Genes, enzymes and regulation of arginine biosynthesis in plants

Slocum, Robert D.

doi:10.1016/j.plaphy.2005.06.007

Cited by 253 publications

(271 citation statements)

References 88 publications

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“…The biological significance of these changes remains to be elucidated, but elevated arginine levels may reflect altered flux through to this metabolite pool due to the decreased utilization of ornithine, which is produced from arginine, in tropane alkaloid synthesis as a result of ArAT4 silencing (Slocum, 2005). Similarly, while reduced levels of phenyllactate, hyoscyamine, and scopolamine and increased tropine content were expected in ArAT4-silenced lines, an unexpected reduction in tropinone levels was also observed ( Figure 5A).…”

Section: Discussionmentioning

confidence: 91%

A Root-Expressed l-Phenylalanine:4-Hydroxyphenylpyruvate Aminotransferase Is Required for Tropane Alkaloid Biosynthesis in Atropa belladonna

et al. 2014

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The tropane alkaloids, hyoscyamine and scopolamine, are medicinal compounds that are the active components of several therapeutics. Hyoscyamine and scopolamine are synthesized in the roots of specific genera of the Solanaceae in a multistep pathway that is only partially elucidated. To facilitate greater understanding of tropane alkaloid biosynthesis, a de novo transcriptome assembly was developed for Deadly Nightshade (Atropa belladonna). Littorine is a key intermediate in hyoscyamine and scopolamine biosynthesis that is produced by the condensation of tropine and phenyllactic acid. Phenyllactic acid is derived from phenylalanine via its transamination to phenylpyruvate, and mining of the transcriptome identified a phylogenetically distinct aromatic amino acid aminotransferase (ArAT), designated Ab-ArAT4, that is coexpressed with known tropane alkaloid biosynthesis genes in the roots of A. belladonna. Silencing of Ab-ArAT4 disrupted synthesis of hyoscyamine and scopolamine through reduction of phenyllactic acid levels. Recombinant Ab-ArAT4 preferentially catalyzes the first step in phenyllactic acid synthesis, the transamination of phenylalanine to phenylpyruvate. However, rather than utilizing the typical keto-acid cosubstrates, 2-oxoglutarate, pyruvate, and oxaloacetate, Ab-ArAT4 possesses strong substrate preference and highest activity with the aromatic keto-acid, 4-hydroxyphenylpyruvate. Thus, Ab-ArAT4 operates at the interface between primary and specialized metabolism, contributing to both tropane alkaloid biosynthesis and the direct conversion of phenylalanine to tyrosine.

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Section: Discussionmentioning

confidence: 91%

A Root-Expressed l-Phenylalanine:4-Hydroxyphenylpyruvate Aminotransferase Is Required for Tropane Alkaloid Biosynthesis in Atropa belladonna

et al. 2014

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“…This arrest can be reversed by adding the nucleobase uracil (Chen and Slocum, 2008). In general, it is assumed that pyrimidine de novo synthesis is exclusively located in plastids with the exception of the reaction catalyzed by dihydroorotate dehydrogenase (DHODH) (Slocum, 2005). However, direct experimental evidence for this assumption is lacking.…”

Section: Introductionmentioning

confidence: 99%

De Novo Pyrimidine Nucleotide Synthesis Mainly Occurs outside of Plastids, but a Previously Undiscovered Nucleobase Importer Provides Substrates for the Essential Salvage Pathway in Arabidopsis

et al. 2012

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Nucleotide de novo synthesis is highly conserved among organisms and represents an essential biochemical pathway. In plants, the two initial enzymatic reactions of de novo pyrimidine synthesis occur in the plastids. By use of green fluorescent protein fusions, clear support is provided for a localization of the remaining reactions in the cytosol and mitochondria. This implies that carbamoyl aspartate, an intermediate of this pathway, must be exported and precursors of pyrimidine salvage (i.e., nucleobases or nucleosides) are imported into plastids. A corresponding uracil transport activity could be measured in intact plastids isolated from cauliflower (Brassica oleracea) buds. PLUTO (for plastidic nucleobase transporter) was identified as a member of the Nucleobase:Cation-Symporter1 protein family from Arabidopsis thaliana, capable of transporting purine and pyrimidine nucleobases. A PLUTO green fluorescent protein fusion was shown to reside in the plastid envelope after expression in Arabidopsis protoplasts. Heterologous expression of PLUTO in an Escherichia coli mutant lacking the bacterial uracil permease uraA allowed a detailed biochemical characterization. PLUTO transports uracil, adenine, and guanine with apparent affinities of 16.4, 0.4, and 6.3 mM, respectively. Transport was markedly inhibited by low concentrations of a proton uncoupler, indicating that PLUTO functions as a proton-substrate symporter. Thus, a protein for the absolutely required import of pyrimidine nucleobases into plastids was identified.

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“…I n photosynthetic organisms nitrogen can be stored by synthesizing arginine (1,2) and, therefore, feedback inhibition of arginine synthesis must be relieved when nitrogen is abundant. The enzyme of arginine biosynthesis that is the target of arginine inhibition, N-acetyl-L-glutamate (NAG) kinase (NAGK) (1,(3)(4)(5), was found in cyanobacteria and plants (2,(4)(5)(6)(7)(8) to be a target of the carbon/ nitrogen P II signaling protein (9,10), forming with it a complex in which arginine inhibition is alleviated (6,7).…”

mentioning

confidence: 99%

“…The enzyme of arginine biosynthesis that is the target of arginine inhibition, N-acetyl-L-glutamate (NAG) kinase (NAGK) (1,(3)(4)(5), was found in cyanobacteria and plants (2,(4)(5)(6)(7)(8) to be a target of the carbon/ nitrogen P II signaling protein (9,10), forming with it a complex in which arginine inhibition is alleviated (6,7). P II signaling proteins are homotrimers of a 12-to 13-kDa subunit that interact with enzymes, transcription factors, and ammonia channels, regulating their activity (9,10) and carbon/ nitrogen homeostasis.…”

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confidence: 99%

The crystal structure of the complex of P _II and acetylglutamate kinase reveals how P _II controls the storage of nitrogen as arginine

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Contreras

Forchhammer

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

106

165

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Photosynthetic organisms can store nitrogen by synthesizing arginine, and, therefore, feedback inhibition of arginine synthesis must be relieved in these organisms when nitrogen is abundant. This relief is accomplished by the binding of the P II signal transduction protein to acetylglutamate kinase (NAGK), the controlling enzyme of arginine synthesis. Here, we describe the crystal structure of the complex between NAGK and P II of Synechococcus elongatus, at 2.75-Å resolution. We prove the physiological relevance of the observed interactions by site-directed mutagenesis and functional studies. The complex consists of two polar P II trimers sandwiching one ring-like hexameric NAGK (a trimer of dimers) with the threefold axes of these molecules aligned. The binding of P II favors a narrow ring conformation of the NAGK hexamer that is associated with arginine sites having low affinity for this inhibitor. Each PII subunit contacts one NAGK subunit only. The contacts map in the inner circumference of the NAGK ring and involve two surfaces of the P II subunit. One surface is on the PII body and interacts with the C-domain of the NAGK subunit, helping widen the arginine site found on the other side of this domain. The other surface is at the distal region of a protruding large loop (T-loop) that presents a novel compact shape. This loop is inserted in the interdomain crevice of the NAGK subunit, contacting mainly the N-domain, and playing key roles in anchoring P II on NAGK, in activating NAGK, and in complex formation regulation by MgATP, ADP, 2-oxoglutarate, and by phosphorylation of serine-49.arginine synthesis ͉ regulation ͉ x-ray structure ͉ signaling ͉ cyanobacteria I n photosynthetic organisms nitrogen can be stored by synthesizing arginine (1, 2) and, therefore, feedback inhibition of arginine synthesis must be relieved when nitrogen is abundant. The enzyme of arginine biosynthesis that is the target of arginine inhibition, N-acetyl-L-glutamate (NAG) kinase (NAGK) (1, 3-5), was found in cyanobacteria and plants (2, 4-8) to be a target of the carbon/ nitrogen P II signaling protein (9, 10), forming with it a complex in which arginine inhibition is alleviated (6, 7). P II signaling proteins are homotrimers of a 12-to 13-kDa subunit that interact with enzymes, transcription factors, and ammonia channels, regulating their activity (9, 10) and carbon/ nitrogen homeostasis. Numerous structures of P II proteins, including those for cyanobacteria and plants (9-12), are known, but it was unclear how P II proteins carry out their functions. The body of the P II trimer is roughly hemispheric. Its subunits have ␤␣␤␤␣␤ topology, with ␣ helices looking outward and the ␤ sheet inward and providing the intersubunit interactions. Each subunit has three loops: the B-and C-loops and the larger flexible T-loop. The T-loop residues Y51 and S49 are, respectively, the sites of the regulatory uridylylation and phosphorylation in enterobacterial and cyanobacterial P II proteins (9, 10), with S49 phosphorylation abolishing interaction wi...

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Genes, enzymes and regulation of arginine biosynthesis in plants

Cited by 253 publications

References 88 publications

A Root-Expressed l-Phenylalanine:4-Hydroxyphenylpyruvate Aminotransferase Is Required for Tropane Alkaloid Biosynthesis in Atropa belladonna

A Root-Expressed l-Phenylalanine:4-Hydroxyphenylpyruvate Aminotransferase Is Required for Tropane Alkaloid Biosynthesis in Atropa belladonna

De Novo Pyrimidine Nucleotide Synthesis Mainly Occurs outside of Plastids, but a Previously Undiscovered Nucleobase Importer Provides Substrates for the Essential Salvage Pathway in Arabidopsis

The crystal structure of the complex of P _II and acetylglutamate kinase reveals how P _II controls the storage of nitrogen as arginine

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Genes, enzymes and regulation of arginine biosynthesis in plants

Cited by 253 publications

References 88 publications

A Root-Expressed l-Phenylalanine:4-Hydroxyphenylpyruvate Aminotransferase Is Required for Tropane Alkaloid Biosynthesis in Atropa belladonna

A Root-Expressed l-Phenylalanine:4-Hydroxyphenylpyruvate Aminotransferase Is Required for Tropane Alkaloid Biosynthesis in Atropa belladonna

De Novo Pyrimidine Nucleotide Synthesis Mainly Occurs outside of Plastids, but a Previously Undiscovered Nucleobase Importer Provides Substrates for the Essential Salvage Pathway in Arabidopsis

The crystal structure of the complex of P II and acetylglutamate kinase reveals how P II controls the storage of nitrogen as arginine

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The crystal structure of the complex of P _II and acetylglutamate kinase reveals how P _II controls the storage of nitrogen as arginine