Refined fibril structures: the hydrophobic core in Alzheimer's amyloid beta-protein and prion as revealed by X-ray diffraction.
Refined fibril structures: the hydrophobic core in Alzheimer's amyloid beta-protein and prion as revealed by X-ray diffraction.
复制标题
精制原纤维结构：X 射线衍射揭示了阿尔茨海默氏症淀粉样蛋白 β 蛋白和朊病毒的疏水核心。
DOI：
10.1002/9780470514924.ch3
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Kirschner,DA
中科院分区：
文献类型：
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作者：
Inouye,H;Kirschner,DA
根据β-淀粉样蛋白类似物的广角赤道X射线数据，我们之前计算了β-微晶成分的电子密度，β-微晶在构建淀粉样蛋白纤维时组装成多聚体（四到六个微晶）。在间距 < ∼ 10Å 的散射区域中，观察到的反射由具有 a= 9.44Å、b= 6.92Å 和 c= 10.76Å 的晶胞的正交晶格索引。这些相位最初源自 β-角蛋白主链的原子坐标，并通过在随后的傅立叶迭代中包含新峰（作为点原子或球体）进行优化。观测到的振幅和计算得到的振幅之间的 R 因子被细化为 35%。在进一步发展我们的分析时，我们现在通过消除负电子密度对优化应用了替代约束，并发现在三次迭代后 R 因子下降至 19%。精细的电子密度图符合苯丙氨酸，表明淀粉样蛋白核心可能来自疏水性 Leu-Val-Phe-Phe 残基。我们对 priqn 蛋白的疏水性 H1 结构域应用了相同类型的优化，使用 β-silk 作为初始相模型，其单斜晶胞常数面积 = 9.51Å，b = 7.06Å，c = 15.94Å 和 β = 88.4°。两次迭代后，R 因子从 64% 下降到 11%。电子密度图显示了 β 片层的丝状四分之一交错排列，在片间方向上，一个 β 片层具有圆形峰，而交替的 β 片层具有细长峰。这些峰被解释为来自 C 端富含丙氨酸的结构域和 N 端疏水残基。这些核心区域的骨架原子模型支持这种解释。
From the wide‐angle, equatorial X‐ray data of a β‐amyloid analogue, we previously calculated the electron density of the constituent β‐crystallite, which assembles as multimers (four to six crystallites) in building the amyloid fibre. In the scattering region where the spacingd< ∼ 10Å, the observed reflections were indexed by an orthogonal lattice with a unit cell havinga= 9.44Å,b= 6.92Å andc= 10.76Å. The phases were initially derived from the atomic coordinates of the β‐keratin backbone and were optimized by including new peaks (as point atom or sphere) in the subsequent Fourier iteration. The R‐factor between the observed and calculated amplitudes was refined to 35%. In further developing our analysis, we have now applied an alternative constraint to the optimization by eliminating the negative electron densities, and found that the R‐factor decreased to 19% after three iterations. The refined electron density map fits phenylalanine, indicating that the amyloid core likely comes from the hydrophobic Leu‐Val‐Phe‐Phe residues. We have applied the same type of optimization, using β‐silk as an initial phase model, to the hydrophobic H1 domaip of the priqn protein for which the monoclinic unit cell constants area= 9.51Å,b= 7.06Å,c= 15.94Å and β = 88.4°. The R‐factor decreased to 11% from 64% after two iterations. The electron density map shows a silk‐like quarter‐staggered arrangement of β‐sheets which, in the intersheet direction, have circular peaks in one β‐sheet and elongated peaks in the alternating β‐sheet. These peaks were interpreted as arising from the C‐terminal alanine‐rich domain and N‐terminal hydrophobic residues. Skeletal atomic models for these core regions support this interpretation.