Kinetic Study On The Adsorption Of Myelin Basic Protein At The Interface Of Phospholipid Monolayer

There are different types of membrane structures in cells,one of which is the myelin structure composed of the concentric membrane of phospholipid.The image of myelin in the cell(lipid-water system)has been described as the liquid crystal structure of the biofilm.The composition of myelin not only involves phospholipid,but also myelin protein.Myelin protein is mainly divided into myelin protein lipoprotein(MPLP)and myelin basic protein(MBP).Myelin basic protein(MBP)is one of the main myelin proteins,and MBP is a strong alkali membrane protein,accounting for about 1/3 of the total amount of myelin sheath protein.Its interaction with different phospholipids in the myelin membrane not only promotes the fusion of the cytoplasmic surface of oligodendrocytes into the main dense lines of the multilayer membrane structure,but also maintains the closeness of the sheath structure.Moreover,secondary structure can be formed to maintain the stability of myelin structure and function of central nervous system,and cause the conformation of protein to change.MBP is a basic structure involved in the myelin formation of the central nervous system.It is related to experimental allergic encephalomyelitis(EAE),multiple sclerosis(MS)and many other neurological diseases.At present,the study on the characteristics of monolayer based on the interaction of proteins with different lipid components has a certain guiding significance for the study of the structural changes of supramolecular aggregates in biomembrane and the pathogenesis and treatment of related diseases.By analyzing the surface pressure-mean average molecular area(?-A),surface pressure-adsorption time(?-T)isotherm data,the physical characteristics of biomimetic membrane formed by the interaction of MBP with myelin membrane lipid molecules were studied in this paper.The partition coefficients of the molecular interactions between MBP and neutral lipids,negatively charged lipids,alcohols and various types of mixed monolayer lipids,as well as the binding parameters of protein molecules embedded into cell membranes were calculated.For example,the increment of surface pressure(??),the maximum insert pressure(MIP)and the synergistic factor,etc.The surface morphology of lipids adsorbed on the membrane of MBP was observed by AFM and verified by??-T curve.The dynamic characteristics and stability of protein-lipid interaction are described qualitatively and quantitatively.An artificial membrane(bionic membrane)which is similar to biological membrane is established,which provides a new idea for understanding and mastering the mechanism of life.1.The physical Mechanism of the interaction between MBP and cholesterol.The interaction of MBP with cholesterol monolayer was investigated at three surface pressures on 10mM Tris-HCl buffer with the different concentrations of MBP.The results show that ?-A isotherms shift to larger molecular area at all pressures.By means of analyzing ?-T curves,a surface pressure increase was obtained.Results indicated that the greater the protein concentration in the subphase,the larger the increase of surface pressure.In addition,changes in monolayer surface morphology and domain formation were performed by AFM.These results provide more direct and convincing evidence for the MBP interaction with cholesterol.The MBP-cholesterol interaction suggests a significant concentrations and surface pressure dependence and is probably governed by hydrogen bonds.2.Mechanism of adsorption of myelin basic protein onto lipid monolayers,we have designed MBP-incorporated model lipid monolayers and studied the phase behavior of MBP adsorbed on the plasma membrane at the air/water interface by thermodynamic method and AFM.By analyzing the ?-A and ?-T isotherms,univariate linear regression equation was obtained.In addition,the elastic modulus,surface pressure increase,maximal insertion pressure,and synergy factor of monolayers were detected.These parameters can be used to modulate the monolayers binding of protein,and the results show that MBP has the strongest affinity for 1,2-dipalmitoyl-sn-glycero-3-phosphoserine(DPPS)monolayer,followed by DPPC/DPPS mixed and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine(DPPC)monolayers via electrostatic and hydrophobic interactions.AFM images of DPPS and DPPC/DPPS mixed monolayers in the presence of MBP(5nM)show a phase separation texture at the surface pressure of 20mN/m and the incorporation of MBP put into the DPPC monolayers has exerted a significant effect on the domain structure.MBP is not an integral membrane protein but,due to its positive charge,interacts with the lipid head groups and stabilizes the membranes.3.We use AFM and thermodynamic methods to study the intermolecular interaction of MBP adsorbed on different types of mixed monolayers at the air/subphase interface.The experimental results show that the mean molecular area increases when the protein is embedded in the mixed monolayer films.By analyzing ?-A isotherm data and mass conservation equation,it is calculated that when the surface pressure of monolayer is 10 mN/m,one MBP molecule can bind 70±3 POPC molecules and the molecular area of MBP at different concentrations.The linear regression equation is used to analyze the three characteristic parameters(??,MIP and synergy factor)of MBP adsorbed or embedded into "healthy myelin" and "disease myelin" monolayer.The characteristic parameters can be used to determine whether the myelin is a normal state or a pathological state.The analysis results of ?-A curve,compression modulus and adsorption characteristic parameters were further verified by AFM images.It is well understood that the interaction between myelin basic protein and mixed monolayer with different lipid components can maintain the stability of myelin multilayer membrane structure.