title: Minimal lipidation of pre-beta HDL by ABCA1 results in reduced ability to interact with ABCA1.
abstract: OBJECTIVE
  The aim of this study was to determine the role of ATP binding cassette transporter A1 (ABCA1) on generation of different-sized nascent HDLs.
  
  
  RESULTS
  HEK293 cells stably-transfected with ABCA1 (HEK293-ABCA1) or non-transfected (control) cells were incubated with lipid free 125I-apoA-I for 24 hours. Incubation of apoA-I with HEK293-ABCA1 cells, but not control cells, led to the formation of heterogeneous-sized, pre-beta migrating nascent HDL subpopulations (pre-beta1 to -4) that varied in size (7.1 to 15.7 nm), lipid, and apoA-I content. Kinetic studies suggested that all subpopulations were formed simultaneously, with no evidence for a precursor-product relationship between smaller and larger-sized particles. When isolated nascent pre-beta HDLs (pre-beta1 to -4) were added back to HEK293-ABCA1 cells, their ability to bind to ABCA1 and efflux lipid was severely compromised. Heat-denaturation of pre-beta1 HDL resulted in partial recovery of ABCA1 binding, suggesting that initial interaction of apoA-I with ABCA1 results in a constrained conformation of apoA-I that decreases subsequent binding.
  
  
  CONCLUSIONS
  Interaction of apoA-I with ABCA1 results in the simultaneous generation of pre-beta HDLs of discrete size and chemical composition. These nascent particles are poor substrates for subsequent lipidation by ABCA1 and presumably require additional non-ABCA1-mediated lipidation for further maturation.
authors.affiliation: Department of Pathology/Section on Lipid Sciences, Wake Forest University Health Sciences, Medical Center Blvd., Winston-Salem, NC 27157-1040, USA.
authors.forename: Anny
authors.initials: A
authors.lastname: Mulya
authors.forename: Ji-Young
authors.initials: JY
authors.lastname: Lee
authors.forename: Abraham K
authors.initials: AK
authors.lastname: Gebre
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Thomas
authors.forename: Perry L
authors.initials: PL
authors.lastname: Colvin
authors.forename: John S
authors.initials: JS
authors.lastname: Parks
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000494:pharmacology*; D050197:Atherosclerosis / Q000503:physiopathology; D001667:Binding, Competitive; D002478:Cells, Cultured; D053480:Cholesterol Ester Transfer Proteins; D003470:Culture Media; D053442:High-Density Lipoproteins, Pre-beta / Q000378:metabolism*; D006801:Humans; D008075:Lipoproteins, HDL / Q000096:biosynthesis*; D011336:Probability; D012680:Sensitivity and Specificity; D014162:Transfection
chemical_list: D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D053480:Cholesterol Ester Transfer Proteins; D003470:Culture Media; D053442:High-Density Lipoproteins, Pre-beta; D008075:Lipoproteins, HDL