Structure and mechanism of Zn2+-transporting P-type ATPases

Zinc is an essential micronutrient for all living organisms. It is required for signalling and proper functioning of a range of proteins involved in, for example, DNA binding and enzymatic catalysis(1). In prokaryotes and photosynthetic eukaryotes, Zn2+-transporting P-type ATPases of class IB (ZntA) are crucial for cellular redistribution and detoxification of Zn2+ and related elements(2,3). Here we present crystal structures representing the phosphoenzyme ground state (E2P) and a dephosphorylation intermediate (E2.P-i) of ZntA from Shigella sonnei, determined at 3.2 angstrom and 2.7 angstrom resolution, respectively. The structures reveal a similar fold to Cu+-ATPases, with an amphipathic helix at the membrane interface. A conserved electronegative funnel connects this region to the intramembranous high-affinity ion-binding site and may promote specific uptake of cellular Zn2+ ions by the transporter. The E2P structure displays a wide extracellular release pathway reaching the invariant residues at the high-affinity site, including C392, C394 and D714. The pathway closes in the E2.P-i state, in which D714 interacts with the conserved residue K693, which possibly stimulates Zn2+ release as a built-in counter ion, as has been proposed for H+-ATPases. Indeed, transport studies in liposomes provide experimental support for ZntA activity without counter transport. These findings suggest a mechanistic link between P-IB-type Zn2+-ATPases and P-III-type H+-ATPases and at the same time show structural features of the extracellular release pathway that resemble P-II-type ATPases such as the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase(4,5) (SERCA) and Na+, K+-ATPase(6). These findings considerably increase our understanding of zinc transport in cells and represent new possibilities for biotechnology and biomedicine.