Chaperone properties of Escherichia coli thioredoxin and thioredoxin reductase

From ubiquity to specificity: The diverse functions of bacterial thioredoxin systems

The thioredoxin (Trx) system, found universally, is responsible for the regeneration of reversibly oxidized protein thiols in living cells. This system is made up of a Trx and a Trx reductase, and it plays a central role in maintaining thiol-based redox homeostasis by reducing oxidized protein thiols, such as disulfide bonds in proteins. Some Trxs also possess a chaperone function that is independent of thiol-disulfide exchange, in addition to their thiol-disulfide reductase activity. These two activities of the Trx system are involved in numerous physiological processes in bacteria. This review describes the diverse physiological roles of the Trx system that have emerged throughout bacterial evolution. The Trx system is essential for responding to oxidative and nitrosative stress. Beyond this primary function, the Trx system also participates in redox regulation and signal transduction, and in controlling metabolism, motility, biofilm formation, and virulence. This range of functions has evolved alongside the diversity of bacterial lifestyles and their specific constraints. This evolution can be characterized by the multiplication of the systems and by the specialization of cofactors or targets to adapt to the constraints of atypical lifestyles, such as photosynthesis, insect endosymbiosis, or spore-forming bacteria.

Resolving the challenge of insoluble production of mature human growth differentiation factor 9 protein (GDF9) in E. coli using bicistronic expression with thioredoxin

Growth differentiation factor 9 (GDF9) is an oocyte-derived protein with fundamental functions in folliculogenesis. While the crucial contributions of GDF9 in follicular survival have been revealed, crystallographic studies of GDF9 structure have not yet been carried out, essentially due to the insoluble expression of GDF9 in E. coli and lack of appropriate source for structural studies. Therefore, in this study, we investigated the impact of different expression rate of bacterial thioredoxin (TrxA) using bicistronic expression constructs to induce the soluble expression of mature human GDF9 (hGDF9) driven by T7 promoter in E. coli. Our findings revealed that in BL21(DE3), the high rate of TrxA co-expression at 30 °C was sufficiently potent for the soluble expression of hGDF9 and reduction of inclusion body formation by 4 fold. We also successfully confirmed the bioactivity of the purified soluble hGDF9 protein by evaluation of follicle-stimulating hormone receptor gene expression in bovine cumulus cells derived from small follicles. This study is the first to present an effective approach for expression of bioactive form of hGDF9 using TrxA co-expression in E. coli, which may unravel the current issues regarding structural analysis of hGDF9 protein and consequently provide a better insight into hGDF9 functions and interactions.

Promiscuity of response regulators for thioredoxin steers bacterial virulence

The exquisite specificity between a sensor kinase and its cognate response regulator ensures faithful partner selectivity within two-component pairs concurrently firing in a single bacterium, minimizing crosstalk with other members of this conserved family of paralogous proteins. We show that conserved hydrophobic and charged residues on the surface of thioredoxin serve as a docking station for structurally diverse response regulators. Using the OmpR protein, we identify residues in the flexible linker and the C-terminal β-hairpin that enable associations of this archetypical response regulator with thioredoxin, but are dispensable for interactions of this transcription factor to its cognate sensor kinase EnvZ, DNA or RNA polymerase. Here we show that the promiscuous interactions of response regulators with thioredoxin foster the flow of information through otherwise highly dedicated two-component signaling systems, thereby enabling both the transcription of Salmonella pathogenicity island-2 genes as well as growth of this intracellular bacterium in macrophages and mice.

Active site center redesign increases protein stability preserving catalysis in thioredoxin

The stabilization of natural proteins is a long‐standing desired goal in protein engineering. Optimizing the hydrophobicity of the protein core often results in extensive stability enhancements. However, the presence of totally or partially buried catalytic charged residues, essential for protein function, has limited the applicability of this strategy. Here, focusing on the thioredoxin, we aimed to augment protein stability by removing buried charged residues in the active site without loss of catalytic activity. To this end, we performed a charged‐to‐hydrophobic substitution of a buried and functional group, resulting in a significant stability increase yet abolishing catalytic activity. Then, to simulate the catalytic role of the buried ionizable group, we designed a combinatorial library of variants targeting a set of seven surface residues adjacent to the active site. Notably, more than 50% of the library variants restored, to some extent, the catalytic activity. The combination of experimental study of 2% of the library with the prediction of the whole mutational space by partial least squares regression revealed that a single point mutation at the protein surface is sufficient to fully restore the catalytic activity without thermostability cost. As a result, we engineered one of the highest thermal stabilities reported for a protein with a natural occurring fold (137°C). Further, our hyperstable variant preserves the catalytic activity both in vitro and in vivo.

The Thioredoxin System of Mammalian Cells and Its Modulators

Oxidative stress involves the increased production and accumulation of free radicals, peroxides, and other metabolites that are collectively termed reactive oxygen species (ROS), which are produced as by-products of aerobic respiration. ROS play a significant role in cell homeostasis through redox signaling and are capable of eliciting damage to macromolecules. Multiple antioxidant defense systems have evolved to prevent dangerous ROS accumulation in the body, with the glutathione and thioredoxin/thioredoxin reductase (Trx/TrxR) systems being the most important. The Trx/TrxR system has been used as a target to treat cancer through the thiol–disulfide exchange reaction mechanism that results in the reduction of a wide range of target proteins and the generation of oxidized Trx. The TrxR maintains reduced Trx levels using NADPH as a co-substrate; therefore, the system efficiently maintains cell homeostasis. Being a master regulator of oxidation–reduction processes, the Trx-dependent system is associated with cell proliferation and survival. Herein, we review the structure and catalytic properties of the Trx/TrxR system, its role in cellular signaling in connection with other redox systems, and the factors that modulate the Trx system.

The Functions of Thioredoxin 1 in Neurodegeneration

Significance: Thioredoxin 1 (Trx1) is a ubiquitous protein that is found in organisms ranging from prokaryotes to eukaryotes. Trx1 acts as reductases in redox regulation and protects proteins from oxidative aggregation and inactivation. Trx1 helps the cells to cope with various environmental stresses and inhibits programmed cell death. It is beneficial to neuroregeneration and resistance against oxidative stress-associated neuron damage. Trx1 also plays important roles in suppressing neurodegenerative disorders. Recent Advances: Trx1 is a redox regulating protein involved in neuronal protection. According to a previous study, Trx1 expression is increased by nerve growth factor (NGF) and necessary for neurite outgrowth of PC12 cells. Trx1 has been shown to promote the growth of neurons. Trx1 knockout or knockdown has the worse impact on cell viability and survival. Critical Issues: Trx1 has functions in central nervous system. Trx1 plays the defensive roles against oxidative stress in neurodegenerative diseases. Future Directions: In this review, we focus on the structure of Trx1 and basic functions of Trx1. Trx1 plays a neuroprotective role by suppressing endoplasmic reticulum stress in Parkinson's disease. Neurodegenerative diseases have no cure and carry a high cost to the health care system and patient's families. Trx1 may be taken as a new target for neurodegenerative disorder therapy. Further studies of the Trx1 roles and mechanisms on neurodegenerative diseases are needed. Antioxid. Redox Signal. 36, 1023-1036.

Thiol-based switching mechanisms of stress-sensing chaperones

Thiol-based redox switches evolved as efficient post-translational regulatory mechanisms that enable individual proteins to rapidly respond to sudden environmental changes. While some protein functions need to be switched off to save resources and avoid potentially error-prone processes, protective functions become essential and need to be switched on. In this review, we focus on thiol-based activation mechanisms of stress-sensing chaperones. Upon stress exposure, these chaperones convert into high affinity binding platforms for unfolding proteins and protect cells against the accumulation of potentially toxic protein aggregates. Their chaperone activity is independent of ATP, a feature that becomes especially important under oxidative stress conditions, where cellular ATP levels drop and canonical ATP-dependent chaperones no longer operate. Vice versa, reductive inactivation and substrate release require the restoration of ATP levels, which ensures refolding of client proteins by ATP-dependent foldases. We will give an overview over the different strategies that cells evolved to rapidly increase the pool of ATP-independent chaperones upon oxidative stress and provide mechanistic insights into how stress conditions are used to convert abundant cellular proteins into ATP-independent holding chaperones.

Targeting Bacterial Antioxidant Systems for Antibiotics Development

The emergence of multidrug-resistant bacteria has become an urgent issue in modern medicine which requires novel strategies to develop antibiotics. Recent studies have supported the hypothesis that antibiotic-induced bacterial cell death is mediated by Reactive Oxygen Species (ROS). The hypothesis also highlighted the importance of antioxidant systems, the defense mechanism which contributes to antibiotic resistance. Thioredoxin and glutathione systems are the two major thiol-dependent systems which not only provide antioxidant capacity but also participate in various biological events in bacteria, such as DNA synthesis and protein folding. The biological importance makes them promising targets for novel antibiotics development. Based on the idea, ebselen and auranofin, two bacterial thioredoxin reductase inhibitors, have been found to inhibit the growth of bacteria lacking the GSH efficiently. A recent study combining ebselen and silver exhibited a strong synergistic effect against Multidrug-Resistant (MDR) Gram-negative bacteria which possess both thioredoxin and glutathione systems. These drug-repurposing studies are promising for quick clinical usage due to their well-known profile.

Functional Improvement of Human Cardiotrophin 1 Produced in Tobacco Chloroplasts by Co-expression with Plastid Thioredoxin m

Human cardiotrophin 1 (CT1), a cytokine with excellent therapeutic potential, was previously expressed in tobacco chloroplasts. However, the growth conditions required to reach the highest expression levels resulted in an impairment of its bioactivity. In the present study, we have examined new strategies to modulate the expression of this recombinant protein in chloroplasts so as to enhance its production and bioactivity. In particular, we assessed the effect of both the fusion and co-expression of Trx m with CT1 on the production of a functional CT1 by using plastid transformation. Our data revealed that the Trx m fusion strategy was useful to increase the expression levels of CT1 inside the chloroplasts, although CT1 bioactivity was significantly impaired, and this was likely due to steric hindrance between both proteins. By contrast, the expression of functional CT1 was increased when co-expressed with Trx m, because we demonstrated that recombinant CT1 was functionally active during an in vitro signaling assay. While Trx m/CT1 co-expression did not increase the amount of CT1 in young leaves, our results revealed an increase in CT1 protein stability as the leaves aged in this genotype, which also improved the recombinant protein's overall production. This strategy might be useful to produce other functional biopharmaceuticals in chloroplasts.

An essential thioredoxin-type protein of Trypanosoma brucei acts as redox-regulated mitochondrial chaperone

Most known thioredoxin-type proteins (Trx) participate in redox pathways, using two highly conserved cysteine residues to catalyze thiol-disulfide exchange reactions. Here we demonstrate that the so far unexplored Trx2 from African trypanosomes (Trypanosoma brucei) lacks protein disulfide reductase activity but functions as an effective temperature-activated and redox-regulated chaperone. Immunofluorescence microscopy and fractionated cell lysis revealed that Trx2 is located in the mitochondrion of the parasite. RNA-interference and gene knock-out approaches showed that depletion of Trx2 impairs growth of both mammalian bloodstream and insect stage procyclic parasites. Procyclic cells lacking Trx2 stop proliferation under standard culture conditions at 27°C and are unable to survive prolonged exposure to 37°C, indicating that Trx2 plays a vital role that becomes augmented under heat stress. Moreover, we found that Trx2 contributes to the in vivo infectivity of T. brucei. Remarkably, a Trx2 version, in which all five cysteines were replaced by serine residues, complements for the wildtype protein in conditional knock-out cells and confers parasite infectivity in the mouse model. Characterization of the recombinant protein revealed that Trx2 can coordinate an iron sulfur cluster and is highly sensitive towards spontaneous oxidation. Moreover, we discovered that both wildtype and mutant Trx2 protect other proteins against thermal aggregation and preserve their ability to refold upon return to non-stress conditions. Activation of the chaperone function of Trx2 appears to be triggered by temperature-mediated structural changes and inhibited by oxidative disulfide bond formation. Our studies indicate that Trx2 acts as a novel chaperone in the unique single mitochondrion of T. brucei and reveal a new perspective regarding the physiological function of thioredoxin-type proteins in trypanosomes.

Evolution of the thioredoxin system as a step enabling adaptation to oxidative stress

Thioredoxins (Trxs) are low-molecular-weight proteins that participate in the reduction of target enzymes. Trxs contain a redox-active disulfide bond, in the form of a WCGPC amino acid sequence motif, that enables them to perform dithiol-disulfide exchange reactions with oxidized protein substrates. Widely distributed across the three domains of life, Trxs form an evolutionarily conserved family of ancient origin. Thioredoxin reductases (TRs) are enzymes that reduce Trxs. According to their evolutionary history, TRs have diverged, thereby leading to the emergence of variants of the enzyme that in combination with different types of Trxs meet the needs of the cell. In addition to participating in the regulation of metabolism and defense against oxidative stress, Trxs respond to environmental signals-an ability that developed early in evolution. Redox regulation of proteins targeted by Trx is accomplished with a pair of redox-active cysteines located in strategic positions on the polypeptide chain to enable reversible oxidative changes that result in structural and functional modifications target proteins. In this review, we present a general overview of the thioredoxin system and describe recent structural studies on the diversity of its components.

Mycobacterial transcript cleavage factor Gre, exhibits chaperone-like activity

Gre factors reactivate stalled elongation complexes by enhancing the intrinsic transcript cleavage activity of RNA polymerase. Previous work by us has shown that unlike in Escherichia coli (E.coli), Mycobacterium tuberculosis Gre factor is essential for its survival. Apart from their role in transcription regulation Gre factors have been implicated in stress response. A recent study has shown the role of E.coli GreA as a cellular chaperone, which inhibits aggregation of substrate proteins under heat stress condition. Moreover it was shown that GreA enables E.coli to survive heat shock and oxidative stress. In the current work, we have characterized the moonlighting chaperone activity and its plausible mechanism in Mycobacterium smegmatis Gre (MsGre) factor. We show here that MsGre prevents heat-induced aggregation of the substrate protein and also protects enzymatic activity. Interestingly Gre factor exists as a dimer in solution and does not undergo heat induced oligomerization. From the 8-anilino-1-naphthalene sulfonate (ANS) binding studies MsGre was shown to expose hydrophobic surface upon heat stress that would allow binding to unfolded or partially folded substrate protein. From Circular Dichroism (CD) studies, we also show that MsGre has a stable secondary structure under thermal stress. We propose that the presence of C-terminal FKBP-like fold in MsGre factor that might contribute to its chaperone-like function.

Redox-dependent and redox-independent functions of Caenorhabditis elegans thioredoxin 1

Thioredoxins (TRX) are traditionally considered as enzymes catalyzing redox reactions. However, redox-independent functions of thioredoxins have been described in different organisms, although the underlying molecular mechanisms are yet unknown. We report here the characterization of the first generated endogenous redox-inactive thioredoxin in an animal model, the TRX-1 in the nematode Caenorhabditis elegans. We find that TRX-1 dually regulates the formation of an endurance larval stage (dauer) by interacting with the insulin pathway in a redox-independent manner and the cGMP pathway in a redox-dependent manner. Moreover, the requirement of TRX-1 for the extended longevity of worms with compromised insulin signalling or under calorie restriction relies on TRX-1 redox activity. In contrast, the nuclear translocation of the SKN-1 transcription factor and increased LIPS-6 protein levels in the intestine upon trx-1 deficiency are strictly redox-independent. Finally, we identify a novel function of C. elegans TRX-1 in male food-leaving behaviour that is redox-dependent. Taken together, our results position C. elegans as an ideal model to gain mechanistic insight into the redox-independent functions of metazoan thioredoxins, overcoming the limitations imposed by the embryonic lethal phenotypes of thioredoxin mutants in higher organisms.

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C. elegans expressing endogenous “redox-dead” TRX-1 are viable.

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The extended lifespan extension of worm daf-2 and eat-2 mutants and the food-leaving behaviour of C. elegans males requires a redox-active TRX-1.

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The SKN-1 nuclear translocation and increased lips-6 expression upon TRX-1 deficiency is redox-independent.

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TRX-1 regulates dauer formation by both redox-dependent and redox-independent mechanisms.

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C. elegans is an ideal model to interrogate on the molecular mechanisms underlying the redox-independent functions of metazoan thioredoxins.

Protein Promiscuity in H2O2 Signaling

SIGNIFICANCE

Decrypting the cellular response to oxidative stress relies on a comprehensive understanding of the redox signaling pathways stimulated under oxidizing conditions. Redox signaling events can be divided into upstream sensing of oxidants, midstream redox signaling of protein function, and downstream transcriptional redox regulation. Recent Advances: A more and more accepted theory of hydrogen peroxide (H₂O₂) signaling is that of a thiol peroxidase redox relay, whereby protein thiols with low reactivity toward H₂O₂ are instead oxidized through an oxidative relay with thiol peroxidases.

CRITICAL ISSUES

These ultrareactive thiol peroxidases are the upstream redox sensors, which form the first cellular port of call for H₂O₂. Not all redox-regulated interactions between thiol peroxidases and cellular proteins involve a transfer of oxidative equivalents, and the nature of redox signaling is further complicated through promiscuous functions of redox-regulated "moonlighting" proteins, of which the precise cellular role under oxidative stress can frequently be obscured by "polygamous" interactions. An ultimate goal of redox signaling is to initiate a rapid response, and in contrast to prokaryotic oxidant-responsive transcription factors, mammalian systems have developed redox signaling pathways, which intersect both with kinase-dependent activation of transcription factors, as well as direct oxidative regulation of transcription factors through peroxiredoxin (Prx) redox relays.

FUTURE DIRECTIONS

We highlight that both transcriptional regulation and cell fate can be modulated either through oxidative regulation of kinase pathways, or through distinct redox-dependent associations involving either Prxs or redox-responsive moonlighting proteins with functional promiscuity. These protein associations form systems of crossregulatory networks with multiple nodes of potential oxidative regulation for H₂O₂-mediated signaling.

Identification of thioredoxin domain-containing protein 17 from big-belly seahorse Hippocampus abdominalis: Molecular insights, immune responses, and functional characterization

Thioredoxin domain-containing protein 17 (TXNDC17) is a small protein (∼14 kDa) involved in maintaining cellular redox homeostasis via a thiol-disulfide reductase activity. In this study, TXNDC17 was identified and characterized from Hippocampus abdominalis. The open reading frame (ORF) consisted of 369 bp and 123 amino acids. Similar to the other thioredoxins, TXNDC17 contained a conserved WCXXC functional motif. The highest spatial mRNA expressions of HaTXNDC17 were observed in the muscle, brain, and intestine. Interestingly, the mRNA expression of HaTXNDC17 in blood showed significant upregulation at 48 h against all the pathogen associated molecular patterns (PAMPs) and bacteria. Further, HaTXNDC17 transcripts in the trunk kidney were significantly upregulated at 24-48 h by bacterial endotoxin lipopolysaccharides (LPS), viral mimic polyinosinic: polycytidylic acid (poly I:C), and gram-negative bacteria (Edwardsiella tarda). The DPPH assay showed that the radical scavenging activity varies in a concentration-dependent manner. The insulin reduction assay demonstrated a significant logarithmic relationship with the concentration of rHaTXNDC17. Moreover, FHM cells treated with recombinant HaTXNDC17 significantly enhanced cellular viability under oxidative stress. Together, these results show that HaTXNDC17 function is important for maintaining cellular redox homeostasis and that it is also involved in the immune mechanism in seahorses.

Proteomics investigation of molecular mechanisms affected by EnBase culture system in anti-VEGF fab fragment producing E. coli BL21 (DE3)

Aggregation of recombinant proteins, a major problem in E. coli expression system, is improved by using EnBase culture system based on slow release of glucose. In the present study, to understand the intracellular mechanisms involved in increased solubility of the target recombinant protein through EnBase system, the effect of this system was investigated on E. coli cells proteome profile. The proteome profile of E. coli cells cultured in EnBase and conventional batch mode was analyzed by two-dimensional gel electrophoresis. The proteins with significant expressional changes were identified through MALDI-TOF/TOF mass spectrometry. In EnBase system, the expressions of carbon metabolism-related proteins, sugar transport system-related proteins, and amino acids metabolism-related proteins were significantly altered. Furthermore, the expression of Thioredoxin 1 as the facilitator of protein folding was up-regulated in EnBase system that could be related to the increased solubility of recombinant protein. The proteomics analysis of E. coli cells cultured in EnBase system revealed that Thioredoxin 1 can be a potential candidate for future studies aiming at increased anti-VEGF fab fragment solubility. Studying proteomics is a valuable tool for revealing the target proteins that play the central role in EnBase culture system for increasing the solubility.

Grxcr2 is required for stereocilia morphogenesis in the cochlea

Hearing and balance depend upon the precise morphogenesis and mechanosensory function of stereocilia, the specialized structures on the apical surface of sensory hair cells in the inner ear. Previous studies of Grxcr1 mutant mice indicated a critical role for this gene in control of stereocilia dimensions during development. In this study, we analyzed expression of the paralog Grxcr2 in the mouse and evaluated auditory and vestibular function of strains carrying targeted mutations of the gene. Peak expression of Grxcr2 occurs during early postnatal development of the inner ear and GRXCR2 is localized to stereocilia in both the cochlea and in vestibular organs. Homozygous Grxcr2 deletion mutants exhibit significant hearing loss by 3 weeks of age that is associated with developmental defects in stereocilia bundle orientation and organization. Despite these bundle defects, the mechanotransduction apparatus assembles in relatively normal fashion as determined by whole cell electrophysiological evaluation and FM1-43 uptake. Although Grxcr2 mutants do not exhibit overt vestibular dysfunction, evaluation of vestibular evoked potentials revealed subtle defects of the mutants in response to linear accelerations. In addition, reduced Grxcr2 expression in a hypomorphic mutant strain is associated with progressive hearing loss and bundle defects. The stereocilia localization of GRXCR2, together with the bundle pathologies observed in the mutants, indicate that GRXCR2 plays an intrinsic role in bundle orientation, organization, and sensory function in the inner ear during development and at maturity.

Further characterization of the Maillard deglycase DJ-1 and its prokaryotic homologs, deglycase 1/Hsp31, deglycase 2/YhbO, and deglycase 3/YajL

We reported recently that the Parkinsonism-associated protein DJ-1 and its bacterial homologs Hsp31, YhbO and YajL function as deglycases that repair proteins and nucleotides from endogeneous glycation by glyoxal and methylglyoxal, two reactive by-products of glucose metabolism responsible for up to 60% of glycation damage. Here, we show that DJ-1, deglycase 1 and deglycase 2 repair glyoxal- and methylglyoxal-glycated substrates, whereas deglycase 3 principally repairs glyoxal-glycated substrates. Moreover, deglycase 1 and 2 are overexpressed in stationary phase, whereas deglycase 3 is steadily expressed throughout bacterial growth. Finally, deglycase mutants overexpress glyoxalases, aldoketoreductases, glutathione-S-transferase and efflux pumps to alleviate carbonyl stress. In the discussion, we present an overview of the multiple functions of DJ-1 proteins. Our thourough work on deglycases provides compelling evidence that their previously reported glyoxalase III activity merely reflects their deglycase activity. Moreover, for their deglycase activity the Maillard deglycases likely recruit: i) their chaperone activity to interact with glycated proteins, ii) glyoxalase 1 activity to catalyze the rearrangement of Maillard products (aminocarbinols and hemithioacetals) into amides and thioesters, respectively, iii) their protease activity to cleave amide bonds of glycated arginine, lysine and guanine, and iv) glyoxalase 2 activity to cleave thioester bonds of glycated cysteine. Finally, because glycation affects many cellular processes, the discovery of the Maillard deglycases, awaited since 1912, likely constitutes a major advance for medical research, including ageing, cancer, atherosclerosis, neurodegenerative, post-diabetic, renal and autoimmune diseases.

Production of recombinant salmon insulin-like growth factor binding protein-1 subtypes

Insulin-like growth factor (IGF)-I is a growth promoting hormone that exerts its actions through endocrine, paracrine and autocrine modes. Local IGF-I is essential for normal growth, whereas circulating IGF-I plays a crucial role in regulating the production and secretion of growth hormone (GH) by the pituitary gland. These actions of IGF-I are modulated by six insulin-like growth factor binding proteins (IGFBPs). In teleosts, two subtypes of each IGFBP are present due to an extra round of whole-genome duplication. IGFBP-1 is generally inhibitory to IGF-I action under catabolic conditions such as fasting and stress. In salmon, IGFBP-1a and -1b are two of three major circulating IGFBPs and assumed to affect growth through modulating IGF-I action. However, exact functions of salmon IGFBP-1 subtypes on growth regulation are not known due to the lack of purified or recombinant protein. We expressed recombinant salmon (rs) IGFBP-1a and -1b with a fusion protein (thioredoxin, Trx) and a His-tag using the pET-32a(+) vector expression system in Escherichia coli. Trx.His.rsIGFBP-1s were isolated by Ni-affinity chromatography, enzymatically cleaved by enterokinase to remove the fusion partners and further purified by reversed-phase HPLC. We next examined effects of rsIGFBP-1a and -1b in combination with human IGF-I on GH release from cultured masu salmon (Oncorhynchus masou) pituitary cells. Unexpectedly, IGF-I increased GH release and an addition of rsIGFBP-1a, but not rsIGFBP-1b, restored GH levels. The results suggest that IGFBP-1a can inhibit IGF-I action on the pituitary in masu salmon. Availability of recombinant salmon IGFBP-1s should facilitate further functional analyses and assay development.

Recombinant expression of Intrepicalcin from the scorpion Vaejovis intrepidus and its effect on skeletal ryanodine receptors

BACKGROUND

Scorpion venoms contain toxins that modulate ionic channels, among which are the calcins, a small group of short, basic peptides with an Inhibitor Cystine Knot (ICK) motif that target calcium release channels/ryanodine receptors (RyRs) with high affinity and selectivity. Here we describe the heterologous expression of Intrepicalcin, identified by transcriptomic analysis of venomous glands from Vaejovis intrepidus.

METHODS

Recombinant Intrepicalcin was obtained in Escherichia coli BL21-DE3 (periplasm) by fusing the Intrepicalcin gene to sequences coding for signal-peptide, thioredoxin, His-tag and enterokinase cleavage site.

RESULTS

[³H]Ryanodine binding, used as a functional index of RyR activity, revealed that recombinant Intrepicalcin activates skeletal RyR (RyR1) dose-dependently with K_d=17.4±4.0nM. Intrepicalcin significantly augments the bell-shaped [Ca²⁺]-[³H]ryanodine binding curve at all [Ca²⁺] ranges, as is characteristic of the calcins. In single channel recordings, Intrepicalcin induces the appearance of a subconductance state in RyR1 with a fractional value ∼55% of the full conductance state, very close to that of Vejocalcin. Furthermore, Intrepicalcin stimulates Ca²⁺ release at an initial dose=45.3±2.5nM, and depletes ~50% of Ca²⁺ load from skeletal sarcoplasmic reticulum vesicles.

CONCLUSIONS

We conclude that active recombinant Intrepicalcin was successfully obtained without the need of manual oxidation, enabling it to target RyR1s with high affinity.

GENERAL SIGNIFICANCE

This is the first calcin heterologously expressed in the periplasma of Escherichia coli BL21-DE3, shown to be pharmacologically effective, thus paving the way for the generation of Intrepicalcin variants that are required for structure-function relationship studies of calcins and RyRs.

DJ-1 family Maillard deglycases prevent acrylamide formation

The presence of acrylamide in food is a worldwide concern because it is carcinogenic, reprotoxic and neurotoxic. Acrylamide is generated in the Maillard reaction via condensation of reducing sugars and glyoxals arising from their decomposition, with asparagine, the amino acid forming the backbone of the acrylamide molecule. We reported recently the discovery of the Maillard deglycases (DJ-1/Park7 and its prokaryotic homologs) which degrade Maillard adducts formed between glyoxals and lysine or arginine amino groups, and prevent glycation damage in proteins. Here, we show that these deglycases prevent acrylamide formation, likely by degrading asparagine/glyoxal Maillard adducts. We also report the discovery of a deglycase from the hyperthermophilic archaea Pyrococcus furiosus, which prevents acrylamide formation at 100 °C. Thus, Maillard deglycases constitute a unique enzymatic method to prevent acrylamide formation in food without depleting the components (asparagine and sugars) responsible for its formation.

ICP35 Is a TREX-Like Protein Identified in White Spot Syndrome Virus

ICP35 is a non-structural protein from White spot syndrome virus believed to be important in viral replication. Since ICP35 was found to localize in the host nucleus, it has been speculated that the function of ICP35 might be involved in the interaction of DNA. In this study, we overexpressed, purified and characterized ICP35. The thioredoxin-fused ICP35 (thio-ICP35) was strongly expressed in E. coli and be able to form itself into dimers. Investigation of the interaction between ICP35 and DNA revealed that ICP35 can perform DNase activity. Structural model of ICP35 was successfully built on TREX1, suggesting that ICP35 might adopt the folding similar to that of TREX1 protein. Several residues important for dimerization in TREX1 are also conserved in ICP35. Residue Asn126 and Asp132, which are seen to be in close proximity to metal ions in the ICP35 model, were shown through site-directed mutagenesis to be critical for DNase activity.

Functional analysis of thioredoxin from the desert lichen-forming fungus, Endocarpon pusillum Hedwig, reveals its role in stress tolerance

Endocarpon pusillum is a lichen-forming fungus with an outstanding stress resistance property closely related to its antioxidant system. In this study, thioredoxin (Trx), one of the main components of antioxidant defense systems in E. pusillum (EpTrx), was characterized and analyzed both in transgenic yeasts and in vitro. Our analyses identified that the heterologous expression of EpTrx in the yeast Pichia pastoris significantly enhanced its resistance to osmotic and oxidative stresses. Assays in vitro showed EpTrx acted as a disulfide reductase as well as a molecular chaperone by assembling into various polymeric structures. Upon exposure to heat-shock stress, EpTrx exhibited weaker disulfide reductase activity but stronger chaperone activity, which coincided with the switching of the protein complexes from low molecular weight forms to high molecular weight complexes. Specifically, we found that Cys31 near but not at the active site was crucial in promoting the structural and functional transitions, most likely by accelerating the formation of intermolecular disulfide bond. Transgenic Saccharomyces cerevisiae harboring the native EpTrx exhibited stronger tolerance to oxidative, osmotic and high temperature stresses than the corresponding yeast strain containing the mutant EpTrx (C31S). Our results provide the first molecular evidence on how Trx influences stress response in lichen-forming fungi.

Thioredoxin superfamily and its effects on cardiac physiology and pathology

A precise control of oxidation/reduction of protein thiols is essential for intact cardiac physiology. Irreversible oxidative modifications have been proposed to play a role in the pathogenesis of cardiovascular diseases. An imbalance of redox homeostasis with diminution of antioxidant capacities predisposes the heart to oxidant injury. There is growing interest in endoplasmic reticulum (ER) stress in the cardiovascular field, since perturbation of redox homeostasis in the ER is sufficient to cause ER stress. Because a number of human diseases are related to altered redox homeostasis and defects in protein folding, many research efforts have been devoted in recent years to understanding the structure and enzymatic properties of the thioredoxin superfamily. The thioredoxin superfamily has been well documented as thiol oxidoreductases to exert a role in various cell signaling pathways. The redox properties of the thioredoxin motif account for the different functions of several members of the thioredoxin superfamily. While thioredoxin and glutaredoxin primarily act as antioxidants by reducing protein disulfides and mixed disulfide, another member of the superfamily, protein disulfide isomerase (PDI), can act as an oxidant by forming intrachain disulfide bonds that contribute to proper protein folding. Increasing evidence suggests a pivotal role of PDI in the survival pathway that promotes cardiomyocyte survival and leads to more favorable cardiac remodeling. Thus, the thiol redox state is important for cellular redox signaling and survival pathway in the heart. This review summarizes the key features of major members of the thioredoxin superfamily directly involved in cardiac physiology and pathology.

Screening Molecular Chaperones Similar to Small Heat Shock Proteins in Schizosaccharomyces pombe

To screen molecular chaperones similar to small heat shock proteins (sHsps), but without α-crystalline domain, heat-stable proteins from Schizosaccharomyces pombe were analyzed by 2-dimensional electrophoresis and matrix assisted laser desorption/ionization time-of-flight mass spectrometry. Sixteen proteins were identified, and four recombinant proteins, including cofilin, NTF2, pyridoxin biosynthesis protein (Snz1) and Wos2 that has an α-crystalline domain, were purified. Among these proteins, only Snz1 showed the anti-aggregation activity against thermal denaturation of citrate synthase. However, pre-heating of NTF2 and Wos2 at 70℃ for 30 min, efficiently prevented thermal aggregation of citrate synthase. These results indicate that Snz1 and NTF2 possess molecular chaperone activity similar to sHsps, even though there is no α-crystalline domain in their sequences.

Protein plasticity underlines activation and function of ATP-independent chaperones

One of the key issues in biology is to understand how cells cope with protein unfolding caused by changes in their environment. Self-protection is the natural immediate response to any sudden threat and for cells the critical issue is to prevent aggregation of existing proteins. Cellular response to stress is therefore indistinguishably linked to molecular chaperones, which are the first line of defense and function to efficiently recognize misfolded proteins and prevent their aggregation. One of the major protein families that act as cellular guards includes a group of ATP-independent chaperones, which facilitate protein folding without the consumption of ATP. This review will present fascinating insights into the diversity of ATP-independent chaperones, and the variety of mechanisms by which structural plasticity is utilized in the fine-tuning of chaperone activity, as well as in crosstalk within the proteostasis network. Research into this intriguing class of chaperones has introduced new concepts of stress response to a changing cellular environment, and paved the way to uncover how this environment affects protein folding.

Production, secretion and purification of a correctly folded staphylococcal antigen in Lactococcus lactis

Background

Lactococcus lactis, a lactic acid bacterium traditionally used to ferment milk and manufacture cheeses, is also, in the biotechnology field, an interesting host to produce proteins of medical interest, as it is “Generally Recognized As Safe”. Furthermore, as L. lactis naturally secretes only one major endogenous protein (Usp45), the secretion of heterologous proteins in this species facilitates their purification from a protein-poor culture medium. Here, we developed and optimized protein production and secretion in L. lactis to obtain proteins of high quality, both correctly folded and pure to a high extent. As proteins to be produced, we chose the two transmembrane members of the HtrA protease family in Staphylococcus aureus, an important extra-cellular pathogen, as these putative surface-exposed antigens could constitute good targets for vaccine development.

Results

A recombinant ORF encoding a C-terminal, soluble, proteolytically inactive and tagged form of each staphylococcal HtrA protein was cloned into a lactococcal expression-secretion vector. After growth and induction of recombinant gene expression, L. lactis was able to produce and secrete each recombinant rHtrA protein as a stable form that accumulated in the culture medium in similar amounts as the naturally secreted endogenous protein, Usp45. L. lactis growth in fermenters, in particular in a rich optimized medium, led to higher yields for each rHtrA protein. Protein purification from the lactococcal culture medium was easily achieved in one step and allowed recovery of highly pure and stable proteins whose identity was confirmed by mass spectrometry. Although rHtrA proteins were monomeric, they displayed the same secondary structure content, thermal stability and chaperone activity as many other HtrA family members, indicating that they were correctly folded. rHtrA protein immunogenicity was established in mice. The raised polyclonal antibodies allowed studying the expression and subcellular localization of wild type proteins in S. aureus: although both proteins were expressed, only HtrA₁ was found to be, as predicted, exposed at the staphylococcal cell surface suggesting that it could be a better candidate for vaccine development.

Conclusions

In this study, an efficient process was developed to produce and secrete putative staphylococcal surface antigens in L. lactis and to purify them to homogeneity in one step from the culture supernatant. This allowed recovering fully folded, stable and pure proteins which constitute promising vaccine candidates to be tested for protection against staphylococcal infection. L. lactis thus proved to be an efficient and competitive cell factory to produce proteins of high quality for medical applications.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0271-z) contains supplementary material, which is available to authorized users.

Analysis of the isomerase and chaperone-like activities of an amebic PDI (EhPDI)

Protein disulfide isomerases (PDI) are eukaryotic oxidoreductases that catalyze the formation and rearrangement of disulfide bonds during folding of substrate proteins. Structurally, PDI enzymes share as a common feature the presence of at least one active thioredoxin-like domain. PDI enzymes are also involved in holding, refolding, and degradation of unfolded or misfolded proteins during stressful conditions. The EhPDI enzyme (a 38 kDa polypeptide with two active thioredoxin-like domains) has been used as a model to gain insights into protein folding and disulfide bond formation in E. histolytica. Here, we performed a functional complementation assay, using a ΔdsbC mutant of E. coli, to test whether EhPDI exhibits isomerase activity in vivo. Our preliminary results showed that EhPDI exhibits isomerase activity; however, further mutagenic analysis revealed significant differences in the functional role of each thioredoxin-like domain. Additional studies confirmed that EhPDI protects heat-labile enzymes against thermal inactivation, extending our knowledge about its chaperone-like activity. The characterization of EhPDI, as an oxidative folding catalyst with chaperone-like function, represents the initial step to dissect the molecular mechanisms involved in protein folding in E. histolytica.

A cytosolic thioredoxin acts as a molecular chaperone for peroxisome matrix proteins as well as antioxidant in peroxisome

Thioredoxin (TRX) is a disulfide reductase present ubiquitously in all taxa and plays an important role as a regulator of cellular redox state. Recently, a redox-independent, chaperone function has also been reported for some thioredoxins. We previously identified nodulin-35, the subunit of soybean uricase, as an interacting target of a cytosolic soybean thioredoxin, GmTRX. Here we report the further characterization of the interaction, which turns out to be independent of the disulfide reductase function and results in the co-localization of GmTRX and nodulin-35 in peroxisomes, suggesting a possible function of GmTRX in peroxisomes. In addition, the chaperone function of GmTRX was demonstrated in in vitro molecular chaperone activity assays including the thermal denaturation assay and malate dehydrogenase aggregation assay. Our results demonstrate that the target of GmTRX is not only confined to the nodulin-35, but many other peroxisomal proteins, including catalase (AtCAT), transthyretin-like protein 1 (AtTTL1), and acyl-coenzyme A oxidase 4 (AtACX4), also interact with the GmTRX. Together with an increased uricase activity of nodulin-35 and reduced ROS accumulation observed in the presence of GmTRX in our results, especially under heat shock and oxidative stress conditions, it appears that GmTRX represents a novel thioredoxin that is co-localized to the peroxisomes, possibly providing functional integrity to peroxisomal proteins.

Parkinsonism-associated protein DJ-1/Park7 is a major protein deglycase that repairs methylglyoxal- and glyoxal-glycated cysteine, arginine, and lysine residues

Glycation is an inevitable nonenzymatic covalent reaction between proteins and endogenous reducing sugars or dicarbonyls (methylglyoxal, glyoxal) that results in protein inactivation. DJ-1 was reported to be a multifunctional oxidative stress response protein with poorly defined function. Here, we show that human DJ-1 is a protein deglycase that repairs methylglyoxal- and glyoxal-glycated amino acids and proteins by acting on early glycation intermediates and releases repaired proteins and lactate or glycolate, respectively. DJ-1 deglycates cysteines, arginines, and lysines (the three major glycated amino acids) of serum albumin, glyceraldehyde-3-phosphate dehydrogenase, aldolase, and aspartate aminotransferase and thus reactivates these proteins. DJ-1 prevented protein glycation in an Escherichia coli mutant deficient in the DJ-1 homolog YajL and restored cell viability in glucose-containing media. These results suggest that DJ-1-associated Parkinsonism results from excessive protein glycation and establishes DJ-1 as a major anti-glycation and anti-aging protein.

Redox systems in Botrytis cinerea: impact on development and virulence

The thioredoxin system is of great importance for maintenance of cellular redox homeostasis. Here, we show that it has a severe influence on virulence of Botrytis cinerea, demonstrating that redox processes are important for host-pathogen interactions in this necrotrophic plant pathogen. The thioredoxin system is composed of two enzymes, the thioredoxin and the thioredoxin reductase. We identified two genes encoding for thioredoxins (bctrx1, bctrx2) and one gene encoding for a thioredoxin reductase (bctrr1) in the genome of B. cinerea. Knockout mutants of bctrx1 and bctrr1 were severely impaired in virulence and more sensitive to oxidative stress. Additionally, Δbctrr1 showed enhanced H2O2 production and retarded growth. To investigate the impact of the second major cellular redox system, glutathione, we generated deletion mutants for two glutathione reductase genes. The effects were only marginal; deletion of bcglr1 resulted in reduced germination and, correspondingly, to retarded infection as well as reduced growth on minimal medium, whereas bcglr2 deletion had no distinctive phenotype. In summary, we showed that the balanced redox status maintained by the thioredoxin system is essential for development and pathogenesis of B. cinerea, whereas the second major cellular redox system, the glutathione system, seems to have only minor impact on these processes.

Hydration and conformational equilibrium in yeast thioredoxin 1: implication for H(+) exchange

One of the ancestral features of thioredoxins is the presence of a water cavity. Here, we report that a largely hydrated, conserved, buried aspartic acid in the water cavity modulates the dynamics of the interacting loops of yeast thioredoxin 1 (yTrx1). It is well-established that the aspartic acid, Asp24 for yTrx1, works as a proton acceptor in the reduction of the target protein. We propose a complementary role for Asp24 of coupling hydration and conformational motion of the water cavity and interacting loops. The intimate contact between the water cavity and the interacting loops means that motion at the water cavity will affect the interacting loops and vice versa. The D24N mutation alters the conformational equilibrium for both the oxidized and reduced states, quenching the conformational motion in the water cavity. By measuring the hydration and molecular dynamics simulation of wild-type yTrx1 and the D24N mutant, we showed that Asn24 is more exposed to water than Asp24 and the water cavity is smaller in the mutant, closing the inner part of the water cavity. We discuss how the conformational equilibrium contributes to the mechanism of catalysis and H(+) exchange.

Differential proteomics of Helicobacter pylori associated with autoimmune atrophic gastritis

Atrophic autoimmune gastritis (AAG) is a condition of chronic inflammation and atrophy of stomach mucosa, for which development can be partially triggered by the bacterial pathogen Helicobacter pylori (HP). HP can cause a variety of gastric diseases, such as duodenal ulcer (DU) or gastric cancer (GC). In this study, a comparative proteomic approach was used by two-dimensional fluorescence difference gel electrophoresis (DIGE) to identify differentially expressed proteins of HP strains isolated from patients with AAG, to identify markers of HP strain associated with AAG. Proteome profiles of HP isolated from GC or DU were used as a reference to compare proteomic levels. Proteomics analyses revealed 27 differentially expressed spots in AAG-associated HP in comparison with GC, whereas only 9 differential spots were found in AAG-associated HP profiles compared with DU. Proteins were identified after matrix-assisted laser desorption ionization (MALDI)-TOF and peptide mass fingerprinting. Some AAG-HP differential proteins were common between DU- and GC-HP (peroxiredoxin, heat shock protein 70 [HSP70], adenosine 5'-triphosphate [ATP] synthase subunit α, flagellin A). Our results presented here may suggest that comparative proteomes of HP isolated from AAG and DU share more common protein expression than GC and provide subsets of putative AAG-specific upregulated or downregulated proteins that could be proposed as putative markers of AAG-associated HP. Other comparative studies by two-dimensional maps integrated with functional genomics of candidate proteins will undoubtedly contribute to better decipher the biology of AAG-associated HP strains.

The role of thiol oxidative stress response in heat-induced protein aggregate formation during thermotolerance in Bacillus subtilis

Using Bacillus subtilis as a model organism, we investigated thermotolerance development by analysing cell survival and in vivo protein aggregate formation in severely heat-shocked cells primed by a mild heat shock. We observed an increased survival during severe heat stress, accompanied by a strong reduction of heat-induced cellular protein aggregates in cells lacking the ClpXP protease. We could demonstrate that the transcription factor Spx, a regulatory substrate of ClpXP, is critical for the prevention of protein aggregate formation because its regulon encodes redox chaperones, such as thioredoxin, required for protection against thiol-specific oxidative stress. Consequently B. subtilis cells grown in the absence of oxygen were more protected against severe heat shock and much less protein aggregates were detected compared to aerobically grown cells. The presented results indicate that in B. subtilis Spx and its regulon plays not only an important role for oxidative but also for heat stress response and thermotolerance development. In addition, our experiments suggest that the protection of misfolded proteins from thiol oxidation during heat shock can be critical for the prevention of cellular protein aggregation in vivo.

High-level expression of functionally active dengue-2 non-structural antigen 1 production in Escherichia coli

Detection of nonstructural protein (NS1) is an important diagnostic marker during acute phase of dengue infection. Not only for diagnostic purpose, the protein had important role in vaccine design as well, as a candidate for studying virus assembly and maturation. Various researchers employed different expression systems and strategies for recombinant NS1 protein production. Attempts to express NS1 protein in prokaryotic and yeast expression system result in formation of insoluble protein which needs to undergo refolding to attain native structural and functional forms. Here, we report the production of soluble NS1 protein in E. coli by using appropriate vector and employing suitable culture conditions to maximize protein production. Proteins were purified using metal affinity chromatography. SDS-PAGE and western blot analysis reveal the native structure of NS1 protein. Solid phase ELISA using the recombinantly expressed antigen with positive and negative dengue samples showed that the expressed protein retains its antigenic and immunological properties. To our knowledge, this is the first report on the successful production of functionally active recombinant dengue-2 NS1 protein production without undergoing any in vitro posttranslational modification process.

Thioredoxin reductase type C (NTRC) orchestrates enhanced thermotolerance to Arabidopsis by its redox-dependent holdase chaperone function

Genevestigator analysis has indicated heat shock induction of transcripts for NADPH-thioredoxin reductase, type C (NTRC) in the light. Here we show overexpression of NTRC in Arabidopsis (NTRC°(E)) resulting in enhanced tolerance to heat shock, whereas NTRC knockout mutant plants (ntrc1) exhibit a temperature sensitive phenotype. To investigate the underlying mechanism of this phenotype, we analyzed the protein's biochemical properties and protein structure. NTRC assembles into homopolymeric structures of varying complexity with functions as a disulfide reductase, a foldase chaperone, and as a holdase chaperone. The multiple functions of NTRC are closely correlated with protein structure. Complexes of higher molecular weight (HMW) showed stronger activity as a holdase chaperone, while low molecular weight (LMW) species exhibited weaker holdase chaperone activity but stronger disulfide reductase and foldase chaperone activities. Heat shock converted LMW proteins into HMW complexes. Mutations of the two active site Cys residues of NTRC into Ser (C217/454S-NTRC) led to a complete inactivation of its disulfide reductase and foldase chaperone functions, but conferred only a slight decrease in its holdase chaperone function. The overexpression of the mutated C217/454S-NTRC provided Arabidopsis with a similar degree of thermotolerance compared with that of NTRC°(E) plants. However, after prolonged incubation under heat shock, NTRC°(E) plants tolerated the stress to a higher degree than C217/454S-NTRC°(E) plants. The results suggest that the heat shock-mediated holdase chaperone function of NTRC is responsible for the increased thermotolerance of Arabidopsis and the activity is significantly supported by NADPH.

Functional divergence of the glutathione S-transferase supergene family in Physcomitrella patens reveals complex patterns of large gene family evolution in land plants

Plant glutathione S-transferases (GSTs) are multifunctional proteins encoded by a large gene family that play major roles in the detoxification of xenobiotics and oxidative stress metabolism. To date, studies on the GST gene family have focused mainly on vascular plants (particularly agricultural plants). In contrast, little information is available on the molecular characteristics of this large gene family in nonvascular plants. In addition, the evolutionary patterns of this family in land plants remain unclear. In this study, we identified 37 GST genes from the whole genome of the moss Physcomitrella patens, a nonvascular representative of early land plants. The 37 P. patens GSTs were divided into 10 classes, including two new classes (hemerythrin and iota). However, no tau GSTs were identified, which represent the largest class among vascular plants. P. patens GST gene family members showed extensive functional divergence in their gene structures, gene expression responses to abiotic stressors, enzymatic characteristics, and the subcellular locations of the encoded proteins. A joint phylogenetic analysis of GSTs from P. patens and other higher vascular plants showed that different class GSTs had distinct duplication patterns during the evolution of land plants. By examining multiple characteristics, this study revealed complex patterns of evolutionary divergence among the GST gene family in land plants.

Transcription elongation factor GreA has functional chaperone activity

BACKGROUND

Bacterial GreA is an indispensable factor in the RNA polymerase elongation complex. It plays multiple roles in transcriptional elongation, and may be implicated in resistance to various stresses.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we show that Escherichia coli GreA inhibits aggregation of several substrate proteins under heat shock condition. GreA can also effectively promote the refolding of denatured proteins. These facts reveal that GreA has chaperone activity. Distinct from many molecular chaperones, GreA does not form stable complexes with unfolded substrates. GreA overexpression confers the host cells with enhanced resistance to heat shock and oxidative stress. Moreover, GreA expression in the greA/greB double mutant could suppress the temperature-sensitive phenotype, and dramatically alleviate the in vivo protein aggregation. The results suggest that bacterial GreA may act as chaperone in vivo.

CONCLUSIONS/SIGNIFICANCE

These results suggest that GreA, in addition to its function as a transcription factor, is involved in protection of cellular proteins against aggregation.

Pathogenicity of Salmonella enterica in Caenorhabditis elegans relies on disseminated oxidative stress in the infected host

Feeding Caenorhabditis elegans with Salmonella enterica serovar Typhimurium significantly shortens the lifespan of the nematode. S. Typhimurium-infected C. elegans, stained with 2′,7′-dichlorodihydrofluorescein diacetate which fluoresces upon exposure to reactive oxygen species, revealed intestinal luminal staining that along with the time of infection progressed to a strong staining in the hypodermal tissues of the nematode. Still, we could not detect invasion beyond the nematode's intestinal epithelium at any stage of the infection. A similar dispersion of oxidative response was also noted in nematodes infected with S. Dublin, but not with non-pathogenic Escherichia coli or the defined pathogen Burkholderia thailandensis. Addition of catalase or the reductant ascorbic acid significantly restored the lifespan of S. Typhimurium-infected nematodes. Mutational inactivation of the bacterial thioredoxin 1 resulted in total ablation of the hypodermal oxidative response to infection, and in a strong attenuation of virulence. Virulence of the thioredoxin 1 mutant was restored by trans-complementation with redox-active variants of thioredoxin 1 or, surprisingly, by exposing the thioredoxin 1 mutant to sublethal concentrations of the disulphide catalyst copper chloride prior to infection. In summary, our observations define a new aspect in virulence of S. enterica that apparently does not involve the classical invasive or intracellular phenotype of the pathogen, but that depends on the ability to provoke overwhelming systemic oxidative stress in the host through the redox activity of bacterial thioredoxin 1.

Acid stress response and protein induction in Campylobacter jejuni isolates with different acid tolerance

Background

During the transmission route from poultry to the human host, the major foodborne pathogen C. jejuni may experience many types of stresses, including low pH caused by different acids. However, not all strains are equally sensitive to the stresses. The aim of this study was to investigate the response to acid stress of three sequenced C. jejuni strains with different acid tolerances using HCl and acetic acid.

Results

Two-dimensional gel electrophoresis was used for proteomic analysis and proteins were radioactively labelled with methionine to identify proteins only related to acid exposure. To allow added radioactive methionine to be incorporated into induced proteins, a modified chemically defined broth was developed with the minimal amount of methionine necessary for satisfactory growth of all strains. Protein spots were analyzed using image software and identification was done with MALDI-TOF-TOF. The most acid-sensitive isolate was C. jejuni 327, followed by NCTC 11168 and isolate 305 as the most tolerant. Overall, induction of five proteins was observed within the pI range investigated: 19 kDa periplasmic protein (p19), thioredoxin-disulfide (TrxB), a hypothetical protein Cj0706 (Cj0706), molybdenum cofactor biosynthesis protein (MogA), and bacterioferritin (Dps). Strain and acid type dependent differences in the level of response were observed. For strain NCTC 11168, the induced proteins and the regulator fur were analysed at the transcriptomic level using qRT-PCR. In this transcriptomic analysis, only up-regulation of trxB and p19 was observed.

Conclusions

A defined medium that supports the growth of a range of Campylobacter strains and suitable for proteomic analysis was developed. Mainly proteins normally involved in iron control and oxidative stress defence were induced during acid stress of C. jejuni. Both strain and acid type affected sensitivity and response.

Two thioredoxin reductases, trxr-1 and trxr-2, have differential physiological roles in Caenorhabditis elegans

Thioredoxin reductase (TrxR) is a member of the pyridine nucleotide-disulfide reductase family, which mainly functions in the thioredoxin system. TrxR is found in all living organisms and exists in two major ubiquitous isoenzymes in higher eukaryotic cells; One is cytosolic and the other mitochondrial. Mitochondrial TrxR functions to protect mitochondria from oxidative stress, where reactive oxidative species are mainly generated, while cytosolic TrxR plays a role to maintain optimal oxido-reductive status in cytosol. In this study, we report differential physiological functions of these two TrxRs in C. elegans. trxr-1, the cytosolic TrxR, is highly expressed in pharynx, vulva and intestine, whereas trxr-2, the mitochondrial TrxR, is mainly expressed in pharyngeal and body wall muscles. Deficiency of the non-selenoprotein trxr-2 caused defects in longevity and delayed development under stress conditions, while deletion mutation of the selenoprotein trxr-1 resulted in interference in acidification of lysosomal compartment in intestine. Interestingly, the acidification defect of trxr-1(jh143) deletion mutant was rescued, not only by selenocystein-containing wild type TRXR-1, but also cysteine-substituted mutant TRXR-1. Both trxr-1 and trxr-2 were up-regulated when worms were challenged by environmental stress such as heat shock. These results suggest that trxr-1 and trxr-2 function differently at organismal level presumably by their differential sub-cellular localization in C. elegans.

WhiB2/Rv3260c, a cell division-associated protein of Mycobacterium tuberculosis H37Rv, has properties of a chaperone

whiB-like genes have been found in all actinomycetes sequenced so far. The amino-acid sequences of WhiB proteins of Mycobacterium tuberculosis H37Rv are highly conserved and participate in several cellular functions. Unlike other WhiB proteins of M. tuberculosis that have properties of protein disulfide reductases, WhiB2 showed properties like a chaperone as it suppressed the aggregation of several model substrates (e.g. citrate synthase, rhodanese and luciferase). Suppression of aggregation of the model substrates did not require ATP. Four cysteine residues of WhiB2 form two intramolecular disulfide bonds; however, chaperone function was unaffected by the redox state of the cysteines. WhiB2 also restored the activity of chemically denatured citrate synthase and did not require either ATP or a co-chaperone for refolding. The results indicate that WhiB2, which has been shown to be associated with cell division in mycobacteria and streptomyces, has evolved independently of other WhiBs, although it retains basic properties of this group of proteins. This is the first report to show that a WhiB protein has chaperone-like function; therefore, this report will have major implications in attempts to understand the role of WhiB proteins in mycobacteria, particularly in cell division.

Properties of the endogenous components of the thioredoxin system in the psychrophilic eubacterium Pseudoalteromonas haloplanktis TAC 125

The endogenous components of the thioredoxin system in the Antarctic eubacterium Pseudoalteromonas haloplanktis have been purified and characterised. The temperature dependence of the activities sustained by thioredoxin (PhTrx) and thioredoxin reductase (PhTrxR) pointed to their adaptation in the cold growth environment. PhTrxR was purified as a flavoenzyme and its activity was significantly enhanced in the presence of molar concentration of monovalent cations. The energetics of the partial reactions leading to the whole electron transfer from NADPH to the target protein substrate in the reconstituted thioredoxin system was also investigated. While the initial electron transfer from NADPH to PhTrxR was energetically favoured, the final passage to the heterologous protein substrate enhanced the energetic barrier of the whole process. The energy of activation of the heat inactivation process essentially reflected the psychrophilic origin of PhTrxR. Vice versa, PhTrx possessed an exceptional heat resistance (half-life, 4.4 h at 95 °C), ranking this protein among the most thermostable enzymes reported so far in psychrophiles. PhTrxR was covalently modified by glutathione, mainly by its oxidised or nitrosylated forms. A mutagenic analysis realised on three non catalytic cysteines of the flavoenzyme allowed the identification of C(303) as the target for the S-glutathionylation reaction.

Overproduction of anti-Tn antibody MLS128 single-chain Fv fragment in Escherichia coli cytoplasm using a novel pCold-PDI vector

Overproduction of recombinant proteins in Escherichia coli is often hampered by their failure to fold correctly, leading to their accumulation within inclusion bodies. To overcome the problem, a variety of techniques aimed at soluble expression have been developed including low temperature expression and/or fusion of soluble tags and chaperones. However, a general protocol for bacterial expression of disulfide bond-containing proteins has hitherto not been established. Single chain Fv fragments (scFvs) are disulfide bond-containing proteins often difficult to express in soluble forms in E. coli. We here examine in detail the E. coli expression of a scFv originating from an anti-carbohydrate MLS128 antibody as a model system. We combine three techniques: (1) tagging scFv with thioredoxin, DsbC and protein disulfide isomerase (PDI), (2) expressing the proteins at low temperature using the pCold vector system, and (3) using Origami E. coli strains with mutations in the thioredoxin reductase and glutathione reductase genes. We observed a high expression level of soluble MLS128-scFv in the Origami strain only when PDI is used as a tag. The recombinant protein retains full binding activity towards synthetic carbohydrate antigens. The developed "pCold-PDI" vector has potential for overproduction of other scFvs and disulfide-containing proteins in the Origami strains.

Chaperone-like properties of tobacco plastid thioredoxins f and m

Thioredoxins (Trxs) are ubiquitous disulphide reductases that play important roles in the redox regulation of many cellular processes. However, some redox-independent functions, such as chaperone activity, have also been attributed to Trxs in recent years. The focus of our study is on the putative chaperone function of the well-described plastid Trxs f and m. To that end, the cDNA of both Trxs, designated as NtTrxf and NtTrxm, was isolated from Nicotiana tabacum plants. It was found that bacterially expressed tobacco Trx f and Trx m, in addition to their disulphide reductase activity, possessed chaperone-like properties. In vitro, Trx f and Trx m could both facilitate the reactivation of the cysteine-free form of chemically denatured glucose-6 phosphate dehydrogenase (foldase chaperone activity) and prevent heat-induced malate dehydrogenase aggregation (holdase chaperone activity). Our results led us to infer that the disulphide reductase and foldase chaperone functions prevail when the proteins occur as monomers and the well-conserved non-active cysteine present in Trx f is critical for both functions. By contrast, the holdase chaperone activity of both Trxs depended on their oligomeric status: the proteins were functional only when they were associated with high molecular mass protein complexes. Because the oligomeric status of both Trxs was induced by salt and temperature, our data suggest that plastid Trxs could operate as molecular holdase chaperones upon oxidative stress, acting as a type of small stress protein.

Expression and purification of soluble bio-active rice plant catalase-A from recombinant Escherichia coli

Catalase in plants is a heme-coordinated tetrameric protein that primarily disproportionates hydrogen peroxide into water and oxygen. It plays an important role in maintaining cellular concentration of hydrogen peroxide to a level, necessary for all aspects of normal plant growth and development. Except for its recombinant expression in transgenic plants and insect cell line, the protein is yet to be synthesized in its bio-active form in prokaryotic expression system. Attempts made in past for recombinant expression of plant catalase in Escherichia coli consistently resulted in formation of insoluble and inactive aggregates of inclusion body. Here we have shown the specific requirement of a thioredoxin fusion partner, the involvement of trigger factor protein and the low temperature treatment during induction period for synthesis of completely solubilized rice plant catalase-A in recombinant E. coli. Furthermore, the bacteria required the supplementation of δ-aminolevulinic acid to produce bio-active recombinant rice catalase-A. The molecular and biochemical properties of the purified recombinant protein showed the characteristic features of a typical mono-functional plant catalase. These results attest to the usefulness of the present protocol for production of plant catalase using E. coli as heterologous expression system.

Heat-induced chaperone activity of serine/threonine protein phosphatase 5 enhances thermotolerance in Arabidopsis thaliana

• This study reports that Arabidopsis thaliana protein serine/threonine phosphatase 5 (AtPP5) plays a pivotal role in heat stress resistance. A high-molecular-weight (HMW) form of AtPP5 was isolated from heat-treated A. thaliana suspension cells. AtPP5 performs multiple functions, acting as a protein phosphatase, foldase chaperone, and holdase chaperone. The enzymatic activities of this versatile protein are closely associated with its oligomeric status, ranging from low oligomeric protein species to HMW complexes. • The phosphatase and foldase chaperone functions of AtPP5 are associated primarily with the low-molecular-weight (LMW) form, whereas the HMW form exhibits holdase chaperone activity. Transgenic over-expression of AtPP5 conferred enhanced heat shock resistance to wild-type A. thaliana and a T-DNA insertion knock-out mutant was defective in acquired thermotolerance. A recombinant phosphatase mutant (H290N) showed markedly increased holdase chaperone activity. • In addition, enhanced thermotolerance was observed in transgenic plants over-expressing H290N, which suggests that the holdase chaperone activity of AtPP5 is primarily responsible for AtPP5-mediated thermotolerance. • Collectively, the results from this study provide the first evidence that AtPP5 performs multiple enzymatic activities that are mediated by conformational changes induced by heat-shock stress.