Lateral diffusion of phospholipids in the lipid surface of human low-density lipoprotein measured with a pyrenyl phospholipid probe.
Human low-density lipoprotein (LDL) was labelled with the excimeric fluorescent phospholipid analogue 1-palmitoyl-2-(1'-pyreneoctanoyl)-sn-glycero-3-phosphocholine by using phosphatidylcholine-specific transfer protein for the probe insertion. The lateral diffusivity of the probe in the phospholipid/cholesterol surface monolayer of LDL was determined from the measured dependence of the pyrene monomer fluorescence yield on probe concentration. The data were analyzed by the milling-crowd model (J. Eisinger et al. (1986) Biophys. J. 49, 987-1001] to obtain the short-range lateral diffusivity of the probe. The lateral mobility of the probe in LDL was compared to that in model lipid systems, i.e. in protein-free LDL-like lipid particles and in small unilamellar vesicles, with a phospholipid/cholesterol composition characteristic of LDL. This analysis with the probability PE = 1 for excimer production between nearest-neighbour probes gives the lower limits for f, the frequency of translational lipid--lipid exchanges of the probe of 0.62 x 10(8), 0.19 x 10(8) and 0.19 x 10(8)s-1 in LDL, LDL-like lipid particles, and small unilamellar vesicles, respectively. The lower limits for the corresponding lateral diffusion constants are 16, 5 and 5 microns 2 s-1. The results suggest that the translational mobility of phospholipid molecules in the lipid--protein surface of LDL is not constrained by the apolipoprotein B-100 moiety or the neutral lipid core of the lipoprotein. Instead, the protein moiety may perturb the lipid order with the lipid--associating peptide domains and thus fluidize the amphiphilic surface monolayer of LDL relative to the protein-free model systems. In general, lateral diffusivity of the pyrenyl phospholipid probe in LDL and the model lipid systems is comparable to the lateral mobility of lipid analogue probes in a variety of model and biological membranes.
Vauhkonen
M
M
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York.
Sassaroli
M
M
Somerharju
P
P
Eisinger
J
J
D000727:Androgen-Binding Protein; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002417:Cattle; D002784:Cholesterol; D004058:Diffusion; D005456:Fluorescent Dyes; D006801:Humans; D007700:Kinetics; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008433:Mathematics; D008954:Models, Biological; D010713:Phosphatidylcholines / Q000378:metabolism*; D049488:Phosphatidylethanolamine Binding Protein; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000378:metabolism*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013499:Surface Properties
D000727:Androgen-Binding Protein; D002352:Carrier Proteins; D005456:Fluorescent Dyes; D008077:Lipoproteins, LDL; C511482:PEBP1 protein, human; D010713:Phosphatidylcholines; D049488:Phosphatidylethanolamine Binding Protein; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; C062484:1-palmitoyl-2-(1'-pyreneoctanoyl)glycero-3-phosphochine; D002784:Cholesterol