title: Binding of zinc(II) and copper(II) to the full-length Alzheimer's amyloid-beta peptide.
abstract: There is evidence that binding of metal ions like Zn2+ and Cu2+ to amyloid beta-peptides (Abeta) may contribute to the pathogenesis of Alzheimer's disease. Cu2+ and Zn2+ form complexes with Abeta peptides in vitro; however, the published metal-binding affinities of Abeta vary in an enormously large range. We studied the interactions of Cu2+ and Zn2+ with monomeric Abeta(40) under different conditions using intrinsic Abeta fluorescence and metal-selective fluorescent dyes. We showed that Cu(2+) forms a stable and soluble 1 : 1 complex with Abeta(40), however, buffer compounds act as competitive copper-binding ligands and affect the apparent K(D). Buffer-independent conditional K(D) for Cu(II)-Abeta(40) complex at pH 7.4 is equal to 0.035 micromol/L. Interaction of Abeta(40) with Zn2+ is more complicated as partial aggregation of the peptide occurs during zinc titration experiment and in the same time period (within 30 min) the initial Zn-Abeta(40) complex (K(D) = 60 micromol/L) undergoes a transition to a more tight complex with K(D) approximately 2 micromol/L. Competition of Abeta(40) with ion-selective fluorescent dyes Phen Green and Zincon showed that the K(D) values determined from intrinsic fluorescence of Abeta correspond to the binding of the first Cu2+ and Zn2+ ions to the peptide with the highest affinity. Interaction of both Zn2+ and Cu2+ ions with Abeta peptides may occur in brain areas affected by Alzheimer's disease and Zn2+-induced transition in the peptide structure might contribute to amyloid plaque formation.
authors.affiliation: Department of Gene Technology, Tallinn University of Technology, Akadeemia tee, Tallinn, Estonia. vello.tougu@ttu.ee
authors.forename: Vello
authors.initials: V
authors.lastname: Tõugu
authors.forename: Ann
authors.initials: A
authors.lastname: Karafin
authors.forename: Peep
authors.initials: P
authors.lastname: Palumaa
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D001667:Binding, Competitive; D001923:Brain Chemistry; D002413:Cations, Divalent / Q000737:chemistry / Q000378:metabolism; D003300:Copper / Q000737:chemistry / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry / Q000378:metabolism*
chemical_list: D016229:Amyloid beta-Peptides; D002413:Cations, Divalent; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); D003300:Copper; D015032:Zinc