On the self-assembly of αB-crystallin.

The molecular chaperone αB-crystallin is a small heat shock protein that inhibits the aggregation of, among others, Aβ42 and α-synuclein. These proteins are major hallmarks of Alzheimer's and Parkinson's disease, respectively. In order to understand the mechanism with which αB-crystallin performs its chaperone function it is essential to characterize its self-assembly in terms of aggregate size distribution, structure, and critical concentration.

The Role of α-Synuclein-DNAJB6b Coaggregation in Amyloid Suppression.

Chaperones may retard the aggregation of other proteins and increase their solubility. An important goal is a thermodynamic understanding of such an action. Here, the chaperone DNAJB6b (JB6) is found to suppress amyloid formation of the protein α-synuclein (α-syn) leading to a reduced rate of fibril formation and an increase in apparent solubility of α-syn.

Residues 2 to 7 of α-synuclein regulate amyloid formation via lipid-dependent and lipid-independent pathways.

Amyloid formation by α-synuclein (αSyn) occurs in Parkinson's disease, multiple system atrophy, and dementia with Lewy bodies. Deciphering the residues that regulate αSyn amyloid fibril formation will not only provide mechanistic insight but may also reveal targets to prevent and treat disease. Previous investigations have identified several regions of αSyn to be important in the regulation of amyloid formation, including the non-amyloid-β component (NAC), P1 region (residues 36 to 42), and residues in the C-terminal domain.

The role of shear forces in primary and secondary nucleation of amyloid fibrils.

Shear forces affect self-assembly processes ranging from crystallization to fiber formation. Here, the effect of mild agitation on amyloid fibril formation was explored for four peptides and investigated in detail for A[Formula: see text]42, which is associated with Alzheimer's disease. To gain mechanistic insights into the effect of mild agitation, nonseeded and seeded aggregation reactions were set up at various peptide concentrations with and without an inhibitor.

Aβ Oligomer Dissociation Is Catalyzed by Fibril Surfaces.

Oligomeric assemblies consisting of only a few protein subunits are key species in the cytotoxicity of neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Their lifetime in solution and abundance, governed by the balance of their sources and sinks, are thus important determinants of disease. While significant advances have been made in elucidating the processes that govern oligomer production, the mechanisms behind their dissociation are still poorly understood.

Structural evolution of fibril polymorphs during amyloid assembly.

Cryoelectron microscopy (cryo-EM) has provided unprecedented insights into amyloid fibril structures, including those associated with disease. However, these structures represent the endpoints of long assembly processes, and their relationship to fibrils formed early in assembly is unknown. Consequently, whether different fibril architectures, with potentially different pathological properties, form during assembly remains unknown.

The C-terminal domain of the antiamyloid chaperone DNAJB6 binds to amyloid-β peptide fibrils and inhibits secondary nucleation.

The DNAJB6 chaperone inhibits fibril formation of aggregation-prone client peptides through interaction with aggregated and oligomeric forms of the amyloid peptides. Here, we studied the role of its C-terminal domain (CTD) using constructs comprising either the entire CTD or the first two or all four of the CTD β-strands grafted onto a scaffold protein. Each construct was expressed as WT and as a variant with alanines replacing five highly conserved and functionally important serine and threonine residues in the first β-strand.

Direct observation of secondary nucleation along the fibril surface of the amyloid 42 peptide.

Alzheimer's disease is a neurodegenerative condition which involves heavy neuronal cell death linked to oligomers formed during the aggregation process of the amyloid peptide 42 (A42). The aggregation of A42 involves both primary and secondary nucleation. Secondary nucleation dominates the generation of oligomers and involves the formation of new aggregates from monomers on catalytic fibril surfaces.

A Kinetic Map of the Influence of Biomimetic Lipid Model Membranes on Aβ Aggregation.

The aggregation of the amyloid β (Aβ) peptide is one of the molecular hallmarks of Alzheimer's disease (AD). Although Aβ deposits have mostly been observed extracellularly, various studies have also reported the presence of intracellular Aβ assemblies. Because these intracellular Aβ aggregates might play a role in the onset and progression of AD, it is important to investigate their possible origins at different locations of the cell along the secretory pathway of the amyloid precursor protein, from which Aβ is derived by proteolytic cleavage.

Role of Hydrophobicity at the N-Terminal Region of Aβ42 in Secondary Nucleation.

The self-assembly of the amyloid β 42 (Aβ42) peptide is linked to Alzheimer's disease, and oligomeric intermediates are linked to neuronal cell death during the pathology of the disease. These oligomers are produced prolifically during secondary nucleation, by which the aggregation of monomers is catalyzed on fibril surfaces. Significant progress has been made in understanding the aggregation mechanism of Aβ42; still, a detailed molecular-level understanding of secondary nucleation is lacking.

A Palette of Fluorescent A42 Peptides Labelled at a Range of Surface-Exposed Sites.

Fluorescence-based single molecule techniques provide important tools towards understanding the molecular mechanism of complex neurodegenerative diseases. This requires efficient covalent attachment of fluorophores. Here we create a series of cysteine mutants (S8C, Y10C, S26C, V40C, and A42C) of Aβ42, involved in Alzheimer's disease, based on exposed positions in the fibril structure and label them with the Alexa-fluorophores using maleimide chemistry.

The role of fibril structure and surface hydrophobicity in secondary nucleation of amyloid fibrils.

Crystals, nanoparticles, and fibrils catalyze the generation of new aggregates on their surface from the same type of monomeric building blocks as the parent assemblies. This secondary nucleation process can be many orders of magnitude faster than primary nucleation. In the case of amyloid fibrils associated with Alzheimer's disease, this process leads to the multiplication and propagation of aggregates, whereby short-lived oligomeric intermediates cause neurotoxicity.