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Glycobiology Advance Access published online on June 22, 2005
Glycobiology, doi:10.1093/glycob/cwj001
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© The Author 2005. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oupjournals.org
Received May 25, 2005
Revised June 17, 2005
Accepted June 21, 2005

Article

Effects of the sugar headgroup of a glycoglycerolipid on the phase behavior of phospholipid model membranes in the dry state

Antoaneta V. Popova 1 and Dirk K. Hincha 2*

1 permanent address: Institute of Biophysics; Bulgarian Academy of Sciences; 1113 Sofia
2 Max-Planck-Institut für Molekulare Pflanzenphysiologie, D-14424 Potsdam; Germany

* To whom correspondence should be addressed.
Dirk K. Hincha, E-mail: hincha{at}mpimp-golm.mpg.de


  Abstract

Glycolipids are important components of almost all biological membranes. They possess unique properties that have only been incompletely characterized so far. The plant glycolipid digalactosyldiacylglycerol (DGDG) strongly influences the physical behavior of phospholipid model membranes in both the dry and hydrated state. It was, however, unclear whether the strong effect of DGDG on the gel to liquid-crystalline phase transition temperature (Tm) in dry phosphatidylcholine (PC) bilayers is mainly due to the high degree of unsaturation of the DGDG fatty acyl chains, or to interactions between the DGDG and PC headgroups. Also, no information on the relative effectiveness of membrane-bound and free sugars on membrane phase behavior was available. We have used Fourier-transform infrared spectroscopy (FTIR) to investigate the phase properties and H-bonding patterns in dry membranes made from POPC containing one saturated and one monounsaturated (16:0/18:1) fatty acid and different fractions of DGDG or DLPC (18:3/18:3). This was compared to the effects of galactose and digalactose. All additives depressed Tm of the dry membranes, but DGDG was much more effective than DLPC or galactose. Digalactose had a similar effect as DGDG, pointing to the sugar headgroup as the component with the strongest influence on membrane phase behavior. A combination of DLPC and digalactose, which should theoretically be equivalent to DGDG, was much more effective than the galactolipid. H-bonding interactions with the P=O group of PC were also stronger for free digalactose than for DGDG, indicating that the free sugar may be structurally more flexible to adopt an optimal conformation for interactions with the PC headgroup.

Keywords: desiccation/glycolipid/membranes/phase transition/phospholipid.
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