title: Posttranslational Control of ALA Synthesis Includes GluTR Degradation by Clp Protease and Stabilization by GluTR-Binding Protein.
abstract: 5-Aminolevulinic acid (ALA) is the first committed substrate of tetrapyrrole biosynthesis and is formed from glutamyl-tRNA by two enzymatic steps. Glutamyl-tRNA reductase (GluTR) as the first enzyme of ALA synthesis is encoded by HEMA genes and tightly regulated at the transcriptional and posttranslational levels. Here, we show that the caseinolytic protease (Clp) substrate adaptor ClpS1 and the ClpC1 chaperone as well as the GluTR-binding protein (GBP) interact with the N terminus of GluTR Loss-of function mutants of ClpR2 and ClpC1 proteins show increased GluTR stability, whereas absence of GBP results in decreased GluTR stability. Thus, the Clp protease system and GBP contribute to GluTR accumulation levels, and thereby the rate-limiting ALA synthesis. These findings are supported with Arabidopsis (Arabidopsis thaliana) hema1 mutants expressing a truncated GluTR lacking the 29 N-terminal amino acid residues of the mature protein. Accumulation of this truncated GluTR is higher in dark periods, resulting in increased protochlorophyllide content. It is proposed that the proteolytic activity of Clp protease counteracts GBP binding to assure the appropriate content of GluTR and the adequate ALA synthesis for chlorophyll and heme in higher plants.
authors.affiliation: Department of Plant Physiology, Humboldt University Berlin, 10115 Berlin, Germany (J.A., J.S., A.W., B.H., B.G.); andSchool of Integrative Plant Science, Section of Plant Biology, Cornell University, Ithaca, New York 14853 (K.N., K.J.v.W.).
authors.forename: Janina
authors.initials: J
authors.lastname: Apitz
authors.affiliation: Department of Plant Physiology, Humboldt University Berlin, 10115 Berlin, Germany (J.A., J.S., A.W., B.H., B.G.); andSchool of Integrative Plant Science, Section of Plant Biology, Cornell University, Ithaca, New York 14853 (K.N., K.J.v.W.).
authors.forename: Kenji
authors.initials: K
authors.lastname: Nishimura
authors.affiliation: Department of Plant Physiology, Humboldt University Berlin, 10115 Berlin, Germany (J.A., J.S., A.W., B.H., B.G.); andSchool of Integrative Plant Science, Section of Plant Biology, Cornell University, Ithaca, New York 14853 (K.N., K.J.v.W.).
authors.forename: Judith
authors.identifier: 0000-0001-8813-4588
authors.initials: J
authors.lastname: Schmied
authors.affiliation: Department of Plant Physiology, Humboldt University Berlin, 10115 Berlin, Germany (J.A., J.S., A.W., B.H., B.G.); andSchool of Integrative Plant Science, Section of Plant Biology, Cornell University, Ithaca, New York 14853 (K.N., K.J.v.W.).
authors.forename: Anja
authors.initials: A
authors.lastname: Wolf
authors.affiliation: Department of Plant Physiology, Humboldt University Berlin, 10115 Berlin, Germany (J.A., J.S., A.W., B.H., B.G.); andSchool of Integrative Plant Science, Section of Plant Biology, Cornell University, Ithaca, New York 14853 (K.N., K.J.v.W.).
authors.forename: Boris
authors.initials: B
authors.lastname: Hedtke
authors.affiliation: Department of Plant Physiology, Humboldt University Berlin, 10115 Berlin, Germany (J.A., J.S., A.W., B.H., B.G.); andSchool of Integrative Plant Science, Section of Plant Biology, Cornell University, Ithaca, New York 14853 (K.N., K.J.v.W.).
authors.forename: Klaas J
authors.identifier: 0000-0001-9536-0487
authors.initials: KJ
authors.lastname: van Wijk
authors.affiliation: Department of Plant Physiology, Humboldt University Berlin, 10115 Berlin, Germany (J.A., J.S., A.W., B.H., B.G.); andSchool of Integrative Plant Science, Section of Plant Biology, Cornell University, Ithaca, New York 14853 (K.N., K.J.v.W.) bernhard.grimm@rz.hu-berlin.de.
authors.forename: Bernhard
authors.identifier: 0000-0002-9730-1074
authors.initials: B
authors.lastname: Grimm
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D000622:Aminolevulinic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D049071:Endopeptidase Clp / Q000378:metabolism*; D004795:Enzyme Stability; D005453:Fluorescence; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D059748:Proteolysis; D011521:Protochlorophyllide / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D018832:Molecular Chaperones; D011521:Protochlorophyllide; D000622:Aminolevulinic Acid; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase; D049071:Endopeptidase Clp