Chauhan V, Wang X, Ramsamy T, Milne R W, Sparks D L
Lipoprotein and Atherosclerosis Group, University of Ottawa Heart Institute, Ontario, Canada.
Biochemistry. 1998 Mar 17;37(11):3735-42. doi: 10.1021/bi9718853.
The structural organization and stability of apoB100 in complexes containing triglyceride (TG) and phospholipid have been examined. LDL was delipidated to form aqueous soluble apoB100-TG complexes that retain approximately 70% of LDL TG, but contain no other lipids. The apoB100-TG complexes exhibited reduced amphipathic alpha-helical content (17%) and net negative charge (-2.9 mV) as compared to native LDL-apoB100 (49% and -6 mV, respectively). Of 28 anti-apoB monoclonal antibodies tested, 15 showed partial or full reactivity with apoB100-TG. The immunoreactive epitopes of apoB100-TG were restricted to those situated in either the amino terminal globular domain (4 of 6) or in regions of apoB100 that are predicted to be composed of amphipathic beta-strands (11 of 13). Incubation of the apoB100-TG complex with palmitoyloleoylphosphatidylcholine (POPC) spontaneously (< 10 min) formed homogeneous lipoproteins (20 nm) that contained approximately 300 molecules of POPC per particle (apoB100-PC). Phospholipidation of apoB100-TG complexes partially recovered the alpha-helical content (34%) and net negative charge (-4.9 mV) of the native LDL and restored resistance of apoB100 to denaturation by guanidine HCl (5.8 M). Addition of phospholipids to apoB100-TG also increased the immunoreactivity of specific epitopes that are located primarily in regions of apoB100 that are thought to be constituted of amphipathic beta-strands. The effects of TG and phospholipid on apoB100 conformation appear to be highly domain-specific. On the basis of these results, we propose that the beta-strands of apoB100 may represent a nonflexible lipid-associating backbone, while the amphipathic alpha-helical domains may represent flexible lipid-binding regions that allow the particle to accommodate varying amounts of lipid.
已对载脂蛋白B100（apoB100）在含有甘油三酯（TG）和磷脂的复合物中的结构组织和稳定性进行了研究。低密度脂蛋白（LDL）脱脂后形成水溶性的apoB100 - TG复合物，这些复合物保留了约70%的LDL甘油三酯，但不含其他脂质。与天然LDL - apoB100相比（分别为49%和 - 6 mV），apoB100 - TG复合物的两亲性α - 螺旋含量降低（17%），净负电荷减少（ - 2.9 mV）。在测试的28种抗apoB单克隆抗体中，15种与apoB100 - TG表现出部分或完全反应性。apoB100 - TG的免疫反应性表位局限于位于氨基末端球状结构域的表位（6个中的4个）或apoB100中预计由两亲性β - 链组成的区域（13个中的11个）。将apoB100 - TG复合物与棕榈酰油酰磷脂酰胆碱（POPC）孵育会自发地（<10分钟）形成均匀的脂蛋白（20纳米），每个颗粒（apoB100 - PC）含有约300个POPC分子。apoB100 - TG复合物的磷脂化部分恢复了天然LDL的α - 螺旋含量（34%）和净负电荷（ - 4.9 mV），并恢复了apoB100对盐酸胍（5.8 M）变性的抗性。向apoB100 - TG中添加磷脂也增加了主要位于apoB100中被认为由两亲性β - 链构成区域的特定表位的免疫反应性。TG和磷脂对apoB100构象的影响似乎具有高度的结构域特异性。基于这些结果，我们提出apoB100的β - 链可能代表一个非柔性的脂质结合骨架，而两亲性α - 螺旋结构域可能代表柔性的脂质结合区域，使颗粒能够容纳不同量的脂质。
