Purification and characterization of two high-density-lipoprotein-binding proteins from rat and human liver.
The liver plays a major role in the metabolism of plasma high-density lipoprotein (HDL). Several groups have postulated, but others refuted, the existence of a classical membrane receptor which recognizes HDL. In the present study, we identified and purified two liver HDL-binding proteins of 120 kDa (HB1) and 100 kDa (HB2), with apparent specificity for HDL3 devoid of E apolipoprotein. The plasma membrane was the richest source of the HDL-binding protein. Both proteins bound A-I and A-II apolipoproteins and retained HDL-binding activity after final purification. HB1 activity, but not that of HB2, was lost after treatment with beta-mercaptoethanol, but reduction did not change the apparent molecular mass of either protein. Antibodies against HB1 or HB2 did not cross-react, and preliminary structural investigations provide evidence to suggest that HB1 and HB2 are not structurally related. We thus provide evidence for at least two liver plasma-membrane proteins which bind HDL apolipoproteins, suggesting that protein-protein interaction participates to some degree in the mechanism of HDL recognition by cells.
Tozuka
M
M
Baker Medical Research Institute, Prahran, Melbourne, Victoria, Australia.
Fidge
N
N
D000818:Animals; D002352:Carrier Proteins; D002462:Cell Membrane / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008075:Lipoproteins, HDL / Q000378:metabolism*; D053440:Lipoproteins, HDL3; D008099:Liver / Q000032:analysis* / Q000648:ultrastructure; D016601:RNA-Binding Proteins; D051381:Rats; D011956:Receptors, Cell Surface / Q000302:isolation & purification*; D018110:Receptors, Lipoprotein
D002352:Carrier Proteins; D008075:Lipoproteins, HDL; D053440:Lipoproteins, HDL3; D016601:RNA-Binding Proteins; D011956:Receptors, Cell Surface; D018110:Receptors, Lipoprotein; C031616:high density lipoprotein receptors; C075197:high density lipoprotein binding protein