Marcel Y L, Innerarity T L, Spilman C, Mahley R W, Protter A A, Milne R W
Arteriosclerosis. 1987 Mar-Apr;7(2):166-75. doi: 10.1161/01.atv.7.2.166.
A minimum of 16 epitopes which provide a group of topographical markers to study the conformation of apolipoprotein (apo) B have been mapped in relation to elements of the sequence of apo B-100. Six of these epitopes are identified by monoclonal antibodies (Mabs) directed against low density lipoprotein (LDL) apo B, while at least 10 others react with Mabs obtained by immunization with delipidated and solubilized apo B. Five epitopes which are also expressed on apo B-48 have been assigned to the thrombolytic fragment T4 on the N-terminal side of apo B-100. None of these five epitopes requires the presence of lipids for its expression, suggesting that the conformation of the T4 region of apo B is more dependent on peptide-chain interactions than on peptide-lipid interactions. Four distinct epitopes have been assigned to the median thrombolytic fragment T3 of apo B-100, all of which require the presence of lipids for their expression; those epitopes closer to the C-terminus of T3 require specific interaction with cholesteryl esters. The same lipid dependence also characterizes a cluster of epitopes mapped to the N-terminal region of fragment T2. The epitopes that are close to the T2/T3 cleavage site and depend on the presence of cholesteryl esters for their expression are also those that react with the Mabs that inhibit the binding of LDL to its receptor. Therefore this region, which in addition contains two sequences with structural homology to the apo E receptor binding domain, probably constitutes a physiologically important receptor binding site for apo B. Finally, four other distinct epitopes which do not require the presence of lipids for their expression have been mapped on T2. In conclusion, the present report presents evidence that the immunochemical analogy of apo B-48 and apo B-100 is on the N-terminal half of apo B-100, whereas the apo B receptor binding domain is localized on the C-terminal half of apo B-100 close to the T2/T3 cleavage site.
为研究载脂蛋白（apo）B的构象，已绘制了至少16个表位，这些表位提供了一组拓扑标记，与apo B - 100的序列元件相关。其中6个表位由针对低密度脂蛋白（LDL）apo B的单克隆抗体（Mabs）鉴定，而至少还有10个表位与通过用脱脂和溶解的apo B免疫获得的Mabs反应。在apo B - 100 N端一侧的溶栓片段T4上已确定了5个也在apo B - 48上表达的表位。这5个表位中没有一个表位的表达需要脂质的存在，这表明apo B的T4区域的构象更多地依赖于肽链相互作用而非肽 - 脂质相互作用。已将4个不同的表位指定给apo B - 100的中间溶栓片段T3，所有这些表位的表达都需要脂质的存在；那些更靠近T3 C端的表位需要与胆固醇酯进行特异性相互作用。相同的脂质依赖性也表征了映射到片段T2 N端区域的一组表位。靠近T2/T3切割位点且其表达依赖于胆固醇酯存在的表位也是那些与抑制LDL与其受体结合的Mabs反应的表位。因此，该区域除了包含两个与apo E受体结合域具有结构同源性的序列外，可能构成apo B在生理上重要的受体结合位点。最后，在T2上已绘制了另外4个其表达不需要脂质存在的不同表位。总之，本报告提供了证据表明apo B - 48和apo B - 100的免疫化学相似性在apo B - 100的N端一半，而apo B受体结合域位于apo B - 100靠近T2/T3切割位点的C端一半。
