The Study Of The Interaction Between Lysozyme And Lipid Molecules At The Air/Water Interface

Biological membrane is a natural barrier that maintains cell and organelle with relatively independent and stable environments and is mainly composed of phospholipids and proteins.Phospholipids,mostly liquid crystal and the most abundant lipids in cell membranes,are used in a wide range of applications for the detection and characterization of biomolecular interactions,including biological sensing,transmembrane transport,receptor interactions,and cellular signaling.Lipids and proteins are the basis of the biological membrane structure and the interaction between them are directly related to many activities in the living body,such as cell signaling,molecular recognition and so on.Therefore,in-depth study the interaction between lipid and protein is important for understanding the structural properties and bio-chemical processes of biofilms.Lysozyme(LZM)is a globular antibacterial protein,which can be found in the human body,such as blood and saliva and is believed has antibacterial activity.The detection of lysozyme in serum can play an important role in the early diagnosis of leukemia.Eye conjunctivitis can lead to the decrease of the concentration of lysozyme.The content of lysozyme in cerebrospinal fluid is a sensitive signal to diagnose inflammation and central nervous system diseases.So far,the mechanism of membrane fusion in the process of lysozyme is not completely understood.Although it has been reported in the literature,this process is related to the interaction of lysozyme and phospholipids,which may be caused by the penetration of lysozyme into the lipid layer.We have used Langmuir-Blodgett(LB)technology and atomic force microscopy(AFM)to investigate the biological mechanism of the interaction between lysozyme with zwitterionic lipid dipalmitoyl phosphatidylcholine(DPPC)and dipalmitoyl phosphatidylethanolamine(DPPE)and the mixture of lipid DPPC and cholesterol(Chol)monolayer(1)The interaction between LZM and zwitterionic lipids DPPC and DPPE.The purpose of this study was to compare the penetration degree of lysozyme into DPPC and DPPE by analyzing the data of surface pressure-area(?-A)isotherms and surface pressure-Time(?-T)curves.The results showed that with the increase of lysozyme concentration,the ?-A isotherms shifted to the direction of the larger molecular area,indicating that more and more proteins were adsorbed on the lipid membrane.Lysozyme can both penetrate into DPPC and DPPE monolayer because of the increase of surface pressure at initial pressure of 15 mN/m.But the changes of DPPE is larger than DPPC,indicating that lysozyme interacts with DPPE are stronger than DPPC.The reason may be due to the different head groups and phase state of DPPC and DPPE monolayer at surface pressure of 15 mN/m.Atomic force microscopy reveals that lysozyme were absorbed by DPPC and DPPE monolayers,which occurring self-aggregation and self-assembly,forming irregular multimers and conical multimeric.Through analysis,we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers.(2)The interaction between lysozyme and DPPC/Chol mixed monolayer.In this paper,the interaction between lysozyme and mixed monolayer was studied by observing the surface topography and analyzing the thermodynamic isotherm,compression curve and adsorption curves of the ternary system monolayer.Cholesterol added to the DPPC can change the interface properties of the lipid monolayer,the ?-A isotherms has changed significantly and it may due to the molecules were rearranged.By analyzing the ?-T curves,it was found that the equilibrium pressure of the ternary system decreased with the increase of the ratio of lysozyme.This was because when the surface pressure was 15 mN/m,a large amount of lysozyme was adsorbed on the surface of DPPC/Chol monolayer and occurring self-aggregation and self-assembly,then the lipid membrane arrangement was damaged and the polymer into the sub-phase;Analysis of circular curve found that with the increase of lysozyme,the surface material loss of the ternary system increases,further indicating that the lysozyme adsorbs on the lipid membrane and changes its molecular arrangement.AFM observations showed that DPPC/Chol monolayer was becoming more and more loose as the ratio of lysozyme increased,and the protein adsorbed on the lipid membrane was reduced,and around the lysozyme aggregates were found to be defective,and the lysozyme might accumulate forming polymer and pull into the subphase,this verify the ?-T curve analysis results.As an adjunctive comparison,the interaction of different ratios of lysozyme with DPPC monolayer was studied.The results showed that lysozyme interacted with DPPC and changed the molecular arrangement of lipid monolayer.With the increase of lysozyme ratio,the amount of lysozyme adsorbed to DPPC monolayer gradually increased.In this paper,it is found that the interaction between lysozyme and DPPC/Chol mixed monolayer can lead to the decrease of the surface tension of the monolayer,the breakthrough of the lysozyme into the monolayer,leading to the structural reorganization.The membrane fusion process accompanied by lysozyme may be related to the interaction of lysozyme and phospholipid,which is of great reference for biofilm diseases.