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Exclusion of the native alpha-helix from the amyloid fibrils of a mixed alpha/beta protein

机译：从混合的α/β蛋白的淀粉样原纤维中排除天然α-螺旋

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摘要

Members of the cystatin superfamily are involved in an inherited form of cerebral amyloid angiopathy and readily form amyloid fibrils in vitro. We have determined the structured core of human stefin B (cystatin B) amyloid fibrils using quenched hydrogen exchange and NMR. The core contains residues from four of the five strands of the native beta-sheet, delimited by unprotected loop regions analogous to those of the native monomeric structure. However, non-native features are also apparent, the most striking of which is the exclusion of the native alpha-helix. Before forming amyloid in vitro, cystatins dimerise via 3D domain swapping, and assemble into tetramers with trans to cis isomerism of a conserved proline. In the fibril, the hinge loop that forms an extended beta-structure in the dimer remains protected, consistent with the domain-swapping interface being maintained. However, the fibril data are not compatible with a simple 3D domain-swapping model for amyloid formation, and the displacement of the helix points to alternative packing arrangements of native-like beta-structure, in which proline isomerism is important in preventing steric clashing. (C) 2007 Elsevier Ltd. All rights reserved.
机译：胱抑素超家族成员参与遗传性脑淀粉样血管病，并在体外容易形成淀粉样原纤维。我们已经使用淬灭的氢交换和NMR确定了人类Stefin B（胱抑素B）淀粉样蛋白原纤维的结构核心。核心包含来自天然β-折叠的5条链中4条的残基，其残基由与天然单体结构类似的未保护环区域界定。但是，非本机特征也很明显，其中最引人注目的是排除了本机alpha螺旋。在体外形成淀粉样蛋白之前，半胱氨酸蛋白酶抑制剂通过3D结构域交换而二聚化，并组装成具有保守脯氨酸反式至顺式异构体的四聚体。在原纤维中，在二聚体中形成扩展的β-结构的铰链环仍受保护，与维持的域交换界面一致。然而，原纤维数据与淀粉样蛋白形成的简单3D域交换模型不兼容，并且螺旋结构的位移指向天然类似β结构的替代堆积排列，其中脯氨酸异构在防止空间冲突方面很重要。 （C）2007 Elsevier Ltd.保留所有权利。

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