Interaction of Cytochrome-C with Monoolein Liquid Crystals Mesophases

Phase behaviour and structural properties of monoacylglycerides in water have been investigated for a long time, due to their extended polymorphism. In particular, monoolein (MO) in water shows several mesophases, characterized by a high disordered conformation of the hydrocarbon chains. At such conditions, an embedded protein can influence the physical properties of the lipid matrix, depending on the protein size and polarity. We take advantage of the structural properties of monoolein and cytochrome-c to extensively study the temperature effects on the cubic transition from Pn3m to Im3m by means of small-angle X-ray scattering technique (SAXS) and electronic absorption spectroscopy (EAS). To do so, we made samples composed of monoolein (50 mg/ml) in the presence of 1, 10 and 50 mg/ml of cytochrome-c. Ours preliminary SAXS results indicate that cyto-c is able to change the monoolein water channels, from cubic Pn3m to Im3m. Moreover, such kinetic behaviour is too slow, taking place within some days. EAS measurements indicate that the incorporation of cyto-c within the Monoolein water channels begins after two or three days (after the sample preparation). Besides, after one week of sample preparation the amount of cyto-c within the Monoolein water channels is equal to 60% and 34% for 1 and 10 mg/ml of cyto-c, respectively. Interestingly, increasing the temperature, the unity cell parameter decreases, indicating that water is going out from the unity cell and the symmetry of the liquid crystal phase can changes to another cubic or to hexagonal, depending on the temperature and the sample composition. We believe that these results could bring more insights on the protein-liquid crystal interaction.