Physiological analysis of His-rich loop of Arabidopsis vacuolar membrane Zn transporter AtMTP1

Abstract

In Arabidopsis thaliana , vacuolar membrane Metal Tolerance Protein 1 (MTP1) plays important role for zinc homeostasis. We reported that AtMTP1 is a Zn²⁺/H⁺ exchanger and involved in zinc tolerance in plants by transporting excess cytoplasmic zinc into vacuoles. Furthermore, we demonstrated that deletion of a His-rich loop caused marked increase in V_max value and proposed that the His-rich loop is essential for maintenance of t the cytoplasmic zinc level (JBC, 283: 8374-8383, 2008; PCP, 50: 1156-1170, 2009). In this study, we made Arabidopsis plants overexpressing AtMTP1 or AtMTP1Δ185-216 and analyzed metal tolerance under zinc excess conditions and zinc distribution in cells by using a zinc fluorescent probe Zinpyr-1 in order to elucidate physiological role of the His-rich loop. We also examined differences in protein stability, ion selectivity and zinc transport ability between AtMTP1 and AtMTP1Δ185-216 in A. thaliana. We will discuss about molecular function and physiological role of the His-rich loop.