Peroxiredoxin-1 from the human hookworm Ancylostoma ceylanicum forms a stable oxidized decamer and is covalently inhibited by conoidin A

PRDX1 inhibits ferroptosis by binding to Cullin-3 as a molecular chaperone in colorectal cancer

Peroxiredoxin 1 (PRDX1) is a potent antioxidant protein that displays a unique molecular chaperone activity. However, the role of overexpression of PRDX1 in colorectal cancer (CRC) was elusive. Herein, we found that the number of AOM/DSS-induced colitis-associated CRC in PRDX1 knockout mice was significantly lower than that in wild-type mice, concomitant with the downregulation of NRF2 and GPX4. Mechanistically, RNA sequencing results indicated that knockdown of PRDX1 resulted in a significant reduction of NRF2, which further triggered ROS-induced mitochondrial dysfunction and lipid peroxidation-induced ferroptosis in CRC cells. Notably, PRDX1 inhibited NRF2 degradation and promoted NRF2 nuclear translocation, thereby triggering the transcription of GPX4. Immunoprecipitation-mass spectrometry (IP-MS) and Co-immunoprecipitation (Co-IP) assays revealed that PRDX1 could act as a molecular chaperone by binding to CUL3 to inhibit NRF2 ubiquitination. Importantly, the binding of PRDX1 to CUL3 was enhanced by conoidin A but abolished by the PRDX1 Cys83Ser mutant. The inhibitory effects of PRDX1 knockdown on CRC could be attenuated by NRF2 activation or ferrostatin-1 administration in vivo. Collectively, these results provide a novel insight into the molecular chaperone activity of PRDX1 in promoting CRC progression through suppression of CUL3-mediated NRF2 degradation, suggesting PRDX1 Cys83 is a potential drug target in inhibiting CRC.

Comparative Analysis of Inhibitor Binding to Peroxiredoxins from Candidatus Liberibacter asiaticus and Its Host Citrus sinensis

The peroxiredoxins (Prxs), potential drug targets, constitute an important class of antioxidant enzymes present in both pathogen and their host. The comparative binding potential of inhibitors to Prxs from pathogen and host could be an important step in drug development against pathogens. Huanglongbing (HLB) is a most devastating disease of citrus caused by Candidatus Liberibacter asiaticus (CLa). In this study, the binding of conoidin-A (conoidin) and celastrol inhibitor molecules to peroxiredoxin of bacterioferritin comigratory protein family from CLa (CLaBCP) and its host plant peroxiredoxin from Citrus sinensis (CsPrx) was assessed. The CLaBCP has a lower specific activity than CsPrx and is efficiently inhibited by conoidin and celastrol molecules. The biophysical studies showed conformational changes and significant thermal stability of CLaBCP in the presence of inhibitor molecules as compared to CsPrx. The surface plasmon resonance (SPR) studies revealed that the conoidin and celastrol inhibitor molecules have a strong binding affinity (KD) with CLaBCP at 33.0 µM, and 18.5 µM as compared to CsPrx at 52.0 µM and 61.6 µM, respectively. The docked complexes of inhibitor molecules showed more structural stability of CLaBCP as compared to CsPrx during the run of molecular dynamics-based simulations for 100 ns. The present study suggests that the conoidin and celastrol molecules can be exploited as potential inhibitor molecules against the CLa to manage the HLB disease.

Comprehensive approach to in silico identification and in vitro validation of anti-filarial hit molecules targeting the dimer interface of thioredoxin peroxidase 1 in Wuchereria bancrofti: a progress in anti-filariasis drug development

Lymphatic filariasis (LF) remains a significant health challenge for populations in developing countries. LF is a parasitic disease transmitted by mosquitoes, mainly caused by the filarial nematode, Wuchereria bancrofti, prevalent in tropical and subtropical regions. Since the present drugs develop complications, including adverse side effects, lack of specificity, and development of drug resistance, the present study focused on developing the potential anti-filariasis drugs targeting crucial proteins for the nematode life cycle. We have identified the therapeutic compounds by targeting the enzyme thioredoxin peroxidase 1 (WbTPx1), which facilitates the conversion of hydrogen peroxide into water, an essential mechanism by which the nematode survives against oxidative stress in the host. This approach might resolve treatment efficacy and activity difficulties at various stages of filarial parasitic worms. We modeled the structure of WbTPx1 and employed the structure-based virtual screening approach, focusing on the dimer interface region of the protein. ADMET prediction profiles of the non-toxic, top-ranked hits with higher docking scores demonstrate higher affinity to the nematode protein than its human homolog. The molecular dynamic simulation studies show WbTPx1-hit complexes' stability and the intactness of hits in the binding site. Further, in vitro validation of identified hits using Setaria digitata, a cattle nematode, showed better IC50 and higher inhibition than the standard drug ivermectin, indicating the potential to inhibit enzyme activity and the development of drug candidates for controlling LF.

Temporal coordination of the transcription factor response to H2O2 stress

Oxidative stress from excess H2O2 activates transcription factors that restore redox balance and repair oxidative damage. Although many transcription factors are activated by H2O2, it is unclear whether they are activated at the same H2O2 concentration, or time. Dose-dependent activation is likely as oxidative stress is not a singular state and exhibits dose-dependent outcomes including cell-cycle arrest and cell death. Here, we show that transcription factor activation is both dose-dependent and coordinated over time. Low levels of H2O2 activate p53, NRF2 and JUN. Yet under high H2O2, these transcription factors are repressed, and FOXO1, NF-κB, and NFAT1 are activated. Time-lapse imaging revealed that the order in which these two groups of transcription factors are activated depends on whether H2O2 is administered acutely by bolus addition, or continuously through the glucose oxidase enzyme. Finally, we provide evidence that 2-Cys peroxiredoxins control which group of transcription factors are activated.

Temporal Coordination of the Transcription Factor Response to H2O2 stress

Oxidative stress from excess H2O2 activates transcription factors (TFs) that restore redox balance and repair oxidative damage. Though many TFs are activated by H2O2, it is unknown whether they are activated at the same H2O2 concentration or time after H2O2 stress. We found TF activation is tightly coordinated over time and dose dependent. We first focused on p53 and FOXO1 and found that in response to low H2O2, p53 is activated rapidly while FOXO1 remains inactive. In contrast, cells respond to high H2O2 in two temporal phases. In the first phase FOXO1 rapidly shuttles to the nucleus while p53 remains inactive. In the second phase FOXO1 shuts off and p53 levels rise. Other TFs are activated in the first phase with FOXO1 (NF-κB, NFAT1), or the second phase with p53 (NRF2, JUN), but not both. The two phases result in large differences in gene expression. Finally, we provide evidence that 2-Cys peroxiredoxins control which TF are activated and the timing of TF activation.

Temporal Coordination of the Transcription Factor Response to H2O2 stress

The p53 and FOXO transcription factors (TFs) share many similarities despite their distinct evolutionary origins. Both TFs are activated by a variety of cellular stresses and upregulate genes in similar pathways including cell-cycle arrest and apoptosis. Oxidative stress from excess H2O2 activates both FOXO1 and p53, yet whether they are activated at the same time is unclear. Here we found that cells respond to high H2O2 levels in two temporal phases. In the first phase FOXO1 rapidly shuttles to the nucleus while p53 levels remain low. In the second phase FOXO1 exits the nucleus and p53 levels rise. We found that other oxidative stress induced TFs are activated in the first phase with FOXO1 (NF-κB, NFAT1), or the second phase with p53 (NRF2, JUN) but not both following H2O2 stress. The two TF phases result in large differences in gene expression patterns. Finally, we provide evidence that 2-Cys peroxiredoxins control the timing of the TF phases in response to H2O2.

Characterization of a cytoplasmic 2-Cys peroxiredoxin from Citrus sinensis and its potential role in protection from oxidative damage and wound healing

In present work, the recombinant cytoplasmic 2-Cys peroxiredoxin from Citrus sinensis (CsPrx) was purified and characterized. The peroxidase activity was examined with different substrates using DTT, a non-physiological electron donor. The conformational studies, in oxidized and reduced states, were performed using circular dichroism (CD) and fluorescence measurement. The CD analysis showed higher α-helical content for reduced state of the protein. The thermal stability studies of CsPrx by Differential Scanning Calorimetry (DSC) showed that oxidized state is more stable as compared to the reduced state of CsPrx. In vitro studies showed that the CsPrx provides a protective shield against ROS and free radicals that participate in the degradation of plasmid DNA. The pre-treatment of 10 μM CsPrx provide almost 100% protection against peroxide-mediated cell killing in the Vero cells. CsPrx showed significant cell proliferation and wound healing properties. The superior morphology of viable cells and wound closure was found at 20 μM CsPrx treated for 12 h. The results demonstrated that CsPrx is a multifaceted protein with a significant role in cell proliferation, wound healing and protection against hydrogen peroxide-induced cellular damage. This could be the first report of a plant peroxiredoxin being characterized for biomedical applications.

FoxO-promoted peroxiredoxin1 expression induced by Helicoverpa armigera single nucleopolyhedrovirus infection mediates host development and defensive responses

Helicoverpa armigera single nucleopolyhedrovirus (HearNPV) has a long coevolutionary history with its host, exerting profound effects on larval development, physiology and immune responses, although the mechanisms mediating these effects remain unclear. We demonstrate that HearNPV infection constrains the growth and development of larvae by inducing high levels of reactive oxygen species (ROS), which increase the expression of forkhead box O transcription factor (FoxO). FoxO upregulates the expression of peroxiredoxin 1 (Prx1) which serves to regulate larval development and immune responses following HearNPV infection. Collectively, our results provide novel insights into the role of Prx1 in larval development and immunity subsequent to HearNPV infection. Further investigation of the oxidative stress induced by HearNPV in H. armigera and its interactions with host immunity could yield novel insights useful in agricultural pest control.

Hookworm infections: Reappraising the evidence for a role of Neutrophils in light of NETosis

In Hookworm infection, neutrophils have long had the image of the villain, being recruited to the site of larval migration because of damage but participating themselves in tissue injury. With recent developments in neutrophil biology, there is an increasing body of evidence for the role of neutrophils as effector cells in hookworm immunity. In particular, their ability to release extracellular traps, or neutrophil extracellular traps (NETs), confer neutrophils a larvicidal activity. Here, we review recent evidence in this nascent field and discuss the avenue for future research on NETs/hookworm interactions.

Trypanosoma cruzi Mitochondrial Peroxiredoxin Promotes Infectivity in Macrophages and Attenuates Nifurtimox Toxicity

Trypanosoma cruzi is the causative agent of Chagas disease which is currently treated by nifurtimox (NFX) and benznidazole (BZ). Nevertheless, the mechanism of action of NFX is not completely established. Herein, we show the protective effects of T. cruzi mitochondrial peroxiredoxin (MPX) in macrophage infections and in response to NFX toxicity. After a 3-day treatment of epimastigotes with NFX, MPX content increased (2.5-fold) with respect to control, and interestingly, an MPX-overexpressing strain was more resistant to the drug. The generation of mitochondrial reactive species and the redox status of the low molecular weight thiols of the parasite were not affected by NFX treatment indicating the absence of oxidative stress in this condition. Since MPX was shown to be protective and overexpressed in drug-challenged parasites, non-classical peroxiredoxin activity was studied. We found that recombinant MPX exhibits holdase activity independently of its redox state and that its overexpression was also observed in temperature-challenged parasites. Moreover, increased holdase activity (2-fold) together with an augmented protease activity (proteasome-related) and an enhancement in ubiquitinylated proteins was found in NFX-treated parasites. These results suggest a protective role of MPX holdase activity toward NFX toxicity. Trypanosoma cruzi has a complex life cycle, part of which involves the invasion of mammalian cells, where parasite replication inside the host occurs. In the early stages of the infection, macrophages recognize and engulf T. cruzi with the generation of reactive oxygen and nitrogen species toward the internalized parasite. Parasites overexpressing MPX produced higher macrophage infection yield compared with wild-type parasites. The relevance of peroxidase vs. holdase activity of MPX during macrophage infections was assessed using conoidin A (CA), a covalent, cell-permeable inhibitor of peroxiredoxin peroxidase activity. Covalent adducts of MPX were detected in CA-treated parasites, which proves its action in vivo. The pretreatment of parasites with CA led to a reduced infection index in macrophages revealing that the peroxidase activity of peroxiredoxin is crucial during this infection process. Our results confirm the importance of peroxidase activity during macrophage infection and provide insights for the relevance of MPX holdase activity in NFX resistance.

The Role of Peroxiredoxins in the Regulation of Sepsis

Oxidative stress, a result of a disturbance in redox homeostasis, is considered to be one of the main aggravating events in the pathogenesis of immune disorders. Peroxiredoxins (Prdxs) are an enzyme family that catalyzes the reduction of peroxides, including hydrogen peroxide, lipid peroxides, and nitrogen peroxides. Although the maintenance of cellular redox homeostasis through Prdxs is essential for surviving in adverse environments, Prdxs also participate in the regulation of cellular signal transduction by modulating the activities of a panel of molecules involved in the signal transduction process. Although Prdxs were discovered as intracellular anti-oxidative enzymes, recent research has revealed that Prdxs also play important roles in the extracellular milieu. Indeed, Prdxs have been shown to have the capacity to activate immune cells through ligation with innate immune receptors such as toll-like receptors (TLRs). In this review, we will summarize the intracellular as well as extracellular roles of Prdxs for and against the pathogenesis of inflammatory disorders including sepsis, hemorrhagic shock, and drug-induced liver injury.

Mining nematode protein secretomes to explain lifestyle and host specificity

Parasitic nematodes are highly successful pathogens, inflicting disease on humans, animals and plants. Despite great differences in their life cycles, host preference and transmission modes, these parasites share a common capacity to manipulate their host's immune system. This is at least partly achieved through the release of excretory/secretory proteins, the most well-characterized component of nematode secretomes, that are comprised of functionally diverse molecules. In this work, we analyzed published protein secretomes of parasitic nematodes to identify common patterns as well as species-specific traits. The 20 selected organisms span 4 nematode clades, including plant pathogens, animal parasites, and the free-living species Caenorhabditis elegans. Transthyretin-like proteins were the only component common to all adult secretomes; many other protein classes overlapped across multiple datasets. The glycolytic enzymes aldolase and enolase were present in all parasitic species, but missing from C. elegans. Secretomes from larval stages showed less overlap between species. Although comparison of secretome composition across species and life-cycle stages is challenged by the use of different methods and depths of sequencing among studies, our workflow enabled the identification of conserved protein families and pinpointed elements that may have evolved as to enable parasitism. This strategy, extended to more secretomes, may be exploited to prioritize therapeutic targets in the future.

Current status of quinoxaline and quinoxaline 1,4-di-N-oxides derivatives as potential antiparasitic agents

Parasitic diseases are a public health problem, especially in developing countries where millions of people are affected every year. Current treatments have several drawbacks: emerging resistance to the existing drugs, lack of efficacy, and toxic side effects. Therefore, new antiparasitic drugs are urgently needed to treat and control diseases that affect human health, such as malaria, Chagas disease, leishmaniasis, amebiasis, giardiasis schistosomiasis, and filariasis, among others. Quinoxaline is a compound containing a benzene ring and a pyrazine ring. The oxidation of both pyrazine ring nitrogens allows the obtention of quinoxaline 1,4-di-N-oxides (QdNOs) derivatives. By modifying the chemical structure of these compounds, it is possible to obtain a wide variety of biological properties. This review investigated the activity of quinoxaline derivatives and QdNOs against different protozoan parasites and helminths. We also cover the structure-activity relationship (SAR) and summarize the main findings related to their mechanisms of action from published works in recent years. However, further studies are needed to determine specific molecular targets. This review aims to highlight the new development of antiparasitic drugs with better pharmacological profiles than current treatments.

Structural determinants of multimerization and dissociation in 2-Cys peroxiredoxin chaperone function

Peroxiredoxins (PRDXs) are abundant peroxidases present in all kingdoms of life. Recently, they have been shown to also carry out additional roles as molecular chaperones. To address this emerging supplementary function, this review focuses on structural studies of 2-Cys PRDX systems exhibiting chaperone activity. We provide a detailed understanding of the current knowledge of structural determinants underlying the chaperone function of PRDXs. Specifically, we describe the mechanisms which may modulate their quaternary structure to facilitate interactions with client proteins and how they are coordinated with the functions of other molecular chaperones. Following an overview of PRDX molecular architecture, we outline structural details of the presently best-characterized peroxiredoxins exhibiting chaperone function and highlight common denominators. Finally, we discuss the remarkable structural similarities between 2-Cys PRDXs, small HSPs, and J-domain-independent Hsp40 holdases in terms of their functions and dynamic equilibria between low- and high-molecular-weight oligomers.

Repurposing of auranofin and honokiol as antifungals against Scedosporium species and the related fungus Lomentospora prolificans

The slowing-down de novo drug-discovery emphasized the importance of repurposing old drugs. This is particularly true when combating infections caused by therapy-refractory microorganisms, such as Scedosporium species and Lomentospora prolificans. Recent studies on Scedosporium responses to oxidative stress underscored the importance of targeting the underlying mechanisms. Auranofin, ebselen, PX-12, honokiol, and to a lesser extent, conoidin A are known to disturb redox-homeostasis systems in many organisms. Their antifungal activity was assessed against 27 isolates belonging to the major Scedosporium species: S. apiospermum, S. aurantiacum, S. boydii, S. dehoogii, S. minutisporum, and Lomentospora prolificans. Auranofin and honokiol were the most active against all Scedosporium species (mean MIC₅₀ values of 2.875 and 6.143 μg/ml, respectively) and against L. prolificans isolates (mean MIC₅₀ values of 4.0 and 3.563μg/ml respectively). Combinations of auranofin with voriconazole or honokiol revealed additive effects against 9/27 and 18/27 isolates, respectively. Synergistic interaction between auranofin and honokiol was only found against one isolate of L. prolificans. The effects of auranofin upon exposure to oxidative stress were also investigated. For all species except S. dehoogii, the maximal growth in the presence of auranofin significantly decreased when adding a sublethal dose of menadione. The analysis of the expression of genes encoding oxidoreductase enzymes upon exposure of S. apiospermum to honokiol unveiled the upregulation of many genes, especially those coding peroxiredoxins, thioredoxin reductases, and glutaredoxins. Altogether, these data suggest that auranofin and honokiol act via dampening the redox balance and support their repurposing as antifungals against Scedosporium species and L. prolificans.

Cullin-5 neddylation-mediated NOXA degradation is enhanced by PRDX1 oligomers in colorectal cancer

NOXA, a BH3-only proapoptotic protein involved in regulating cell death decisions, is highly expressed but short-lived in colorectal cancer (CRC). Neddylated cullin-5 (CUL5)-mediated ubiquitination and degradation of NOXA is crucial to prevent its overaccumulation and maintain an appropriate action time. However, how this process is manipulated by CRC cells commonly exposed to oxidative stress remain unknown. The peroxiredoxin PRDX1, a conceivable antioxidant overexpressed in CRC tissues, has been shown to inhibit apoptosis and TRAF6 ubiquitin-ligase activity. In this study, we found that PRDX1 inhibits CRC cell apoptosis by downregulating NOXA. Mechanistically, PRDX1 promotes NOXA ubiquitination and degradation, which completely depend on CUL5 neddylation. Further studies have demonstrated that PRDX1 oligomers bind with both the Nedd8-conjugating enzyme UBE2F and CUL5 and that this tricomplex is critical for CUL5 neddylation, since silencing PRDX1 or inhibiting PRDX1 oligomerization greatly dampens CUL5 neddylation and NOXA degradation. An increase in reactive oxygen species (ROS) is not only a hallmark of cancer cells but also the leading driving force for PRDX1 oligomerization. As shown in our study, although ROS play a role in upregulating NOXA mRNA transcription, ROS scavenging in CRC cells by N-acetyl-L-cysteine (NAC) can significantly reduce CUL5 neddylation and extend the NOXA protein half-life. Therefore, in CRC, PRDX1 plays a key role in maintaining intracellular homeostasis under conditions of high metabolic activity by reinforcing UBE2F-CUL5-mediated degradation of NOXA, which is also evidenced in the resistance of CRC cells to etoposide treatment. Based on these findings, targeting PRDX1 could be an effective strategy to overcome the resistance of CRC to DNA damage-inducing chemotherapeutics.

Real-time monitoring of peroxiredoxin oligomerization dynamics in living cells

Peroxiredoxins are most central to the cellular adaptation against oxidative stress. They act as oxidant scavengers, stress sensors, transmitters of signals, and chaperones, and they possess a unique quaternary switch that is intimately related to these functions. However, so far it has not been possible to monitor peroxiredoxin structural changes in the intact cellular environment. This study presents genetically encoded probes, based on homo-FRET (Förster resonance energy transfer between identical fluorophores) fluorescence polarization, that allow following these quaternary changes in real time, in living cells. We envisage that these probes can be used to address a broad range of questions related to the function of peroxiredoxins.

Peroxiredoxins are central to cellular redox homeostasis and signaling. They serve as peroxide scavengers, sensors, signal transducers, and chaperones, depending on conditions and context. Typical 2-Cys peroxiredoxins are known to switch between different oligomeric states, depending on redox state, pH, posttranslational modifications, and other factors. Quaternary states and their changes are closely connected to peroxiredoxin activity and function but so far have been studied, almost exclusively, outside the context of the living cell. Here we introduce the use of homo-FRET (Förster resonance energy transfer between identical fluorophores) fluorescence polarization to monitor dynamic changes in peroxiredoxin quaternary structure inside the crowded environment of living cells. Using the approach, we confirm peroxide- and thioredoxin-related quaternary transitions to take place in cellulo and observe that the relationship between dimer–decamer transitions and intersubunit disulfide bond formation is more complex than previously thought. Furthermore, we demonstrate the use of the approach to compare different peroxiredoxin isoforms and to identify mutations and small molecules affecting the oligomeric state inside cells. Mutagenesis experiments reveal that the dimer–decamer equilibrium is delicately balanced and can be shifted by single-atom structural changes. We show how to use this insight to improve the design of peroxiredoxin-based redox biosensors.

Intracerebral Hemorrhage-Induced Brain Injury in Rats: the Role of Extracellular Peroxiredoxin 2

Red blood cell (RBC) lysis within the hematoma causes brain injury following intracerebral hemorrhage. Peroxiredoxin 2 (PRX-2) is the third most abundant protein in RBCs and this study examined the potential role of PRX-2 in inducing brain injury in rats. First, adult male Sprague-Dawley rats had an intracaudate injection of lysed RBCs or saline. Brains were harvested at 1 h to measure PRX-2 levels. Second, rats had an intracaudate injection of either recombinant PRX-2, heat-inactivated PRX-2, or saline. Third, rats had intracaudate co-injection of lysed RBCs with conoidin A, a PRX-2 inhibitor, or vehicle. For the second and third parts of studies, behavioral tests were performed and all rats had magnetic resonance imaging prior to euthanasia for brain immunohistochemistry and Western blotting. We found that brain PRX-2 levels were increased after lysed RBC injection. Intracaudate injection of PRX-2 resulted in blood-brain barrier disruption, brain swelling, neutrophil infiltration, microglia activation, neuronal death, and neurological deficits. Intracerebral injection of lysed RBCs induced brain injury, which was reduced by conoidin A. These results suggest that extracellular PRX-2 released from hematoma can cause brain injury following brain hemorrhage and could be a potential therapeutic target.

Twenty-five-year research progress in hookworm excretory/secretory products

Hookworm infection is a major public health problem that threatens about 500 million people throughout tropical areas of the world. Adult hookworms survive for many years in the host intestine, where they suck blood, causing iron deficiency anemia and malnutrition. Numerous molecules, named excretory/secretory (ES) products, are secreted by hookworm adults and/or larvae to aid in parasite survival and pathobiology. Although the molecular cloning and characterization of hookworm ES products began 25 years ago, the biological role and molecular nature of many of them are still unclear. Hookworm ES products, with distinct structures and functions, have been linked to many essential events in the disease pathogenesis. These events include host invasion and tissue migration, parasite nourishment and reproduction, and immune modulation. Several of these products represent promising vaccine targets for controlling hookworm disease and therapeutic targets for many inflammatory diseases. This review aims to summarize our present knowledge about hookworm ES products, including their role in parasite biology, host-parasite interactions, and as vaccine and pharmaceutical targets and to identify research gaps and future research directions in this field.

Characterisation of a niche-specific excretory-secretory peroxiredoxin from the parasitic nematode Teladorsagia circumcincta

Background

The primary cause of parasitic gastroenteritis in small ruminants in temperate regions is the brown stomach worm, Teladorsagia circumcincta. Host immunity to this parasite is slow to develop, consistent with the ability of T. circumcincta to suppress the host immune response. Previous studies have shown that infective fourth-stage T. circumcincta larvae produce excretory–secretory products that are able to modulate the host immune response. The objective of this study was to identify immune modulatory excretory–secretory proteins from populations of fourth-stage T. circumcincta larvae present in two different host-niches: those associated with the gastric glands (mucosal-dwelling larvae) and those either loosely associated with the mucosa or free-living in the lumen (lumen-dwelling larvae).

Results

In this study excretory–secretory proteins from mucosal-dwelling and lumen-dwelling T. circumcincta fourth stage larvae were analysed using comparative 2-dimensional gel electrophoresis. A total of 17 proteins were identified as differentially expressed, with 14 proteins unique to, or enriched in, the excretory–secretory proteins of mucosal-dwelling larvae. One of the identified proteins, unique to mucosal-dwelling larvae, was a putative peroxiredoxin (T. circumcincta peroxiredoxin 1, Tci-Prx1). Peroxiredoxin orthologs from the trematode parasites Schistosoma mansoni and Fasciola hepatica have previously been shown to alternatively activate macrophages and play a key role in promoting parasite induced Th2 type immunity. Here we demonstrate that Tci-Prx1 is expressed in all infective T. circumcincta life-stages and, when produced as a recombinant protein, has peroxidase activity, whereby hydrogen peroxide (H₂O₂) is reduced and detoxified. Furthermore, we use an in vitro macrophage stimulation assay to demonstrate that, unlike peroxiredoxins from trematode parasites Schistosoma mansoni and Fasciola hepatica, Tci-Prx1 is unable to alternatively activate murine macrophage cells.

Conclusions

In this study, we identified differences in the excretory–secretory proteome of mucosal-dwelling and lumen-dwelling infective fourth-stage T. circumcincta larvae, and demonstrated the utility of this comparative proteomic approach to identify excretory–secretory proteins of potential importance for parasite survival and/or host immune modulation.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3593-6) contains supplementary material, which is available to authorized users.

Engineering peroxiredoxin 3 to facilitate control over self-assembly

Oligomeric proteins are abundant in nature and are useful for a range of nanotechnological applications; however, a key requirement in using these proteins is controlling when and how they form oligomeric assemblies. Often, protein oligomerisation is triggered by various cellular signals, allowing for controllable oligomerisation. An example of this is human peroxiredoxin 3 (Prx), a stable protein that natively forms dimers, dodecameric rings, stacks, and tubes in response to a range of environmental stimuli. Although we know the key environmental stimuli for switching between different oligomeric states of Prx, we still have limited molecular knowledge and control over the formation and size of the protein's stacks and tubes. Here, we have generated a range of Prx mutants with either a decreased or knocked out ability to stack, and used both imaging and solution studies to show that Prx stacks through electrostatic interactions that are stabilised by a hydrogen bonding network. Furthermore, we show that altering the length of the polyhistidine tag will alter the length of the Prx stacks, with longer polyhistidine tags giving longer stacks. Finally, we have analysed the effect a variety of heavy metals have on the oligomeric state of Prx, wherein small transition metals like nickel enhances Prx stacking, while larger positively charged metals like tungstate ions can prevent Prx stacking. This work provides further structural characterisation of Prx, to enhance its use as a platform from which to build protein nanostructures for a variety of applications.

Frenolicin B Targets Peroxiredoxin 1 and Glutaredoxin 3 to Trigger ROS/4E-BP1-Mediated Antitumor Effects

Peroxiredoxin 1 (Prx1) and glutaredoxin 3 (Grx3) are two major antioxidant proteins that play a critical role in maintaining redox homeostasis for tumor progression. Here, we identify the prototypical pyranonaphthoquinone natural product frenolicin B (FB) as a selective inhibitor of Prx1 and Grx3 through covalent modification of active-site cysteines. FB-targeted inhibition of Prx1 and Grx3 results in a decrease in cellular glutathione levels, an increase of reactive oxygen species (ROS), and concomitant inhibition of cancer cell growth, largely by activating the peroxisome-bound tuberous sclerosis complex to inhibit mTORC1/4E-BP1 signaling axis. FB structure-activity relationship studies reveal a positive correlation between inhibition of 4E-BP1 phosphorylation, ROS-mediated cancer cell cytotoxicity, and suppression of tumor growth in vivo. These findings establish FB as the most potent Prx1/Grx3 inhibitor reported to date and also notably highlight 4E-BP1 phosphorylation status as a potential predictive marker in response to ROS-based therapies in cancer.

A Secreted 'Candidatus Liberibacter asiaticus' Peroxiredoxin Simultaneously Suppresses Both Localized and Systemic Innate Immune Responses In Planta

The oxidative (H₂O₂) burst is a seminal feature of the basal plant defense response to attempted pathogen invasions. In 'Candidatus Liberibacter asiaticus' UF506, expression of the SC2 prophage-encoded secreted peroxidase (F489_gp15) increases bacterial fitness and delays symptom progression in citrus. Two chromosomal 1-Cys peroxiredoxin genes, CLIBASIA_RS00940 (Lasprx5) and CLIBASIA_RS00445 (Lasbcp), are conserved among all sequenced 'Ca. L. asiaticus' strains, including those lacking prophages. Both LasBCP and LasdPrx5 have only a single conserved peroxidatic Cys (C_P/SH) and lack the resolving Cys (C_R/SH). Lasprx5 appeared to be a housekeeping gene with similar moderate transcript abundance in both 'Ca. L. asiaticus'-infected psyllids and citrus. By contrast, Lasbcp was expressed only in planta, similar to the expression of the SC2 peroxidase. Since 'Ca. L. asiaticus' is uncultured, Lasbcp and Lasprx5 were functionally validated in a cultured surrogate species, Liberibacter crescens, and both genes significantly increased oxidative stress tolerance and cell viability in culture. LasBCP was nonclassically secreted and, in L. crescens, conferred 214-fold more resistance to tert-butyl hydroperoxide (tBOOH) than wild type. Transient overexpression of Lasbcp in tobacco suppressed H₂O₂-mediated transcriptional activation of RbohB, the key gatekeeper of the systemic plant defense signaling cascade. Lasbcp expression did not interfere with the perception of 'Ca. L. asiaticus' flagellin (flg22_Las) but interrupted the downstream activation of RbohB and stereotypical deposition of callose in tobacco. Critically, LasBCP also protected against tBOOH-induced peroxidative degradation of lipid membranes in planta, preventing subsequent accumulation of antimicrobial oxylipins that can also trigger the localized hypersensitive cell death response.

Hookworms in Emergency Department: The ＂Vampire＂ Within

Hookworms infection is a soil-transmitted helminthic disease particularly endemic in developing counties of tropical regions. It is attributed mainly to two human pathogens nematodes namely Necator americanus and Ancylostoma duodenale. Although the disease has been characterized as "neglected" is very diffi cult to be eliminated and the economic consequences are great. Worms are fed with blood of hosts in small intestine and cause typically iron deficiency anemia with relevant symptoms as well as eosinophilia. Patients admitted in emergency department claim often diffuse general symptoms, whereas cases with obscure gastrointestinal bleeding can be seen. Within this brief review, after introducing some basic elements of hookworms' epidemiology, taxonomy and socioeconomic problem is emphasized, pathogenesis, and life cycle of parasite are concisely explained. Furthermore, clinical manifestations often or rarely seen in emergency department are described. Therapeutic options are also enclosed. Awareness of the problem and critical thinking of patients coming from endemic regions could result to identifying more hookworm cases and their therapy will efficiently alleviate not only the patients per se but health system and societies as well.

Piecing Together How Peroxiredoxins Maintain Genomic Stability

Peroxiredoxins, a highly conserved family of thiol oxidoreductases, play a key role in oxidant detoxification by partnering with the thioredoxin system to protect against oxidative stress. In addition to their peroxidase activity, certain types of peroxiredoxins possess other biochemical activities, including assistance in preventing protein aggregation upon exposure to high levels of oxidants (molecular chaperone activity), and the transduction of redox signals to downstream proteins (redox switch activity). Mice lacking the peroxiredoxin Prdx1 exhibit an increased incidence of tumor formation, whereas baker's yeast (Saccharomyces cerevisiae) lacking the orthologous peroxiredoxin Tsa1 exhibit a mutator phenotype. Collectively, these findings suggest a potential link between peroxiredoxins, control of genomic stability, and cancer etiology. Here, we examine the potential mechanisms through which Tsa1 lowers mutation rates, taking into account its diverse biochemical roles in oxidant defense, protein homeostasis, and redox signaling as well as its interplay with thioredoxin and thioredoxin substrates, including ribonucleotide reductase. More work is needed to clarify the nuanced mechanism(s) through which this highly conserved peroxidase influences genome stability, and to determine if this mechanism is similar across a range of species.

Luteolin ameliorates rat myocardial ischaemia-reperfusion injury through activation of peroxiredoxin II

BACKGROUND AND PURPOSE

Antioxidants provide a promising therapeutic effect for the cardiovascular disease. Luteolin, a polyphenolic bioflavonoid, is known to confer cardioprotection, although the underlying mechanisms, especially the role of luteolin on the antioxidant enzymes, such as the peroxiredoxin family, remain unknown.

EXPERIMENTAL APPROACH

We measured the effects of luteolin on myocardial ischaemia/reperfusion (MI/R) injury in vivo (Sprague-Dawley rats) and in vitro, together with the underlying mechanisms, with a focus on signalling by peroxiredoxins. H9c2 cells were used to assess the changes in peroxiredoxins and the other antioxidant enzymes. Oxidative stress, cardiac function, LDH release, ROS and infarct size were also assayed.

KEY RESULTS

Luteolin exerted significant cardioprotective effects in vivo and in vitro via improving cardiac function, increasing the expression of anti-apoptotic protein Bcl-2 and decreasing the pro-apoptotic protein Bax and active caspases 3 and 9, associated with MI/R. Mechanistically, luteolin markedly enhanced expression of peroxiredoxin II, without significant effects on other forms of peroxiredoxin, catalase or SOD1. Molecular docking showed that luteolin could indeed bind to the enzymic active pocket of peroxiredoxin II. Furthermore, down-regulation of peroxiredoxin II by peroxiredoxin II-antisense, administered by adenovirus infection of H9c2 cardiomyocytes, and inhibition of peroxiredoxin II in vivo significantly reversed the cardioprotective effects of luteolin.

CONCLUSIONS AND IMPLICATIONS

Our findings, for the first time, demonstrate that luteolin protects against MI/R injury through promoting signalling through the endogenous antioxidant enzyme, peroxiredoxin II, indicating the important beneficial role of this antioxidant system in the heart.

Evidence for the interaction of peroxiredoxin-4 with the store-operated calcium channel activator STIM1 in liver cells

Ca²⁺ entry through store-operated Ca²⁺ channels (SOCs) in the plasma membrane (PM) of hepatocytes plays a central role in the hormonal regulation of liver metabolism. SOCs are composed of Orai1, the channel pore protein, and STIM1, the activator protein, and are regulated by hormones and reactive oxygen species (ROS). In addition to Orai1, STIM1 also interacts with several other intracellular proteins. Most previous studies of the cellular functions of Orai1 and STIM1 have employed immortalised cells in culture expressing ectopic proteins tagged with a fluorescent polypeptide such as GFP. Little is known about the intracellular distributions of endogenous Orai1 and STIM1. The aims are to determine the intracellular distribution of endogenous Orai1 and STIM1 in hepatocytes and to identify novel STIM1 binding proteins. Subcellular fractions of rat liver were prepared by homogenisation and differential centrifugation. Orai1 and STIM1 were identified and quantified by western blot. Orai1 was found in the PM (0.03%), heavy (44%) and light (27%) microsomal fractions, and STIM1 in the PM (0.09%), and heavy (85%) and light (13%) microsomal fractions. Immunoprecipitation of STIM1 followed by LC/MS or western blot identified peroxiredoxin-4 (Prx-4) as a potential STIM1 binding protein. Prx-4 was found principally in the heavy microsomal fraction. Knockdown of Prx-4 using siRNA, or inhibition of Prx-4 using conoidin A, did not affect Ca²⁺ entry through SOCs but rendered SOCs susceptible to inhibition by H₂O₂. It is concluded that, in hepatocytes, a considerable proportion of endogenous Orai1 and STIM1 is located in the rough ER. In the rough ER, STIM1 interacts with Prx-4, and this interaction may contribute to the regulation by ROS of STIM1 and SOCs.

A PRDX1-p38α heterodimer amplifies MET-driven invasion of IDH-wildtype and IDH-mutant gliomas

The Peroxiredoxin 1 (PRDX1) gene maps to chromosome arm 1p and is hemizygously deleted and epigenetically silenced in isocitrate dehydrogenase 1 or 2 (IDH)-mutant and 1p/19q-codeleted oligodendroglial tumors. In contrast, IDH-wildtype astrocytic gliomas including glioblastomas mostly lack epigenetic silencing and express PRDX1 protein. In our study, we investigated how PRDX1 contributes to the infiltrative growth of IDH-wildtype gliomas. Focusing on p38α-dependent pathways, we analyzed clinical data from 133 patients of the NOA-04 trial cohort to look for differences in the gene expression profiles of gliomas with wildtype or mutant IDH. Biochemical interaction studies as well as in vitro and ex vivo migration studies were used to establish a biological role of PRDX1 in maintaining pathway activity. Whole-brain high-resolution ultramicroscopy and survival analyses of pre-clinical mouse models for IDH-wildtype gliomas were then used for in vivo confirmation. Based on clinical data, we found that the absence of PRDX1 is associated with changes in the expression of MET/HGF signaling components. PRDX1 forms a heterodimer with p38α mitogen-activated protein kinase 14 (MAPK14), stabilizing phospho-p38α in glioma cells. This process amplifies hepatocyte growth factor (HGF)-mediated signaling and stimulates actin cytoskeleton dynamics that promote glioma cell migration. Whole-brain high-resolution ultramicroscopy confirms these findings, indicating that PRDX1 promotes glioma brain invasion in vivo. Finally, reduced expression of PRDX1 increased survival in mouse glioma models. Thus, our preclinical findings suggest that PRDX1 expression levels may serve as a molecular marker for patients who could benefit from targeted inhibition of MET/HGF signaling.

Structural and biochemical analyses reveal ubiquitin C-terminal hydrolase-L1 as a specific client of the peroxiredoxin II chaperone

Peroxiredoxins (Prxs) play dual roles as both thiol-peroxidases and molecular chaperones. Peroxidase activity enables various intracellular functions, however, the physiological roles of Prxs as chaperones are not well established. To study the chaperoning function of Prx, we previously sought to identify heat-induced Prx-binding proteins as the clients of a Prx chaperone. By using His-tagged Prx I as a bait, we separated ubiquitin C-terminal hydrolase-L1 (UCH-L1) as a heat-induced Prx I binding protein from rat brain crude extracts. Protein complex immunoprecipitation with HeLa cell lysates revealed that both Prx I and Prx II interact with UCH-L1. However, Prx II interacted considerably more favorably with UCH-L1 than Prx I. Prx II exhibited more effective molecular chaperone activity than Prx I when UCH-L1 was the client. Prx II interacted with UCH-L1 through its C-terminal region to protect UCH-L1 from thermal or oxidative inactivation. We found that chaperoning via interaction through C-terminal region (specific-client chaperoning) is more efficient than that involving oligomeric structural change (general-client chaperoning). Prx II binds either thermally or oxidatively unfolding early intermediates of specific clients and thereby shifted the equilibrium towards their native state. We conclude that this chaperoning mechanism provides a very effective and selective chaperoning activity.

Active-site plasticity revealed in the asymmetric dimer of AnPrx6 the 1-Cys peroxiredoxin and molecular chaperone from Anabaena sp. PCC 7210

Peroxiredoxins (Prxs) are vital regulators of intracellular reactive oxygen species levels in all living organisms. Their activity depends on one or two catalytically active cysteine residues, the peroxidatic Cys (C_P) and, if present, the resolving Cys (C_R). A detailed catalytic cycle has been derived for typical 2-Cys Prxs, however, little is known about the catalytic cycle of 1-Cys Prxs. We have characterized Prx6 from the cyanobacterium Anabaena sp. strain PCC7120 (AnPrx6) and found that in addition to the expected peroxidase activity, AnPrx6 can act as a molecular chaperone in its dimeric state, contrary to other Prxs. The AnPrx6 crystal structure at 2.3 Å resolution reveals different active site conformations in each monomer of the asymmetric obligate homo-dimer. Molecular dynamic simulations support the observed structural plasticity. A FSH motif, conserved in 1-Cys Prxs, precedes the active site PxxxTxxCp signature and might contribute to the 1-Cys Prx reaction cycle.

Pro-Apoptotic Effects of JDA-202, a Novel Natural Diterpenoid, on Esophageal Cancer Through Targeting Peroxiredoxin I

AIMS

Esophageal cancer (EC) is an aggressive malignancy and the most common solid tumor of gastrointestinal tract all over the world, with high incidence in Asia. The current study was designed to investigate the anticancer efficacy and mechanism that is involved in the action of a natural ent-kaurene diterpenoid, JDA-202, targeting EC.

RESULTS

We found that an antioxidant protein peroxiredoxin I (Prx I) was upregulated in human EC tissues as well as in EC cell lines. JDA-202, a novel natural compound isolated from Isodon rubescens (Labiatae), was proved to possess strong anti-proliferative activities on those cell lines. Importantly, JDA-202 does not only bind to Prx I directly and markedly inhibit the activity of Prx I in vitro, but it also significantly induces hydrogen peroxide (H₂O₂)-related cell death. Furthermore, overexpression of Prx I significantly reversed EC109 cell apoptosis caused by JDA-202, whereas short interfering RNA (siRNA)-induced Prx I knockdown resulted in marked cell death even without JDA-202 pretreatment. On the other hand, the increased phosphorylation of mitogen-activated protein kinase (MAPK) proteins (c-Jun N-terminal kinase [JNK], p38, and extracellular signal-regulated kinase [ERK]) by JDA-202 was suppressed by N-acetylcysteine (NAC) or catalase, a known reactive oxygen species (ROS) or H₂O₂ scavenger. JDA-202 also significantly inhibited the growth of EC109 tumor xenograft, without significant body weight loss and multi-organ toxicities. Innovation and Conclusion: Our findings, for the first time, demonstrated that JDA-202 may serve as a lead compound, targeting the overexpressed Prx I in EC cell lines and ROS accumulation as well as inhibiting the activation of their downstream targets in MAPKs. Antioxid. Redox Signal. 27, 73-92.

Interaction of tankyrase and peroxiredoxin II is indispensable for the survival of colorectal cancer cells

Mammalian 2-Cys peroxiredoxin (Prx) enzymes are overexpressed in most cancer tissues, but their specific signaling role in cancer progression is poorly understood. Here we demonstrate that Prx type II (PrxII) plays a tumor-promoting role in colorectal cancer by interacting with a poly(ADP-ribose) polymerase (PARP) tankyrase. PrxII deletion in mice with inactivating mutation of adenomatous polyposis coli (APC) gene reduces intestinal adenomatous polyposis via Axin/β-catenin axis and thereby promotes survival. In human colorectal cancer cells with APC mutations, PrxII depletion consistently reduces the β-catenin levels and the expression of β-catenin target genes. Essentially, PrxII depletion hampers the PARP-dependent Axin1 degradation through tankyrase inactivation. Direct binding of PrxII to tankyrase ARC4/5 domains seems to be crucial for protecting tankyrase from oxidative inactivation. Furthermore, a chemical compound targeting PrxII inhibits the expansion of APC-mutant colorectal cancer cells in vitro and in vivo tumor xenografts. Collectively, this study reveals a redox mechanism for regulating tankyrase activity and implicates PrxII as a targetable antioxidant enzyme in APC-mutation-positive colorectal cancer.

2-Cys peroxiredoxin (Prx) enzymes are highly expressed in most cancers but how they promote cancer progression is unclear. Here the authors show that in colorectal cancers with APC mutation, PrxII binds to tankyrase and prevents its oxidative inactivation, thereby preventing Axin1-dependent degradation of ²b-catenin.

Trapping redox partnerships in oxidant-sensitive proteins with a small, thiol-reactive cross-linker

A broad range of redox-regulated proteins undergo reversible disulfide bond formation on oxidation-prone cysteine residues. Heightened reactivity of the thiol groups in these cysteines also increases susceptibility to modification by organic electrophiles, a property that can be exploited in the study of redox networks. Here, we explored whether divinyl sulfone (DVSF), a thiol-reactive bifunctional electrophile, cross-links oxidant-sensitive proteins to their putative redox partners in cells. To test this idea, previously identified oxidant targets involved in oxidant defense (namely, peroxiredoxins, methionine sulfoxide reductases, sulfiredoxin, and glutathione peroxidases), metabolism, and proteostasis were monitored for cross-link formation following treatment of Saccharomyces cerevisiae with DVSF. Several proteins screened, including multiple oxidant defense proteins, underwent intermolecular and/or intramolecular cross-linking in response to DVSF. Specific redox-active cysteines within a subset of DVSF targets were found to influence cross-linking; in addition, DVSF-mediated cross-linking of its targets was impaired in cells first exposed to oxidants. Since cross-linking appeared to involve redox-active cysteines in these proteins, we examined whether potential redox partners became cross-linked to them upon DVSF treatment. Specifically, we found that several substrates of thioredoxins were cross-linked to the cytosolic thioredoxin Trx2 in cells treated with DVSF. However, other DVSF targets, like the peroxiredoxin Ahp1, principally formed intra-protein cross-links upon DVSF treatment. Moreover, additional protein targets, including several known to undergo S-glutathionylation, were conjugated via DVSF to glutathione. Our results indicate that DVSF is of potential use as a chemical tool for irreversibly trapping and discovering thiol-based redox partnerships within cells.

Quinoxaline 1,4-di-N-Oxides: Biological Activities and Mechanisms of Actions

Quinoxaline 1,4-di-N-oxides (QdNOs) have manifold biological properties, including antimicrobial, antitumoral, antitrypanosomal and antiinflammatory/antioxidant activities. These diverse activities endow them broad applications and prospects in human and veterinary medicines. As QdNOs arouse widespread interest, the evaluation of their medicinal chemistry is still in progress. In the meantime, adverse effects have been reported in some of the QdNO derivatives. For example, genotoxicity and bacterial resistance have been found in QdNO antibacterial growth promoters, conferring urgent need for discovery of new QdNO drugs. However, the modes of actions of QdNOs are not fully understood, hindering the development and innovation of these promising compounds. Here, QdNOs are categorized based on the activities and usages, among which the antimicrobial activities are consist of antibacterial, antimycobacterial and anticandida activities, and the antiprotozoal activities include antitrypanosomal, antimalarial, antitrichomonas, and antiamoebic activities. The structure-activity relationship and the mode of actions of each type of activity of QdNOs are summarized, and the toxicity and the underlying mechanisms are also discussed, providing insight for the future research and development of these fascinating compounds.

Typical 2-Cys peroxiredoxins in human parasites: Several physiological roles for a potential chemotherapy target

Peroxiredoxins (Prxs) are ubiquitary proteins able to play multiple physiological roles, that include thiol-dependent peroxidase, chaperone holdase, sensor of H2O2, regulator of H2O2-dependent signal cascades, and modulator of the immune response. Prxs have been found in a great number of human pathogens, both eukaryotes and prokaryotes. Gene knock-out studies demonstrated that Prxs are essential for the survival and virulence of at least some of the pathogens tested, making these proteins potential drug targets. However, the multiplicity of roles played by Prxs constitutes an unexpected obstacle to drug development. Indeed, selective inhibitors of some of the functions of Prxs are known (namely of the peroxidase and holdase functions) and are here reported. However, it is often unclear which function is the most relevant in each pathogen, hence which one is most desirable to inhibit. Indeed there are evidences that the main physiological role of Prxs may not be the same in different parasites. We here review which functions of Prxs have been demonstrated to be relevant in different human parasites, finding that the peroxidase and chaperone activities figure prominently, whereas other known functions of Prxs have rarely, if ever, been observed in parasites, or have largely escaped detection thus far.

Shared weapons of blood- and plant-feeding insects: Surprising commonalities for manipulating hosts

Insects that reprogram host plants during colonization remind us that the insect side of plant-insect story is just as interesting as the plant side. Insect effectors secreted by the salivary glands play an important role in plant reprogramming. Recent discoveries point to large numbers of salivary effectors being produced by a single herbivore species. Since genetic and functional characterization of effectors is an arduous task, narrowing the field of candidates is useful. We present ideas about types and functions of effectors from research on blood-feeding parasites and their mammalian hosts. Because of their importance for human health, blood-feeding parasites have more tools from genomics and other - omics than plant-feeding parasites. Four themes have emerged: (1) mechanical damage resulting from attack by blood-feeding parasites triggers "early danger signals" in mammalian hosts, which are mediated by eATP, calcium, and hydrogen peroxide, (2) mammalian hosts need to modulate their immune responses to the three "early danger signals" and use apyrases, calreticulins, and peroxiredoxins, respectively, to achieve this, (3) blood-feeding parasites, like their mammalian hosts, rely on some of the same "early danger signals" and modulate their immune responses using the same proteins, and (4) blood-feeding parasites deploy apyrases, calreticulins, and peroxiredoxins in their saliva to manipulate the "danger signals" of their mammalian hosts. We review emerging evidence that plant-feeding insects also interfere with "early danger signals" of their hosts by deploying apyrases, calreticulins and peroxiredoxins in saliva. Given emerging links between these molecules, and plant growth and defense, we propose that these effectors interfere with phytohormone signaling, and therefore have a special importance for gall-inducing and leaf-mining insects, which manipulate host-plants to create better food and shelter.

How pH modulates the dimer-decamer interconversion of 2-Cys peroxiredoxins from the Prx1 subfamily

2-Cys peroxiredoxins belonging to the Prx1 subfamily are Cys-based peroxidases that control the intracellular levels of H2O2 and seem to assume a chaperone function under oxidative stress conditions. The regulation of their peroxidase activity as well as the observed functional switch from peroxidase to chaperone involves changes in their quaternary structure. Multiple factors can modulate the oligomeric transitions of 2-Cys peroxiredoxins such as redox state, post-translational modifications, and pH. However, the molecular basis for the pH influence on the oligomeric state of these enzymes is still elusive. Herein, we solved the crystal structure of a typical 2-Cys peroxiredoxin from Leishmania in the dimeric (pH 8.5) and decameric (pH 4.4) forms, showing that conformational changes in the catalytic loop are associated with the pH-induced decamerization. Mutagenesis and biophysical studies revealed that a highly conserved histidine (His(113)) functions as a pH sensor that, at acidic conditions, becomes protonated and forms an electrostatic pair with Asp(76) from the catalytic loop, triggering the decamerization. In these 2-Cys peroxiredoxins, decamer formation is important for the catalytic efficiency and has been associated with an enhanced sensitivity to oxidative inactivation by overoxidation of the peroxidatic cysteine. In eukaryotic cells, exposure to high levels of H2O2 can trigger intracellular pH variations, suggesting that pH changes might act cooperatively with H2O2 and other oligomerization-modulator factors to regulate the structure and function of typical 2-Cys peroxiredoxins in response to oxidative stress.