bims-toxgon 2024-09-08 papers

bims-toxgon

Biomed News

on Toxoplasma gondii metabolism

Issue of 2024–09–08
fourteen papers selected by
Lakesh Kumar, BITS Pilani

The Toxoplasma gondii mitochondrial transporter ABCB7L is essential for the biogenesis of cytosolic and nuclear iron-sulfur cluster proteins and cytosolic translation.
The initiation and early development of apical-basal polarity in Toxoplasma gondii.
Cell cycle-regulated transcription factor AP2XII-9 is a key activator for asexual division and apicoplast inheritance in Toxoplasma gondii tachyzoite.
A Toxoplasma gondii thioredoxin with cell adhesion and antioxidant function.
Activation and inhibition of sirtuins: From bench to bedside.
Live-attenuated PruΔgra72 strain of Toxoplasma gondii induces strong protective immunity against acute and chronic toxoplasmosis in mice.
Multifaceted regulation of Sirtuin 2 (Sirt2) Deacetylase Activity.
The ULK1 effector BAG2 regulates autophagy initiation by modulating AMBRA1 localization.
The mTOR pathway controls phosphorylation of BRAF at T401.
Lactam Truncation Yields a Dihydroquinazolinone Scaffold with Potent Antimalarial Activity that Targets PfATP4.
Crossing the membrane - what does it take to flip a phospholipid? Structural and biochemical advances on P4-ATPase flippases.
Post-translational modifications of pyruvate dehydrogenase complex in cardiovascular disease.
Apicoplast-derived isoprenoids are essential for biosynthesis of GPI protein anchors, and consequently for egress and invasion in Plasmodium falciparum.
Interaction with IP6K1 supports pyrophosphorylation of substrate proteins by the inositol pyrophosphate 5-InsP7.

mBio. 2024 Aug 29. e0087224

The Toxoplasma gondii mitochondrial transporter ABCB7L is essential for the biogenesis of cytosolic and nuclear iron-sulfur cluster proteins and cytosolic translation.

Andrew E Maclean, Megan A Sloan, Eléa A Renaud, Blythe E Argyle, William H Lewis, Jana Ovciarikova, Vincent Demolombe, Ross F Waller, Sébastien Besteiro, Lilach Sheiner.

  Iron-sulfur (Fe-S) clusters are ubiquitous inorganic cofactors required for numerous essential cellular pathways. Since they cannot be scavenged from the environment, Fe-S clusters are synthesized de novo in cellular compartments such as the apicoplast, mitochondrion, and cytosol. The cytosolic Fe-S cluster biosynthesis pathway relies on the transport of an intermediate from the mitochondrial pathway. An ATP-binding cassette (ABC) transporter called ABCB7 is responsible for this role in numerous commonly studied organisms, but its role in the medically important apicomplexan parasites has not yet been studied. Here we identify and characterize a Toxoplasma gondii ABCB7 homolog, which we name ABCB7-like (ABCB7L). Genetic depletion shows that it is essential for parasite growth and that its disruption triggers partial stage conversion. Characterization of the knock-down line highlights a defect in the biogenesis of cytosolic and nuclear Fe-S proteins leading to defects in protein translation and other pathways including DNA and RNA replication and metabolism. Our work provides support for a broad conservation of the connection between mitochondrial and cytosolic pathways in Fe-S cluster biosynthesis and reveals its importance for parasite survival.
IMPORTANCE: Iron-sulfur (Fe-S) clusters are inorganic cofactors of proteins that play key roles in numerous essential biological processes, for example, respiration and DNA replication. Cells possess dedicated biosynthetic pathways to assemble Fe-S clusters, including a pathway in the mitochondrion and cytosol. A single transporter, called ABCB7, connects these two pathways, allowing an essential intermediate generated by the mitochondrial pathway to be used in the cytosolic pathway. Cytosolic and nuclear Fe-S proteins are dependent on the mitochondrial pathway, mediated by ABCB7, in numerous organisms studied to date. Here, we study the role of a homolog of ABCB7, which we name ABCB7-like (ABCB7L), in the ubiquitous unicellular apicomplexan parasite Toxoplasma gondii. We generated a depletion mutant of Toxoplasma ABCB7L and showed its importance for parasite fitness. Using comparative quantitative proteomic analysis and experimental validation of the mutants, we show that ABCB7L is required for cytosolic and nuclear, but not mitochondrial, Fe-S protein biogenesis. Our study supports the conservation of a protein homologous to ABCB7 and which has a similar function in apicomplexan parasites and provides insight into an understudied aspect of parasite metabolism.

Keywords:  ABCB7L; Toxoplasma gondii; cofactor biosynthesis; cytosolic iron-sulfur assembly pathway; iron-sulfur cluster; mitochondria

DOI:  https://doi.org/10.1128/mbio.00872-24
J Cell Sci. 2024 Sep 06. pii: jcs.263436. [Epub ahead of print]

The initiation and early development of apical-basal polarity in Toxoplasma gondii.

Luisa F Arias Padilla, Jonathan Munera Lopez, Aika Shibata, John M Murray, Ke Hu.

  The body plan of the human parasite Toxoplasma gondii has a well-defined polarity. The minus ends of the 22 cortical microtubules are anchored to the apical polar ring, a putative microtubule-organizing center. The basal complex caps and constricts the parasite posterior end, and is critical for cytokinesis. How this apical-basal polarity is initiated was unknown. Here we examined the development of the apical polar ring and the basal complex using expansion microscopy. We found that substructures in the apical polar ring have different sensitivity to perturbations. In addition, apical-basal differentiation is already established upon nucleation of the cortical microtubule array: arc forms of the apical polar ring and basal complex associate with opposite ends of the microtubules. As the nascent daughter framework grows towards the centrioles, the apical and basal arcs co-develop ahead of the microtubule array. Lastly, two apical polar ring components, APR2 and KinesinA, act synergistically. The removal of individual proteins has modest impact on the lytic cycle. However, the loss of both results in abnormalities in the microtubule array and highly reduced plaquing and invasion efficiency.

Keywords:  Apical polar ring; Basal complex; Cell polarity; Microtubule; Organizing center; Toxoplasma

DOI:  https://doi.org/10.1242/jcs.263436
mBio. 2024 Aug 29. e0133624

Cell cycle-regulated transcription factor AP2XII-9 is a key activator for asexual division and apicoplast inheritance in Toxoplasma gondii tachyzoite.

Yuehong Shi, Xuan Li, Yingying Xue, Dandan Hu, Xingju Song.

  Toxoplasma gondii is an intracellular parasitic protozoan that poses a significant risk to the fetus carried by a pregnant woman or to immunocompromised individuals. T. gondii tachyzoites duplicate rapidly in host cells during acute infection through endodyogeny. This highly regulated division process is accompanied by complex gene regulation networks. TgAP2XII-9 is a cell cycle-regulated transcription factor, but its specific role in the parasite cell cycle is not fully understood. In this study, we demonstrate that TgAP2XII-9 is identified as a nuclear transcription factor and is dominantly expressed during the S/M phase of the tachyzoite cell cycle. Cleavage Under Targets and Tagmentation (CUT&Tag) results indicate that TgAP2XII-9 targets key genes for the moving junction machinery (RON2, 4, and 8) and daughter cell inner membrane complex (IMC). TgAP2XII-9 deficiency resulted in a significant downregulation of rhoptry proteins and rhoptry neck proteins, leading to a severe defect in the invasion and egress efficiency of tachyzoites. Additionally, the loss of TgAP2XII-9 correlated with a substantial downregulation of multiple IMC and apicoplast proteins, leading to disorders of daughter bud formation and apicoplast inheritance and further contributing to the inability of cell division and intracellular proliferation. Our study reveals that TgAP2XII-9 acts as a critical S/M-phase regulator that orchestrates the endodyogeny and apicoplast division in T. gondii tachyzoites. This study contributes to a broader understanding of the complexity of the parasite's cell cycle and its key regulators.
IMPORTANCE: The intracellular apicoplast parasite Toxoplasma gondii poses a great threat to the public health. The acute infection of T. gondii tachyzoites relies on efficient invasion by forming a moving junction structure and also fast replication by highly regulated endodyogeny. This study shows that an ApiAP2 transcription factor, TgAP2XII-9, acts as an activator for the S/M-phase gene expression, including genes related to daughter buds and moving junction formation. Loss of TgAP2XII-9 results in significant growth defects and disorders in endodyogeny and apicoplast inheritance of the parasites. Our results provide valuable insights into the transcriptional regulation of the parasite cell cycle and invading machinery in T. gondii.

Keywords:  ApiAP2; RON; Toxoplasma gondii; apicoplast; cell cycle; cell division; inner membrane complex

DOI:  https://doi.org/10.1128/mbio.01336-24
Front Cell Infect Microbiol. 2024 ;14 1404120

A Toxoplasma gondii thioredoxin with cell adhesion and antioxidant function.

Dawei Wang, Yuyi Shi, Ziwen Cheng, Like Luo, Kuo Cheng, Shengqi Gan, Che Liu, Zeliang Chen, Baoling Yang.

   Background: Toxoplasma gondii (T. gondii) is a widespread, zoonotic protozoan intracellular parasite with a complex life cycle, which can cause toxoplasmosis, a potentially serious disease. During the invasion process, T. gondii proteins first bind to the relevant host cell receptors, such as glycosaminoglycan molecule (GAG-binding motif), which is one of the main receptors for parasites or virus to infect host cells. However, research on TGME49_216510 (T. gondii Trx21), a protein from Toxoplasma gondii, is limited.
Methods: Bioinformatics analysis of the Trx21 protein was performed firstly. And specific primers were then designed using the conserved domain and GAG-binding motif to amplify, express, and purify a fragment of the Trx21 protein. The purified Trx21-GST protein was used for antioxidant and cell adhesion experiments. Simultaneously, mice were immunized with Trx21-His to generate specific polyclonal antibodies for subcellular localization analysis.
Results: The Trx21 protein, consisting of 774 amino acids, included a transmembrane region, three GAG-binding motifs, and a Thioredoxin-like domain. The recombinant Trx21-His protein had a molecular mass of about 31 kDa, while the Trx21-GST protein had a molecular mass of about 55 kDa, which was analyzed by SDS-PAGE and Western blot. Subcellular localization analysis by IFA revealed that Trx21 is predominantly distributed in the cytoplasm of T. gondii. Furthermore, Trx21 exhibited a protective effect on supercoiled DNA against metal-catalyzed oxidation (MCO) and demonstrated adhesion abilities to Vero cells.
Conclusions: These results indicate that Trx21 plays an important role in host cell interaction and oxidative damage.

Keywords:  Toxoplasma gondii; antioxidant; cell adhesion; glycosaminoglycan; thioredoxin

DOI:  https://doi.org/10.3389/fcimb.2024.1404120
Med Res Rev. 2024 Aug 31.

Activation and inhibition of sirtuins: From bench to bedside.

Francesco Fiorentino, Emanuele Fabbrizi, Antonello Mai, Dante Rotili.

  The sirtuin family comprises seven NAD+-dependent enzymes which catalyze protein lysine deacylation and mono ADP-ribosylation. Sirtuins act as central regulators of genomic stability and gene expression and control key processes, including energetic metabolism, cell cycle, differentiation, apoptosis, and aging. As a result, all sirtuins play critical roles in cellular homeostasis and organism wellness, and their dysregulation has been linked to metabolic, cardiovascular, and neurological diseases. Furthermore, sirtuins have shown dichotomous roles in cancer, acting as context-dependent tumor suppressors or promoters. Given their central role in different cellular processes, sirtuins have attracted increasing research interest aimed at developing both activators and inhibitors. Indeed, sirtuin modulation may have therapeutic effects in many age-related diseases, including diabetes, cardiovascular and neurodegenerative disorders, and cancer. Moreover, isoform selective modulators may increase our knowledge of sirtuin biology and aid to develop better therapies. Through this review, we provide critical insights into sirtuin pharmacology and illustrate their enzymatic activities and biological functions. Furthermore, we outline the most relevant sirtuin modulators in terms of their modes of action, structure-activity relationships, pharmacological effects, and clinical applications.

Keywords:  cancer; drug discovery; metabolism; protein lysine deacylation; sirtuins

DOI:  https://doi.org/10.1002/med.22076
Parasit Vectors. 2024 Sep 05. 17(1): 377

Live-attenuated PruΔgra72 strain of Toxoplasma gondii induces strong protective immunity against acute and chronic toxoplasmosis in mice.

Jing Li, Yu Kang, Ze-Xuan Wu, Shu-Feng Yang, Yu-Yang Tian, Xing-Quan Zhu, Xiao-Nan Zheng.

   BACKGROUND: Toxoplasma gondii is an intracellular opportunistic pathogenic protozoan that poses serious threats, particularly in immunocompromised individuals. In the absence of a robust prophylactic measure, the mitigation and management of toxoplasmosis present formidable challenges to public health. We recently found that GRA72 plays an important role in parasitophorous vacuole (PV) morphology, growth and virulence of T. gondii. However, whether gra72-deficient strain can be used as a vaccine remains unknown.
METHODS: We first examined the attenuated virulence of gra72 gene knockout strain (PruΔgra72) and the parasite load in organs of the infected mice. Subsequently, we evaluated the immune-protective effects of the PruΔgra72 vaccination against challenge with various types of T. gondii tachyzoites and Pru cysts. Furthermore, levels of antibodies and cytokines induced by PruΔgra72 vaccination were examined. Statistical analysis was conducted by Student's t-test or Mantel-Cox log-rank test based on data obtained from three independent experiments with GraphPad Prism 8.0.
RESULTS: We found that PruΔgra72 strain exhibited a significantly attenuated virulence even at the highest dose of 5 × 107 tachyzoites in Kunming mice model. The significant decrease of brain cyst burden and parasite load in the organs of the PruΔgra72-infected mice suggested its potentiality as a live-attenuated vaccine. Hence, we explored the protective immunity of PruΔgra72 vaccination against toxoplasmosis. Results showed that vaccination with 5 × 106 PruΔgra72 tachyzoites triggered a strong and sustained Th1-biased immune response, marked by significantly increased levels of anti-T. gondii IgG antibodies, and significantly higher levels of Th1 type cytokines (IL-2, IL-12 and IFN-γ) compared to that of Th2 type (IL-4 and IL-10). Vaccination with 5 × 106 PruΔgra72 tachyzoites in mice conferred long-term protection against T. gondii infection by less virulent tachyzoites (ToxoDB#9 PYS and Pru strains) and Pru cysts, provided partial protection against acute infection by high virulent Type I RH tachyzoites and significantly decreased brain cyst burden of chronically infected mice.
CONCLUSIONS: The avirulent PruΔgra72 induced strong protective immunity against acute and chronic T. gondii infection and is a promising candidate for developing a safe and effective live-attenuated vaccine against T. gondii infection.

Keywords:   Toxoplasma gondii ; Acute and chronic infection; Immune responses; Live-attenuated vaccine; PruΔgra72

DOI:  https://doi.org/10.1186/s13071-024-06461-9
J Biol Chem. 2024 Aug 28. pii: S0021-9258(24)02223-3. [Epub ahead of print] 107722

Multifaceted regulation of Sirtuin 2 (Sirt2) Deacetylase Activity.

Maheeshi Yapa Abeywardana, Samuel D Whedon, Kwangwoon Lee, Eunju Nam, Rafael Dovarganes, Sarah Dubois-Coyne, Ishraq A Haque, Zhipeng A Wang, Philip A Cole.

Sirtuin 2 (Sirt2) is a member of the sirtuin family of NAD-dependent lysine deacylases and plays important roles in regulation of the cell cycle and gene expression. As a nucleocytoplasmic deacetylase, Sirt2 has been shown to target both histone and non-histone acetylated protein substrates. The central catalytic domain of Sirt2 is flanked by flexible N- and C-termini, which vary in length and composition with alternative splicing. These termini are further subject to post-translational modifications (PTMs) including phosphorylation. Here we investigate the function of the N- and C-termini on deacetylation of nuclear substrates by Sirt2. Remarkably, we find that the C-terminus autoinhibits deacetylation, while the N-terminus enhances deacetylation of proteins and peptides, but not nucleosomes-a chromatin model substrate. Using protein semisynthesis we characterize the effect of cell cycle-linked N-terminal phosphorylation at two major phosphorylation sites (Ser23/Ser25) and find that these further enhance protein/peptide deacetylation, with no effect on nucleosome deacetylation. Additionally, we find that VRK1, an established binding partner of both Sirt2 and nucleosomes, can stimulate deacetylation of nucleosomes by Sirt2, likely through an electrostatic mechanism. Taken together, these findings reveal multiple mechanisms regulating the activity of Sirt2, which allow for a broad range of activities across its multiple biological roles.

DOI: https://doi.org/10.1016/j.jbc.2024.107722
Cell Rep. 2024 Aug 27. pii: S2211-1247(24)01040-4. [Epub ahead of print]43(9): 114689

The ULK1 effector BAG2 regulates autophagy initiation by modulating AMBRA1 localization.

Devanarayanan Siva Sankar, Stephanie Kaeser-Pebernard, Christine Vionnet, Sebastian Favre, Lais de Oliveira Marchioro, Benjamin Pillet, Jianwen Zhou, Michael Stumpe, Werner Josef Kovacs, Dieter Kressler, Manuela Antonioli, Gian Maria Fimia, Jӧrn Dengjel.

  Autophagy initiation is regulated by the ULK1 kinase complex. To gain insights into functions of the holo-complex, we generated a deep interactome by combining affinity purification- and proximity labeling-mass spectrometry of all four complex members: ULK1, ATG13, ATG101, and RB1CC1/FIP200. Under starvation conditions, the ULK1 complex interacts with several protein and lipid kinases and phosphatases, implying the formation of a signalosome. Interestingly, several selective autophagy receptors also interact with ULK1, indicating the activation of selective autophagy pathways by nutrient starvation. One effector of the ULK1 complex is the HSC/HSP70 co-chaperone BAG2, which regulates the subcellular localization of the VPS34 lipid kinase complex member AMBRA1. Depending on the nutritional status, BAG2 has opposing roles. In growth conditions, the unphosphorylated form of BAG2 sequesters AMBRA1, attenuating autophagy induction. In starvation conditions, ULK1 phosphorylates BAG2 on Ser31, which supports the recruitment of AMBRA1 to the ER membrane, positively affecting autophagy.

Keywords:  AP-MS; BioID; CP: Cell biology; CP: Molecular biology; ER; autophagy; interactome; kinase; mass spectromtery; proteomics; signaling; signalosome

DOI:  https://doi.org/10.1016/j.celrep.2024.114689
Cell Commun Signal. 2024 Sep 02. 22(1): 428

The mTOR pathway controls phosphorylation of BRAF at T401.

Daniel Christen, Manuel Lauinger, Melanie Brunner, Jörn Dengjel, Tilman Brummer.

BRAF serves as a gatekeeper of the RAS/RAF/MEK/ERK pathway, which plays a crucial role in homeostasis. Since aberrant signalling of this axis contributes to cancer and other diseases, it is tightly regulated by crosstalk with the PI3K/AKT/mTOR pathway and ERK mediated feedback loops. For example, ERK limits BRAF signalling through phosphorylation of multiple residues. One of these, T401, is widely considered as an ERK substrate following acute pathway activation by growth factors. Here, we demonstrate that prominent T401 phosphorylation (pT401) of endogenous BRAF is already observed in the absence of acute stimulation in various cell lines of murine and human origin. Importantly, the BRAF/RAF1 inhibitor naporafenib, the MEK inhibitor trametinib and the ERK inhibitor ulixertinib failed to reduce pT401 levels in these settings, supporting an alternative ERK-independent pathway to T401 phosphorylation. In contrast, the mTOR inhibitor torin1 and the dual-specific PI3K/mTOR inhibitor dactolisib significantly suppressed pT401 levels in all investigated cell types, in both a time and concentration dependent manner. Conversely, genetic mTOR pathway activation by oncogenic RHEB (Q64L) and mTOR (S2215Y and R2505P) mutants substantially increased pT401, an effect that was reverted by dactolisib and torin1 but not by trametinib. We also show that shRNAmir mediated depletion of the mTORC1 complex subunit Raptor significantly enhanced the suppression of T401 phosphorylation by a low torin1 dose, while knockdown of the mTORC2 complex subunit Rictor was less effective. Using mass spectrometry, we provide further evidence that torin1 suppresses the phosphorylation of T401, S405 and S409 but not of other important regulatory phosphorylation sites such as S446, S729 and S750. In summary, our data identify the mTOR axis and its inhibitors of (pre)clinical relevance as novel modulators of BRAF phosphorylation at T401.

DOI: https://doi.org/10.1186/s12964-024-01808-2
ChemMedChem. 2024 Aug 30. e202400549

Lactam Truncation Yields a Dihydroquinazolinone Scaffold with Potent Antimalarial Activity that Targets PfATP4.

Trent D Ashton, Petar P S Calic, Madeline G Dans, Zi Kang Ooi, Qingmiao Zhou, Katie Loi, Kate E Jarman, Josephine Palandri, Deyun Qiu, Adele M Lehane, Bikash Maity, Nirupam De, Mufuliat T Famodimu, Michael J Delves, Emma Y Mao, Maria R Gancheva, Danny W Wilson, Mrittika Chowdury, Tania F de Koning-Ward, Delphine Baud, Stephen Brand, Paul F Jackson, Alan F Cowman, Brad E Sleebs.

  The emergence of resistance against current antimalarial treatments has necessitated the need for the development of novel antimalarial chemotypes. Toward this goal, we recently optimised the antimalarial activity of the dihydroquinazolinone scaffold and showed it targeted PfATP4. Here, we deconstruct the lactam moiety of the tricyclic dihydroquinazolinone scaffold and investigate the structure-activity relationship of the truncated scaffold. It was shown that SAR between scaffolds was largely transferrable and generated analogues with potent asexual stage activity. Evaluation of the truncated analogues against PfATP4 mutant drug resistant parasite strains and in assays measuring PfATP4-associated ATPase activity demonstrated retention of PfATP4 as the molecular target. Analogues exhibited activity against both male and female gametes and multidrug resistant parasites. Limited efficacy of analogues in a P. berghei asexual stage mouse model was attributed to their moderate metabolic stability and low aqueous stability. Further development is required to address these attributes toward the potential use of the dihydroquinazolinone class in a curative and transmission blocking combination antimalarial therapy.

Keywords:  antimalarial, Malaria, PfATP4, Plasmodium, quinazolinone

DOI:  https://doi.org/10.1002/cmdc.202400549
J Biol Chem. 2024 Sep 02. pii: S0021-9258(24)02239-7. [Epub ahead of print] 107738

Crossing the membrane - what does it take to flip a phospholipid? Structural and biochemical advances on P4-ATPase flippases.

Kadambari Vijay Sai, Jyh-Yeuan Lee.

  Membrane asymmetry is critical for maintenance of several different processes such as cell signalling, apoptosis, and vesicular transport in various eukaryotic systems. Flippases of the P4-ATPase family are associated with flipping phospholipids from the luminal or exoplasmic leaflet to the cytosolic leaflet. P4-ATPases belong to the P-type ATPase family, which are activated by phosphorylation and couple ATPase activity to substrate translocation. These proteins possess a transmembrane domain responsible for substrate transport, while the cytosolic machinery perform the necessary ATP hydrolysis for this process. Several high-resolution structures of human or yeast P4-ATPases have recently been resolved, but a comprehensive overview of the changes for reaction cycle in different members was crucial for future research. In this review, we have compiled available data reflecting the reaction cycle-associated changes in conformation of P4-ATPases. Together, this will provide an improved understanding of the similarities and differences between these members, which will drive further structural, functional and computational studies to understand the mechanisms of these flippases.

Keywords:  Cryo‐electron microscopy; Lipid transport; Membrane protein; Membrane structure; P4-ATPase; Phospholipid; Phospholipid vesicle; Sphingolipid; X-Ray crystallography

DOI:  https://doi.org/10.1016/j.jbc.2024.107738
iScience. 2024 Sep 20. 27(9): 110633

Post-translational modifications of pyruvate dehydrogenase complex in cardiovascular disease.

Bo Guo, Fujiao Zhang, Yue Yin, Xingmin Ning, Zihui Zhang, Qinglei Meng, Ziqi Yang, Wenhua Jiang, Manling Liu, Yishi Wang, Lijuan Sun, Lu Yu, Nan Mu.

  Pyruvate dehydrogenase complex (PDC) is a crucial enzyme that connects glycolysis and the tricarboxylic acid (TCA) cycle pathway. It plays an essential role in regulating glucose metabolism for energy production by catalyzing the oxidative decarboxylation of pyruvate to acetyl coenzyme A. Importantly, the activity of PDC is regulated through post-translational modifications (PTMs), phosphorylation, acetylation, and O-GlcNAcylation. These PTMs have significant effects on PDC activity under both physiological and pathophysiological conditions, making them potential targets for metabolism-related diseases. This review specifically focuses on the PTMs of PDC in cardiovascular diseases (CVDs) such as myocardial ischemia/reperfusion injury, diabetic cardiomyopathy, obesity-related cardiomyopathy, heart failure (HF), and vascular diseases. The findings from this review offer theoretical references for the diagnosis, treatment, and prognosis of CVD.

Keywords:  Biochemistry; Cardiovascular medicine; Cell biology; Molecular biology

DOI:  https://doi.org/10.1016/j.isci.2024.110633
PLoS Pathog. 2024 Sep 06. 20(9): e1012484

Apicoplast-derived isoprenoids are essential for biosynthesis of GPI protein anchors, and consequently for egress and invasion in Plasmodium falciparum.

Michaela S Bulloch, Long K Huynh, Kit Kennedy, Julie E Ralton, Malcolm J McConville, Stuart A Ralph.

Glycophosphatidylinositol (GPI) anchors are the predominant glycoconjugate in Plasmodium parasites, enabling modified proteins to associate with biological membranes. GPI biosynthesis commences with donation of a mannose residue held by dolichol-phosphate at the endoplasmic reticulum membrane. In Plasmodium dolichols are derived from isoprenoid precursors synthesised in the Plasmodium apicoplast, a relict plastid organelle of prokaryotic origin. We found that treatment of Plasmodium parasites with apicoplast inhibitors decreases the synthesis of isoprenoid and GPI intermediates resulting in GPI-anchored proteins becoming untethered from their normal membrane association. Even when other isoprenoids were chemically rescued, GPI depletion led to an arrest in schizont stage parasites, which had defects in segmentation and egress. In those daughter parasites (merozoites) that did form, proteins that would normally be GPI-anchored were mislocalised, and when these merozoites were artificially released they were able to attach to but not invade new red blood cells. Our data provides further evidence for the importance of GPI biosynthesis during the asexual cycle of P. falciparum, and indicates that GPI biosynthesis, and by extension egress and invasion, is dependent on isoprenoids synthesised in the apicoplast.

DOI: https://doi.org/10.1371/journal.ppat.1012484
Biosci Rep. 2024 Sep 04. pii: BSR20240792. [Epub ahead of print]

Interaction with IP6K1 supports pyrophosphorylation of substrate proteins by the inositol pyrophosphate 5-InsP7.

Rashna Bhandari, Aisha Hamid, Jayashree S Ladke, Akruti Shah, Shubhra Ganguli, Monisita Pal, Arpita Singh.

  Inositol pyrophosphates (PP-InsPs) are a sub-family of water soluble inositol phosphates that possess one or more diphosphate groups. PP-InsPs can transfer their β-phosphate group to a phosphorylated Ser residue to generate pyrophosphorylated Ser. This unique post-translational modification occurs on Ser residues that lie in acidic stretches within an intrinsically disordered protein sequence. Serine pyrophosphorylation is dependent on the presence of Mg2+ ions, but does not require an enzyme for catalysis. The mechanisms by which cells regulate PP-InsP-mediated pyrophosphorylation are still unknown. We performed mass spectrometry to identify interactors of IP6K1, an enzyme responsible for the synthesis of the PP-InsP 5-InsP7. Interestingly, IP6K1 interacted with several proteins that are known to undergo 5-InsP7-mediated pyrophosphorylation, including the nucleolar proteins NOLC1, TCOF and UBF1, and AP3B1, the β subunit of the AP3 adaptor protein complex. The IP6K1 interactome also included CK2, a protein kinase that phosphorylates Ser residues prior to pyrophosphorylation. We observe the formation of a protein complex between IP6K1, AP3B1, and the catalytic α-subunit of CK2, and show that disrupting IP6K1 binding to AP3B1 lowers its in vivo pyrophosphorylation. We propose that assembly of a substrate-CK2-IP6K complex would allow for coordinated pre-phosphorylation and pyrophosphorylation of the target serine residue, and provide a mechanism to regulate this enzyme-independent modification.

Keywords:  IP6 kinases; Inositol pyrophosphates; Protein pyrophosphorylation; cell signalling; metabolic messenger; post translational modification

DOI:  https://doi.org/10.1042/BSR20240792