title: The G-M-N motif determines ion selectivity in the yeast magnesium channel Mrs2p.
abstract: The highly conserved G-M-N motif of the CorA-Mrs2-Alr1 family of Mg(2+) channels has been shown to be essential for Mg(2+) transport. We performed random mutagenesis of the G-M-N sequence of Saccharomyces cerevisiae Mrs2p in an unbiased genetic screen. A large number of mutants still capable of Mg(2+) influx, albeit below the wild-type level, were generated. Growth complementation assays, performed in media supplemented with Ca(2+) or Co(2+) or Mn(2+) or Zn(2+) at varying concentrations, lead to identification of mutants with reduced growth in the presence of Mn(2+) and Zn(2+). We hereby conclude that (1) at least two, but predominantly all three amino acids of the G-M-N motif must be replaced by certain combinations of other amino acids to remain functional, (2) replacement of any single amino acid within the G-M-N motif always impairs the function of Mrs2p, and (3) we show that the G-M-N motif determines ion selectivity, likely in concurrence with the negatively charged loop at the entrance of the channel thereby forming the Mrs2p selectivity filter.
authors.affiliation: Department of Microbiology, Immunobiology, Genetics, Max F. Perutz Laboratories, University of Vienna, Vienna, Austria.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sponder
authors.forename: Soňa
authors.initials: S
authors.lastname: Svidová
authors.forename: Muhammad Bashir
authors.initials: MB
authors.lastname: Khan
authors.forename: Martin
authors.initials: M
authors.lastname: Kolisek
authors.forename: Rudolf J
authors.initials: RJ
authors.lastname: Schweyen
authors.forename: Oliviero
authors.initials: O
authors.lastname: Carugo
authors.forename: Kristina
authors.initials: K
authors.lastname: Djinović-Carugo
mesh_terms: D002118:Calcium / Q000378:metabolism; D003035:Cobalt / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity; D015032:Zinc / Q000378:metabolism
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D003035:Cobalt; D008345:Manganese; D008274:Magnesium; D015032:Zinc; D002118:Calcium