Cross-beta order and diversity in nanocrystals of an amyloid-forming peptide

The seven-residue peptide GNNQQNY from the N-terminal region of the yeast prion protein Sup35, which forms amyloid fibers, colloidal aggregates and highly ordered nanocrystals, provides a model system for characterizing the elusively protean cross-beta conformation. Depending on preparative conditions, orthorhombic and monoclinic crystals with similar lath-shaped morphology have been obtained. Ultra high-resolution (,0.5 A ˚ spacing) electron diffraction patterns from single nanocrystals show that the peptide chains pack in parallel cross-beta columns with,4.86 A ˚ axial spacing. Mosaic striations 20–50 nm wide observed by electron microscopy indicate lateral size-limiting crystal growth related to amyloid fiber formation. Frequently obtained orthorhombic forms, with apparent space group symmetry P212121; have cell dimensions ranging from lal 22:7 – 21:2 A ˚ , lbl 39:9 – 39:3 A ˚ , lcl 4:89 – 4:86 A for wet to dried states. Electron diffraction data from single nanocrystals, recorded in tilt series of still frames, have been mapped in reciprocal space. However, reliable integrated intensities cannot be obtained fro

Structure of the cross-ß spine of amyloid-like fibrils

Numerous soluble proteins convert to insoluble amyloid-like fibrils having common properties. Amyloid fibrils are associated with fatal diseases such as Alzheimer’s, and amyloid-like fibrils can be formed in vitro. For the yeast protein Sup35, conversion to amyloid-like fibrils is associated with a transmissible infection akin to that caused by mammalian prions. A seven-residue peptide segment from Sup35 forms amyloid-like fibrils and closely related microcrystals, which here reveal the atomic structure of the cross-β spine. It is a double β-sheet, with each sheet formed from parallel segments stacked in-register. Sidechains protruding from the two sheets form a dry, tightly self-complementing steric zipper, bonding the sheets. Within each sheet, every segment is bound to its two neighbouring segments via stacks of both backbone and sidechain hydrogen bonds. The structure illuminates the stability of amyloid fibrils, their self-seeding characteristic, and their tendency to form polymorphic structures

The structural biology of protein aggregation diseases:fundamental questions and some answers

Amyloid fibrils are found in association with at least two dozen fatal diseases. The tendency of numerous proteins to convert into amyloid-like fibrils poses fundamental questions for structural biology, and for protein science in general. Among these are: What is the structure of the cross-β spine, common to amyloid-like fibrils? Is there a sequence signature for proteins that form amyloid-like fibrils? What is the nature of the structural conversion from native to amyloid states, and do fibril-forming proteins have two distinct, stable states, the native state and the amyloid state? What is the basis of protein complementarity, in which a protein chain can bind to itself? We offer tentative answers here, based on our own recent structural studies, recognizing that there is much complementary research in the field, some of which is summarized in other papers in this issue, as well as elsewhere1–11

Small molecules disaggregate alpha-synuclein and prevent seeding from patient brain-derived fibrils.

The amyloid aggregation of alpha-synuclein within the brain is associated with the pathogenesis of Parkinson's disease (PD) and other related synucleinopathies, including multiple system atrophy (MSA). Alpha-synuclein aggregates are a major therapeutic target for treatment of these diseases. We identify two small molecules capable of disassembling preformed alpha-synuclein fibrils. The compounds, termed CNS-11 and CNS-11g, disaggregate recombinant alpha-synuclein fibrils in vitro, prevent the intracellular seeded aggregation of alpha-synuclein fibrils, and mitigate alpha-synuclein fibril cytotoxicity in neuronal cells. Furthermore, we demonstrate that both compounds disassemble fibrils extracted from MSA patient brains and prevent their intracellular seeding. They also reduce in vivo alpha-synuclein aggregates in C. elegans. Both compounds also penetrate brain tissue in mice. A molecular dynamics-based computational model suggests the compounds may exert their disaggregating effects on the N terminus of the fibril core. These compounds appear to be promising therapeutic leads for targeting alpha-synuclein for the treatment of synucleinopathies

D-peptide-magnetic nanoparticles fragment tau fibrils and rescue behavioral deficits in a mouse model of Alzheimer’s disease

Amyloid fibrils of tau are increasingly accepted as a cause of neuronal death and brain atrophy in Alzheimer's disease (AD). Diminishing tau aggregation is a promising strategy in the search for efficacious AD therapeutics. Previously, our laboratory designed a six-residue, nonnatural amino acid inhibitor D-TLKIVW peptide (6-DP), which can prevent tau aggregation in vitro. However, it cannot block cell-to-cell transmission of tau aggregation. Here, we find D-TLKIVWC (7-DP), a d-cysteine extension of 6-DP, not only prevents tau aggregation but also fragments tau fibrils extracted from AD brains to neutralize their seeding ability and protect neuronal cells from tau-induced toxicity. To facilitate the transport of 7-DP across the blood-brain barrier, we conjugated it to magnetic nanoparticles (MNPs). The MNPs-DP complex retains the inhibition and fragmentation properties of 7-DP alone. Ten weeks of MNPs-DP treatment appear to reverse neurological deficits in the PS19 mouse model of AD. This work offers a direction for development of therapies to target tau fibrils