Solution structure of the N-domain of Wilson disease protein: Distinct nucleotide-binding environment and effects of disease mutations

Wilson disease protein (ATP7B) is a copper-transporting P-1B-type ATPase that regulates copper homeostasis and biosynthesis of copper-containing enzymes in human tissues. Inactivation of ATP7B or related ATP7A leads to severe neurodegenerative disorders, whereas their overexpression contributes to cancer cell resistance to chemotherapeutics. Copper-transporting ATPases differ from other P-type ATPases in their topology and the sequence of their nucleotide-binding domain (N-domain). To gain insight into the structural basis of ATP7B function, we have solved the structure of the ATP7B N-domain in the presence of ATP by using heteronuclear multidimensional NMR spectroscopy. The N-domain consists of a six-stranded beta-sheet with two adjacent alpha-helical hairpins and, unexpectedly, shows higher similarity to the bacterial K+-transporting ATPase KdpB than to the mammalian Ca2+-ATPase or Na+,K+-ATPase. The common core structure of P-type ATPases is retained in the 3D fold of the N-domain; however, the nucleotide coordination environment of ATP7B within this fold is different. The residues H1069, 61099, 61101, 11102, 61149, and N1150 conserved in the P-1B-ATPase subfamily contribute to ATP binding. Analysis of the frequent disease mutation H1069Q demonstrates that this mutation does not significantly affect the structure of the N-domain but prevents tight binding of ATP. The structure of the N-domain accounts for the disruptive effects of > 30 known Wilson disease mutations. The unique features of the N-domain provide a structural basis for the development of specific inhibitors and regulators of ATP7B.