title: C-terminal interactions of apolipoprotein E4 respond to the postprandial state.
abstract: Increased triglyceride-rich lipoproteins (TGRLs) in the postprandial state are associated with atherosclerosis. We investigated whether the postprandial state induced structural changes at the apolipoprotein E4 (apoE4) C terminus, its principal lipid binding domain, using electron paramagnetic resonance (EPR) spectroscopy of a site-directed spin label attached to the cysteine of apoE4-W264C. Spin coupling between labels located in the C termini was followed after mixing with preprandial and postprandial human plasma samples. Our results indicate that postprandial plasma triggers a reorganization of the protein such that the dipolar broadening is diminished, indicating a reduction in C-terminal interaction. The loss of spectral broadening was directly correlated with an increase in postprandial plasma triglycerides and was reduced with delipidated plasma. The spin-labeled apoE4 displayed a lipid preference of VLDL > LDL > HDL in the preprandial and postprandial states. The apoE4 shift to VLDL during the postprandial state was accompanied by a loss in spectral broadening of the protein. These findings suggest that apoE4 associated with LDL maintains self-association via its C terminus and that this association is diminished in VLDL-associated protein. Lipolyzed TGRL reflected a depletion of the C-terminal interaction of apoE4. Addition of palmitate to VLDL gave a similar response as lipolyzed TGRL, suggesting that lipolysis products play a major role in reorganizing apoE4 during the postprandial state.
authors.affiliation: Department of Internal Medicine, Division of Endocrinology, Clinical Nutrition, and Vascular Medicine, University of California, Davis, 95616, USA. skanakagiri@ucdavis.edu
authors.forename: Sarada D
authors.initials: SD
authors.lastname: Tetali
authors.forename: Madhu S
authors.initials: MS
authors.lastname: Budamagunta
authors.forename: John C
authors.initials: JC
authors.lastname: Voss
authors.forename: John C
authors.initials: JC
authors.lastname: Rutledge
mesh_terms: D001057:Apolipoproteins E / Q000097:blood* / Q000737:chemistry*; D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D066298:In Vitro Techniques; D008066:Lipolysis; D008077:Lipoproteins, LDL / Q000097:blood; D008079:Lipoproteins, VLDL / Q000097:blood; D008958:Models, Molecular; D015394:Molecular Structure; D019518:Postprandial Period / Q000502:physiology*; D011485:Protein Binding; D013113:Spin Labels; D014280:Triglycerides / Q000097:blood
chemical_list: D001057:Apolipoproteins E; D008077:Lipoproteins, LDL; D008079:Lipoproteins, VLDL; D013113:Spin Labels; D014280:Triglycerides