Amyloid Beta Aggregation in the Presence of Temperature-Sensitive Polymers

Photocontrolled Reversible Amyloid Fibril Formation of Parathyroid Hormone-Derived Peptides

Peptide fibrillization is crucial in biological processes such as amyloid-related diseases and hormone storage, involving complex transitions between folded, unfolded, and aggregated states. We here employ light to induce reversible transitions between aggregated and nonaggregated states of a peptide, linked to the parathyroid hormone (PTH). The artificial light-switch 3-{[(4-aminomethyl)phenyl]diazenyl}benzoic acid (AMPB) is embedded into a segment of PTH, the peptide PTH25-37, to control aggregation, revealing position-dependent effects. Through in silico design, synthesis, and experimental validation of 11 novel PTH25-37-derived peptides, we predict and confirm the amyloid-forming capabilities of the AMPB-containing peptides. Quantum-chemical studies shed light on the photoswitching mechanism. Solid-state NMR studies suggest that β-strands are aligned parallel in fibrils of PTH25-37, while in one of the AMPB-containing peptides, β-strands are antiparallel. Simulations further highlight the significance of π-π interactions in the latter. This multifaceted approach enabled the identification of a peptide that can undergo repeated phototriggered transitions between fibrillated and defibrillated states, as demonstrated by different spectroscopic techniques. With this strategy, we unlock the potential to manipulate PTH to reversibly switch between active and inactive aggregated states, representing the first observation of a photostimulus-responsive hormone.

Amphiphilic (di-)gradient copoly(2-oxazoline)s are potent amyloid fibril formation inhibitors

MOTIVATION

Amyloidoses are diseases caused by the accumulation of normally soluble proteins in the form of insoluble amyloids, leading to the gradual dysfunction and failure of various organs and tissues. Inhibiting amyloid formation is therefore an important therapeutic target.

HYPOTHESIS

We hypothesized that mono- and di-gradient amphiphilic copolymers of hydrophilic 2-(m)ethyl-2-oxazoline and hydrophobic 2-aryl-2-oxazolines may inhibit amyloid fibril formation.

EXPERIMENTS

In the model system with hen egg white lysozyme (HEWL) as amyloidogenic protein we determined the effect of these polymers on the amyloid formation by making use of the thioflavin T fluorescence, transmission electron microscopy, isothermal titration calorimetry, and dynamic light scattering.

FINDINGS

We found that some gradient copolymers possess very potent concentration-dependent inhibitory effects on HEWL amyloid formation. Structure-activity relationship revealed that copolymers with higher ratios of aromatic monomeric units had stronger amyloid suppression effects, most plausibly due to the combination of hydrophobic and π-π interactions. The measurements also revealed that the polymers that inhibit amyloid formation most plausibly do so in the form of micelles that interact with the growing amyloid fibril ends, not with isolated HEWL molecules in solution. These findings suggest the potential use of these gradient copolymers as therapeutic agents for amyloidoses.

Protein-Inspired Control over Synthetic Polymer Folding for Structured Functional Nanoparticles in Water

The folding of proteins into functional nanoparticles with defined 3D structures has inspired chemists to create simple synthetic systems mimicking protein properties. The folding of polymers into nanoparticles in water proceeds via different strategies, resulting in the global compaction of the polymer chain. Herein, we review the different methods available to control the conformation of synthetic polymers and collapse/fold them into structured, functional nanoparticles, such as hydrophobic collapse, supramolecular self-assembly, and covalent cross-linking. A comparison is made between the design principles of protein folding to synthetic polymer folding and the formation of structured nanocompartments in water, highlighting similarities and differences in design and function. We also focus on the importance of structure for functional stability and diverse applications in complex media and cellular environments.

Modulating the Fibrillization of Parathyroid-Hormone (PTH) Peptides: Azo-Switches as Reversible and Catalytic Entities

We here report a novel strategy to control the bioavailability of the fibrillizing parathyroid hormone (PTH)-derived peptides, where the concentration of the bioactive form is controlled by an reversible, photoswitchable peptide. PTH1–84, a human hormone secreted by the parathyroid glands, is important for the maintenance of extracellular fluid calcium and phosphorus homeostasis. Controlling fibrillization of PTH1–84 represents an important approach for in vivo applications, in view of the pharmaceutical applications for this protein. We embed the azobenzene derivate 3-{[(4-aminomethyl)phenyl]diazenyl}benzoic acid (3,4′-AMPB) into the PTH-derived peptide PTH25–37 to generate the artificial peptide AzoPTH25–37 via solid-phase synthesis. AzoPTH25–37 shows excellent photostability (more than 20 h in the dark) and can be reversibly photoswitched between its cis/trans forms. As investigated by ThT-monitored fibrillization assays, the trans-form of AzoPTH25–37 fibrillizes similar to PTH25–37, while the cis-form of AzoPTH25–37 generates only amorphous aggregates. Additionally, cis-AzoPTH25–37 catalytically inhibits the fibrillization of PTH25–37 in ratios of up to one-fifth. The approach reported here is designed to control the concentration of PTH-peptides, where the bioactive form can be catalytically controlled by an added photoswitchable peptide.

From Small Molecules to Synthesized Polymers: Potential Role in Combating Amyloidogenic Disorders

The concept of developing novel anti-amyloid inhibitors in the scientific community has engrossed remarkable research interests and embraced significant potential to resolve numerous pathological conditions including neurological as well as non-neuropathic disorders associated with amyloid protein aggregation. These pathological conditions have harmful effects on cellular activities which include malfunctioning of organs and tissue, cellular impairment, etc. To date, different types of small molecular probes like polyphenolic compounds, nanomaterials, surfactants, etc. have been developed to address these issues. Recently synthetic polymeric materials are extensively investigated to explore their role in the protein aggregation pathway. On the basis of these perspectives, in this review article, we have comprehensively summarized the current perspectives on protein misfolding and aggregation and importance of therapeutic approaches in designing novel effective inhibitors. The main purpose of this review article is to provide a detailed perspective of the current landscape as well as trailblazing voyage of various inhibitors ranging from small molecular probes to polymeric scaffolds in the field of protein misfolding and aggregation. A particular emphasis is given on the structural role and molecular mechanistic pathway involved in modulating the aggregation pathway to further inspire the researchers and shed light in this bright research field.

Synthesis and Aggregation of Polymer-Amyloid β Conjugates

Modulating the assembly of medically relevant peptides and proteins via macromolecular engineering is an important step in modifying their overall pathological effects. The synthesis of polymer-peptide conjugates composed of the amyloidogenic Alzheimer peptide, Aβ_1-40 , and poly(oligo(ethylene glycol)_m acrylates) (m = 2,3) with different molecular weights (M_n = 1400-6600 g mol^-1 ) is presented here. The challenging conjugation of a synthetic polymer to an in situ aggregating protein is established via two different coupling strategies, only successful for polymers with molecular weights not exceeding 6600 g mol^-1 , relying on resin-based synthesis or solution-based coupling chemistries. The conjugates are characterized by high-performance liquid chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The aggregation of these polymer-Aβ_1-40 conjugates, as monitored via thioflavine-T (ThT)-fluorescence spectroscopy, is accelerated mainly upon attaching the polymers. However, the appearance of the observed fibrils is different from those composed of native Aβ_1-40, specifically with respect to length and morphology of the obtained aggregates. Instead of long, unbranched fibrils characteristic for Aβ_1-40 , bundles of short aggregates are observed for the conjugates. Finally, the ThT kinetics and morphologies of Aβ_1-40 fibrils formed in the presence of the conjugates give some mechanistic insights.

Modulation of amyloid β peptide aggregation by hydrophilic polymers

Careful balance of hydrophilicity of precisely engineered polymers alters aggregation of the amyloidogenic protein Aβ_1–40.

One-Pot Synthesis of Thermoresponsive Amyloidogenic Peptide-Polymer Conjugates via Thio-Bromo "Click" Reaction of RAFT Polymers

A synthetic strategy to efficiently prepare main-chain peptide-polymer conjugates probing their aggregation in solution is described. An in situ tandem reaction based on aminolysis/thio-bromo "click" reaction is performed to tether an amyloidogenic peptide fragment amyloid-β_17-20 (Leu-Val-Phe-Phe (LVFF)) to the ω-chain end of poly(diethylene glycol methyl ether acrylate) (PDEGA), prepared via reversible addition fragmentation chain transfer polymerization. Structural confirmation of the constructed conjugates PDEGA-LVFF (M_n,SEC = 5600, Ð = 1.21), (M_n,SEC = 7600, Ð = 1.16), and (M_n,SEC = 8900, Ð = 1.15) is successfully made by combined studies of ¹ H NMR, size-exclusion chromatography, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry. The effect of the peptidic constituent on the thermoresponsive behavior of the polymer is examined by UV-vis spectroscopy, and the self-assembly behavior of the amphiphilic conjugate is further exploited, exhibiting micellar morphology in aqueous solution.