title: Visualization and analysis of apolipoprotein A-I interaction with binary phospholipid bilayers.
abstract: Apolipoprotein A-I (apoA-I) interaction with specific cell lipid domains was suggested to trigger cholesterol and phospholipid efflux. We analyzed here apoA-I interaction with dimyristoylphosphatidylcholine/distearoylphosphatidylcholine (DMPC/DSPC) bilayers at a temperature showing phase coexistence. Solid and liquid-crystalline domains were visualized by two-photon fluorescence microscopy on giant unilamellar vesicles (GUVs) labeled with 6-dodecanoyl-2-dimethyl-amino-naphthalene (Laurdan). A decrease of vesicle size was detected as long as they were incubated with lipid-free apoA-I, together with a shape deformation and a relative enrichment in DSPC. Selective lipid removal mediated by apoA-I from different domains was followed in real time by changes in the Laurdan generalized polarization. The data show a selective interaction of apoA-I with liquid-crystalline domains, from which it removes lipids, at a molar ratio similar to the domain compositions. Next, apoA-I was incubated with DMPC/DSPC small unilamellar vesicles, and products were isolated and quantified. Protein solubilized both lipids but formed complexes relatively enriched in the liquid component. We also show changes in the GUV morphology when cooling down. Our results suggest that the most efficient reaction between apoA-I and DMPC/DSPC occurs in particular bilayer conditions, probably when small fluid domains are nucleated within a continuous gel phase and interfacial packing defects are maximal.
authors.affiliation: Instituto de Investigaciones Bioquímicas, Consejo Nacional de Investigaciones Cientificas y Technológicas-Universidad Nacional de La Plata, La Plata, Argentina, 1900.
authors.forename: M Alejandra
authors.initials: MA
authors.lastname: Tricerri
authors.forename: Juan D
authors.initials: JD
authors.lastname: Toledo
authors.forename: Susana A
authors.initials: SA
authors.lastname: Sanchez
authors.forename: Theodore L
authors.initials: TL
authors.lastname: Hazlett
authors.forename: Enrico
authors.initials: E
authors.lastname: Gratton
authors.forename: Ana
authors.initials: A
authors.lastname: Jonas
authors.forename: Horacio A
authors.initials: HA
authors.lastname: Garda
mesh_terms: D016632:Apolipoprotein A-I / Q000378:metabolism*; D002722:Chlorobenzenes / Q000378:metabolism; D004134:Dimyristoylphosphatidylcholine / Q000378:metabolism; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D013696:Temperature
chemical_list: D016632:Apolipoprotein A-I; D002722:Chlorobenzenes; D008051:Lipid Bilayers; D008081:Liposomes; D010743:Phospholipids; C004944:chlorfenethol; D004134:Dimyristoylphosphatidylcholine