Hui D Y, Innerarity T L, Mahley R W
J Biol Chem. 1984 Jan 25;259(2):860-9.
Apolipoprotein (apo-) E2 and beta-migrating very low density lipoproteins (beta-VLDL) (which were isolated from type III hyperlipoproteinemic subjects) both demonstrated defective binding to apo-E and apo-B,E receptors on dog liver membranes and to apo-B,E low density lipoproteins (LDL) receptors on fibroblasts. The defective binding activity of the apo-E2 and beta-VLDL varied from very poor to nearly normal. The ability of the beta-VLDL to interact with hepatic apo-E receptors was enhanced by the addition of normal apo-E3 to the beta-VLDL. Furthermore, cysteamine treatment of the apo-E2 in beta-VLDL enhanced binding of the beta-VLDL to both apo-E and apo-B,E receptors. The importance of apo-E in mediating the receptor binding of beta-VLDL to these receptors was confirmed by using monoclonal antibodies. The residual binding activity of beta-VLDL to apo-E and apo-B,E receptors was inhibited by greater than 90% with anti-apo-E, while the addition of anti-apo-B had little effect. The apo-B in the beta-VLDL was capable of binding to apo-B,E receptors after the hydrolysis of the beta-VLDL triglycerides with milk lipoprotein lipase. Lipase treatment yielded, two subfractions of beta-VLDL. One fraction (d = 1.02 to 1.03 g/ml) was enriched with apo-B100; the other fraction (d less than 1.006 g/ml) was enriched with apo-B48 and apo-E2. Significantly increased amounts of the apo-B100-enriched fraction bound to apo-B,E receptors. Inhibition of this binding caused by the addition of anti-apo-B indicated that the binding activity of this subfraction was mediated by apo-B100. The apo-B48-enriched fraction did not show a significant increase in receptor binding, suggesting that apo-B48 does not bind to these receptors. In a control experiment, it was shown that triglyceride-rich VLDL, which contain normal apo-E3 and apo-B100, bind significantly to both liver apo-E receptors and fibroblast apo-B,E receptors. This binding activity was inhibited by greater than 90% with anti-apo-E. Lipase hydrolysis of the VLDL did not further enhance their receptor-binding activity. These results demonstrate that apo-E, and not apo-B, is the major determinant mediating the receptor-binding activity of cholesterol-rich beta-VLDL and triglyceride-rich VLDL.
载脂蛋白（apo-）E2和β-迁移极低密度脂蛋白（β-VLDL）（从III型高脂蛋白血症患者中分离得到）均表现出与犬肝细胞膜上的apo-E和apo-B、E受体以及成纤维细胞上的apo-B、E低密度脂蛋白（LDL）受体结合存在缺陷。apo-E2和β-VLDL的结合活性缺陷程度从极差到接近正常不等。向β-VLDL中添加正常的apo-E3可增强其与肝脏apo-E受体相互作用的能力。此外，对β-VLDL中的apo-E2进行半胱胺处理可增强β-VLDL与apo-E和apo-B、E受体的结合。使用单克隆抗体证实了apo-E在介导β-VLDL与这些受体的受体结合中的重要性。抗apo-E可使β-VLDL与apo-E和apo-B、E受体的残余结合活性受到大于90%的抑制，而添加抗apo-B的影响则很小。用乳脂蛋白脂肪酶水解β-VLDL中的甘油三酯后，其中的apo-B能够与apo-B、E受体结合。脂肪酶处理产生了β-VLDL的两个亚组分。一个组分（d = 1.02至1.03 g/ml）富含apo-B100；另一个组分（d小于1.006 g/ml）富含apo-B48和apo-E2。富含apo-B100的组分与apo-B、E受体结合的量显著增加。添加抗apo-B导致这种结合受到抑制，表明该亚组分的结合活性是由apo-B100介导的。富含apo-B48的组分在受体结合方面未显示出显著增加，这表明apo-B48不与这些受体结合。在对照实验中表明，富含甘油三酯的VLDL含有正常的apo-E3和apo-B100，它们与肝脏apo-E受体和成纤维细胞apo-B、E受体均有显著结合。抗apo-E可使这种结合活性受到大于90%的抑制。VLDL经脂肪酶水解后并未进一步增强其受体结合活性。这些结果表明，介导富含胆固醇的β-VLDL和富含甘油三酯的VLDL受体结合活性的主要决定因素是apo-E，而非apo-B。
