Abstract:
:Lateral organization of cholesterol in dioleoyl-phosphatidylcholine (DOPC) lipid bilayers at high cholesterol concentration (>45 mol%) was investigated using steady-state fluorescence anisotropy and fluorescent resonance energy transfer techniques. The recently devised Low Temperature Trap method was used to prepare compositionally uniform cholesterol/DOPC liposomes to avoid the problem of lipid demixing. The fluorescence anisotropy of diphenylhexatrience chain-labeled phosphatidylcholine (DPH-PC) in these liposomes exhibited local maxima at cholesterol mol fractions of 0.50 and 0.57, and a sharp drop at 0.67. For the liposomes labeled with both dehydroergosterol and DPH-PC, the fluorescent resonance energy transfer efficiency from dehydroergosterol to DPH-PC displayed a steep jump at cholesterol mol fraction of 0.5, and dips at 0.57 and 0.68. These results indicate the presence of highly ordered cholesterol regular distribution domains at those observed critical compositions. The observed critical mol fraction at 0.67 agreed favorably with the solubility limit of cholesterol in DOPC bilayers as independently measured by light scattering and optical microscopy. The regular distribution at 0.57 was previously predicted from a Monte Carlo simulation based on the Umbrella model. The results strongly support the hypothesis that the primary requirement for cholesterol-phospholipid mixing is that the polar phospholipid headgroups need to cover the nonpolar body of cholesterol to avoid the exposure of cholesterol to water.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Parker A,Miles K,Cheng KH,Huang Jdoi
10.1016/S0006-3495(04)74221-6subject
Has Abstractpub_date
2004-03-01 00:00:00pages
1532-44issue
3eissn
0006-3495issn
1542-0086pii
S0006-3495(04)74221-6journal_volume
86pub_type
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