Localization and functionality of microsporidian iron-sulphur cluster assembly proteins

METTL17 is an Fe-S cluster checkpoint for mitochondrial translation

Friedreich's ataxia (FA) is a debilitating, multisystemic disease caused by the depletion of frataxin (FXN), a mitochondrial iron-sulfur (Fe-S) cluster biogenesis factor. To understand the cellular pathogenesis of FA, we performed quantitative proteomics in FXN-deficient human cells. Nearly every annotated Fe-S cluster-containing protein was depleted, indicating that as a rule, cluster binding confers stability to Fe-S proteins. We also observed depletion of a small mitoribosomal assembly factor METTL17 and evidence of impaired mitochondrial translation. Using comparative sequence analysis, mutagenesis, biochemistry, and cryoelectron microscopy, we show that METTL17 binds to the mitoribosomal small subunit during late assembly and harbors a previously unrecognized [Fe4S4]2+ cluster required for its stability. METTL17 overexpression rescued the mitochondrial translation and bioenergetic defects, but not the cellular growth, of FXN-depleted cells. These findings suggest that METTL17 acts as an Fe-S cluster checkpoint, promoting translation of Fe-S cluster-rich oxidative phosphorylation (OXPHOS) proteins only when Fe-S cofactors are replete.

Biogenesis, inheritance, and 3D ultrastructure of the microsporidian mitosome

During the reductive evolution of obligate intracellular parasites called microsporidia, a tiny remnant mitochondrion (mitosome) lost its typical cristae, organellar genome, and most canonical functions. Here, we combine electron tomography, stereology, immunofluorescence microscopy, and bioinformatics to characterise mechanisms of growth, division, and inheritance of this minimal mitochondrion in two microsporidia species (grown within a mammalian RK13 culture-cell host). Mitosomes of Encephalitozoon cuniculi (2-12/cell) and Trachipleistophora hominis (14-18/nucleus) displayed incremental/non-phasic growth and division and were closely associated with an organelle identified as equivalent to the fungal microtubule-organising centre (microsporidian spindle pole body; mSPB). The mitosome-mSPB association was resistant to treatment with microtubule-depolymerising drugs nocodazole and albendazole. Dynamin inhibitors (dynasore and Mdivi-1) arrested mitosome division but not growth, whereas bioinformatics revealed putative dynamins Drp-1 and Vps-1, of which, Vps-1 rescued mitochondrial constriction in dynamin-deficient yeast (Schizosaccharomyces pombe). Thus, microsporidian mitosomes undergo incremental growth and dynamin-mediated division and are maintained through ordered inheritance, likely mediated via binding to the microsporidian centrosome (mSPB).

Functional characterization of Nosema bombycis (microsporidia) trehalase 3

Nosema bombycis, an obligate intracellular parasite, is a single-celled eukaryote known to infect various tissues of silkworms, leading to the manifestation of pebrine. Trehalase, a glycosidase responsible for catalyzing the hydrolysis of trehalose into two glucose molecules, assumes a crucial role in thermal stress tolerance, dehydration, desiccation stress, and asexual development. Despite its recognized importance in these processes, the specific role of trehalase in N. bombycis remains uncertain. This investigation focused on exploring the functions of trehalase 3 in N. bombycis (NbTre3). Immunofluorescence analysis of mature (dormant) spores indicated that NbTre3 primarily localizes to the spore membrane or spore wall, suggesting a potential involvement in spore germination. Reverse transcription-quantitative polymerase chain reaction results indicated that the transcriptional level of NbTre3 peaked at 6 h post N. bombycis infection, potentially contributing to energy storage for proliferation. Throughout the life cycle of N. bombycis within the host cell, NbTre3 was detected in sporoplasm during the proliferative stage rather than the sporulation stage. RNA interference experiments revealed a substantial decrease in the relative transcriptional level of NbTre3, accompanied by a certain reduction in the relative transcriptional level of Nb16S rRNA. These outcomes suggest that NbTre3 may play a role in the proliferation of N. bombycis. The application of the His pull-down technique identified 28 proteins interacting with NbTre3, predominantly originating from the host silkworm. This finding implies that NbTre3 may participate in the metabolism of the host cell, potentially utilizing the host cell's energy resources.

Molecular and cellular characterization of four putative nucleotide transporters from the shrimp microsporidian Enterocytozoon hepatopenaei (EHP)

Microsporidia are obligate intracellular parasites that lost several enzymes required in energy production. The expansion of transporter families in these organisms enables them to hijack ATP from hosts. In this study, nucleotide transporters of the microsporidian Enterocytozoon hepatopenaei (EHP), which causes slow growth in economically valuable Penaeus shrimp, were characterized. Analysis of the EHP genome suggested the presence of four putative nucleotide transporter genes, namely EhNTT1, EhNTT2, EhNTT3, and EhNTT4. Sequence alignment revealed four charged amino acids that are conserved in previously characterized nucleotide transporters. Phylogenetic analysis suggested that EhNTT1, 3, and 4 were derived from one horizontal gene transfer event, which was independent from that of EhNTT2. Localization of EhNTT1 and EhNTT2 using immunofluorescence analysis revealed positive signals within the envelope of developing plasmodia and on mature spores. Knockdown of EhNTT2 by double administration of sequence specific double-stranded RNA resulted in a significant reduction in EHP copy numbers, suggesting that EhNTT2 is crucial for EHP replication in shrimp. Taken together, the insight into the roles of NTTs in microsporidian proliferation can provide the biological basis for the development of alternative control strategies for microsporidian infection in shrimp.

Adaptation of the late ISC pathway in the anaerobic mitochondrial organelles of Giardia intestinalis

Mitochondrial metabolism is entirely dependent on the biosynthesis of the [4Fe-4S] clusters, which are part of the subunits of the respiratory chain. The mitochondrial late ISC pathway mediates the formation of these clusters from simpler [2Fe-2S] molecules and transfers them to client proteins. Here, we characterized the late ISC pathway in one of the simplest mitochondria, mitosomes, of the anaerobic protist Giardia intestinalis that lost the respiratory chain and other hallmarks of mitochondria. In addition to IscA2, Nfu1 and Grx5 we identified a novel BolA1 homologue in G. intestinalis mitosomes. It specifically interacts with Grx5 and according to the high-affinity pulldown also with other core mitosomal components. Using CRISPR/Cas9 we were able to establish full bolA1 knock out, the first cell line lacking a mitosomal protein. Despite the ISC pathway being the only metabolic role of the mitosome no significant changes in the mitosome biology could be observed as neither the number of the mitosomes or their capability to form [2Fe-2S] clusters in vitro was affected. We failed to identify natural client proteins that would require the [2Fe-2S] or [4Fe-4S] cluster within the mitosomes, with the exception of [2Fe-2S] ferredoxin, which is itself part of the ISC pathway. The overall uptake of iron into the cellular proteins remained unchanged as also observed for the grx5 knock out cell line. The pull-downs of all late ISC components were used to build the interactome of the pathway showing specific position of IscA2 due to its interaction with the outer mitosomal membrane proteins. Finally, the comparative analysis across Metamonada species suggested that the adaptation of the late ISC pathway identified in G. intestinalis occurred early in the evolution of this supergroup of eukaryotes.

The intracellular parasite Anncaliia algerae induces a massive miRNA down-regulation in human cells

Anncaliia algerae belongs to microsporidia, a group of obligate intracellular parasites related to fungi. These parasites are largely spread in water and food-webs and can infect a wide variety of hosts ranging from invertebrates to vertebrates including humans. In humans, microsporidian infections are mainly opportunistic as immunocompetent hosts can clear parasites naturally. Recent studies however have reported persistent microsporidian infections and have highlighted them as a risk factor in colon cancer. This may be a direct result of cell infection or may be an indirect effect of the infectious microenvironment and the host's response. In both cases, this raises the question of the effects of microsporidian infection at the host and host-cell levels. We aimed to address the question of human host intracellular response to microsporidian infection through a transcriptomic kinetic study of human foreskin fibroblasts (HFF) infected with A.algerae, a human infecting microsporidia with an exceptionally wide host range. We focused solely on host response studying both coding and small non-coding miRNA expression. Our study revealed a generalized down-regulation of cell miRNAs throughout infection with up to 547 different miRNAs downregulated at some timepoints and also transcriptomic dysregulations that could facilitate parasite development with immune and lipid metabolism genes modulation. We also hypothesize possible small nucleic acid expropriation explaining the miRNA downregulation. This work contributes to a better understanding of the dialogue that can occur between an intracellular parasite and its host at the cellular level, and can guide future studies on microsporidian infection biology to unravel the mode of action of these minimalist parasites at the tissue or host levels.We have also generated a kinetic and comprehensive transcriptomic data set of an infectious process that can help support comparative studies in the broader field of parasitology. Lastly, these results may warrant for caution regarding microsporidian exposure and persistent infections.

How mitochondria showcase evolutionary mechanisms and the importance of oxygen

Darwinian evolution can be simply stated: natural selection of inherited variations increasing differential reproduction. However, formulated thus, links with biochemistry, cell biology, ecology, and population dynamics remain unclear. To understand interactive contributions of chance and selection, higher levels of biological organization (e.g., endosymbiosis), complexities of competing selection forces, and emerging biological novelties (such as eukaryotes or meiotic sex), we must analyze actual examples. Focusing on mitochondria, I will illuminate how biology makes sense of life's evolution, and the concepts involved. First, looking at the bacterium - mitochondrion transition: merging with an archaeon, it lost its independence, but played a decisive role in eukaryogenesis, as an extremely efficient aerobic ATP generator and internal ROS source. Second, surveying later mitochondrion adaptations and diversifications illustrates concepts such as constructive neutral evolution, dynamic interactions between endosymbionts and hosts, the contingency of life histories, and metabolic reprogramming. Without oxygen, mitochondria disappear; with (intermittent) oxygen diversification occurs in highly complex ways, especially upon (temporary) phototrophic substrate supply. These expositions show the Darwinian model to be a highly fruitful paradigm.

Essential mitochondrial role in iron-sulfur cluster assembly of the cytoplasmic isopropylmalate isomerase Leu1 in Saccharomyces cerevisiae

Iron-sulfur (Fe-S) cluster assembly in mitochondria and cytoplasm is essential for cell viability. In the yeast S. cerevisiae, Leu1 [4Fe-4S] is the cytoplasmic isopropylmalate isomerase involved in leucine biosynthesis. Using permeabilized Δleu1 cells and recombinant apo-Leu1^R, here we show that the [4Fe-4S] cluster assembly on Leu1^R can be reconstituted in a physiologic manner requiring both mitochondria and cytoplasm, as judged by conversion of the inactive enzyme to an active form. The mitochondrial contribution to this reconstitution assay is abrogated by inactivating mutations in the mitochondrial ISC (iron-sulfur cluster assembly) machinery components (such as Nfs1 cysteine desulfurase and Ssq1 chaperone) or the mitochondrial exporter Atm1. Likewise, depletion of a CIA (cytoplasmic iron-sulfur protein assembly) component Dre2 leads to impaired Leu1^R reconstitution. Mitochondria likely make and export an intermediate, called X-S or (Fe-S)_int, that is needed for cytoplasmic Fe-S cluster biosynthesis. Here we show that once exported, the same intermediate can be used for both [2Fe-2S] and [4Fe-4S] cluster biogenesis in the cytoplasm, with no further requirement of mitochondria. Our data also suggest that the exported intermediate can activate defective/latent CIA components in cytoplasm isolated from nfs1 or Δatm1 mutant cells. These findings may provide a way to isolate X-S or (Fe-S)_int.

Inhibition of mitosomal alternative oxidase causes lifecycle arrest of early-stage Trachipleistophora hominis meronts during intracellular infection of mammalian cells

Mitosomes are highly reduced forms of mitochondria which have lost two of the 'defining' features of the canonical organelle, the mitochondrial genome, and the capacity to generate energy in the form of ATP. Mitosomes are found in anaerobic protists and obligate parasites and, in most of the studied organisms, have a conserved function in the biosynthesis of iron-sulfur clusters (ISC) that are indispensable cofactors of many essential proteins. The genomes of some mitosome-bearing human pathogenic Microsporidia encode homologues of an alternative oxidase (AOX). This mitochondrial terminal respiratory oxidase is absent from the human host, and hence is a potential target for the development of new antimicrobial agents. Here we present experimental evidence for the mitosomal localization of AOX in the microsporidian Trachipleistophora hominis and demonstrate that it has an important role during the parasite's life cycle progression. Using a recently published methodology for synchronising T. hominis infection of mammalian cell lines, we demonstrated specific inhibition of T. hominis early meront growth and replication by an AOX inhibitor colletochlorin B. Treatment of T. hominis-infected host cells with the drug also inhibited re-infection by newly formed dispersive spores. Addition of the drug during the later stages of the parasite life cycle, when our methods suggest that AOX is not actively produced and T. hominis mitosomes are mainly active in Fe/S cluster biosynthesis, had no inhibitory effects on the parasites. Control experiments with the AOX-deficient microsporidian species Encephalitozoon cuniculi, further demonstrated the specificity of inhibition by the drug. Using the same methodology, we demonstrate effects of two clinically used anti-microsporidian drugs albendazole and fumagillin on the cell biology and life cycle progression of T. hominis infecting mammalian host cells. In summary, our results reveal that T. hominis mitosomes have an active role to play in the progression of the parasite life cycle as well as an important role in the biosynthesis of essential Fe/S clusters. Our work also demonstrates that T. hominis is a useful model for testing the efficacy of therapeutic agents and for studying the physiology and cell biology of microsporidian parasites growing inside infected mammalian cells.

Iron metabolism, ferroptosis, and lncRNA in cancer: knowns and unknowns

Cancer cells undergo substantial metabolic alterations to sustain increased energy supply and uncontrolled proliferation. As an essential trace element, iron is vital for many biological processes. Evidence has revealed that cancer cells deploy various mechanisms to elevate the cellular iron concentration to accelerate proliferation. Ferroptosis, a form of cell death caused by iron-catalyzed excessive peroxidation of polyunsaturated fatty acids (PUFAs), is a promising therapeutic target for therapy-resistant cancers. Previous studies have reported that long noncoding RNA (lncRNA) is a group of critical regulators involved in modulating cell metabolism, proliferation, apoptosis, and ferroptosis. In this review, we summarize the associations among iron metabolism, ferroptosis, and ferroptosis-related lncRNA in tumorigenesis. This information will help deepen understanding of the role of lncRNA in iron metabolism and raise the possibility of targeting lncRNA and ferroptosis in cancer combination therapy.

Review: A history and perspective of mitochondria in the context of anoxia tolerance

Symbiosis is found throughout nature, but perhaps nowhere is it more fundamental than mitochondria in all eukaryotes. Since mitochondria were discovered and mechanisms of oxygen reduction characterized, an understanding gradually emerged that these organelles were involved not just in the combustion of oxygen, but also in the sensing of oxygen. While multiple hypotheses exist to explain the mitochondrial involvement in oxygen sensing, key elements are developing that include potassium channels and reactive oxygen species. To understand how mitochondria contribute to oxygen sensing, it is informative to study a model system which is naturally adapted to survive extended periods without oxygen. Amongst air-breathing vertebrates, the most highly adapted are western painted turtles (Chrysemys picta bellii), which overwinter in ice-covered and anoxic water bodies. Through research of this animal, it was postulated that metabolic rate depression is key to anoxic survival and that mitochondrial regulation is a key aspect. When faced with anoxia, excitatory neurotransmitter receptors in turtle brain are inhibited through mitochondrial calcium release, termed "channel arrest". Simultaneously, inhibitory GABAergic signalling contributes to the "synaptic arrest" of excitatory action potential firing through a pathway dependent on mitochondrial depression of ROS generation. While many pathways are implicated in mitochondrial oxygen sensing in turtles, such as those of adenosine, ATP turnover, and gaseous transmitters, an apparent point of intersection is the mitochondria. In this review we will explore how an organelle that was critical for organismal complexity in an oxygenated world has also become a potentially important oxygen sensor.

Phagocytosis Is the Sole Arm of Drosophila melanogaster Known Host Defenses That Provides Some Protection Against Microsporidia Infection

Microsporidia are obligate intracellular parasites able to infest specifically a large range of species, including insects. The knowledge about the biology of microsporidial infections remains confined to mostly descriptive studies, including molecular approaches such as transcriptomics or proteomics. Thus, functional data to understand insect host defenses are currently lacking. Here, we have undertaken a genetic analysis of known host defenses of the Drosophila melanogaster using an infection model whereby Tubulinosema ratisbonensis spores are directly injected in this insect. We find that phagocytosis does confer some protection in this infection model. In contrast, the systemic immune response, extracellular reactive oxygen species, thioester proteins, xenophagy, and intracellular antiviral response pathways do not appear to be involved in the resistance against this parasite. Unexpectedly, several genes such as PGRP-LE seem to promote this infection. The prophenol oxidases that mediate melanization have different functions; PPO1 presents a phenotype similar to that of PGRP-LE whereas that of PPO2 suggests a function in the resilience to infection. Similarly, eiger and Unpaired3, which encode two cytokines secreted by hemocytes display a resilience phenotype with a strong susceptibility to T. ratisbonensis.

The Function and Structure of the Microsporidia Polar Tube

Microsporidia are obligate intracellular pathogens that were initially identified about 160 years ago. Current phylogenetic analysis suggests that they are grouped with Cryptomycota as a basal branch or sister group to the fungi. Microsporidia are found worldwide and can infect a wide range of animals from invertebrates to vertebrates, including humans. They are responsible for a variety of diseases once thought to be restricted to immunocompromised patients but also occur in immunocompetent individuals. The small oval spore containing a coiled polar filament, which is part of the extrusion and invasion apparatus that transfers the infective sporoplasm to a new host, is a defining characteristic of all microsporidia. When the spore becomes activated, the polar filament uncoils and undergoes a rapid transition into a hollow tube that will transport the sporoplasm into a new cell. The polar tube has the ability to increase its diameter from approximately 100 nm to over 600 nm to accommodate the passage of an intact sporoplasm and penetrate the plasmalemma of the new host cell. During this process, various polar tube proteins appear to be involved in polar tube attachment to host cell and can interact with host proteins. These various interactions act to promote host cell infection.

Sulfur Administration in Fe-S Cluster Homeostasis

Mitochondria are the key organelles of Fe–S cluster synthesis. They contain the enzyme cysteine desulfurase, a scaffold protein, iron and electron donors, and specific chaperons all required for the formation of Fe–S clusters. The newly formed cluster can be utilized by mitochondrial Fe–S protein synthesis or undergo further transformation. Mitochondrial Fe–S cluster biogenesis components are required in the cytosolic iron–sulfur cluster assembly machinery for cytosolic and nuclear cluster supplies. Clusters that are the key components of Fe–S proteins are vulnerable and prone to degradation whenever exposed to oxidative stress. However, once degraded, the Fe–S cluster can be resynthesized or repaired. It has been proposed that sulfurtransferases, rhodanese, and 3-mercaptopyruvate sulfurtransferase, responsible for sulfur transfer from donor to nucleophilic acceptor, are involved in the Fe–S cluster formation, maturation, or reconstitution. In the present paper, we attempt to sum up our knowledge on the involvement of sulfurtransferases not only in sulfur administration but also in the Fe–S cluster formation in mammals and yeasts, and on reconstitution-damaged cluster or restoration of enzyme’s attenuated activity.

A Prioritized and Validated Resource of Mitochondrial Proteins in Plasmodium Identifies Unique Biology

Plasmodium species have a single mitochondrion that is essential for their survival and has been successfully targeted by antimalarial drugs. Most mitochondrial proteins are imported into this organelle, and our picture of the Plasmodium mitochondrial proteome remains incomplete. Many data sources contain information about mitochondrial localization, including proteome and gene expression profiles, orthology to mitochondrial proteins from other species, coevolutionary relationships, and amino acid sequences, each with different coverage and reliability. To obtain a comprehensive, prioritized list of Plasmodium falciparum mitochondrial proteins, we rigorously analyzed and integrated eight data sets using Bayesian statistics into a predictive score per protein for mitochondrial localization. At a corrected false discovery rate of 25%, we identified 445 proteins with a sensitivity of 87% and a specificity of 97%. They include proteins that have not been identified as mitochondrial in other eukaryotes but have characterized homologs in bacteria that are involved in metabolism or translation. Mitochondrial localization of seven Plasmodium berghei orthologs was confirmed by epitope labeling and colocalization with a mitochondrial marker protein. One of these belongs to a newly identified apicomplexan mitochondrial protein family that in P. falciparum has four members. With the experimentally validated mitochondrial proteins and the complete ranked P. falciparum proteome, which we have named PlasmoMitoCarta, we present a resource to study unique proteins of Plasmodium mitochondria. IMPORTANCE The unique biology and medical relevance of the mitochondrion of the malaria parasite Plasmodium falciparum have made it the subject of many studies. However, we actually do not have a comprehensive assessment of which proteins reside in this organelle. Many omics data are available that are predictive of mitochondrial localization, such as proteomics data and expression data. Individual data sets are, however, rarely complete and can provide conflicting evidence. We integrated a wide variety of available omics data in a manner that exploits the relative strengths of the data sets. Our analysis gave a predictive score for the mitochondrial localization to each nuclear encoded P. falciparum protein and identified 445 likely mitochondrial proteins. We experimentally validated the mitochondrial localization of seven of the new mitochondrial proteins, confirming the quality of the complete list. These include proteins that have not been observed mitochondria before, adding unique mitochondrial functions to P. falciparum.

Microsporidiosis in Humans

Microsporidia are obligate intracellular pathogens identified ∼150 years ago as the cause of pébrine, an economically important infection in silkworms. There are about 220 genera and 1,700 species of microsporidia, which are classified based on their ultrastructural features, developmental cycle, host-parasite relationship, and molecular analysis. Phylogenetic analysis suggests that microsporidia are related to the fungi, being grouped with the Cryptomycota as a basal branch or sister group to the fungi. Microsporidia can be transmitted by food and water and are likely zoonotic, as they parasitize a wide range of invertebrate and vertebrate hosts. Infection in humans occurs in both immunocompetent and immunodeficient hosts, e.g., in patients with organ transplantation, patients with advanced human immunodeficiency virus (HIV) infection, and patients receiving immune modulatory therapy such as anti-tumor necrosis factor alpha antibody. Clusters of infections due to latent infection in transplanted organs have also been demonstrated. Gastrointestinal infection is the most common manifestation; however, microsporidia can infect virtually any organ system, and infection has resulted in keratitis, myositis, cholecystitis, sinusitis, and encephalitis. Both albendazole and fumagillin have efficacy for the treatment of various species of microsporidia; however, albendazole has limited efficacy for the treatment of Enterocytozoon bieneusi. In addition, immune restoration can lead to resolution of infection. While the prevalence rate of microsporidiosis in patients with AIDS has fallen in the United States, due to the widespread use of combination antiretroviral therapy (cART), infection continues to occur throughout the world and is still seen in the United States in the setting of cART if a low CD4 count persists.

From the discovery to molecular understanding of cellular iron-sulfur protein biogenesis

Protein cofactors often are the business ends of proteins, and are either synthesized inside cells or are taken up from the nutrition. A cofactor that strictly needs to be synthesized by cells is the iron-sulfur (Fe/S) cluster. This evolutionary ancient compound performs numerous biochemical functions including electron transfer, catalysis, sulfur mobilization, regulation and protein stabilization. Since the discovery of eukaryotic Fe/S protein biogenesis two decades ago, more than 30 biogenesis factors have been identified in mitochondria and cytosol. They support the synthesis, trafficking and target-specific insertion of Fe/S clusters. In this review, I first summarize what led to the initial discovery of Fe/S protein biogenesis in yeast. I then discuss the function and localization of Fe/S proteins in (non-green) eukaryotes. The major part of the review provides a detailed synopsis of the three major steps of mitochondrial Fe/S protein biogenesis, i.e. the de novo synthesis of a [2Fe-2S] cluster on a scaffold protein, the Hsp70 chaperone-mediated transfer of the cluster and integration into [2Fe-2S] recipient apoproteins, and the reductive fusion of [2Fe-2S] to [4Fe-4S] clusters and their subsequent assembly into target apoproteins. Finally, I summarize the current knowledge of the mechanisms underlying the maturation of cytosolic and nuclear Fe/S proteins.

Genome and Evolutionary Analysis of Nosema ceranae: A Microsporidian Parasite of Honey Bees

Microsporidia comprise a phylum of single cell, intracellular parasites and represent the earliest diverging branch in the fungal kingdom. The microsporidian parasite Nosema ceranae primarily infects honey bee gut epithelial cells, leading to impaired memory, suppressed host immune responses and colony collapse under certain circumstances. As the genome of N. ceranae is challenging to assembly due to very high genetic diversity and repetitive region, the genome was re-sequenced using long reads. We present a robust 8.8 Mbp genome assembly of 2,280 protein coding genes, including a high number of genes involved in transporting nutrients and energy, as well as drug resistance when compared with sister species Nosema apis. We also describe the loss of the critical protein Dicer in approximately half of the microsporidian species, giving new insights into the availability of RNA interference pathway in this group. Our results provided new insights into the pathogenesis of N. ceranae and a blueprint for treatment strategies that target this parasite without harming honey bees. The unique infectious apparatus polar filament and transportation pathway members can help to identify treatments to control this parasite.

[Fe-S] biogenesis and unusual assembly of the ISC scaffold complex in the Plasmodium falciparum mitochondrion

The malaria parasite harbors two [Fe-S] biogenesis pathways of prokaryotic origin-the SUF and ISC systems in the apicoplast and mitochondrion, respectively. While the SUF machinery has been delineated, there is little experimental evidence on the ISC pathway. We confirmed mitochondrial targeting of Plasmodium falciparum ISC proteins followed by analyses of cysteine desulfurase, scaffold, and [Fe-S]-carrier components. PfIscU functioned as the scaffold in complex with the PfIscS-PfIsd11 cysteine desulfurase and could directly assemble [4Fe-4S] without prior [2Fe-2S] formation seen in other homologs. Small angle X-ray scattering and spectral studies showed that PfIscU, a trimer, bound one [4Fe-4S]. In a deviation from reported complexes from other organisms, the P. falciparum desulfurase-scaffold complex assembled around a PfIscS tetramer instead of a dimer, resulting in a symmetric hetero-hexamer [2× (2PfIscS-2PfIsd11-2PfIscU)]. PfIscU directly transferred [4Fe-4S] to the apo-protein aconitase B thus abrogating the requirement of intermediary proteins for conversion of [2Fe-2S] to [4Fe-4S] before transfer to [4Fe-4S]-recipients. Among the putative cluster-carriers, PfIscA2 was more efficient than PfNifU-like protein; PfIscA1 primarily bound iron, suggesting its potential role as a Fe²⁺ carrier/donor. Our results identify the core P. falciparum ISC machinery and reveal unique features compared with those in bacteria or yeast and human mitochondria.

Transcriptome analysis reveals changes in silkworm energy metabolism during Nosema bombycis infection

Energy metabolism is important for the proliferation of microsporidia in infected host cells, but there is limited information on the host response. The energy metabolism response of silkworm (Bombyx mori) to microsporidia may help manage Nosema bombycis infections. We analyzed differentially expressed genes in the B.mori midgut transcriptome at two significant time points of microsporidia infection. A total of 1448 genes were up-regulated, while 315 genes were down-regulated. A high proportion of genes were involved in the phosphatidylinositol signaling system, protein processing in the endoplasmic reticulum, and glycerolipid metabolism at 48 h post infection (h p.i.), and a large number of genes were involved in the TCA cycle and protein processing at 120 h p.i. These results showed that the early stages of microsporidia infection affected the basic metabolism and biosynthesis processes of the silkworm. Knockout of Bm_nscaf2860_46 (Bombyx mori isocitrate dehydrogenase, BmIDH) and Bm_nscaf3027_062 (Bombyx mori hexokinase, BmHXK) reduced the production of ATP and inhibited microsporidia proliferation. Host fatty acid degradation, glycerol metabolism, glycolysis pathway, and TCA cycle response to microsporidia infection were also analyzed, and their importance to microsporidia proliferation was verified. These results increase our understanding of the molecular mechanisms involved in N. bombycis infection and provide new insights for research on microsporidia control. IMPORTANCE: Nosema bombycis can be vertically transmitted in silkworm eggs. The traditional prevention and control strategies for microsporidia are difficult and time-consuming, and this is a problem in silkworm culture. Research has mainly focused on host gene functions related to microsporidia infection and host immune responses after microsporidia infection. Little is known about the metabolic changes occurring in the host after infection. Understanding the metabolic changes in the silkworm host could aid in the recognition of host genes important for microsporidia infection and growth. We analyzed host metabolic changes and the main participating pathways at two time points after microsporidia infection and screened the microsporidia-dependent host energy metabolism genes BmIDH and BmHXK. The results revealed genes that are important for the proliferation of Nosema bombycis. These results illustrate how microsporidia hijack the host genome for their growth and reproduction.

Increased survival of the honey bee Apis mellifera infected with the microsporidian Nosema ceranae by effective gene silencing

This study examined the control of nosemosis caused by Nosema ceranae, one of the hard-to-control diseases of honey bees, using RNA interference (RNAi) technology. Double-stranded RNA (dsRNA) for RNAi application targeted the mitosome-related genes of N. ceranae. Among the various mitosome-related genes, NCER_100882, NCER_101456, NCER_100157, and NCER_100686 exhibited relatively low homologies with the orthologs of Apis mellifera. Four gene-specific dsRNAs were prepared against the target genes and applied to the infected A. mellifera to analyze Nosema proliferation and honey bee survival. Two dsRNAs specifics to NCER_101456 and NCER_100157 showed high inhibitory effects on spore production by exhibiting only 62% and 67%, respectively, compared with the control. In addition, these dsRNA treatments significantly rescued the honey bees from the fatal nosemosis. It was confirmed that the inhibition of Nosema spore proliferation and the increase in the survival rate of honey bees were resulted from a decrease in the expression level of each target gene by dsRNA treatment. However, dsRNA mixture treatment was no more effective than single treatments in the rescue from the nosemosis. It is expected that the four newly identified mitosome-related target genes in this study can be effectively used for nosemosis control using RNAi technology.

Convergent Evolution of Hydrogenosomes from Mitochondria by Gene Transfer and Loss

Hydrogenosomes are H2-producing mitochondrial homologs found in some anaerobic microbial eukaryotes that provide a rare intracellular niche for H2-utilizing endosymbiotic archaea. Among ciliates, anaerobic and aerobic lineages are interspersed, demonstrating that the switch to an anaerobic lifestyle with hydrogenosomes has occurred repeatedly and independently. To investigate the molecular details of this transition, we generated genomic and transcriptomic data sets from anaerobic ciliates representing three distinct lineages. Our data demonstrate that hydrogenosomes have evolved from ancestral mitochondria in each case and reveal different degrees of independent mitochondrial genome and proteome reductive evolution, including the first example of complete mitochondrial genome loss in ciliates. Intriguingly, the FeFe-hydrogenase used for generating H2 has a unique domain structure among eukaryotes and appears to have been present, potentially through a single lateral gene transfer from an unknown donor, in the common aerobic ancestor of all three lineages. The early acquisition and retention of FeFe-hydrogenase helps to explain the facility whereby mitochondrial function can be so radically modified within this diverse and ecologically important group of microbial eukaryotes.

Mechanistic concepts of iron-sulfur protein biogenesis in Biology

Iron-sulfur (Fe/S) proteins are present in virtually all living organisms and are involved in numerous cellular processes such as respiration, photosynthesis, metabolic reactions, nitrogen fixation, radical biochemistry, protein synthesis, antiviral defense, and genome maintenance. Their versatile functions may go back to the proposed role of their Fe/S cofactors in the origin of life as efficient catalysts and electron carriers. More than two decades ago, it was discovered that the in vivo synthesis of cellular Fe/S clusters and their integration into polypeptide chains requires assistance by complex proteinaceous machineries, despite the fact that Fe/S proteins can be assembled chemically in vitro. In prokaryotes, three Fe/S protein biogenesis systems are known; ISC, SUF, and the more specialized NIF. The former two systems have been transferred by endosymbiosis from bacteria to mitochondria and plastids, respectively, of eukaryotes. In their cytosol, eukaryotes use the CIA machinery for the biogenesis of cytosolic and nuclear Fe/S proteins. Despite the structural diversity of the protein constituents of these four machineries, general mechanistic concepts underlie the complex process of Fe/S protein biogenesis. This review provides a comprehensive and comparative overview of the various known biogenesis systems in Biology, and summarizes their common or diverging molecular mechanisms, thereby illustrating both the conservation and diverse adaptions of these four machineries during evolution and under different lifestyles. Knowledge of these fundamental biochemical pathways is not only of basic scientific interest, but is important for the understanding of human 'Fe/S diseases' and can be used in biotechnology.

The ins and outs of host-microsporidia interactions during invasion, proliferation and exit

Microsporidia are a large group of fungal-related obligate intracellular parasites. They are responsible for infections in humans as well as in agriculturally and environmentally important animals. Although microsporidia are abundant in nature, many of the molecular mechanisms employed during infection have remained enigmatic. In this review, we highlight recent work showing how microsporidia invade, proliferate and exit from host cells. During invasion, microsporidia use spore wall and polar tube proteins to interact with host receptors and adhere to the host cell surface. In turn, the host has multiple defence mechanisms to prevent and eliminate these infections. Microsporidia encode numerous transporters and steal host nutrients to facilitate proliferation within host cells. They also encode many secreted proteins which may modulate host metabolism and inhibit host cell defence mechanisms. Spores exit the host in a non-lytic manner that is dependent on host actin and endocytic recycling proteins. Together, this work provides a fuller picture of the mechanisms that these fascinating organisms use to infect their hosts.

Mechanisms of Mitochondrial Iron-Sulfur Protein Biogenesis

Mitochondria are essential in most eukaryotes and are involved in numerous biological functions including ATP production, cofactor biosyntheses, apoptosis, lipid synthesis, and steroid metabolism. Work over the past two decades has uncovered the biogenesis of cellular iron-sulfur (Fe/S) proteins as the essential and minimal function of mitochondria. This process is catalyzed by the bacteria-derived iron-sulfur cluster assembly (ISC) machinery and has been dissected into three major steps: de novo synthesis of a [2Fe-2S] cluster on a scaffold protein; Hsp70 chaperone-mediated trafficking of the cluster and insertion into [2Fe-2S] target apoproteins; and catalytic conversion of the [2Fe-2S] into a [4Fe-4S] cluster and subsequent insertion into recipient apoproteins. ISC components of the first two steps are also required for biogenesis of numerous essential cytosolic and nuclear Fe/S proteins, explaining the essentiality of mitochondria. This review summarizes the molecular mechanisms underlying the ISC protein-mediated maturation of mitochondrial Fe/S proteins and the importance for human disease.

Characterization of Hsp70 gene family provides insight into its functions related to microsporidian proliferation

Heat shock protein 70 (Hsp70), a highly conserved protein family, is widely distributed in organisms and plays fundamental roles in biotic and abiotic stress responses. However, reports on Hsp70 genes are scarce in microsporidia, a very large group of obligate intracellular parasites that can infect nearly all animals, including humans. In this study, we identified 37 Hsp70 proteins from eight microsporidian genomes and classified them into four subfamilies (A-D). The number of Hsp70 genes in these microsporidia was significantly fewer than in Rozella allomycis and yeast. All microsporidian species contained genes from each subfamily and similar subcellular locations (mitochondria, endoplasmic reticulum, cytosol, and cytosol and/or nucleus), indicating that each Hsp70 member may fulfil distinct functions. The conserved structures and motifs of the Hsp70 proteins in the same subfamily were highly similar. Expression analysis indicated that the subfamily C cytosol (cyto)-associated Hsp70s is functional during microsporidia development. Immunofluorescence assays revealed that Cyto-NbHsp70 was cytoplasmically located in the proliferation-stage of Nosema bombycis. Cyto-NbHsp70 antiserum also labeled Encephalitozoon hellem within infected cells, suggesting that this antiserum is a potential molecular marker for labeling the proliferative phases of different microsporidian species. The propagation of N. bombycis was significantly inhibited following RNAi of Cyto-NbHsp70, indicating that Cyto-NbHsp70 is important for pathogen proliferation. Our phylogenetic data suggest that Hsp70 proteins evolved during microsporidia adaption to intracellular parasitism, and they play important roles in pathogen development.

Invasion of Host Cells by Microsporidia

Microsporidia are found worldwide and both vertebrates and invertebrates can serve as hosts for these organisms. While microsporidiosis in humans can occur in both immune competent and immune compromised hosts, it has most often been seen in the immune suppressed population, e.g., patients with advanced HIV infection, patients who have had organ transplantation, those undergoing chemotherapy, or patients using other immune suppressive agents. Infection can be associated with either focal infection in a specific organ (e.g., keratoconjunctivitis, cerebritis, or hepatitis) or with disseminated disease. The most common presentation of microsporidiosis being gastrointestinal infection with chronic diarrhea and wasting syndrome. In the setting of advanced HIV infection or other cases of profound immune deficiency microsporidiosis can be extremely debilitating and carries a significant mortality risk. Microsporidia are transmitted as spores which invade host cells by a specialized invasion apparatus the polar tube (PT). This review summarizes recent studies that have provided information on the composition of the spore wall and PT, as well as insights into the mechanism of invasion and interaction of the PT and spore wall with host cells during infection.

Major Changes in Plastid Protein Import and the Origin of the Chloroplastida

Core components of plastid protein import and the principle of using N-terminal targeting sequences are conserved across the Archaeplastida, but lineage-specific differences exist. Here we compare, in light of plastid protein import, the response to high-light stress from representatives of the three archaeplastidal groups. Similar to land plants, Chlamydomonas reinhardtii displays a broad response to high-light stress, not observed to the same degree in the glaucophyte Cyanophora paradoxa or the rhodophyte Porphyridium purpureum. We find that only the Chloroplastida encode both Toc75 and Oep80 in parallel and suggest that elaborate high-light stress response is supported by changes in plastid protein import. We propose the origin of a phenylalanine-independent import pathway via Toc75 allowed higher import rates to rapidly service high-light stress, but with the cost of reduced specificity. Changes in plastid protein import define the origin of the green lineage, whose greatest evolutionary success was arguably the colonization of land.

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Chloroplastida evolved a dual system, Toc75/Oep80, for high throughput protein import

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Loss of F-based targeting led to dual organelle targeting using a single ambiguous NTS

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Relaxation of functional constraints allowed a wider Toc/Tic modification

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A broad response to high-light stress appears unique to Chloroplastida

On the Origin of Iron/Sulfur Cluster Biosynthesis in Eukaryotes

Iron and sulfur are indispensable elements of every living cell, but on their own these elements are toxic and require dedicated machineries for the formation of iron/sulfur (Fe/S) clusters. In eukaryotes, proteins requiring Fe/S clusters (Fe/S proteins) are found in or associated with various organelles including the mitochondrion, endoplasmic reticulum, cytosol, and the nucleus. These proteins are involved in several pathways indispensable for the viability of each living cell including DNA maintenance, protein translation and metabolic pathways. Thus, the formation of Fe/S clusters and their delivery to these proteins has a fundamental role in the functions and the evolution of the eukaryotic cell. Currently, most eukaryotes harbor two (located in cytosol and mitochondrion) or three (located in plastid) machineries for the assembly of Fe/S clusters, but certain anaerobic microbial eukaryotes contain sulfur mobilization (SUF) machineries that were previously thought to be present only in archaeal linages. These machineries could not only stipulate which pathway was present in the last eukaryotic common ancestor (LECA), but they could also provide clues regarding presence of an Fe/S cluster machinery in the proto-eukaryote and evolution of Fe/S cluster assembly machineries in all eukaryotes.

A new scope for orlistat: Effect of approved anti-obesity drug against experimental microsporidiosis

As the current therapies for intestinal microsporidiosis are either inconsistent in their efficacies or hampered by several adverse effects, alternative antimicrosporidial agents are being sought. The present study is the first that was designed to evaluate the potency of orlistat, an approved anti-obesity drug, against intestinal microsporidiosis caused by both Enterocytozoon bieneusi and Encephalitozoon intestinalis. Results were assessed through studying fecal and intestinal spore load, intestinal histopathological changes, viability, and infectivity of spores from treated animals. Results showed that orlistat has promising antimicrosporidia potential, with better results in E. intestinalis than E. bieneusi. The animals that received orlistat showed statistically significant decrease in the fecal and intestinal spore load, when compared to the corresponding control infected nontreated mice. The results were insignificant compared to fumagillin and albendazole. Light microscopic examination of stained intestinal sections revealed amelioration of the pathological changes and decreased inflammatory cells detected in the control infected nontreated mice. Spores encountered from stool of orlistat-treated E. bieneusi and E. intestinalis mice showed low viability and significant reduction of infectivity versus their control. Thus, considering the results of the present work, orlistat proved its effectiveness against the intestinal microsporidial infection.

Energy metabolism in anaerobic eukaryotes and Earth's late oxygenation

Eukaryotes arose about 1.6 billion years ago, at a time when oxygen levels were still very low on Earth, both in the atmosphere and in the ocean. According to newer geochemical data, oxygen rose to approximately its present atmospheric levels very late in evolution, perhaps as late as the origin of land plants (only about 450 million years ago). It is therefore natural that many lineages of eukaryotes harbor, and use, enzymes for oxygen-independent energy metabolism. This paper provides a concise overview of anaerobic energy metabolism in eukaryotes with a focus on anaerobic energy metabolism in mitochondria. We also address the widespread assumption that oxygen improves the overall energetic state of a cell. While it is true that ATP yield from glucose or amino acids is increased in the presence of oxygen, it is also true that the synthesis of biomass costs thirteen times more energy per cell in the presence of oxygen than in anoxic conditions. This is because in the reaction of cellular biomass with O2, the equilibrium lies very far on the side of CO2. The absence of oxygen offers energetic benefits of the same magnitude as the presence of oxygen. Anaerobic and low oxygen environments are ancient. During evolution, some eukaryotes have specialized to life in permanently oxic environments (life on land), other eukaryotes have remained specialized to low oxygen habitats. We suggest that the Km of mitochondrial cytochrome c oxidase of 0.1-10 μM for O2, which corresponds to about 0.04%-4% (avg. 0.4%) of present atmospheric O2 levels, reflects environmental O2 concentrations that existed at the time that the eukaryotes arose.

A new family of cell surface located purine transporters in Microsporidia and related fungal endoparasites

Plasma membrane-located transport proteins are key adaptations for obligate intracellular Microsporidia parasites, because they can use them to steal host metabolites the parasites need to grow and replicate. However, despite their importance, the functions and substrate specificities of most Microsporidia transporters are unknown. Here, we provide functional data for a family of transporters conserved in all microsporidian genomes and also in the genomes of related endoparasites. The universal retention among otherwise highly reduced genomes indicates an important role for these transporters for intracellular parasites. Using Trachipleistophora hominis, a Microsporidia isolated from an HIV/AIDS patient, as our experimental model, we show that the proteins are ATP and GTP transporters located on the surface of parasites during their intracellular growth and replication. Our work identifies a new route for the acquisition of essential energy and nucleotides for a major group of intracellular parasites that infect most animal species including humans.

Microsporidia are a group of microscopic parasites that spend part of their lives inside the cells of a broad range of animal hosts, including humans. These parasites are considered to be related to fungi, some of which also live within the cells of other species and are known as fungal endoparasites. One of the shared characteristics of these parasites is that they cannot make nucleotides, molecules that are both the main source of energy of the cell and also the building blocks of DNA. Instead, they take nucleotides, or the materials needed to make nucleotides, from their host cells. Once Microsporidia have depleted a host cell, they turn into spores that can survive outside the host until they invade a new cell, starting the cycle anew.

Microsporidia have proteins on their surface, including nucleotide transporter family proteins (NTT), that enable them to import nucleotides from their host into themselves. Although most fungal endoparasites are also thought to steal nucleotides from their hosts, many do not have NTT proteins, raising the question of how they import the nucleotides. A group of proteins called the Major Facilitator Superfamily (MFS) consists of proteins that were thought to transport the materials cells need to make nucleotides (which are also called nucleotide precursors). Members of this family are found throughout Microsporidia and related fungal endoparasites.

These proteins could explain how fungal endoparasites take nucleotides from their hosts. To test this hypothesis, Major et al. infected mammalian cells with Microsporidia and then checked where two MFS proteins were located during infection. This showed that the proteins were on the surface of the endoparasites, implying that they could be nucleotide precursor transporters. Next, Major et al. genetically modified Escherichia coli bacteria so they would produce MFS proteins, and showed that the proteins could transport two types of nucleotides. Together these results show that MFS proteins could be responsible for nucleotide transport in fungal endoparasites.

In addition to humans, Microsporidia and related fungal endoparasites infect a wide range of animals, including pollinating insects, which have ecological and economic importance. Given that Microsporidia can only survive if they take nucleotides from their hosts, knowing more about the proteins that import the nucleotides could lead to new cures for Microsporidia infections.

Fe-S Cluster Assembly in Oxymonads and Related Protists

The oxymonad Monocercomonoides exilis was recently reported to be the first eukaryote that has completely lost the mitochondrial compartment. It was proposed that an important prerequisite for such a radical evolutionary step was the acquisition of the SUF Fe–S cluster assembly pathway from prokaryotes, making the mitochondrial ISC pathway dispensable. We have investigated genomic and transcriptomic data from six oxymonad species and their relatives, composing the group Preaxostyla (Metamonada, Excavata), for the presence and absence of enzymes involved in Fe–S cluster biosynthesis. None possesses enzymes of mitochondrial ISC pathway and all apparently possess the SUF pathway, composed of SufB, C, D, S, and U proteins, altogether suggesting that the transition from ISC to SUF preceded their last common ancestor. Interestingly, we observed that SufDSU were fused in all three oxymonad genomes, and in the genome of Paratrimastix pyriformis. The donor of the SUF genes is not clear from phylogenetic analyses, but the enzyme composition of the pathway and the presence of SufDSU fusion suggests Firmicutes, Thermotogae, Spirochaetes, Proteobacteria, or Chloroflexi as donors. The inventory of the downstream CIA pathway enzymes is consistent with that of closely related species that retain ISC, indicating that the switch from ISC to SUF did not markedly affect the downstream process of maturation of cytosolic and nuclear Fe–S proteins.

A cytonaut's guide to protein trafficking in Giardia lamblia

Over the past years, the subcellular organization of the Excavata member Giardia lamblia (syn. duodenalis, intestinalis) has been investigated in considerable detail. There are several reasons for this endeavour which go beyond this parasite's medical importance and are mostly concerned with its reduced subcellular complexity and debated evolutionary status. One may say that simplification has emerged as a paradigm for the evolution of Giardia's subcellular architecture. However, a complete appreciation of the evolutionary and ecological significance of this phenomenon is far from complete. In this chapter, we present and discuss the most recent data on the main trafficking pathways in G. lamblia which include endo- and exo-cytosis, organellar import and function. We provide perspectives on open questions concerning organelle replication and inheritance and include a technical outlook on methods and approaches to genetic manipulations in G. lamblia. A better understanding of G. lamblia subcellular organization at the morphological and molecular level complements any effort aimed at elucidating this parasitic species' evolutionary status and could provide us with the basis for novel strategies to interfere with parasite transmission and/or pathogenesis.

A secretory hexokinase plays an active role in the proliferation of Nosema bombycis

The microsporidian Nosema bombycis is an obligate intracellular parasite of Bombyx mori, that lost its intact tricarboxylic acid cycle and mitochondria during evolution but retained its intact glycolysis pathway. N. bombycis hexokinase (NbHK) is not only a rate-limiting enzyme of glycolysis but also a secretory protein. Indirect immunofluorescence assays and recombinant HK overexpressed in BmN cells showed that NbHK localized in the nucleus and cytoplasm of host cell during the meront stage. When N. bombycis matured, NbHK tended to concentrate at the nuclei of host cells. Furthermore, the transcriptional profile of NbHK implied it functioned during N. bombycis’ proliferation stages. A knock-down of NbHK effectively suppressed the proliferation of N. bombycis indicating that NbHK is an important protein for parasite to control its host.

Reinventing an Organelle: The Reduced Mitochondrion in Parasitic Protists

Mitochondria originated from the endosymbiotic event commencing from the engulfment of an ancestral α-proteobacterium by the first eukaryotic ancestor. Establishment of niches has led to various adaptations among eukaryotes. In anaerobic parasitic protists, the mitochondria have undergone modifications by combining features shared from the aerobic mitochondria with lineage-specific components and mechanisms; a diversified class of organelles emerged and are generally called mitochondrion-related organelles (MROs). In this review we summarize and discuss the recent advances in the knowledge of MROs from parasitic protists, particularly the themes such as metabolic functions, contribution to parasitism, dynamics, protein targeting, and novel lineage- specific proteins, with emphasis on the diversity among these organelles.

The invasive cell coat at the microsporidian Trachipleistophora hominis-host cell interface contains secreted hexokinases

Microsporidia are obligate intracellular parasites causing significant disease in humans and economically important animals. In parallel to their extreme genetic reduction, Microsporidia have evolved novel mechanisms for exploiting host metabolism. A number of microsporidians confer secretion of otherwise cytosolic proteins by coding for signal peptides that direct entry into the endoplasmic reticulum. The human pathogen Trachipleistophora hominis encodes for four hexokinases, three of which have signal peptides at the N‐terminus. Here, we localized hexokinase 2 and hexokinase 3 through developmental stages of T. hominis using light and electron microscopy. Both proteins were concentrated in an extracellular coat previously termed the plaque matrix (PQM). The PQM (containing hexokinases) was morphologically dynamic, infiltrating the host cytoplasm predominantly during replicative stages. Throughout development the PQM interacted closely with endoplasmic reticulum that was demonstrated to be active in membrane protein biosynthesis and export. The impact of hexokinase on the host metabolism was probed using the fluorescent analog of glucose, 2‐NBDG, which displayed spatially restricted increases in signal intensity at the parasite/vacuole surface, coincident with hexokinase/PQM distribution. Gross metabolic aberrations, measured using metabolic profiling with the Seahorse XF Analyzer, were not detectable in mixed stage cocultures. Overall, these results highlight a role for the extended cell coat of T. hominis in host–parasite interactions, within which secreted hexokinases may work as part of a metabolic machine to increase glycolytic capacity or ATP generation close to the parasite surface.

Localization of Fe-S Biosynthesis Machinery in Cryptosporidium parvum Mitosome

Cryptosporidium is a protozoan, apicomplexan, parasite that poses significant risk to humans and animals, as a common cause of potentially fatal diarrhea in immunodeficient hosts. The parasites have evolved a number of unique biological features that allow them to thrive in a highly specialized parasitic lifestyle. For example, the genome of Cryptosporidium parvum is highly reduced, encoding only 3,805 proteins, which is also reflected in its reduced cellular and organellar content and functions. As such, its remnant mitochondrion, dubbed a mitosome, is one of the smallest mitochondria yet found. While numerous studies have attempted to discover the function(s) of the C. parvum mitosome, most of them have been focused on in silico predictions. Here, we have localized components of a biochemical pathway in the C. parvum mitosome, in our investigations into the functions of this peculiar mitochondrial organelle. We have shown that three proteins involved in the mitochondrial iron-sulfur cluster biosynthetic pathway are localized in the organelle, and one of them can functionally replace its yeast homolog. Thus, it seems that the C. parvum mitosome is involved in iron-sulfur cluster biosynthesis, supporting the organellar and cytosolic apoproteins. These results spearhead further research on elucidating the functions of the mitosome and broaden our understanding in the minimalistic adaptations of these organelles.

Invertebrate host responses to microsporidia infections

Microsporidia are a group of fungi-like intracellular and unicellular parasites, which infect nearly all animals. As "master parasites", over 1400 microsporidian species have been described to date. Microsporidia infections in economical invertebrates (e.g., silkworm, shrimp) cause huge financial losses, while other microsporidia infections in daphnia, nematode, locust, honeybee and mosquito play important roles in the regulation of their population size. Research investigating invertebrate host responses following microsporidia infections has yielded numerous interesting results, especially pertaining to the innate immune response to these pathogens. In this review, we comparatively summarize the invertebrate host responses to various microsporidia infections. We discuss numerous critical events in host responses including ubiquitin-mediated resistance, production of reactive oxygen species, melanization and innate immune pathways, and the increased basic metabolism and the accumulation of juvenile hormone in infected hosts. Recent studies progressing our understanding of microsporidia infection are also highlighted. Collectively, these advances shed more light on general rules of invertebrate host immune responses and pathogenesis mechanisms of microsporidia, and concurrently offer valuable clues for further research on the crosstalk between hosts and intracellular pathogens.

Transporter gene acquisition and innovation in the evolution of Microsporidia intracellular parasites

The acquisition of genes by horizontal transfer can impart entirely new biological functions and provide an important route to major evolutionary innovation. Here we have used ancient gene reconstruction and functional assays to investigate the impact of a single horizontally transferred nucleotide transporter into the common ancestor of the Microsporidia, a major radiation of intracellular parasites of animals and humans. We show that this transporter provided early microsporidians with the ability to steal host ATP and to become energy parasites. Gene duplication enabled the diversification of nucleotide transporter function to transport new substrates, including GTP and NAD⁺, and to evolve the proton-energized net import of nucleotides for nucleic acid biosynthesis, growth and replication. These innovations have allowed the loss of pathways for mitochondrial and cytosolic energy generation and nucleotide biosynthesis that are otherwise essential for free-living eukaryotes, resulting in the highly unusual and reduced cells and genomes of contemporary Microsporidia.

Molecular and biochemical responses in the midgut of the silkworm, Bombyx mori, infected with Nosema bombycis

BACKGROUND

Microsporidia are a group of eukaryotic intracellular parasites that infect almost all vertebrates and invertebrates. However, there is little information available of how microsporidia obtain nutrients and energy from host cells. The purpose of this study was to investigate the energy and material requirements of Nosema bombycis for the invasion procedure through analyzing the global variation of the gene expression, protein abundance, fatty acids level and ATP flux induced by the microsporidia N. bombycis infection in the midgut of the silkworm Bombyx mori.

METHODS

A suppression subtractive hybridization (SSH) and quantitative real-time PCR (qPCR) analysis were performed to identify the genes upregulated in the midgut of B. mori 48 h following N. bombycis infection. Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were used to annotate and summarize the differentially expressed genes, according to the categories 'molecular function', 'cellular component' and 'biological process'. To evaluate the nutrition material and energy costs in B.mori infected by N. bombycis, biochemical analysis was performed to determine the variation of protein abundance, fatty acid levels and ATP flux with or without the microsporidia N. bombycis infection in the midgut of the silkworm B. mori.

RESULTS

A total of 744 clones were obtained, 288 clones were randomly selected for sequencing, and 110 unigenes were generated. Amongst these, 49.21%, 30.16% and 14.29% genes were involved in 19 molecular functions, 19 biological processes and nine cellular components, respectively. A total of 11 oxidative phosphorylation- and eight proton-coupled ATP synthesis-related genes were upregulated. Seven protein degradation-, three fat degradation-related genes were upregulated, and no genes related to the de novo synthesis of amino acids and fatty acids were significantly upregulated. The data from the biochemical analysis showed the contents of total protein and ATP of B. mori midgut tissues decreased significantly, whereas the fatty acid content did not significantly change after four days of N. bombycis infection. Microsporidia N. bombycis infection upregulated the expression level of genes involved in host ATP synthesis, protein and fat degradation, which eventually causes the obvious decline of protein content and ATP synthesis in the host midgut, whereas the fatty acids content did not change significantly.

CONCLUSIONS

This study suggested to some extent that N. bombycis invasion can activate the host protein degradation and accelerate the production of host ATP. Microsporidia of N. bombycis show preference for proteins rather than fatty acids from the host to ensure the material preparation required by their parasitic life-cycle. Requirements of N. bombycis for energy were also mainly dependent on the host ATP production. This study provides a new data that may help our understanding of the molecular mechanisms of obtaining energy and nutrients from the host by the microsporidium N. bombycis.

Biochemical Reconstitution and Spectroscopic Analysis of Iron-Sulfur Proteins

Iron-sulfur (Fe/S) proteins are involved in numerous key biological functions such as respiration, metabolic processes, protein translation, DNA synthesis, and DNA repair. The simplest types of Fe/S clusters include [2Fe-2S], [3Fe-4S], and [4Fe-4S] forms that sometimes are present in multiple copies. De novo assembly of Fe/S cofactors and their insertion into apoproteins in living cells requires complex proteinaceous machineries that are frequently highly conserved. In eukaryotes such as yeast and mammals, the mitochondrial iron-sulfur cluster assembly machinery and the cytosolic iron-sulfur protein assembly system consist of more than 30 components that cooperate in the generation of some 50 cellular Fe/S proteins. Both the mechanistic dissection of the intracellular Fe/S protein assembly pathways and the identification and characterization of Fe/S proteins rely on tool boxes of in vitro and in vivo methods. These cell biological, biochemical, and biophysical techniques help to determine the extent, stability, and type of bound Fe/S cluster. They also serve to distinguish bona fide Fe/S proteins from other metal-binding proteins containing similar cofactor coordination motifs. Here, we present a collection of in vitro methods that have proven useful for basic biochemical and biophysical characterization of Fe/S proteins. First, we describe the chemical assembly of [2Fe-2S] or [4Fe-4S] clusters on purified apoproteins. Then, we summarize a reconstitution system reproducing the de novo synthesis of a [2Fe-2S] cluster in mitochondria. Finally, we explain the use of UV-vis, CD, electron paramagnetic resonance, and Mössbauer spectroscopy for the routine characterization of Fe/S proteins.

A Resumable Fluorescent Probe BHN-Fe3O4@SiO2 Hybrid Nanostructure for Fe3+ and its Application in Bioimaging

A multifunctional fluorescent probe BHN-Fe₃O₄@SiO₂ nanostructure for Fe³⁺ was designed and developed. It has a good selective response to Fe³⁺ with fluorescence quenching and can be recycled using an external magnetic field. With adding EDTA (2.5 × 10^-5 M) to the consequent product Fe³⁺-BHN-Fe₃O₄@SiO₂, Fe³⁺ can be removed from the complex, and its fluorescence probing ability recovers, which means that this constituted on-off type fluorescence probe could be reversed and reused. At the same time, the probe has been successfully applied for quantitatively detecting Fe³⁺ in a linear mode with a low limit of detection 1.25 × 10^-8 M. Furthermore, the BHN-Fe₃O₄@SiO₂ nanostructure probe is successfully used to detect Fe³⁺ in living HeLa cells, which shows its great potential in bioimaging detection.

The single cyclic nucleotide-specific phosphodiesterase of the intestinal parasite Giardia lamblia represents a potential drug target

Background

Giardiasis is an intestinal infection correlated with poverty and poor drinking water quality, and treatment options are limited. According to the Center for Disease Control and Prevention, Giardia infections afflict nearly 33% of people in developing countries, and 2% of the adult population in the developed world. This study describes the single cyclic nucleotide-specific phosphodiesterase (PDE) of G. lamblia and assesses PDE inhibitors as a new generation of anti-giardial drugs.

Methods

An extensive search of the Giardia genome database identified a single gene coding for a class I PDE, GlPDE. The predicted protein sequence was analyzed in-silico to characterize its domain structure and catalytic domain. Enzymatic activity of GlPDE was established by complementation of a PDE-deficient Saccharomyces cerevisiae strain, and enzyme kinetics were characterized in soluble yeast lysates. The potency of known PDE inhibitors was tested against the activity of recombinant GlPDE expressed in yeast and against proliferating Giardia trophozoites. Finally, the localization of epitope-tagged and ectopically expressed GlPDE in Giardia cells was investigated.

Results

Giardia encodes a class I PDE. Catalytically important residues are fully conserved between GlPDE and human PDEs, but sequence differences between their catalytic domains suggest that designing Giardia-specific inhibitors is feasible. Recombinant GlPDE hydrolyzes cAMP with a K_m of 408 μM, and cGMP is not accepted as a substrate. A number of drugs exhibit a high degree of correlation between their potency against the recombinant enzyme and their inhibition of trophozoite proliferation in culture. Epitope-tagged GlPDE localizes as dots in a pattern reminiscent of mitosomes and to the perinuclear region in Giardia.

Conclusions

Our data strongly suggest that inhibition of G. lamblia PDE activity leads to a profound inhibition of parasite proliferation and that GlPDE is a promising target for developing novel anti-giardial drugs.

Cellular signaling by the cyclic nucleotides cAMP and cGMP is ubiquitously found in organisms from human to unicellular parasites. Cyclic nucleotide-specific phosphodiesterases (PDEs) are pivotal regulators of these signaling processes and these enzymes represent important drug targets for a variety of diseases. Eleven PDE families are distinguished in humans and selective inhibition of a single human PDE family without targeting others is feasible. In parasites, interference in the signaling mechanism by PDE inhibition may be fatal. The diarrhea-causing parasite Giardia lamblia contains only one single PDE, named GlPDE. GlPDE activity is highly impaired by a range of PDE inhibitors, which also suppress parasite proliferation in vitro. Thus, there is a good agreement between PDE inhibition and parasite drug susceptibility. We demonstrate molecular differences between human PDEs and GlPDE that can be exploited for the development of GlPDE-selective inhibitors. Finally, our data may suggest localization of GlPDE to mitosome organelles, which are absent in human cells and thus are in the focus as possible targets for the treatment of giardiasis. This may add to the notion that GlPDE represents a potential target for the development of novel anti-giardial drugs.

Giardia's primitive GPL biosynthesis pathways with parasitic adaptation 'patches': implications for Giardia's evolutionary history and for finding targets against Giardiasis

Giardia is a worldwide spread protozoan parasite colonizing in small intestines of vertebrates, causing Giardiasis. The controversy about whether it is an extremely primitive eukaryote or just a highly evolved parasite has become a fetter to its uses as a model for both evolutionary and parasitological studies for years. Glycerophospholipid (GPL) synthesis is a conserved essential cellular process, and thus may retain some original features reflecting its evolutionary position, and this process should also have undergone parasitic adaptation to suit Giardia’s dietary lipid-rich environment. Thus, GPL synthesis pathways may be a perfect object to examine the controversy over Giardia. Here, we first clarified Giardia’s previously confusing GPL synthesis by re-identifying a reliable set of GPL synthesis genes/enzymes. Then using phylogenetic and comparative genomic analyses, we revealed that these pathways turn out to be evolutionarily primitive ones, but with many secondary parasitic adaptation ‘patches’ including gene loss, rapid evolution, product relocation, and horizontal gene transfer. Therefore, modern Giardia should be a mosaic of ‘primary primitivity’ and ‘secondary parasitic adaptability’, and to make a distinction between the two categories of features would restart the studies of eukaryotic evolution and parasitic adaptation using Giardia as a model system.

Genomic Survey of a Hyperparasitic Microsporidian Amphiamblys sp. (Metchnikovellidae)

Metchnikovellidae are a group of unusual microsporidians that lack some of the defining ultrastructural features characteristic of derived Microsporidia and are thought to be one of their earliest-branching lineages. The basal position of metchnikovellids was never confirmed by molecular phylogeny in published research, and thus far no genomic data for this group were available. In this work, we obtain a partial genome of metchnikovellid Amphiamblys sp. using multiple displacement amplification, next-generation sequencing, and metagenomic binning approaches. The partial genome, which we estimate to be close to 90% complete, displays genome compaction on par with gene-dense microsporidian genomes, but contains an unusual repertoire of unique repeat elements. Phylogenetic analyses of multigene datasets place Amphiamblys sp. as the first branch of the microsporidian lineage following the divergence of a mitochondriate microsporidian Mitosporidium. We find evidence for a mitochondrial remnant presumably functionally equivalent to a mitosome in Amphiamblys sp. and the common enzymatic complement for microsporidian anaerobic metabolism. Comparative genomic analyses identify the conservation of components for clathrin vesicle formation as one of the key features distinguishing the metchnikovellid from its highly derived relatives. The presented data confirm the notion of Metchnikovellidae as a less derived microsporidian group, and provide an additional stepping stone for reconstruction of an evolutionary transition from the early diverging parasitic fungi to derived Microsporidia.