Journal Article

An Arabidopsis GluTR Binding Protein Mediates Spatial Separation of 5-Aminolevulinic Acid Synthesis in Chloroplasts

Schröter, Yvonne, Hedtke, Boris, Czarnecki, Olaf, Melzer, Michael, Rothbart, Maxi, Pfannschmidt, Thomas, Grimm, Bernhard, Richter, Andreas

2011

Overview

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.

• Publisher: American Society of Plant Biologists
• Subject: Agrobacterium tumefaciens / Agrobacterium tumefaciens - genetics / Agrobacterium tumefaciens - metabolism / Aldehyde Oxidoreductases / Aldehyde Oxidoreductases - genetics / Aldehyde Oxidoreductases - metabolism / Amino Acid Sequence / Aminolevulinic Acid / Aminolevulinic Acid - metabolism / Arabidopsis / Arabidopsis - genetics / Arabidopsis - metabolism / Arabidopsis Proteins / Arabidopsis Proteins - genetics / Arabidopsis Proteins - metabolism / Arabidopsis thaliana / binding proteins / biochemical pathways / Biosynthesis / Carrier Proteins / Carrier Proteins - genetics / Carrier Proteins - metabolism / chlorophyll / Chlorophyll - biosynthesis / Chlorophyll - genetics / Chlorophylls / Chloroplasts / Chloroplasts - metabolism / Chloroplasts - ultrastructure / Enzymes / Escherichia coli / Escherichia coli - genetics / Escherichia coli - metabolism / Gene Expression Regulation, Plant / Genes, Plant / genetics / glutamates / glutamyl-tRNA reductase / heme / Heme - genetics / Heme - metabolism / metabolism / Molecular Sequence Data / mutants / Nicotiana - genetics / Nicotiana - metabolism / Plants / Plants, Genetically Modified / Plants, Genetically Modified - genetics / Plants, Genetically Modified - metabolism / Plasmids / Plasmids - genetics / Plasmids - metabolism / Protein Interaction Mapping / Proteins / protons / Recombinant Proteins / Recombinant Proteins - genetics / Recombinant Proteins - metabolism / RNA Interference / RNA, Plant / RNA, Plant - genetics / RNA, Plant - metabolism / Seedlings / Tetrapyrroles / Thylakoid Membrane Proteins / Thylakoid Membrane Proteins - genetics / Thylakoid Membrane Proteins - metabolism / Thylakoids / Tobacco / transamination / Transcription, Genetic / Two-Hybrid System Techniques / ultrastructure / Yeasts