Conformational and hydrational properties during the Lβ- to Lα- and Lα- to HII-phase transition in phosphatidylethanolamine (original) (raw)
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Biochimica et Biophysica Acta (BBA) - Biomembranes, 1989
The disaccharides, sucrose and trehalose, markedly decreased (up to 17-13C ° ) the temperature of the lamellar to hexagonal (L,, ~ Hit) phase transition and simultaneously increase by 2-4 C ° the temperature of the lamellar gel to lameUar liquid-crystal (L# ~ L a) phase transition in hydrated dihexadecylphosphatidylethanolamine and distearoylphosphatidylethanolamine. These two transitions merge and convert into a single La-Hn phase transition when disper~.,ed in 2A M sucrose. These results are inconsistent with recent reports by Crowe et at. (19g7) Biuchem. J. 242, 1-10, (1988) Biochim. Biophys. Acta 947, 367-394) which suggest that trehalnse stabilizes the L a phase relative to the Hit phase and shifts upwards beyond detectability the L,-H n transition. The present results are considered as a manifestation of the Ho|meister effect in which the sugars act a~ ltosmotropic reagents stabilizing the structure of bulk water. This t(:nds io decrease th~ area of contact between the lipid and the aqueous phases and favours the H n and IL~ phases relative to L a phase. This hypothesis is consistent with the effects of chaotropic reagents on the L,-H n phase transition (Yeagle and Sen Biochemistry 25, 7518-7522) and on the stability of the lamellar phase of dipalmitoylpbosphatidylcholine (Oku and MacDonald (1983) J. Biol. Chem. 258, 8733-8738). J J J J J
Biochemistry, 1992
The phase diagram of DOPE/water dispersions was investigated by N M R and X-ray diffraction in the water concentration range from 2 to 20 water molecules per lipid and in the temperature range from-5 to +50 OC. At temperatures above 22 OC, the dispersions form an inverse (HII) phase at all water concentrations. Below 25 " C , an HII phase occurs at high water concentrations, an L, phase is formed at intermediate water concentrations, and finally the system switches back to an HII phase at low water concentrations. The enthalpy of the L,-HII-phase transition is +0.3 kcal/mol as measured by differential scanning calorimetry. Using 31P and 2H N M R and X-ray diffraction, we measured the trapped water volumes in HII and L, phases as a function of osmotic pressure. The change of the HII-phase free energy as a function Work in the Princeton laboratory was supported by grants from the US.
Effect of PEG-lipid conjugates on the phase behavior of phosphatidylethanolamine dispersions
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999
The phase behavior of binary mixtures of hydrated dielaidoylphosphatidylethanolamine (DEPE) with two different PEG-lipid conjugates at a molar fraction below 0.2 has been studied by using time-resolved X-ray diffraction, and partial phase diagrams have been constructed. The studied conjugates comprise two saturated hydrocarbon acyl chains 14 carbon atoms long and PEG550 or PEG5000 chains covalently attached to a phosphoethanolamine polar head group, DMPE(PEG550) and DMPE(PEGSOOO), respectively. When added in small amounts (lo-20 mol%) to DEPE aqueous dispersions, both PEG-lipids favor the lamellar liquid crystalline (L,) phase at the expense of the lamellar gel (L,) and the inverted hexagonal (H,,) phases. One of the conjugates, DMPE(PEG550), shifts the L,H,, transition of DEPE to higher temperatures by 2.5"C per mol% PEG-lipid, and induces the spontaneous formation of a cubic phase of space group Im3m in the DEPE dispersions. The cubic phase intrudes between the lamellar liquid crystalline and the inverted hexagonal phases in the DEPE/DMPE(PEG550) phase diagram. Low amounts of the DMPE(PEG5000) conjugate only shift the L,.H,, transition of DEPE to higher temperatures, at 5.2"C per mol% PEG-lipid, but does not promote the formation of additional phases. The respective slopes for the L,-L, transition temperature depression are 10-l 5 times smaller. At > 15 mol% DMPE( PEG550) and at > 5 mol% DMPE( PEG5000), the non-lamellar phases are eliminated from the phase diagrams. Structural data on the organization of the pure hydrated PEG-lipid conjugates are also provided, suggesting that these lipids form micelles and lamellae. 0 1999 Elsevier Science B.V. All rights reserved.
BMC biophysics, 2011
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. 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 nonb...
Phases and phase transitions of the hydrated phosphatidylethanolamines
Chemistry and Physics of Lipids, 1994
LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. Here, a review of the LIPIDAT data subset refering to hydrated phosphatidylethanolamines (PE) is presented together with an analysis of these data. The PE subset represents 14% of all LIPIDAT records. It includes data collected over a 38year period and consists of 1511 records obtained from 203 articles in 35 different journals. An analysis of the data in the subset has allowed us to identify trends in synthetic PE phase behavior reflecting changes in lipid chain length, chain unsaturation (number, isomeric type and position of double bonds), chain asymmetry and branching, type of chain-glycerol linkage (ether vs. ester) and headgroup modification. Also included is a summary of the data concerning the effect of pH, stereochemical purity, and different additives such as salts, saccharides, alcohols, amino adds and alkanes on PE phase behavior. Information on the phase behavior of biologically derived PE is also presented. This review includes 236 references.
Low amounts of PEG-lipid induce cubic phase in phosphatidylethanolamine dispersions
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1997
Ž . By using time-resolved X-ray diffraction we demonstrate that low amounts 5-10 mol% of a phospholipid with two saturated hydrocarbon acyl chains 14 carbon atoms long and PEG550 chain covalently attached to its phosphoethanolamine Ž . Ž polar head group, DMPE PEG550 , induce spontaneous formation of a cubic phase with lattice constant 20.5 nm cubic . Ž. aspect a8, space group Im3m in aqueous dispersions of dielaidoylphosphatidylethanolamine DEPE . This phase displays a highly resolved X-ray diffraction pattern with 17 low-angle reflections. The cubic phase was found to intrude in the Ž . Ž . temperature range between the lamellar liquid crystalline L phase and the inverted hexagonal phase H known to form a II Ž . in pure DEPErwater dispersions. A higher DMPE PEG550 amount of 20 mol% was found to eliminate the non-lamellar phases in the temperature scale up to 1008C. DMPE grafted with PEG5000 only shifts the L -H transition of DEPE to a II higher temperatures but does not promote formation of cubic phase. These findings indicate that, consistent with their bulky head groups, the PEG-lipids decrease the tendency for negative interfacial mean curvature of the DEPE bilayers.
An ordered metastable phase in hydrated phosphatidylethanolamine: the Y-transition
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1999
By using time-resolved X-ray diffraction, differential scanning calorimetry and scanning densitometry, we observed rapid formation at low temperature of a metastable ordered phase, termed L R1 phase, in fully hydrated dihexadecylphosphatidylethanolamine (DHPE). The L R1 phase has the same lamellar repeat period as the gel L L phase but differs from the latter in its more ordered, orthorhombic hydrocarbon chain arrangement. It forms at about 12³C upon cooling and manifests itself as splitting of the sharp, symmetric wide-angle X-ray peak of the DHPE gel phase into two reflections. This transition, designated the`Y-transition', is readily reversible and proceeds with almost no hysteresis between cooling and heating scans. Calorimetrically, the L R1 CL L transition is recorded as a low-enthalpy (0.2 kcal/mol) endothermic event. The formation of the L R1 phase from the gel phase is associated with a small, about 2 Wl/g, decrease of the lipid partial specific volume recorded by scanning densitometry, in agreement with a volume calculation based on the X-ray data. The formation of the equilibrium L c phase was found to take place from within the L R1 phase. This appears to be the only observable pathway for crystallisation of DHPE upon low-temperature incubation. Once formed, the L c phase of this lipid converts directly into L L phase at 50³C, skipping the L R1 phase. Thus, the L R1 phase of DHPE can only be entered by cooling of the gel L L phase. The data disclose certain similarities between the low-temperature polymorphism of DHPE and that of long-chain normal alkanes. ß -ray di¡raction 0005-2736 / 99 / $^see front matter ß 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 3 6 ( 9 8 ) 0 0 2 5 9 -
Biophysical Journal, 2002
The thermodynamic properties of fully-hydrated lipids provide important information about the stability of membranes and the energetic interactions of lipid bilayers with membrane proteins (Nagle and Scott, Physics Today, 2:39, 1978). The lamellar/inverse hexagonal (L ␣ -H II ) phase transition of 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) water mixtures is a first-order transition and, therefore, at constant pressure, must have a thermodynamically well-defined equilibrium transition temperature. The observed transition temperature is known to be dependent upon the rate at which the temperature is changed, which accounts for the many different values in the literature. X-ray diffraction was used to study the phase transition of fully-hydrated DOPE to determine the rate-independent transition temperature, T LH . Samples were heated or cooled for a range of rates, 0.212 Ͻ r Ͻ 225°C/hr, and the rate-dependent apparent phase transition temperatures, T A (r) were determined from the x-ray data. By use of a model-free extrapolation method, the transition temperature was found to be T LH ϭ 3.33 Ϯ 0.16°C. The hysteresis, ͉T A (r) Ϫ T LH ͉, was identical for heating and cooling rates, Ϯr, and varied as ͉r͉  for  Ϸ 1 ⁄4. This unexpected power-law relationship is consistent with a previous study (Tate et al., Biochemistry, 31:1081-1092 but differs markedly from the exponential behavior of activation barrier kinetics. The methods used in this study are general and provide a simple way to determine the true mesomorphic phase transition temperatures of other lipid and lyotropic systems.
Biophysical Journal, 1996
The bilayer-to-hexagonal phase transition temperatures (TH) of di-1 8:1 C phosphatidylethanolamine with double bonds at positions 6, 9, and 11 are 370C, 80C, and 280C, respectively, as measured by differential scanning calorimetry and x-ray diffraction. Thus TH exhibits a minimum when the C=C is around position 9, similar to what has been found for the gel-to-liquid crystalline phase transition temperature in other lipids. Factors that may contribute to the dependence of TH on double bond position were studied by x-ray diffraction of the hexagonal phases in the presence and absence of added alkane, with or without the osmotic stress of polyethylene glycol, and over a wide temperature range. The lattice dimensions show that the intrinsic radius of lipid monolayer curvature increases as the double bond is moved toward the tail ends. A measure of the bending moduli of these lipid monolayers shows a higher value for the 9 position, and lower values for the other two. Consideration of the bilayer-to-hexagonal transition in terms of bending and interstitial energies provides a rationale for the relative values of TH.