Calorimetric Measurement of Phospholipid Interaction with Methyl-β-Cyclodextrin

Abstract

Cyclodextrins are able to bind hydrophobic molecules in their interior cavity and as such have received a great deal of attention as carriers of cholesterol, lipophilic drugs, and other sparingly soluble compounds. Despite the importance of these biochemical applications, relatively little is known about the interactions of cyclodextrins with phospholipid membranes. Here we characterize the binding of randomly methylated β-cyclodextrin (mβCD) to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) using right-angle light scattering and isothermal titration calorimetry. Existing models of lipophile−membrane interactions are inadequate to describe the observed binding; we introduce a modified chemical reaction model in which the chemical activity of the phospholipid is independent of its concentration. We find that an average of four mβCD molecules bind to each POPC molecule with an enthalpy of reaction of 46 kJ mol-1 and an equilibrium constant of 90 M-3. These results are consistent with earlier qualititative observations and suggest that disruption of phospholipid membranes may be minimized if the concentration of mβCD is kept below about 15 mM.

Preparation and Properties of Asymmetric Vesicles That Mimic Cell Membranes

“…Void volume fractions contained the lipid vesicles (SUVs and residual MLVs) (not shown). To incorporate cholesterol the exchange vesicles were then incubated with CLC using a lower M␤CD concentration (generally 2.5 mM for PC SUVs and 7.5 mM for POPE:POPS SUVs) so that the M␤CD would not bind phospholipid (43). In the final step, the cholesterol-containing asymmetric SUVs were separated from other components on a Sepharose CL-4B column.…”

“…It works with many different lipids and can be used at elevated temperatures that might aid exchange for lipids with high T m values. Introduction of cholesterol without disruption of the vesicles is possible because cholesterol-M␤CD complexes can be prepared at M␤CD concentrations too low to bind phospholipids (43) and is no doubt aided by rapid cholesterol equilibration between the inner and outer leaflets (69). Although the final cholesterol concentration in the inner and outer leaflets is unknown, the need to maintain mass balance between the leaflets requires a similar final mole fraction of cholesterol in the two leaflets.…”

“…In this report, we introduce such a method. This procedure is based on the observation that methyl-␤-cyclodextrin (M␤CD) binds phospholipids at very high M␤CD concentrations (42,43). Using this method asymmetric vesicles were prepared with an external leaflet rich in sphingomyelin (SM) and an internal leaflet rich in PE and PS, similar to eukaryotic plasma membranes.…”

Phosphatidylethanolamine of Helicobacter pylori Functions as a Steroid-Binding Lipid in the Assimilation of Free Cholesterol and 3 -Hydroxl Steroids into the Bacterial Cell Membrane

“…A recent study by another group demonstrated that a phosphatidylcholine carrying a palmitic acid molecule and an oleic acid molecule (POPC) binds the four molecules of methyl-␤-cyclodextrin (M␤CD, but not dM␤CD) and has further suggested that each fatty acid chain of the POPC molecule is embedded inside the ring structure of one or two molecules of M␤CD (2). No earlier investigations, however, have revealed the molecular interaction between ␤CDs (including M␤CD and dM␤CD) and other glycerophospholipids, such as PE and PG-CL.…”

Lateral Diffusion, Function, and Expression of the Slow Channel Congenital Myasthenia Syndrome αC418W Nicotinic Receptor Mutation with Changes in Lipid Raft Components

“…M␤CD, a water-soluble cyclic oligosaccharide, has a high affinity for cholesterol and has been extensively used as an effective tool for the transport of cholesterol away from cell surfaces (33). M␤CD incubations selectively remove cholesterol from cell membranes while not affecting membrane integrity when concentrations do not exceed 15 mM (34,35). After the incubation period, cells were washed with PBS once and the media was changed.…”