Escherichia coli thioredoxin inhibition by cadmium: two mutually exclusive binding sites involving Cys32 and Asp26

Genomic and proteomic insights into the heavy metal bioremediation by cyanobacteria

Heavy metals (HMs) pose a global ecological threat due to their toxic effects on aquatic and terrestrial life. Effective remediation of HMs from the environment can help to restore soil's fertility and ecological vigor, one of the key Sustainable Development Goals (SDG) set by the United Nations. The cyanobacteria have emerged as a potential option for bioremediation of HMs due to their unique adaptations and robust metabolic machineries. Generally, cyanobacteria deploy multifarious mechanisms such as biosorption, bioaccumulation, activation of metal transporters, biotransformation and induction of detoxifying enzymes to sequester and minimize the toxic effects of heavy metals. Therefore, understanding the physiological responses and regulation of adaptation mechanisms at molecular level is necessary to unravel the candidate genes and proteins which can be manipulated to improve the bioremediation efficiency of cyanobacteria. Chaperons, cellular metabolites (extracellular polymers, biosurfactants), transcriptional regulators, metal transporters, phytochelatins and metallothioneins are some of the potential targets for strain engineering. In the present review, we have discussed the potential of cyanobacteria for HM bioremediation and provided a deeper insight into their genomic and proteomic regulation of various tolerance mechanisms. These approaches might pave new possibilities of implementing genetic engineering strategies for improving bioremediation efficiency with a future perspective.

Cross-Kingdom Comparative Transcriptomics Reveals Conserved Genetic Modules in Response to Cadmium Stress

It is known that organisms have developed various mechanisms to cope with cadmium (Cd) stress, while we still lack a system-level understanding of the functional isomorphy among them. In the present study, a cross-kingdom comparison was conducted among Escherichia coli, Saccharomyces cerevisiae, and Chlamydomonas reinhardtii, through toxicological tests, comparative transcriptomics, as well as conventional functional genomics. An equivalent level of Cd stress was determined via inhibition tests. Through transcriptome comparison, the three organisms exhibited differential gene expression under the same Cd stress relative to the corresponding no-treatment control. Results from functional enrichment analysis of differentially expressed genes (DEGs) showed that four metabolic pathways responsible for combating Cd stress were commonly regulated in the three organisms, including antioxidant reactions, sulfur metabolism, cell wall remodeling, and metal transport. In vivo expression patterns of 43 DEGs from the four pathways were further examined using quantitative PCR and resulted in a relatively comparable dynamic of gene expression patterns with transcriptome sequencing (RNA-seq). Cross-kingdom comparison of typical Cd stress-responding proteins resulted in the detection of 12 groups of homologous proteins in the three species. A class of potential metal transporters were subjected to cross-transformation to test their functional complementation. An ABC transporter gene in E. coli, possibly homologous to the yeast ycf1, was heterologously expressed in S. cerevisiae, resulting in enhanced Cd tolerance. Overall, our findings indicated that conserved genetic modules against Cd toxicity were commonly regulated among distantly related microbial species, which will be helpful for utilizing them in modifying microbial traits for bioremediation.

IMPORTANCE Research is establishing a systems biology view of biological response to Cd stress. It is meaningful to explore whether there is regulatory isomorphy among distantly related organisms. A transcriptomic comparison was done among model microbes, leading to the identification of a conserved cellular model pinpointing the generic strategies utilized by microbes for combating Cd stress. A novel E. coli transporter gene substantially increased yeast’s Cd tolerance. Knowledge on systems understanding of the cellular response to metals provides the basis for developing bioengineering remediation technology.

Uranium bioremediation with U(VI)-reducing bacteria

Uranium (U) pollution is an environmental hazard caused by the development of the nuclear industry. Microbial reduction of hexavalent uranium (U(VI)) to tetravalent uranium (U(IV)) reduces U solubility and mobility and has been proposed as an effective method to remediate uranium contamination. In this review, U(VI) remediation with respect to U(VI)-reducing bacteria, mechanisms, influencing factors, products, and reoxidation are systematically summarized. Reportedly, some metal- and sulfate-reducing bacteria possess excellent U(VI) reduction capability through mechanisms involving c-type cytochromes, extracellular pili, electron shuttle, or thioredoxin reduction. In situ remediation has been demonstrated as an ideal strategy for large-scale degradation of uranium contaminants than ex situ. However, U(VI) reduction efficiency can be affected by various factors, including pH, temperature, bicarbonate, electron donors, and coexisting metal ions. Furthermore, it is noteworthy that the reduction products could be reoxidized when exposed to oxygen and nitrate, inevitably compromising the remediation effects, especially for non-crystalline U(IV) with weak stability.

Identification and Characterization of an OSH1 Thiol Reductase from Populus Trichocarpa

Interferon gamma-induced lysosomal thiol reductase (GILT) is abundantly expressed in antigen-presenting cells and participates in the treatment and presentation of antigens by major histocompatibility complex II. Also, GILT catalyzes the reduction of disulfide bonds, which plays an important role in cellular immunity. (1) Background: At present, the studies of GILT have mainly focused on animals. In plants, GILT homologous gene (Arabidopsis thalianaOSH1: AtOSH1) was discovered in the forward screen of mutants with compromised responses to sulphur nutrition. However, the complete properties and functions of poplar OSH1 are unclear. In addition, CdCl2 stress is swiftly engulfing the limited land resources on which humans depend, restricting agricultural production. (2) Methods: A prokaryotic expression system was used to produce recombinant PtOSH1 protein, and Western blotting was performed to identify its activity. In addition, a simplified version of the floral-dip method was used to transform A. thaliana. (3) Results: Here, we describe the identification and characterization of OSH1 from Populus trichocarpa. The deduced PtOSH1 sequence contained CQHGX2ECX2NX4C and CXXC motifs. The transcript level of PtOSH1 was increased by cadmium (Cd) treatment. In addition, recombinant PtOSH1 reduced disulfide bonds. A stress assay showed that PtOSH1-overexpressing (OE) A. thaliana lines had greater resistance to Cd than wild-type (WT) plants. Also, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in PtOSH1-OE plants were significantly higher than those in WT A. thaliana. These results indicate that PtOSH1 likely plays an important role in the response to Cd by regulating the reactive oxygen species (ROS)-scavenging system. (4) Conclusions: PtOSH1 catalyzes the reduction of disulfide bonds and behaves as a sulfhydryl reductase under acidic conditions. The overexpression of PtOSH1 in A. thaliana promoted root development, fresh weight, and dry weight; upregulated the expression levels of ROS scavenging-related genes; and improved the activity of antioxidant enzymes, enhancing plant tolerance to cadmium (Cd) stress. This study aimed to provide guidance that will facilitate future studies of the function of PtOSH1 in the response of plants to Cd stress.

Bioinformatic Exploration of Metal-Binding Proteome of Zoonotic Pathogen Orientia tsutsugamushi

Metal ions are involved in many essential biological processes and are crucial for the survival of all organisms. Identification of metal-binding proteins (MBPs) of human affecting pathogens may provide the blueprint for understanding biological metal usage and their putative roles in pathogenesis. This study is focused on the analysis of MBPs from Orientia tsutsugamushi (Ott), a causal agent of scrub typhus in humans. A total of 321 proteins were predicted as putative MBPs, based on sequence search and three-dimensional structure analysis. Majority of proteins could bind with magnesium, and the order of metal binding was Mg > Ca > Zn > Mn > Fe > Cd > Ni > Co > Cu, respectively. The predicted MBPs were functionally classified into nine broad classes. Among them, gene expression and regulation, metabolism, cell signaling, and transport classes were dominant. It was noted that the putative MBPs were localized in all subcellular compartments of Ott, but majorly found in the cytoplasm. Additionally, it was revealed that out of 321 predicted MBPs 245 proteins were putative bacterial toxins and among them, 98 proteins were nonhomologous to human proteome. Sixty putative MBPs showed the ability to interact with drug or drug-like molecules, which indicate that they may be used as broad-spectrum drug targets. These predicted MBPs from Ott could play vital role(s) in various cellular activities and virulence, hence may serve as plausible therapeutic targets to design metal-based drugs to curtail its infection.

Adaptive laboratory evolution of cadmium tolerance in Synechocystis sp. PCC 6803

BACKGROUND

Cadmium has been a significant threat to environment and human health due to its high toxicity and wide application in fossil-fuel burning and battery industry. Cyanobacteria are one of the most dominant prokaryotes, and the previous studies suggested that they could be valuable in removing Cd2+ from waste water. However, currently, the tolerance to cadmium is very low in cyanobacteria. To further engineer cyanobacteria for the environmental application, it is thus necessary to determine the mechanism that they respond to high concentration of cadmium.

RESULTS

In this study, a robust strain of Synechocystis PCC 6803 (named ALE-9.0) tolerant to CdSO4 with a concentration up to 9.0 µM was successfully isolated via adaptive laboratory evolution over 802-day continuous passages under cadmium stress. Whole-genome re-sequencing was then performed and nine mutations were identified for the evolved strain compared to the wild-type strain. Among these mutations, a large fragment deletion in slr0454 encoding a cation or drug efflux system protein was found to contribute directly to the resistance to Cd2+ stress. In addition, five other mutations were also demonstrated related to the improved Cd2+ tolerance in ALE-9.0. Moreover, the evolved ALE-9.0 strain was found to obtain cross tolerance to some other heavy metals like zinc and cobalt as well as higher resistance to high light.

CONCLUSIONS

The work here identified six genes and their mutations related to Cd2+ tolerance in Synechocystis PCC 6803, and demonstrated the feasibility of adaptive laboratory evolution in tolerance modifications. This work also provided valuable information regarding the cadmium tolerance mechanism in Synechocystis PCC 6803, and useful insights for cyanobacterial robustness and tolerance engineering.

Mitochondria targeting by environmental stressors: Implications for redox cellular signaling

Mitochondria are cellular powerhouses as well as metabolic and signaling hubs regulating diverse cellular functions, from basic physiology to phenotypic fate determination. It is widely accepted that reactive oxygen species (ROS) generated in mitochondria participate in the regulation of cellular signaling, and that some mitochondria chronically operate at a high ROS baseline. However, it is not completely understood how mitochondria adapt to persistently high ROS states and to environmental stressors that disturb the redox balance. Here we will review some of the current concepts regarding how mitochondria resist oxidative damage, how they are replaced when excessive oxidative damage compromises function, and the effect of environmental toxicants (i.e. heavy metals) on the regulation of mitochondrial ROS (mtROS) production and subsequent impact.

Transition Metal Homeostasis

This chapter focuses on transition metals. All transition metal cations are toxic-those that are essential for Escherichia coli and belong to the first transition period of the periodic system of the element and also the "toxic-only" metals with higher atomic numbers. Common themes are visible in the metabolism of these ions. First, there is transport. High-rate but low-affinity uptake systems provide a variety of cations and anions to the cells. Control of the respective systems seems to be mainly through regulation of transport activity (flux control), with control of gene expression playing only a minor role. If these systems do not provide sufficient amounts of a needed ion to the cell, genes for ATP-hydrolyzing high-affinity but low-rate uptake systems are induced, e.g., ABC transport systems or P-type ATPases. On the other hand, if the amount of an ion is in surplus, genes for efflux systems are induced. By combining different kinds of uptake and efflux systems with regulation at the levels of gene expression and transport activity, the concentration of a single ion in the cytoplasm and the composition of the cellular ion "bouquet" can be rapidly adjusted and carefully controlled. The toxicity threshold of an ion is defined by its ability to produce radicals (copper, iron, chromate), to bind to sulfide and thiol groups (copper, zinc, all cations of the second and third transition period), or to interfere with the metabolism of other ions. Iron poses an exceptional metabolic problem due its metabolic importance and the low solubility of Fe(III) compounds, combined with the ability to cause dangerous Fenton reactions. This dilemma for the cells led to the evolution of sophisticated multi-channel iron uptake and storage pathways to prevent the occurrence of unbound iron in the cytoplasm. Toxic metals like Cd2+ bind to thiols and sulfide, preventing assembly of iron complexes and releasing the metal from iron-sulfur clusters. In the unique case of mercury, the cation can be reduced to the volatile metallic form. Interference of nickel and cobalt with iron is prevented by the low abundance of these metals in the cytoplasm and their sequestration by metal chaperones, in the case of nickel, or by B12 and its derivatives, in the case of cobalt. The most dangerous metal, copper, catalyzes Fenton-like reactions, binds to thiol groups, and interferes with iron metabolism. E. coli solves this problem probably by preventing copper uptake, combined with rapid efflux if the metal happens to enter the cytoplasm.

Microarray analysis of the Escherichia coli response to CdTe-GSH Quantum Dots: understanding the bacterial toxicity of semiconductor nanoparticles

Background

Most semiconductor nanoparticles used in biomedical applications are made of heavy metals and involve synthetic methods that require organic solvents and high temperatures. This issue makes the development of water-soluble nanoparticles with lower toxicity a major topic of interest. In a previous work our group described a biomimetic method for the aqueous synthesis of CdTe-GSH Quantum Dots (QDs) using biomolecules present in cells as reducing and stabilizing agents. This protocol produces nanoparticles with good fluorescent properties and less toxicity than those synthesized by regular chemical methods. Nevertheless, biomimetic CdTe-GSH nanoparticles still display some toxicity, so it is important to know in detail the effects of these semiconductor nanoparticles on cells, their levels of toxicity and the strategies that cells develop to overcome it.

Results

In this work, the response of E. coli exposed to different sized-CdTe-GSH QDs synthesized by a biomimetic protocol was evaluated through transcriptomic, biochemical, microbiological and genetic approaches. It was determined that: i) red QDs (5 nm) display higher toxicity than green (3 nm), ii) QDs mainly induce expression of genes involved with Cd⁺² stress (zntA and znuA) and tellurium does not contribute significantly to QDs-mediated toxicity since cells incorporate low levels of Te, iii) red QDs also induce genes related to oxidative stress response and membrane proteins, iv) Cd²⁺ release is higher in red QDs, and v) QDs render the cells more sensitive to polymyxin B.

Conclusion

Based on the results obtained in this work, a general model of CdTe-GSH QDs toxicity in E. coli is proposed. Results indicate that bacterial toxicity of QDs is mainly associated with cadmium release, oxidative stress and loss of membrane integrity. The higher toxicity of red QDs is most probably due to higher cadmium content and release from the nanoparticle as compared to green QDs. Moreover, QDs-treated cells become more sensitive to polymyxin B making these biomimetic QDs candidates for adjuvant therapies against bacterial infections.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1099) contains supplementary material, which is available to authorized users.

Global transcriptome analysis of hexavalent chromium stress responses in Staphylococcus aureus LZ-01

Staphylococcus aureus strain LZ-01, isolated from the Lanzhou reaches of the Yellow River, is capable of reducing Cr(VI) to Cr(III) aerobically. We employed transcriptome sequencing analysis to identify genes involved in Cr(VI) stress responses in S. aureus LZ-01. Our results showed that 512 of the 2,370 predicted genes displayed up-regulation (>2-fold), and 49 genes were down-regulated (<50 %) after Cr(VI) exposure. Among up-regulated genes, 128 genes were annotated to encode proteins involved in cellular processes; 68 were categorized to transport and binding proteins; 26 were involved in DNA repair and 32 were associated with regulatory functions. To further elucidate the Cr(VI) resistance and reduction mechanism, we carried out physiological tests and quantitative PCR analysis. Both RNA-seq and qRT-PCR data showed genes encoding a thioredoxin reductase and main subunits of cytochrome c oxidase complex were up-regulated upon Cr(VI) treatment. Either cadmium or NaN3 treatment could inhibit Cr(VI) reduction which indicates that thioredoxin and cytochrome are involved in Cr(VI) reduction strain LZ-01. 29 ABC-type metal/multidrug transporters and efflux pumps were up-regulated, suggesting that they are involved in Cr(VI) resistance by pumping chromium ions out of cells. The up-regulation of 26 DNA repair genes demonstrate that Cr(VI) is toxic to DNA and those DNA protection proteins need to be responded for Cr(VI) stress. Based on these results, the mechanism of strain LZ-01 resists and reduces Cr(VI) is revealed.

Characterization of the biochemical-pathway of uranium (VI) reduction in facultative anaerobic bacteria

Cultures of U(VI) reducing bacteria sourced from abandoned uranium mine tailing dam were evaluated for their ability to reduce U(VI) to U(IV). The species in the cultures reduced U(VI) in solutions with initial U(VI) concentration up to 400mgL(-)(1) under a near neutral pH of 6.5. The electron flow pathway and fate of reduced species was also analysed in the individual species in order to evaluate the potential for control and optimisation of the reduction potential at the biochemical level. The results showed that U(VI) reduction in live cells was completely blocked by the NADH-dehydrogenase inhibitor, rotenone (C23H22O6), and thioredoxin inhibitor, cadmium chloride (CdCl2), showing that U(VI) reduction involves the electron flow through NADH-dehydrogenase, a primary electron donor to the electron transport respiratory (ETR) system. Mass balance analysis of uranium species aided by visual and electron microscopy suggest that most U(VI) reduction occurred on the cell surface of the isolated species. This finding indicates the possibility of easy uranium recovery for beneficial use through biological remediation. Should the U(VI) be reduced inside the cell, recovery would require complete disruption of the cells and therefore would be difficult. The study contributes new knowledge on the underlying mechanisms in the U(VI) reduction in facultative anaerobes.

Ferredoxin:NADP+ oxidoreductase as a target of Cd2+ inhibitory action--biochemical studies

The ferredoxin:NADP+ oxidoreductase (FNR) catalyses the ferredoxin-dependent reduction of NADP+ to NADPH in linear photosynthetic electron transport. The enzyme also transfers electrons from reduced ferredoxin (Fd) or NADPH to the cytochrome b(6)f complex in cyclic electron transport. In vitro, the enzyme catalyses the NADPH-dependent reduction of various substrates, including ferredoxin, the analogue of its redox centre - ferricyanide, and the analogue of quinones, which is dibromothymoquinone. This paper presents results on the cadmium-induced inhibition of FNR. The K(i) value calculated for research condition was 1.72 mM. FNR molecule can bind a large number of cadmium ions, as shown by the application of cadmium-selective electrode, but just one ion remains bound after dialysis. The effect of cadmium binding is significant disturbance in the electron transfer process from flavin adenine dinucleotide (FAD) to dibromothymoqinone, but less interference with the reduction of ferricyanide. However, it caused a strong inhibition of Fd reduction, indicating that Cd-induced changes in the FNR structure disrupt Fd binding. Additionally, the protonation of the thiol groups is shown to be of great importance in the inhibition process. A mechanism for cadmium-caused inhibition is proposed and discussed with respect to the in vitro and in vivo situation.

Environmental stresses inhibit splicing in the aquatic fungus Blastocladiella emersonii

Background

Exposure of cells to environmental stress conditions can lead to the interruption of several intracellular processes, in particular those performed by macromolecular complexes such as the spliceosome.

Results

During nucleotide sequencing of cDNA libraries constructed using RNA isolated from B. emersonii cells submitted to heat shock and cadmium stress, a large number of ESTs with retained introns was observed. Among the 6,350 ESTs obtained through sequencing of stress cDNA libraries, 181 ESTs presented putative introns (2.9%), while sequencing of cDNA libraries from unstressed B. emersonii cells revealed only 0.2% of ESTs containing introns. These data indicate an enrichment of ESTs with introns in B. emersonii stress cDNA libraries. Among the 85 genes corresponding to the ESTs that retained introns, 19 showed more than one intron and three showed three introns, with intron length ranging from 55 to 333 nucleotides. Canonical splicing junctions were observed in most of these introns, junction sequences being very similar to those found in introns from genes previously characterized in B. emersonii, suggesting that inhibition of splicing during stress is apparently a random process. Confirming our observations, analyses of gpx3 and hsp70 mRNAs by Northern blot and S1 protection assays revealed a strong inhibition of intron splicing in cells submitted to cadmium stress.

Conclusion

In conclusion, data indicate that environmental stresses, particularly cadmium treatment, inhibit intron processing in B. emersonii, revealing a new adaptive response to cellular exposure to this heavy metal.

Thioredoxin is involved in U(VI) and Cr(VI) reduction in Desulfovibrio desulfuricans G20

A transposon insertion mutant has been identified in a Desulfovibrio desulfuricans G20 mutant library that does not grow in the presence of 2 mM U(VI) in lactate-sulfate medium. This mutant has also been shown to be deficient in the ability to grow with 100 microM Cr(VI) and 20 mM As(V). Experiments with washed cells showed that this mutant had lost the ability to reduce U(VI) or Cr(VI), providing an explanation for the lower tolerance. A gene encoding a cyclic AMP (cAMP) receptor protein (CRP) was identified as the site of the transposon insertion. The remainder of the mre operon (metal reduction) contains genes encoding a thioredoxin, thioredoxin reductase, and an additional oxidoreductase whose substrate has not been predicted. Expression studies showed that in the mutant, the entire operon is downregulated, suggesting that the CRP may be involved in regulating expression of the whole operon. Exposure of the cells to U(VI) resulted in upregulation of the entire operon. CdCl(2), a specific inhibitor of thioredoxin activity, inhibits U(VI) reduction by washed cells and inhibits growth of cells in culture when U(VI) is present, confirming a role for thioredoxin in U(VI) reduction. The entire mre operon was cloned into Escherichia coli JM109 and the transformant developed increased U(VI) resistance and the ability to reduce U(VI) to U(IV). The oxidoreductase protein (MreG) from this operon was expressed and purified from E. coli. In the presence of thioredoxin, thioredoxin reductase, and NADPH, this protein was shown to reduce both U(VI) and Cr(VI), providing a mechanism for the cytoplasmic reduction of these metals.

Oenococcus oeni genome plasticity is associated with fitness

Oenococcus oeni strains are well-known for their considerable phenotypic variations in terms of tolerance to harsh wine conditions and malolactic activity. Genomic subtractive hybridization (SH) between two isolates with differing enological potentials was used to elucidate the genetic bases of this intraspecies diversity and identify novel genes involved in adaptation to wine. SH revealed 182 tester-specific fragments corresponding to 126 open reading frames (ORFs). A large proportion of the chromosome-related ORFs resembled genes involved in carbohydrate transport and metabolism, cell wall/membrane/envelope biogenesis, and replication, recombination, and repair. Six regions of genomic plasticity were identified, and their analysis suggested that both limited recombination and insertion/deletion events contributed to the vast genomic diversity observed in O. oeni. The association of selected sequences with adaptation to wine was further assessed by screening a large collection of strains using PCR. No sequences were found to be specific to highly performing (HP) strains alone. However, there was a statistically significant positive association between HP strains and the presence of eight gene sequences located on regions 2, 4, and 5. Gene expression patterns were significantly modified in HP strains, following exposure to one or more of the common stresses in wines. Regions 2 and 5 showed no traces of mobile elements and had normal GC content. In contrast, region 4 had the typical hallmarks of horizontal transfer, suggesting that the strategy of acquiring genes from other bacteria enhances the fitness of O. oeni strains.

Molecular responses of Campylobacter jejuni to cadmium stress

Cadmium ions are a potent carcinogen in animals, and cadmium is a toxic metal of significant environmental importance for humans. Response curves were used to investigate the effects of cadmium chloride on the growth of Camplyobacter jejuni. In vitro, the bacterium showed reduced growth in the presence of 0.1 mm cadmium chloride, and the metal ions were lethal at 1 mm concentration. Two-dimensional gel electrophoresis combined with tandem mass spectrometry analysis enabled identification of 67 proteins differentially expressed in cells grown without and with 0.1 mm cadmium chloride. Cellular processes and pathways regulated under cadmium stress included fatty acid biosynthesis, protein biosynthesis, chemotaxis and mobility, the tricarboxylic acid cycle, protein modification, redox processes and the heat-shock response. Disulfide reductases and their substrates play many roles in cellular processes, including protection against reactive oxygen species and detoxification of xenobiotics, such as cadmium. The effects of cadmium on thioredoxin reductase and disulfide reductases using glutathione as a substrate were studied in bacterial lysates by spectrophotometry and nuclear magnetic resonance spectroscopy, respectively. The presence of 0.1 mm cadmium ions modulated the activities of both enzymes. The interactions of cadmium ions with oxidized glutathione and reduced glutathione were investigated using nuclear magnetic resonance spectroscopy. The data suggested that, unlike other organisms, C. jejuni downregulates thioredoxin reductase and upregulates other disulfide reductases involved in metal detoxification in the presence of cadmium.

The Arabidopsis putative selenium-binding protein family: expression study and characterization of SBP1 as a potential new player in cadmium detoxification processes

In Arabidopsis (Arabidopsis thaliana), the putative selenium-binding protein (SBP) gene family is composed of three members (SBP1-SBP3). Reverse transcription-polymerase chain reaction analyses showed that SBP1 expression was ubiquitous. SBP2 was expressed at a lower level in flowers and roots, whereas SBP3 transcripts were only detected in young seedling tissues. In cadmium (Cd)-treated seedlings, SBP1 level of expression was rapidly increased in roots. In shoots, SBP1 transcripts accumulated later and for higher Cd doses. SBP2 and SBP3 expression showed delayed or no responsiveness to Cd. In addition, luciferase (LUC) activity recorded on Arabidopsis lines expressing the LUC gene under the control of the SBP1 promoter further showed dynamic regulation of SBP1 expression during development and in response to Cd stress. Western-blot analysis using polyclonal antibodies raised against SBP1 showed that SBP1 protein accumulated in Cd-exposed tissues in correlation with SBP1 transcript amount. The sbp1 null mutant displayed no visible phenotype under normal and stress conditions that was explained by the up-regulation of SBP2 expression. SBP1 overexpression enhanced Cd accumulation in roots and reduced sensitivity to Cd in wild type and, more significantly, in Cd-hypersensitive cad mutants that lack phytochelatins. Similarly, in Saccharomyces cerevisiae, SBP1 expression led to increased Cd tolerance of the Cd-hypersensitive ycf1 mutant. In vitro experiments showed that SBP1 has the ability to bind Cd. These data highlight the importance of maintaining the adequate SBP protein level under healthy and stress conditions and suggest that, during Cd stress, SBP1 accumulation efficiently helps to detoxify Cd potentially through direct binding.

Role of metallothioneins in superoxide radical generation during copper redox cycling: Defining the fundamental function of metallothioneins

In order to demonstrate the in vivo antioxidant properties of metallothioneins (MTs), the bacteria Escherichia coli was used as a cell reactor in which we compared the metal binding and antioxidative functions of MTs from different species, with different structures and polypeptide lengths. No protective effects of cytoplasmic MTs from cadmium (Cd) or zinc (Zn) contamination were observed in a wild-type E. coli strain, although these MTs can efficiently bind both Cd and Zn. To test their antioxidant properties, MTs were expressed within the cytoplasm of a sodA sodB deficient mutated strain (QC1726). However, a paradoxical MT toxicity was found when this strain was contaminated with Cd and Zn, suggesting that in a wild-type strain, superoxide dismutase counteracts MT toxicity. The most toxic MT was the one with the strongest Cd and Zn binding capacities. This toxic effect was linked to the generation of superoxide radicals, since a Cd-contaminated QC1726 strain expressing oyster MT isoforms produced 75-85% more O(2)*(-) than the control QC1726 strain. Conversely, under anaerobiosis or in the presence of a copper chelator, MTs protected QC1726 strain from Cd and Zn contamination. A model is proposed to explain the observed MT toxicity.

Crystal Structures of a Poplar Thioredoxin Peroxidase that Exhibits the Structure of Glutathione Peroxidases: Insights into Redox-driven Conformational Changes

Glutathione peroxidases (GPXs) are a group of enzymes that regulate the levels of reactive oxygen species in cells and tissues, and protect them against oxidative damage. Contrary to most of their counterparts in animal cells, the higher plant GPX homologues identified so far possess cysteine instead of selenocysteine in their active site. Interestingly, the plant GPXs are not dependent on glutathione but rather on thioredoxin as their in vitro electron donor. We have determined the crystal structures of the reduced and oxidized form of Populus trichocarpaxdeltoides GPX5 (PtGPX5), using a selenomethionine derivative. PtGPX5 exhibits an overall structure similar to that of the known animal GPXs. PtGPX5 crystallized in the assumed physiological dimeric form, displaying a pseudo ten-stranded beta sheet core. Comparison of both redox structures indicates that a drastic conformational change is necessary to bring the two distant cysteine residues together to form an intramolecular disulfide bond. In addition, a computer model of a complex of PtGPX5 and its in vitro recycling partner thioredoxin h1 is proposed on the basis of the crystal packing of the oxidized form enzyme. A possible role of PtGPX5 as a heavy-metal sink is also discussed.

Synuclein-gamma targeting peptide inhibitor that enhances sensitivity of breast cancer cells to antimicrotubule drugs

Synuclein-gamma (SNCG) plays oncogenic roles in breast carcinogenesis. Although the expression of SNCG is abnormally high in advanced and metastatic breast carcinomas, SNCG is not expressed in normal or benign breast tissues. SNCG is an intrinsically disordered protein known to interact with BubR1, a mitotic checkpoint kinase. The SNCG-BubR1 interaction inhibits mitotic checkpoint control upon spindle damage caused by anticancer drugs, such as nocodazole and taxol. Antimicrotubule drugs that cause mitotic arrest and subsequent apoptosis of cancer cells are frequently used to treat breast cancer patients with advanced or metastatic diseases. However, patient response rates to this class of chemotherapeutic agents vary significantly. In this study, we have designed a novel peptide (ANK) and shown its interaction with SNCG using fluorometry, surface plasmon resonance, and isothermal titration calorimetry. Binding of the ANK peptide did not induce folding of SNCG, suggesting that SNCG can function biologically in its intrinsically disordered state. Microinjection of the ANK peptide in breast cancer cell line overexpressing SNCG (MCF7-SNCG) exhibited a similar cell killing response by nocodazole as in the SNCG-negative MCF7 cells. Overexpression of enhanced green fluorescent protein-tagged ANK reduces SNCG-mediated resistance to paclitaxel treatment by approximately 3.5-fold. Our coimmunoprecipitation and colocalization results confirmed the intracellular association of the ANK peptide with SNCG. This is likely due to the disruption of the interaction of SNCG with BubR1 interaction. Our findings shed light on the molecular mechanism of the ANK peptide in releasing SNCG-mediated drug resistance.

Regulation of the cadmium stress response through SCF-like ubiquitin ligases: comparison between Saccharomyces cerevisiae, Schizosaccharomyces pombe and mammalian cells

Saccharomyces cerevisiae has developed several mechanisms to cope with exposure to cadmium. In particular, the sulfur compound glutathione plays a pivotal role in cadmium detoxification, and exposure to cadmium leads to a wide reorganization of S. cerevisiae transcriptome and proteome, resulting in a significant increase in glutathione synthesis. Met4, the transcriptional activator of the sulfur metabolism enzymes, is a critical actor in this reorganization. Recent work has uncovered a part of the mechanism of cadmium-induced Met4 regulation, and showed that it occurs trough the SCF ubiquitin ligase complex SCF(Met30). We discuss this regulation in S. cerevisiae and compare it with the regulation of two other transcriptional activators involved in cadmium detoxification: the Schizosaccharomyces pombe Zip1, regulated by SCF(Pof1), and the mammalian Nrf2, regulated by the SCF-like ubiquitin ligase Cul3:Rbx1:Keap1.

Inhibition of Thermus thermophilus HB8 thioredoxin activity by platinum(II)

A 1:1 thioredoxin-Pt(bpy) complex was prepared by adding [Pt(bpy)(en)]Cl(2)(bpy = 2,2'-bipyridine, en = ethylenediamine) to Thermus thermophilus HB8 thioredoxin in pH 8 phosphate buffer. Matrix-assisted laser desorption-ionization time of flight mass spectrometry (MALDI-TOF MS) and UV spectra of indicate the formation of Pt(bpy)(cys-Ala-Pro-cys-containing peptide fragment). These findings suggest that the Pt(bpy)(2+) unit binds to the active site of thioredoxin. The thioredoxin-platinum complex has no catalytic activity for the reduction of glutathione disulfide in the presence of NADPH and thioredoxin reductase, so that the platinum complex functions as an inhibitor.

Survey of the year 2004: literature on applications of isothermal titration calorimetry

The market for commercially available isothermal titration calorimeters continues to grow as new applications and methodologies are developed. Concomitantly the number of users (and abusers) increases dramatically, resulting in a steady increase in the number of publications in which isothermal titration calorimetry (ITC) plays a role. In the present review, we will focus on areas where ITC is making a significant contribution and will highlight some interesting applications of the technique. This overview of papers published in 2004 also discusses current issues of interest in the development of ITC as a tool of choice in the determination of the thermodynamics of molecular recognition and interaction.