Nanoscale Structure and Dynamics of Model Membrane Lipid Raft Systems, Studied by Neutron Scattering Methods

Quasi-elastic neutron scattering (QENS) and small angle (SANS), in combination with isotopic contrast variation, have been used to determine the structure dynamics of three-component lipid membranes, form vesicles, comprising an unsaturated [palmitoyl-oleoyl-phosphatidylcholine (POPC) or dioleoyl-phosphatidylcholine (DOPC)], a saturated phospholipid (dipalmitoyl-phosphatidylcholine (DPPC)), cholesterol, as function temperature composition. SANS studies showed vesicle membranes composed 1:1:1 molar ratio DPPC:DOPC:cholesterol 2:2:1 DPPC:POPC:cholesterol phase separated, forming rafts ∼18 ∼7 nm diameter respectively, when decreasing from 308 297 K. Phase separation was reversible upon increasing temperature. The larger observed systems containing DOPC are attributed greater mis-match alkyl chains between DPPC, than for POPC DPPC. QENS studies, over range 283–323K, that resulting data were best modelled by two Lorentzian functions: narrow component, describing “in-plane” diffusion, broader chain segmental relaxation. overall diffusion found show significant reduction due transitioning one where component lipids homogeneously mixed. use different combinations allowed measured in-plane be understood terms increase DPPC corresponding decrease DOPC/POPC lipid. As considered principally breakdown decreases exposure cholesterol whilst These results sensitivity local concentration, importance considering local, rather global composition membrane understanding processes within membrane. novel allows non-intrusive approach characterize occurring phase-separated model which designed mimic lateral heterogeneity seen cellular membranes–a can pathological consequences.