The effect of cholesterol on membrane molecular dynamics in unilamellar vesicles: a fast field-cycling NMR relaxometry study.

FRAENZA, CARLA CECILIA; ANOARDO, ESTEBAN; MELEDANDRI C. J.; BROUGHAM D.F.

Torino

Conferencia; 8th Conference on Fast Field Cycling NMR Relaxometry; 2013

Fast field cycling (FFC) 1H NMR spin-lattice relaxation rate dispersions of liposomes have been explained by a physical model that accounts for the molecular and collective dynamics of the lipids [1,2].  The FFC NMR method turned to be a useful tool for the study of the molecular dynamics of lipids and the viscoelastic properties of membranes composed of a single lipid type. It has been claimed that in the case of cholesterol containing membranes, the system remains in the disordered liquid crystalline phase (ld) up to a certain concentration of the sterol [3,4]. However, other authors define a region around each cholesterol molecule within which lipids become strongly ordered, partitioning the lipid population into affected and unaffected pools, depending on the proximity to a cholesterol molecule [5-9]. The unaffected lipids are considered to be in the ld phase, while the affected lipids are described as being in an ordered liquid crystalline phase (lo). In this work we confront both interpretations with new experimental data, as a further refinement of our model. We analyze experimental FFC relaxation rate dispersion curves obtained at 298 K for liposomes of radius between 68 and 80 nm composed of DOPC and cholesterol at 10 and 25 mol%. The consistency obtained by this analysis suggests that the model, previously used to explain the relaxation rate dispersions in single lipid membranes, can be extended for the study of cholesterol containing liposomes.     References: [1] Meledandri C. J., Perlo J., Farrher E., Brougham D. F., Anoardo E., J. Phys. Chem. B, 2009, 11, 15532. [2] Perlo J., Meledandri C. J., Anoardo E., Brougham D. F. J. Phys. Chem. B, 2011, 115, 3444. [3] Filippov A., Orädd G., Lindblom G. Biophys. J. 2003, 84, 3079. [4] Filippov A., Orädd G., Lidblom G., Langmuir 2003, 19, 6397. [5] Edholm O., Nyberg A. M., Biophys J. 1992, 63, 1081. [6] Robinson A. J., Richards W. G., Thomas P. J., Hann M. M. Biophys J. 1995, 68, 164. [7] Chiu S. W., Jakobsson E., Mashl R. J., Scott H. L. Biophys J. 2002, 83, 1842. [8] Jedlovszky P., Mezei M., J. Phys. Chem. B, 2003, 107, 5311. [9] Dai J., Alwarawrah M., Huang J. J. Phys. Chem. B, 2010, 114, 840.