Isotope-edited FTIR reveals distinct aggregation and structural behaviors of unmodified and pyroglutamylated amyloid β peptides.
Isotope-edited FTIR reveals distinct aggregation and structural behaviors of unmodified and pyroglutamylated amyloid β peptides.
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DOI：
10.1039/c5cp03343h
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发表时间：
2015-12-28
期刊：
影响因子：
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通讯作者：
Tatulian SA
中科院分区：
文献类型：
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作者：
Goldblatt G;Matos JO;Gornto J;Tatulian SA
淀粉样 β 肽 (Aβ) 与阿尔茨海默病 (AD) 密切相关，N 末端截短和焦谷氨酰化的 Aβ 肽 (AβpE) 通过未知机制发挥毒性作用。最近的证据表明 Aβ 前原纤维寡聚体，而不是原纤维，是普遍存在的细胞毒性物质。因此，Aβ 和 AβpE 寡聚物的结构表征对于更好地了解其毒性作用非常重要。在这里，我们使用同位素编辑的傅立叶变换红外 (FTIR) 光谱来识别 Aβ1-42 和 AβpE3-42 单独和以 1:1 摩尔组合聚集时的构象变化。在暴露于水性缓冲液的前两个小时内，肽经历从大部分 α-螺旋结构转变为大部分 β-折叠结构。在 K16L17V18 或 V36G37G38V39 处标记的肽 13C,15N 的数据允许构建单体和早期寡聚物的结构模型。该肽单体包含一个 β-发夹，涉及 K16L17V18 序列上游的残基和一个 N 端 α-螺旋。寡聚物是通过相邻 β-发夹的 β-链之间的非氢键相互作用形成的，以横向或交错方式，其中链平行或反平行。 Aβ1-42 和 AβpE3-42 的相对 α 螺旋和 β 折叠倾向取决于缓冲液的离子强度，这强调了离子相互作用在 Aβ 肽结构和聚集中的重要性。据推测，AβpE3-42 的 N 端修饰影响螺旋稳定性，从而调节 β-折叠寡聚体的形成。因此，这些数据通过强调 N 端瞬时 α 螺旋结构的作用并确定寡聚物分子组织的结构约束，为 Aβ 寡聚的分子机制提供了新的见解。
Amyloid β peptide (Aβ) is causatively associated with Alzheimer’s disease (AD), and N-terminally truncated and pyroglutamylated Aβ peptides (AβpE) exert hypertoxic effect by an unknown mechanism. Recent evidence has identified the prefibrillar oligomers of Aβ, not the fibrils, as the prevalent cytotoxic species. Structural characterization of Aβ and AβpE oligomers is therefore important for better understanding of their toxic effect. Here we have used isotope-edited Fourier transform infrared (FTIR) spectroscopy to identify the conformational changes in Aβ1-42 and AβpE3-42 upon aggregation, individually and in 1:1 molar combination. During the first two hours of exposure to aqueous buffer, the peptides undergo transition from mostly α-helical to mostly β-sheet structure. Data on peptides 13C,15N-labeled at K16L17V18 or V36G37G38V39 allowed construction of structural models for the monomer and early oligomers. The peptide monomer comprises a β-hairpin that involves residues upstream of the K16L17V18 sequence and an N-terminal α-helix. The oligomers form by non-H-bonding interactions between the β-strands of neighboring β-hairpins, in lateral or staggered manner, with the strands running parallel or antiparallel. Relative α-helical and β-sheet propensities of Aβ1-42 and AβpE3-42 depend on the ionic strength of the buffer, emphasizing the importance of ionic interactions in Aβ peptide structure and aggregation. It is inferred that N-terminal modification of AβpE3-42 affects the helix stability and thereby modulates β-sheet oligomer formation. The data thus provide new insight into the molecular mechanism of Aβ oligomerization by emphasizing the role of the N-terminal transient α-helical structure and by identifying structural constraints for molecular organization of the oligomers.