bims-toxgon Biomed News
on Toxoplasma gondii metabolism
Issue of 2022–11–06
sixteen papers selected by
Lakesh Kumar, BITS Pilani
  1. A VPS15-like kinase regulates apicoplast biogenesis and autophagy by promoting PI3P generation in Toxoplasma gondii.
  2. Identification of new components of the basal pole of Toxoplasma gondii provides novel insights into its molecular organization and functions.
  3. Toxoplasma Shelph, a Phosphatase Located in the Parasite Endoplasmic Reticulum, Is Required for Parasite Virulence.
  4. Experimental infection of Mongolian gerbils with Toxoplasma gondii: pathological and immunohistochemical evaluations.
  5. The Toxoplasma effector GRA28 promotes parasite dissemination by inducing dendritic cell-like migratory properties in infected macrophages.
  6. IMC10 and LMF1 mediate mitochondrial morphology by mitochondrion-pellicle contact sites in Toxoplasma gondii.
  7. Immunomagnetic separation of Toxoplasma gondii and Hammondia spp. tissue cysts generated in cell culture.
  8. Nanoscale imaging of the conoid and functional dissection of its dynamics in Apicomplexa.
  9. Erratum: Toxoplasma gondii Induces Apoptosis via Endoplasmic Reticulum Stress-Derived Mitochondrial Pathway in Human Small Intestinal Epithelial Cell-Line.
  10. New insights into activation and function of the AMPK.
  11. Toxoplasmosis vaccines: what we have and where to go?
  12. Absence of ULK1 decreases AMPK activity in the kidney, leading to chronic kidney disease progression.
  13. Cryo-electron tomography with mixed-scale dense neural networks reveals key steps in deployment of Toxoplasma invasion machinery.
  14. Probing coenzyme A homeostasis with semisynthetic biosensors.
  15. Metabolic adaptation and ATP homeostasis in Pseudomonas fluorescens exposed to phosphate stress.
  16. Control of central metabolism's architecture in Escherichia coli: An overview.
  1. PLoS Pathog. 2022 Nov;18(11): e1010922
    A VPS15-like kinase regulates apicoplast biogenesis and autophagy by promoting PI3P generation in Toxoplasma gondii.
    Rahul Singh Rawat, Priyanka Bansal, Pushkar Sharma.
      Phosphoinositides are important second messengers that regulate key cellular processes in eukaryotes. While it is known that a single phosphoinositol-3 kinase (PI3K) catalyses the formation of 3'-phosphorylated phosphoinositides (PIPs) in apicomplexan parasites like Plasmodium and Toxoplasma, how its activity and PI3P formation is regulated has remained unknown. Present studies involving a unique Vps15 like protein (TgVPS15) in Toxoplasma gondii provides insight into the regulation of phosphatidyl-3-phosphate (PI3P) generation and unravels a novel pathway that regulates parasite development. Detailed investigations suggested that TgVPS15 regulates PI3P formation in Toxoplasma gondii, which is important for the inheritance of the apicoplast-a plastid like organelle present in most apicomplexans and parasite replication. Interestingly, TgVPS15 also regulates autophagy in T. gondii under nutrient-limiting conditions as it promotes autophagosome formation. For both these processes, TgVPS15 uses PI3P-binding protein TgATG18 and regulates trafficking and conjugation of TgATG8 to the apicoplast and autophagosomes, which is important for biogenesis of these organelles. TgVPS15 has a protein kinase domain but lacks several key residues conserved in conventional protein kinases. Interestingly, two critical residues in its active site are important for PI3P formation and parasitic functions of this kinase. Collectively, these studies unravel a signalling cascade involving TgVPS15, a novel effector of PI3-kinase in T. gondii and possibly other Apicomplexa, that regulate critical processes like apicoplast biogenesis and autophagy.
    DOI:  https://doi.org/10.1371/journal.ppat.1010922
  2. Front Cell Infect Microbiol. 2022 ;12 1010038
    Identification of new components of the basal pole of Toxoplasma gondii provides novel insights into its molecular organization and functions.
    Chloé Roumégous, Aya Abou Hammoud, Damien Fuster, Jean-William Dupuy, Corinne Blancard, Bénédicte Salin, Derrick R Robinson, Patricia Renesto, Isabelle Tardieux, Karine Frénal.
      The Toxoplasma gondii tachyzoite is a singled-cell obligate intracellular parasite responsible for the acute phase of toxoplasmosis. This polarized cell exhibits an apical complex, a hallmark of the phylum Apicomplexa, essential for motility, invasion, and egress from the host cell. Located on the opposite end of the cell is the basal complex, an elaborated cytoskeletal structure that also plays critical roles in the lytic cycle of the parasite, being involved in motility, cell division, constriction and cytokinesis, as well as intravacuolar cell-cell communication. Nevertheless, only a few proteins of this structure have been described and functionally assessed. In this study, we used spatial proteomics to identify new basal complex components (BCC), and in situ imaging, including ultrastructure expansion microscopy, to position them. We thus confirmed the localization of nine BCCs out of the 12 selected candidates and assigned them to different sub-compartments of the basal complex, including two new domains located above the basal ring and below the posterior cup. Their functional investigation revealed that none of these BCCs are essential for parasite growth in vitro. However, one BCC is critical for constricting of the basal complex, likely through direct interaction with the class VI myosin heavy chain J (MyoJ), and for gliding motility. Four other BCCs, including a phosphatase and a guanylate-binding protein, are involved in the formation and/or maintenance of the intravacuolar parasite connection, which is required for the rosette organization and synchronicity of cell division.
    Keywords:  Apicomplexa; Toxoplasma gondii; basal complex; cell-cell communication; constriction; cytoskeleton; expansion microscopy; myosin heavy chain (MHC)
    DOI:  https://doi.org/10.3389/fcimb.2022.1010038
  3. mSphere. 2022 Nov 03. e0035022
    Toxoplasma Shelph, a Phosphatase Located in the Parasite Endoplasmic Reticulum, Is Required for Parasite Virulence.
    Rania Najm, Maguy Hamie, Laurence Berry-Sterkers, Maryse Lebrun, Hiba El Hajj, Mauld H Lamarque.
      Toxoplasma gondii is a single-celled parasitic eukaryote that evolved to successfully propagate in any nucleated cell. As with any other eukaryote, its life cycle is regulated by signaling pathways controlled by kinases and phosphatases. T. gondii encodes an atypical bacterial-like phosphatase absent from mammalian genomes, named Shelph, after its first identification in the psychrophilic bacterium Schewanella sp. Here, we demonstrate that Toxoplasma Shelph is an active phosphatase localized in the parasite endoplasmic reticulum. The phenotyping of a shelph knockout (KO) line showed a minor impairment in invasion on human fibroblasts, while the other steps of the parasite lytic cycle were not affected. In contrast with Plasmodium ortholog Shelph1, this invasion deficiency was not correlated with any default in the biogenesis of secretory organelles. However, Shelph-KO parasites displayed a much-pronounced defect in virulence in vivo. These phenotypes could be rescued by genetic complementation, thus supporting an important function for Shelph in the context of a natural infection. IMPORTANCE Toxoplasma gondii belongs to the Apicomplexa phylum, which comprises more than 5,000 species, among which is Plasmodium falciparum, the notorious agent of human malaria. Intriguingly, the Apicomplexa genomes encode at least one phosphatase closely related to the bacterial Schewanella phosphatase, or Shelph. To better understand the importance of these atypical bacterial enzymes in eukaryotic parasites, we undertook the functional characterization of T. gondii Shelph. Our results uncovered its subcellular localization and its enzymatic activity, revealed its subtle involvement during the tachyzoite invasion step of the lytic cycle, and more importantly, highlighted a critical requirement of this phosphatase for parasite propagation in mice. Overall, this study revealed an unexpected role for T. gondii Shelph in the maintenance of parasite virulence in vivo.
    Keywords:  Toxoplasma gondii; enzyme kinetics; infectious disease; parasitology; reverse genetic analysis; serine/threonine phosphatases; subcellular localization
    DOI:  https://doi.org/10.1128/msphere.00350-22
  4. Vet Res Forum. 2022 Sep;13(3): 293-299
    Experimental infection of Mongolian gerbils with Toxoplasma gondii: pathological and immunohistochemical evaluations.
    Sila Kahyaoglu, Hasan Tarik Atmaca.
      Toxoplasma gondii is a protozoon parasite which causes toxoplasmosis both in human and warm-blooded animals. Toxoplasmosis is a worldwide disease and largely threats human and animal health consequently causing economic losses. Also, it affects the visceral organs in different severity degrees according to the strain of parasite and the host. In this study, experimental toxoplasmosis was performed via intra-peritoneal route in 12 gerbils by administrating 5.00 × 103 tachyzoites of T. gondii RH strain. The gerbils were sacrificed 7 days after inoculation. All systemic organs were obtained via necropsy and examined by immunohistochemical and histopathological methods. Lesions infected with T. gondii mostly observed in the serosa of abdominal cavity organs including stomach, liver, spleen, intestines, and kidneys. The lesions were most severe in liver. The parasite showed an affinity for the hepatic tissue. To our knowledge, this is the first experimental study of acute T. gondii infection in gerbil evaluating macroscopic, microscopic and immunohistochemical findings. It is concluded that Mongolian gerbils can be used as experimental animals to investigate toxoplasmosis. Also, these animals are very suitable hosts to study liver pathology and pathobiology of T. gondii-related hepatitis.
    Keywords:  Immunohistochemistry; Mongolian gerbil; Pathology; Toxoplasma gondii; Toxoplasmosis
    DOI:  https://doi.org/10.30466/vrf.2020.126993.2937
  5. Cell Host Microbe. 2022 Oct 20. pii: S1931-3128(22)00512-1. [Epub ahead of print]
    The Toxoplasma effector GRA28 promotes parasite dissemination by inducing dendritic cell-like migratory properties in infected macrophages.
    Arne L Ten Hoeve, Laurence Braun, Matias E Rodriguez, Gabriela C Olivera, Alexandre Bougdour, Lucid Belmudes, Yohann Couté, Jeroen P J Saeij, Mohamed-Ali Hakimi, Antonio Barragan.
      Upon pathogen detection, macrophages normally stay sessile in tissues while dendritic cells (DCs) migrate to secondary lymphoid tissues. The obligate intracellular protozoan Toxoplasma gondii exploits the trafficking of mononuclear phagocytes for dissemination via unclear mechanisms. We report that, upon T. gondii infection, macrophages initiate the expression of transcription factors normally attributed to DCs, upregulate CCR7 expression with a chemotactic response, and perform systemic migration when adoptively transferred into mice. We show that parasite effector GRA28, released by the MYR1 secretory pathway, cooperates with host chromatin remodelers in the host cell nucleus to drive the chemotactic migration of parasitized macrophages. During in vivo challenge studies, bone marrow-derived macrophages infected with wild-type T. gondii outcompeted those challenged with MYR1- or GRA28-deficient strains in migrating and reaching secondary organs. This work reveals how an intracellular parasite hijacks chemotaxis in phagocytes and highlights a remarkable migratory plasticity in differentiated cells of the mononuclear phagocyte system.
    Keywords:  apicomplexa; cell motility; chemokine receptor 7; chemotaxis; host-pathogen; immune evasion; intracellular parasitism; mononuclear phagocyte; protozoa
    DOI:  https://doi.org/10.1016/j.chom.2022.10.001
  6. J Cell Sci. 2022 Oct 31. pii: jcs.260083. [Epub ahead of print]
    IMC10 and LMF1 mediate mitochondrial morphology by mitochondrion-pellicle contact sites in Toxoplasma gondii.
    Rodolpho Ornitz Oliveira Souza, Kylie N Jacobs, Peter S Back, Peter J Bradley, Gustavo Arrizabalaga.
      The single mitochondrion of Toxoplasma gondii is highly dynamic, being predominantly in a peripherally distributed lasso-shape in intracellular parasites and collapsed in extracellular ones. The peripheral positioning of the mitochondrion is associated with apparent contacts between the mitochondrion membrane and the parasite pellicle. The outer mitochondrial membrane-associated protein LMF1 is critical for the correct positioning of the mitochondrion. Intracellular parasites lacking LMF1 fail to form the lasso-shaped mitochondrion. To identify other proteins that tether the parasite's mitochondrion to the pellicle, we performed a yeast two-hybrid screen for LMF1 interactors. We identified 70 putative interactors localized in different cellular compartments, such as the parasite's apical end, mitochondrial membrane, and the inner membrane complex (IMC). Using protein-protein interaction assays, we confirmed the interaction of LMF1 with the pellicle protein IMC10. Conditional knockdown of IMC10 does not affect parasite viability but severely affects mitochondrial morphology in intracellular parasites and mitochondrial distribution to the daughter cells during division. In effect, IMC10 knockdown phenocopies disruption of LMF1, suggesting that these two proteins define a novel membrane tether between Toxoplasma's mitochondrion and the IMC.
    Keywords:   Toxoplasma gondii ; Inner Membrane Complex; LMF1; Membrane Contact Site; Mitochondrion
    DOI:  https://doi.org/10.1242/jcs.260083
  7. Front Vet Sci. 2022 ;9 1033380
    Immunomagnetic separation of Toxoplasma gondii and Hammondia spp. tissue cysts generated in cell culture.
    Mariana M Rezende-Gondim, Aristeu V da Silva, Jitender P Dubey, Gereon R M Schares, Luís F P Gondim.
      Toxoplasma gondii is commonly transmitted among animals and humans by ingestion of infected animal tissues or by consumption of food and water contaminated with environmentally-resistant oocysts excreted by cats. Tissue cysts and oocysts have different walls, whose structures and compositions are poorly known. Herein, we describe an immunomagnetic separation (IMS) method that was successfully used for purification of T. gondii tissue cysts generated in cell culture. We used an IgG monoclonal antibody (mAb) that reacts against antigens in tissue cyst walls. Many in vitro produced cysts were obtained by this IMS; >2,000 T. gondii cysts were isolated from a single culture flask of 25 cm2. Tissue cysts from two Hammondia spp., H. hammondi, and H. heydorni, produced in cell culture were also separated using this method. As a reference, purification of tissue cysts by Percoll gradients was used. Percoll was able to separate T. gondii tissue cysts produced in mice but was not suitable for purifying T. gondii tissue cysts produced in vitro. The IMS described here should favor proteomic studies involving tissue cysts of T. gondii.
    Keywords:  Hammondia hammondi; Hammondia heydorni; Toxoplasma gondii; immunomagnetic; monoclonal antibody; tissue cyst wall
    DOI:  https://doi.org/10.3389/fvets.2022.1033380
  8. Curr Opin Microbiol. 2022 Nov 01. pii: S1369-5274(22)00110-2. [Epub ahead of print]70 102226
    Nanoscale imaging of the conoid and functional dissection of its dynamics in Apicomplexa.
    Romuald Haase, Nicolas Dos Santos Pacheco, Dominique Soldati-Favre.
      Members of the Apicomplexa phylum are unified by an apical complex tailored for motility and host cell invasion. It includes regulated secretory organelles and a conoid attached to the apical polar ring (APR) from which subpellicular microtubules emerge. In coccidia, the conoid is composed of a cone of spiraling tubulin fibers, two preconoidal rings, and two intraconoidal microtubules. The conoid extrudes through the APR in motile parasites. Recent advances in proteomics, cryo-electron tomography, super-resolution, and expansion microscopy provide a more comprehensive view of the spatial and temporal resolution of proteins belonging to the conoid subcomponents. In combination with the phenotyping of targeted mutants, the biogenesis, turnover, dynamics, and function of the conoid begin to be elucidated.
    DOI:  https://doi.org/10.1016/j.mib.2022.102226
  9. Korean J Parasitol. 2022 Oct;60(5): 371
    Erratum: Toxoplasma gondii Induces Apoptosis via Endoplasmic Reticulum Stress-Derived Mitochondrial Pathway in Human Small Intestinal Epithelial Cell-Line.
      
    DOI:  https://doi.org/10.3347/kjp.2022.60.5.371
  10. Nat Rev Mol Cell Biol. 2022 Oct 31.
    New insights into activation and function of the AMPK.
    Gregory R Steinberg, D Grahame Hardie.
      The classical role of AMP-activated protein kinase (AMPK) is as a cellular energy sensor activated by falling energy status, signalled by increases in AMP to ATP and ADP to ATP ratios. Once activated, AMPK acts to restore energy homeostasis by promoting ATP-producing catabolic pathways while inhibiting energy-consuming processes. In this Review, we provide an update on this canonical (AMP/ADP-dependent) activation mechanism, but focus mainly on recently described non-canonical pathways, including those by which AMPK senses the availability of glucose, glycogen or fatty acids and by which it senses damage to lysosomes and nuclear DNA. We also discuss new findings on the regulation of carbohydrate and lipid metabolism, mitochondrial and lysosomal homeostasis, and DNA repair. Finally, we discuss the role of AMPK in cancer, obesity, diabetes, nonalcoholic steatohepatitis (NASH) and other disorders where therapeutic targeting may exert beneficial effects.
    DOI:  https://doi.org/10.1038/s41580-022-00547-x
  11. NPJ Vaccines. 2022 Oct 31. 7(1): 131
    Toxoplasmosis vaccines: what we have and where to go?
    Yizhuo Zhang, Dan Li, Shaohong Lu, Bin Zheng.
      Despite recent major advances in developing effective vaccines against toxoplasmosis, finding new protective vaccination strategies remains a challenging and elusive goal as it is critical to prevent the disease. Over the past few years, various experimental approaches have shown that developing an effective vaccine against T. gondii is achievable. However, more remains unknown due to its complicated life cycle, difficulties in clinical translation, and lack of a standardized platform. This minireview summarizes the recent advances in the development of T. gondii vaccines and the main obstacles to developing a safe, effective and durable T. gondii vaccine. The successes and failures in developing and testing vaccine candidates for the T. gondii vaccine are also discussed, which may facilitate the future development of T. gondii vaccines.
    DOI:  https://doi.org/10.1038/s41541-022-00563-0
  12. Genes Cells. 2022 Nov 01.
    Absence of ULK1 decreases AMPK activity in the kidney, leading to chronic kidney disease progression.
    Tomoki Yanagi, Hiroaki Kikuchi, Koichiro Susa, Naohiro Takahashi, Hiroki Bamba, Takefumi Suzuki, Yuta Nakano, Tamami Fujiki, Yutaro Mori, Fumiaki Ando, Shintaro Mandai, Takayasu Mori, Koh Takeuchi, Shinya Honda, Satoru Torii, Shigeomi Shimizu, Tatemitsu Rai, Shinichi Uchida, Eisei Sohara.
      AMP-activated protein kinase (AMPK) inactivation in chronic kidney disease (CKD) leads to energy status deterioration in the kidney, constituting the vicious cycle of CKD exacerbation. Unc-51-like kinase 1 (ULK1) is considered a downstream molecule of AMPK; however, it was recently reported that the activity of AMPK could be regulated by ULK1 conversely. We demonstrated that AMPK and ULK1 activities were decreased in the kidneys of CKD mice. However, whether and how ULK1 is involved in the underlying mechanism of CKD exacerbation remains unknown. In this study, we investigated the ULK1 involvement in CKD, using ULK1 knockout mice. The CKD model of Ulk1-/- mice exhibited significantly exacerbated renal function and worsening renal fibrosis. In the kidneys of the CKD model of Ulk1-/- mice, reduced AMPK and its downstream β-oxidation could be observed, leading to an energy deficit of increased AMP/ATP ratio. In addition, AMPK signaling in the kidney was reduced in control Ulk1-/- mice with normal renal function compared to control wild-type mice, suggesting that ULK1 deficiency suppressed AMPK activity in the kidney. This study is the first to present ULK1 as a novel therapeutic target for CKD treatment, which regulates AMPK activity in the kidney. This article is protected by copyright. All rights reserved.
    Keywords:  AMPK; Chronic kidney disease, CKD, Renal fibrosis; ULK1
    DOI:  https://doi.org/10.1111/gtc.12989
  13. PNAS Nexus. 2022 Sep;1(4): pgac183
    Cryo-electron tomography with mixed-scale dense neural networks reveals key steps in deployment of Toxoplasma invasion machinery.
    Li-Av Segev-Zarko, Peter D Dahlberg, Stella Y Sun, Daniël M Pelt, Chi Yong Kim, Elizabeth S Egan, James A Sethian, Wah Chiu, John C Boothroyd.
      Host cell invasion by intracellular, eukaryotic parasites within the phylum Apicomplexa is a remarkable and active process involving the coordinated action of apical organelles and other structures. To date, capturing how these structures interact during invasion has been difficult to observe in detail. Here, we used cryogenic electron tomography to image the apical complex of Toxoplasma gondii tachyzoites under conditions that mimic resting parasites and those primed to invade through stimulation with calcium ionophore. Through the application of mixed-scale dense networks for image processing, we developed a highly efficient pipeline for annotation of tomograms, enabling us to identify and extract densities of relevant subcellular organelles and accurately analyze features in 3-D. The results reveal a dramatic change in the shape of the anteriorly located apical vesicle upon its apparent fusion with a rhoptry that occurs only in the stimulated parasites. We also present information indicating that this vesicle originates from the vesicles that parallel the intraconoidal microtubules and that the latter two structures are linked by a novel tether. We show that a rosette structure previously proposed to be involved in rhoptry secretion is associated with apical vesicles beyond just the most anterior one. This result, suggesting multiple vesicles are primed to enable rhoptry secretion, may shed light on the mechanisms Toxoplasma employs to enable repeated invasion attempts. Using the same approach, we examine Plasmodium falciparum merozoites and show that they too possess an apical vesicle just beneath a rosette, demonstrating evolutionary conservation of this overall subcellular organization.
    DOI:  https://doi.org/10.1093/pnasnexus/pgac183
  14. Nat Chem Biol. 2022 Oct 31.
    Probing coenzyme A homeostasis with semisynthetic biosensors.
    Lin Xue, Paul Schnacke, Michelle S Frei, Birgit Koch, Julien Hiblot, Richard Wombacher, Sebastian Fabritz, Kai Johnsson.
      Coenzyme A (CoA) is one of the central cofactors of metabolism, yet a method for measuring its concentration in living cells is missing. Here we introduce the first biosensor for measuring CoA levels in different organelles of mammalian cells. The semisynthetic biosensor is generated through the specific labeling of an engineered GFP-HaloTag fusion protein with a fluorescent ligand. Its readout is based on CoA-dependent changes in Förster resonance energy transfer efficiency between GFP and the fluorescent ligand. Using this biosensor, we probe the role of numerous proteins involved in CoA biosynthesis and transport in mammalian cells. On the basis of these studies, we propose a cellular map of CoA biosynthesis that suggests how pools of cytosolic and mitochondrial CoA are maintained.
    DOI:  https://doi.org/10.1038/s41589-022-01172-7
  15. World J Microbiol Biotechnol. 2022 Nov 02. 38(12): 255
    Metabolic adaptation and ATP homeostasis in Pseudomonas fluorescens exposed to phosphate stress.
    Félix Legendre, Alex MacLean, Sujeenthar Tharmalingam, Vasu D Appanna.
      Phosphate (Pi) is essential for life as it is an integral part of the universal chemical energy adenosine triphosphate (ATP), and macromolecules such as, DNA, RNA proteins and lipids. Despite the core roles and the need of this nutrient in living cells, some bacteria can grow in environments that are poor in Pi. The metabolic mechanisms that enable bacteria to proliferate in a low phosphate environment are not fully understood. In this study, the soil microbe Pseudomonas (P.) fluorescens was cultured in a control and a low Pi (stress) medium in order to delineate how energy homeostasis is maintained. Although there was no significant variation in biomass yield in these cultures, metabolites like isocitrate, oxaloacetate, pyruvate and phosphoenolpyruvate (PEP) were markedly increased in the phosphate-starved condition. Components of the glycolytic, glyoxylate and tricarboxylic acid cycles operated in tandem to generate ATP by substrate level phosphorylation (SLP) as NADH-producing enzymes were impeded. The α-ketoglutarate (KG) produced when glutamine, the sole carbon nutrient was transformed into phosphoenol pyruvate (PEP) and succinyl-CoA (SC), two high energy moieties. The metabolic reprogramming orchestrated by isocitrate lyase (ICL), phosphoenolpyruvate synthase (PEPS), pyruvate phosphate dikinase (PPDK), and succinyl-CoA synthetase fulfilled the ATP budget. Cell free extract experiments confirmed ATP synthesis in the presence of such substrates as PEP, oxaloacetate and isocitrate respectively. Gene expression profiling revealed elevated transcripts associated with numerous enzymes including ICL, PEPS, and succinyl-CoA synthetase (SCS). This microbial adaptation will be critical in promoting biological activity in Pi-poor ecosystems.
    DOI:  https://doi.org/10.1007/s11274-022-03432-z
  16. Microbiol Res. 2022 Oct 17. pii: S0944-5013(22)00264-6. [Epub ahead of print]266 127224
    Control of central metabolism's architecture in Escherichia coli: An overview.
    Mansi El-Mansi.
      Understanding metabolic networks' architecture is central to successfully manipulating metabolic fluxes in microbial cell factories. The transition of central metabolism's architecture from acetogenic to gluconeogenic and from the canonical monocyclic architecture of the Krebs tricarboxylic acids (TCA) cycle to a bicyclic architecture in which the TCA and the dicarboxylic acids (DCA) cycles work in unison, with the glyoxylate bypass fulfilling the anaplerotic function, has been the subject of much debate and remains elusive. In this article, the author sheds light on the intricacies surrounding the transition of central metabolism from one architecture to another and shows that the transition from the monocyclic architecture to the bicyclic architecture is triggered in response to a minimum threshold signal of growth rate (≲0.40h-1) and is a consequence of competitions, on the one hand. between phosphotransacetylase (PTA) and α-ketoglutarate dehydrogenase (α-KGDH) for their common co-factor, free HS-CoA, and, on the other hand, between catabolic and anaplerotic routs for acetyl phosphate. Further restriction of carbon supply in the bioreactor to the point of starvation forces E. coli to further modify its central metabolism to the PEP-glyoxylate architecture to maintain the redox balance. Interestingly the sudden change from hunger ('famine') to carbon excess ('feast') leads to yet another architecture in which the methylglyoxal pathway figure prominently to maintain the adenylate energy charge. Moreover, the author sheds light on the biochemical implications of each architecture.
    Keywords:  Central metabolism’s architecture; Competitions at metabolic junctions; Escherichia coli; Methylglyoxal bypass; Monocyclic and bicyclic architectures; PEP-glyoxylate cycle
    DOI:  https://doi.org/10.1016/j.micres.2022.127224
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