Solution Structure and Backbone Dynamics of the Cu(I) and Apo Forms of the Second Metal-Binding Domain of the Menkes Protein ATP7A<sup>†</sup>

The second domain of the human Menkes protein (MNK2), formed by 72 residues, has been expressed in <i>Escherichia coli</i>, and its structure has been determined by NMR in both the apo and copper-loaded forms. The structures, obtained with <sup>13</sup>C- and <sup>15</sup>N-labeled samples, are of high quality with backbone rmsd values of 0.51 and 0.41 Å and CYANA target functions of 0.39 and 0.38 Å<sup>2</sup>, respectively. The loop involved in copper binding is part of a hydrophobic patch, which is maintained in both forms. Conformational mobility is observed in the apo form in the same loop. A comparison with metallochaperones and soluble domains of P-type ATPases allows us to relate the primary structure to the occurrence of structural rearrangements upon copper binding.