title: An Arabidopsis GluTR binding protein mediates spatial separation of 5-aminolevulinic acid synthesis in chloroplasts.
abstract: 5-Aminolevulinic acid (ALA) is the universal precursor for tetrapyrrole biosynthesis and is synthesized in plants in three enzymatic steps: ligation of glutamate (Glu) to tRNA(Glu) by glutamyl-tRNA synthetase, reduction of activated Glu to Glu-1-semialdehyde by glutamyl-tRNA reductase (GluTR), and transamination to ALA by Glu 1-semialdehyde aminotransferase. ALA formation controls the metabolic flow into the tetrapyrrole biosynthetic pathway. GluTR is proposed to be the key regulatory enzyme that is tightly controlled at transcriptional and posttranslational levels. We identified a GluTR binding protein (GluTRBP; previously called PROTON GRADIENT REGULATION7) that is localized in chloroplasts and part of a 300-kD protein complex in the thylakoid membrane. Although the protein does not modulate activity of ALA synthesis, the knockout of GluTRBP is lethal in Arabidopsis thaliana, whereas mutants expressing reduced levels of GluTRBP contain less heme. GluTRBP expression correlates with a function in heme biosynthesis. It is postulated that GluTRBP contributes to subcompartmentalized ALA biosynthesis by maintaining a portion of GluTR at the plastid membrane that funnels ALA into the heme biosynthetic pathway. These results regarding GluTRBP support a model of plant ALA synthesis that is organized in two separate ALA pools in the chloroplast to provide appropriate substrate amounts for balanced synthesis of heme and chlorophyll.
authors.affiliation: Department of Plant Physiology, Institute of Biology, Humboldt University Berlin, Berlin, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Czarnecki
authors.forename: Boris
authors.initials: B
authors.lastname: Hedtke
authors.forename: Michael
authors.initials: M
authors.lastname: Melzer
authors.forename: Maxi
authors.initials: M
authors.lastname: Rothbart
authors.forename: Andreas
authors.initials: A
authors.lastname: Richter
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Schröter
authors.forename: Thomas
authors.initials: T
authors.lastname: Pfannschmidt
authors.forename: Bernhard
authors.initials: B
authors.lastname: Grimm
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000622:Aminolevulinic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002734:Chlorophyll / Q000096:biosynthesis / Q000235:genetics; D002736:Chloroplasts / Q000378:metabolism* / Q000648:ultrastructure; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006418:Heme / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics / Q000378:metabolism; D025941:Protein Interaction Mapping; D034622:RNA Interference; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D060431:Thylakoid Membrane Proteins / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D018749:RNA, Plant; D011994:Recombinant Proteins; D060431:Thylakoid Membrane Proteins; D002734:Chlorophyll; D006418:Heme; D000622:Aminolevulinic Acid; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase