The Diversity And Stability Of The Self-assembly Structures Of Cardiolipin In Electrolyte Solutions

Biomembrane is the basic structure and functional unit of cell, which not only acts as the physical screen of the cell, but also participates in many physiological processes, such as substance exchange, energy transport and the interaction between cells. In these processes, the characteristic and topology structure of the lipid bilayer takes a critical role. For example, the topology structure of mitochondrial inner membrane changes along with the transition of the functional states. Therefore, to clarify the stability and the morphorlogy transformation mechanism of the structure of lipid bilayers will help us to understand the origination of many physiological phenomena. Cardiolipin is a unique Phospholipid with dimeric structure, carrying four acyl groups and two negative charges. And it is found that cardiolipin exclusively exists in mitochondrial membranes and is related to the inner membrane topology transition. As a model membrane, a lot of investigators have paied attention to it. But until now, few investigations are concerned with the assembly structure of cardiolipin and its action to the related factors, which may have a potential signification for exploring the function of cardiolipin in the cell. In this thesis, our aim is to investigate the diversity of the self-assembly structures formed from cardiolipin and the formation mechanism. By control the electrolyte concentration, the morphology stability of the self-assembly structures was studied, the main results of this thesis are presented as following:1) We study the diversity of the self-assembly structures of cardiolipin in electrolyte solution around physiological concentration by direct-hydration method. Four primary structures are found formed from cardiolipin film including myelin, torus, raspberry and honeycomb figures. Myelin figure is a typical structure formed from the amphiphile/water interface, while the other three structures are intermediate structures, which are peculiar in other phospholipids, and emerge at different water content of the swelling cardiolipin film. The self-assembly structures are also depend on the initial electrolyte concentration, the uneven distribution of electrolyte concentration and the shear of water flow, et al. 2) In the study of the dynamics of myelin growth, we find there are two kinds of growth mechanism of myelin. In the electrolyte solution with concentration from 0.005M to 0.37M, the first kind of myelin growth is driven by external stress, which is related to the water flow, when the shear of water flow decreased to a certain point the myelin will retract, while the second kind of myelin growth is driven by thermodynamic stress. When the intermembrane pressure between bilayers is too large at the initial stage of swelling, a morphology transition from flat membrane to myelin figure can happen to reduce the energy. And the formed myelin will stabilize at the longest length for a period. Then it retracts back again to the base due to the electrolyte concentration increasing or water penetrating. The steady time and the retract velocity of the second kind of myelin are different from each other in electrolyte solution with different initial concentration. In the lower initial electrolyte concentration, the electrostatic shielding effect is more sensitive to the electrolyte concentration, so that the steady time of the myelin at its longest length is shorter and the retract velocity is larger too.3) We modulate the electrolyte concentration nearby a steady myelin by solvent-evaporation and microinjection in experiments. It is found that many ripples of membranes emerge in the myelin, which is called the crimple myelin. The ripples of crimple myelin will be smooth again as the electrolyte concentration decreased by injecting water nearby. Comparing the electrolyte concentration shifting along the time with the membrane surface potential shifting along the electrolyte concentration, the crimple phenomenon is related to the shift rate of electrolyte concentration and to the shift range of the membrane surface potential. Because the basic characteristics of myelin figure is similar to that of mitochondria, we presume that all the electrolyte concentration, space confinement, intermembrane electrostatic interaction and thermo-undulation of the membrane can contribute to the mitochondrial inner membrane topology transition, besides the membrane spontaneous curvature change induced by the proteins adhering on or inserting into the bilayer.