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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

νP=Oas 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 5: νP=Oas 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: Figure 5 shows the positions of the P=O peaks of the dry samples. For EPC and DMPC liposomes the P=O peak was situated at 1262 cm-1, clearly indicating that the samples in the vacuum cuvette of the FTIR spectrometer were anhydrous. For pure EPE the peak was situated at 1230 cm-1, indicating massive H-bonding between P=O and ethanolamine groups, in agreement with earlier reports [9]. In EPE/EPC and EPE/DMPC bilayers the P=O peak showed an intermediate position between the pure lipids due to both a reduction in EPE content and a shift of H-bonding of ethanolamine groups from P=O to C=O groups, as described above. Similar intermediate positions were observed for the P=O peak of MGDG/EPC and MGDG/DMPC liposomes. Obviously, no P=O peaks were present in the spectra from pure MGDG, as this galactolipid does not contain P=O groups. For liposomes containing PC and galactolipid the downfield shift of the P=O peak position in comparison with pure EPC and DMPC could be expected, as the galactose residues in MGDG should show a similar H-bonding behavior as those in digalactosyldiacylglycerol (DGDG) [14,56]. Interestingly, the positions of the P=O peaks of all mixed dry liposomes containing EPE or MGDG are very similar, indicating that the strength and/or amount of H-bonds between P=O groups and the ethanolamine or galactose moieties are comparable.


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

Popova AV, Hincha DK - BMC Biophys (2011)

νP=Oas 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 5: νP=Oas 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: Figure 5 shows the positions of the P=O peaks of the dry samples. For EPC and DMPC liposomes the P=O peak was situated at 1262 cm-1, clearly indicating that the samples in the vacuum cuvette of the FTIR spectrometer were anhydrous. For pure EPE the peak was situated at 1230 cm-1, indicating massive H-bonding between P=O and ethanolamine groups, in agreement with earlier reports [9]. In EPE/EPC and EPE/DMPC bilayers the P=O peak showed an intermediate position between the pure lipids due to both a reduction in EPE content and a shift of H-bonding of ethanolamine groups from P=O to C=O groups, as described above. Similar intermediate positions were observed for the P=O peak of MGDG/EPC and MGDG/DMPC liposomes. Obviously, no P=O peaks were present in the spectra from pure MGDG, as this galactolipid does not contain P=O groups. For liposomes containing PC and galactolipid the downfield shift of the P=O peak position in comparison with pure EPC and DMPC could be expected, as the galactose residues in MGDG should show a similar H-bonding behavior as those in digalactosyldiacylglycerol (DGDG) [14,56]. Interestingly, the positions of the P=O peaks of all mixed dry liposomes containing EPE or MGDG are very similar, indicating that the strength and/or amount of H-bonds between P=O groups and the ethanolamine or galactose moieties are comparable.

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