The glycosylphosphatidyl inositol(GPI)-anchored proteins are localized on the outer of the plasma membrane and clustered in membrane microdomain known as lipid rafts. Among them, mammalian alkaline phosphatase(AP) is ...The glycosylphosphatidyl inositol(GPI)-anchored proteins are localized on the outer of the plasma membrane and clustered in membrane microdomain known as lipid rafts. Among them, mammalian alkaline phosphatase(AP) is an enzyme widely distributed. So, it has important biological significance to study the combination of AP with lipid monolayer. In our work, the interaction between AP and sphingomyelin has been studied at the air-buffer interface as a biomimetic membrane system by the Langmuir film technique and atomic force microscopy. The surface pressure-area isotherm for the mixed alkaline phosphatase/sphingomyelin monolayer shown the presence of a transition from a liquid-expanded phase to the liquid-expanded/liquidcondensed coexist phase. And the surface compressional modulus suggested the mixed alkaline phosphatase/sphingomyelin monolayer has larger compressibility compared with the pure sphingomyelin monolayer. Besides, according to the micrographs, we inferred when combined with lipid monolayer at the air-buffer interface, the AP molecules formed polymer not multilayer or micelle. And, according to the limiting molecules area of AP, we inferred that 12 AP molecules formed a hexagon polymer unit.展开更多
Lipid rafts are of a dynamic microdomain structure found in recent years, enriched in sphingolipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseas...Lipid rafts are of a dynamic microdomain structure found in recent years, enriched in sphingolipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseases. In this work, the monolayer behavior of mixed systems of D-sphingosine with cholesterol was investigated in terms of the mean surface area per molecule (A m), excess molecular area (ΔA ex), surface excess Gibbs energy (ΔG ex), interaction parameter (ω), activity coefficients (f 1 and f 2) as well as elasticity (C s ?1) of formed films. The deposited Langmuir-Blodgett (LB) monolayers were investigated with atomic force microscopy (AFM). Thermodynamic analysis indicates ΔA ex and ΔG ex in the binary systems with negative deviations from the ideal behavior, suggesting attractive interaction between molecules. The stability, elasticity and activity coefficients show a marked dependence on the mole faction of D-sphingosine. The results of observation by AFM show that the single D-sphingosine molecular film took on small granule structure. When mixing the D-sphingosine and cholesterol at different ratios, the mixed films transform from the chains structure to larger slice and net coexisting structure with the increasing of the cholesterol content. In the end, pure cholesterol forms more aggregated structure. AFM experiments effectively support the above findings and interpretation.展开更多
Amphotericin B（AmB） has been widely used in antifungal therapy. AraB molecules combine with cholesterol to form pores that can be toxic to human cells, thus greatly limiting its clinical application. The interaction...Amphotericin B（AmB） has been widely used in antifungal therapy. AraB molecules combine with cholesterol to form pores that can be toxic to human cells, thus greatly limiting its clinical application. The interaction between Arab and the cell membrane may be influenced by potassimn, sodium and calcium ions. Lq this study, the bilayer in large unilamellar lipid-drug liposomes with or without cholesterol was employed as a model membrane. N-（7-Nitrobenz-2-oxa-1,3-diazol-4-yl）-1,2-dipalmitoyl-sn-glycero-3-phosphoetheanolamine（N-BD-PE） and 1-palmi-toyl-2-[6（7-nitrobenz-2-oxa-1,3-diazol-4-yl）aminodoclecanoyl]-sn-glysero-3-phosphocholine（6-NBD-PC） are two kinds of fluorescent lipid probes, and the NBD group is attached to the polar lipid headgroup in the former, but to the sn-2 fatty acyl chain in the latter. The effect of these metal cations on the lipid-drug membrane was monitored by red edge excitation shift（REES）, fluorescence polarization, and the fluorescence lifetime of lipid probes in hydrophilic and hydrophobic areas of the membrane. These ions have different effects on the lipid-AraB membrane. Cholesterol can strengthen the packing ability of the membrane, which is influenced differently by potassium, sodium and calcium ions. Moreover, the influence of these ions on the membrane may be relative to the method of ion transportation through the membrane. This study is significant to understand the reduction of AraB＇s cellular toxicity.展开更多
基金Foundamental Research Funds for the Central Universities(GK201402010)the Natural Science Basic Research Plan in Shaanxi Province of China(2012JQ1002)Innovation Funds of Graduate Programs,SNU(2012CXS033)for supporting this work
文摘The glycosylphosphatidyl inositol(GPI)-anchored proteins are localized on the outer of the plasma membrane and clustered in membrane microdomain known as lipid rafts. Among them, mammalian alkaline phosphatase(AP) is an enzyme widely distributed. So, it has important biological significance to study the combination of AP with lipid monolayer. In our work, the interaction between AP and sphingomyelin has been studied at the air-buffer interface as a biomimetic membrane system by the Langmuir film technique and atomic force microscopy. The surface pressure-area isotherm for the mixed alkaline phosphatase/sphingomyelin monolayer shown the presence of a transition from a liquid-expanded phase to the liquid-expanded/liquidcondensed coexist phase. And the surface compressional modulus suggested the mixed alkaline phosphatase/sphingomyelin monolayer has larger compressibility compared with the pure sphingomyelin monolayer. Besides, according to the micrographs, we inferred when combined with lipid monolayer at the air-buffer interface, the AP molecules formed polymer not multilayer or micelle. And, according to the limiting molecules area of AP, we inferred that 12 AP molecules formed a hexagon polymer unit.
基金Supported by the National Natural Science Foundation of China (Grant No. 20772077)the National Basic Research Program of China (Grant No. 104167)
文摘Lipid rafts are of a dynamic microdomain structure found in recent years, enriched in sphingolipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseases. In this work, the monolayer behavior of mixed systems of D-sphingosine with cholesterol was investigated in terms of the mean surface area per molecule (A m), excess molecular area (ΔA ex), surface excess Gibbs energy (ΔG ex), interaction parameter (ω), activity coefficients (f 1 and f 2) as well as elasticity (C s ?1) of formed films. The deposited Langmuir-Blodgett (LB) monolayers were investigated with atomic force microscopy (AFM). Thermodynamic analysis indicates ΔA ex and ΔG ex in the binary systems with negative deviations from the ideal behavior, suggesting attractive interaction between molecules. The stability, elasticity and activity coefficients show a marked dependence on the mole faction of D-sphingosine. The results of observation by AFM show that the single D-sphingosine molecular film took on small granule structure. When mixing the D-sphingosine and cholesterol at different ratios, the mixed films transform from the chains structure to larger slice and net coexisting structure with the increasing of the cholesterol content. In the end, pure cholesterol forms more aggregated structure. AFM experiments effectively support the above findings and interpretation.
基金Supported by the National Natural Science Foundation of China（No.21402114）.
文摘Amphotericin B（AmB） has been widely used in antifungal therapy. AraB molecules combine with cholesterol to form pores that can be toxic to human cells, thus greatly limiting its clinical application. The interaction between Arab and the cell membrane may be influenced by potassimn, sodium and calcium ions. Lq this study, the bilayer in large unilamellar lipid-drug liposomes with or without cholesterol was employed as a model membrane. N-（7-Nitrobenz-2-oxa-1,3-diazol-4-yl）-1,2-dipalmitoyl-sn-glycero-3-phosphoetheanolamine（N-BD-PE） and 1-palmi-toyl-2-[6（7-nitrobenz-2-oxa-1,3-diazol-4-yl）aminodoclecanoyl]-sn-glysero-3-phosphocholine（6-NBD-PC） are two kinds of fluorescent lipid probes, and the NBD group is attached to the polar lipid headgroup in the former, but to the sn-2 fatty acyl chain in the latter. The effect of these metal cations on the lipid-drug membrane was monitored by red edge excitation shift（REES）, fluorescence polarization, and the fluorescence lifetime of lipid probes in hydrophilic and hydrophobic areas of the membrane. These ions have different effects on the lipid-AraB membrane. Cholesterol can strengthen the packing ability of the membrane, which is influenced differently by potassium, sodium and calcium ions. Moreover, the influence of these ions on the membrane may be relative to the method of ion transportation through the membrane. This study is significant to understand the reduction of AraB＇s cellular toxicity.
