Antibodies to the carboxyl terminus of human apolipoprotein A-I. The putative cellular binding domain of high density lipoprotein 3 and carboxyl-terminal structural homology between apolipoproteins A-I and A-II.
We have studied the binding of 125I-labeled high density lipoproteins (HDL3) to liver plasma membranes, which are thought to contain specific HDL receptor sites, using anti-peptide antibodies directed against two sites in the carboxyl-terminal region of human apoA-I. Two distinct antibody populations raised to peptides corresponding to amino acid residues 205-220 and 230-243, respectively, recognized regions of apoA-I that are exposed in the lipid environment of HDL3. However, anti-AI[230-243] IgG, but not anti-AI[205-220] IgG, recognized HDL2, suggesting that residues 205-220 of apoA-I are expressed differently in the two HDL populations. In addition, anti-AI[230-243] IgG showed strong cross-reactivity toward apoA-II. Epitope mapping studies showed that anti-AI[230-243] binds to an epitope located in the carboxyl-terminus of apoA-II, demonstrating significant structural homology between the carboxyl-terminal of apoA-II, demonstrating significant structural homology between the carboxyl-terminal regions of apoA-I and A-II, two candidate proteins for mediating the specific cellular interaction of HDL3. Fab fragments from anti-AI[205-220] and anti-AI[230-243] inhibited the binding of 125I-HDL3 to liver plasma membranes by approximately 80% and 60%, respectively. These findings are in agreement with our recent work using isolated CNBr fragments of apoA-I (Morrison, J., Fidge, N. H., and Tozuka, M. (1991) J. Biol. Chem. 266, 18780-18785), which suggest that the carboxyl-terminal region of apoA-I contains a binding domain which mediates the specific interaction of HDL3 with liver plasma membranes, possibly through the involvement of specific HDL receptors.
Allan
C M
CM
Protein Chemistry and Molecular Biology Unit, Baker Medical Research Institute, Victoria, Prahran, Australia.
Fidge
N H
NH
Kanellos
J
J
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology*; D000918:Antibody Specificity; D016632:Apolipoprotein A-I / Q000737:chemistry / Q000276:immunology*; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D000939:Epitopes / Q000276:immunology; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007457:Iodine Radioisotopes; D008075:Lipoproteins, HDL / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D051381:Rats
D000906:Antibodies; D016632:Apolipoprotein A-I; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments; D007457:Iodine Radioisotopes; D008075:Lipoproteins, HDL