Effect of dehydration and hydrostatic pressure on phosphatidylinositol bilayers: an infrared spectroscopic study

Abstract

The influence of hydration and hydrostatic pressure on the conformation and local interactions of phosphatidylinositol (PI) has been investigated using infrared spectroscopy. In hydrated PI bilayers, the phosphate groups and a major proportion of the carbonyl groups undergo strong hydrogen bonding with water molecules. These bonds strengthen upon compression to 5–7 kbar but above that, the proportion of bonded carbonyls decreases dramatically, probably due to water expulsion. In dehydrated PI bilayers, the strong H-bonds of the phosphate, carbonyl and inositol hydroxyl groups weaken rapidly up to 2 kbar. Above 2 kbar, the H-bonds of the hydroxyl and carbonyl groups slowly get stronger. This suggests an extension of the inositol rings from the phosphate group vicinity out to the bilayer surface at elevated pressure. This modulation of the inositol availability at the surface according to the balance between steric factors, hydration forces and intra- and intermolecular interactions might be crucial for PI specific biological roles.