Molecular Hydration Investigated using Extended Membrane Surfaces

Abstract

In biological cells and in solutions, biomolecules are in constant competition for water. The availability of water is critical to a wide array of processes such as protein folding, molecular recognition, and cell signaling. To understand these mechanisms, we distinguish between the water molecules residing in the vicinity of biological macromolecules and the most distant water molecules in the bath. What happens on the surface of macromolecules? How to investigate the role and the properties of interfacial water? The problem is that the spatial extent of hydration layers is very small, on the order of nanometers or less. How to produce an experimentally measurable signal? Our approach to investigate the many remaining mysteries of molecular hydration is by using the naturally extended water surfaces within multilamellar lipid structures. We show how addition of salts, sugars, and most buffers make the interlamellar (D) spacing of synthetic phospholipids membranes to increase. In contrast to this behavior, low concentrations of highly hygroscopic molecules such as PEG (polyethylene glycol) and DMSO (dimethyl sulfide) are found to decrease the D-spacing. A very interesting case is that of the small molecular weight PEG 400 with unusual effects on the interfacial hydration, in such a way that at some concentration threshold the PEG molecules overcome a mixing barrier and become included in the forbidding interlamellar water space. This behavior is due to competitions between the strong exclusions forces from extended hydration surfaces and entropy. We are currently investigating how biological relevant molecules such as “Factor V” (BSA Bovine Serum Albumin) are modifying cellular osmoregulation and its effects on membranes stress. Knowing how molecules interact at the lipid-water interface could prove beneficial in the drug design of anesthetics, cryoprotectants of mammalian cells, and in general, of molecular stressor affecting biological cells.