Zinc binding to the NH₂-terminal domain of the Wilson disease copper-transporting ATPase. Implications for in vivo metal ion-mediated regulation of ATPase activity

Mutations in the Wilson disease copper transporting, P-type ATPase lead to the accumulation of toxic levels of copper in the liver, brain, and kidney causing extensive tissue damage and eventual death. The NH₂-terminal domain (∼70 kDa), which contains six copies of the heavy metal-associated repeat GMT/HCXXC, is also able to bind zinc. We have used circular dichroism (CD) and x-ray absorption spectroscopy (XAS) to characterize zinc binding to the NH₂-terminal metal-binding domain. These studies have revealed that zinc is able to bind to this domain with a stoichiometry of 6:1, and upon binding, induces conformational changes in the NH₂-terminal domain. These conformational changes are completely different from those previously observed for copper binding to the domain and lead to an overall loss of secondary structure in the domain. The XAS spectra indicate that zinc is ligated primarily by nitrogen atoms and therefore has low affinity for the heavy metal-associated repeats where copper has been shown to bind. The differences between zinc and copper binding may serve as the basis for the metal-ion mediated regulation of the ATPase in vivo.