Murine Aβ4–x Peptides Retain High-Affinity Redox-Silent Cu2+ Binding

Abstract β-Amyloid peptides N-truncated at Phe4 (Aβ4–x) contain an amino-terminal Cu- and Ni-binding (ATCUN) motif that can form high-affinity, redox-silent Cu2+ complexes. Human Aβ4–40/42 is present in the brains of individuals with and without Alzheimer’s disease, and soluble Aβ4–9 can be generated by neprilysin proteolysis of Aβ1–40/42 in vitro. These observations led to the proposal that Aβ4–x may be functional Cu2+-binding peptides. Because amyloid precursor protein is constitutively expressed in mammals, this study assessed whether murine Aβ4–x peptides retain the properties of the human analogues. Cu2+ coordination, binding affinity, and redox activity were compared for murine and human Aβ4–9 and Aβ4–16. The murine peptides formed Cu2+ complexes with spectroscopic parameters closely matching those of the human peptides. Competitive binding against glycylglycylhistidine gave conditional Cu2+ dissociation constants at pH 7.4 of 3–4 fM for murine Aβ4–x and 8–10 fM for human Aβ4–x. All Cu(Aβ4–x) complexes were redox-silent in an aminophenyl fluorescein/ascorbate assay. Thus, murine Aβ4–x has the chemical capacity required for a Cu2+-binding role if generated in vivo. However, because endogenous murine Aβ4–x has not been detected in wild-type mice, the present findings challenge the support for a broadly conserved physiological role for Aβ4–x in mammalian Cu2+ handling.