Highly purified scavenger receptor class B, type I reconstituted into phosphatidylcholine/cholesterol liposomes mediates high affinity high density lipoprotein binding and selective lipid uptake.
The murine class B, type I scavenger receptor mSR-BI is a high and low density lipoprotein (HDL and LDL) receptor that mediates selective uptake of cholesteryl esters. Here we describe a reconstituted phospholipid/cholesterol liposome assay of the binding and selective uptake activities of SR-BI derived from detergent-solubilized cells. The assay, employing lysates from epitope-tagged receptor (mSR-BI-t1)-expressing mammalian and insect cells, recapitulated many features of SR-BI activity in intact cells, including high affinity and saturable (125)I-HDL binding, selective lipid uptake from [(3)H]cholesteryl ether-labeled HDL, and poor inhibition of HDL receptor activity by LDL. The novel properties of a mutated receptor (Q402R/Q418R, normal LDL binding but loss of most HDL binding) were reproduced in the assay, as was the ability of the SR-BI homologue CD36 to bind HDL but not mediate efficient lipid uptake. In this assay, essentially homogeneously pure mSR-BI-t1, prepared by single-step immunoaffinity chromatography, mediated high affinity HDL binding and efficient selective lipid uptake from HDL. Thus, SR-BI-mediated HDL binding and selective lipid uptake are intrinsic properties of the receptor that do not require the intervention of other proteins or specific cellular structures or compartments.
Liu
Bin
B
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Krieger
Monty
M
D000818:Animals; D018955:CD36 Antigens / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D019556:COS Cells; D002784:Cholesterol / Q000378:metabolism; D002846:Chromatography, Affinity; D006801:Humans; D050356:Lipid Metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism*; D008565:Membrane Proteins; D010713:Phosphatidylcholines / Q000378:metabolism; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D018411:Spodoptera; D014162:Transfection
D018955:CD36 Antigens; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D008081:Liposomes; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C495124:SCARB1 protein, human; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D002784:Cholesterol