Metal Binding Domains 3 and 4 of the Wilson Disease Protein: Solution Structure and Interaction with the Copper(I) Chaperone HAH1†,‡

ABSTRACT: The Wilson disease protein or ATP7B is a P1B-type ATPase involved in human copper homeostasis. The extended N-terminus of ATP7B protrudes into the cytosol and contains six Cu(I) binding domains. This report presents the NMR structure of the polypeptide consisting of soluble Cu(I) binding domains 3 and 4. The two domains exhibit ferredoxin-like folds, are linked by a flexible loop, and act independently of one another. Domains 3 and 4 tend to aggregate in a concentration-dependent manner involving nonspecific intermolecular interactions. Both domains can be loaded with Cu(I) when provided as an acetonitrile complex or by the chaperone HAH1. HAH1 forms a 70 % complex with domain 4 that is in fast exchange with the free protein in solution. The ability of HAH1 to form a complex only with some domains of ATP7B is an interesting property of this class of proteins and may have a signaling role in the function of the ATPases. Human ATP7B (WLN)1 is a member of the P1B-type ATPase family that plays a crucial role in copper transport and homeostasis in the body (1). The WLN protein, like the other human copper ATPase, the Menkes protein (MNK hereafter), delivers copper to the secretory pathway of th