The Route from the Folded to the Amyloid State: Exploring the Potential Energy Surface of a Drug-Like Miniprotein |
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Authors: | Nóra Taricska Dániel Horváth Dr Dóra K Menyhárd Hanna Ákontz-Kiss Masahiro Noji Dr Masatomo So Prof Dr Yuji Goto Prof Dr Toshimichi Fujiwara Prof Dr András Perczel |
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Institution: | 1. Laboratory of Structural Chemistry and Biology &, MTA-ELTE Protein Modeling Research Group, Eötvös Loránd University, Pázmány Péter sétány 1A, 1117 Budapest, Hungary;2. Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871 Japan |
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Abstract: | The amyloid formation of the folded segment of a variant of Exenatide (a marketed drug for type-2 diabetes mellitus) was studied by electronic circular dichroism (ECD) and NMR spectroscopy. We found that the optimum temperature for E5 protein amyloidosis coincides with body temperature and requires well below physiological salt concentration. Decomposition of the ECD spectra and its barycentric representation on the folded-unfolded-amyloid potential energy surface allowed us to monitor the full range of molecular transformation of amyloidogenesis. We identified points of no return (e.g.; T=37 °C, pH 4.1, cE5=250 μm , cNaCl=50 mm , t>4–6 h) that will inevitably gravitate into the amyloid state. The strong B-type far ultraviolet (FUV)-ECD spectra and an unexpectedly strong near ultraviolet (NUV)-ECD signal (Θ≈275–285 nm) indicate that the amyloid phase of E5 is built from monomers of quasi-elongated backbone structure (φ≈−145°, ψ≈+145°) with strong interstrand Tyr↔Trp interaction. Misfolded intermediates and the buildup of “toxic” early-stage oligomers leading to self-association were identified and monitored as a function of time. Results indicate that the amyloid transition is triggered by subtle misfolding of the α-helix, exposing aromatic and hydrophobic side chains that may provide the first centers for an intermolecular reorganization. These initial clusters provide the spatial closeness and sufficient time for a transition to the β-structured amyloid nucleus, thus the process follows a nucleated growth mechanism. |
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Keywords: | aggregation amyloid beta-peptides protein folding protein modeling |
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