title: Identification of the N-terminal region of TjZNT2, a Zrt/Irt-like protein family metal transporter, as a novel functional region involved in metal ion selectivity.
abstract: The Zrt/Irt-like protein (ZIP) family of transporter proteins is involved in the uptake of essential metal elements in plants. Two homologous ZIP genes from Thlaspi japonicum, TjZNT1 and TjZNT2, encode products that share high amino acid sequence similarity except at the N-terminus and the cytoplasmic loop between transmembrane domains III and IV, and that have been shown to be Zn(2+) and Mn(2+) transporters, respectively. To identify the region that determines the ion selectivity of these transporters, we constructed a series of TjZNT1 and TjZNT2 chimeric genes and assayed for the Zn(2+) uptake of yeast cells expressing them. As a result, the extracellular N-terminal ends were identified as regions involved in Zn(2+) selectivity. TjZNT2 possesses a 36 amino acid hydrophilic extension at its N-terminus that is absent in native TjZNT1, and a mutant TjZNT2 lacking the N-terminal extension was shown to possess Zn(2+) uptake activity. This suggests that the extended N-terminal region inhibits Zn(2+) transport by TjZNT2. Further studies showed that it is the first 25 amino acid region of the N-terminus that is important for the inhibition of Zn(2+) transport. Furthermore, the N-terminal truncated TjZNT2 lacked Mn(2+) uptake activity. These findings suggest that the N-terminal region is a novel substrate selector in the ZIP family of transporters.
authors.affiliation: Graduate School of Bioresources, Mie University, Tsu, Japan.
authors.forename: Sho
authors.initials: S
authors.lastname: Nishida
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Morinaga
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Obata
authors.forename: Takafumi
authors.initials: T
authors.lastname: Mizuno
mesh_terms: D001692:Biological Transport / Q000235:genetics / Q000502:physiology*; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008670:Metals / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D031227:Thlaspi / Q000235:genetics / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D008670:Metals; D010940:Plant Proteins; D015032:Zinc