Tjernberg Lars O, Tjernberg Agneta, Bark Niklas, Shi Yuan, Ruzsicska Bela P, Bu Zimei, Thyberg Johan, Callaway David J E
NEUROTEC, Karolinska Institutet, S141 86 Stockholm, Sweden.
Biochem J. 2002 Aug 15;366(Pt 1):343-51. doi: 10.1042/BJ20020229.
The amyloid plaque, consisting of amyloid beta-peptide (Abeta) fibrils surrounded by dystrophic neurites, is an invariable feature of Alzheimer's disease. The determination of the molecular structure of Abeta fibrils is a significant goal that may lead to the structure-based design of effective therapeutics for Alzheimer's disease. Technical challenges have thus far rendered this goal impossible. In the present study, we develop an alternative methodology. Rather than determining the structure directly, we design conformationally constrained peptides and demonstrate that only certain 'bricks' can aggregate into fibrils morphologically identical to Abeta fibrils. The designed peptides include variants of a decapeptide fragment of Abeta, previously shown to be one of the smallest peptides that (1) includes a pentapeptide sequence necessary for Abeta-Abeta binding and aggregation and (2) can form fibrils indistinguishable from those formed by full-length Abeta. The secondary structure of these bricks is monitored by CD spectroscopy, and electron microscopy is used to study the morphology of the aggregates formed. We then made various residue deletions and substitutions to determine which structural features are essential for fibril formation. From the constraints, statistical analysis of side-chain pair correlations in beta-sheets and experimental data, we deduce a detailed model of the peptide strand alignment in fibrils formed by these bricks. Our results show that the constrained decapeptide dimers rapidly form an intramolecular, antiparallel beta-sheet and polymerize into amyloid fibrils at low concentrations. We suggest that the formation of an exposed beta-sheet (e.g. an Abeta dimer formed by interaction in the decapeptide region) could be a rate-limiting step in fibril formation. A theoretical framework that explains the results is presented in parallel with the data.
由淀粉样β肽（Aβ）原纤维被营养不良性神经突包围构成的淀粉样斑块是阿尔茨海默病的一个不变特征。确定Aβ原纤维的分子结构是一个重要目标，可能会导向基于结构设计针对阿尔茨海默病的有效治疗方法。然而，技术挑战使得这一目标目前无法实现。在本研究中，我们开发了一种替代方法。我们不是直接确定结构，而是设计构象受限肽，并证明只有某些“砖块”能够聚集成形态与Aβ原纤维相同的原纤维。设计的肽包括Aβ十肽片段的变体，该片段先前已被证明是最小的肽之一，它（1）包含Aβ-Aβ结合和聚集所需的五肽序列，（2）能够形成与全长Aβ形成的原纤维无法区分的原纤维。通过圆二色光谱监测这些“砖块”的二级结构，并使用电子显微镜研究形成的聚集体的形态。然后我们进行了各种残基缺失和替换，以确定哪些结构特征对于原纤维形成至关重要。根据这些限制条件、β折叠中侧链对相关性的统计分析以及实验数据，我们推导出了由这些“砖块”形成的原纤维中肽链排列的详细模型。我们的结果表明，受限的十肽二聚体迅速形成分子内反平行β折叠，并在低浓度下聚合成淀粉样原纤维。我们认为，暴露的β折叠（例如由十肽区域相互作用形成的Aβ二聚体）的形成可能是原纤维形成中的限速步骤。与数据并行呈现了一个解释结果的理论框架。
