bims-toxgon Biomed News
on Toxoplasma gondii metabolism
Issue of 2025–03–30
ten papers selected by
Lakesh Kumar, BITS Pilani



  1. mSphere. 2025 Mar 28. e0011125
      Intracellular replication is crucial for the success of apicomplexan parasites, including Toxoplasma gondii. Therefore, essential players in parasite replication represent potential targets for drug development. We have characterized TgGSK, a glycogen synthase kinase homolog that plays an important role in Toxoplasma endodyogeny. We have shown that TgGSK has a dynamic localization that is concurrent with the cell cycle. In non-dividing parasites, this kinase is highly concentrated in the nucleus. However, during division, TgGSK displays a cytosolic localization, with concentration foci at the centrosomes, a key organelle involved in parasite division, and the basal end. Conditional knockdown of TgGSK determined that it is essential for the completion of the lytic cycle and proper parasite division. Parasites lacking endogenous protein levels of TgGSK exhibited defects in division synchronicity and the segregation of the nucleus and apicoplast into forming daughter cells. These phenotypes are associated with defects in centrosome duplication and fission. Global phosphoproteomic analysis determined TgGSK-dependent phosphorylation of RNA-processing, basal end, and centrosome proteins. Consistent with the putative regulation of RNA-processing proteins, global transcriptomic analysis suggests that TgGSK is needed for proper splicing. Finally, we show that TgGSK interacts with GCN5b, a well-characterized acetyltransferase with roles in transcriptional control. Conversely, GCN5b chemical inhibition results in specific degradation of TgGSK. Thus, these studies reveal the involvement of TgGSK in various crucial processes, including endodyogeny and splicing, and identify acetylation as a possible mechanism by which this essential kinase is regulated.
    IMPORTANCE: While infection with the parasite Toxplasma gondii is largely asymptomatic in healthy adults, severe disease and death can result in immunocompromised individuals and in those infected congenitally. With minimal treatments for toxoplasmosis available, it is crucial to study parasite-specific processes to identify new drug targets. This study investigated the protein TgGSK, uncovering its essentiality for parasite proper division and survival. We performed an in-depth study of the functional role of this kinase. Importantly, TgGSK was shown to bear higher homology to plant proteins than its mammalian counterparts, which may allow for specific targeting of this protein.
    DOI:  https://doi.org/10.1128/msphere.00111-25
  2. J Neuroimmunol. 2025 Mar 19. pii: S0165-5728(25)00068-2. [Epub ahead of print]403 578588
      Obligate intracellular pathogens such as the protozoan Toxoplasma gondii exploit host cell mechanisms to facilitate their survival and replication. While T. gondii can infect any nucleated mammalian cell, it exhibits a particular affinity for central nervous system cells, including neurons, astrocytes, and microglia. Among these, astrocytes play a pivotal role in maintaining neuroimmune balance, and their infection by T. gondii induces structural and functional alterations. Emerging evidence suggests that these changes may contribute to the pathophysiology of schizophrenia (SCZ). Although a direct causal link between T. gondii-induced astrocytic dysfunction and SCZ remains unproven, infection has been associated with increased kynurenic acid production, elevated dopamine levels, and heightened inflammatory cytokines-all of which are implicated in SCZ pathology. Additionally, T. gondii infection disrupts crucial neurobiological processes, including N-methyl-d-aspartate receptor signaling, blood-brain barrier integrity, and gray matter volume, further aligning with SCZ-associated neuropathology. This review underscores the need for targeted research into T. gondii-mediated astrocytic dysfunction as a potential factor in SCZ development. Understanding the mechanistic links between T. gondii infection, astrocytic alterations, and psychiatric disorders may open new avenues for therapeutic interventions.
    Keywords:  Astrocytes; Immune response; Infection; Neuroinflammation; Schizophrenia; Toxoplasma gondii
    DOI:  https://doi.org/10.1016/j.jneuroim.2025.578588
  3. Phys Life Rev. 2025 Mar 21. pii: S1571-0645(25)00050-8. [Epub ahead of print]53 225-235
      Sirtuins's central role in governing metabolic processes has been known for decades. However, over the past two decades, sirtuin functions have been linked to immune regulation and immunity. Sirtuins are NAD+ dependent protein deacylases involved in the regulation of several important biological processes ranging from energy homeostasis, metabolism, aging, apoptosis, autophagy, immunity, adipocyte, and muscle differentiation. Here, in this review, we discuss the role of sirtuins in several infectious diseases including viral, bacterial, and protozoan infections with detailed emphasis on bacterial-host interactions. We have aimed to explore both host and bacterial sirtuin functions contributing to the infection progression, host responses and their influence on the everlasting host-pathogen tug-of-war. In order to manipulate host pathways, pathogens such as intracellular bacteria have evolved parallelly and harbor bacterial sirtuins. The recent discoveries of bacterial sirtuins influencing the host-pathogen interaction outcomes pave the way for the discovery of potential therapeutic targets.
    Keywords:  Bacterial sirtuins; Host-pathogen interactions; Immune modulators; Infections; Sirtuins
    DOI:  https://doi.org/10.1016/j.plrev.2025.03.020
  4. Autophagy. 2025 Mar 27. 1-5
      ATG8ylation of membranes has been increasingly reported over the last few years, in various configurations and across different eukaryotic models. While the unconventional conjugation of ATG8 to the outermost membrane of the plastid in apicomplexan parasites was first observed over a decade ago, it is often overlooked in literature reviews focusing on the ATG8ylation of non-autophagosomal membranes. Here, I provide a brief overview of the current knowledge on plastid ATG8ylation in these parasites and discuss a possible parallel between the evolutionary origin of this plastid and other ATG8ylation processes, such as LC3-associated phagocytosis.
    Keywords:  ATG8ylation; Apicomplexa; apicoplast; evolution; organelle division
    DOI:  https://doi.org/10.1080/15548627.2025.2483445
  5. Nat Chem Biol. 2025 Mar 26.
      The dynamic modification of proteins by many metabolites suggests an intimate link between energy metabolism and post-translational modifications (PTMs). For instance, starvation and low-carbohydrate diets lead to the accumulation of β-hydroxybutyrate (BHB), whose blood concentrations can reach millimolar levels, concomitant with the accumulation of lysine β-hydroxybutyrylation (Kbhb) of proteins. Here we report that class I histone deacetylases (HDACs) unexpectedly catalyze the formation of Kbhb. Through mutational analysis, we show a shared reliance on key active site amino acids for classical deacetylation and noncanonical HDAC-catalyzed β-hydroxybutyrylation. On the basis of these data, we propose that HDACs catalyze a condensation reaction between the free amine group on lysine and the BHB carboxylic acid, thereby generating an amide bond. This reversible HDAC activity is not limited to BHB and extends to multiple short-chain fatty acids, representing a novel mechanism of PTM deposition relevant to metabolically sensitive proteome modifications.
    DOI:  https://doi.org/10.1038/s41589-025-01869-5
  6. Microbiol Spectr. 2025 Mar 26. e0204024
      Toxoplasma gondii is a pathogen characterized by a large variety of strains whose virulence and clinical severity are likely linked to their genotype. Currently, the strains are genotyped using restriction fragment length polymorphism, multilocus sequence typing, and microsatellite markers. This typing requires the strain's DNA, which is difficult to obtain. A serotyping test could overcome the constraints of genotyping, the challenge being to identify type-specific proteins. We identified immunogenic T. gondii proteins from co-immunoprecipitations for three tachyzoite strains (strain FOU from Africa 1 type, ME49 from Type II, and VEG from Type III) with hyperimmune murine sera and conducted an in silico polymorphism search for the identified proteins. A variant calling analysis was conducted on the next-generation sequencing sequences of 117 T. gondii isolates with the objective of identifying mutations present in the genes encoding the antigenic proteins previously identified. A total of 727 immunogenic proteins were identified, including 16% dense granule protein (GRA), rhoptry protein (ROP/RON), and surface antigen protein (SAG). Genetic analysis revealed the presence of 36 single-nucleotide polymorphisms (SNPs) in over 70% of isolates belonging to the same type, while less than 30% of isolates belonging to the other types exhibited these polymorphisms. Of these, only 15 are located on coding DNA sequence regions, while four are located on genes encoding apicomplexan proteins: two SNPs on the ROP5 gene and two on the ROP7 gene. The results of this study indicate that a significant number of T. gondii immunogenic proteins can be identified using an in vivo approach. The in silico study identified SNPs that could be genotype-specific.
    IMPORTANCE: Toxoplasma gondii is a unique species that exhibits genotype diversity related to clinical virulence. Currently, genotyping is restricted, which limits epidemiological knowledge of the strains. To overcome this limitation, we aimed to develop serotyping tests. First, we used a murine in vivo, non-targeted experimental approach based on proteomics techniques through which we were able to identify a panel of more than 700 antigenic proteins from T. gondii. Then, we analyzed the polymorphism of these proteins using a whole-genome sequencing database containing the genomes of 117 genotyped strains. We showed that none of the 986 non-silent SNPs detected is specific to the strain type. The in vivo approach is the first that allowed the identification of such a large panel of antigenic proteins. Moreover, the polymorphism analysis, the first based on a large next-generation sequencing database, showed the limits that currently restrict the development of a serotyping technique.
    Keywords:  Toxoplasma; antigenic protein; mass spectrometry; polymorphism; variant call analysis
    DOI:  https://doi.org/10.1128/spectrum.02040-24
  7. Cancers (Basel). 2025 Mar 17. pii: 1009. [Epub ahead of print]17(6):
      Acute myeloid leukemia (AML) corresponds to a heterogeneous group of clonal hematopoietic diseases, which are characterized by uncontrolled proliferation of malignant transformed myeloid precursors and their inability to differentiate into mature blood cells. The prognosis of AML depends on many variables, including the genetic features of the disease. Treatment outcomes, despite the introduction of new targeted therapies, are still unsatisfactory. Recently, there have been an increasing number of reports on enzymatic proteins of the sirtuin family and their potential importance in cancer in general. Sirtuins are a group of 7 (SIRT1-7) NAD+-dependent histone deacetylases with pleiotropic effects on metabolism, aging processes, and cell survival. They are not only responsible for post-translational modification of histones but also play various biochemical functions and interact with other proteins regulating cell survival, such as p53. Thus, their role in key mechanisms of tumorigenesis makes them a worthwhile topic in AML. Different sirtuins have been shown to act oppositely depending on the biological context, the mechanism of which requires further exploration. This review provides a comprehensive description of the significance and role of sirtuins in AML in light of the current state of knowledge. It focuses in particular on molecular mechanisms regulated by sirtuins and signaling pathways involved in leukemogenesis, as well as clinical aspects and potential therapeutic targets in AML.
    Keywords:  SIRTs; acute myeloid leukemia; epigenetics; sirtuins; targeted treatment
    DOI:  https://doi.org/10.3390/cancers17061009
  8. J Biol Chem. 2025 Mar 25. pii: S0021-9258(25)00295-9. [Epub ahead of print] 108446
      Sirtuin 6 (SIRT6) is an NAD-dependent protein deacylase that targets lysine residues in histones in the cell nucleus, where it helps maintain genome stability and links metabolism to epigenetic control. Dysregulation of SIRT6 is believed to be associated with aging and cancer, making it of pharmacological interest. In this study, we use cryogenic electron microscopy (cryo-EM) and enzymology to explore SIRT6 preference and adaptability towards different nucleosomal substrates. We have visualized a trapped complex of SIRT6 in the process of deacylating H3K27, demonstrating how SIRT6 undergoes conformational changes to remove differently positioned histone marks. Additional biochemical studies further reveal SIRT6's plasticity, which accommodates various metabolism-linked modifications such as lysine lactylation and β-hydroxybutyrylation. To further understand the basis for substrate selectivity of SIRT6, we explore the effects of an established G60A enzyme mutation, proximal H3 modifications, and small molecule modulators. These findings highlight SIRT6's versatility and provide key mechanistic insights into its molecular recognition.
    Keywords:  Chromatin; chromatin modification; histone deacetylase (HDAC); histone modification; sirtuin
    DOI:  https://doi.org/10.1016/j.jbc.2025.108446
  9. Proc Natl Acad Sci U S A. 2025 Apr;122(13): e2426929122
      3-Phosphoinositides (3-PIs), phosphatidylinositol (3,4) bisphosphate [PI(3,4)P2] and phosphatidylinositol (3,4,5) trisphosphate (PIP3), are important lipid second messengers in the Phosphoinositide 3-Kinase (PI3K)/Akt signaling pathway, which is crucial to cell growth and frequently dysregulated in cancer. Emerging evidence suggests these lipid second messengers may be present in membranes beyond the plasma membrane, yet their spatial regulation within other membrane compartments is not well understood. To dissect the spatial regulation of specific 3-PI species, we developed genetically encodable biosensors with selectivity for PIP3 or PI(3,4)P2. Using these biosensors, we showed that PIP3 significantly accumulated at the lysosome upon growth factor stimulation, in contrast to the conventional view that PIP3 is exclusively present in the plasma membrane. Furthermore, we showed that lysosomal PIP3 originates from the plasma membrane and relies on dynamin-dependent endocytosis for lipid internalization. Thus, PIP3 can exploit dynamic trafficking pathways to access subcellular compartments and regulate signaling in a spatially selective manner.
    Keywords:  3-phosphoinositide; cellular signaling; fluorescent biosensor; lysosome; spatiotemporal regulation
    DOI:  https://doi.org/10.1073/pnas.2426929122
  10. Mol Cell. 2025 Mar 19. pii: S1097-2765(25)00186-8. [Epub ahead of print]
      Phosphatidylinositol 3-kinase (PI3K) phosphorylates PI(4,5)P2 to produce PI(3,4,5)P3, thereby activating AKT and other effector proteins. However, whether PI3K has non-PI(3,4,5)P3-related functions critical for tumor development remains unclear. Here, we demonstrate that high glucose induces PI3Kβ binding to O-linked β-D-N-acetylglucosamine (O-GlcNAc) transferase (OGT) in glioblastoma cells, dependent on hexokinase 1 (HK1)-mediated OGT Y889 phosphorylation and subsequent p85α recruitment. Importantly, PI3Kβ functions as a protein kinase, phosphorylating OGT at T985 and enhancing OGT activity and total cellular protein O-GlcNAcylation. Activated OGT O-GlcNAcylates ATP-citrate synthase (ACLY) at T639 and S667, leading to ACLY activation-dependent acetyl-coenzyme A (CoA) production to increase fatty acid levels and histone H3 acetylation for gene transcription. Intervention in PI3Kβ-mediated OGT phosphorylation and ACLY O-GlcNAcylation inhibits glioblastoma cell proliferation and tumor growth in xenografts. These findings underscore the critical role of PI3Kβ in governing protein O-GlcNAcylation, fatty acid metabolism, and chromatin modification through its protein kinase activity and provide instrumental insight into the roles of PI3K in tumor progression.
    Keywords:  ACLY; HK1; OGT; PI3K; acetyl-CoA; fatty acid production; histone; tumor
    DOI:  https://doi.org/10.1016/j.molcel.2025.02.024