The human metallochaperone HAH1 has been produced in Escherichia coli with four additional amino acids at the C-terminus and characterized in solution by NMR spectroscopy, both with and without copper(I). The solution structure of the apo-HAH1 monomer has a root-mean-square-deviation (RMSD) of 0.50 A for the coordinates of the backbone atoms and 0.96 A for all heavy atoms. These values compare, respectively, with 0.45 and 0.95 A for copper(I)-HAH1. There are only minor structural rearrangements upon copper(I) binding. In particular, the variation of interatomic interactions around the metal-binding region is limited to a movement of Lys60 toward the metal site. The protein structures are similar to those obtained by X-ray crystallography in a variety of derivatives, with backbone RMSD values below 1 A. In the holoprotein, copper(I) is confirmed to be two coordinated. If these data are compared with those of orthologue proteins, we learn that HAH1 has a lower tendency to change coordination number from two to three. Such a switch in coordination is a key step in copper transfer.