title: Identification of an apolipoprotein A-I structural element that mediates cellular cholesterol efflux and stabilizes ATP binding cassette transporter A1.
abstract: Synthetic peptides were used in this study to identify a structural element of apolipoprotein (apo) A-I that stimulates cellular cholesterol efflux and stabilizes the ATP binding cassette transporter A1 (ABCA1). Peptides (22-mers) based on helices 1 (amino acids 44-65) and 10 (amino acids 220-241) of apoA-I had high lipid binding affinity but failed to mediate ABCA1-dependent cholesterol efflux, and they lacked the ability to stabilize ABCA1. The addition of helix 9 (amino acids 209-219) to either helix 1 (creates a 1/9 chimera) or 10 (9/10 peptide) endowed cholesterol efflux capability and ABCA1 stabilization activity similar to full-length apoA-I. Adding helix 9 to helix 1 or 10 had only a small effect on lipid binding affinity compared with the 22-mer peptides, indicating that helix length and/or determinants on the polar surface of the amphipathic alpha-helices is important for cholesterol efflux. Cholesterol efflux was specific for the structure created by the 1/9 and 9/10 helical combinations, as 33-mers composed of helices 1 and 3 (1/3), 2/9, and 4/9 failed to mediate cholesterol efflux in an ABCA1-dependent manner. Transposing helices 9 and 10 (10/9 peptide) did not change the class Y structure, hydrophobicity, or amphiphilicity of the helical combination, but the topography of negatively charged amino acids on the polar surface was altered, and the 10/9 peptide neither mediated ABCA1-dependent cholesterol efflux nor stabilized ABCA1 protein. These results suggest that a specific structural element possessing a linear array of acidic residues spanning two apoA-I amphipathic alpha-helices is required to mediate cholesterol efflux and stabilize ABCA1.
authors.affiliation: Lawrence Berkeley National Laboratory, Donner Laboratory MS1-224, University of California at Berkeley, California 94720, USA.
authors.forename: Pradeep
authors.initials: P
authors.lastname: Natarajan
authors.forename: Trudy M
authors.initials: TM
authors.lastname: Forte
authors.forename: Berbie
authors.initials: B
authors.lastname: Chu
authors.forename: Michael C
authors.initials: MC
authors.lastname: Phillips
authors.forename: John F
authors.initials: JF
authors.lastname: Oram
authors.forename: John K
authors.initials: JK
authors.lastname: Bielicki
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism / Q000502:physiology*; D000255:Adenosine Triphosphate / Q000737:chemistry*; D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry*; D001692:Biological Transport; D002784:Cholesterol / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D051379:Mice; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D021381:Protein Transport; D013997:Time Factors
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D008055:Lipids; D010455:Peptides; D000255:Adenosine Triphosphate; D002784:Cholesterol