title: Superoxide inhibits 4Fe-4S cluster enzymes involved in amino acid biosynthesis. Cross-compartment protection by CuZn-superoxide dismutase.
abstract: Among the phenotypes of Saccharomyces cerevisiae mutants lacking CuZn-superoxide dismutase (Sod1p) is an aerobic lysine auxotrophy; in the current work we show an additional leaky auxotrophy for leucine. The lysine and leucine biosynthetic pathways each contain a 4Fe-4S cluster enzyme homologous to aconitase and likely to be superoxide-sensitive, homoaconitase (Lys4p) and isopropylmalate dehydratase (Leu1p), respectively. We present evidence that direct aerobic inactivation of these enzymes in sod1 Delta yeast results in the auxotrophies. Located in the cytosol and intermembrane space of the mitochondria, Sod1p likely provides direct protection of the cytosolic enzyme Leu1p. Surprisingly, Lys4p does not share a compartment with Sod1p but is located in the mitochondrial matrix. The activity of a second matrix protein, the tricarboxylic acid cycle enzyme aconitase, was similarly lowered in sod1 Delta mutants. We measured only slight changes in total mitochondrial iron and found no detectable difference in mitochondrial "free" (EPR-detectable) iron making it unlikely that a gross defect in mitochondrial iron metabolism is the cause of the decreased enzyme activities. Thus, we conclude that when Sod1p is absent a lysine auxotrophy is induced because Lys4p is inactivated in the matrix by superoxide that originates in the intermembrane space and diffuses across the inner membrane.
authors.affiliation: Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095-1569, USA.
authors.forename: Matthew Alan
authors.initials: MA
authors.lastname: Wallace
authors.forename: Lee-Loung
authors.initials: LL
authors.lastname: Liou
authors.forename: Jacob
authors.initials: J
authors.lastname: Martins
authors.forename: Matthew H S
authors.initials: MH
authors.lastname: Clement
authors.forename: Sasaneh
authors.initials: S
authors.lastname: Bailey
authors.forename: Valter D
authors.initials: VD
authors.lastname: Longo
authors.forename: Joan Selverstone
authors.initials: JS
authors.lastname: Valentine
authors.forename: Edith Butler
authors.initials: EB
authors.lastname: Gralla
mesh_terms: D000596:Amino Acids / Q000096:biosynthesis*; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005838:Genotype; D006836:Hydro-Lyases / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D007930:Leucine / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D010269:Paraquat; D010641:Phenotype; D010957:Plasmids / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D013482:Superoxide Dismutase / Q000737:chemistry*; D013481:Superoxides / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000596:Amino Acids; D007506:Iron-Sulfur Proteins; D013481:Superoxides; D007501:Iron; D013482:Superoxide Dismutase; D006836:Hydro-Lyases; C107855:homoaconitate hydratase; D007930:Leucine; D008239:Lysine; D010269:Paraquat