Molecular determinants and thermodynamics of the amyloid precursor protein transmembrane domain implicated in Alzheimer's disease.
Molecular determinants and thermodynamics of the amyloid precursor protein transmembrane domain implicated in Alzheimer's disease.
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DOI：
10.1016/j.jmb.2011.03.028
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发表时间：
2011-05-20
影响因子：
5.6
通讯作者：
Ubarretxena-Belandia I
中科院分区：
文献类型：
--
作者：
Wang H;Barreyro L;Provasi D;Djemil I;Torres-Arancivia C;Filizola M;Ubarretxena-Belandia I
毒性淀粉样蛋白-β肽（Aβ）聚集物在脑中的沉积是阿尔茨海默病的标志。淀粉样前体蛋白羧基端片段（APP-βCTF）的γ-分泌酶膜内蛋白水解是Aβs产生的最后一步。越来越多的证据表明，APP-βCTF是一种跨膜结构域（TMD）二聚体，二聚化可能调节易于聚集的Aβ物质的产生，因此毒性最大。我们结合实验和计算方法来研究APP-βCTF二聚化的分子决定因素和热力学，并产生了一个统一的结构模型，调和了许多已发表的数据。使用利用二聚化依赖性转录激活因子的细胞测定，我们鉴定了主要位于APP-βCTF的TMD的N-末端的特异性二聚化破坏突变。通过荧光共振能量转移实验证实了所选突变体破坏全长APP-βCTF二聚化的能力。通过增强的分子动力学模拟，对APP-βCTF的野生型（WT）和TMD突变体的自由能估计表明，二聚体状态由不同的排列组成，其中709 GXXXA 713或700 GXXXG 704 GXXXG 708相互作用基序可以参与对称或不对称缔合。发现APP-βCTF的TMD沿着突变可调节二聚体构型的相对自由能，并不同地影响二聚体状态内的界面分布。这一观察结果可能具有重要的生物学意义，因为具有不同排列的跨膜螺旋的二聚体可能被γ-分泌酶不同地识别，并导致Aβ水平的变化。
The deposition of toxic amyloid-β peptide (Aβ) aggregates in the brain is a hallmark of Alzheimer's disease. The intramembrane proteolysis by γ-secretase of the amyloid precursor protein carboxy-terminal fragment (APP-βCTF) constitutes the final step in the production of Aβs. Mounting evidence suggests that APP-βCTF is a transmembrane domain (TMD) dimer, and that dimerization might modulate the production of Aβ species that are prone to aggregation, and therefore most toxic. We combined experimental and computational approaches to study the molecular determinants and thermodynamics of APP-βCTF dimerization, and produced a unifying structural model that reconciles much of the published data. Using a cell assay, which exploits a dimerization-dependent activator of transcription, we identified specific dimerization-disrupting mutations located mostly at the N-terminus of the TMD of APP-βCTF. The ability of selected mutants to disrupt the dimerization of full length APP-βCTF was confirmed by fluorescence resonance energy transfer experiments. Free-energy estimates of wild-type (WT) and mutants of the TMD of APP-βCTF derived from enhanced molecular dynamics simulations showed that the dimeric state is comprised of different arrangements, in which either 709GXXXA713 or 700GXXXG704GXXXG708 interaction motifs can engage in symmetric or asymmetric associations. Mutations along the TMD of APP-βCTF were found to modulate the relative free energy of the dimeric configurations, and to differently affect the distribution of interfaces within the dimeric state. This observation might have important biological implications, since dimers with a different arrangement of the transmembrane helices are likely to be recognized differently by γ-secretase and lead to a variation of Aβ levels.
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