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  • Title: Ferric Ions Inhibit the Amyloid Fibrillation of β-Lactoglobulin at High Temperature.
    Author: Guzzi R, Rizzuti B, Labate C, Zappone B, De Santo MP.
    Journal: Biomacromolecules; 2015 Jun 08; 16(6):1794-801. PubMed ID: 25989053.
    Abstract:
    The energetics of amyloid fibrillar aggregation of β-lactoglobulin (βLG) following incubation at high temperature and acid pH was studied by differential scanning calorimetry in the presence of Cu(2+) or Fe(3+) cations, and without any metal. Cu(2+) and metal-free protein solutions showed a distinct exothermic response that disappeared almost completely when the Fe(3+) molar concentration was ten times greater than the βLG concentration. Thioflavin T fluorescence studies in solution and atomic force microscopy analysis of the deposit left on flat mica substrates by heat-incubated βLG solutions correlated the absence of exothermic response of Fe(3+)-βLG solutions with a lack of fibril production. In contrast, abundant fibril deposits were observed for Cu(2+)-βLG solutions, with a rich polymorphism of multistrand fibrillar structures. Electron paramagnetic resonance revealed that Fe(3+) permanently binds to βLG in the aggregate state whereas Cu(2+) plays a catalytic role without binding to the protein. We propose that Fe(3+) inhibits fibril production after binding to a key region of the protein sequence, possibly interfering with the nucleation step of the fibrillation process and opening a nonfibrillar aggregation pathway. These findings suggest that transition metal ions can be utilized to effectively modulate protein self-assembly into a variety of structures with distinct morphologies at the nanoscale level.
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