Plant sterols in “rafts”: a better way to regulate membrane thermal shocks

Abstract

Specialized lipid domains (rafts) that are generally enriched in sterols and sphingolipids, are most likely present in cell membranes of animals, plants and fungi. While cholesterol and ergosterol are predominant in vertebrates and fungi, plants possess complex sterol profiles, dominated by sitosterol and stigmasterol in Arabidopsis thaliana. Fully hydrated model membranes of composition approaching those found in rafts of mammals, fungi and plants were investigated by means of solid-state 2H-NMR, using deuterated dipalmitoylphosphatidylcholine (2H(62)-DPPC). The dynamics of such membranes was determined through measuring of membrane ordering or disordering properties. The presence of the liquid-ordered, lo, phase, which may be an indicator of rigid sterol-sphingolipid domains, was detected in all binary or ternary mixtures of all sterols investigated. Of great interest, the dynamics of ternary mixtures mimicking rafts in plants (phytosterol/glucosylcerebroside/DPPC), showed a lesser temperature sensitivity to thermal shocks, on comparing to systems mimicking rafts in mammals and fungi. This effect was particularly marked with sitosterol. The presence of an ethyl group branched on the alkyl chain of sitosterol and stigmasterol is proposed as reinforcing the membrane cohesion by additional attractive van der Waals interactions with the alkyl chains of sphingolipids and phospholipids. As a side result, the elevated resolution of NMR spectra in the presence of sitosterol also suggests domains of smaller size than with other sterols. Finally, the role of phytosterols in maintaining plant membranes in a state of dynamics less sensitive to temperature shocks is discussed.

Modification of Plasma Membrane Organization in Tobacco Cells Elicited by Cryptogein

“…Accordingly, both the clustering in domains of remorin and PIP2;1 were dramatically affected by treatment with cyclodextrin (Raffaele et al, 2009;Li et al, 2012), indicating a major role for sterols in the spatial segregation of these proteins in membrane domains. This treatment also induced an overall increase in acyl chain disorder and a reduction in liquid phase heterogeneity of isolated tobacco PM (Roche et al, 2008), in line with the ability of phytosterols to induce a Lo phase in ternary mixtures of lipids (Beck et al, 2007). Here, we contribute new evidence in support of the developing "membrane raft" concept by revealing a large-range distribution of the steroldependent ordered level of nanoscale assemblies in plant suspension cells.…”

The effects of cholesterol and β-sitosterol on the structure of saturated diacylphosphatidylcholine bilayers

“…Other authors also observed the lower ability of b-sitosterol to order phospholipid chains in the fluid phase compared with cholesterol (Beck et al 2007;Bernsdorff and Winter 2003) and, vice versa, to disturb the arrangement in the gel phase (Beck et al 2007). However, these distinct effects of cholesterol or b-sitosterol on d L are not observed in our measurements.…”

Sterols and membrane dynamics

“…They have been proposed as key molecules to maintain membranes in a state of fluidity adequate for function. For instance, phytosterols have been recently shown to increase membrane cohesion in order to maintain plant membranes in a state of dynamics less sensitive to temperature shocks [6,7]. In this review, the impact of different classes of sterols on membrane dynamics from mammals to archebacteria will be discussed.…”