The role of His-rich loop of AtMTP1, a vacuolar Zn²⁺/H⁺ antiporter of Arabidopsis thaliana

Abstract

Arabidopsis thaliana metal tolerance protein 1 (AtMTP1) transports zinc into vacuoles by Zn²⁺/H⁺ exchanger mechanism. AtMTP1 has six transmembrane domains and a histidine-rich (His-rich) loop between the 4th and 5th transmembrane domains. Deletion of the most part of the loop decreased Km for Zn²⁺ and increased Vmax of AtMTP1.
In this study, we divided the His-rich loop (25 His residues) into 5 sections, which contain 5 His residues, and substituted His residues in each section with Ala. The AtMTP1 mutants were expressed in a zinc sensitive strain (Δzrc1cot1) of Saccharomyces cerevisiae. The growth of yeast varied with AtMTP mutants under excess Zn conditions. This indicates that each His residue in the loop has an individual role in transport of Zn. Furthermore, we examined the growth of yeast expressing mutant AtMTP1 in the presence of Co²⁺, Cd²⁺, Mn²⁺ or Ni²⁺. We will discuss the metal selectivity of these AtMTP1 mutants.