An amphipathic helical region of the N-terminal barrel of phospholipid transfer protein is critical for ABCA1-dependent cholesterol efflux.
Phospholipid lipid transfer protein (PLTP) mimics high-density lipoprotein apolipoproteins in removing cholesterol and phospholipids from cells through the ATP-binding cassette transporter A1 (ABCA1). Because amphipathic alpha-helices are the structural determinants for ABCA1 interactions, we examined the ability of synthetic peptides corresponding to helices in PLTP to remove cellular cholesterol by the ABCA1 pathway. Of the seven helices tested, only one containing PLTP residues 144-163 (p144), located at the tip of the N-terminal barrel, promoted ABCA1-dependent cholesterol efflux and stabilized ABCA1 protein. Mutating methionine 159 (Met-159) in this helix in PLTP to aspartate (M159D) or glutamate (M159E) nearly abolished the ability of PLTP to remove cellular cholesterol and dramatically reduced PLTP binding to phospholipid vesicles and its phospholipid transfer activity. These mutations impaired PLTP binding to ABCA1-generated lipid domains and PLTP-mediated stabilization of ABCA1 but increased PLTP binding to ABCA1. PLTP interactions with ABCA1 also mimicked apolipoproteins in activating Janus kinase 2; however, the M159D/E mutants were also able to activate this kinase. Structural analyses showed that the M159D/E mutations had only minor effects on PLTP conformation. These findings indicate that PLTP helix 144-163 is critical for removing lipid domains formed by ABCA1, stabilizing ABCA1 protein, interacting with phospholipids, and promoting phospholipid transfer. Direct interactions with ABCA1 and activation of signaling pathways likely involve other structural determinants of PLTP.
Oram
John F
JF
Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, Box 356426, University of Washington, Seattle, Washington 98195, USA. joram@u.washington.edu
Wolfbauer
Gertrud
G
Tang
Chongren
C
Davidson
W Sean
WS
Albers
John J
JJ
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism; D008055:Lipids / Q000737:chemistry; D008074:Lipoproteins / Q000737:chemistry; D008954:Models, Biological; D009154:Mutation; D049294:Phospholipid Transfer Proteins / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015398:Signal Transduction
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D008055:Lipids; D008074:Lipoproteins; D049294:Phospholipid Transfer Proteins; D053614:Janus Kinase 2