Monolayer Study Of The Interaction Between Bovine Serum Albumin And Lipid

Exploring the structure and function of complex biomolecular system at interface is one of the hot issues in biomolecular membrane research.Lipid monolayers are widely used in biological detection,biomimetic membrane materials,molecular self-assembly,molecular recognition and so on.Bovine serum albumin(BSA)is the main protein in bovine serum.And it has been widely used in medical,material and pharmaceutical fields,which was because of its abundance,low cost,unusual ligand-binding properties and its being homologous with human serum albumin(HSA).The study of the interaction between BSA and lipid monolayers at interface has an important physiological significance for understanding the physical,biological and chemical processes in vivo and in vitro.In this study,the interaction between BSA and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine(DSPE),1.2-dipalmitoyl-sn-glycero-3-[phosphor-rac-(1-glycerol](DPPG)and 1,2-dioleoyl-3-trimethylammonium-propane(DOTAP)lipid monolayers at air/water interface was studied by using Langmuir-Blodgett(LB)technology and atomic force microscopy(AFM)technology.1.The research of the interaction between BSA and DSPE lipid monolayer.By changing the pH value of subphase and the concentration of BSA([BSA]),the surface pressure-mean molecular area(?-A)isotherms,compression and decompression cycle curves,adsorption(?-t)curves of DSPE lipid monolayer were obtained.The experimental results indicated that:(1)The interaction between BSA and DSPE lipid monolayers was affected by the pH value of subphase.When pH=3,5 and 7,the hydrophobic interaction between BSA and DSPE played the dominant role.While at pH=9,a combination of hydrophobic interaction and electrostatic interaction dominated the interaction of BSA with DSPE lipid monolayer.And the interaction was the strongest at pH=3 and the weakest at pH=7.(2)The adsorption of BSA on DSPE lipid monolayer was a one-step reaction process.And the adsorptive capacity of BSA on lipid monolayer has reached a certain threshold,which was affected by the pH value of subphase.(3)The interaction between BSA and DSPE lipid monolayer could affect the phase transition behavior,stability and compressibility of DSPE lipid monolayer.AFM observation showed that the adsorption of BSA on DSPE lipid monolayer,subphase's pH value and surface pressure could change the morphology structure of DSPE lipid monolayer,and the change characteristics were consistent with the analysis results obtained from surface pressure isotherms.2.The research of the interaction between BSA with DPPG as well as DOTAP lipid monolayers.By changing the pH value of subphase and the concentration of BSA([BSA]),the surface pressure-mean molecular area(?-A)isotherms,the limiting molecular area-[BSA](Alim-[BSA])curves,the difference value of mean molecular area-[BSA](?A-[BSA])curves of DPPG and DOTAP lipid monolayers were obtained.The experimental results indicated that there was a significant difference in the adsorption of BSA by DPPG and DOTAP lipid monolayers.For DPPG/BSA system:(1)At pH=3 and 5,the mean molecular area of DPPG lipid monolayer increased with the increase of[BSA]in subphase.However,at pH=10,the ?-A isotherms didn't change obviously because of the changes in[BSA].So the interaction between BSA and DPPG was affected by the pH value of subphase.At pH=3 and 5,BSA adsorbed on DPPG lipid monolayer was mainly dominated by hydrophobic interaction,and the strength of hydrophobic interaction at pH=3 was stronger than the case of pH=5.While at pH=10,there was a strong electrostatic repulsion between BSA and DPPG molecules.So the adsorption of BSA on DPPG lipid monolayer was the strongest at pH=3,and the weakest at pH=10.(2)The number of BSA molecules adsorbed on DPPG lipid monolayer has researched a threshold value.(3)At pH=3,both adsorption and desorption behavior of BSA appeared in the system,while only desorption behavior appeared at pH=5 and 10.For DOTAP/BSA system:(1)the ?-A isotherms of DOTAP lipid monolayer moved towards larger mean molecular area when[BSA]increased.(2)The amount of BSA adsorbed on DOTAP lipid monolayer reached a threshold value at a[BSA]of 5×10-8 M.(3)BSA desorbed from DOTAP lipid monolayer as time goes by for all pHs.(4)The interaction between BSA and DOTAP at interface was affected by the pH value of subphase.When pH=10,BSA molecules could be well separated and purified from the complex mixtures,which was because the interaction between BSA and DOTAP was the combination of hydrophobic interaction and electrostatic attraction.AFM images showed that both pH value and[BSA]could affect the morphological features of DPPG and DOTAP lipid monolayers and the dynamic adsorption behavior of BSA on lipid monolayers.And the result was consistent with the analysis results obtained from surface pressure curves.