Binding of high density lipoprotein (HDL) and discoidal reconstituted HDL to the HDL receptor scavenger receptor class B type I. Effect of lipid association and APOA-I mutations on receptor binding.
The binding of apoA-I-containing ligands to the HDL receptor scavenger receptor class B type I (SR-BI) was characterized using two different assays. The first employed conventional binding or competition assays with (125)I-labeled ligands. The second is a new nonradioactive ligand binding assay, in which the receptor-associated ligand is detected by quantitative immunoblotting ("immunoreceptor assay"). Using both methods, we observed that the K(d) value for spherical HDL (density = 1.1-1.13 g/ml) was approximately 16 microgram of protein/ml, while the values for discoidal reconstituted HDL (rHDL) containing proapoA-I or plasma apoA-I were substantially lower (approximately 0.4-5 microgram of protein/ml). We also observed reduced affinity and/or competition for spherical (125)I-HDL cell association by higher relative to lower density HDL and very poor competition by lipid-free apoA-I and pre-beta-1 HDL. Deletion of either 58 carboxyl-terminal or 59 amino-terminal residues from apoA-I, relative to full-length control apoA-I, resulted in little or no change in the affinity of corresponding rHDL particles. However, rHDL particles containing a double mutant lacking both terminal domains competed poorly with spherical (125)I-HDL for binding to SR-BI. These findings suggest an important role for apoA-I and its conformation/organization within particles in mediating HDL binding to SR-BI and indicate that the NH(2) and COOH termini of apoA-I directly or indirectly contribute independently to binding to SR-BI.
Liadaki
K N
KN
University of Crete, Department of Biochemistry and Institute of Molecular Biology and Biotechnology, Heraklion, Crete, Greece 71110.
Liu
T
T
Xu
S
S
Ishida
B Y
BY
Duchateaux
P N
PN
Krieger
J P
JP
Kane
J
J
Krieger
M
M
Zannis
V I
VI
D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D018955:CD36 Antigens / Q000737:chemistry / Q000378:metabolism*; D005091:Exons; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D008024:Ligands; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008565:Membrane Proteins; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011869:Radioligand Assay; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein / Q000378:metabolism; D051116:Receptors, Scavenger; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D051122:Scavenger Receptors, Class B; D017384:Sequence Deletion; D014162:Transfection; D014407:Tumor Cells, Cultured
D016632:Apolipoprotein A-I; D018955:CD36 Antigens; D007457:Iodine Radioisotopes; D008024:Ligands; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D011994:Recombinant Proteins; C495124:SCARB1 protein, human; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B