Using chiral peptide substitutions to probe the structure function relationship of a key residue of Aβ42

The rippled β-sheet layer configuration-a novel supramolecular architecture based on predictions by Pauling and Corey

The rippled β-sheet is a peptidic structural motif related to but distinct from the pleated β-sheet. Both motifs were predicted in the 1950s by Pauling and Corey. The pleated β-sheet was since observed in countless proteins and peptides and is considered common textbook knowledge. Conversely, the rippled β-sheet only gained a meaningful experimental foundation in the past decade, and the first crystal structural study of rippled β-sheets was published as recently as this year. Noteworthy, the crystallized assembly stopped at the rippled β-dimer stage. It did not form the extended, periodic rippled β-sheet layer topography hypothesized by Pauling and Corey, thus calling the validity of their prediction into question. NMR work conducted since moreover shows that certain model peptides rather form pleated and not rippled β-sheets in solution. To determine whether the periodic rippled β-sheet layer configuration is viable, the field urgently needs crystal structures. Here we report on crystal structures of two racemic and one quasi-racemic aggregating peptide systems, all of which yield periodic rippled antiparallel β-sheet layers that are in excellent agreement with the predictions by Pauling and Corey. Our study establishes the rippled β-sheet layer configuration as a motif with general features and opens the road to structure-based design of unique supramolecular architectures.

Biophysical characterization as a tool to predict amyloidogenic and toxic properties of amyloid-β42 peptides

Amyloid-β42 (Aβ42) peptides are central to the amyloid pathology in Alzheimer's disease (AD). As biological mimetics, properties of synthetic Aβ peptides usually vary between vendors and batches, thus impacting the reproducibility of experimental studies. Here, we tested recombinantly expressed Aβ42 (Asp1 to Ala42) against synthetic Aβ42 from different suppliers using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), circular dichroism (CD) spectroscopy, thioflavin T aggregation, surface plasmon resonance and MTT cell viability assays. Overall, our recombinant Aβ42 provided a reproducible mimetic of desired properties. Across experimental approaches, the combined detection of Aβ42 dimers and random coil to β-sheet transition only correlated with aggregation-prone and cytotoxic peptides. Conclusively, combining MALDI-MS with CD appears to provide a rapid, reliable means to predict the "bioactivity" of Aβ42.

Artificial Chiral Interfaces against Amyloid-β Peptide Aggregation: Research Progress and Challenges

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by an imbalance between the production and clearance of amyloid-β (Aβ) species. AD not only influences the life quality of the patients but also heavily burdens the families and society. Therefore, it is an urgent mission to research and develop some new anti-amyloid aggregation drugs. In recent years, there were research and development of engineered nanostructures as Aβ amyloid inhibitors have attracted extensive attention and become a new frontier in nanomedicine. The effects of nanostructural surface properties (e.g., morphology, charge, hydrophobicity) on inhibition of Aβ aggregation are modulated by adsorbed Aβ peptides. Nevertheless, chirality has been seldom considered in recognition of Aβ species and modulation of Aβ aggregations. Moreover, a more relevant question for chiral inhibitors is little known about the molecular mechanism of how to interface chiral effects Aβ targeting recognition and effective mitigation of amyloidosis at the molecular level. Herein, we review recent experimental and theoretical results acquired in the specific areas of artificial chiral nanostructure inhibitors. This article will be essential to provide a microlevel insight into the effects of chiral nanointerfaces on amyloidosis processes as well as the development of chiral inhibitor drugs against Aβ fibrillation.

Surface-enhanced Raman scattering sensing platform for detecting amyloid-β peptide interaction with an aggregation inhibitor

Soluble, small amyloid-β oligomers (AβO) are recognized as significant contributors to the pathology of Alzheimer's disease (AD). Although drugs for treating AD symptoms have been approved, no therapy targeting amyloid-β (Aβ) capable of modifying the course of the disease is available. In an effort to develop a label-free method for screening new anti-AD therapeutic agents, we show the use of a surface-enhanced Raman scattering (SERS) active substrate for detecting the interactions between Aβ peptides and spin-labeled fluorine (SLF), a peptide aggregation inhibitor. Changes in the peak positions and intensity ratios of two spectral peaks near 1600cm^-1 and 2900cm^-1 can be used to monitor the molecular interactions between SLF and Aβ. This study demonstrates the potential of SERS spectroscopy for rapidly screening and identifying new anti-Aβ therapeutic agents.

Aggregation and Amyloidogenicity of the Nuclear Coactivator Binding Domain of CREB-Binding Protein

The nuclear coactivator binding domain (NCBD) of transcriptional co-regulator CREB-binding protein (CBP) is an example of conformationally malleable proteins that can bind to structurally unrelated protein targets and adopt distinct folds in the respective protein complexes. Here, we show that the folding landscape of NCBD contains an alternative pathway that results in protein aggregation and self-assembly into amyloid fibers. The initial steps of such protein misfolding are driven by intermolecular interactions of its N-terminal α-helix bringing multiple NCBD molecules into contact. These oligomers then undergo slow but progressive interconversion into β-sheet-containing aggregates. To reveal the concealed aggregation potential of NCBD we used a chemically synthesized mirror-image d-NCBD form. The addition of d-NCBD promoted self-assembly into amyloid precipitates presumably due to formation of thermodynamically more stable racemic β-sheet structures. The unexpected aggregation of NCBD needs to be taken into consideration given the multitude of protein-protein interactions and resulting biological functions mediated by CBP.