Gunzburg Menachem J, Perugini Matthew A, Howlett Geoffrey J
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
J Biol Chem. 2007 Dec 7;282(49):35831-41. doi: 10.1074/jbc.M706425200. Epub 2007 Oct 4.
Apolipoprotein (apo) E is a well characterized lipid-binding protein in plasma that also exists as a common nonfibrillar component of both cerebral and systemic amyloid deposits. A genetic link between a common isoform of apoE, apoE4, and the incidence of late onset Alzheimer disease has drawn considerable attention to the potential roles of apoE in amyloid-related disease. We examined the interactions of apoE with amyloid fibrils composed of apoC-II and the amyloid-beta (Abeta) peptide. Aggregates of apoE with Abeta and apoC-II are found in Alzheimer and atherosclerotic plaques, respectively. Sedimentation velocity and fibril size distribution analysis showed that apoE3 and E4 isoforms bind and noncovalently cross-link apoC-II fibrils in a similar manner. This ability to cross-link apoC-II fibrils was abolished by the dissociation of the apoE tetramer to monomers or by thrombin cleavage to yield separate N- and C-terminal domains. Preparative ultracentrifuge binding studies indicated that apoE and the isolated N- and C-terminal domains of apoE bind with submicromolar affinities to both apoC-II and Abeta fibrils. Fluorescence quenching and resonance energy transfer experiments confirmed that both domains of apoE interact with apoC-II fibrils and demonstrated that the binding of the isolated N-terminal domain of apoE to apoC-II or Abeta fibrils is accompanied by a significant conformational change with helix three of the domain moving relative to helix one. We propose a model involving the interaction of apoE with patterns of aligned residues that could explain the general ability of apoE to bind to a diverse range of amyloid fibrils.
载脂蛋白（apo）E是血浆中一种特征明确的脂质结合蛋白，同时也是脑和全身淀粉样沉积物常见的非纤维成分。apoE的一种常见异构体apoE4与晚发型阿尔茨海默病的发病率之间的遗传联系，引起了人们对apoE在淀粉样相关疾病中潜在作用的极大关注。我们研究了apoE与由apoC-II和β淀粉样蛋白（Aβ）肽组成的淀粉样纤维的相互作用。分别在阿尔茨海默病斑块和动脉粥样硬化斑块中发现了apoE与Aβ和apoC-II的聚集体。沉降速度和纤维大小分布分析表明，apoE3和E4异构体以相似的方式结合并非共价交联apoC-II纤维。apoE四聚体解离为单体或经凝血酶切割产生单独的N端和C端结构域后，这种交联apoC-II纤维的能力就消失了。制备型超速离心结合研究表明，apoE及其分离的N端和C端结构域以亚微摩尔亲和力与apoC-II和Aβ纤维结合。荧光猝灭和共振能量转移实验证实，apoE的两个结构域均与apoC-II纤维相互作用，并表明apoE分离的N端结构域与apoC-II或Aβ纤维的结合伴随着显著的构象变化，该结构域的螺旋3相对于螺旋1移动。我们提出了一个涉及apoE与排列残基模式相互作用的模型，该模型可以解释apoE结合多种淀粉样纤维的一般能力。
