Molecular Simulation On Interactions Between Band 3 Protein And Lipid Nanodomains In Erythrocyte Membrane

Band 3 or human anion exchange 1?AE1?,is an important transmembrane protein,which is responsible for the exchange of chloride/bicarbonate across the erythrocyte membrane.It plays an important role in the transport of CO₂ across membranes and in the exhalation of CO₂ from lungs.In recent years,some relevant studies have shown that the interaction between Band 3 and membranes,especially the interaction between Band 3 and lipid rafts?special microdomain in erythrocyte membrane?,has a significant influence on the function of Band 3.Therefore,it is of great significance for us to reveal the microscopic physical mechanism of the interaction between Band 3 and membrane domains to understand the anion exchange function of Band 3,as well as the treatment of erythrocyte diseases.Many theoretical and experimental studies have focused on understanding the interactions between Band 3 and membranes,including the interactions between Band 3and various lipids or the cytoskeleton proteins,as well as the distribution of Band 3 in lipid rafts of erythrocyte membranes.These studies paid more attention on the interaction between Band 3 and homogeneous or monophasic membranes.However,since the native erythrocyte membrane is composed of complex proteins and various lipid molecules,phase separation occurs between different lipid molecules,forming microdomains with different structures,such as liquid-ordered?Lo?domain and liquid-disordered?Ld?domain.Nevertheless,due to the limitations of experimental techniques,it is difficult to observe the structure of the microdomains experimentally,so that it is also difficult to understand the interaction between Band 3 and microdomains from the molecular scale.In addition,few theoretical simulation studies have involved in the interaction between Band 3 and membrane domains in the phase-separated membrane.Therefore,the microscopic mechanism of the interaction between Band 3 and different domains in erythrocyte membrane is not fully understood yet.In addition to the neutral lipid molecules,erythrocyte membrane also contains a high percentage of cholesterol and charged lipid molecules.Cholesterol and charged lipid molecules have important effects on the structure and properties of lipid domains,which may also affect the interaction between Band 3 and lipid domains.In this thesis,using all-atom molecular dynamics simulation,we studied the interactions between Band 3 and lipid domains in ternary phase-separated membranes.We considered three different ternary membrane systems.Through calculating the fraction of contact,the number of hydrogen bond between Band 3 and different lipid domains and so on,we revealed the microscopic mechanism of the effects of cholesterol concentration and anionic lipids on the interactions between Band 3 and membrane domains in detail at the molecular scale.The main results are as follows:1.In the bilayer composed of DPPC/DLi PC/CHOL with a lower cholesterol concentration,Band 3 shows asymmetric interactions with membrane domains in the outer and inner leaflets,resulting in the asymmetric distribution of the membrane domains in the outer and inner leaflet of bilayer.2.In the bilayer composed of DPPC/DLi PC/CHOL with a higher cholesterol concentration,cholesterol exhibits an obvious influence on the size of lipid domains,and there is a strong interaction between Band 3 and cholesterol,but the interaction is nonspecific.The strong interaction significantly affects the stability of the protein structure,which further affects the interaction between Band 3 and membrane domains,making Band 3 more likely to distribute in the Ld domains.3.In the bilayer composed of DSPS/DLi PC/CHOL containing negatively charged lipid DSPS,the electrostatic interaction between the negatively charged head group of DSPS and the positively charged amino acids Lys and Arg on the surface of Band 3 leads to stable contact sites between Band 3 and the negatively charged membrane domains,that is,the electrostatic interaction dominates the interaction between Band3 and membrane domains.The results of this work provide some theoretical insights into understanding the distribution of Band 3 in the microdomain of erythrocyte membrane.Meanwhile,the MD simulations also provide molecular details of the interactions of Band 3 with membrane domains and may be helpful to understand the function of Band 3 in the plasma membrane of erythrocytes.