Jiménez José L, Nettleton Ewan J, Bouchard Mario, Robinson Carol V, Dobson Christopher M, Saibil Helen R
Department of Crystallography, Birkbeck College, Malet Street, London WC1E 7HX, United Kingdom.
Proc Natl Acad Sci U S A. 2002 Jul 9;99(14):9196-201. doi: 10.1073/pnas.142459399. Epub 2002 Jul 1.
Under solution conditions where the native state is destabilized, the largely helical polypeptide hormone insulin readily aggregates to form amyloid fibrils with a characteristic cross-beta structure. However, there is a lack of information relating the 4.8 A beta-strand repeat to the higher order assembly of amyloid fibrils. We have used cryo-electron microscopy (EM), combining single particle analysis and helical reconstruction, to characterize these fibrils and to study the three-dimensional (3D) arrangement of their component protofilaments. Low-resolution 3D structures of fibrils containing 2, 4, and 6 protofilaments reveal a characteristic, compact shape of the insulin protofilament. Considerations of protofilament packing indicate that the cross-beta ribbon is composed of relatively flat beta-sheets rather than being the highly twisted, beta-coil structure previously suggested by analysis of globular protein folds. Comparison of the various fibril structures suggests that very small, local changes in beta-sheet twist are important in establishing the long-range coiling of the protofilaments into fibrils of diverse morphology.
在天然状态不稳定的溶液条件下,主要呈螺旋状的多肽激素胰岛素很容易聚集形成具有特征性交叉β结构的淀粉样纤维。然而,关于4.8埃β链重复与淀粉样纤维的高阶组装之间的关系,目前还缺乏相关信息。我们利用冷冻电子显微镜(EM),结合单颗粒分析和螺旋重建技术,对这些纤维进行表征,并研究其组成原纤维的三维(3D)排列。含有2、4和6条原纤维的纤维的低分辨率3D结构揭示了胰岛素原纤维的特征性紧凑形状。对原纤维堆积的考虑表明,交叉β带由相对扁平的β片层组成,而不是先前通过球状蛋白折叠分析所提出的高度扭曲的β螺旋结构。各种纤维结构的比较表明,β片层扭曲中非常小的局部变化对于将原纤维长程盘绕成不同形态的纤维至关重要。