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Báo cáo Y học: Differences in the binding capacity of human apolipoprotein E3 and E4 to size-fractionated lipid emulsions

We describe sensitive new approaches for detecting and quantitatingprotein–lipid interactionsusinganalytical ultra-centrifugation and continuous size-distribution analysis [Schuck (2000)Biophys. J.78,1606–1619]. The newmethods were developed to investigate the binding of human apo-lipoprotein E (apoE) isoforms to size-fractionated lipid emulsions, and demonstrate that apoE3 binds preferentially tosmall lipidemulsions,whereas apoE4exhibits apreference for large lipid particles. | Eur. J. Biochem. 269 5939-5949 2002 FEBS 2002 doi 10.1046 j.1432-1033.2002.03319.x Differences in the binding capacity of human apolipoprotein E3 and E4 to size-fractionated lipid emulsions Matthew A. Perugini1 Peter Schuck2 and Geoffrey J. Howlett1 1 Department of Biochemistry and Molecular Biology The University of Melbourne Parkville VIC Australia 2Division of Bioengineering and Physical Science ORS OD National Institutes of Health Bethesda MD USA We describe sensitive new approaches for detecting and quantitating protein-lipid interactions using analytical ultracentrifugation and continuous size-distribution analysis Schuck 2000 Biophys. J. 78 1606-1619 . The newmethods were developed to investigate the binding of human apolipoprotein E apoE isoforms to size-fractionated lipid emulsions and demonstrate that apoE3 binds preferentially to small lipid emulsions whereas apoE4 exhibits a preference for large lipid particles. Although the apparent binding affinity for large emulsions is similar Kd w 0.5 M the maximum binding capacity for apoE4 is significantly higher than for apoE3 3.0 cud 1.8 amino acids per phosphoiipid. respectively . This indicates that apoE4 has a smaller binding footprint at saturation. We propose that apoE isoforms differentiate between lipid surfaces on the basis of size and that these differences in lipid binding are due to a greater propensity of apoE4 to adopt a more compact closed conformation. Implications for the role of apoE4 in blood lipid transport and disease are discussed. Keywords Alzheimer s disease apolipoprotein E open conformation lipid binding analytical ultracentrifugation. Traditional methods for monitoring protein-lipid interactions have employed a variety of lipid systems including emulsions phospholipid vesicles and phospholipid micelles 1-6 . However the methodologies and heterogeneity of lipids employed in these studies do not allow a thorough investigation into the effect of particle size on protein binding. This may