Quantification of the binding properties of Cu2+ to the amyloid beta peptide: coordination spheres for human and rat peptides and implication on Cu2+-induced aggregation.
There is no consensus on the coordinating ligands for Cu(2+) by Abeta. However, the differences in peptide sequence between human and rat have been hypothesized to alter metal ion binding in a manner that alters Cu(2+)-induced aggregation of Abeta. Herein, we employ isothermal titration calorimetry (ITC), circular dichroism (CD), and electron paramagnetic resonance (EPR) spectroscopy to examine the Cu(2+) coordination spheres to human and rat Abeta and an extensive set of Abeta(16) mutants. EPR of the mutant peptides is consistent with a 3N1O binding geometry, like the native human peptide at pH 7.4. The thermodynamic data reveal an equilibrium between three coordination spheres, {NH(2), O, N(Im)(His6), N(-)}, {NH(2), O, N(Im)(His6), N(Im)(His13)}, and {NH(2), O, N(Im)(His6), N(Im)(His14)}, for human Abeta(16) but one dominant coordination for rat Abeta(16), {NH(2), O, N(Im)(His6), N(-)}, at pH 7.4-6.5. ITC and CD data establish that the mutation R5G is sufficient for reproducing this difference in Cu(2+) binding properties at pH 7.4. The substitution of bulky and positively charged Arg by Gly is proposed to stabilize the coordination {NH(2), O-, N(Im)(His6), N(-)} that then results in one dominating coordination sphere for the case of the rat peptide. The differences in the coordination geometries for Cu(2+) by the human and rat Abeta are proposed to contribute to the variation in the ability of Cu(2+) to induce aggregation of Abeta peptides.
Hong
Lian
L
Department of Chemistry, Duke University, Durham, North Carolina 27708, USA. lian.hong@duke.edu
Carducci
Tessa M
TM
Bush
William D
WD
Dudzik
Christopher G
CG
Millhauser
Glenn L
GL
Simon
John D
JD
D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D000818:Animals; D002151:Calorimetry; D002942:Circular Dichroism; D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D051381:Rats; D013816:Thermodynamics
D016229:Amyloid beta-Peptides; D008024:Ligands; D003300:Copper