The Study Of Interaction Between Cytochrome C And Mimic Inner Membrane Of Mitochondrion

In recent years, biomembrane has been studied in various fields of biology and medicine. Various diseases (such as mitochondrial diseases, Alzheimer’s disease, Parkinson’s disease, diabetes, cardiovascular disease, etc.) were related to the changes of biomembrane and biomembrane lipids or proteins. Therefore, studying the interaction between protein and lipid has an important medical and biological value for exploring many diseases in the molecular level. However, we can not directly to study biomembrane because of its complex structure and function, so we transformed biomembrane into a simple monolayer system. In this paper, we used Langmuir-Blodgett (LB) as a simple model.Mitochondrion is a kind of typical organelle, which has a double membrane structure. Cytochrome C (Cyt c) is widely present in the mitochondrial inner membrane. It plays a very important role in the mitochondrial respiratory chain. Moreover, Cyt c is closely related to many diseases such as apoptosis and anti-oxidation. This article focuses on the interaction of Cyt c and mitochondrial inner membrane lipids (PC, PE and CL).(1) The interaction between Cyt c and DPPC/DPPE lipid mono layers. We used Langmuir-Blodgett monolayer technique combined with AFM to study the interaction of Cyt c with lipid mono layers at air-buffer interface. In this paper, we have also studied the interaction of Cyt c with anionic lipid (DPPS) and zwitterionic lipid (DPPC/DPPE) monolayers, the adsorption capacity of Cyt c on lipid monolayers is DPPS> DPPE> DPPC, which is attributed to their different headgroup structures. π-A isothermal data show that Cyt c molecules are at maximum adsorption quantity on lipid monolayer. Moreover, Cyt c molecules would form aggregations and drag some lipids with them into subphase if the protein exceeds the maximum adsorption quantity. π-T curve indicates that it takes more time for Cyt c molecular conformation to rearrange on DPPE monolayer than on DPPC. The compressibility study reveals that the adsorption or intermolecular aggregation of Cyt c molecules on lipid monolayers will change the membrane fluidization. In order to quantitatively estimate Cyt c molecular adsorption properties on lipid monolayers, we fit the experimental isotherm with a simple surface state equation. A theoretical model is also introduced to analyze the liquid expanded (LE) to liquid condensed (LC) phase transition of DPPC monolayer. The results of theoretical analysis are in good agreement with the experiment.(2) The interaction between Cyt c and CL lipid monolayer. Cardiolipin (CL) is one of main phospholipids in the inner membrance of eukaryotic cell mitochondrion. Cytochrome c (Cyt c) is an essential component of the inner mitochondrial respiratory chain. Studying the interaction between Cyt c and CL can provide important information for researching some diseases caused by abnormal mitochondrion. We used Langmuir-Blodgett monolayer technique combined with AFM to study the interaction between different concentrations of Cyt c and CL monolayer at air-buffer interface. It indicates that there is a threshold value of the adsorption quantity of Cyt c on CL monolayer, if the amount of Cyt c exceeds the value, they will sink into the subphase, inducing a smaller mean molecular area. The hysteresis curves indicate that the molecules of the monolayer have almost no loss at the air-buffer interface after the compression-expansion cycle under a low pressure of 5 mN/m and 10 mN/m. However, the expansion curves lag the compression curves under a high pressure of 20 mN/m. With the increment of Cyt c, the hysteresis phenomenon is more and more obvious, the number of losing molecules also increased. Moreover, when the monolayer experiences continuous compression-expansion cycles, the number of losing molecules will increase continuously. The Volmer theoretical model was also introduced to quantitatively calculate the number of interfacial molecular loss. When the concentration of Cyt c is 0 nM,1.04 nM and 2.08 nM, the number of losing molecules only accounts for 1/1000 of the total molecules, but the concentration of Cyt c is 4.16 nM and 6.24 nM, the number of losing molecules accounts for 1/100 of the total molecules. With increasing the amount of Cyt c, the mixed monolayer becoming more and more loose and the adsorption quantity of Cyt c on the lipid monolayer is reduced, Cyt c molecules will be a circle around some defects. This phenomenon may be associated with some mitochondrial disease. Therefore, studying the interaction between Cyt c and CL has an important biological and medical significance.