Sulfur mobilization for Fe-S cluster assembly by the essential SUF pathway in the Plasmodium falciparum apicoplast and its inhibition

Fe-S biogenesis by SMS and SUF pathways: A focus on the assembly step

FeS clusters are prosthetic groups present in all organisms. Proteins with FeS centers are involved in most cellular processes. ISC and SUF are machineries necessary for the formation and insertion of FeS in proteins. Recently, a phylogenetic analysis on more than 10,000 genomes of prokaryotes have uncovered two new systems, MIS and SMS, which were proposed to be ancestral to ISC and SUF. SMS is composed of SmsBC, two homologs of SufBC(D), the scaffolding complex of SUF. In this review, we will specifically focus on the current knowledge of the SUF system and on the new perspectives given by the recent discovery of its ancestor, the SMS system.

Apicoplast-Resident Processes: Exploiting the Chink in the Armour of Plasmodium falciparum Parasites

The discovery of a relict plastid, also known as an apicoplast (apicomplexan plastid), that houses housekeeping processes and metabolic pathways critical to Plasmodium parasites' survival has prompted increased research on identifying potent inhibitors that can impinge on apicoplast-localised processes. The apicoplast is absent in humans, yet it is proposed to originate from the eukaryote's secondary endosymbiosis of a primary symbiont. This symbiotic relationship provides a favourable microenvironment for metabolic processes such as haem biosynthesis, Fe-S cluster synthesis, isoprenoid biosynthesis, fatty acid synthesis, and housekeeping processes such as DNA replication, transcription, and translation, distinct from analogous mammalian processes. Recent advancements in comprehending the biology of the apicoplast reveal it as a vulnerable organelle for malaria parasites, offering numerous potential targets for effective antimalarial therapies. We provide an overview of the metabolic processes occurring in the apicoplast and discuss the organelle as a viable antimalarial target in light of current advances in drug discovery. We further highlighted the relevance of these metabolic processes to Plasmodium falciparum during the different stages of the lifecycle.

The interdependence of isoprenoid synthesis and apicoplast biogenesis in malaria parasites

Isoprenoid precursor synthesis is an ancient and fundamental function of plastid organelles and a critical metabolic activity of the apicoplast in Plasmodium malaria parasites [1-3]. Over the past decade, our understanding of apicoplast properties and functions has increased enormously [4], due in large part to our ability to rescue blood-stage parasites from apicoplast-specific dysfunctions by supplementing cultures with isopentenyl pyrophosphate (IPP), a key output of this organelle [5,6]. In this Pearl, we explore the interdependence between isoprenoid metabolism and apicoplast biogenesis in P. falciparum and highlight critical future questions to answer.

The Plasmodium falciparum apicoplast cysteine desulfurase provides sulfur for both iron-sulfur cluster assembly and tRNA modification

Iron-sulfur clusters (FeS) are ancient and ubiquitous protein cofactors that play fundamental roles in many aspects of cell biology. These cofactors cannot be scavenged or trafficked within a cell and thus must be synthesized in any subcellular compartment where they are required. We examined the FeS synthesis proteins found in the relict plastid organelle, called the apicoplast, of the human malaria parasite Plasmodium falciparum. Using a chemical bypass method, we deleted four of the FeS pathway proteins involved in sulfur acquisition and cluster assembly and demonstrated that they are all essential for parasite survival. However, the effect that these deletions had on the apicoplast organelle differed. Deletion of the cysteine desulfurase SufS led to disruption of the apicoplast organelle and loss of the organellar genome, whereas the other deletions did not affect organelle maintenance. Ultimately, we discovered that the requirement of SufS for organelle maintenance is not driven by its role in FeS biosynthesis, but rather, by its function in generating sulfur for use by MnmA, a tRNA modifying enzyme that we localized to the apicoplast. Complementation of MnmA and SufS activity with a bacterial MnmA and its cognate cysteine desulfurase strongly suggests that the parasite SufS provides sulfur for both FeS biosynthesis and tRNA modification in the apicoplast. The dual role of parasite SufS is likely to be found in other plastid-containing organisms and highlights the central role of this enzyme in plastid biology.

The ferredoxin redox system - an essential electron distributing hub in the apicoplast of Apicomplexa

The apicoplast, a relict plastid found in most species of the phylum Apicomplexa, harbors the ferredoxin redox system which supplies electrons to enzymes of various metabolic pathways in this organelle. Recent reports in Toxoplasma gondii and Plasmodium falciparum have shown that the iron-sulfur cluster (FeS)-containing ferredoxin is essential in tachyzoite and blood-stage parasites, respectively. Here we review ferredoxin's crucial contribution to isoprenoid and lipoate biosynthesis as well as tRNA modification in the apicoplast, highlighting similarities and differences between the two species. We also discuss ferredoxin's potential role in the initial reductive steps required for FeS synthesis as well as recent evidence that offers an explanation for how NADPH required by the redox system might be generated in Plasmodium spp.

Disrupting the plastidic iron-sulfur cluster biogenesis pathway in Toxoplasma gondii has pleiotropic effects irreversibly impacting parasite viability

Like many other apicomplexan parasites, Toxoplasma gondii contains a plastid harboring key metabolic pathways, including the sulfur utilization factor (SUF) pathway that is involved in the biosynthesis of iron-sulfur clusters. These cofactors are crucial for a variety of proteins involved in important metabolic reactions, potentially including plastidic pathways for the synthesis of isoprenoid and fatty acids. It was shown previously that impairing the NFS2 cysteine desulfurase, involved in the first step of the SUF pathway, leads to an irreversible killing of intracellular parasites. However, the metabolic impact of disrupting the pathway remained unexplored. Here, we generated another mutant of this pathway, deficient in the SUFC ATPase, and investigated in details the phenotypic consequences of TgNFS2 and TgSUFC depletion on the parasites. Our analysis confirms that Toxoplasma SUF mutants are severely and irreversibly impacted in division and membrane homeostasis, and suggests a defect in apicoplast-generated fatty acids. However, we show that increased scavenging from the host or supplementation with exogenous fatty acids do not fully restore parasite growth, suggesting that this is not the primary cause for the demise of the parasites and that other important cellular functions were affected. For instance, we also show that the SUF pathway is key for generating the isoprenoid-derived precursors necessary for the proper targeting of GPI-anchored proteins and for parasite motility. Thus, we conclude plastid-generated iron-sulfur clusters support the functions of proteins involved in several vital downstream cellular pathways, which implies the SUF machinery may be explored for new potential anti-Toxoplasma targets.

Lipoic Acid Metabolism as a Potential Chemotherapeutic Target Against Plasmodium falciparum and Staphylococcus aureus

Lipoic acid (LA) is an organic compound that plays a key role in cellular metabolism. It participates in a posttranslational modification (PTM) named lipoylation, an event that is highly conserved and that occurs in multimeric metabolic enzymes of very distinct microorganisms such as Plasmodium sp. and Staphylococcus aureus, including pyruvate dehydrogenase (PDH) and α-ketoglutarate dehydrogenase (KDH). In this mini review, we revisit the recent literature regarding LA metabolism in Plasmodium sp. and Staphylococcus aureus, by covering the lipoate ligase proteins in both microorganisms, the role of lipoate ligase proteins and insights for possible inhibitors of lipoate ligases.

Bacterial Approaches for Assembling Iron-Sulfur Proteins

Building iron-sulfur (Fe-S) clusters and assembling Fe-S proteins are essential actions for life on Earth. The three processes that sustain life, photosynthesis, nitrogen fixation, and respiration, require Fe-S proteins. Genes coding for Fe-S proteins can be found in nearly every sequenced genome. Fe-S proteins have a wide variety of functions, and therefore, defective assembly of Fe-S proteins results in cell death or global metabolic defects. Compared to alternative essential cellular processes, there is less known about Fe-S cluster synthesis and Fe-S protein maturation. Moreover, new factors involved in Fe-S protein assembly continue to be discovered. These facts highlight the growing need to develop a deeper biological understanding of Fe-S cluster synthesis, holo-protein maturation, and Fe-S cluster repair. Here, we outline bacterial strategies used to assemble Fe-S proteins and the genetic regulation of these processes. We focus on recent and relevant findings and discuss future directions, including the proposal of using Fe-S protein assembly as an antipathogen target.

Differential contribution of two organelles of endosymbiotic origin to iron-sulfur cluster synthesis and overall fitness in Toxoplasma

Iron-sulfur (Fe-S) clusters are one of the most ancient and ubiquitous prosthetic groups, and they are required by a variety of proteins involved in important metabolic processes. Apicomplexan parasites have inherited different plastidic and mitochondrial Fe-S clusters biosynthesis pathways through endosymbiosis. We have investigated the relative contributions of these pathways to the fitness of Toxoplasma gondii, an apicomplexan parasite causing disease in humans, by generating specific mutants. Phenotypic analysis and quantitative proteomics allowed us to highlight notable differences in these mutants. Both Fe-S cluster synthesis pathways are necessary for optimal parasite growth in vitro, but their disruption leads to markedly different fates: impairment of the plastidic pathway leads to a loss of the organelle and to parasite death, while disruption of the mitochondrial pathway trigger differentiation into a stress resistance stage. This highlights that otherwise similar biochemical pathways hosted by different sub-cellular compartments can have very different contributions to the biology of the parasites, which is something to consider when exploring novel strategies for therapeutic intervention.

The Multifaceted Bacterial Cysteine Desulfurases: From Metabolism to Pathogenesis

Living cells have developed a relay system to efficiently transfer sulfur (S) from cysteine to various thio-cofactors (iron-sulfur (Fe-S) clusters, thiamine, molybdopterin, lipoic acid, and biotin) and thiolated tRNA. The presence of such a transit route involves multiple protein components that allow the flux of S to be precisely regulated as a function of environmental cues to avoid the unnecessary accumulation of toxic concentrations of soluble sulfide (S²⁻). The first enzyme in this relay system is cysteine desulfurase (CSD). CSD catalyzes the release of sulfane S from L-cysteine by converting it to L-alanine by forming an enzyme-linked persulfide intermediate on its conserved cysteine residue. The persulfide S is then transferred to diverse acceptor proteins for its incorporation into the thio-cofactors. The thio-cofactor binding-proteins participate in essential and diverse cellular processes, including DNA repair, respiration, intermediary metabolism, gene regulation, and redox sensing. Additionally, CSD modulates pathogenesis, antibiotic susceptibility, metabolism, and survival of several pathogenic microbes within their hosts. In this review, we aim to comprehensively illustrate the impact of CSD on bacterial core metabolic processes and its requirement to combat redox stresses and antibiotics. Targeting CSD in human pathogens can be a potential therapy for better treatment outcomes.

[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.

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.

Fe-S cluster biogenesis by the bacterial Suf pathway

Biogenesis of iron-sulfur (FeS) clusters in an essential process in living organisms due to the critical role of FeS cluster proteins in myriad cell functions. During biogenesis of FeS clusters, multi-protein complexes are used to drive the mobilization and protection of reactive sulfur and iron intermediates, regulate assembly of various FeS clusters on an ATPase-dependent, multi-protein scaffold, and target nascent clusters to their downstream protein targets. The evolutionarily ancient sulfur formation (Suf) pathway for FeS cluster assembly is found in bacteria and archaea. In Escherichia coli, the Suf pathway functions as an emergency pathway under conditions of iron limitation or oxidative stress. In other pathogenic bacteria, such as Mycobacterium tuberculosis and Enterococcus faecalis, the Suf pathway is the sole source for FeS clusters and therefore is a potential target for the development of novel antibacterial compounds. Here we summarize the considerable progress that has been made in characterizing the first step of mobilization and protection of reactive sulfur carried out by the SufS-SufE or SufS-SufU complex, FeS cluster assembly on SufBC₂D scaffold complexes, and the downstream trafficking of nascent FeS clusters to A-type carrier (ATC) proteins. Cell Biology of Metals III edited by Roland Lill and Mick Petris.

Repurposing Drugs to Fight Hepatic Malaria Parasites

Malaria remains one of the most prevalent infectious diseases worldwide, primarily affecting some of the most vulnerable populations around the globe. Despite achievements in the treatment of this devastating disease, there is still an urgent need for the discovery of new drugs that tackle infection by Plasmodium parasites. However, de novo drug development is a costly and time-consuming process. An alternative strategy is to evaluate the anti-plasmodial activity of compounds that are already approved for other purposes, an approach known as drug repurposing. Here, we will review efforts to assess the anti-plasmodial activity of existing drugs, with an emphasis on the obligatory and clinically silent liver stage of infection. We will also review the current knowledge on the classes of compounds that might be therapeutically relevant against Plasmodium in the context of other communicable diseases that are prevalent in regions where malaria is endemic. Repositioning existing compounds may constitute a faster solution to the current gap of prophylactic and therapeutic drugs that act on Plasmodium parasites, overall contributing to the global effort of malaria eradication.

Discovery of a Natural Product That Binds to the Mycobacterium tuberculosis Protein Rv1466 Using Native Mass Spectrometry

Elucidation of the mechanism of action of compounds with cellular bioactivity is important for progressing compounds into future drug development. In recent years, phenotype-based drug discovery has become the dominant approach to drug discovery over target-based drug discovery, which relies on the knowledge of a specific drug target of a disease. Still, when targeting an infectious disease via a high throughput phenotypic assay it is highly advantageous to identifying the compound’s cellular activity. A fraction derived from the plant Polyalthia sp. showed activity against Mycobacterium tuberculosis at 62.5 μge/μL. A known compound, altholactone, was identified from this fraction that showed activity towards M. tuberculosis at an minimum inhibitory concentration (MIC) of 64 μM. Retrospective analysis of a target-based screen against a TB proteome panel using native mass spectrometry established that the active fraction was bound to the mycobacterial protein Rv1466 with an estimated pseudo-K_d of 42.0 ± 6.1 µM. Our findings established Rv1466 as the potential molecular target of altholactone, which is responsible for the observed in vivo toxicity towards M. tuberculosis.

The SUF system: an ABC ATPase-dependent protein complex with a role in Fe-S cluster biogenesis

Iron-sulfur (Fe-S) clusters are considered one of the most ancient and versatile inorganic cofactors present in the three domains of life. Fe-S clusters can act as redox sensors or catalysts and are found to be used by a large number of functional and structurally diverse proteins. Here, we cover current knowledge of the SUF multiprotein machinery that synthesizes and inserts Fe-S clusters into proteins. Specific focus is put on the ABC ATPase SufC, which contributes to building Fe-S clusters, and appeared early on during evolution.

Targeting the apicoplast in malaria

Malaria continues to be one of the leading causes of human mortality in the world, and the therapies available are insufficient for eradication. Severe malaria is caused by the apicomplexan parasite Plasmodium falciparum Apicomplexan parasites, including the Plasmodium spp., are descendants of photosynthetic algae, and therefore they possess an essential plastid organelle, named the apicoplast. Since humans and animals have no plastids, the apicoplast is an attractive target for drug development. Indeed, after its discovery, the apicoplast was found to host the target pathways of some known antimalarial drugs, which motivated efforts for further research into its biological functions and biogenesis. Initially, many apicoplast inhibitions were found to result in 'delayed death', whereby parasite killing is seen only at the end of one invasion-egress cycle. This slow action is not in line with the current standard for antimalarials, which seeded scepticism about the potential of compounds targeting apicoplast functions as good candidates for drug development. Intriguingly, recent evidence of apicoplast inhibitors causing rapid killing could put this organelle back in the spotlight. We provide an overview of drugs known to inhibit apicoplast pathways, alongside recent findings in apicoplast biology that may provide new avenues for drug development.

Functional analysis of iron-sulfur cluster biogenesis (SUF pathway) from Plasmodium vivax clinical isolates

Iron-sulfur (Fe-S) clusters are critical metallo-cofactors required for cell function. Assembly of these cofactors is a carefully controlled process in cells to avoid toxicity from free iron and sulfide. In Plasmodium, two pathways for these Fe-S cluster biogenesis have been reported; ISC pathway in the mitochondria and SUF pathway functional in the apicoplast. Amongst these, SUF pathway is reported essential for the apicoplast maintenance and parasite survival. Many of its components have been studied from P. falciparum and P. berghei in recent years, still few queries remain to be addressed; one of them being the assembly and transfer of Fe-S clusters. In this study, using P. vivax clinical isolates, we have shown the in vitro interaction of SUF pathway proteins SufS and SufE responsible for sulfur mobilization in the apicoplast. The sulfur mobilized by the SufSE complex assembles on the scaffold protein PvSufA along with iron provided by the external source. Here, we demonstrate in vitro transfer of these labile Fe-S clusters from the scaffold protein on to an apo-protein, PvIspG (a protein involved in penultimate step of Isoprenoids biosynthesis pathway) in order to provide an insight into the interaction of different components for the biosynthesis and transfer of Fe-S clusters. Our analysis indicate that inspite of the presence of variations in pathway proteins, the overall pathway remains well conserved in the clinical isolates when compared to that reported in lab strains.

Recent Advances in the [Fe-S] Cluster Biogenesis (SUF) Pathway Functional in the Apicoplast of Plasmodium

Iron-sulfur [Fe-S] clusters are one of the most ancient, ubiquitous, structurally and functionally versatile natural biosynthetic prosthetic groups required by various proteins involved in important metabolic processes. Genome mining and localization studies in Plasmodium have shown two evolutionarily distinct biogenesis pathways: the ISC pathway in mitochondria and the SUF pathway in the apicoplast. In recent years, the myriad efforts made to elucidate the SUF pathway have deciphered the role of various proteins involved in the pathway and their importance for the parasite life cycle in both asexual and sexual stages. This review aims to discuss recent research in the apicoplast [Fe-S] biogenesis pathway from Plasmodium to enhance our current understanding of parasite biology with an overall aim to identify gaps to strengthen our fight against malaria.

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.

Iron-sulfur clusters biogenesis by the SUF machinery: close to the molecular mechanism understanding

Iron–sulfur clusters (Fe–S) are amongst the most ancient and versatile inorganic cofactors in nature which are used by proteins for fundamental biological processes. Multiprotein machineries (NIF, ISC, SUF) exist for Fe–S cluster biogenesis which are mainly conserved from bacteria to human. SUF system (sufABCDSE operon) plays a general role in many bacteria under conditions of iron limitation or oxidative stress. In this mini-review, we will summarize the current understanding of the molecular mechanism of Fe–S biogenesis by SUF. The advances in our understanding of the molecular aspects of SUF originate from biochemical, biophysical and recent structural studies. Combined with recent in vivo experiments, the understanding of the Fe–S biogenesis mechanism considerably moved forward.

Exploiting the apicoplast: apicoplast-targeting drugs and malaria vaccine development

The apicoplast, a relic plastid found in most Apicomplexan parasites, is a notable drug target. Certain antibiotics elicit a delayed death phenotype by targeting this organelle. Here, we review apicoplast-targeting drugs and their targets, particularly those that cause delayed death, and highlight its potential uses in malaria vaccine development.

Molecular basis of function and the unusual antioxidant activity of a cyanobacterial cysteine desulfurase

Cysteine desulfurases, which supply sulfur for iron-sulfur cluster biogenesis, are broadly distributed in all phyla including cyanobacteria, the progenitors of plant chloroplasts. The SUF (sulfur utilization factor) system is responsible for Fe-S cluster biosynthesis under stress. The suf operon from cyanobacterium Anabaena PCC 7120 showed the presence of a cysteine desulfurase, sufS (alr2495), but not the accessory sulfur-accepting protein (SufE). However, an open reading frame (alr3513) encoding a SufE-like protein (termed AsaE, Anabaena sulfur acceptor E) was found at a location distinct from the suf operon. The purified SufS protein existed as a pyridoxal 5' phosphate (PLP)-containing dimer with a relatively low desulfurase activity. Interestingly, in the presence of the AsaE protein, the catalytic efficiency of this reaction increased 10-fold. In particular, for sulfur mobilization, the AsaE protein partnered only SufS and not other cysteine desulfurases from Anabaena. The SufS protein was found to physically interact with the AsaE protein, demonstrating that AsaE was indeed the missing partner of Anabaena SufS. The conserved cysteine of the SufS or the AsaE protein was essential for activity but not for their physical association. Curiously, overexpression of the SufS protein in Anabaena caused reduced formation of reactive oxygen species on exposure to hydrogen peroxide (H₂O₂), resulting in superior oxidative stress tolerance to the oxidizing agent when compared with the wild-type strain. Overall, the results highlight the functional interaction between the two proteins that mediate sulfur mobilization, in the cyanobacterial SUF pathway, and further reveal that overexpression of SufS can protect cyanobacteria from oxidative stress.

An intact plastid genome is essential for the survival of colorless Euglena longa but not Euglena gracilis

Euglena gracilis growth with antibacterial agents leads to bleaching, permanent plastid gene loss. Colorless Euglena (Astasia) longa resembles a bleached E. gracilis. To evaluate the role of bleaching in E. longa evolution, the effect of streptomycin, a plastid protein synthesis inhibitor, and ofloxacin, a plastid DNA gyrase inhibitor, on E. gracilis and E. longa growth and plastid DNA content were compared. E. gracilis growth was unaffected by streptomycin and ofloxacin. Quantitative PCR analyses revealed a time dependent loss of plastid genes in E. gracilis demonstrating that bleaching agents produce plastid gene deletions without affecting cell growth. Streptomycin and ofloxacin inhibited E. longa growth indicating that it requires plastid genes to survive. This suggests that evolutionary divergence of E. longa from E. gracilis was triggered by the loss of a cytoplasmic metabolic activity also occurring in the plastid. Plastid metabolism has become obligatory for E. longa cell growth. A process termed "intermittent bleaching", short term exposure to subsaturating concentrations of reversible bleaching agents followed by growth in the absence of a bleaching agent, is proposed as the molecular mechanism for E. longa plastid genome reduction. Various non-photosynthetic lineages could have independently arisen from their photosynthetic ancestors via a similar process.

Computer-Aided Drug Discovery Approaches against the Tropical Infectious Diseases Malaria, Tuberculosis, Trypanosomiasis, and Leishmaniasis

Despite the tremendous improvement in overall global health heralded by the adoption of the Millennium Declaration in the year 2000, tropical infections remain a major health problem in the developing world. Recent estimates indicate that the major tropical infectious diseases, namely, malaria, tuberculosis, trypanosomiasis, and leishmaniasis, account for more than 2.2 million deaths and a loss of approximately 85 million disability-adjusted life years annually. The crucial role of chemotherapy in curtailing the deleterious health and economic impacts of these infections has invigorated the search for new drugs against tropical infectious diseases. The research efforts have involved increased application of computational technologies in mainstream drug discovery programs at the hit identification, hit-to-lead, and lead optimization stages. This review highlights various computer-aided drug discovery approaches that have been utilized in efforts to identify novel antimalarial, antitubercular, antitrypanosomal, and antileishmanial agents. The focus is largely on developments over the past 5 years (2010-2014).

Recent advances in the Suf Fe-S cluster biogenesis pathway: Beyond the Proteobacteria

Fe-S clusters play critical roles in cellular function throughout all three kingdoms of life. Consequently, Fe-S cluster biogenesis systems are present in most organisms. The Suf (sulfur formation) system is the most ancient of the three characterized Fe-S cluster biogenesis pathways, which also include the Isc and Nif systems. Much of the first work on the Suf system took place in Gram-negative Proteobacteria used as model organisms. These early studies led to a wealth of biochemical, genetic, and physiological information on Suf function. From those studies we have learned that SufB functions as an Fe-S scaffold in conjunction with SufC (and in some cases SufD). SufS and SufE together mobilize sulfur for cluster assembly and SufA traffics the complete Fe-S cluster from SufB to target apo-proteins. However, recent progress on the Suf system in other organisms has opened up new avenues of research and new hypotheses about Suf function. This review focuses primarily on the most recent discoveries about the Suf pathway and where those new models may lead the field. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases.