bims-toxgon 2024-10-13 papers

bims-toxgon

Biomed News

on Toxoplasma gondii metabolism

Issue of 2024–10–13
eightteen papers selected by
Lakesh Kumar, BITS Pilani

THE ESSENTIAL KINASE TGGSK REGULATES CENTROSOME DIVISION AND ENDODYOGENY IN TOXOPLASMA GONDII.
Theft of Host Transferrin Receptor-1 by Toxoplasma gondii is required for infection.
Involvement of extracellular vesicles in the interaction of hosts and Toxoplasma gondii.
Myosin A and F-Actin play a critical role in mitochondrial dynamics and inheritance in Toxoplasma gondii.
Motility-dependent processes in Toxoplasma gondii tachyzoites and bradyzoites: same same but different.
Molecular modelling and experimental validation identified a new therapeutic inhibitor of toxoplasmosis.
N-terminal targeting sequences and coding sequences act in concert to determine the localization and trafficking pathway of apicoplast proteins in Toxoplasma gondii.
Reporter parasite lines: valuable tools for the study of Plasmodium biology.
Metabolic mechanisms orchestrated by Sirtuin family to modulate inflammatory responses.
Dysregulation of lysine acetylation in the pathogenesis of digestive tract cancers and its clinical applications.
Histone deacetylase 7 activates 6-phosphogluconate dehydrogenase via an enzyme-independent mechanism that involves the N-terminal protein-protein interaction domain.
Metabolite regulation of epigenetics in cancer.
Metabolic reprogramming in skeletal cell differentiation.
Biochemical Characterization and Inhibitor Discovery for Pf Sir2A - New Tricks for An Old Enzyme.
Heterochromatin dynamics during the initial stages of sexual development in Plasmodium falciparum.
A Genetically Encoded Fluorescent Biosensor for Intracellular Measurement of Malonyl-CoA.
Metabolic regulation of mitochondrial morphologies in pancreatic beta cells: coupling of bioenergetics and mitochondrial dynamics.
Nicotinamide Adenine Dinucleotide (NAD)-Dependent Protein Deacetylase, Sirtuin, as a Biomarker of Healthy Life Expectancy: A Mini-Review.

bioRxiv. 2024 Sep 27. pii: 2024.09.27.615374. [Epub ahead of print]

THE ESSENTIAL KINASE TGGSK REGULATES CENTROSOME DIVISION AND ENDODYOGENY IN TOXOPLASMA GONDII.

Amanda Krueger, Sofia Horjales, Chunlin Yang, William J Blakely, Maria E Francia, Gustavo Arrizabalaga.

Intracellular replication is crucial for the success of apicomplexan parasites, including Toxoplasma gondii . Therefore, essential players in parasite replication present potential targets for drug development. In this study, 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.
AUTHOR SUMMARY: Toxoplasma gondii infects nearly a third of the world's human population. While infection is largely asymptomatic in healthy adults, in immunocompromised or immunosuppressed individuals it can lead to brain lesions and even death. Similarly, toxoplasmosis can result in stillbirth, birth defects, and blindness of a developing fetus in the case of a congenital infection. With minimal treatments for Toxoplasmosis available, it is crucial to study parasite-specific processes that could be potential drug targets for the treatment of Toxoplasmosis. In this study, we investigated the protein TgGSK that is essential for parasite survival and proper division. We showed that TgGSK may perform its essential functions through interaction with the centrosome, an organelle that plays a major role in cell division in many organisms. We also show in this study a role for TgGSK in proper processing of messenger RNAs. Taken together, we have performed an in-depth study of the functional role of the essential protein TgGSK in Toxoplasma gondii . Importantly, TgGSK was shown to have more similarity to plant proteins than mammalian proteins which may allow for the possibility of targeting of this protein for therapeutic treatment of toxoplasmosis.

DOI: https://doi.org/10.1101/2024.09.27.615374
bioRxiv. 2023 Jun 24. pii: 2023.06.23.546322. [Epub ahead of print]

Theft of Host Transferrin Receptor-1 by Toxoplasma gondii is required for infection.

Stephen L Denton, Alexa Mejia, Lindsay L Nevarez, Miguel P Soares, Barbara A Fox, David J Bzik, Jason P Gigley.

Nutrient acquisition by apicomplexan parasites is essential to drive their intracellular replication, yet the mechanisms that underpin essential nutrient acquisition are not defined. Using the apicomplexan model Toxoplasma gondii , we show that host cell proteins including the transferrin receptor 1, transferrin, ferritin heavy and light chains, and clathrin light chain are robustly taken up by tachyzoites. Tachyzoite acquisition of host cell protein was not related to host cell type or parasite virulence phenotypes. Bradyzoites possessed little capacity to acquire host cell proteins consistent with the cyst wall representing a barrier to host cell protein cargo. Increased trafficking of host cell transferrin receptor 1 and transferrin to endolysosomes boosted tachyzoite acquisition of host proteins and growth rate. Theft of host transferrin 1 and transferrin did not significantly affect iron levels in the tachyzoite. This study provides insight into essential functions associated with parasite theft of host iron sequestration and storage proteins.

DOI: https://doi.org/10.1101/2023.06.23.546322
Curr Top Membr. 2024 ;pii: S1063-5823(24)00011-5. [Epub ahead of print]94 133-155

Involvement of extracellular vesicles in the interaction of hosts and Toxoplasma gondii.

Letícia Pereira Pedrini Vicentini, Vera Lucia Pereira-Chioccola, Blima Fux.

  Toxoplasma gondii, the causative agent of toxoplasmosis, is widely distributed. This protozoan parasite is one of the best adapted, being able to infect innumerous species of animals and different types of cells. This chapter reviews current literature on extracellular vesicles secreted by T. gondii and by its hosts. The topics describe the life cycle and transmission (1); toxoplasmosis epidemiology (2); laboratorial diagnosis approach (3); The T. gondii interaction with extracellular vesicles and miRNAs (4); and the perspectives on T. gondii infection. Each topic emphases the host immune responses to the parasite antigens and the interaction with the extracellular vesicles and miRNAs.

Keywords:  Extracellular vesicles; Host immune system; Toxoplasma gondii; Toxoplasmosis; Virulence

DOI:  https://doi.org/10.1016/bs.ctm.2024.06.003
PLoS Pathog. 2024 Oct 07. 20(10): e1012127

Myosin A and F-Actin play a critical role in mitochondrial dynamics and inheritance in Toxoplasma gondii.

Rodolpho Ornitz Oliveira Souza, Chunlin Yang, Gustavo Arrizabalaga.

The single mitochondrion of the obligate intracellular parasite Toxoplasma gondii is highly dynamic. Toxoplasma's mitochondrion changes morphology as the parasite moves from the intracellular to the extracellular environment and during division. Toxoplasma's mitochondrial dynamic is dependent on an outer mitochondrion membrane-associated protein LMF1 and its interaction with IMC10, a protein localized at the inner membrane complex (IMC). In the absence of either LMF1 or IMC10, parasites have defective mitochondrial morphology and inheritance defects. As little is known about mitochondrial inheritance in Toxoplasma, we have used the LMF1/IMC10 tethering complex as an entry point to dissect the machinery behind this process. Using a yeast two-hybrid screen, we previously identified Myosin A (MyoA) as a putative interactor of LMF1. Although MyoA is known to be located at the parasite's pellicle, we now show through ultrastructure expansion microscopy (U-ExM) that this protein accumulates around the mitochondrion in the late stages of parasite division. Parasites lacking MyoA show defective mitochondrial morphology and a delay in mitochondrion delivery to the daughter parasite buds during division, indicating that this protein is involved in organellar inheritance. Disruption of the parasite's actin network also affects mitochondrion morphology. We also show that parasite-extracted mitochondrion vesicles interact with actin filaments. Interestingly, mitochondrion vesicles extracted out of parasites lacking LMF1 pulled down less actin, showing that LMF1 might be important for mitochondrion and actin interaction. Accordingly, we are showing for the first time that actin and Myosin A are important for Toxoplasma mitochondrial morphology and inheritance.

DOI: https://doi.org/10.1371/journal.ppat.1012127
bioRxiv. 2024 Sep 28. pii: 2024.09.28.615543. [Epub ahead of print]

Motility-dependent processes in Toxoplasma gondii tachyzoites and bradyzoites: same same but different.

Robyn S Kent, Gary E Ward.

The tachyzoite stage of the apicomplexan parasite Toxoplasma gondii utilizes motility for multiple purposes during its lytic cycle, including host cell invasion, egress from infected cells, and migration to new uninfected host cells to repeat the process. Bradyzoite stage parasites, which establish a new infection in a naïve host, must also use motility to escape from the cysts that are ingested by the new host and then migrate to the gut wall, where they either invade cells of the intestinal epithelium or squeeze between these cells to infect the underlying connective tissue. We know very little about the motility of bradyzoites, which we analyze in detail here and compare to the well-characterized motility and motility-dependent processes of tachyzoites. Unexpectedly, bradyzoites were found to be as motile as tachyzoites in a 3D model extracellular matrix, and they showed increased invasion into and transmigration across certain cell types, consistent with their need to establish the infection in the gut. The motility of the two stages was inhibited to the same extent by cytochalasin D and KNX-002, compounds known to target the parasite's actomyosin-based motor. In contrast, other compounds that impact tachyzoite motility (tachyplegin and enhancer 5) have less of an effect on bradyzoites, and rapid bradyzoite egress from infected cells is not triggered by treatment with calcium ionophores, as it is with tachyzoites. The similarities and differences between these two life cycle stages highlight the need to characterize both tachyzoites and bradyzoites for a more complete understanding of the role of motility in the parasite life cycle and the effect that potential therapeutics targeting parasite motility will have on disease establishment and progression.

DOI: https://doi.org/10.1101/2024.09.28.615543
Comput Biol Med. 2024 Oct 07. pii: S0010-4825(24)01321-0. [Epub ahead of print]183 109236

Molecular modelling and experimental validation identified a new therapeutic inhibitor of toxoplasmosis.

Oluyomi Stephen Adeyemi, Titilayo Johnson, Tobiloba Maduakolam-Aniobi, Kentaro Kato.

  Toxoplasmosis is a widespread parasitic disease, caused by Toxoplasma gondii, that affects nearly one-third of the human population. The lack of effective treatments drives the demand for novel anti-toxoplasmosis therapeutic options. In the present study, we used computational approaches and experimental validation to identify therapeutic inhibitors of toxoplasmosis. Initially, using the structure of the co-crystallized ligand of T. gondii calcium-dependent protein kinase 1 (TgCDPK1), we retrieved 3000 compounds from the database of COCONUT (COlleCtion of Open Natural ProdUcTs). These compounds were docked against the crystal structure of TgCDPK1 on the Glide Ligand Docking panel of Maestro 12.5 (Schrödinger Suite 2020-3). Based on the docking scores, we assessed promising molecules for toxicity potential on the ProTox-II online server, while the ADME profiling was done on the SwissADME server. Following the computational studies, we selected nine promising compounds for experimental validation against T. gondii in vitro. Of the compounds, C4, C5, C6, and C8 exhibited dose-dependent anti-T. gondii action with EC50 values ranging from 3.3 to 120.2 μg/mL. Host toxicity profiling revealed differential cytotoxic action with a selectivity index (SI) of <1 for the compounds except C5, which had an SI of 1.8. To validate our screening assay, we used sulfadiazine, a standard drug for toxoplasmosis and showed that it inhibited parasite growth. Further experiments showed that C5, an imidazole-based natural compound, has strong but reversible anti-parasitic action that peaks within the first 8 h. In addition, C5 exhibited similar toxic tendencies towards T. gondii within (intracellular) and outside (extracellular) the host, suggesting it likely has a parasite target(s). C5 showed no effect on host invasion but strongly impeded parasite replication and growth, thereby affecting the T. gondii lytic cycle. Furthermore, C5 treatment raised the reactive oxygen species level, but this may be a secondary effect because augmentation with Trolox antioxidant failed to block C5 anti-T. gondii action. In addition, molecular dynamics simulations of C5 and TgCDPK1 complex revealed relative stability within 100 ns run time. Collectively, our findings support the potential of imidazole-based compounds as novel, alternative anti-parasitic agents.

Keywords:  Computational drug design; Imidazoles; Medicinal biochemistry; Natural products; Therapeutic inhibitors; Zoonosis

DOI:  https://doi.org/10.1016/j.compbiomed.2024.109236
Biol Cell. 2024 Oct 10. e202400027

N-terminal targeting sequences and coding sequences act in concert to determine the localization and trafficking pathway of apicoplast proteins in Toxoplasma gondii.

Sofia Anjum, Aparna Prasad, Pragati Mastud, Geetanjali Mishra, Swati Patankar.

   BACKGOUND INFORMATION: Toxoplasma gondii has a relict plastid, the apicoplast, to which nuclear-encoded proteins are targeted after synthesis in the cytosol. Proteins exclusively found in the apicoplast use a Golgi-independent route for trafficking, while dually targeted proteins found in both the apicoplast and the mitochondrion use a Golgi-dependent route. For apicoplast targeting, N-terminal signal sequences have been shown to direct the localization of different reporters. In this study, we use chimeric proteins to dissect out the roles of N-terminal sequences and coding sequences in apicoplast localization and the choice of the trafficking route.
RESULTS: We show that when the N-termini of a dually targeted protein, TgTPx1/2, or of an apicoplast protein, TgACP, are fused with the reporter protein, enhanced green fluorescent protein (eGFP) or endogenous proteins, TgSOD2, TgSOD3, TgACP, or TgTPx1/2, the chimeric proteins exhibit flexibility in apicoplast targeting depending on the coding sequences. Further, the chimeras that are localized to the apicoplast use different trafficking pathways depending on the combination of the N-terminal signals and the coding sequences.
CONCLUSION AND SIGNIFICANCE: This report shows, for the first time, that in addition to the N-terminal signal sequences, targeting and trafficking signals also reside within the coding sequences of apicoplast proteins.

Keywords:  Golgi; Toxoplasma gondii; apicoplast; mitochondrion; signal sequences; trafficking pathways

DOI:  https://doi.org/10.1111/boc.202400027
Trends Parasitol. 2024 Oct 09. pii: S1471-4922(24)00246-0. [Epub ahead of print]

Reporter parasite lines: valuable tools for the study of Plasmodium biology.

Yukiko Miyazaki, Shinya Miyazaki.

  The human malaria parasite Plasmodium falciparum causes the most severe form of malaria in endemic regions and is transmitted via mosquito bites. To better understand the biology of this deadly pathogen, a variety of P. falciparum reporter lines have been generated using transgenic approaches to express reporter proteins, such as fluorescent proteins and luciferases. This review discusses the advances in recently generated P. falciparum transgenic reporter lines, which will aid in the investigation of parasite physiology and the discovery of novel antimalarial drugs. Future prospects for the generation of new and superior human malaria parasite reporter lines are also discussed, and unresolved questions in malaria biology are highlighted to help boost support for the development and implementation of malaria treatments.

Keywords:  Plasmodium falciparum; drug discovery; fluorescent protein; luciferase; reporter line

DOI:  https://doi.org/10.1016/j.pt.2024.09.003
Front Immunol. 2024 ;15 1448535

Metabolic mechanisms orchestrated by Sirtuin family to modulate inflammatory responses.

Xiaoqing Li, Yunjia Li, Quan Hao, Jing Jin, Yi Wang.

  Maintaining metabolic homeostasis is crucial for cellular and organismal health throughout their lifespans. The intricate link between metabolism and inflammation through immunometabolism is pivotal in maintaining overall health and disease progression. The multifactorial nature of metabolic and inflammatory processes makes study of the relationship between them challenging. Homologs of Saccharomyces cerevisiae silent information regulator 2 protein, known as Sirtuins (SIRTs), have been demonstrated to promote longevity in various organisms. As nicotinamide adenine dinucleotide-dependent deacetylases, members of the Sirtuin family (SIRT1-7) regulate energy metabolism and inflammation. In this review, we provide an extensive analysis of SIRTs involved in regulating key metabolic pathways, including glucose, lipid, and amino acid metabolism. Furthermore, we systematically describe how the SIRTs influence inflammatory responses by modulating metabolic pathways, as well as inflammatory cells, mediators, and pathways. Current research findings on the preferential roles of different SIRTs in metabolic disorders and inflammation underscore the potential of SIRTs as viable pharmacological and therapeutic targets. Future research should focus on the development of promising compounds that target SIRTs, with the aim of enhancing their anti-inflammatory activity by influencing metabolic pathways within inflammatory cells.

Keywords:  SIRTs; epigenetics; inflammation; metabolism; post-translational modifications

DOI:  https://doi.org/10.3389/fimmu.2024.1448535
Front Cell Dev Biol. 2024 ;12 1447939

Dysregulation of lysine acetylation in the pathogenesis of digestive tract cancers and its clinical applications.

Penghui Li, Yuan Xue.

  Recent advances in high-resolution mass spectrometry-based proteomics have improved our understanding of lysine acetylation in proteins, including histones and non-histone proteins. Lysine acetylation, a reversible post-translational modification, is catalyzed by lysine acetyltransferases (KATs) and lysine deacetylases (KDACs). Proteins comprising evolutionarily conserved bromodomains (BRDs) recognize these acetylated lysine residues and consequently activate transcription. Lysine acetylation regulates almost all cellular processes, including transcription, cell cycle progression, and metabolic functions. Studies have reported the aberrant expression, translocation, and mutation of genes encoding lysine acetylation regulators in various cancers, including digestive tract cancers. These dysregulated lysine acetylation regulators contribute to the pathogenesis of digestive system cancers by modulating the expression and activity of cancer-related genes or pathways. Several inhibitors targeting KATs, KDACs, and BRDs are currently in preclinical trials and have demonstrated anti-cancer effects. Digestive tract cancers, including encompass esophageal, gastric, colorectal, liver, and pancreatic cancers, represent a group of heterogeneous malignancies. However, these cancers are typically diagnosed at an advanced stage owing to the lack of early symptoms and are consequently associated with poor 5-year survival rates. Thus, there is an urgent need to identify novel biomarkers for early detection, as well as to accurately predict the clinical outcomes and identify effective therapeutic targets for these malignancies. Although the role of lysine acetylation in digestive tract cancers remains unclear, further analysis could improve our understanding of its role in the pathogenesis of digestive tract cancers. This review aims to summarize the implications and pathogenic mechanisms of lysine acetylation dysregulation in digestive tract cancers, as well as its potential clinical applications.

Keywords:  clinical application; digestive tract cancers; expression; lysine acetylation; pathogenic mechanisms

DOI:  https://doi.org/10.3389/fcell.2024.1447939
Biochem J. 2024 Oct 07. pii: BCJ20240380. [Epub ahead of print]

Histone deacetylase 7 activates 6-phosphogluconate dehydrogenase via an enzyme-independent mechanism that involves the N-terminal protein-protein interaction domain.

Yizhuo Wang, James Eb Curson, Divya Ramnath, Kaustav Das Gupta, Robert C Reid, Denuja Karunakaran, David Fairlie, Matthew J Sweet.

  Histone deacetylase 7 (HDAC7) is a member of the class IIa family of classical HDACs with important roles in cell development, differentiation, and activation, including in macrophages and other innate immune cells. HDAC7 and other class IIa HDACs act as transcriptional repressors in the nucleus but, in some cell types, they can also act in the cytoplasm to modify non-nuclear proteins and/or scaffold signalling complexes. In macrophages, HDAC7 is a cytoplasmic protein with both pro- and anti-inflammatory functions, with the latter activity involving activation of the pentose phosphate pathway (PPP) enzyme 6-phosphogluconate dehydrogenase (6PGD) and the generation of anti-inflammatory metabolite ribulose-5-phosphate. Here, we used ectopic expression systems and biochemical approaches to investigate the mechanism by which HDAC7 promotes 6PGD enzyme activity. We reveal that HDAC7 enzyme activity is not required for its activation of 6PGD and that the N-terminal protein-protein interaction domain of HDAC7 is sufficient to initiate this response. Mechanistically, the N-terminus of HDAC7 increases the affinity of 6PGD for NADP+, promotes the generation of a shorter form of 6PGD, and enhances the formation of higher order protein complexes, implicating its scaffolding function in engagement of the PPP. This contrasts with the pro-inflammatory function of HDAC7 in macrophages, in which it promotes deacetylation of the glycolytic enzyme pyruvate kinase M2 for inflammatory cytokine production.

Keywords:  6-phosphogluconate dehydrogenase; HDACs; histone deacetylase 7; inflammation; lysine deacetylase; scaffolding

DOI:  https://doi.org/10.1042/BCJ20240380
Cell Rep. 2024 Oct 04. pii: S2211-1247(24)01166-5. [Epub ahead of print]43(10): 114815

Metabolite regulation of epigenetics in cancer.

Pu Wang, Lei-Lei Chen, Yue Xiong, Dan Ye.

  The catalytic activity of most epigenetic enzymes requires a metabolite produced by central carbon metabolism as a cofactor or (co-)substrate. The concentrations of these metabolites undergo dynamic changes in response to nutrient levels and environmental conditions, reprogramming metabolic processes and epigenetic landscapes. Abnormal accumulations of epigenetic modulatory metabolites resulting from mutations in metabolic enzymes contribute to tumorigenesis. In this review, we first present the concept that metabolite regulation of gene expression represents an evolutionarily conserved mechanism from prokaryotes to eukaryotes. We then review how individual metabolites affect epigenetic enzymes and cancer development. Lastly, we discuss the advancement of and opportunity for therapeutic targeting of metabolite-epigenetic regulation in cancer therapy.

Keywords:  CP: Cancer; CP: Metabolism

DOI:  https://doi.org/10.1016/j.celrep.2024.114815
Bone Res. 2024 Oct 11. 12(1): 57

Metabolic reprogramming in skeletal cell differentiation.

Joshua C Bertels, Guangxu He, Fanxin Long.

The human skeleton is a multifunctional organ made up of multiple cell types working in concert to maintain bone and mineral homeostasis and to perform critical mechanical and endocrine functions. From the beginning steps of chondrogenesis that prefigures most of the skeleton, to the rapid bone accrual during skeletal growth, followed by bone remodeling of the mature skeleton, cell differentiation is integral to skeletal health. While growth factors and nuclear proteins that influence skeletal cell differentiation have been extensively studied, the role of cellular metabolism is just beginning to be uncovered. Besides energy production, metabolic pathways have been shown to exert epigenetic regulation via key metabolites to influence cell fate in both cancerous and normal tissues. In this review, we will assess the role of growth factors and transcription factors in reprogramming cellular metabolism to meet the energetic and biosynthetic needs of chondrocytes, osteoblasts, or osteoclasts. We will also summarize the emerging evidence linking metabolic changes to epigenetic modifications during skeletal cell differentiation.

DOI: https://doi.org/10.1038/s41413-024-00374-0
bioRxiv. 2024 Sep 27. pii: 2024.09.25.614941. [Epub ahead of print]

Biochemical Characterization and Inhibitor Discovery for Pf Sir2A - New Tricks for An Old Enzyme.

Dickson Donu, Emily Boyle, Alyson Curry, Yana Cen.

The Sir2 enzyme from Plasmodium falciparum ( Pf Sir2A) is essential for the antigenic variation of this parasite, and its inhibition is expected to have therapeutic effects for malaria. Selective Pf Sir2A inhibitors are not available yet, partially due to the fact that this enzyme demonstrates extremely weak in vitro deacetylase activity, making the characterization of its inhibitors rather challenging. In the current study, we report the biochemical characterization and inhibitor discovery for this enzyme. Pf Sir2A exhibits greater enzymatic activity in the presence of DNA for both the peptide and histone protein substrates, suggesting that nucleosomes may be the real substrates of this enzyme. Indeed, it demonstrates robust deacetylase activity against nucleosome substrates, stemming primarily from the tight binding interactions with the nucleosome. In addition to DNA/nucleosome, free fatty acids (FFAs) are also identified as endogenous Pf Sir2A regulators. Myristic acid, a biologically relevant FFA, shows differential regulation of the two distinct activities of Pf Sir2A: activates deacetylation, but inhibits defatty-acylation. The structural basis of this differential regulation was further explored. Moreover, synthetic small molecule inhibitors of Pf Sir2A were discovered through the screening of a library of human sirtuin regulators. The mechanism of inhibition of the lead compounds were investigated. Collectively, the mechanistic insights and inhibitors described in this study will facilitate the future development of small molecule Pf Sir2A inhibitors as antimalarial agents.

DOI: https://doi.org/10.1101/2024.09.25.614941
Sci Rep. 2024 10 05. 14(1): 23180

Heterochromatin dynamics during the initial stages of sexual development in Plasmodium falciparum.

Sandra Nhim, Elisabet Tintó-Font, Núria Casas-Vila, Lucas Michel-Todó, Alfred Cortés.

  Asexual replication of Plasmodium falciparum in the human blood results in exponential parasite growth and causes all clinical symptoms of malaria. However, at each round of the replicative cycle, some parasites convert into sexual precursors called gametocytes, which develop through different stages until they become infective to mosquito vectors. The genome-wide distribution of heterochromatin, a type of chromatin generally refractory to gene expression, is identical at all asexual blood stages, but is altered in stage II/III and more mature gametocytes. However, it is not known if these changes occur concomitantly with sexual conversion or at a later time during gametocyte development. Using a transgenic line in which massive sexual conversion can be conditionally induced, we show that the genome-wide distribution of heterochromatin at the initial stages of sexual development (i.e., sexual rings and stage I gametocytes) is almost identical to asexual blood stages, and major changes do not occur until stage II/III. However, we found that at loci with heterochromatin alterations, transcriptional changes associated with sexual development typically precede, rather than follow, changes in heterochromatin occupancy.

Keywords:   Plasmodium falciparum ; Gametocytes; H3K9me3; Heterochromatin; Malaria; Transcription

DOI:  https://doi.org/10.1038/s41598-024-73981-w
bioRxiv. 2024 Sep 28. pii: 2024.09.27.615526. [Epub ahead of print]

A Genetically Encoded Fluorescent Biosensor for Intracellular Measurement of Malonyl-CoA.

Brodie L Ranzau, Tiffany D Robinson, Jack M Scully, Edmund D Kapelczack, Teagan S Dean, Tara TeSlaa, Danielle L Schmitt.

Malonyl-CoA is the essential building block of fatty acids and regulates cell function through protein malonylation and allosteric regulation of signaling networks. Accordingly, the production and use of malonyl-CoA is finely tuned by the cellular energy status. Most studies of malonyl-CoA dynamics rely on bulk approaches that take only a snapshot of the average metabolic state of a population of cells, missing out on dynamic changes in malonyl-CoA and fatty acid biosynthesis that could be occurring within a single cell. To overcome this limitation, we have developed a genetically encoded fluorescent protein-based biosensor for malonyl-CoA that can be used to capture malonyl-CoA dynamics in single cells. This biosensor, termed Malibu (malonyl-CoA i ntracellular biosensor to understand dynamics), exhibits an excitation-ratiometric change in response to malonyl-CoA binding. We first used Malibu to monitor malonyl-CoA dynamics during inhibition of fatty acid biosynthesis using cerulenin in E. coli , observing an increase in Malibu response in a time- and dose-dependent manner. In HeLa cells, we used Malibu to monitor the impact of fatty acid biosynthesis inhibition on malonyl-CoA dynamics in single cells, finding that two inhibitors of fatty acid biosynthesis, cerulenin and orlistat, which inhibit different steps of fatty acid biosynthesis, increase malonyl-CoA levels. Altogether, we have developed a new genetically encoded biosensor for malonyl-CoA, which can be used to sensitively study malonyl-CoA dynamics in single cells, providing an unparalleled view into fatty acid biosynthesis.

DOI: https://doi.org/10.1101/2024.09.27.615526
Commun Biol. 2024 Oct 05. 7(1): 1267

Metabolic regulation of mitochondrial morphologies in pancreatic beta cells: coupling of bioenergetics and mitochondrial dynamics.

Wen-Wei Tseng, Ching-Hsiang Chu, Yi-Ju Lee, Shirui Zhao, Chen Chang, Yi-Ping Ho, An-Chi Wei.

Cellular bioenergetics and mitochondrial dynamics are crucial for the secretion of insulin by pancreatic beta cells in response to elevated levels of blood glucose. To elucidate the interactions between energy production and mitochondrial fission/fusion dynamics, we combine live-cell mitochondria imaging with biophysical-based modeling and graph-based network analysis. The aim is to determine the mechanism that regulates mitochondrial morphology and balances metabolic demands in pancreatic beta cells. A minimalistic differential equation-based model for beta cells is constructed that includes glycolysis, oxidative phosphorylation, calcium dynamics, and fission/fusion dynamics, with ATP synthase flux and proton leak flux as main regulators of mitochondrial dynamics. The model shows that mitochondrial fission occurs in response to hyperglycemia, starvation, ATP synthase inhibition, uncoupling, and diabetic conditions, in which the rate of proton leakage exceeds the rate of mitochondrial ATP synthesis. Under these metabolic challenges, the propensities of tip-to-tip fusion events simulated from the microscopy images of the mitochondrial networks are lower than those in the control group and prevent the formation of mitochondrial networks. The study provides a quantitative framework that couples bioenergetic regulation with mitochondrial dynamics, offering insights into how mitochondria adapt to metabolic challenges.

DOI: https://doi.org/10.1038/s42003-024-06955-3
Curr Aging Sci. 2024 Oct 04.

Nicotinamide Adenine Dinucleotide (NAD)-Dependent Protein Deacetylase, Sirtuin, as a Biomarker of Healthy Life Expectancy: A Mini-Review.

Yodo Sugishita, Yuki Suzuki-Takahashi, Kazuo Yudoh.

  Although a variety of disease-specific biomarkers have been identified for common lifestyle- or aging-related diseases, there are currently no indices available to measure general health or the existence of pre-symptomatic conditions in various types of tissue and organ damage. A rising body of research suggests that sirtuins may have the potential to be used as an index to assess overall health status and the existence of pre-symptomatic illness states. Sirtuins (SIRTs) are nicotinamide adenine dinucleotide (NAD)-dependent deacetylases expressed in a variety of human somatic cells both in health and disease conditions. The activity and expression of SIRTs affect important metabolic pathways, such as cell survival, senescence, proliferation, energy production, stress tolerance, DNA repair, and apoptosis, thereby closely linked to aging and longevity. Given the broad significance of SIRTs in physiological function maintenance, their activity in somatic cells may reflect the early cross-sectional status of tissue damage caused by aging or systemic inflammatory responses that are too early to be detected by disease-specific biomarkers. In this mini-review, we discuss the utility of SIRTs as a surrogate clinical biomarker for health status to evaluate and monitor health life expectancy and the presence of pre-symptomatic illness states.

Keywords:  Aging; healthy life expectancy biomarkers; sirtuin.; surrogate markers

DOI:  https://doi.org/10.2174/0118746098319674240827104612