Abstract
The physical effects of small sugars on membranes have been studied for decades, primarily because of their membrane stabilization in cold or dehydrated environments. We studied the effects of up to 20 mol% glucose in bilayers made of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at low hydration by combining X-ray diffraction and Molecular Dynamics (MD) simulations. In agreement with previous studies, we observe membrane thinning at low and membrane thickening at high sugar concentrations. Glucose was found to preferentially localize to the outer head region of phospholipid bilayers at all concentrations, and partitioning of sugar in the membranes was found to monotonically increase with increasing sugar concentration. While the number of gauche defects in the lipid acyl tails and the lipid packing in the presence of sugar resembled values of a fluid lipid bilayer, tail dynamics, as assessed by autocorrelation of the carbon atoms in the phospholipid tails, were slowed down significantly with increasing glucose content. Thus, our findings suggest that sugar leads to a a disordered, glassy state of the hydrophobic membrane core. The non-monotonic effect of glucose on membrane thickness was found to be an effect of fluidification at low concentrations and decreased interdigitation in the higher sugar concentration regime.
Highlights
Sugars are ubiquitous components in all living organisms
We studied the interaction between glucose and dehydrated lipid membranes by combining X-ray diffraction and Molecular Dynamics (MD) simulations
Membranes were prepared on silicon wafers for X-ray diffraction experiments, and analogous systems were constructed in silico based on experimental parameters, such that results between simulations and experiments could be compared directly
Summary
Sugars are ubiquitous components in all living organisms. They serve in a variety of structural and functional roles, from primary metabolic precursors to important intercellular signalling tools.While there exist protein-mediated mechanisms by which sugars can be translocated across cellular membranes in eukaryotic organisms, the basic interaction between sugars and lipid bilayers influences a variety of membrane properties [1,2,3,4,5,6,7]. Anhydrobiotic organisms with the ability to survive severe cold or dehydration were found to accumulate sugars in high concentrations [1,17,18], and it was hypothesized that this provided membrane protection and stabilization to prevent cellular rupturing. These concepts were extended to industrial applications, making simple sugars attractive as an additive in commercial products spanning the fields of agriculture to cosmetics to pharmaceuticals [19]. This inspired much research into the realm of membrane stabilization in dehydrated systems using sugars [3,7,9,14,16,20,21,22,23,24,25,26]
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