Using Lipoamidase as a Novel Probe To Interrogate the Importance of Lipoylation in Plasmodium falciparum

ABSTRACT Lipoate is a redox active cofactor that is covalently bound to key enzymes of oxidative metabolism. Plasmodium falciparum is auxotrophic for lipoate during the intraerythrocytic stages, but it is not known whether lipoate attachment to protein is required or whether attachment is required in a specific subcellular compartment of the parasite. To address these questions, we used an enzyme called lipoamidase (Lpa) as a probe of lipoate metabolism. Lpa was first described in Enterococcus faecalis, and it specifically cleaves protein-bound lipoate, inactivating enzymes requiring this cofactor. Enzymatically active Lpa could be expressed in the cytosol of P. falciparum without any effect on protein lipoylation or parasite growth. Similarly, Lpa could be expressed in the apicoplast, and although protein lipoylation was reduced, parasite growth was not inhibited. By contrast, while an inactive mutant of Lpa could be expressed in the mitochondrion, the active enzyme could not. We designed an attenuated mutant of Lpa and found that this enzyme could be expressed in the parasite mitochondrion, but only in conjunction with a chemical bypass system. These studies suggest that acetyl-CoA production and a cryptic function of the H protein are both required for parasite survival. Our study validates Lpa as a novel probe of metabolism that can be used in other systems and provides new insight into key aspects of mitochondrial metabolism that are responsible for lipoate auxotrophy in malaria parasites. IMPORTANCE Lipoate is an essential cofactor for a small number of enzymes that are important for central metabolism. Malaria parasites require lipoate scavenged from the human host for growth and survival; however, it is not known why this cofactor is so important. To address this question, we designed a probe of lipoate activity based on the bacterial enzyme lipoamidase (Lpa). Expression of this probe in different subcellular locations allowed us to define the mitochondrion as the compartment housing essential lipoate metabolism. To gain further insight into the specific uses of lipoate in the mitochondrion, we designed a series of catalytically attenuated probes and employed the probes in conjunction with a chemical bypass system. These studies suggest that two lipoylated proteins are required for parasite survival. We were able to express Lpa with different catalytic abilities in different subcellular compartments and driven by different promoters, demonstrating the versatility of this tool and suggesting that it can be used as a probe of lipoate metabolism in other organisms.

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Interaction of Plasmodium falciparum apicortin with α- and β-tubulin is critical for parasite growth and survival

Scientific Reports ◽

10.1038/s41598-021-83513-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Malabika Chakrabarti ◽

Nishant Joshi ◽

Geeta Kumari ◽

Preeti Singh ◽

Rumaisha Shoaib ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Life Cycle ◽

Specific Protein ◽

Parasite Growth ◽

Growth And Survival ◽

Apicomplexan Parasites ◽

Parasite Replication ◽

Main Components ◽

Β Tubulin

AbstractCytoskeletal structures of Apicomplexan parasites are important for parasite replication, motility, invasion to the host cell and survival. Apicortin, an Apicomplexan specific protein appears to be a crucial factor in maintaining stability of the parasite cytoskeletal assemblies. However, the function of apicortin, in terms of interaction with microtubules still remains elusive. Herein, we have attempted to elucidate the function of Plasmodium falciparum apicortin by monitoring its interaction with two main components of parasite microtubular structure, α-tubulin-I and β-tubulin through in silico and in vitro studies. Further, a p25 domain binding generic drug Tamoxifen (TMX), was used to disrupt PfApicortin-tubulin interactions which led to the inhibition in growth and progression of blood stage life cycle of P. falciparum.

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Malaria Parasite Schizont Egress Antigen-1 Plays an Essential Role in Nuclear Segregation during Schizogony

mBio ◽

10.1128/mbio.03377-20 ◽

2021 ◽

Vol 12 (2) ◽

Author(s):

Abigail J. Perrin ◽

Claudine Bisson ◽

Peter A. Faull ◽

Matthew J. Renshaw ◽

Rebecca A. Lees ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Vaccine Antigen ◽

Malaria Parasites ◽

Content Type ◽

Dependent Protein ◽

Low Efficiency ◽

And Function ◽

Parasite Egress ◽

Kinetochore Function ◽

Merozoite Egress

ABSTRACT Malaria parasites cause disease through repeated cycles of intraerythrocytic proliferation. Within each cycle, several rounds of DNA replication produce multinucleated forms, called schizonts, that undergo segmentation to form daughter merozoites. Upon rupture of the infected cell, the merozoites egress to invade new erythrocytes and repeat the cycle. In human malarial infections, an antibody response specific for the Plasmodium falciparum protein PF3D7_1021800 was previously associated with protection against malaria, leading to an interest in PF3D7_1021800 as a candidate vaccine antigen. Antibodies to the protein were reported to inhibit egress, resulting in it being named schizont egress antigen-1 (SEA1). A separate study found that SEA1 undergoes phosphorylation in a manner dependent upon the parasite cGMP-dependent protein kinase PKG, which triggers egress. While these findings imply a role for SEA1 in merozoite egress, this protein has also been implicated in kinetochore function during schizont development. Therefore, the function of SEA1 remains unclear. Here, we show that P. falciparum SEA1 localizes in proximity to centromeres within dividing nuclei and that conditional disruption of SEA1 expression severely impacts the distribution of DNA and formation of merozoites during schizont development, with a proportion of SEA1-null merozoites completely lacking nuclei. SEA1-null schizonts rupture, albeit with low efficiency, suggesting that neither SEA1 function nor normal segmentation is a prerequisite for egress. We conclude that SEA1 does not play a direct mechanistic role in egress but instead acts upstream of egress as an essential regulator required to ensure the correct packaging of nuclei within merozoites. IMPORTANCE Malaria is a deadly infectious disease. Rationally designed novel therapeutics will be essential for its control and eradication. The Plasmodium falciparum protein PF3D7_1021800, annotated as SEA1, is under investigation as a prospective component of a malaria vaccine, based on previous indications that antibodies to SEA1 interfere with parasite egress from infected erythrocytes. However, a consensus on the function of SEA1 is lacking. Here, we demonstrate that SEA1 localizes to dividing parasite nuclei and is necessary for the correct segregation of replicated DNA into individual daughter merozoites. In the absence of SEA1, merozoites develop defectively, often completely lacking a nucleus, and, consequently, egress is impaired and/or aberrant. Our findings provide insights into the divergent mechanisms by which intraerythrocytic malaria parasites develop and divide. Our conclusions regarding the localization and function of SEA1 are not consistent with the hypothesis that antibodies against it confer protective immunity to malaria by blocking merozoite egress.

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Tolerance of Gambian Plasmodium falciparum to Dihydroartemisinin and Lumefantrine Detected by Ex Vivo Parasite Survival Rate Assay

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00720-20 ◽

2020 ◽

Vol 65 (1) ◽

pp. e00720-20

Author(s):

Haddijatou Mbye ◽

Fatoumata Bojang ◽

Aminata Seedy Jawara ◽

Bekai Njie ◽

Nuredin Ibrahim Mohammed ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Survival Rate ◽

Drug Exposure ◽

Ex Vivo ◽

Ring Stage ◽

Color Flow ◽

Continuous Growth ◽

Content Type ◽

Parasite Survival ◽

Survival Assay

ABSTRACTMonitoring of Plasmodium falciparum sensitivity to antimalarial drugs in Africa is vital for malaria elimination. However, the commonly used ex vivo/in vitro 50% inhibitory concentration (IC50) test gives inconsistent results for several antimalarials, while the alternative ring-stage survival assay (RSA) for artemisinin derivatives has not been widely adopted. Here, we applied an alternative two-color flow cytometry-based parasite survival rate assay (PSRA) to detect ex vivo antimalarial tolerance in P. falciparum isolates from The Gambia. The PSRA infers parasite viability by quantifying reinvasion of uninfected cells following 3 consecutive days of drug exposure (10-fold the IC50 of drug for field isolates). The drug survival rate is obtained for each isolate from the slope of the growth/death curve. We obtained parasite survival rates of 41 isolates for dihydroartemisinin (DHA) and lumefantrine (LUM) out of 51 infections tested by ring-stage survival assay (RSA) against DHA. We also determined the genotypes for known drug resistance genetic loci in the P. falciparum genes Pfdhfr, Pfdhps, Pfmdr, Pfcrt, and Pfk13. The PSRA results determined for 41 Gambian isolates showed faster killing and lower variance after treatment with DHA than after treatment with LUM, despite a strong correlation between the two drugs. Four and three isolates were tolerant to DHA and LUM, respectively, with continuous growth during drug exposure. Isolates with the PfMDR1-Y184F mutant variant showed increased LUM survival, though the results were not statistically significant. Sulfadoxine/pyrimethamine (SP) resistance markers were fixed, while all other antimalarial variants were prevalent in more than 50% of the population. The PSRA detected ex vivo antimalarial tolerance in Gambian P. falciparum. This calls for its wider application and for increased vigilance against resistance to artemisinin combination therapies (ACTs) in this population.

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The Exported Chaperone PfHsp70x Is Dispensable for the Plasmodium falciparum Intraerythrocytic Life Cycle

mSphere ◽

10.1128/msphere.00363-17 ◽

2017 ◽

Vol 2 (5) ◽

Cited By ~ 22

Author(s):

David W. Cobb ◽

Anat Florentin ◽

Manuel A. Fierro ◽

Michelle Krakowiak ◽

Julie M. Moore ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Life Cycle ◽

Host Cell ◽

Protein Trafficking ◽

Human Disease ◽

Clinical Manifestations ◽

Parasite Protein ◽

Content Type ◽

Parasite Survival ◽

Outstanding Question

ABSTRACT Half of the world’s population lives at risk for malaria. The intraerythrocytic life cycle of Plasmodium spp. is responsible for clinical manifestations of malaria; therefore, knowledge of the parasite’s ability to survive within the erythrocyte is needed to combat the deadliest agent of malaria, P. falciparum. An outstanding question in the field is how P. falciparum undertakes the essential process of trafficking its proteins within the host cell. In most organisms, chaperones such as Hsp70 are employed in protein trafficking. Of the Plasmodium species causing human disease, the chaperone PfHsp70x is unique to P. falciparum, and it is the only parasite protein of its kind exported to the host (S. Külzer et al., Cell Microbiol 14:1784–1795, 2012). This has placed PfHsp70x as an ideal target to inhibit protein trafficking and kill the parasite. However, we show that PfHsp70x is not required for export of parasite effectors and it is not essential for parasite survival inside the RBC. Export of parasite proteins into the host erythrocyte is essential for survival of Plasmodium falciparum during its asexual life cycle. While several studies described key factors within the parasite that are involved in protein export, the mechanisms employed to traffic exported proteins within the host cell are currently unknown. Members of the Hsp70 family of chaperones, together with their Hsp40 cochaperones, facilitate protein trafficking in other organisms, and are thus likely used by P. falciparum in the trafficking of its exported proteins. A large group of Hsp40 proteins is encoded by the parasite and exported to the host cell, but only one Hsp70, P. falciparum Hsp70x (PfHsp70x), is exported with them. PfHsp70x is absent in most Plasmodium species and is found only in P. falciparum and closely related species that infect apes. Herein, we have utilized clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 genome editing in P. falciparum to investigate the essentiality of PfHsp70x. We show that parasitic growth was unaffected by knockdown of PfHsp70x using both the dihydrofolate reductase (DHFR)-based destabilization domain and the glmS ribozyme system. Similarly, a complete gene knockout of PfHsp70x did not affect the ability of P. falciparum to proceed through its intraerythrocytic life cycle. The effect of PfHsp70x knockdown/knockout on the export of proteins to the host red blood cell (RBC), including the critical virulence factor P. falciparum erythrocyte membrane protein 1 (PfEMP1), was tested, and we found that this process was unaffected. These data show that although PfHsp70x is the sole exported Hsp70, it is not essential for the asexual development of P. falciparum. IMPORTANCE Half of the world’s population lives at risk for malaria. The intraerythrocytic life cycle of Plasmodium spp. is responsible for clinical manifestations of malaria; therefore, knowledge of the parasite’s ability to survive within the erythrocyte is needed to combat the deadliest agent of malaria, P. falciparum. An outstanding question in the field is how P. falciparum undertakes the essential process of trafficking its proteins within the host cell. In most organisms, chaperones such as Hsp70 are employed in protein trafficking. Of the Plasmodium species causing human disease, the chaperone PfHsp70x is unique to P. falciparum, and it is the only parasite protein of its kind exported to the host (S. Külzer et al., Cell Microbiol 14:1784–1795, 2012). This has placed PfHsp70x as an ideal target to inhibit protein trafficking and kill the parasite. However, we show that PfHsp70x is not required for export of parasite effectors and it is not essential for parasite survival inside the RBC.

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Artemisinin activity-based probes identify multiple molecular targets within the asexual stage of the malaria parasites Plasmodium falciparum 3D7

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1600459113 ◽

2016 ◽

Vol 113 (8) ◽

pp. 2080-2085 ◽

Cited By ~ 113

Author(s):

Hanafy M. Ismail ◽

Victoria Barton ◽

Matthew Phanchana ◽

Sitthivut Charoensutthivarakul ◽

Michael H. L. Wong ◽

...

Keyword(s):

Plasmodium Falciparum ◽

Drug Targets ◽

Antioxidant Defense ◽

Protein Profiling ◽

Parasite Protein ◽

Know How ◽

Parasite Survival ◽

Hemoglobin Degradation ◽

Insight Into

The artemisinin (ART)-based antimalarials have contributed significantly to reducing global malaria deaths over the past decade, but we still do not know how they kill parasites. To gain greater insight into the potential mechanisms of ART drug action, we developed a suite of ART activity-based protein profiling probes to identify parasite protein drug targets in situ. Probes were designed to retain biological activity and alkylate the molecular target(s) of Plasmodium falciparum 3D7 parasites in situ. Proteins tagged with the ART probe can then be isolated using click chemistry before identification by liquid chromatography–MS/MS. Using these probes, we define an ART proteome that shows alkylated targets in the glycolytic, hemoglobin degradation, antioxidant defense, and protein synthesis pathways, processes essential for parasite survival. This work reveals the pleiotropic nature of the biological functions targeted by this important class of antimalarial drugs.

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Knockdown of the translocon protein EXP2, reduces growth and protein export in malaria parasites

10.1101/420034 ◽

2018 ◽

Author(s):

Sarah C. Charnaud ◽

Rasika Kumarasingha ◽

Hayley E. Bullen ◽

Brendan S. Crabb ◽

Paul R. Gilson

Keyword(s):

Parasite Growth ◽

Protein Export ◽

Cell Protein ◽

Host Cell Protein ◽

Growth Reduction ◽

Malaria Parasites ◽

Asexual Blood Stage ◽

Parasite Survival ◽

Core Components ◽

Exported Protein

AbstractMalaria parasites remodel their host erythrocytes to gain nutrients and avoid the immune system. Host erythrocytes are modified by hundreds of effectors proteins exported from the parasites into the host cell. Protein export is mediated by the PTEX translocon comprising five core components of which EXP2 is considered to form the putative pore that spans the vacuole membrane enveloping the parasite within its erythrocyte. To explore the function and importance of EXP2 for parasite survival in the asexual blood stage of Plasmodium falciparum we inducibly knocked down the expression of EXP2. Reduction in EXP2 expression strongly reduced parasite growth proportional to the degree of protein knockdown and tended to stall development about half way through the asexual cell cycle. Once the knockdown inducer was removed and EXP2 expression restored, parasite growth recovered dependent upon the length and degree of knockdown. To establish EXP2 function and hence the basis for growth reduction, the trafficking of an exported protein was monitored following EXP2 knockdown. This resulted in severe attenuation of protein export and is consistent with EXP2, and PTEX in general, being the conduit for export of proteins into the host compartment.

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ROP16-Mediated Activation of STAT6 Suppresses Host Cell Reactive Oxygen Species Production, Facilitating Type III Toxoplasma gondii Growth and Survival

mBio ◽

10.1128/mbio.03305-20 ◽

2021 ◽

Vol 12 (2) ◽

Author(s):

Joshua A. Kochanowsky ◽

Kaitlin K. Thomas ◽

Anita A. Koshy

Keyword(s):

Reactive Oxygen Species ◽

Toxoplasma Gondii ◽

Host Cell ◽

Parasite Growth ◽

Effector Proteins ◽

Oxygen Species ◽

Content Type ◽

Growth And Survival ◽

Type Iii ◽

Ifn Γ

ABSTRACT Polymorphic effector proteins determine the susceptibility of Toxoplasma gondii strains to IFN-γ-mediated clearance mechanisms deployed by murine host cells. However, less is known about the influence of these polymorphic effector proteins on IFN-γ-independent clearance mechanisms. Here, we show that deletion of one such polymorphic effector protein, ROP16, from a type III background leads to a defect in parasite growth and survival in unstimulated human fibroblasts and murine macrophages. Rescue of these defects requires a ROP16 with a functional kinase domain and the ability to activate a specific family of host cell transcription factors (STAT3, 5a, and 6). The growth and survival defects correlate with an accumulation of host cell reactive oxygen species (ROS) and are prevented by treatment with an ROS inhibitor. Exogenous activation of STAT3 and 6 suppresses host cell ROS production during infection with ROP16-deficient parasites and depletion of STAT6, but not STAT3 or 5a, causes an accumulation of ROS in cells infected with wild-type parasites. Pharmacological inhibition of NOX2 and mitochondrially derived ROS also rescues growth and survival of ROP16-deficient parasites. Collectively, these findings reveal an IFN-γ-independent mechanism of parasite restriction in human cells that is subverted by injection of ROP16 by type III parasites. IMPORTANCE Toxoplasma gondii is an obligate intracellular parasite that infects up to one-third of the world’s population. Control of the parasite is largely accomplished by IFN-γ-dependent mechanisms that stimulate innate and adaptive immune responses. Parasite suppression of IFN-γ-stimulated responses has been linked to proteins that the parasite secretes into its host cell. These secreted proteins vary by T. gondii strain and determine strain-specific lethality in mice. How these strain-specific polymorphic effector proteins affect IFN-γ-independent parasite control mechanisms in human and murine cells is not well known. This study shows that one such secreted protein, ROP16, enables efficient parasite growth and survival by suppressing IFN-γ-independent production of ROS by human and mouse cells.

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Assessment of biological role and insight into druggability of the Plasmodium falciparum protease plasmepsin V

10.1101/426486 ◽

2018 ◽

Cited By ~ 4

Author(s):

Alexander J. Polino ◽

S. Nasamu Armiyaw ◽

Jacquin C. Niles ◽

Daniel E. Goldberg

Keyword(s):

Plasmodium Falciparum ◽

Host Cell ◽

Drug Targets ◽

Parasite Growth ◽

Aspartic Protease ◽

Protein Export ◽

New Drugs ◽

Functional Studies ◽

Parasite Survival ◽

Post Transcriptional Regulation

AbstractUpon infection of a red blood cell (RBC), the malaria parasite Plasmodium falciparum drastically remodels its host by exporting hundreds of proteins into the RBC cytosol. This program of protein export is essential for parasite survival, hence there is interest in export-related proteins as potential drug targets. One proposed target is plasmepsin V (PMV), an aspartic protease that cleaves export-destined proteins in the parasite ER at a motif called the Plasmodium export element (PEXEL). This cleavage is essential for effector export across the vacuolar membrane. Despite long-standing interest in PMV, functional studies have been hindered by the failure of current technologies to produce a regulatable lethal depletion of PMV. To overcome this technical barrier, we designed a facile system for stringent post-transcriptional regulation, allowing a tightly controlled, tunable knockdown of PMV. Under maximal knockdown conditions, parasite growth was arrested, validating PMV as essential for parasite survival in RBCs. We found that PMV levels had to be dramatically depleted to affect parasite growth, suggesting that the parasite maintains this enzyme in substantial excess. This has important implications for antimalarial development. Additionally, we found that PMV-depleted parasites arrest immediately after invasion of the host cell, suggesting that PMV has an unappreciated role in early development that is distinct from its previously reported role in protein export in later-stage parasites.ImportanceMalaria is endemic to large swaths of the developing world, causing nearly 500,000 deaths each year. While infection can be treated with antimalarial drugs, resistance continues to emerge to frontline antimalarials, spurring calls for new drugs and targets to feed the drug development pipeline. One proposed target is the aspartic protease plasmepsin V (PMV) that processes exported proteins, enabling the export program that remodels the host cell. This work uses facile genetic tools to produce lethal depletion of PMV, validating it as a drug target and showing that PMV is made in substantial excess in blood-stage parasites. Unexpectedly, PMV depletion leads to parasite death immediately after invasion of RBCs, distinct from other disruptions of the export pathway. This suggests that PMV inhibitors could lead to relatively rapid parasite death, and that PMV has additional unexplored role(s) during RBC infection.

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Inhibition of PfMYST Histone Acetyltransferase Activity Blocks Plasmodium falciparum Growth and Survival

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00953-20 ◽

2020 ◽

Vol 65 (1) ◽

pp. e00953-20

Author(s):

Utsav Sen ◽

Akshaykumar Nayak ◽

Juhi Khurana ◽

Deepu Sharma ◽

Ashish Gupta

Keyword(s):

Catalytic Activity ◽

Drug Target ◽

Cell Cycle Progression ◽

Histone Acetyltransferase ◽

Antigenic Variation ◽

Therapeutic Potential ◽

Parasite Growth ◽

Trophozoite Stage ◽

Content Type ◽

Growth And Survival

ABSTRACTOne of the major barriers in the prevention and control of malaria programs worldwide is the growing emergence of multidrug resistance in Plasmodium parasites, and this necessitates continued efforts to discover and develop effective drug molecules targeting novel proteins essential for parasite survival. In recent years, epigenetic regulators have evolved as an attractive drug target option owing to their crucial role in survival and development of Plasmodium at different stages of its life cycle. PfMYST, a histone acetyltransferase protein, is known to regulate key cellular processes, such as cell cycle progression, DNA damage repair, and antigenic variation, that facilitate parasite growth, adaptation, and survival inside its host. With the aim of assessing the therapeutic potential of PfMYST as a novel drug target, we examined the effect of NU9056 (an HsTIP60 inhibitor) on the rate of parasite growth and survival. In the present study, by using a yeast complementation assay, we established that PfMYST is a true homolog of TIP60 and showed that NU9056 can inhibit PfMYST catalytic activity and kill P. falciparum parasites in culture. Inhibiting the catalytic activity of PfMYST arrests the parasite in the trophozoite stage and inhibits its further transition to the schizont stage, eventually leading to its death. Overall, our study provides proof of concept that PfMYST catalytic activity is essential for parasite growth and survival and that PfMYST can be a potential target for antimalarial therapy.

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Activity of Epigenetic Inhibitors against Plasmodium falciparum Asexual and Sexual Blood Stages

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02523-19 ◽

2020 ◽

Vol 64 (7) ◽

Cited By ~ 4

Author(s):

Leen N. Vanheer ◽

Hao Zhang ◽

Gang Lin ◽

Björn F. C. Kafsack

Keyword(s):

Gene Expression ◽

Plasmodium Falciparum ◽

Epigenetic Regulation ◽

Malaria Parasite ◽

Regulation Of Gene Expression ◽

Life Stages ◽

Content Type ◽

Promising Target ◽

Parasite Survival ◽

Multiple Stages

ABSTRACT Earlier genetic and inhibitor studies showed that epigenetic regulation of gene expression is critical for malaria parasite survival in multiple life stages and a promising target for new antimalarials. We therefore evaluated the activity of 350 diverse epigenetic inhibitors against multiple stages of Plasmodium falciparum. We observed ≥90% inhibition at 10 μM for 28% of compounds against asexual blood stages and early gametocytes, of which a third retained ≥90% inhibition at 1 μM.

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