Badania układów błonowych metodami modelowania molekularnego

Abstrakt

Biological membranes enclose every cell (plasma membrane) and some intracellular organelles (internal membranes). The main structural element of a biological membrane is a liquid-crystalline lipid bilayer. Experimental studies of lipid bilayers are difficult to carry out and to interpret because of their structural disorder and superposition of motions occurring in different time scales. Besides, due to limited spatial and time resolutions, they provide only an averaged behaviour of the molecules in the bilayer. Detailed information about the dynamical structure and time scales of events in the membrane can be obtained using molecular dynamics (MD) simulation methods. Although MD simulation is, in principle, characterized by an atomic resolution and time resolution in the femtosecond time scale in principle, the total simulation time is limited at present to several hundred nanoseconds. So, the method allows observation of the processes up to the 10-7 s time scale. MD simulation studies of hydrated lipid bilayers have shown that at the membrane/water interface there are numerous but short-lived hydrogen (H-) bonds between lipid headgroups and water molecules as well as an extended network of interlipid links via water molecules that are simultaneously H-bonded to two lipid molecules, i.e., so called water bridges. Exchange of H2O by D2O affects the time-averaged properties of the PC bilayer to some extent. When the bilayer is hydrated by D2O it becomes more compact than in the case of H2O. This can be assigned to the more stable H-bonds between PC and D2O than H2O and, particularly, to the more stable network of D2O water bridges compared with the H2O ones. In effect, the self-diffusion coefficient of D2O averaged over all water molecules in the bilayer is almost twice smaller than that of H2O and ?2.5 times smaller than in pure D2O (?1.7 in the case of H2O).