Fig. 2

Diverse speciation of copper in chaperons and targets. Upper row left: The two Cys residues Cys22 and Cys25 of the first domain of CCS chaperone (PDB code: 2rsq) [149] bind copper (yellow) with an average distance of 2.2 Å. Upper panel right: Copper (yellow) delivered to the target enzyme Cu, Zn-SOD1 (PDB code: 2C9V) [150] is bound by four His residues His46, His48, His63 and His120, and characterized by a range of Cu-His distances from 2.1 Å to 2.5 Å. Lower panel: The position of copper in the chaperon-Cu-target complex between chaperon HAH1 (magenta) and the first domain of the target ATP7A (Menkes protein, MNK1) (green) (PDB code: 2k1r) [152]). Three Cys residues fitting in both HAH1 (Cys12, Cys15) and MNK1 (Cys15, Cys18) CXXC motifs participate in the transition of copper from HAH1 to MNK1 [152]. Specifically, Cys12 of HAH1 and Cys15 of MNK1 are required for the formation of the HAH1-Cu-MNK1 complex, while the third Cys may be either of the Cys15 of HAH1 or the Cys18 of MNK1. Three coordinating Cys side chains are shown around the copper ion, all with a distance of 2.1 Å, the fourth Cys, which does not bind the metal thus far, is shown in green