Physicochemical Characterization of Tetraetherlipids from Thermoplasma acidophilum

Abstract

By means of differential thermoanalysis, the miscibility of the main polar tetraether lipid of Thermoplasma acidophilum with two ester lipids, dipalmitoyl phosphatidylcholine and dipalmitoyl phosphatidylglycerol, resp., in the presence of excess water was studied. It is shown that with increasing fraction of tetraether lipid in the mixture, the transition range of dipalmitoyl phosphatidylcholine is broadened and the temperature of the maximum heat flow (Tm) is shifted to lower temperatures; furthermore, the enthaply change (ΔH) of the transition declines. Similar results were obtained with mixtures of tetraether lipid with dipalmitoyl phosphatidylglycerol. It is therefore concluded that the main polar tetraether lipid of Thermoplasma acidophilum , which essentially forms monomolecular layers, is able to form stable common phases with bilayer-forming ester lipids. Miscibility of the tetraether lipid with dipalmitoyl phosphatidylglycerol, which are both monovalent anions at neutral pH, is also observed in the presence of high proton or calcium ion concentrations.

The Main (Glyco) Phospholipid (MPL) of Thermoplasma acidophilum

“…All DTA/DSC determinations [22,26,27,28,29,30,31,32,33,34] were conducted with hydrated lipids at various degrees of hydration, directly mixed into the analysis pans (details refer to the respective references), without checking planar or spherical membrane formation. Thus, all values presented are related to “hydrated lipid”.…”

“…MPL was mixed with other lipids (Table 4), diether lipids, methyl-branched diphytanyl-glucosylglycerol (DPhGG) and unbranched dipalmitylglucosylglycerol (DPGG) [27] and with ester lipids, DPPG and dipalmitoyl phosphatidylcholine (DPPC) [31].…”

“…The other three lipids differ in their behavior; they form also mixed phases with MPL, however with tendency to phase separation forming domains with high content and those with low content of the respective lipid. This does neither depend on ether or ester bonds of the lipid, nor on charges of the polar head group and is only marginally influenced by concentration of calcium ions or protons (pH) [27,31].…”

“…In comparison of the two ether lipids, MPL obviously exerts a condition between the branched diether lipid without phase transition (except for the rigid-glass transition) and sharp and intensive phase transition of the unbranched diether lipid at 62–65 °C [27]. The ester lipids investigated form mixed phases with MPL, but all of them tend to phase separation and to form distinct domains with high and low molar ratios [31].…”