The role of hydrophobic and negatively charged surface patches of lipid-free apolipoprotein A-I in lipid binding and ABCA1-mediated cholesterol efflux.
Recent models of lipid-free apolipoprotein A-I, including a cross-link/homology model and an X-ray crystal structure have identified two potential functionally relevant "patches" on the protein surface. The first is a hydrophobic surface patch composed of leucine residues 42, 44, 46, and 47 and the second a negatively charged patch composed of glutamic acid residues 179, 191, and 198. To determine if these domains play a functional role, these surface patches were disrupted by site-directed mutagenesis and the bacterially expressed mutants were compared with respect to their ability to bind lipid and stimulate ABCA1-mediated cholesterol efflux. It was found that neither patch plays a significant functional role in the ability of apoA-I to accept cholesterol in an ABCA1-dependent manner, but that the hydrophobic patch did affect the ability of apoA-I to clear DMPC liposomes. Interestingly, contrary to previous predictions, disruption of the hydrophobic surface patch enhanced the lipid binding ability of apoA-I. The hydrophobic surface patch may be important to the structural stability of lipid-free apoA-I or may be a necessary permissive structural element for lipid binding.
Department of Pathology and Laboratory Medicine, University of Cincinnati, 2120 East Galbraith Road, Cincinnati, OH 45237-0507, USA.
Loren E
LE
Smith
W Sean
WS
Davidson
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D002784:Cholesterol / Q000378:metabolism*; D018360:Crystallography, X-Ray; D057927:Hydrophobic and Hydrophilic Interactions; D050356:Lipid Metabolism; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D013329:Structure-Activity Relationship
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D002784:Cholesterol