Partitioning of pyrene-labeled phospho- and sphingolipids between ordered and disordered bilayer domains |
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| Authors: | Koivusalo Mirkka Alvesalo Joni Virtanen Jorma A Somerharju Pentti |
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| Affiliation: | Institute of Biomedicine, Department of Biochemistry, University of Helsinki, Helsinki, Finland. |
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| Abstract: | Here we have studied how the length of the pyrene-labeled acyl chain (n) of a phosphatidylcholine, sphingomyelin, or galactosylceramide affects the partitioning of these lipids between 1), gel and fluid domains coexisting in bovine brain sphingomyelin (BB-SM) or BB-SM/spin-labeled phosphatidylcholine (PC) bilayers or 2), between liquid-disordered and liquid-ordered domains in BB-SM/spin-labeled PC/cholesterol bilayers. The partitioning behavior was deduced either from modeling of pyrene excimer/monomer ratio versus temperature plots, or from quenching of the pyrene monomer fluorescence by spin-labeled PC. New methods were developed to model excimer formation and pyrene lipid quenching in segregated bilayers. The main result is that partition to either gel or liquid-ordered domains increased significantly with increasing length of the labeled acyl chain, probably because the pyrene moiety attached to a long chain perturbs these ordered domains less. Differences in partitioning were also observed between phosphatidylcholine, sphingomyelin, and galactosylceramide, thus indicating that the lipid backbone and headgroup-specific properties are not severely masked by the pyrene moiety. We conclude that pyrene-labeled lipids could be valuable tools when monitoring domain formation in model and biological membranes as well as when assessing the role of membrane domains in lipid trafficking and sorting. |
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| Keywords: | BB-SM, bovine brain sphingomyelin DOPC, dioleoylphosphatidylcholine DPPC, dipalmitoylphosphatidylcholine DSPC, distearoylphosphatidylcholine MLV, multilamellar vesicle ld, liquid-disordered lo, liquid-ordered PyrnPC, 1-palmitoyl-2-pyrenylacyl-phosphatidylcholine (n = number of aliphatic carbons in the labeled acyl chain) PyrnSM, pyrenylacylsphingomyelin PyrnGalCer, pyrenylacylgalactosylceramide 7-SLPC, 1-palmitoyl-2-(7-doxyl)-stearoyl-phosphatidylcholine 12-SLPC, 1-palmitoyl-2-(12-doxyl)-stearoyl-phosphatidylcholine |
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