bims-toxgon Biomed News
on Toxoplasma gondii metabolism
Issue of 2022‒10‒09
six papers selected by
Lakesh Kumar
BITS Pilani

  1. mBio. 2022 Oct 06. e0196522
      Toxoplasma gondii is an intracellular apicomplexan parasite that relies on cyclic GMP (cGMP)-dependent signaling to trigger timely egress from host cells in response to extrinsic and intrinsic signals. A guanylate cyclase (GC) complex, conserved across the Apicomplexa, plays a pivotal role in integrating these signals, such as the key lipid mediator phosphatidic acid and changes in pH and ionic composition. This complex is composed of an atypical GC fused to a flippase-like P4-ATPase domain and assembled with the cell division control protein CDC50.1 and a unique GC organizer (UGO). While the dissemination of the fast-replicating tachyzoites responsible for acute infection is well understood, it is less clear if the cyst-forming bradyzoites can disseminate and contribute to cyst burden. Here, we characterized a novel component of the GC complex recently termed signaling linking factor (SLF). Tachyzoites conditionally depleted in SLF are impaired in microneme exocytosis, conoid extrusion, and motility and hence unable to invade and egress. A stage-specific promoter swap strategy allowed the generation of SLF- and GC-deficient bradyzoites that are viable as tachyzoites but show a reduction in cyst burden during the onset of chronic infection. Upon oral infection, SLF-deficient cysts failed to establish infection in mice, suggesting SLF's importance for the natural route of T. gondii infection. IMPORTANCE Toxoplasma gondii is an obligate intracellular parasite of the phylum Apicomplexa. This life-threatening opportunistic pathogen establishes a chronic infection in human and animals that is resistant to immune attacks and chemotherapeutic intervention. The slow-growing parasites persist in tissue cysts that constitute a predominant source of transmission. Host cell invasion and egress are two critical steps of the parasite lytic cycle that are governed by a guanylate cyclase complex conserved across the Apicomplexa. A signaling linked factor is characterized here as an additional component of the complex that not only is essential during acute infection but also plays a pivotal role during natural oral infection with tissue cysts' dissemination and persistence.
    Keywords:  Toxoplasma gondii; apicomplexan parasites; bradyzoite; chronic infection; egress; guanylate cyclase; invasion; signaling; tissue cyst
  2. Cell Mol Life Sci. 2022 Sep 28. 79(10): 532
      Toxoplasma gondii is a widespread eukaryotic pathogen that causes life-threatening diseases in humans and diverse animals. It has a complex life cycle with multiple developmental stages, which are timely adjusted according to growth conditions. But the regulatory mechanisms are largely unknown. Here we show that the AMP-activated protein kinase (AMPK), a key regulator of energy homeostasis in eukaryotes, plays crucial roles in controlling the cell cycle progression and bradyzoite development in Toxoplasma. Deleting the β regulatory subunit of AMPK in the type II strain ME49 caused massive DNA damage and increased spontaneous conversion to bradyzoites (parasites at chronic infection stage), leading to severe growth arrest and reduced virulence of the parasites. Under alkaline stress, all Δampkβ mutants converted to a bradyzoite-like state but the cell division pattern was significantly impaired, resulting in compromised parasite viability. Moreover, we found that phosphorylation of the catalytic subunit AMPKα was greatly increased in alkaline stressed parasites, whereas AMPKβ deletion mutants failed to do so. Phosphoproteomics found that many proteins with predicted roles in cell cycle and cell division regulation were differentially phosphorylated after AMPKβ deletion, under both normal and alkaline stress conditions. Together, these results suggest that the parasite AMPK has critical roles in safeguarding cell cycle progression, and guiding the proper exist of the cell cycle to form mature bradyzoites when the parasites are stressed. Consistent with this model, growth of parasites was not significantly altered when AMPKβ was deleted in a strain that was naturally reluctant to bradyzoite development.
    Keywords:  AMPK; Bradyzoite development; Cell cycle; Phosphorylation; Toxoplasma gondii
  3. Nat Commun. 2022 Oct 01. 13(1): 5778
      Toxoplasma gondii is a cyst-forming apicomplexan parasite of virtually all warm-blooded species, with all true cats (Felidae) as definitive hosts. It is the etiologic agent of toxoplasmosis, a disease causing substantial public health burden worldwide. Few intercontinental clonal lineages represent the large majority of isolates worldwide. Little is known about the evolutionary forces driving the success of these lineages, the timing and the mechanisms of their global dispersal. In this study, we analyse a set of 156 genomes and we provide estimates of T. gondii mutation rate and generation time. We elucidate how the evolution of T. gondii populations is intimately linked to the major events that have punctuated the recent history of cats. We show that a unique haplotype, whose length represents only 0.16% of the whole T. gondii genome, is common to all intercontinental lineages and hybrid populations derived from these lineages. This haplotype has accompanied wildcats (Felis silvestris) during their emergence from the wild to domestic settlements, their dispersal in the Old World, and their expansion in the last five centuries to the Americas. The selection of this haplotype is most parsimoniously explained by its role in sexual reproduction of T. gondii in domestic cats.
  4. Acta Crystallogr F Struct Biol Commun. 2022 Oct 01. 78(Pt 10): 363-370
      Succinyl-CoA synthetase (SCS) catalyzes a three-step reaction in the citric acid cycle with succinyl-phosphate proposed as a catalytic intermediate. However, there are no structural data to show the binding of succinyl-phosphate to SCS. Recently, the catalytic mechanism underlying acetyl-CoA production by ATP-citrate lyase (ACLY) has been debated. The enzyme belongs to the family of acyl-CoA synthetases (nucleoside diphosphate-forming) for which SCS is the prototype. It was postulated that the amino-terminal portion catalyzes the full reaction and the carboxy-terminal portion plays only an allosteric role. This interpretation was based on the partial loss of the catalytic activity of ACLY when Glu599 was mutated to Gln or Ala, and on the interpretation that the phospho-citryl-CoA intermediate was trapped in the 2.85 Å resolution structure from cryogenic electron microscopy (cryo-EM). To better resolve the structure of the intermediate bound to the E599Q mutant, the equivalent mutation, E105αQ, was made in human GTP-specific SCS. The structure of the E105αQ mutant shows succinyl-phosphate bound to the enzyme at 1.58 Å resolution when the mutant, after phosphorylation in solution by Mg2+-ATP, was crystallized in the presence of magnesium ions, succinate and desulfo-CoA. The E105αQ mutant is still active but has a specific activity that is 120-fold less than that of the wild-type enzyme, with apparent Michaelis constants for succinate and CoA that are 50-fold and 11-fold higher, respectively. Based on this high-resolution structure, the cryo-EM maps of the E599Q ACLY complex reported previously should have revealed the binding of citryl-phosphate and CoA and not phospho-citryl-CoA.
    Keywords:  ATP-citrate lyase; catalytic intermediates; cryogenic electron microscopy; succinyl-CoA synthetase; succinyl-phosphate
  5. Curr Drug Targets. 2022 Oct 03.
      Protein acetylation is a reversible central mechanism to control gene expression and cell signaling events. Current evidence suggests that pharmacological inhibitors for protein deacetylation have already been used in various disease conditions. Accumulating reports showed that several compounds that enhance histone acetylation in cells are in both the preclinical and clinical development stages targeting non-communicable diseases, which include cancerous and non-cancerous especially cardiovascular complications. These compounds are, in general, enzyme inhibitors and target a family of enzymes- called histone deacetylases (HDACs). Since HDAC inhibitors have shown to be helpful in preclinical models of cardiac complications, further research on developing novel compounds with high efficacy and low toxicity may be essential for treating cardiovascular diseases. In this review, we have highlighted the roles of HDAC and its inhibitors in cardiac complications.
    Keywords:  Cardiac hypertrophy; Cardiomyopathy; Cardiovascular; HDAC; Myocardial infraction; SAHA
  6. Nat Microbiol. 2022 Oct 03.
      Defence-associated sirtuins (DSRs) comprise a family of proteins that defend bacteria from phage infection via an unknown mechanism. These proteins are common in bacteria and harbour an N-terminal sirtuin (SIR2) domain. In this study we report that DSR proteins degrade nicotinamide adenine dinucleotide (NAD+) during infection, depleting the cell of this essential molecule and aborting phage propagation. Our data show that one of these proteins, DSR2, directly identifies phage tail tube proteins and then becomes an active NADase in Bacillus subtilis. Using a phage mating methodology that promotes genetic exchange between pairs of DSR2-sensitive and DSR2-resistant phages, we further show that some phages express anti-DSR2 proteins that bind and repress DSR2. Finally, we demonstrate that the SIR2 domain serves as an effector NADase in a diverse set of phage defence systems outside the DSR family. Our results establish the general role of SIR2 domains in bacterial immunity against phages.