1-monooleoyl-rac-glycerol and distearoyl-phosphatidylglycerol

The aqueous phase behavior of phytantriol (PT) in mixtures of monoolein (MO), distearoylphosphatidylglycerol (DSPG), propylene glycol (PG), polyethylene glycol 400 (PEG 400) and 2-methyl-2,4-pentanediol (MPD) was investigated by visual inspection, polarized light microscopy and small angle X-ray diffraction at room temperature. The phase diagrams of PT and MO in water are qualitatively very similar and PT/MO mixtures in excess water form one cubic phase of space group Pn3m irrespective of mixing ratio. The addition of the charged membrane lipid DSPG to the PT system gives rise to a considerable water swelling of the cubic phases as well as the occurrence of a cubic phase of space group Im3m. Whereas all three solvents studied give rise to a sponge (L3) phase in the MO-water system, this phase was only found when MPD was added to the PT-water system. The results are discussed with respect to the chemical differences between PT and MO.

Topics: Fatty Alcohols; Glycerides; Glycols; Membranes, Artificial; Phosphatidylglycerols; Polyethylene Glycols; Propylene Glycol; Scattering, Small Angle; Solvents; Thermodynamics; Unilamellar Liposomes; Water; X-Ray Diffraction

The cubic phase of monoolein (MO) has successfully been used for crystallization of membrane proteins. It is likely that the transition to a lamellar phase upon dehydration is important for the crystallization process, and that the internal dimensions of the lipid phases (i.e., water pore diameter) are crucial for the inclusion and the diffusion of membrane proteins. In the present study, we investigated the cubic-to-lamellar phase transitions in the MO-water and the MO-distearoyl phosphatidyl glycerol (DSPG) systems. The MO-water system was investigated by means of isothermal sorption and desorption microcalorimetry. We show that the transition from cubic to lamellar phase induced by desorption is driven by entropy. At 25 degrees C, this occurs at a water activity of 0.98 with a transition enthalpy of 860 J/mol (MO). The phase behavior was also investigated in the presence of a small amount of the transmembrane protein bacteriorhodopsin (bR), and a detergent, octyl glucoside (OG), and it was shown that both bR and OG stabilize the lamellar phase. Analogous results were obtained for the MO-DSPG-water system. The latter system resembles the MO-water system in that a cubic-to-lamellar phase transition is induced by dehydration, although the structural properties of these phases are slightly different. Finally, we demonstrate that bR can be crystallized from a cubic phase of MO-DSPG-buffer.

Topics: Bacteriorhodopsins; Calorimetry; Detergents; Entropy; Glucosides; Glycerides; Phase Transition; Phosphatidylglycerols; Water

X-ray diffraction and Raman scattering spectroscopy have been used to study phase transitions and changes in molecular organization of the cubic Pn3m monoolein (MO)-H2O phase upon introducing low amounts of distearoylphosphatidylglycerol (DSPG) and lysozyme (LSZ). X-ray diffraction measurements indicated a phase transition Pn3m-Im3m brought about by DSPG and LSZ, however DSPG also induced formation of the lamellar phase. Raman spectra have demonstrated that incorporation of DSPG into the lipid bilayer decreases the mobility of acyl chains and increases the number of hydrogen-bonded C=O groups of MO. On the other hand, LSZ exerts identical effect on the latter parameter, while no effect on the state of acyl chains order was observed. This result and differential scanning calorimetric measurements indicate that LSZ is located in the water channel system of the cubic phase. The results are discussed on the basis of an infinite periodical lipid bilayer structure and lipid parameter concepts.

Topics: Animals; Calorimetry, Differential Scanning; Chemical Phenomena; Chemistry, Physical; Crystallization; Crystallography, X-Ray; Glycerides; In Vitro Techniques; Molecular Structure; Muramidase; Phosphatidylglycerols; Spectrum Analysis, Raman; Water; X-Ray Diffraction