A native Zn/Cd pumping P(1B) ATPase from natural overexpression in a hyperaccumulator plant

We report here the first purification of a P(1B) type ATPase, a group of transporters that occurs in bacteria, plants and animals incl. humans, from a eukaryotic organism in native state. TcHMA4 is a P(1B) type ATPase that is highly expressed in the Cd/Zn hyperaccumulator plant Thlaspi caerulescens and contains a C-terminal 9-histidine repeat. After isolation from roots, we purified TcHMA4 protein via metal affinity chromatography. The purified protein exhibited Cd- and Zn-activated ATPase activity after reconstitution into lipid vesicles, showing that it was in its native state. Gels of crude root extract and of the purified protein revealed TcHMA4-specific bands of about 50 and 60kDa, respectively, while the TcHMA4 mRNA predicts a single protein with a size of 128kDa. This indicates the occurrence of post-translational processing; the properties of the two bands were characterised by their activity and binding properties.