Comparison of the stabilities and unfolding pathways of human apolipoprotein E isoforms by differential scanning calorimetry and circular dichroism
Comparison of the stabilities and unfolding pathways of human apolipoprotein E isoforms by differential scanning calorimetry and circular dichroism
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DOI：
10.1016/s1388-1981(02)00263-9
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发表时间：
2002-09-05
影响因子：
4.8
通讯作者：
Snow, J
中科院分区：
文献类型：
--
作者：
Acharya, P;Segall, ML;Snow, J
用差示扫描量热法和圆二色谱实验研究了人载脂蛋白E的常见亚型(apo2、apoE3和apoE4)及其N端22 kDa片段之间的结构差异。在这里，我们检查了表征异构体之间结构差异的热力学性质，以及它们展开行为的差异。22-kDa片段和它们的全长对应片段在热稳定性方面表现出类似的差异(apoE4<；apoE3<；APOE2；T-max分别接近52<；56<；59℃)。22-kDa apoE3在变性开始和变性完成时(量热法监测)的螺旋含量分别约为51%和35%。高达70%的22-kDa apoE3的展开热可能是由于a-螺旋的破坏。单体22-kDa片段以不同的方式展开，apoE3和apoE4都表现出展开的中间产物，而APOE2则按照两态机制展开。与C-末端结构域的相互作用似乎破坏了全长APOE2和apoE3的N-末端结构域的稳定性，但对全长apoE4的影响较小。较高浓度(1.5-2.5 mg/ml)的全长载脂蛋白E的自结合，以及全长载脂蛋白E与磷脂的相互作用，提高了热稳定性。圆二色谱监测到，全长apoE3和apoE4的二级结构协同变化开始于37℃左右，这表明全长apoE3和apoE4，而不是APOE2，可能在体内部分展开。这种稳定性和去折叠行为的差异可能是载脂蛋白E基因多态性导致脂质转运和神经功能缺陷的分子基础。(C)2002 Elsevier Science B.V.保留所有权利。
Differential scanning calorimetry and circular dichroism experiments were performed to study structural differences among the common isoforms of human apolipoprotein E (apoE2, apoE3, and apoE4) and their N-terminal, 22-kDa fragments. Here, we examine thermodynamic properties that characterize the structural differences among isoforms, and also differences in their unfolding behavior The 22-kDa fragments and their full-length counterparts were found to exhibit similar differences in thermal stability (apoE4 < apoE3 < apoE2; T-max approximate to 52 < 56 < 59 degreesC, respectively). Helical contents at the onset and completion of denaturation (as monitored calorimetrically) were about 51% and 35%, respectively, for 22-kDa apoE3. As much as 70% of the unfolding enthalpy for 22-kDa apoE3 could be due to disruption of a-helix. The monomeric 22-kDa fragments unfold differently, with both apoE3 and apoE4 exhibiting unfolding intermediates, whereas apoE2 unfolds according to a two-state mechanism. Interactions with the C-terminal domain appear to destabilize the N-terminal domains in full-length apoE2 and apoE3, but less so for full-length apoE4. Self-association of full-length apoE at higher concentrations (1.5-2.5 mg/ml), as well as interaction of full-length apoE with phospholipid, enhances thermal stability. Cooperative changes in secondary structure, as monitored by circular dichroism, begin near 37 degreesC for full-length apoE3 and apoE4, indicating that full-length apoE3 and apoE4, but not apoE2, may be partially unfolded in vivo. The differences in stability and unfolding behavior are likely to contribute to the molecular basis for defects in lipid transport and neurological function induced by apoE polymorphism. (C) 2002 Elsevier Science B.V. All rights reserved.