Partition of membrane probes in a gel/fluid two-component lipid system: a fluorescence resonance energy transfer study.
A non-ideal lipid binary mixture (dilauroylphosphatidylcholine/distearoylphosphatidylcholine), which exhibits gel/fluid phase coexistence for wide temperature and composition ranges, was studied using photophysical techniques, namely fluorescence anisotropy, lifetime and resonance energy transfer (FRET) measurements. The FRET donor, N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-dilauroylphosphatidylethanol amine, and a short-tailed FRET acceptor, 1,1'-didodecil-3,3,3',3'-tetramethylindocarbocyanine (DiIC12(3)), were shown to prefer the fluid phase by both intrinsic anisotropy, lifetime and FRET measurements, in agreement with published reports. The other studied FRET acceptor, long-tailed probe 1,1'-dioctadecil-3,3,3',3'-tetramethylindocarbocyanine (DiIC18(3)), is usually reported in the literature as partitioning mainly to the gel. While intrinsic lifetime studies indeed indicated preferential partition of DiIC18(3) into a rigidified environment, FRET analysis pointed to an increased donor-acceptor proximity as a consequence of phase separation. These apparently conflicting results were rationalized on the basis of segregation of DiIC18(3) to the gel/fluid interphase. In order to fluid-located donors sense these interphase-located acceptors, fluid domains should be small (not exceed approximately 10-15 nm). It is concluded that membrane probes which apparently prefer the gel phase may indeed show a non-random distribution in this medium, and tend to locate in an environment which simultaneously leads to less strict packing constraints and to favorable hydrophobic matching interactions.
Centro de Química-Física Molecular, Instituto Superior Técnico, Lisboa, Portugal. pclloura@alfa.ist.utl.pt
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Loura
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Fedorov
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Prieto
D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives*; D002232:Carbocyanines; D005456:Fluorescent Dyes / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D010714:Phosphatidylethanolamines; D013050:Spectrometry, Fluorescence; D013696:Temperature
D002232:Carbocyanines; D005456:Fluorescent Dyes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C015153:1,2-dilauroylphosphatidylcholine; C024286:3,3'-dioctadecylindocarbocyanine; C072024:carbocyanine dye DiIC12(3); C042461:N-NBD-1,2-dilauroylphosphatidylethanolamine; C010942:1,2-distearoyllecithin; D009327:4-Chloro-7-nitrobenzofurazan