Anisotropic Motion of Cholesterol in Oriented DPPC Bilayers Studied by Quasielastic Neutron Scattering: The Liquid-Ordered Phase

Abstract

Quasielastic neutron scattering (QENS) at two energy resolutions (1 and 14 microeV) was employed to study high-frequency cholesterol motion in the liquid ordered phase (lo-phase) of oriented multilayers of dipalmitoylphosphatidylcholine at three temperatures: T = 20 degrees C, T = 36 degrees C, and T = 50 degrees C. We studied two orientations of the bilayer stack with respect to the incident neutron beam. This and the two energy resolutions for each orientation allowed us to determine the cholesterol dynamics parallel to the normal of the membrane stack and in the plane of the membrane separately at two different time scales in the GHz range. We find a surprisingly high, model-independent motional anisotropy of cholesterol within the bilayer. The data analysis using explicit models of molecular motion suggests a superposition of two motions of cholesterol: an out-of-plane diffusion of the molecule parallel to the bilayer normal combined with a locally confined motion within the bilayer plane. The rather high amplitude of the out-of-plane diffusion observed at higher temperatures (T >/= 36 degrees C) strongly suggests that cholesterol can move between the opposite leaflets of the bilayer while it remains predominantly confined within its host monolayer at lower temperatures (T = 20 degrees C). The locally confined in-plane cholesterol motion is dominated by discrete, large-angle rotational jumps of the steroid body rather than a quasicontinous rotational diffusion by small angle jumps. We observe a significant increase of the rotational jump rate between T = 20 degrees C and T = 36 degrees C, whereas a further temperature increase to T = 50 degrees C leaves this rate essentially unchanged.

Quasielastic neutron scattering in soft matter

“…Experiments probing the motion of cholesterol find high anisotropy within the bilayer [42], similar to that observed from other sterols [43] which show fast mobility out-of-the bilayer plane.…”

Potential of BODIPY-cholesterol for analysis of cholesterol transport and diffusion in living cells

“…Membrane condensation can be assessed by a variety of techniques including fluorescence polarization of appropriate probes including fluorescent sterols (Chong and Thompson, 1986;Kinosita et al, 1977) and solvent relaxation around environmentally sensitive probes as Laurdan or Prodan (Bagatolli, 2006;Zhang et al, 2006) but also by neutron scattering (Gliss et al, 1999) or extraction of sterols with aqueous carriers, as cyclodextrin (Milles et al, 2013;Ohvo-Rekila et al, 2000). The ability of cholesterol to order membranes in the fluid state comes together with a disordering effect on lipid bilayers in the gel state, i.e.…”

Modeling the structure of the StART domains of MLN64 and StAR proteins in complex with cholesterol

“…Superimposition of the structure of MLN64 and PITPa, as shown by Yoder et al (63), suggests that a common mechanism for the opening of their cavities may exist and that the membrane anchoring and the presentation of the ligand may be similar. Bearing in mind that the orientation of cholesterol in the membrane is such that its polar head points toward the water-lipid interface (64)(65)(66), only binding modes in the IN configuration appear to be mechanistically plausible. Consistent with this argument, the orientation of the PC lipid bound to the crystal structure of the PCTP StART domain is such that its polar head group points toward the end of the binding cavity, and not its entrance (31).…”