Reconstituted discoidal ApoE-phospholipid particles are ligands for the scavenger receptor BI. The amino-terminal 1-165 domain of ApoE suffices for receptor binding.
The high density lipoprotein receptor, scavenger receptor class B type I (SR-BI), recognizes lipid-bound apolipoprotein A-I (apoA-I) and other apolipoproteins. Here, we have used large scale cultures of apoE-expressing cells to purify apoE and prepare apoE containing reconstituted discoidal 1-palmitoyl-2-oleoyl-l-phosphatidylcholine (POPC)-apoE particles. These particles have been used to examine their binding to wild-type and mutant forms of SR-BI expressed in transfected ldlA-7 cells. Specific binding to SR-BI was determined by subtracting from the total binding, nonspecific values measured using either control untransfected ldlA-7 cells or by inhibiting SR-BI-mediated binding with a high titer antireceptor-blocking antibody. POPC-apoE particles generated using apoE2, apoE3, apoE4, or the carboxyl-terminally truncated forms apoE165, apoE202, apoE229, and apoE259 all bound tightly to wild-type SR-BI with similar affinities (K(d) = 35-45 microg/ml). Binding was nearly abolished in a cell line expressing the ldlA (Q402R/Q418R) double mutant form of SR-BI that is unable to bind native high density lipoprotein but binds low density lipoprotein normally. The findings establish that apoE is a ligand for SR-BI and that the receptor binding domain is located in the amino-terminal 1-165-region of the protein. SR-BI-apoE interactions may contribute to cholesterol homeostasis in tissues and cells expressing SR-BI that are accessible to apoE-containing lipoproteins.
Li
Xiaoping
X
Section of Molecular Genetics, Whitaker Cardiovascular Institute, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Kan
Horng-Yuan
HY
Lavrentiadou
Sophia
S
Krieger
Monty
M
Zannis
Vassilis
V
D000818:Animals; D001057:Apolipoproteins E / Q000737:chemistry* / Q000378:metabolism*; D001483:Base Sequence; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D018955:CD36 Antigens / Q000737:chemistry* / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D007700:Kinetics; D008024:Ligands; D015674:Mammary Neoplasms, Animal / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009154:Mutation; D010743:Phospholipids / Q000737:chemistry*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D014162:Transfection; D014407:Tumor Cells, Cultured
D001057:Apolipoproteins E; D018955:CD36 Antigens; D018076:DNA, Complementary; D008024:Ligands; D008565:Membrane Proteins; D010743:Phospholipids; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B