In proteins, Zn(II) can play both structural and/or catalytic roles. Zn(II) displays high flexibility with respect to the number of ligands it can coordinate in its first coordination shell. In aqueous solution, Zn(II) is found to bind six different ligands in octahedral coordination . However, inside proteins, it is usually found coordinating four ligands adopting a tetrahedral geometry. In some catalytic binding sites, Zn(II) appears pentacoordinated and, rarely, hexacoordinated . Within proteins, Zn(II) coordinates to different amino acid types, with cysteine (33%), histidine (31%) and aspartic/glutamic acid (11% and 7%, respectively) being the most prevalent . In the specific case of Aβ-Zn(II) systems, coordination exclusively happens via multiple combinations of histidine and glutamic/aspartic acid residues (see Figure ).