Inhibition of p-aminobenzoate and folate syntheses in plants and apicomplexan parasites by natural product rubreserine.

Glutamine amidotransferase/aminodeoxychorismate synthase (GAT-ADCS) is a bifunctional enzyme involved in the synthesis of p-aminobenzoate, a central component part of folate cofactors. GAT-ADCS is found in eukaryotic organisms autonomous for folate biosynthesis, such as plants or parasites of the phylum Apicomplexa. Based on an automated screening to search for new inhibitors of folate biosynthesis, we found that rubreserine was able to inhibit the glutamine amidotransferase activity of the plant GAT-ADCS with an apparent IC(50) of about 8 μM.

Differential interactions of the formins INF2, mDia1, and mDia2 with microtubules.

A number of cellular processes use both microtubules and actin filaments, but the molecular machinery linking these two cytoskeletal elements remains to be elucidated in detail. Formins are actin-binding proteins that have multiple effects on actin dynamics, and one formin, mDia2, has been shown to bind and stabilize microtubules through its formin homology 2 (FH2) domain. Here we show that three formins, INF2, mDia1, and mDia2, display important differences in their interactions with microtubules and actin.

The synthesis of pABA: Coupling between the glutamine amidotransferase and aminodeoxychorismate synthase domains of the bifunctional aminodeoxychorismate synthase from Arabidopsis thaliana.

Aminodeoxychorismate (ADC) synthase in plants is a bifunctional enzyme containing glutamine amidotransferase (GAT) and ADC synthase (ADCS) domains. The GAT domain releases NH(3) from glutamine and the ADCS domain uses NH(3) to aminate chorismate. This enzyme is involved in folate (vitamin B9) biosynthesis.

C1 metabolism and chlorophyll synthesis: the Mg-protoporphyrin IX methyltransferase activity is dependent on the folate status.

* Tetrahydrofolate derivatives are central cofactors of C1 metabolism. Using methotrexate as a specific inhibitor of folate biosynthesis, we altered the folate status in 10-d-old etiolated pea (Pisum sativum) leaves and followed the rate of chlorophyll synthesis upon illumination. * In our conditions, the folate concentration decreased only from 5.

A genome-wide and metabolic analysis determined the adaptive response of Arabidopsis cells to folate depletion induced by methotrexate.

Control of folate homeostasis is essential to sustain the demand for one-carbon (C1) units that are necessary for major biological functions, including nucleotide synthesis and methylation reactions. In this study, we analyzed the genome-wide and metabolic adaptive response of Arabidopsis (Arabidopsis thaliana) cells to folate depletion induced by the antifolate methotrexate. Drug treatment induced a response typical to xenobiotic stress and important changes in folate content and composition.

Folate synthesis in plants: purification, kinetic properties, and inhibition of aminodeoxychorismate synthase.

pABA (p-aminobenzoate) is a precursor of folates and, besides esterification to glucose, has no other known metabolic fate in plants. It is synthesized in two steps from chorismate and glutamine, the first step being their conversion into glutamate and ADC (4-aminodeoxychorismate). In Escherichia coli, two proteins forming a heterodimeric complex are required for this reaction, but, in plants and lower eukaryotes, a single protein is involved.

Folate metabolism in plants: an Arabidopsis homolog of the mammalian mitochondrial folate transporter mediates folate import into chloroplasts.

The distribution of folates in plant cells suggests a complex traffic of the vitamin between the organelles and the cytosol. The Arabidopsis thaliana protein AtFOLT1 encoded by the At5g66380 gene is the closest homolog of the mitochondrial folate transporters (MFTs) characterized in mammalian cells. AtFOLT1 belongs to the mitochondrial carrier family, but GFP-tagging experiments and Western blot analyses indicated that it is targeted to the envelope of chloroplasts.

Tetrahydrofolate biosynthesis and distribution in higher plants.

One-carbon transfer reactions are mediated by H4F (tetrahydrofolate), a soluble coenzyme (vitamin B9) that is synthesized de novo by plants and microorganisms, and absorbed from the diet by animals. H4F synthesis in plants is quartered between the plastids, the cytosol and the mitochondria, a spatial distribution that is not observed in the other organisms and that suggests a complex intracellular traffic. Also, the activity of H4F synthesis fluctuates during plant growth, depending on the tissue and the developmental stage of the seedling, thus illustrating the flexibility of one-carbon metabolism in these organisms.