bims-toxgon 2026-09-20 papers

Issue of 2026–09–20
seven papers selected by
Lakesh Kumar, BITS Pilani

Elife. 2026 Sep 17. pii: RP102511. [Epub ahead of print]13

Screening the MMV Pathogen Box reveals the mitochondrial bc1-complex as a drug target in mature Toxoplasma gondii bradyzoites.

Deborah Maus, Elyzana Putrianti, Tobias Hoffmann, Michael Laue, Frank Seeber, Martin Blume.

The apicomplexan parasite Toxoplasma gondii infects 25-30% of the global human population and can cause life-threatening diseases in immunocompromised patients. The chronically infectious forms of the parasite, bradyzoites, persist within cysts in brain and muscle tissue, and are responsible for its transmission and remission of the disease. Currently available treatment options are very limited and are only effective against the fast-replicating tachyzoites, but fail to eradicate the chronic stages of T. gondii. The cause of these treatment failures remains unclear. Here, we utilized our recently developed human myotube-based culture model to screen compounds from the MMV Pathogen Box against pan-resistant in vitro bradyzoites, and identified multiple compounds with simultaneous activity against tachyzoites and bradyzoites. Stable isotope-resolved metabolic profiling on tachyzoites and bradyzoites identified the mitochondrial bc1-complex as a target of bradyzocidal compounds and defined their metabolic impacts on both parasite forms. Our data suggest that mature bradyzoites rely on mitochondrial ATP production.

Keywords: Toxoplasma gondii; biochemistry; bradyzoite; chemical biology; chronic infection; compound screen; energy metabolism; infectious disease; metabolomics; microbiology

DOI: https://doi.org/10.7554/eLife.102511

Vet Parasitol. 2026 Sep 11. pii: S0304-4017(26)00237-2. [Epub ahead of print]348 110918

Targeting sexual stage-specific flagellar proteins to develop vaccines for feline toxoplasmosis.

Andongma Esack Fonda, Xiaopei Cao, Huiqiang Li, Yimeng Ge, Zhou Zhou, Chaoyue Wang, Bang Shen.

Toxoplasma gondii mainly relies on feline-shed oocysts for environmental transmission, making the blockade of oocyst shedding an effective strategy for toxoplasmosis control. Although cilia- and flagella-associated proteins (CFAPs) are essential for flagellar assembly, maturation, and motility in mammalian male gametes, their biological roles and transmission-blocking vaccine potential in apicomplexan parasites remain unexplored. Here, we identified CFAP221 as a sexual stage-exclusive antigen of T. gondii. CRISPR/Cas9-mediated knockout of CFAP221 did not affect tachyzoite growth or mouse virulence, but completely abolished oocyst shedding in cats, confirming its involvement in sexual development. To assess vaccine efficacy, cats were immunized with developmentally defective Δcfap221 tachyzoites or recombinant CFAP221 (rCFAP221) subunit vaccines. Comprehensive physical, hematological, and biochemical monitoring confirmed that all vaccine candidates were safe and well tolerated in cats. Upon oral challenge with PRU tissue cysts, daily fecal output was monitored from day 2 post-challenge for two weeks. Δcfap221 immunization reduced oocyst shedding by 70%, while unadjuvanted rCFAP221 decreased oocyst output by over 90%. Remarkably, adjuvanted rCFAP221 achieved complete blockage of oocyst shedding. These findings indicate CFAP221 as a highly promising transmission-blocking vaccine candidate against T. gondii.

Keywords: Definitive host; Felines; Sexual development; Toxoplasma gondii; Toxoplasmosis; Transmission-blocking vaccines

DOI: https://doi.org/10.1016/j.vetpar.2026.110918

Animals (Basel). 2026 Aug 31. pii: 2704. [Epub ahead of print]16(17):

Asexual Development and Virulence Are Not Affected by Knockout of Five Sexual-Stage Candidate Genes in Toxoplasma gondii.

Xing Tian, Chen-Ran Tian, Xin-Sheng Lu, Wen-Bo Hao, Zhi Zheng, Jun-Jun He, Xing-Quan Zhu, Xiao-Nan Zheng.

Toxoplasma gondii is a widespread intracellular parasite posing serious risks to immunocompromised individuals and pregnant women, and causing significant economic losses to the livestock industry. Current clinical drugs mainly target acute-stage tachyzoites but are ineffective against chronic cysts, necessitating new interventions. The parasite's sexual stage in the feline intestine remains poorly understood but is critical for transmission. Here, based on our unpublished weighted gene co-expression network analysis of single-cell transcriptomic data of cat intestine after infection with T. gondii, we selected five previously uncharacterized genes, including three CCCH-type zinc finger proteins (TGME49_257130, TGME49_500318, TGME49_313740) and two subtilisin-like proteases (TGME49_248760/sub7, TGME49_235950/sub8). Using the CRISPR-Cas9 system, individual knockout strains were generated from the type II Pru strain. And, we performed phenotypic assessments at this stage as an essential validation to confirm neutrality before feline infection experiments. Phenotypic analyses revealed that none of the knockout strains showed significant differences in vitro growth, replication, egress, in vivo virulence, or cyst formation from the wild-type strain, corroborating the transcriptional prediction. Publicly available ToxoDB transcriptomic data confirmed that four of these genes were highly expressed at the oocyst or feline enteroepithelial stages, but barely expressed in tachyzoites and bradyzoites, consistent with our phenotypic observations. Collectively, these findings indicate that these genes are dispensable for asexual development, while their expression pattern suggests potential involvement in sexual reproduction, a hypothesis that warrants direct experimental validation. This study provides validated knockout strains and candidate genes, establishing an experimental foundation for future functional studies on Toxoplasma sexual development and transmission-blocking strategies.

Keywords: CCCH-type zinc finger protein; CRISPR-Cas9; Toxoplasma gondii; phenotype; subtilisin-like protease

DOI: https://doi.org/10.3390/ani16172704

Proc Natl Acad Sci U S A. 2026 Sep 22. 123(38): e2624510123

Atypical RanGAP drives nucleocytoplasmic transport in a parasitic Alveolate.

Pravin S Dewangan, Michael L Reese.

Transport of macromolecules between the nucleus and cytoplasm requires a gradient of the small GTPase, Ran. Ran:GTP marks the nucleus because Ran activity requires a cytoplasmic GTPase activating protein (RanGAP) for GTP hydrolysis. As expected for such central and essential cellular machinery, both Ran and RanGAP are conserved across the vast majority of eukaryotes. Many Alveolates, including apicomplexan parasites, however, lack a canonical RanGAP. Here, we biochemically purify RanGAP activity from the model Alveolate Toxoplasma gondii. We demonstrate that this activity is provided by a neofunctionalized RabGAP-fold protein, called TBC9. We find that TBC9 is sufficient to provide RanGAP activity in yeast, and is absolutely required to maintain active nucleocytoplasmic transport in Toxoplasma. By purifying Toxoplasma Ran and TBC9, we demonstrate that TBC9 is a robust and specific GAP for Ran. Finally, we delineate an essential, conserved low complexity motif in the C-terminus of TBC9 that drives interaction with Ran and is required for its full RanGAP activity. We use this C-terminal motif to identify TBC9 orthologs in all nonciliate clades of Alveolata, which suggests that the canonical RanGAP has been replaced by the neofunctionalized TBC9 RanGAP in these lineages.

Keywords: GTPase; cell signaling; cellular trafficking; molecular evolution; parasite

DOI: https://doi.org/10.1073/pnas.2624510123

Microbiol Spectr. 2026 Sep 17. e0182726

Role of Toxoplasma gondii calcium-binding protein (TgpCaBP) and its implications for the development of attenuated live vaccines.

Yiwei Zhang, Hongyu Li, Yuqi Jing, Weisong Sun, Bin Wei, Zhiming Wei, Ning Jiang.

Toxoplasma gondii is an obligate intracellular protozoan parasite and the causative agent of toxoplasmosis in humans and animals. To date, an ideal vaccine against toxoplasmosis has not yet been developed. Our previous study demonstrated that deletion of the TgpCaBP gene, which encodes a calcium-binding EF-hand protein, impaired calcium flux, invasion, and egress, thereby reducing T. gondii virulence. However, the mechanisms underlying this loss of virulence and the potential of RHΔTgpCaBP as a live attenuated vaccine remain unclear. Here, we showed that TgpCaBP deletion significantly downregulated the expression of proteins associated with invasion, egress, and pyrimidine metabolism. In vivo evaluations revealed that co-administration of RHΔTgpCaBP and sulfadiazine showed limited pathological adverse effects in mice-all mice survived immunization with 100 tachyzoites without obvious organ injury, and conferred protection against lethal wild-type RH strain challenge (≤1,000 tachyzoites). Flowcytometry assays demonstrated that RHΔTgpCaBP strain immunization increased IFN-γ production in circulating CD4+ and CD8+ T cells and the frequencies of splenic CD4+ and CD8+ effector memory T cells, memory B cells, and activated B cells. In conclusion, TgpCaBP plays an important role in regulating the virulence of T. gondii by modulating the expression of proteins related to pyrimidine metabolism, invasion, and egress. Co-immunization with 100 RHΔTgpCaBP tachyzoites and sulfadiazine shows favorable safety profiles and protective efficacy in mice, triggers observable immune memory, and may serve as a promising candidate for an attenuated live vaccine against toxoplasmosis.
IMPORTANCE: Toxoplasmosis, caused by T. gondii, poses substantial public health and economic burdens worldwide. Although medicinal plants are traditionally the most promising source for the treatment of toxoplasmosis, no effective therapeutic regimen has been developed to date. Thus, the development of safe, effective, and long-lasting vaccines has become key for the prevention and control of toxoplasmosis. This study demonstrated that the deletion of TgpCaBP, a gene encoding an EF-hand calcium-binding protein, profoundly attenuated the virulence of the virulent RH strain by disrupting key pathogenic processes. More importantly, the RHΔTgpCaBP strain, administered in combination with sulfadiazine, emerged as a promising live attenuated vaccine candidate. It exhibited favorable safety profiles in mice and elicited an immunomodulatory trend. Although further optimization is warranted, this study establishes a foundational framework for developing live attenuated vaccines against toxoplasmosis.

Keywords: Toxoplasma gondii; attenuated live vaccines; calcium-binding protein; effector memory T cell

DOI: https://doi.org/10.1128/spectrum.01827-26

Elife. 2026 Sep 14. pii: RP111494. [Epub ahead of print]15

Acyl carrier protein is essential for apicoplast biogenesis in malaria parasites independent of fatty acid synthesis.

Sage W R Geher, Seyi Falekun, Jessica N Pita-Aquino, Russell P Swift, Megan Okada, Yasaman Jami-Alahmadi, James A Wohlschlegel, Sean T Prigge, Paul A Sigala.

Acyl carrier protein (ACP) and its 4-phosphopantetheine prosthetic group canonically function as the soluble scaffold for acyl chain assembly and elongation during type II fatty acid biosynthesis (FASII). Plasmodium malaria parasites retain a FASII pathway in the apicoplast organelle that has been the subject of considerable scrutiny and confusion. Although apicoplast FASII is essential for Plasmodium falciparum growth within mosquitoes and the human liver, this pathway is dispensable and largely inactive in blood-stage parasites that can scavenge host fatty acids. In contrast to FASII enzymes that can be disrupted without fitness defect, we report that knockout or ligand-dependent knockdown of apicoplast ACP is lethal to blood-stage P. falciparum, indicating an essential FASII-independent function. Loss of ACP impairs the biosynthesis of essential isoprenoid precursors and blocks apicoplast biogenesis. Using proximity biotinylation and biochemical interaction studies, we identified a key role for ACP in binding and stabilizing apicoplast pyruvate kinase II (PKII). This critical enzyme is the only known source of nucleoside triphosphates (NTPs) in this organelle and is required for isoprenoid synthesis and apicoplast biogenesis. Our work reveals that ACP knockdown results in destabilization and loss of PKII, which is sufficient to explain ACP essentiality in this stage. This work unveils essential ACP function at a key biochemical hub controlling broad apicoplast metabolism in malaria parasites that is independent of the canonical ACP role in FASII.

Keywords: FASII; P. falciparum; acyl carrier protein; apicoplast; biochemistry; chemical biology; infectious disease; malaria parasites; metabolic regulation; microbiology; pyruvate kinase

DOI: https://doi.org/10.7554/eLife.111494

Plant Sci. 2026 Sep 18. pii: S0168-9452(26)00488-7. [Epub ahead of print] 113460

Histone deacetylase 19 interacts with GLK2 to inhibit chlorophyll synthesis and photosynthetic activity in Populus davidiana.

Yuanfu Liu, Tingyu Cao, Meiqi Lu, Siyuan Li, Zhanchen Ren, Qiushuang Zhao, Jiajia Shen, Yutong Ding, Ling Jin, Haoran Bao, Yunxia Wei, Jiaxin Liu, Yu Zhang, Xinyu Wang, Yue Yu, Su Chen.

Maintaining the homeostasis of chlorophyll biosynthesis is essential for ensuring efficient photosynthesis and preventing photooxidative damage in plants. Histone deacetylases (HDACs) regulate plant development and stress responses, but their role in chlorophyll metabolism and photosynthesis remains unclear. Here, we identified and characterized PdHDA19, an RPD3-type HDAC from Populus davidiana Dode. PdHDA19 is highly expressed in leaves and apical buds, and its expression is induced by light. Overexpression of PdHDA19 leads to light green leaves, reduced chlorophyll content and decreased photosynthetic activity. RT-qPCR results show that PdHDA19 represses genes involved in chlorophyll synthesis and photosystem. Further analysis reveals that PdHDA19 physically interacts with the transcription factor PdGLK2 and suppresses PdGLK2-mediated activation of target genes. Together, these results reveal that PdHDA19 negatively regulates chlorophyll accumulation and photosynthetic activity in poplar via interaction with PdGLK2, providing new insights into epigenetic regulation of photosynthesis in woody plants.

Keywords: Chlorophyll; GLK2; Histone deacetylase; Photosynthesis; Populus davidiana Dode

DOI: https://doi.org/10.1016/j.plantsci.2026.113460