Copper(I)-mediated protein-protein interactions result from suboptimal interaction surfaces

International audienceThe homeostasis of metal ions in cells is the result of the contribution of several cellular pathways that involve transient, often weak, protein-protein interactions. Metal transfer typically implies the formation of adducts where the metal itself acts as a bridge between proteins, by coordinating residues of both interacting partners. Here we addressed the interaction between the human copper(I)-chaperone HAH1 and one metal-binding domain of one of its partners, namely the P-type copper-transporting ATPase ATP7A. The adduct was structurally characterized in solution, in the presence of copper(I), and through X-ray crystallography, upon replacing copper(I) with cadmium(II). Further insight was obtained through molecular modelling techniques and site-directed mutagenesis. It is found that the interaction involves a relatively small interface (less than 1000 Å2) with a low fraction of non-polar atoms. These observations provide a possible explanation for the low affinity of the two apo-proteins. It appears that electrostatics is important in selecting which domain of the ATPase is able to form detectable amounts of the metal-mediatd adduct with HAH1