Allan C M, Fidge N H, Kanellos J
Protein Chemistry and Molecular Biology Unit, Baker Medical Research Institute, Victoria, Prahran, Australia.
J Biol Chem. 1992 Jul 5;267(19):13257-61.
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.
我们使用针对人载脂蛋白A-I羧基末端区域两个位点的抗肽抗体，研究了125I标记的高密度脂蛋白（HDL3）与肝细胞膜的结合情况，肝细胞膜被认为含有特定的HDL受体位点。分别针对对应于氨基酸残基205 - 220和230 - 243的肽产生的两种不同抗体群体，识别出在HDL3脂质环境中暴露的载脂蛋白A-I区域。然而，抗AI[230 - 243] IgG识别HDL2，而抗AI[205 - 220] IgG不识别，这表明载脂蛋白A-I的205 - 220残基在两种HDL群体中的表达不同。此外，抗AI[230 - 243] IgG对载脂蛋白A-II表现出强烈的交叉反应性。表位作图研究表明，抗AI[230 - 243]与位于载脂蛋白A-II羧基末端的一个表位结合，证明了载脂蛋白A-II羧基末端区域与载脂蛋白A-I和A-II羧基末端区域之间存在显著的结构同源性，这两种蛋白是介导HDL3特异性细胞相互作用的候选蛋白。抗AI[205 - 220]和抗AI[230 - 243]的Fab片段分别抑制125I - HDL3与肝细胞膜的结合约80%和60%。这些发现与我们最近使用载脂蛋白A-I的分离溴化氰片段的研究结果一致（莫里森，J.，菲奇，N. H.，和户冢，M.（1991年）《生物化学杂志》266，18780 - 18785），该研究表明载脂蛋白A-I的羧基末端区域含有一个结合结构域，可能通过特定HDL受体的参与介导HDL3与肝细胞膜的特异性相互作用。
