Investigations of phospholipid/cholesterol and cholesterol derivative interactions in model membranes

• Main Author: Trevenen, Alexandra H.
• Other Authors: Magee, Tony ; Seddon, John
• Published: Imperial College London 2010
• Subjects: 572
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.513543

Multinuclear solid state MAS NMR (1H and 31P), 31P CSA solid state NMR, 2H NMR and x-ray diffraction techniques have been used to compare the structure and properties of DPPC: Andro and DPPC: 4β-hydroxycholesterol with that of the properties known of DPPC: Chol mixtures in excess water. The formation of the Lo phase is known to occur with PC: Chol mixtures with sufficient concentrations of cholesterol. The formation and properties of the Lo phase was looked at with the cholesterol derivatives Andro (lacking in the hydrocarbon tail present in cholesterol) and 4β-hydroxycholesterol (possessing an extra hydroxyl group adjacent to the one present at the headgroup region of cholesterol). The Lo phase shows fluid-fluid immisibility when combined with the disordered Lα phase. It is this heterogeneity that is believed to be important in the formation of lipid rafts, which are thought to play a role in the function of living cells. Cholesterol desorption from DOPC model membranes was examined using methyl-β-cyclodextrin, which has a high affinity for cholesterol and facilitates the mechanism of cholesterol desorption from lipid membranes. By running a number of experiments, measuring cholesterol desorption from MLV’s and LUV’s a cholesterol flip-flop rate within DOPC model membranes was measured using 1H solution state NMR. A number of methods were also attempted to synthesise an asymmetric DOPC: DPPC membranes. These included a split glass slides method and a modified version of an emulsion method as described by Pautot et al. lipid asymmetry with respect to the split glass slides and emulsion methods was to be observed by NMR, where any cholesterol asymmetry formed via desorption by methyl-β- cyclodextrin was to be evaluated via the use of paramagnetic NMR experiments, however no asymmetry was observed in either experiment.