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Thermotropic phase behavior and headgroup interactions of the nonbilayer lipids phosphatidylethanolamine and monogalactosyldiacylglycerol in the dry state.

Popova AV, Hincha DK - BMC Biophys (2011)

Bottom Line: Similarly, the ethanolamine moiety of EPE was H-bonded to the carbonyl and choline groups of PC and probably interacted through charge pairing with the phosphate group.This study provides a comprehensive characterization of dry membranes containing the two most important nonbilayer lipids (PE and MGDG) in living cells.These data will be of particular relevance for the analysis of interactions between membranes and low molecular weight solutes or soluble proteins that are presumably involved in cellular protection during anhydrobiosis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam, Germany. hincha@mpimp-golm.mpg.de.

ABSTRACT

Background: Although biological membranes are organized as lipid bilayers, they contain a substantial fraction of lipids that have a strong tendency to adopt a nonlamellar, most often inverted hexagonal (HII) phase. The polymorphic phase behavior of such nonbilayer lipids has been studied previously with a variety of methods in the fully hydrated state or at different degrees of dehydration. Here, we present a study of the thermotropic phase behavior of the nonbilayer lipids egg phosphatidylethanolamine (EPE) and monogalactosyldiacylglycerol (MGDG) with a focus on interactions between the lipid molecules in the interfacial and headgroup regions.

Results: Liposomes were investigated in the dry state by Fourier-transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Dry EPE showed a gel to liquid-crystalline phase transition below 0°C and a liquid-crystalline to HII transition at 100°C. MGDG, on the other hand, was in the liquid-crystalline phase down to -30°C and showed a nonbilayer transition at about 85°C. Mixtures (1:1 by mass) with two different phosphatidylcholines (PC) formed bilayers with no evidence for nonbilayer transitions up to 120°C. FTIR spectroscopy revealed complex interactions between the nonbilayer lipids and PC. Strong H-bonding interactions occurred between the sugar headgroup of MGDG and the phosphate, carbonyl and choline groups of PC. Similarly, the ethanolamine moiety of EPE was H-bonded to the carbonyl and choline groups of PC and probably interacted through charge pairing with the phosphate group.

Conclusions: This study provides a comprehensive characterization of dry membranes containing the two most important nonbilayer lipids (PE and MGDG) in living cells. These data will be of particular relevance for the analysis of interactions between membranes and low molecular weight solutes or soluble proteins that are presumably involved in cellular protection during anhydrobiosis.

No MeSH data available.


Related in: MedlinePlus

νN+(CH3)3as peak positions determined from dry samples containing the indicated lipid compositions (compare Fig. 3). The values represent the means ± SE from at least 3 different samples.
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Figure 6: νN+(CH3)3as peak positions determined from dry samples containing the indicated lipid compositions (compare Fig. 3). The values represent the means ± SE from at least 3 different samples.

Mentions: The terminal part of the PC headgroup is the choline group with a characteristic asymmetric stretching vibration at around 970 cm-1 which is sensitive to interactions with water [39,57] and sugars [40]. When the choline group is involved in interactions with water its vibration is shifted upfield by a maximum of 4 cm-1 [39]. Figure 6 shows the positions of νN+(CH3)3as of dry liposomes containing either EPC or DMPC. The choline peak of EPC is centered at 967.5 cm-1, while for DMPC this peak is situated 1 cm-1 lower, again indicating restrictions of the interactions in more tightly packed bilayers. In all mixed liposomes the choline peak was shifted to higher wavenumbers compared to pure PC, indicating increased interactions. Similar to the P=O peak in mixed membranes, the shift in the choline peak in the presence of EPE or MGDG was of similar magnitude.


Thermotropic phase behavior and headgroup interactions of the nonbilayer lipids phosphatidylethanolamine and monogalactosyldiacylglycerol in the dry state.

Popova AV, Hincha DK - BMC Biophys (2011)

νN+(CH3)3as peak positions determined from dry samples containing the indicated lipid compositions (compare Fig. 3). The values represent the means ± SE from at least 3 different samples.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3116483&req=5

Figure 6: νN+(CH3)3as peak positions determined from dry samples containing the indicated lipid compositions (compare Fig. 3). The values represent the means ± SE from at least 3 different samples.
Mentions: The terminal part of the PC headgroup is the choline group with a characteristic asymmetric stretching vibration at around 970 cm-1 which is sensitive to interactions with water [39,57] and sugars [40]. When the choline group is involved in interactions with water its vibration is shifted upfield by a maximum of 4 cm-1 [39]. Figure 6 shows the positions of νN+(CH3)3as of dry liposomes containing either EPC or DMPC. The choline peak of EPC is centered at 967.5 cm-1, while for DMPC this peak is situated 1 cm-1 lower, again indicating restrictions of the interactions in more tightly packed bilayers. In all mixed liposomes the choline peak was shifted to higher wavenumbers compared to pure PC, indicating increased interactions. Similar to the P=O peak in mixed membranes, the shift in the choline peak in the presence of EPE or MGDG was of similar magnitude.

Bottom Line: Similarly, the ethanolamine moiety of EPE was H-bonded to the carbonyl and choline groups of PC and probably interacted through charge pairing with the phosphate group.This study provides a comprehensive characterization of dry membranes containing the two most important nonbilayer lipids (PE and MGDG) in living cells.These data will be of particular relevance for the analysis of interactions between membranes and low molecular weight solutes or soluble proteins that are presumably involved in cellular protection during anhydrobiosis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Potsdam, Germany. hincha@mpimp-golm.mpg.de.

ABSTRACT

Background: Although biological membranes are organized as lipid bilayers, they contain a substantial fraction of lipids that have a strong tendency to adopt a nonlamellar, most often inverted hexagonal (HII) phase. The polymorphic phase behavior of such nonbilayer lipids has been studied previously with a variety of methods in the fully hydrated state or at different degrees of dehydration. Here, we present a study of the thermotropic phase behavior of the nonbilayer lipids egg phosphatidylethanolamine (EPE) and monogalactosyldiacylglycerol (MGDG) with a focus on interactions between the lipid molecules in the interfacial and headgroup regions.

Results: Liposomes were investigated in the dry state by Fourier-transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Dry EPE showed a gel to liquid-crystalline phase transition below 0°C and a liquid-crystalline to HII transition at 100°C. MGDG, on the other hand, was in the liquid-crystalline phase down to -30°C and showed a nonbilayer transition at about 85°C. Mixtures (1:1 by mass) with two different phosphatidylcholines (PC) formed bilayers with no evidence for nonbilayer transitions up to 120°C. FTIR spectroscopy revealed complex interactions between the nonbilayer lipids and PC. Strong H-bonding interactions occurred between the sugar headgroup of MGDG and the phosphate, carbonyl and choline groups of PC. Similarly, the ethanolamine moiety of EPE was H-bonded to the carbonyl and choline groups of PC and probably interacted through charge pairing with the phosphate group.

Conclusions: This study provides a comprehensive characterization of dry membranes containing the two most important nonbilayer lipids (PE and MGDG) in living cells. These data will be of particular relevance for the analysis of interactions between membranes and low molecular weight solutes or soluble proteins that are presumably involved in cellular protection during anhydrobiosis.

No MeSH data available.


Related in: MedlinePlus