The Cytoophidium and Its Kind: Filamentation and Compartmentation of Metabolic Enzymes

Liu, Ji‐Long

doi:10.1146/annurev-cellbio-111315-124907

Cited by 119 publications

(122 citation statements)

References 106 publications

(251 reference statements)

Supporting

Mentioning

114

Contrasting

Order By: Relevance

“…Fluorescence recovery after photobleaching of the mixed assemblies revealed uniform recovery of fluorescence suggesting that the assemblies may continuously renew subunits and that there was no polarity to the structures. Restoration of DONdepleted GTP pools following treatment of the cells with guanosine effects disassembly of IMPDH2-based assemblies (5). Interestingly, gaps were observed between aligned filaments, again consistent with the notion that the CTPS1 and IMPDH2 filaments associate loosely or require involvement of a third party such as a membrane, or another protein, to act as the 'glue' within (Fig.…”

supporting

confidence: 79%

Anfractuous assemblies of IMP dehydrogenase and CTP synthase: new twists on regulation?

McCluskey

Bearne

2018

The FEBS Journal

View full text Add to dashboard Cite

CTP synthase (CTPS) and IMP dehydrogenase (IMPDH) catalyse the rate‐limiting steps of de novo CTP and guanosine nucleotide biosynthesis, respectively, and form filament assemblies in response to inhibitors. A recent study explores the morphology and dynamics of these assemblies using fluorescence and super‐resolution confocal microscopy with cell lines expressing CTPS1 and IMPDH2 fusion proteins. The formation and dismantling of mixed assemblies depends on nucleotide levels, suggesting a co‐regulation function.

show abstract

supporting

confidence: 79%

Anfractuous assemblies of IMP dehydrogenase and CTP synthase: new twists on regulation?

McCluskey

Bearne

2018

The FEBS Journal

View full text Add to dashboard Cite

show abstract

“…Arabidopsis harbors five putative CTPS isoforms (CTPS1–5), which are highly homologous among each other and to other CTPSs from prokaryotes and eukaryotic organisms across kingdoms (Liu, ). This finding is in line with previous reports on the conservation of proteins involved in purine or pyrimidine nucleotide synthesis (Moffatt and Ashihara, ).…”

Section: Discussionmentioning

confidence: 99%

Characterization of filament‐forming CTP synthases from Arabidopsis thaliana

et al. 2018

View full text Add to dashboard Cite

Cytidine triphosphate (CTP) is essential for DNA, RNA and phospholipid biosynthesis. De novo synthesis is catalyzed by CTP synthases (CTPS). Arabidopsis encodes five CTPS isoforms that unanimously share conserved motifs found across kingdoms, suggesting all five are functional enzymes. Whereas CTPS1-4 are expressed throughout Arabidopsis tissues, CTPS5 reveals exclusive expression in developing embryos. CTPS activity and substrates affinities were determined for a representative plant enzyme on purified recombinant CTPS3 protein. As demonstrated in model organisms such as yeast, fruit fly and mammals, CTPS show the capacity to assemble into large filaments called cytoophidia. Transient expression of N- and C-terminal YFP-CTPS fusion proteins in Nicotiana benthamiana allowed to monitor such filament formation. Interestingly, CTPS1 and 2 always appeared as soluble proteins, whereas filaments were observed for CTPS3, 4 and 5 independent of the YFP-tag location. However, when similar constructs were expressed in Saccharomyces cerevisiae, no filaments were observed, pointing to a requirement for organism-specific factors in vivo. Indications for filament assembly were also obtained in vitro when recombinant CTPS3 protein was incubated in the presence of CTP. T-DNA-insertion mutants in four CTPS loci revealed no apparent phenotypical alteration. In contrast, CTPS2 T-DNA-insertion mutants did not produce homozygous progenies. An initial characterization of the CTPS protein family members from Arabidopsis is presented. We provide evidence for their involvement in nucleotide de novo synthesis and show that only three of the five CTPS isoforms were able to form filamentous structures in the transient tobacco expression system. This represents a striking difference from previous observations in prokaryotes, yeast, Drosophila and mammalian cells. This finding will be highly valuable to further understand the role of filament formation to regulate CTPS activity.

show abstract

“…The question of which enzyme is used for this conversion is complicated by the virtually identical fluxes from α-KG to glutamate and from glutamate to α-KG, which would not be possible in a uniform aqueous solution. However, the cytoplasm does not constitute a uniform solution but is highly compartmentalized [70,71], although it allows inter-compartmental trafficking of metabolites and enzymes as well as trafficking between cytoplasm and organelles, including mitochondria. Furthermore, as discussed below there is likely a temporal separation in vivo between glutamate oxidation and glutamate synthesis due to continuous changes in glutamate concentrations during and between brain activations.…”

Section: Glutamate and Glutamine Formation And Glutamate Oxidationmentioning

confidence: 99%

Glutamine-Glutamate Cycle Flux Is Similar in Cultured Astrocytes and Brain and Both Glutamate Production and Oxidation Are Mainly Catalyzed by Aspartate Aminotransferase

Hertz

Rothman

2017

Biology

View full text Add to dashboard Cite

The glutamine-glutamate cycle provides neurons with astrocyte-generated glutamate/γ-aminobutyric acid (GABA) and oxidizes glutamate in astrocytes, and it returns released transmitter glutamate/GABA to neurons after astrocytic uptake. This review deals primarily with the glutamate/GABA generation/oxidation, although it also shows similarity between metabolic rates in cultured astrocytes and intact brain. A key point is identification of the enzyme(s) converting astrocytic α-ketoglutarate to glutamate and vice versa. Most experiments in cultured astrocytes, including those by one of us, suggest that glutamate formation is catalyzed by aspartate aminotransferase (AAT) and its degradation by glutamate dehydrogenase (GDH). Strongly supported by results shown in Table 1 we now propose that both reactions are primarily catalyzed by AAT. This is possible because the formation occurs in the cytosol and the degradation in mitochondria and they are temporally separate. High glutamate/glutamine concentrations abolish the need for glutamate production from α-ketoglutarate and due to metabolic coupling between glutamate synthesis and oxidation these high concentrations render AAT-mediated glutamate oxidation impossible. This necessitates the use of GDH under these conditions, shown by insensitivity of the oxidation to the transamination inhibitor aminooxyacetic acid (AOAA). Experiments using lower glutamate/glutamine concentration show inhibition of glutamate oxidation by AOAA, consistent with the coupled transamination reactions described here.

show abstract

The Cytoophidium and Its Kind: Filamentation and Compartmentation of Metabolic Enzymes

Cited by 119 publications

References 106 publications

Anfractuous assemblies of IMP dehydrogenase and CTP synthase: new twists on regulation?

Anfractuous assemblies of IMP dehydrogenase and CTP synthase: new twists on regulation?

Characterization of filament‐forming CTP synthases from Arabidopsis thaliana

Glutamine-Glutamate Cycle Flux Is Similar in Cultured Astrocytes and Brain and Both Glutamate Production and Oxidation Are Mainly Catalyzed by Aspartate Aminotransferase

Contact Info

Product

Resources

About