Interaction of apolipoprotein A-I with lecithin-cholesterol vesicles in the presence of phospholipase C

Combined Interaction of Phospholipase C and Apolipoprotein A-I with Small Unilamellar Lecithin-Cholesterol Vesicles: Influence of Apolipoprotein A-I Concentration and Vesicle Composition

“…The present study seeks to test this hypothesis and to confirm and build on the findings of the initial PLC/apo A-I study (11). In particular, we demonstrate that the loss of shielding is indeed possible in cholesterol-free systems provided that the apo A-I concentration is sufficiently low.…”

“…Presuming that shielding ensues until the surface area of DAG in the bilayer exceeds that of bound apo A-I, one would expect to observe rapid aggregation or a microstructural transition to complexes and DAG droplets when the DAG/ bound apo A-I molar ratio exceeds 100 (that is, the ratio of molecular surface areas). The fact that cholesterol-free systems showed essentially no increase in turbidity for DAG/ total apo A-I concentrations up to 109 (11) suggests that K B is near unity in the absence of cholesterol. We therefore set K B ) 1 at 0 mol % cholesterol in this work and determine values for K B for 20, 40, 50, and 60 mol % cholesterol as follows.…”

“…PNFs and ANFs are typically but not always proteins or enzymes. PNFs include phospholipase C (PLC) (5), immunoglobulins (6), fibronectin (7), concanavalin A-binding nonmucous glycoproteins (8), mucous glycoproteins (9), and aminopeptidase N (10), and the most commonly reported ANFs are apolipoprotein A-I (apo A-I) and apolipoprotein A-II (11)(12)(13).…”

“…As a first attempt to investigate interactions between PNFs and ANFs, we recently described the combined effects of PLC and apo A-I in solutions of model bile (11). PLC is a well-studied enzyme that cleaves the phosphoester bond of phosphatidylcholine on the outer leaflet of lecithin-cholesterol vesicles, thereby eliminating polar phosphocholine headgroups and generating hydrophobic diacylglycerol (DAG) moieties within the lipid bilayer (1).…”

Interactions between sphingomyelin and cholesterol in low density lipoproteins and model membranes

“…DL is excluded from l o phases so that the energy transfer efficiency provides a measure of domain size. DHE-to-DL FRET is a well established method for examining phase behavior and compositional changes in phospholipid-cholesterol systems [22][23][24][25]. Especially relevant to this work, the assay has been used to examine lateral phase separation of cholesterol nanodomains [25], nucleation of cholesterol from LDL [6], and methyl-β-cyclodextrin-mediated efflux of DHE [14].…”