title: Probing the binding of Cu(2+) ions to a fragment of the Aβ(1-42) polypeptide using fluorescence spectroscopy, isothermal titration calorimetry and molecular dynamics simulations.
abstract: Steady-state and time-resolved fluorescence quenching measurements supported by isothermal titration calorimetry (ITC) and molecular dynamics simulations (MD), with the NMR-derived restraints, were used to investigate the interactions of Cu(2+) ions with a fragment of the Aβ(1-42) polypeptide, Aβ(5-16) with the following sequence: Ac-Arg-His-Asp-Ser-Gly-Tyr-Glu-Val-His-His-Gln-Lys-NH2, denoted as HZ1. The studies presented in this paper, when compared with our previous results (Makowska et al., Spectrochim. Acta A 153: 451-456), show that the affinity of the peptide to metal ions is conformation-dependent. All the measurements were carried out in 20mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution, pH6.0. The Stern-Volmer equations, along with spectroscopic observations, were used to determine the quenching and binding parameters. The obtained results unequivocally suggest that Cu(2+) ions quench the fluorescence of HZ1 only through a static quenching mechanism, in contrast to the fragment from the N-terminal part of the FPB28 protein, with sequence Ac-Tyr-Lys-Thr-Ala-Asp-Gly-Lys-Thr-Tyr- NH2 (D9) and its derivative with a single point mutation: Ac-Tyr-Lys-Thr-Ala-Asn-Gly-Lys-Thr-Tyr- NH2 (D9_M), where dynamic quenching occurred. The thermodynamic parameters (ΔITCH, ΔITCS) for the interactions between Cu(2+) ions and the HZ1 peptide were determined from the calorimetric data. The conditional thermodynamic parameters suggest that, under the experimental conditions, the formation of the Cu(2+)-HZ1 complex is both an enthalpy and entropy driven process.
authors.affiliation: Faculty of Chemistry, University of Gdańsk, ul. Wita Stwosza 63, 80-308 Gdańsk, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Makowska
authors.affiliation: Faculty of Chemistry, University of Gdańsk, ul. Wita Stwosza 63, 80-308 Gdańsk, Poland. Electronic address: krzysztof.zamojc@ug.edu.pl.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Żamojć
authors.affiliation: Faculty of Chemistry, University of Gdańsk, ul. Wita Stwosza 63, 80-308 Gdańsk, Poland.
authors.forename: Dariusz
authors.initials: D
authors.lastname: Wyrzykowski
authors.affiliation: Intercollegiate Faculty of Biotechnology UG&MUG, University of Gdańsk, ul. Abrahama 58, 80-307 Gdańsk, Poland.
authors.forename: Wioletta
authors.initials: W
authors.lastname: Żmudzińska
authors.affiliation: Faculty of Chemistry, University of Gdańsk, ul. Wita Stwosza 63, 80-308 Gdańsk, Poland.
authors.forename: Dorota
authors.initials: D
authors.lastname: Uber
authors.affiliation: Faculty of Chemistry, University of Gdańsk, ul. Wita Stwosza 63, 80-308 Gdańsk, Poland.
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Wierzbicka
authors.affiliation: Faculty of Chemistry, University of Gdańsk, ul. Wita Stwosza 63, 80-308 Gdańsk, Poland.
authors.forename: Wiesław
authors.initials: W
authors.lastname: Wiczk
authors.affiliation: Faculty of Chemistry, University of Gdańsk, ul. Wita Stwosza 63, 80-308 Gdańsk, Poland.
authors.forename: Lech
authors.initials: L
authors.lastname: Chmurzyński
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D002151:Calorimetry; D002413:Cations, Divalent / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D006801:Humans; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D010446:Peptide Fragments / Q000737:chemistry*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D016229:Amyloid beta-Peptides; D002413:Cations, Divalent; D010446:Peptide Fragments; C075222:amyloid beta-protein (1-42); C000618847:amyloid beta-protein (5-16); D003300:Copper
keywords: Aβ((1–42)) fragments; Fluorescence quenching; Isothermal titration calorimetry; Metal-peptide binding; Molecular dynamics simulations