title: Metal selectivity determinants in a family of transition metal transporters.
abstract: Metal tolerance proteins (MTPs) are plant members of the cation diffusion facilitator (CDF) transporter family involved in cellular metal homeostasis. Members of the CDF family are ubiquitously found in all living entities and show principal selectivity for Zn(2+), Mn(2+), and Fe(2+). Little is known regarding metal selectivity determinants of CDFs. We identified a novel cereal member of CDFs in barley, termed HvMTP1, that localizes to the vacuolar membrane. Unlike its close relative AtMTP1, which is highly selective for Zn(2+), HvMTP1 exhibits selectivity for both Zn(2+) and Co(2+) as assessed by its ability to suppress yeast mutant phenotypes for both metals. Expression of HvMTP1/AtMTP1 chimeras in yeast revealed a five-residue sequence within the AtMTP1 N-segment of the His-rich intracytoplasmic loop that confines specificity to Zn(2+). Furthermore, mutants of AtMTP1 generated through random mutagenesis revealed residues embedded within transmembrane domain 3 that additionally specify the high degree of Zn(2+) selectivity. We propose that the His-rich loop, which might play a role as a zinc chaperone, determines the identity of the metal ions that are transported. The residues within transmembrane domain 3 can also influence metal selectivity, possibly through conformational changes induced at the cation transport site located within the membrane or at the cytoplasmic C-terminal domain.
authors.affiliation: Department of Biology, University of York, York YO10 5DD, United Kingdom. dorina.podar@gmail.com
authors.forename: Dorina
authors.initials: D
authors.lastname: Podar
authors.forename: Judith
authors.initials: J
authors.lastname: Scherer
authors.forename: Zeenat
authors.initials: Z
authors.lastname: Noordally
authors.forename: Pawel
authors.initials: P
authors.lastname: Herzyk
authors.forename: Dietrich
authors.initials: D
authors.lastname: Nies
authors.forename: Dale
authors.initials: D
authors.lastname: Sanders
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D001467:Hordeum / Q000235:genetics / Q000378:metabolism*; D017136:Ion Transport / Q000502:physiology; D008670:Metals / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D014617:Vacuoles / Q000235:genetics / Q000473:pathology*
chemical_list: D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D008670:Metals; D011993:Recombinant Fusion Proteins; C500829:ZAT protein, Arabidopsis