Electron density analysis of the effects of sugars on the structure of lipid bilayers at low hydration - a preliminary study

Conference · Mon Feb 06 04:00:00 EST 2012

OSTI ID:1028496

Lenné, T; Kent, B; Koster, K L; Garvey, C J; Bryant, G ^[1]

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1. ANSTO

Small angle X-ray scattering is used to study the effects of sugars on membranes during dehydration. Previous work has shown that the bilayer and chain-chain repeat spacings of DPPC bilayers are relatively unaffected by the presence of sugars. In this work we present a preliminary analysis of the electron density profiles of DPPC in the presence of sugars at low hydration. The difficulties of determining the correct phasing are discussed. Sugars and other small solutes have been shown to have an important role in improving the tolerance of a range of species to desiccation and freezing. In particular it has been shown that sugars can stabilize membranes in the fluid membrane phase during dehydration, and in the fully dehydrated state. Equivalently, at a particular hydration, the presence of sugars lowers the transition temperature between the fluid and gel phases. There are two competing models for explaining the effects of sugars on membrane phase transition temperatures. One, designated the water replacement hypothesis (WRH) states that sugars hydrogen bond to phospholipid headgroups, thus hindering the fluid-gel phase transition. One version of this model suggests that certain sugars (such as trehalose) achieve the measured effects by inserting between the phospholipid head groups. An alternative model explains the observed effects of sugars in terms of the sugars effect on the hydration repulsion that develops between opposing membranes during dehydration. The hydration repulsion leads to a lateral compressive stress in the bilayer which squeezes adjacent lipids more closely together, resulting in a transition to the gel phase. When sugars are present, their osmotic and volumetric effects reduce the hydration repulsion, reduce the compressive stress in the membranes, and therefore tend to maintain the average lateral separation between lipids. This model is called the hydration forces explanation (HFE). We recently showed that neither mono- nor di-saccharides affect the average distance between lipid chains in the bilayer, supporting the predictions of the HFE. In this paper we further investigate the effects of sugars on membrane structure by conducting electron density analysis of recent data. This preliminary analysis sheds additional light onto the effects of sugars on membrane structure.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: FOREIGN
• OSTI ID: 1028496
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

08 HYDROGEN
CHAINS
DEHYDRATION
ELECTRON DENSITY
FREEZING
HYDRATION
HYDROGEN
HYPOTHESIS
LIPIDS
MEMBRANES
PHOSPHOLIPIDS
SACCHARIDES
SCATTERING
SOLUTES
TOLERANCE
TRANSITION TEMPERATURE
WATER