title: Nascent high density lipoproteins formed by ABCA1 resemble lipid rafts and are structurally organized by three apoA-I monomers.
abstract: This report details the lipid composition of nascent HDL (nHDL) particles formed by the action of the ATP binding cassette transporter A1 (ABCA1) on apolipoprotein A-I (apoA-I). nHDL particles of different size (average diameters of ∼ 12, 10, 7.5, and <6 nm) and composition were purified by size-exclusion chromatography. Electron microscopy suggested that the nHDL were mostly spheroidal. The proportions of the principal nHDL lipids, free cholesterol, glycerophosphocholine, and sphingomyelin were similar to that of lipid rafts, suggesting that the lipid originated from a raft-like region of the cell. Smaller amounts of glucosylceramides, cholesteryl esters, and other glycerophospholipid classes were also present. The largest particles, ∼ 12 nm and 10 nm diameter, contained ∼ 43% free cholesterol, 2-3% cholesteryl ester, and three apoA-I molecules. Using chemical cross-linking chemistry combined with mass spectrometry, we found that three molecules of apoA-I in the ∼ 9-14 nm nHDL adopted a belt-like conformation. The smaller (7.5 nm diameter) spheroidal nHDL particles carried 30% free cholesterol and two molecules of apoA-I in a twisted, antiparallel, double-belt conformation. Overall, these new data offer fresh insights into the biogenesis and structural constraints involved in forming nascent HDL from ABCA1.
authors: Department of Pathology, Section on Lipid Sciences, Wake Forest Baptist Medical Center, Winston-Salem, NC 27157, USA. msthomas@wakehealth.edu
authors: Mary G
authors: MG
authors: Sorci-Thomas
authors: John S
authors: JS
authors: Owen
authors: Brian
authors: B
authors: Fulp
authors: Shaila
authors: S
authors: Bhat
authors: Xuewei
authors: X
authors: Zhu
authors: John S
authors: JS
authors: Parks
authors: Dharika
authors: D
authors: Shah
authors: W Gray
authors: WG
authors: Jerome
authors: Mark
authors: M
authors: Gerelus
authors: Manal
authors: M
authors: Zabalawi
authors: Michael J
authors: MJ
authors: Thomas
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000378:metabolism*; D001692:Biological Transport; D002518:Ceramides / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008075:Lipoproteins, HDL / Q000096:biosynthesis* / Q000737:chemistry* / Q000302:isolation & purification; D021962:Membrane Microdomains / Q000378:metabolism*; D011487:Protein Conformation; D013109:Sphingomyelins / Q000378:metabolism
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D002518:Ceramides; D005227:Fatty Acids; D008075:Lipoproteins, HDL; D013109:Sphingomyelins; D002784:Cholesterol