Glycerol Dialkyl Nonitol Tetraether Research Articles

Langmuir films stability phenomenon of glycerol dialkyl nonitol tetraether at the air-water interface for variations spreading time

Langmuir films behavior of asymmetric glycerol dialkyl nonitol tetraether (GDNT) lipids at the air-water interface (temperature 19℃ ± 1℃) investigated the stability of the mean ratio of Langmuir films for different spreading time prior to the transfer film. Floating monolayer films stability is an important parameter to obtain high-quality Langmuir-Blodgett films for their aplications. Hysteresis loop of the compression-decompression (μ-A) isotherms of Langmuir film GDNT used to analyze the thermodynamic stability of the monolayer films and its features. Langmuir films stability of tetraether lipid GDNT shown more stable at the time of spreading longer than a short time.

Molecular modeling of archaebacterial bipolar tetraether lipid membranes

Membranes composed of glycerol dialkylnonitol tetraether (GDNT) lipids from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius have been studied by molecular modeling. GDNT membranes containing eight cyclopentane rings in the molecule are packed much tighter than those without rings. When containing eight cyclopentane rings, the β- d-galactosyl- d-glucose head-group of GDNT runs almost parallel to the membrane surface. However, when containing no rings, the head-group is oriented perpendicular to the membrane surface. Using molecular dynamics calculations, we have also conducted comparative studies of membrane packing between GDNT and various non-archaebacterial membranes. Compared to gel state dipalmitoylphosphatidylcholine (DPPC) and gel state distearoylphosphatidylcholine (DSPC) bilayers, the GDNT membrane with eight cyclopentane rings has a more negative interaction energy, thus a tighter membrane packing, while the GDNT without rings is less tightly packed than gel state DSPC. Based on the calculated interaction energies, the GDNT membranes (with and without rings) are much more tightly packed than DPhPC (an ester-linked diphytanyl PC) and DPhyPC (an ether-linked diphytanyl PC) bilayers. This suggests that the branched methyl group in the phytanyl chain is not the major contributor of the tight packing of GDNT membranes. The biological implication of this study is that the cyclopentane ring could increase GDNT membrane thermal stability. This explains why the number of cyclopentane rings in archaebacterial lipid increases with increasing growth temperature. Perhaps, through the ring-temperature compensation mechanism, the plasma membrane of thermoacidophilic archaebacteria is able to maintain a tight and rigid structure, consequently, a constant proton gradient between the extracelluar (pH 2.5) and intracelluar compartment (pH 6.5), over a wide range of growth temperatures.

Langmuir-Blodgett films of bipolar lipids from thermophilic archaea

The Langmuir-Blodgett technique is applied for depositing thin films of two lipids extracted from the thermophilic archaeon Sulfolobus Solfataricus as well as of a derivative produced by hydrolysis of total lipid extract. These are monosubstituted glycerol-dialkyl-nonitol tetraether with a β- d-glucopyranosyl group (GL-GDNT), bisubstituted glycerol-dialkyl-nonitol tetraether with β- d-glucopyranosyl and phosphomyoinositol groups (GL-GDNT-PH) and asymmetric non-substituted glycerol-dialkyl-nonitol tetraether (GDNT). Films with satisfactory morphology are deposited by both horizontal and vertical lift techniques, but the results are not reproducible. To improve the quality of deposition and the uniformity of the film, mixtures of the lipid GL-GDNT and arachidic acid are used. After dissolution of arachidic acid from the multilayer by hexane highly uniform films are obtained. Studies of the monolayers at the air-water interface and of the deposited films show that probably the molecules in the monolayer are in a form of a U with close packing of isopranyl chains.

Organization of bipolar lipids in monolayers at the air-water interface

In this paper we report the results of surface pressure-area measurements and fluorescence microscopy of Langmuir monolayers of bipolar lipids extracted from the thermophilic archaeobacterium Sulfolobus solfataricus. We have analysed the two-dimensional phase behaviour of the polar lipid extract, some of its subfractions and the hydrolytic fractions glycerol dialkyl glycerol tetraether (GDGT) and glycerol dialkyl nonitol tetraether (GDNT) in the temperature range 25–45°C. For comparison, films of diphytanoyl phosphatidylcholine were also studied. Only the isotherms of the polar lipid extract exhibit a plateau region. The molecular areas of GDGT and GDNT, even at the collapse pressure, are much larger than those of the other lipid fractions. For the former compounds a U-shaped hydrocarbon chain conformation mixed with an extended chain arrangement is suggested, while all the other fractions display always a vertical arrangement.

Electromechanical stability of planar lipid membranes from bipolar lipids of the thermoacidophilic archebacterium Sulfolobus acidocaldarius

Stable planar membranes have been obtained from the bipolar lipid glycerol dialkyl nonitol tetraether (GDNT) extracted from the thermoacidophilic archebacterium Sulfolobus acidocaldarius. The electric capacity C m, the resistance R m and tension σ of these membranes were measured. The dependence of the bipolar lipid membranes mean life time τ 1 on voltage was investigated. It was shown that the irreversible electric breakdown of membranes from GDNT and usual phospholipids is due to the same mechanism, viz., due to formation of a hydrophilic pore with an overcritical radius. Under electric field the GDNT molecules take U-shape, and the polar headgroups of such molecules cover the pore's interior.

Monopolar-bipolar lipid interactions in model membrane systems

1H-NMR, dynamic light scattering and negative staining electron microscopy have been used to study the formation and physico-chemical properties of aqueous dispersions of mixtures of monopolar lipids with bipolar lipids extracted from Sulfolobus solfataricus. This microorganism is a thermophilic archaeobacterium growing optimally at about 85°C and pH 3. The two hydrolytic fractions of the membrane complex lipids that have been studied are: the symmetric lipid glycerol dialkyl glycerol tetraether (GDGT) and the asymmetric lipid glycerol dialkyl nonitol tetraether (GDNT). Electron micrographs of pure and mixed GDNT and GDGT dispersions show the formation of complex structures. Only above a critical monopolar/bipolar lipid ratio, typical of the bipolar lipid, could closed structures be formed and good agreement was obtained in sizing with NMR, electron microscopy and dynamic light scattering. NMR spectra have been carried out at several temperature from 25° to 85°C, to obtain information on the temperature-dependent structural, dynamic and permeability properties of the co-dispersed vesicles. The results are discussed in terms of the steric constraints and the chemico-physical interactions occurring among the different parts of the molecules and compared with previous studies performed with different physical techniques.

Bipolar tetraether lipid monolayers: correlation between interfacial properties and superficial structures as observed by electron microscopy

The purpose of the present study was to investigate by surface pressure measurements and electron microscopy, GDNT (glycerol dialkyl nonitol tetraether) lipid layers formed at an air-water interface. GDNT has an unusual chemical structure, it is a bipolar tetraether lipid derived from an extreme thermoacidophile archaebacterium. The results show that the molecules could adopt different orientations at the air-water interface, depending on the compression conditions; the upright orientation is metastable.

Purification of glycerol dialkyl nonitol tetraether from Sulfolobus acidocaldarius.

A modified procedure for extraction and purification of hydrolyzed archaebacterial lipids is described. Lipids were extracted from Sulfolobus acidocaldarius using a Soxhlet extraction procedure followed by trichloroacetic acid solvent-extraction of the residue. The yield of total extractable material by this protocol was 14% which, after a two-phase wash, yielded 10% lipid. Modifications to the published steps for purifying the subsequently hydrolyzed lipids were developed to purify glycerol dialkyl nonitol tetraether (GDNT). The nearly colorless final macrocyclic product was characterized by TLC, IR, NMR, and mass spectrometry.

Lipid—polypeptide interaction in monolayers and in black lipid membranes

The purpose of the present paper is to compare monolayers and black lipid membranes (BLM). In particular, mixed monolayers of bipolar lipid glycerol-dialkyl-nonitol-tetraether (GDNT) (which can be found in archaebacteria membranes) and cholesterol or poly-γ-methylglutamate (PγMG) are compared with membranes obtained from the same substances. Measurements of surface pressure and surface potential at the water/air interface at 25°C allow us to state that GDNT and cholesterol are insoluble in a monolayer, while GDNT and PγMG are compatible with each other, with attractive interactions between their hydrophobic chains. Capacitance measurements as a function of temperature in the range 10–70°C and conductance measurements in the presence of two carriers (valinomycin and the ion tetraphenylborate TPhB −) show that cholesterol does not enter the BLM of GDNT, while PγMG is adsorbed at the BLM/solution interface.

A spin label ESR and saturation transfer-ESR study of archaebacteria bipolar lipids

A spin label study has been carried out on bipolar lipids extracted from Sulfolobus solfataricus, an extreme thermophilic archaebacterium growing at about 85°C and pH 3. These lipids are cyclic diisopranyl tetraether molecules, quite different from the usual fatty acid lipids. Two hydrolytic fractions of the membrane complex lipids have been studied: the symmetric lipid glycerol-dialkyl-glycerol-tetraether (GDGT) and the asymmetric lipid glyceroldialkyl-nonitol-tetraether (GDNT). The ESR spectra confirm the results previously obtained from calorimetric and X-ray diffraction experiments showing a polymorphic behaviour of these lipids and indicating the critical temperature ranges at which structural transitions occur. Moreover, the present study adds information on the dynamics of the different portions of the hydrophobic chain. ST-ESR measurements show correlation times ranging from 10-8 s up to 10-5 s, depending upon the lipid sample, the label position and the degree of hydration. At very high temperatures, i.e. the physiological temperatures of Sulfolobus solfataricus, the nonitol head groups of the asymmetric lipids form a strongly immobilized structure. Indeed, the molecular correlation times of the outermost hydrophobic portion of GDNT are higher, by a factor up to 103, than those of usual monopolar lipids. Anisotropic motional behaviour is observed even at such very high temperatures. Possible biological implications are discussed.

Thermotropic properties of bipolar lipids of Sulfolobus solfataricus and of their mixtures with dipalmitoylphosphatidylcholine

The thermotropic properties of the bipolar lipids, glycerol dialkylglycerol tetraether (GDGT) and glycerol dialkylnonitol tetraether (GDNT), were determined at different degrees of hydration and in mixtures with dipalmitoylphosphatidylcholine (DPPC). The number of water molecules rendered unfreezable by the GDNT molecule is 10+/-1.5 and that by the GDGT molecule 2.8+/-0.7 or about 1.1-1.5 H2O molecules per OH group. Binding of water molecules causes randomization of the two polar heads from the oriented form prevailing in the dry state. The hydration seems to be a cooperative process extending over a whole lipid domain. DPPC added in small amounts to GDNT interacts preferentially with the nonitol halves of the molecules separating them from the glycerol half molecules. In the cooperative interaction domain each DPPC molecule is surrounded by up to six GDNT molecules. Cooperative domains formed during the interaction of DPPC with GDGT are less pronounced. In both cases they affect the thermotropic properties of the system.

Structure and polymorphism of bipolar isopranyl ether lipids from archaebacteria.

We describe in this work the structure and polymorphism of a variety of lipids extracted from Sulfolobus solfataricus, an extreme thermoacidophilic archaebacterium growing at about 85 degrees C and pH 2. These lipids are quite different from the usual fatty acid lipids of eukaryotes and prokaryotes: each molecule consists of two C40 omega-omega' biphytanyl residues (with 0 to 4 cyclopentane groups per residue), ether linked at both ends to two (variably substituted) glycerol or nonitol groups. Four lipid preparations were studied; the total and the polar lipid extracts, and two hydrolytic fractions, the symmetric glycerol dialkyl glycerol tetraether and the asymmetric glycerol dialkyl nonitol tetraether, as a function of water content and temperature, using X-ray scattering techniques. The main conclusions from the study of the four lipid preparations can be summarized as follows. (1) As with other lipids, a remarkable number and variety of phases are observed over a temperature-concentration range close to "physiological" conditions. The possibility is discussed that this polymorphism reflects a fundamental property of lipids, closely related to their physiological rôle. (2) As in other lipids, two types of chain conformations are observed: a disordered one (type alpha) at high temperature; at lower temperature, a more ordered packing of stiff chains, all parallel to each other (type beta'). At temperatures and degrees of hydration approaching the conditions prevailing in the living cell, the conformation is of type alpha. (3) In all the phases with chains in the alpha conformation, the unsubstituted glycerol headgroups, whose concentration is high in these lipids, segregate in the hydrocarbon matrix, away from the other polar groups. This property may have interesting biological consequences: for example, the chains of a fraction of the bipolar lipid molecules can span hydrocarbon gaps as wide as 75 A. (4) Two cubic phases are observed in the total and the polar lipid extracts, which display a remarkable degree of metastability, most unusual in lipid phase transitions involving structures with chains in the alpha conformation. This phenomenon can be explained by the interplay of the physical structure of the cubic phases (the two contain two intertwined and unconnected three-dimensional networks of rods) and the chemical structure of the lipid molecules: the two headgroups of most molecules being anchored on each of the two networks of rods, the migration of the lipid molecules is hindered by the two independent diffusion processes and by the entanglement of the chains.(ABSTRACT TRUNCATED AT 400 WORDS)