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Abstract
The vacuolar Zn2+/H+ antiporter of Arabidopsis thaliana, AtMTP1, has a cytosolic histidine‐rich loop (His‐loop). We characterized the structures and Zn2+‐binding properties of the His‐loop and other domains. Circular dichroism analyses revealed that the His‐loop partly consists of a polyproline type II structure and that its conformational change is induced by Zn2+ as well as the C‐terminal domain. Isothermal titration calorimetry of the His‐loop revealed a binding number of four Zn2+ per molecule. Numbers of Ni and Co associated with the His‐loop were approximately one ion per molecule and the thermodynamic parameters of the association with these ions were different from that of Zn2+. These results suggest the involvement of the His‐loop in sensing cytosolic Zn2+ and in the regulation of zinc transport activity through Zn2+‐induced structural change.
