title: Novel components of an active mitochondrial K(+)/H(+) exchange.
abstract: Defects of the mitochondrial K(+)/H(+) exchanger (KHE) result in increased matrix K(+) content, swelling, and autophagic decay of the organelle. We have previously identified the yeast Mdm38 and its human homologue LETM1, the candidate gene for seizures in Wolf-Hirschhorn syndrome, as essential components of the KHE. In a genome-wide screen for multicopy suppressors of the pet(-) (reduced growth on nonfermentable substrate) phenotype of mdm38Delta mutants, we now characterized the mitochondrial carriers PIC2 and MRS3 as moderate suppressors and MRS7 and YDL183c as strong suppressors. Like Mdm38p, Mrs7p and Ydl183cp are mitochondrial inner membrane proteins and constituents of approximately 500-kDa protein complexes. Triple mutant strains (mdm38Delta mrs7Delta ydl183cDelta) exhibit a remarkably stronger pet(-) phenotype than mdm38Delta and a general growth reduction. They totally lack KHE activity, show a dramatic drop of mitochondrial membrane potential, and heavy fragmentation of mitochondria and vacuoles. Nigericin, an ionophore with KHE activity, fully restores growth of the triple mutant, indicating that loss of KHE activity is the underlying cause of its phenotype. Mdm38p or overexpression of Mrs7p, Ydl183cp, or LETM1 in the triple mutant rescues growth and KHE activity. A LETM1 human homologue, HCCR-1/LETMD1, described as an oncogene, partially suppresses the yeast triple mutant phenotype. Based on these results, we propose that Ydl183p and the Mdm38p homologues Mrs7p, LETM1, and HCCR-1 are involved in the formation of an active KHE system.
authors.affiliation: Department of Microbiology, Max F. Perutz Laboratories, Vienna University, A-1030 Vienna, Austria.
authors.forename: Ludmila
authors.initials: L
authors.lastname: Zotova
authors.forename: Markus
authors.initials: M
authors.lastname: Aleschko
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sponder
authors.forename: Roland
authors.initials: R
authors.lastname: Baumgartner
authors.forename: Siegfried
authors.initials: S
authors.lastname: Reipert
authors.forename: Monika
authors.initials: M
authors.lastname: Prinz
authors.forename: Rudolf J
authors.initials: RJ
authors.lastname: Schweyen
authors.forename: Karin
authors.initials: K
authors.lastname: Nowikovsky
mesh_terms: D002846:Chromatography, Affinity; D017353:Gene Deletion; D016681:Genome, Fungal; D006801:Humans; D006859:Hydrogen / Q000378:metabolism*; D047468:Immunoprecipitation; D053078:Membrane Potential, Mitochondrial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D011188:Potassium / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology*; D013489:Suppression, Genetic
chemical_list: C488529:MDM38 protein, S cerevisiae; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D017923:Sodium-Hydrogen Exchangers; C509424:YLH47 protein, S cerevisiae; C549927:Ydl183c protein, S cerevisiae; D006859:Hydrogen; D011188:Potassium