7–8 Sept 2015
Institute for Macromolecular Chemistry, Prague
Europe/Prague timezone

Probing lipid-disaccharide interaction with neutron membrane diffraction

7 Sept 2015, 14:00
30m
Institute for Macromolecular Chemistry, Prague

Institute for Macromolecular Chemistry, Prague

Heyrovského nám.2 162 06 Praha 6 - Břevnov Czech Republic

Speaker

Dr Ben Kent (Helmholtz-Zentrum Berlin)

Description

Sugars, particularly disaccharides, are widely recognised for their ability to protect cellular membranes in environments with scarce liquid water. Despite widespread acceptance, there remain competing theories over the mechanism responsible for this effect. The water replacement hypothesis[1], based on both (indirect) experimental evidence and molecular dynamics simulations[2], suggests that a specific interaction between sugar molecules and lipid headgroups is the primary mechanism of protection. An alternative mechanism ascribes a key role to non-specific volumetric and osmotic effects of the sugars which mediate the compressive stresses induced in membranes brought into close contact by dehydration[3]. This explanation is supported by (indirect) experimental evidence that sugars tend to be excluded from the regions close to the membranes. Phenomenologically, the sugar membrane protection theories differ in the predicted sugar concentration profile between bilayers: in the case of the water replacement hypothesis the sugar concentration should be enhanced at the interface between the water and lipid bilayer; by contrast in the case of the non-specific volumetric based hypothesis, sugar molecules are likely to be more concentrated in the solvent phase constrained by the barrier of the bilayer. In this work we use neutron membrane diffraction of highly orientated samples, effectively one dimensional crystals, and Fourier methods[4] to reconstruct scattering density profiles of lipid bilayer membranes in the presence of sucrose and trehalose. Deuterated sugars have been used to enhance contrast, and variation of the H2O:D2O ratio has been used to phase the reconstruction of the unit cell. Difference profiles calculated from scattering density profiles with selective deuteration show the average position and distribution of sugars within the bilayer unit cell. Sugar distribution profiles, measured over a range of sugar concentrations and hydrations show that sugars impart a cryoprotective effect on lipid bilayer membranes without specific interaction between the sugars and the lipids. (1) Crowe, J. H.; Crowe, L. M.; Chapman, D. Preservation of Membranes in Anhydrobiotic Organisms: The Role of Trehalose. Science 1984, 223 (4637), 701-703. (2) Sum, A. K.; Faller, R.; Pablo, J. J. d. Molecular Simulation Study of Phospholipid Bilayers and Insights of the Interactions with Disaccharides. Biophys. J. 2003, 85 (5), 2830-2844. (3) Bryant, G.; Koster, K. L.; Wolfe, J. Membrane behaviour in seeds and other systems at low water content: the various effects of solutes. Seed Science Research 2001, 11, 17-25. (4) Kent, B.; Hunt, T.; Darwish, T. A.; Hauß, T.; Garvey, C. J.; Bryant, G. Localization of trehalose in partially hydrated DOPC bilayers: insights into cryoprotective mechanisms. Journal of the Royal Society Interface 2014, 11 (95). [1]: http://D:%5CProfile%5Cjih%5CEigene%20Dateien%5CTalks%20and%20posters%5Cfor_abstract.JPG

Primary author

Dr Ben Kent (Helmholtz-Zentrum Berlin)

Co-authors

Dr Christopher Garvey (ANSTO) Prof. Gary Bryant (RMIT University)

Presentation materials