Photocontrol of Reversible Amyloid Formation with a Minimal-Design Peptide

Abstract

Amyloid aggregates are highly ordered fibrillar assemblies of polypeptides involved in a number of neurodegenerative diseases. Very little is known on the pathways of self-assembly of peptides into the final amyloid fibrils, which is due in part to the difficulty of triggering the aggregation process in a controlled manner. Here we present the design and validation of a cross-linked hexapeptide that reversibly aggregates and dissociates under ultraviolet light irradiation control. First molecular dynamics simulations were carried out to identify, among hundreds of possible sequences, those with the highest propensity to form ordered (-sheet) oligomers in the trans state of the azobenzene cross-linker, and at the same time with the highest solubility in the cis state. In the simulations, the peptides were observed to spontaneously form ordered oligomers with cross-contacts when the cross-linker was in the trans state, whereas in the cis state they self-assemble into amorphous aggregates. For the most promising sequence emerging from the simulations (Ac-Cys-His-Gly-Gln-Cys-Lys-NH2 cross-linked at the two cysteine residues), the photoisomerization of the azobenzene group was shown to induce reversible aggregation by time-resolved light scattering and fluorescence measurements. The amyloid-like fibrillar topology was confirmed by electron microscopy. Potential applications of minimally designed peptides with photoswitchable amyloidogenic propensity are briefly discussed. AbstractAmyloid aggregates are highly ordered fibrillar assemblies of polypeptides involved in a number of neurodegenerative diseases. Very little is known on the pathways of self-assembly of peptides into the final amyloid fibrils, which is due in part to the difficulty of triggering the aggregation process in a controlled manner. Here we present the design and validation of a cross-linked hexapeptide that reversibly aggregates and dissociates under ultraviolet light irradiation control. First molecular dynamics simulations were carried out to identify, among hundreds of possible sequences, those with the highest propensity to form ordered (β-sheet) oligomers in the trans state of the azobenzene cross-linker, and at the same time with the highest solubility in the cis state. In the simulations, the peptides were observed to spontaneously form ordered oligomers with cross-β contacts when the cross-linker was in the trans state, whereas in the cis state they self-assemble into amorphous aggregates. For the most promising sequence emerging from the simulations (Ac-Cys-His-Gly-GlnCys-Lys-NH 2 cross-linked at the two cysteine residues), the photo-isomerization of the azobenzene group was shown to induce reversible aggregation by time-resolved light scattering and fluorescence measurements. The amyloid-like fibrillar topology was confirmed by electron microscopy. Potential applications of minimally-designed peptides with photoswitchable amyloidogenic propensity are briefly discussed.

Infrared Laser-Induced Amyloid Fibril Dissociation: A Joint Experimental/Theoretical Study on the GNNQQNY Peptide

“…In vitro experiments have shown that protein modification by including a molecular photoswitch, such as azobenzene chromophore, followed by light excitation can switch the system from favorable to unfavorable aggregates, resulting in protein disassembly. [21][22][23][24][25][26][27] Goto and colleagues have shown that ultrasonication accelerates the depolymerization of fibrils into monomers in vitro. 28,29 Leinenga et al were able to remove cerebral amyloid deposition in the mouse brain by using repeated scanning ultrasound.…”

Tightening up the structure, lighting up the pathway: application of molecular constraints and light to manipulate protein folding, self-assembly and function

“…These include the studies of Waldauer et al [105] and Deeg et al [106], which demonstrated reversible switching between aggregated and non-aggregated states of azobenzene-linked amyloid-like peptides, and the study of Doran et al [107], which used an azobenzene-containing Aβ(1-42) peptide to investigate whether turn nucleation is the rate-limiting step in fibril self-assembly. In addition, Hamil et al [108] have shown that an azobenzene-containing and light-responsive surfactant can inhibit Aβ(1-40) fibril formation when the azobenzene linkage is in the trans form.…”

Nonequilibrium molecular dynamics simulations of infrared laser-induced dissociation of a tetrameric Aβ42 β-barrel in a neuronal membrane model

“…This guarantees that a light excitation can switch the system from favorable to unfavorable aggregates, resulting in protein disassembly. [39][40][41][42][43][44][45] Mid-infrared free electron laser (FEL) experiment with specific oscillation characteristics of a picosecond pulse structure and a tunable wavelength has also been developed and applied to dissociate amyloid fibrils of lysozyme, insulin and short peptide fragments of the thyroid and calcitonin hormones in in-vitro. [46][47][48][49][50] The molecular dissociation mechanisms from amyloid fibril to oligomers have been studied by laser-induced NEMD simulations.…”