Yeast aconitase in two locations and two metabolic pathways: seeing small amounts is believing.
The distribution of identical enzymatic activities between different subcellular compartments is a fundamental process of living cells. At present, the Saccharomyces cerevisiae aconitase enzyme has been detected only in mitochondria, where it functions in the tricarboxylic acid (TCA) cycle and is considered a mitochondrial matrix marker. We developed two strategies for physical and functional detection of aconitase in the yeast cytosol: 1) we fused the alpha peptide of the beta-galactosidase enzyme to aconitase and observed alpha complementation in the cytosol; and 2) we created an ACO1-URA3 hybrid gene, which allowed isolation of strains in which the hybrid protein is exclusively targeted to mitochondria. These strains display a specific phenotype consistent with glyoxylate shunt elimination. Together, our data indicate that yeast aconitase isoenzymes distribute between two distinct subcellular compartments and participate in two separate metabolic pathways; the glyoxylate shunt in the cytosol and the TCA cycle in mitochondria. We maintain that such dual distribution phenomena have a wider occurrence than recorded currently, the reason being that in certain cases there is a small fraction of one of the isoenzymes, in one of the locations, making its detection very difficult. We term this phenomenon of highly uneven isoenzyme distribution "eclipsed distribution."
Regev-Rudzki
Neta
N
Department of Molecular Biology, Hebrew University Medical School, Jerusalem 91120, Israel.
Karniely
Sharon
S
Ben-Haim
Nitzan Natani
NN
Pines
Ophry
O
D000085:Acetates; D000154:Aconitate Hydratase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D003600:Cytosol / Q000201:enzymology; D000431:Ethanol; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D035941:Iron Regulatory Protein 1 / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D030781:Organisms, Genetically Modified; D021381:Protein Transport / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D001616:beta-Galactosidase / Q000378:metabolism
D000085:Acetates; D005656:Fungal Proteins; D007527:Isoenzymes; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D000431:Ethanol; D001616:beta-Galactosidase; D000154:Aconitate Hydratase; D035941:Iron Regulatory Protein 1