Abstract
Scattering techniques have played a key role in our understanding of the structure and function of phospholipid membranes. These techniques have been applied widely to study how different molecules (e.g., cholesterol) can affect phospholipid membrane structure. However, there has been much less attention paid to the effects of molecules that remain in the aqueous phase. One important example is the role played by small solutes, particularly sugars, in protecting phospholipid membranes during drying or slow freezing. In this paper, we present new results and a general methodology, which illustrate how contrast variation small angle neutron scattering (SANS) and synchrotron-based X-ray scattering (small angle (SAXS) and wide angle (WAXS)) can be used to quantitatively understand the interactions between solutes and phospholipids. Specifically, we show the assignment of lipid phases with synchrotron SAXS and explain how SANS reveals the exclusion of sugars from the aqueous region in the particular example of hexagonal II phases formed by phospholipids.
Highlights
Cell membranes exist as selective barriers between the cell cytoplasm, various intracellular compartments and the extracellular world
Access to large scale facilities, in particular, synchrotron and neutron small angle scattering, has allowed us to quantify factors relevant to the dehydration protection and cryo-protection of membranes by small solutes, the distance between lipid membranes and the spacing between lipid molecules packed in the membrane
Synchrotron X-ray scattering techniques provide a rapid method for measuring important structural parameters and allow us to make measurements on more samples and conditions than would be possible using lab-based X-ray equipment
Summary
Cell membranes exist as selective barriers between the cell cytoplasm, various intracellular compartments and the extracellular world. They may facilitate transport or act as a variable permeability barrier for solutes and solvent (water) molecules. Cellular dehydration (caused by freezing and/or dry environments) causes changes in membrane lipid organization, which, in turn, bring about the loss of the normal semi-permeability of the membrane and, death of the cell [3,4,5,6]. The effects of slow cooling are equivalent—when ice forms in the extracellular solution the concentration of extracellular solutes—is increased, and because the membrane is relatively permeable to water, water may be drawn out of the cell much more quickly than solutes may be transported in. Recent work has suggested that the effects of sugars on membranes are very strongly concentration-dependent [8], with sugar lipid interactions at very low sugar concentrations, but exclusion from the membrane surface at higher concentrations [9]
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