title: Ferric Ions Inhibit the Amyloid Fibrillation of β-Lactoglobulin at High Temperature.
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.
authors.affiliation: †Department of Physics, University of Calabria, Ponte P. Bucci 31C, 87036 Rende (CS), Italy.|‡CNISM Unit, University of Calabria, Ponte P. Bucci, Cubo 31C, 87036 Rende (CS), Italy.
authors.forename: Rita
authors.initials: R
authors.lastname: Guzzi
authors.affiliation: §CNR-NANOTEC, LICRYL-UOS Cosenza and CEMIF.Cal, c/o Department of Physics, University of Calabria, 87036 Rende, Italy.
authors.forename: Bruno
authors.initials: B
authors.lastname: Rizzuti
authors.affiliation: †Department of Physics, University of Calabria, Ponte P. Bucci 31C, 87036 Rende (CS), Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Labate
authors.affiliation: §CNR-NANOTEC, LICRYL-UOS Cosenza and CEMIF.Cal, c/o Department of Physics, University of Calabria, 87036 Rende, Italy.
authors.forename: Bruno
authors.initials: B
authors.lastname: Zappone
authors.affiliation: †Department of Physics, University of Calabria, Ponte P. Bucci 31C, 87036 Rende (CS), Italy.
authors.forename: Maria P
authors.initials: MP
authors.lastname: De Santo
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000187:drug effects; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry* / Q000494:pharmacology; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding
chemical_list: D000682:Amyloid; D007782:Lactoglobulins; D007501:Iron