Abstract
Arabidopsis thaliana metal tolerance protein 1 (AtMTP1, 43 kDa) is a member of the cation diffusion facilitator (CDF) family. We previously reported that AtMTP1 was localized in vacuolar membranes and played a key role for Zn tolerance. Heterologous expression of AtMTP1 in a Zn-sensitive zrc1cot1 double mutant strain of Saccharomyces cerevisiae complemented the zinc tolerance in the strain. Vacuolar membrane vesicles prepared from yeast cells of AtMTP1/zrc1cot1 actively incorporated 65Zn2+ in a pH gradient dependent manner, indicating that AtMTP1 functions as a Zn2+/H+ exchanger. However, it is unclear that how AtMTP1 senses zinc concentration and transports zinc ions from the cytosol, where the Zn2+ concentration is is maintained at a very low level. AtMTP1 contains a long His-rich loop between transmembrane domain IV and V. Analysis by site-directed mutagenesis revealed that the His-rich loop is necessary for zinc transport and that several resides are essential.
