Effects of distearoylphosphatidylglycerol and lysozyme on the structure of the monoolein-water cubic phase: X-ray diffraction and Raman scattering studies

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0 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 a basis of an infinite periodical lipid bilayer structure and lipid packing parameter concepts.