Jaroniec Christopher P, MacPhee Cait E, Bajaj Vikram S, McMahon Michael T, Dobson Christopher M, Griffin Robert G
Department of Chemistry and Center for Magnetic Resonance, Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Proc Natl Acad Sci U S A. 2004 Jan 20;101(3):711-6. doi: 10.1073/pnas.0304849101. Epub 2004 Jan 8.
Amyloid fibrils are self-assembled filamentous structures associated with protein deposition conditions including Alzheimer's disease and the transmissible spongiform encephalopathies. Despite the immense medical importance of amyloid fibrils, no atomic-resolution structures are available for these materials, because the intact fibrils are insoluble and do not form diffraction-quality 3D crystals. Here we report the high-resolution structure of a peptide fragment of the amyloidogenic protein transthyretin, TTR(105-115), in its fibrillar form, determined by magic angle spinning NMR spectroscopy. The structure resolves not only the backbone fold but also the precise conformation of the side chains. Nearly complete (13)C and (15)N resonance assignments for TTR(105-115) formed the basis for the extraction of a set of distance and dihedral angle restraints. A total of 76 self-consistent experimental measurements, including 41 restraints on 19 backbone dihedral angles and 35 (13)C-(15)N distances between 3 and 6 A were obtained from 2D and 3D NMR spectra recorded on three fibril samples uniformly (13)C, (15)N-labeled in consecutive stretches of four amino acids and used to calculate an ensemble of peptide structures. Our results indicate that TTR(105-115) adopts an extended beta-strand conformation in the amyloid fibrils such that both the main- and side-chain torsion angles are close to their optimal values. Moreover, the structure of this peptide in the fibrillar form has a degree of long-range order that is generally associated only with crystalline materials. These findings provide an explanation of the unusual stability and characteristic properties of this form of polypeptide assembly.
淀粉样纤维是与包括阿尔茨海默病和可传播性海绵状脑病在内的蛋白质沉积病症相关的自组装丝状结构。尽管淀粉样纤维在医学上具有极其重要的意义，但目前尚无这些材料的原子分辨率结构，因为完整的纤维不溶且不能形成具有衍射质量的三维晶体。在此，我们报告了通过魔角旋转核磁共振光谱法测定的淀粉样蛋白转甲状腺素蛋白（TTR）的肽片段TTR(105 - 115)的高分辨率纤维状结构。该结构不仅解析了主链折叠，还解析了侧链的精确构象。TTR(105 - 115)几乎完整的（13）C和（15）N共振归属为提取一组距离和二面角限制奠定了基础。从在三个均匀（13）C、（15）N标记的连续四个氨基酸片段的纤维样品上记录的二维和三维核磁共振光谱中，总共获得了76个自洽的实验测量值，包括对19个主链二面角的41个限制以及3到6埃之间的35个（13）C - （15）N距离，并用于计算肽结构的集合。我们的结果表明，TTR(105 - 115)在淀粉样纤维中采用延伸的β-链构象，使得主链和侧链扭转角都接近其最佳值。此外，这种纤维状形式的肽结构具有一定程度的长程有序性，通常仅与晶体材料相关。这些发现解释了这种形式的多肽组装体不同寻常的稳定性和特性。
