The curvature of gold nanoparticles influences the exposure of amyloid-β and modulates its aggregation process.

Gold nanoparticles (GNP) are tunable nanomaterials that can be used to develop rational therapeutic inhibitors against the formation of pathological aggregates of proteins. In the case of the pathological aggregation of the amyloid-β protein (Aβ), the shape of the GNP can slow down or accelerate its aggregation kinetics. However, there is a lack of elementary knowledge about how the curvature of GNP alters the interaction with the Aβ peptide and how this interaction modifies key molecular steps of fibril formation.

Somatostatin, an Binder to Aβ Oligomers, Binds to βPFO Tetramers.

Somatostatin (SST14) is strongly related to Alzheimer's disease (AD), as its levels decline during aging, it regulates the proteolytic degradation of the amyloid beta peptide (Aβ), and it binds to Aβ oligomers . Recently, the 3D structure of a membrane-associated β-sheet pore-forming tetramer (βPFO tetramer) has been reported. Here, we show that SST14 binds selectively to the βPFO tetramer with a value of ∼40 μM without binding to monomeric Aβ(1-42).

Aβ(1-42) tetramer and octamer structures reveal edge conductivity pores as a mechanism for membrane damage.

Formation of amyloid-beta (Aβ) oligomer pores in the membrane of neurons has been proposed to explain neurotoxicity in Alzheimer's disease (AD). Here, we present the three-dimensional structure of an Aβ oligomer formed in a membrane mimicking environment, namely an Aβ(1-42) tetramer, which comprises a six stranded β-sheet core. The two faces of the β-sheet core are hydrophobic and surrounded by the membrane-mimicking environment while the edges are hydrophilic and solvent-exposed.

Preparation of a Well-Defined and Stable β-Barrel Pore-Forming Aβ42 Oligomer.

The formation of amyloid-β peptide (Aβ) oligomers at the cellular membrane is considered a crucial process that underlies neurotoxicity in Alzheimer's disease (AD). To obtain structural information on this type of oligomers, we were inspired by membrane protein approaches used to stabilize, characterize, and analyze the function of such proteins. Using these approaches, we developed conditions under which Aβ42, the Aβ variant most strongly linked to the aetiology of AD, assembles into an oligomer that inserts into lipid bilayers as a well-defined pore and adopts a specific structure with characteristics of a β-barrel arrangement.

Stabilization of a Membrane-Associated Amyloid-β Oligomer for Its Validation in Alzheimer's Disease.

We have recently reported on the preparation of a membrane-associated β Aβ42 Oligomer (β). It corresponds to a stable and homogeneous Aβ42 oligomer that inserts into lipid bilayers as a well-defined pore and adopts a specific structure with characteristics of a β-barrel arrangement. As a follow-up of this work, we aim to establish β's relevance in Alzheimer's disease (AD).

Direct Evidence of the Presence of Cross-Linked Aβ Dimers in the Brains of Alzheimer's Disease Patients.

Brain-derived amyloid-β (Aβ) dimers are associated with Alzheimer's disease (AD). However, their covalent nature remains controversial. This feature is relevant, as a covalent cross-link has been proposed to make brain-derived dimers (brain dimers) more synaptotoxic than Aβ monomers and would also make them suitable candidates for biomarker development.

Aβ42 assembles into specific β-barrel pore-forming oligomers in membrane-mimicking environments.

The formation of amyloid-β peptide (Aβ) oligomers at the cellular membrane is considered to be a crucial process underlying neurotoxicity in Alzheimer's disease (AD). Therefore, it is critical to characterize the oligomers that form within a membrane environment. To contribute to this characterization, we have applied strategies widely used to examine the structure of membrane proteins to study the two major Aβ variants, Aβ40 and Aβ42.

SDS-PAGE analysis of Aβ oligomers is disserving research into Alzheimer´s disease: appealing for ESI-IM-MS.

The characterization of amyloid-beta peptide (Aβ) oligomer forms and structures is crucial to the advancement in the field of Alzheimer´s disease (AD). Here we report a critical evaluation of two methods used for this purpose, namely sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), extensively used in the field, and ion mobility coupled to electrospray ionization mass spectrometry (ESI-IM-MS), an emerging technique with great potential for oligomer characterization. To evaluate their performance, we first obtained pure cross-linked Aβ40 and Aβ42 oligomers of well-defined order.

Hydrogen/deuterium exchange-protected oligomers populated during Aβ fibril formation correlate with neuronal cell death.

The aggregation of the amyloid-β peptide (Aβ) to form fibrils and plaques is strongly associated with Alzheimer's disease (AD). Although it is well established that this process generates neurotoxicity, it is also heterogeneous with a variety of species being formed during the conversion process. This heterogeneity makes it difficult to detect and characterize each of the aggregates formed, which precludes establishing the specific features responsible for the neurotoxicity observed.

Reelin delays amyloid-beta fibril formation and rescues cognitive deficits in a model of Alzheimer's disease.

Reelin is an extracellular matrix protein that is crucial for neural development and adult brain plasticity. While the Reelin signalling cascade has been reported to be associated with Alzheimer's disease (AD), the role of Reelin in this pathology is not understood. Here we use an in vitro approach to show that Reelin interacts with amyloid-β (Aβ42) soluble species, delays Aβ42 fibril formation and is recruited into amyloid fibrils.

Template-assisted lateral growth of amyloid-β42 fibrils studied by differential labeling with gold nanoparticles.

Amyloid-β protein (Aβ) aggregation into amyloid fibrils is central to the origin and development of Alzheimer's disease (AD), yet this highly complex process is poorly understood at the molecular level. Extensive studies have shown that Aβ fibril growth occurs through fibril elongation, whereby soluble molecules add to the fibril ends. Nevertheless, fibril morphology strongly depends on aggregation conditions.

Aβ40 and Aβ42 amyloid fibrils exhibit distinct molecular recycling properties.

A critical aspect to understanding the molecular basis of Alzheimer's disease (AD) is the characterization of the kinetics of interconversion between the different species present during amyloid-β protein (Aβ) aggregation. By monitoring hydrogen/deuterium exchange in Aβ fibrils using electrospray ionization mass spectrometry, we demonstrate that the Aβ molecules comprising the fibril continuously dissociate and reassociate, resulting in molecular recycling within the fibril population. Investigations on Aβ40 and Aβ42 amyloid fibrils reveal that molecules making up Aβ40 fibrils recycle to a much greater extent than those of Aβ42.

Structure and intermolecular dynamics of aggregates populated during amyloid fibril formation studied by hydrogen/deuterium exchange.

The aggregation of proteins into amyloid fibrils is a complex and fascinating process associated with debilitating clinical disorders such as Alzheimer's and Parkinson's diseases. The process of aggregation involves a series of steps during which many intermediate aggregation states are populated. Recent evidence points to these intermediate states as the toxic moieties primarily responsible for cell damage or cell death, which are critical steps in the origin and progression of these disorders.

Retro-enantio N-methylated peptides as beta-amyloid aggregation inhibitors.

An emerging and attractive target for the treatment of Alzheimer's disease is to inhibit the aggregation of beta-amyloid protein (Abeta). We applied the retro-enantio concept to design an N-methylated peptidic inhibitor of the Abeta42 aggregation process. This inhibitor, inrD, as well as the corresponding all-L (inL) and all-D (inD) analogues were assayed for inhibition of Abeta42 aggregation.

Experimental characterization of disordered and ordered aggregates populated during the process of amyloid fibril formation.

Recent experimental evidence points to intermediates populated during the process of amyloid fibril formation as the toxic moieties primarily responsible for the development of increasingly common disorders such as Alzheimer's disease and type II diabetes. We describe here the application of a pulse-labeling hydrogen-deuterium (HD) exchange strategy monitored by mass spectrometry (MS) and NMR spectroscopy (NMR) to characterize the aggregation process of an SH3 domain under 2 different conditions, both of which ultimately lead to well-defined amyloid fibrils. Under one condition, the intermediates appear to be largely amorphous in nature, whereas under the other condition protofibrillar species are clearly evident.

Redesign of protein domains using one-bead-one-compound combinatorial chemistry.

A novel combinatorial strategy for the redesign of proteins based on the strength and specificity of intra- and interprotein interactions is described. The strategy has been used to redesign the hydrophobic core of the B domain of protein A. Using one-bead-one-compound combinatorial chemistry, 300 analogues of the C-terminal alpha-helix of the B domain, H3x, have been synthesized using a biocompatible resin and the HMFS linker, allowing the screening to occur while the peptides were bound to the resin.

Molecular recycling within amyloid fibrils.

Amyloid fibrils are thread-like protein aggregates with a core region formed from repetitive arrays of beta-sheets oriented parallel to the fibril axis. Such structures were first recognized in clinical disorders, but more recently have also been linked to a variety of non-pathogenic phenomena ranging from the transfer of genetic information to synaptic changes associated with memory. The observation that many proteins can convert into similar structures in vitro has suggested that this ability is a generic feature of polypeptide chains.

Hydrogen exchange, core modules, and new designed proteins.

A strategy for design of new proteins that mimic folding properties of native proteins is based on peptides modeled on the slow exchange cores of natural proteins. We have synthesized peptides, called core modules, that correspond to the elements of secondary structure that carry the very slowest exchanging amides in a protein. The expectation is that, if soluble in water, core modules will form conformational ensembles that favor native-like structure.

BetaCore, a designed water soluble four-stranded antiparallel beta-sheet protein.

BetaCore is a designed approximately 50-residue protein in which two BPTI-derived core modules, CM I and CM II, are connected by a 22-atom cross-link. At low temperature and pH 3, homo- and heteronuclear NMR data report a dominant folded ('f') conformation with well-dispersed chemical shifts, i, i+1 periodicity, numerous long-range NOEs, and slowed amide hydrogen isotope exchange patterns that is a four-stranded antiparallel beta-sheet with nonsymmetrical and specific association of CM I and CM II. BetaCore 'f' conformations undergo reversible, global, moderately cooperative, non-two-state thermal transitions to an equilibrium ensemble of unfolded 'u' conformations.