Apolipoprotein E4 exhibits intermediates with domain interaction
Apolipoprotein E4 exhibits intermediates with domain interaction
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DOI：
10.1016/j.bbapap.2020.140535
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发表时间：
2020-12-01
影响因子：
3.2
通讯作者：
Garai, Kanchan
中科院分区：
文献类型：
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作者：
Dolai, Subhrajyoti;Cherakara, Sreelakshmi;Garai, Kanchan
ApoE4(C112R) 是阿尔茨海默氏病最强的危险因素，而 apoE3(C112) 被认为是正常的。 C112R 取代被认为会改变 N 端 (NTD) 和 C 端结构域 (CTD) 之间的相互作用，从而导致主要的功能差异。在这里，我们使用精氨酸、丙氨酸、苏氨酸、缬氨酸、亮氨酸和异亮氨酸作为“X”的一系列 C112X 取代来研究 112 位残基的分子特性如何影响结构域相互作用。我们尝试根据全长 apoE 中 NTD (Delta G(NTD)) 和 CTD (Delta G(CTD)) 的稳定性以及 NTD (Delta G(NTF)) 和 CTD (Delta G(CTF)) 片段的稳定性，使用以下关系来确定域相互作用的自由能 (Delta G(INT))：Delta G(INT) = Delta G(NTD) + Delta G(CTD) - Delta G(NTF) )- 德尔塔 G(CTF)。我们发现，尽管 Delta G(NTD) 强烈依赖于 C112X 替代，但 Delta G(NTD) - Delta G(NTF) 很小。此外，Delta G(CTD) 几乎与 Delta G(CTF) 相同。因此，对于 apoE 同工型，Delta G(INT) 估计较小且相似。然而，通过域间福斯特共振能量转移 (FRET) 中尿素依赖性变化监测的域相互作用的稳定性被发现强烈依赖于 C112X 取代。 ApoE4 表现出域间 FRET 变性的最高中点。为了解决明显矛盾的观察结果，我们假设尿素中 apoE4 的较高域间 FRET 可能涉及“中间”状态。 bis-ANS 增强的荧光和对蛋白水解裂解的敏感性支持 apoE4，特别是 apoE4 的 NTD 在天然和轻度变性条件下均具有“中间体”。这些中间体可能是 apoE4 病理功能的关键。
ApoE4(C112R) is the strongest risk factor for Alzheimer's disease, while apoE3(C112) is considered normal. The C112R substitution is believed to alter the interactions between the N-terminal (NTD) and the C-terminal domain (CTD) leading to major functional differences. Here we investigate how the molecular property of the residue at position 112 affects domain interaction using an array of C112X substitutions with arginine, alanine, threonine, valine, leucine and isoleucine as 'X'. We attempt to determine the free energy of domain interaction (Delta G(INT)) from stabilities of the NTD (Delta G(NTD)) and CTD (Delta G(CTD)) in the full-length apoE, and the stabilities of fragments of the NTD (Delta G(NTF)) and CTD (Delta G(CTF)), using the relationship, Delta G(INT) = Delta G(NTD) + Delta G(CTD) - Delta G(NTF )- Delta G(CTF). We find that although Delta G(NTD) is strongly dependent on the C112X substitutions, Delta G(NTD) - Delta G(NTF) is small. Furthermore, Delta G(CTD) remains nearly the same as Delta G(CTF). Therefore, Delta G(INT) is estimated to be small and similar for the apoE isoforms. However, stability of domain interaction monitored by urea dependent changes in interdomain Forster Resonance Energy Transfer (FRET) is found to be strongly dependent on C112X substitutions. ApoE4 exhibits the highest mid-point of denaturation of interdomain FRET. To resolve the apparently contradictory observations, we hypothesize that higher interdomain FRET in apoE4 in urea may involve 'intermediate' states. Enhanced fluorescence of bis-ANS and susceptibility to proteolytic cleavage support that apoE4, specifically, the NTD of apoE4 harbor 'intermediates' in both native and mildly denaturing conditions. The intermediates could hold key to the pathological functions of apoE4.