bims-toxgon Biomed News
on Toxoplasma gondii metabolism
Issue of 2022‒12‒04
six papers selected by
Lakesh Kumar
BITS Pilani

  1. PLoS Pathog. 2022 Nov 30. 18(11): e1011009
      Many apicomplexan parasites harbor a non-photosynthetic plastid called the apicoplast, which hosts important metabolic pathways like the methylerythritol 4-phosphate (MEP) pathway that synthesizes isoprenoid precursors. Yet many details in apicoplast metabolism are not well understood. In this study, we examined the physiological roles of four glycolytic enzymes in the apicoplast of Toxoplasma gondii. Many glycolytic enzymes in T. gondii have two or more isoforms. Endogenous tagging each of these enzymes found that four of them were localized to the apicoplast, including pyruvate kinase2 (PYK2), phosphoglycerate kinase 2 (PGK2), triosephosphate isomerase 2 (TPI2) and phosphoglyceraldehyde dehydrogenase 2 (GAPDH2). The ATP generating enzymes PYK2 and PGK2 were thought to be the main energy source of the apicoplast. Surprisingly, deleting PYK2 and PGK2 individually or simultaneously did not cause major defects on parasite growth or virulence. In contrast, TPI2 and GAPDH2 are critical for tachyzoite proliferation. Conditional depletion of TPI2 caused significant reduction in the levels of MEP pathway intermediates and led to parasite growth arrest. Reconstitution of another isoprenoid precursor synthesis pathway called the mevalonate pathway in the TPI2 depletion mutant partially rescued its growth defects. Similarly, knocking down the GAPDH2 enzyme that produces NADPH also reduced isoprenoid precursor synthesis through the MEP pathway and inhibited parasite proliferation. In addition, it reduced de novo fatty acid synthesis in the apicoplast. Together, these data suggest a model that the apicoplast dwelling TPI2 provides carbon source for the synthesis of isoprenoid precursor, whereas GAPDH2 supplies reducing power for pathways like MEP, fatty acid synthesis and ferredoxin redox system in T. gondii. As such, both enzymes are critical for parasite growth and serve as potential targets for anti-toxoplasmic intervention designs. On the other hand, the dispensability of PYK2 and PGK2 suggest additional sources for energy in the apicoplast, which deserves further investigation.
  2. Front Microbiol. 2022 ;13 1027073
      Toxoplasma gondii is an obligate intracellular zoonotic pathogen capable of infecting almost all cells of warm-blooded vertebrates. In intermediate hosts, this parasite reproduces asexually in two forms, the tachyzoite form during acute infection that proliferates rapidly and the bradyzoite form during chronic infection that grows slowly. Depending on the growth condition, the two forms can interconvert. The conversion of tachyzoites to bradyzoites is critical for T. gondii transmission, and the reactivation of persistent bradyzoites in intermediate hosts may lead to symptomatic toxoplasmosis. However, the mechanisms that control bradyzoite differentiation have not been well studied. Here, we review recent advances in the study of bradyzoite biology and stage conversion, aiming to highlight the determinants associated with bradyzoite development and provide insights to design better strategies for controlling toxoplasmosis.
    Keywords:  Toxoplasma gondii; bradyzoite; cyst; differentiation; immune response; metabolism; tachyzoite
  3. Proc Natl Acad Sci U S A. 2022 Dec 06. 119(49): e2212220119
      De novo lipogenesis is a highly regulated metabolic process, which is known to be activated through transcriptional regulation of lipogenic genes, including fatty acid synthase (FASN). Unexpectedly, we find that the expression of FASN protein remains unchanged during Drosophila larval development from the second to the third instar larval stages (L2 to L3) when lipogenesis is hyperactive. Instead, acetylation of FASN is significantly upregulated in fast-growing larvae. We further show that lysine K813 residue is highly acetylated in developing larvae, and its acetylation is required for elevated FASN activity, body fat accumulation, and normal development. Intriguingly, K813 is autoacetylated by acetyl-CoA (AcCoA) in a dosage-dependent manner independent of acetyltransferases. Mechanistically, the autoacetylation of K813 is mediated by a novel P-loop-like motif (N-xx-G-x-A). Lastly, we find that K813 is deacetylated by Sirt1, which brings FASN activity to baseline level. In summary, this work uncovers a previously unappreciated role of FASN acetylation in developmental lipogenesis and a novel mechanism for protein autoacetylation, through which Drosophila larvae control metabolic homeostasis by linking AcCoA, lysine acetylation, and de novo lipogenesis.
    Keywords:  FASN; acetyl-CoA; animal development; autoacetylation; de novo lipogenesis
  4. J Vet Med Sci. 2022 Dec 01.
      Sarcocystis cruzi is a member of the genus Sarcocystis, infecting bovine animals such as cattle and bison as intermediate hosts, and canids such as dogs and raccoon dogs as definitive hosts. Acute sarcocystosis of S. cruzi causes occasional symptoms in cattle, including weight loss, reduced milk production, abortions, and death, and similar to other Sarcocystis species can potentially cause food poisoning in humans when raw or undercooked infected cattle meat is consumed. Despite these issues, genetic information on S. cruzi is scarce, and there is no specific quantitative method for the detection and quantification of the parasite in infected cattle. In this study, we aimed to develop a method based on high-throughput sequencing of S. cruzi genome and transcriptome that specifically and quantitatively detects the S. cruzi acetyl-CoA synthetase gene (ScACS). Cardiac muscles were collected from slaughterhouses in Saitama Prefecture to obtain sarcocysts from which DNA and RNA were extracted for the high-throughput sequencing. Using the sequences, we developed a specific quantitative PCR assay which could distinguish S. cruzi ACS from that of Toxoplasma gondii by taking advantage of the differences in their exon/intron organizations and validated the assay with the microscopic counting of the S. cruzi bradyzoites. Thus, this assay will be useful for future studies of S. cruzi pathogenesis in cattle and for the surveillance of infected animals, thereby easing public health concerns.
    Keywords:  Sarcocystis cruzi; acetyl-CoA synthetase; bradyzoite; quantitative real-time PCR
  5. Plant Physiol Biochem. 2022 Nov 11. pii: S0981-9428(22)00500-9. [Epub ahead of print]194 236-245
      Sirtuins are part of a gene family of NAD-dependent deacylases that act on histone and non-histone proteins and control a variety of activities in all living organisms. Their roles are mainly related to energy metabolism and include lifetime regulation, DNA repair, stress resistance, and proliferation. A large amount of knowledge concerning animal sirtuins is available, but data about their plant counterparts are scarce. Plants possess few sirtuins that have, like in animals, a recognized role in stress defense and metabolism regulation. However, engagement in proliferation control, which has been demonstrated for mammalian sirtuins, has not been reported for plant sirtuins so far. In this work, srt1 and srt2 Arabidopsis mutant seedlings have been used to evaluate in vivo the role of sirtuins in cell proliferation and regulation of glutamate dehydrogenase, an enzyme demonstrated to be involved in the control of cell cycle in SIRT4-defective human cells. Moreover, bioinformatic analyses have been performed to elucidate sequence, structure, and function relationships between Arabidopsis sirtuins and between each of them and the closest mammalian homolog. We found that cell proliferation and GDH activity are higher in mutant seedlings, suggesting that both sirtuins exert a physiological inhibitory role in these processes. In addition, mutant seedlings show plant growth and root system improvement, in line with metabolic data. Our data also indicate that utilization of an easy to manipulate organism, such as Arabidopsis plant, can help to shed light on the molecular mechanisms underlying the function of genes present in interkingdom species.
    Keywords:  Arabidopsis thaliana; Glutamate dehydrogenase; Proliferation; Sirtuin 3D models; Sirtuins