Project description:Parkinson's disease is a progressive neuropathological disorder that belongs to the class of synucleinopathies, in which the protein alpha-synuclein is found at abnormally high concentrations in affected neurons. Its hallmark are intracellular inclusions called Lewy bodies and Lewy neurites. We here report the structure of cytotoxic alpha-synuclein fibrils (residues 1-121), determined by cryo-electron microscopy at a resolution of 3.4 Å. Two protofilaments form a polar fibril composed of staggered ?-strands. The backbone of residues 38 to 95, including the fibril core and the non-amyloid component region, are well resolved in the EM map. Residues 50-57, containing three of the mutation sites associated with familial synucleinopathies, form the interface between the two protofilaments and contribute to fibril stability. A hydrophobic cleft at one end of the fibril may have implications for fibril elongation, and invites for the design of molecules for diagnosis and treatment of synucleinopathies.
Project description:Posttranslational modifications (PTMs) of α-synuclein (α-syn), e.g., phosphorylation, play an important role in modulating α-syn pathology in Parkinson's disease (PD) and α-synucleinopathies. Accumulation of phosphorylated α-syn fibrils in Lewy bodies and Lewy neurites is the histological hallmark of these diseases. However, it is unclear how phosphorylation relates to α-syn pathology. Here, by combining chemical synthesis and bacterial expression, we obtained homogeneous α-syn fibrils with site-specific phosphorylation at Y39, which exhibits enhanced neuronal pathology in rat primary cortical neurons. We determined the cryo-electron microscopy (cryo-EM) structure of the pY39 α-syn fibril, which reveals a fold of α-syn with pY39 in the center of the fibril core forming an electrostatic interaction network with eight charged residues in the N-terminal region of α-syn. This structure composed of residues 1 to 100 represents the largest α-syn fibril core determined so far. This work provides structural understanding on the pathology of the pY39 α-syn fibril and highlights the importance of PTMs in defining the polymorphism and pathology of amyloid fibrils in neurodegenerative diseases.
Project description:α-Synuclein (aSyn) fibrillar polymorphs have distinct in vitro and in vivo seeding activities, contributing differently to synucleinopathies. Despite numerous prior attempts, how polymorphic aSyn fibrils differ in atomic structure remains elusive. Here, we present fibril polymorphs from the full-length recombinant human aSyn and their seeding capacity and cytotoxicity in vitro. By cryo-electron microscopy helical reconstruction, we determine the structures of the two predominant species, a rod and a twister, both at 3.7 Å resolution. Our atomic models reveal that both polymorphs share a kernel structure of a bent β-arch, but differ in their inter-protofilament interfaces. Thus, different packing of the same kernel structure gives rise to distinct fibril polymorphs. Analyses of disease-related familial mutations suggest their potential contribution to the pathogenesis of synucleinopathies by altering population distribution of the fibril polymorphs. Drug design targeting amyloid fibrils in neurodegenerative diseases should consider the formation and distribution of concurrent fibril polymorphs.
Project description:Catalytic amyloid fibrils are novel types of bioinspired, functional materials that combine the chemical and mechanical robustness of amyloids with the ability to catalyze a certain chemical reaction. In this study we used cryo-electron microcopy to analyze the amyloid fibril structure and the catalytic center of amyloid fibrils that hydrolyze ester bonds. Our findings show that catalytic amyloid fibrils are polymorphic and consist of similarly structured, zipper-like building blocks that consist of mated cross-β sheets. These building blocks define the fibril core, which is decorated by a peripheral leaflet of peptide molecules. The observed structural arrangement differs from previously described catalytic amyloid fibrils and yielded a new model of the catalytic center.
Project description:?-Synuclein (?-syn) amyloid fibrils are the major component of Lewy bodies, which are the pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. High-resolution structure of ?-syn fibril is important for understanding its assembly and pathological mechanism. Here, we determined a fibril structure of full-length ?-syn (1-140) at the resolution of 3.07?Å by cryo-electron microscopy (cryo-EM). The fibrils are cytotoxic, and transmissible to induce endogenous ?-syn aggregation in primary neurons. Based on the reconstructed cryo-EM density map, we were able to unambiguously build the fibril structure comprising residues 37-99. The ?-syn amyloid fibril structure shows two protofilaments intertwining along an approximate 21 screw axis into a left-handed helix. Each protofilament features a Greek key-like topology. Remarkably, five out of the six early-onset PD familial mutations are located at the dimer interface of the fibril (H50Q, G51D, and A53T/E) or involved in the stabilization of the protofilament (E46K). Furthermore, these PD mutations lead to the formation of fibrils with polymorphic structures distinct from that of the wild-type. Our study provides molecular insight into the fibrillar assembly of ?-syn at the atomic level and sheds light on the molecular pathogenesis caused by familial PD mutations of ?-syn.
Project description:Alzheimer's disease (AD) is a fatal neurodegenerative disorder in humans and the main cause of dementia in aging societies. The disease is characterized by the aberrant formation of ?-amyloid (A?) peptide oligomers and fibrils. These structures may damage the brain and give rise to cerebral amyloid angiopathy, neuronal dysfunction, and cellular toxicity. Although the connection between AD and A? fibrillation is extensively documented, much is still unknown about the formation of these A? aggregates and their structures at the molecular level. Here, we combined electron cryomicroscopy, 3D reconstruction, and integrative structural modeling methods to determine the molecular architecture of a fibril formed by A?(1-42), a particularly pathogenic variant of A? peptide. Our model reveals that the individual layers of the A? fibril are formed by peptide dimers with face-to-face packing. The two peptides forming the dimer possess identical tilde-shaped conformations and interact with each other by packing of their hydrophobic C-terminal ?-strands. The peptide C termini are located close to the main fibril axis, where they produce a hydrophobic core and are surrounded by the structurally more flexible and charged segments of the peptide N termini. The observed molecular architecture is compatible with the general chemical properties of A? peptide and provides a structural basis for various biological observations that illuminate the molecular underpinnings of AD. Moreover, the structure provides direct evidence for a steric zipper within a fibril formed by full-length A? peptide.