Abstract
Reconstituted high density lipoprotein has been prepared by sonication and preparative ultracentrifugation of mixtures containing the apoprotein of high density lipoprotein, egg phosphatidylcholine, cholesteryl oleate, and acyl chain deuterated cholesteryl palmitate in aqueous buffer. The resulting structures have a size and chemical composition very similar to native high density lipoprotein. Deuterium NMR spectra and longitudinal relaxation times were obtained at approximately 25 degrees C. The variation of the 2H NMR line width with chain position is consistent with an average conformation such that the ester acyl chain is extended. In addition, 2H NMR line widths and longitudinal relaxation times indicate that the ester acyl chains possess significant mobility.
Highlights
Reconstituted high density lipoproteinhas been pre- DeuteriumNMR is an excellent technique for studying pared by sonication and preparative ultracentrifuga- molecular order and dynamic structure as it monitorasnontion of mixtures containing the apoprotein of high depne-rturbing probe. selective deuteration, combined with the sity lipoprotein, egg phosphatidylcholine, cholesteryl low natural abundance of deuterium, gives unambiguous asoleate, and acyl chain deuterated cholesteryl palmitatesignments and,since the quadrupolar interaction siso strong, in aqueous buffer.The resulting structures have a size dipolar interactions with neighboring nuclei may usually be and chemical composition very similar to native high ignored
High density lipoproteins are of considerable current interest as there is a negative correlation between plasma HDL concentration and threisk of heart disease (Millerand Miller, 1975)
The structure and physical properties of HDL have been studied by a wide variety of techniques including electron microscopy (Forte et al, 1968),x-ray diffraction (Laggnerand Muller, 1978), ESR (Brainard et al, 1980), and NMR (Finer et al, 1975; Henderson et al, 1975; Hamilton et al, 1974; Wassall et al, 1982).HDL' is proposed to be a quasi-spherical particle of6.5-10 nmdiameter(Forte et al, 1968; Scanu, 1979).The apoproteinis thought tobe embedded in an outer, micellar structure formed by phospholipids and cholesterol, while the hydrophobic core of the micelle is filled with the neutral lipids, cholesteryl esters, triglycerides, and cholesterol
Summary
Apoprotein, cholesteryl oleate, deuterated cholesteryl palmi- Cholesteryl oleate/cholester.vl palmita(twet/wt). Copy of these structuresu, sing the negative-staining technique The diameter of these containing cholesteryl palmitate selectively deuterated along structures and their chemical composition is shownin Table the acyl chain. To each of these spectra which, in addition to the absorption '"PNMR spectraof native HDL:, and of reconstituted HDL, due to deuterated cholesteryl palmitate, sometimes contains prepared with egg phosphatidylcholine/cholesteryl oleate/ the narrow,downfield-shifted line from residual deuteriumin cholesteryl palmitate or total HDL:, lipids, respectively, are water.
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