has tandem palmitoyl residues at the carboxyl terminus of eighth helix (8), so that it also has raftophilic singular point on its membrane spanning surface. Gtis a lipidated protein that attaches onto the surface of bilayer with hydrocarbon chains (9, 10). Our previous biochemical study has shown that 15% of Rh is in detergent-resistant membrane fractions (DRM) prepared from rod photoreceptor membranes (11). Furthermore, the affinity ofGtto the DRM was enhanced after photoirradiation in the rod outer segments (ROS), suggesting that the Rh-Gtcomplex was associated with lipid rafts (11). These observations suggest that the raftophilicity of Rh is involved in an essential process of the G protein activation. More generally, a large number of studies indicate that the functions of Rh are strongly affected by the surrounding lipids (12, 13). However , the roles of lipid rafts in regulating the signal transduction of Rh have not been fully understood. One important physical parameter intended for understanding 3,5-Diiodothyropropionic acid the roles of lipid rafts is the raftophilicity. Although the association of molecules to DRM suggests their affinity to lipid raft (6, 3,5-Diiodothyropropionic acid 14), relationship to DRM itself is not suitable for quantitatively evaluating raftophilicity, because 3,5-Diiodothyropropionic acid it is prone to artifacts during the solubilization Rabbit Polyclonal to TAZ and separation processes (15). Artificial model membranes are potentially useful tools intended for quantitatively evaluating the physicochemical properties of membrane-bound molecules. Phase separation of liquid-ordered (Lo) and liquid-disordered (Ld) phases in giant unilamellar vesicles (GUVs) and giant plasma membrane vesicles (GPMVs) has been extensively studied intended for mimicking lipid rafts. Partitioning of membrane-bound molecules inLo/Ldphases has been used as a measure of raftophilicity (16, 17, 18). Another class of model membrane that has been used for studying membrane domains is substrate-supported planar lipid bilayer (SPB), which typically consists of a single lipid bilayer adsorbed on a hydrophilic substrate surface (e. g., glass). TheLo/Ldpartitioning of urokinase receptors and integrin has been evaluated in.