Disturb or stabilise? effects of different molecules on biological membranes

The properties of biological membranes are often regulated by special molecules produced by organisms. Knowledge about the mechanisms by which these molecules affect biological membranes is a key issue in understanding living organisms. The interactions between phospholipid membranes and different molecules were studied using Molecular Dynamics (MD) simulations and the Solvent Relaxation (SR) technique. As a first example how molecules can modulate membrane properties the effect of isoprene on the stability of phospholipid bilayer was investigated. Isoprene is produced by plants and emitted to the atmosphere in large amounts during a rapid temperature rise. MD simulations show that the order parameters of the system with isoprene are similar to the order parameter of the pure phospholipid bilayer at a temperature of 10 degrees lower. By this mechanism thermal damage of the membrane can by prevented. A second example of molecules that specifically interact with cell membranes are resorcinolic lipids. Experimental data show that these lipids can either stabilize or disturb the lamellar structure of membranes. Our results show that resorcinolic lipids stabilize the bilayer by increasing the packing of the alkyl tails of the lipids. Our focus was on three homologs that differ in the length of their alkyl tail. When incorporated into the bilayer from the aqueous solution, however, resorcinolic lipids disturb the lamellar organization of the bilayer. Two different pathways were identified either with or without formation of a water pore. Extreme deformation of the bilayer sometimes leads to transition into a non-lamellar structure. The dual effect of resorcinols was also investigated by the SR method. The hydration level of the bilayer in the region of the ester groups of the phospholipids was studied through a change of the total spectral shift and relaxation times of the fluorescent probe. However, if resorcinols were added to preformed vesicles, a higher level of hydration and faster relaxation times were observed which is indicative of increased disorder in the system.