This short domain, part of the extra-cellular N-terminus of the amyloid precursor protein, APP, can bind both copper and zinc, CuBD. The structure of Cu2+-bound CuBD reveals that the metal ligands are His147, His151, Tyr168 and two water molecules, which are arranged in a square pyramidal geometry. The structure of Cu+-bound CuBD is almost identical to the Cu2+-bound structure except for the loss of one of the water ligands. The geometry of the site is unfavourable for Cu+, thus providing a mechanism by which CuBD could readily transfer Cu ions to other proteins.

1: Structural studies of the Alzheimer's amyloid precursor protein copper-binding domain reveal how it binds copper ions. Kong GK, Adams JJ, Harris HH, Boas JF, Curtain CC, Galatis D, Masters CL, Barnham KJ, McKinstry WJ, Cappai R, Parker MW; J Mol Biol. 2007;367:148-161. PMID:17239395