Crystal structure of the catalytic domain of a human thioredoxin-like protein

TXNL1 has dual functions as a redox active thioredoxin-like protein as well as an ATP- and redox-independent chaperone

TXNL1 (also named TRP32, for thioredoxin related protein of 32 kDa) is a cytosolic thioredoxin-fold protein expressed in all cell types and conserved from yeast to mammals, but with yet poorly known function. Here, we expressed and purified human TXNL1 together with several Cys-to-Ser variants, characterizing their enzymatic properties. TXNL1 could reduce disulfides in insulin, cystine and glutathione disulfide (GSSG) in reactions coupled to thioredoxin reductase (TXNRD1, TrxR1) using NADPH, similarly to thioredoxin (TXN, Trx1), but with lower catalytic efficacy due to at least one order of magnitude higher Km of TrxR1 for TXNL1 compared to Trx1. However, in sharp contrast to Trx1, we found that TXNL1 also had efficient chaperone activity that did not require ATP. TXNL1 made non-covalent complexes with reduced insulin, thereby keeping it in solution, and TXNL1 provided chaperone function towards whole cell lysate proteins by preventing their aggregation during heating. The chaperone activities of TXNL1 did not require its redox activity or any dithiol-disulfide exchange reactions, as revealed using Cys-to-Ser substituted variants, as well as a maintained chaperone activity of TXNL1 also in the absence of TrxR1 and NADPH. These results reveal that TXNL1 has dual functions, supporting TrxR1-driven redox activities in disulfide reduction reactions, as well as being an ATP-independent chaperone that does not require involvement of its redox activity.

Molecular cloning, tissues distribution, and function analysis of thioredoxin-like protein-1 (TXNL1) in Chinese giant salamanders Andrias davidianus

Thioredoxin-like protein-1 (TXNL1) is the member of thioredoxin superfamily, a family of thiol oxidoreductases. TXNL1 plays an important role in scavenging ROS and the maintenance of cellular redox balance. However, its physiological functions in Andrias davidianus have not been well understood. In the present study, the full-length cDNA encoding thioredoxin-like protein-1 (AdTXNL1) of A. davidianus was cloned, the mRNA tissue distribution was analyzed, and the function was characterized. The Adtxnl1 cDNA contained an open reading frame (ORF) of 870 bp encoding a polypeptide of 289 amino acids with the N-terminal TRX domain, a Cys³⁴-Ala³⁵-Pro³⁶-Cys³⁷ (CAPC) motif, and the C-terminal proteasome-interacting thioredoxin domain (PITH). The mRNA of AdTXNL1 was expressed in a wide range of tissues, with the highest level in the liver. The transcript level of AdTXNL1 was significantly up-regulated post Aeromonas hydrophila challenge in liver tissue. Moreover, the recombinant AdTXNL1 protein was produced and purified, and used to investigate the antioxidant activity. In the insulin disulfide reduction assay, rAdTXNL1 exhibited strong antioxidant capability. Altogether, the thioredoxin-like protein-1 may be involved in reduction/oxidation (redox) balance and as an important immunological gene in A. davidianus.

The role of TXNL1 in disease: treatment strategies for cancer and diseases with oxidative stress

Thioredoxin-like protein-1 (TXNL1; also known as thioredoxin-related 32 kDa protein, TRP32) is a thioredoxin involved in the regulation of oxidative stress, which protects cells from damage through redox balance. Studies have shown that TXNL1 has a variety of functions, including cell signal transduction, cell cycle regulation, protein synthesis, modification and degradation, vesicle transport, transcriptional regulation, cell apoptosis, virus replication and oxidative stress regulation, etc., and plays an important role in the occurrence and development of human diseases. Therefore, TXNL1 has a strong correlation with the treatment of cancer and oxidative stress diseases. In this paper, the basic structure, function and potential application value of TXNL1 in diseases are reviewed, so as to open up new targets for the treatment of cancer and oxidative stress-related diseases.

Thioredoxin-related protein 32 (TRP32) specifically reduces oxidized phosphatase of regenerating liver (PRL)

PRL family constitutes a unique class of phosphatases associated with metastasis. The phosphatase activity of PRL has been reported to be important for promoting metastasis, and it is inactivated by reversible oxidation of its catalytic cysteine. Here, we show that TRP32 specifically reduces PRL. Reduction of oxidized PRL in cells is inhibited by 2,4-dinitro-1-chlorobenzene, an inhibitor of TRX reductase. In vitro assays for the reduction of PRL show that only TRP32 can potently reduce oxidized PRL, whereas other TRX-related proteins linked to TRX reductase show little or no reducing activity. Indeed, TRP32 knockdown significantly prolongs the H2O2-induced oxidation of PRL. Binding analyses reveal that the unique C-terminal domain of TRP32 is required and sufficient for its direct interaction with PRL. These results suggest that TRP32 maintains the reduced state of PRL and thus regulates the biological function of PRL.

First report of two thioredoxin homologues in crustaceans: molecular characterization, genomic organization and expression pattern in swimming crab Portunus trituberculatus

Previously, we had reported two homologues of the thioredoxin (Trx) super-family (PtTrx1 and PtTrx2) identified from eyestalk and haemocytes cDNA library of swimming crab Portunus trituberculatus, respectively. It was the first report of two thioredoxin homologues from the same crustacean species. Here, we focused on the molecular characterization, genomic organization and expression pattern of PtTrx1 and PtTrx2. The full-length cDNA sequences of PtTrx1 and PtTrx2 were 739 and 1300 bp, encoding 105 and 133 amino acids, respectively. They both had a conserved CGPC active site and highly similar tertiary structures, which containing four β-sheets and four α-helixes. Specifically, PtTrx2 was encoded by a nuclear gene and its cellular localization was targeted to mitochondria by an N-terminal mitochondrial pre-sequence. Sequence analysis revealed PtTrx1 and PtTrx2 were encoded by different genomic locus. As the first analyzed genomic structure of PtTrxs in crustaceans, two introns with microsatellites were found in the open reading frame region of these genes. Quantitative real-time PCR analysis revealed the mRNA expression of PtTrx1 transcripts were mainly detected in gill, while, PtTrx2 in eyestalk and gill. The temporal expression levels of PtTrxs transcripts in haemocytes showed different expression patterns after challenge with Vibrio alginolyticus, Micrococcus luteus and Pichia pastoris. These results together indicate that PtTrxs should be involved in the responses to pathogen challenge of P. trituberculatus.

Mitochondrial thioredoxin-2 from Manila clam (Ruditapes philippinarum) is a potent antioxidant enzyme involved in antibacterial response

Thioredoxin (TRx) is a ubiquitous protein involved in the regulation of multiple biological processes. The TRx-2 isoform is exclusively expressed in mitochondria, where it contributes to mitochondrial redox state maintenance. In the present study, a novel thioredoxin-2 gene was identified in the Manila clam, Ruditapes philippinarum. The full-length sequence of RpTRx-2 (1561 bp) consists of a 498 bp coding region encoding a 166 amino acid protein. The N-terminal region of RpTRx-2 harbors a mitochondrial localization signal (56 amino acids), while the C-terminal portion contains the characteristic (89)WCGPC(93) catalytic active site. Phylogenetic analysis revealed that RpTRx-2 is closest to its ortholog from abalone. The broad distribution pattern of RpTRx-2 mRNA in healthy animal tissues implicates a generally significant function in normal clam physiology. The transcription level of RpTRx-2, however, is highest in hemocytes. Lipopolysaccharide and Vibrio tapetis bacterium caused up-regulation of the RpTrx-2 transcript levels in gill and hemocytes. Interestingly, clam manganese superoxide dismutase (MnSOD) mRNA levels in hemocytes elicited a corresponding response to these immune challenges. RpTRx-2 was recombinantly expressed in Escherichia coli BL21 (DE3) and used in insulin disulfide reduction assay as well as metal-catalyzed oxidation assay to elucidate its antioxidant property by reducing substrate and protecting super-coiled DNA from oxidative damage through free radical scavenging, respectively. Collectively, our data indicated that RpTRx-2, a mitochondrial TRx-2 family member, is an antioxidant enzyme that may be involved in antibacterial defense of clams.

Thioredoxin-related Protein 32 is an arsenite-regulated Thiol Reductase of the proteasome 19 S particle

Perturbation of the cytoplasmic protein folding environment by exposure to oxidative stress-inducing As(III)-containing compounds challenges the ubiquitin-proteasome system. Here we report on mass spectrometric analysis of As(III)-induced changes in the proteasome's composition in samples prepared by stable isotope labeling with amino acids in cell culture, using mammalian cells in which TRP32 (thioredoxin-related protein of 32 kDa; also referred to as TXNL1) was identified as a novel subunit of the 26 S proteasome. Quantitative genetic interaction mapping, using the epistatic miniarray profiling approach, identified a functional connection between TRP32 and the proteasome. Deletion of txl1, the Schizosaccharomyces pombe homolog of TRP32, results in a slow growth phenotype when combined with deletion of cut8, a gene required for normal proteasome localization. Deletion analysis in vivo, chemical cross-linking, and manipulation of the ATP concentration in vitro during proteasome immunopurification revealed that the C-terminal domain of mammalian TRP32 binds the 19 S regulatory particle in proximity to the proteasome substrate binding site. Thiol modification with polyethylene glycol-maleimide showed disulfide bond formation at the active site of TRP32 in cells exposed to As(III). Pulse-chase labeling showed that TRP32 is a stable protein whose half-life of >6 h is surprisingly reduced to 1 h upon exposure of cells to As(III). These findings reveal a previously undescribed thiol reductase at the proteasome's regulatory particle.

Characterisation of the components of the thioredoxin system in the archaeon Sulfolobus solfataricus

The thioredoxin system is a redox machinery widely distributed in nature and involved in several cellular functions. It is constituted of thioredoxin reductase (Trx-B), its protein substrate thioredoxin (Trx-A) and NADPH. We have previously characterised a Trx-B from the hyperthermophile Sulfolobus solfataricus (SsTrx-B3) (Ruocco et al. in Biochimie 86:883-892, 2004). As in the genome of this archaeon, the gene coding for another Trx-B (SsTrx-B2) and for two Trx-A (SsTrx-A1, SsTrx-A2) have been putatively identified, these proteins were obtained as recombinant forms and characterised. SsTrx-B2, different from SsTrx-B3, did not elicit a thioredoxin reductase activity. S. solfataricus possessed only one Trx-B (SsTrx-B3), which had two thioredoxins (SsTrx-A1 and SsTrx-A2) as substrates. These latter showed a homodimeric structure and catalysed insulin reduction using either DTT or NADPH/SsTrx-B3 as electron donors. In addition, the electron transfer between SsTrx-B3 and either SsTrx-A1 or SsTrx-A2 was fully reversible, thus allowing the determination of the redox potential of the thioredoxin system in S. solfataricus. Among the two thioredoxins, SsTrx-A2 appeared slightly more active and stable than SsTrx-A1. These data, besides shedding light on thioredoxin system in S. solfataricus, will contribute to add further information on this key enzyme system in Archaea.

The redox sensor TXNL1 plays a regulatory role in fluid phase endocytosis

Background

Small GTPases of the Rab family can cycle between a GTP- and a GDP-bound state and also between membrane and cytosol. The latter cycle is mediated by the Guanine Nucleotide Dissociation Inhibitor GDI, which can selectively extract GDP-bound Rab proteins from donor membranes, and then reload them on target membranes. In previous studies, we found that capture of the small GTPase Rab5, a key regulator of endocytic membrane traffic, by GDI is stimulated by oxidative stress via p38MAPK, resulting in increased fluid phase endocytosis.

Methodology/Principal Findings

When purifying the GDI stimulating activity we found that that it copurified with a high MW protein complex, which included p38MAPK. Here we report the identification and characterization of another component of this complex as the thioredoxin-like protein TXNL1. Our observations indicate that TXNL1 play a selective role in the regulation of fluid phase endocytosis, by controlling GDI capacity to capture Rab5.

Conclusions/Significance

Oxidants, which are known to cause cellular damage, can also trigger signaling pathways, in particular via members of the thioredoxin family. We propose that TXNL1 acts as an effector of oxidants or a redox sensor by converting redox changes into changes of GDI capacity to capture Rab5, which in turn modulates fluid phase endocytosis.

The txl1+ gene from Schizosaccharomyces pombe encodes a new thioredoxin-like 1 protein that participates in the antioxidant defence against tert-butyl hydroperoxide

Yeasts are equipped with several putative single-domain thioredoxins located in different subcellular compartments. However, additional proteins containing thioredoxin domains are also encoded by the yeast genomes as described for mammals and other eukaryotic organisms. We report here the characterization of the fission yeast orthologue thioredoxin-like 1 (txl1(+)), which has been previously identified in mammals. Similarly to the human protein, the fission yeast Txl1 is a two-domain protein comprising an N-terminal thioredoxin-like domain and a C-terminal domain of unknown function. Many other yeasts and fungi species contain homologues of txl1(+); however, there is no evidence of txl1(+) orthologues in either Saccharomyces cerevisiae or plants. Txl1 is found in both the nucleus and the cytoplasm of Schizosaccharomyces pombe cells and exhibits a strong reducing activity coupled to thioredoxin reductase. In humans, TXL1 expression is induced by glucose deprivation and overexpression of TXL1 confers resistance against this stress. In contrast, a Sz. pombe Deltatxl1 mutant was not affected in the response against glucose starvation but the Deltatxl1 mutant strain showed a clear hypersensitivity to alkyl hydroperoxide. The mRNA levels of txl1(+) in a h20 strain did not change in response to any oxidative insult (hydrogen peroxide or alkyl hydroperoxide) and the overexpression of an integrated copy of the wild-type txl1(+) gene did not confer a significant increased resistance against alkyl hydroperoxide. Overall, these results indicate that the Txl1 role in the cellular detoxification of alkyl hydroperoxide is exerted through a constitutive transcription of txl1(+).

Involvement of FpTRP26, a thioredoxin-related protein, in oxalic acid-resistance of the brown-rot fungus Fomitopsis palustris

Brown-rot fungus Fomitopsis palustris grows vigorously at high concentrations of oxalic acid (OA), which is fungal metabolite during wood decay. We isolated a cDNA FpTRP26 from F. palustris by functional screening of yeast transformants with cDNAs grown on plates containing OA. FpTRP26 conferred a specific resistance to OA on the transformant. OA-content in transformants grown with 2mM OA decreased by 65% compared to that of the control. The amount of FpTRP26 transcript in F. palustris amplified with increasing OA-accumulation, and was maintained at high levels even in the stationary phase. Its transcription in F. palustris was inducible in response to exogenously added OA. These results suggest that FpTRP26 is involved in the OA-resistance in F. palustris.

Contribution of thioredoxin reductase to T-cell mitogenesis and NF-kappaB DNA-binding promoted by selenite

Although the essential role of selenium for cellular immune responses is obvious, delineation of the functions is lacking because selenium can either promote or inhibit cell growth, cytokine production, and activation of transcription factor nuclear factor-kappaB (NF-kappaB). Studies with human thioredoxin-1 (Trx-1)-transgenic (Tg) mice were conducted to evaluate the relationship between stimulation of T-cell mitogenic response by sodium selenite and the intracellular Trx-1 levels, and the activities of selenoenzymes and NF-kappaB-DNA binding. Concanavalin A-induced mitogenesis of wild-type mouse splenic cells was stimulated by exposure to low levels of selenite (0.02-0.1 microM), with augmentation of NF-kappaB-DNA binding activity. Treatment with NF-kappaB nuclear translocation inhibitor SN50 or thioredoxin reductase (TR) inhibitor aurothioglucose depressed this stimulatory action. The mitogenic response of Trx-1-Tg mouse splenic cells was enhanced by exposure to relatively high levels of selenite (> or = 0.05 microM), compared with the wild-type mouse. Selenite also augmented TR activity but not cellular glutathione peroxidase activity in the Trx-1-overexpressed cells. These results suggest that the stimulation of T-cell mitogenic response by the physiological levels of selenite is predominantly caused by increased TR activity, which may lead to reduction of Trx-1 dependent on the intracellular expression level and promotion of DNA binding of NF-kappaB.

Characterization of human thioredoxin-like-1: Potential involvement in the cellular response against glucose deprivation

The thioredoxin system, composed of thioredoxin (Trx) and thioredoxin reductase (TrxR), emerges as one of the most important thiol-based systems involved in the maintenance of the cellular redox balance. Thioredoxin-like-1 (TXL-1) is a highly conserved protein comprising an N-terminal Trx domain and a C-terminal domain of unknown function. Here we show that TXL-1 is a substrate for the cytosolic selenoprotein TrxR-1. In situ hybridization experiments demonstrates high expression of Txl-1 mRNA in various areas of central nervous system and also in some reproductive organs. Glucose deprivation, but not hydrogen peroxide treatment, reduced the levels of endogenous TXL-1 protein in HEK-293 cell line. Conversely, overexpression of TXL-1 protects against glucose deprivation-induced cytotoxicity. Taken together, the finding that Txl-1 mRNA is highly expressed in tissues which use glucose as a primary energy source and the modulation of TXL-1 levels upon glucose deprivation indicate that TXL-1 might be involved in the cellular response to sugar starvation stress.

Cloning and characterization of rat spermatid protein SSP411: a thioredoxin-like protein

In an attempt to identify new sperm-specific genes that are involved in sperm maturation, fertilization, and embryo development, such as the mammalian ortholog of the sperm-supplied protein gene, spe-11, in Caenorhabditis elegans, we cloned and characterized a new spermatid-specific protein gene, ssp411, from adult rat testes. The ssp411 cDNA shared >85% sequence identity with an unnamed human protein, FLJ21347, and an uncharacterized mouse testicular protein called transcript increased in spermiogenesis 78 (TISP78). A 2.8-kb ssp411 mRNA was expressed in a testis-specific and age-dependent manner; the mRNA was evident at 28 days and remained at high levels throughout adulthood. An SSP411 protein of molecular weight 88 000 was detected in testicular extracts by Western blot analysis. Ssp411 mRNA and SSP411 protein, as analyzed by in situ hybridization and immunohistochemistry, were both expressed in a stage-dependent fashion during the cycle of the seminiferous epithelium. The ssp411 mRNA was predominantly localized to round and elongated spermatids, with maximal expression at stages VII-XII. The SSP411 protein was mainly observed in elongated spermatids and reached its highest levels during stages V-VI. A conserved thioredoxin-like domain was detected in the N-terminal region of SSP411 and its orthologs. An analysis of the predicted 3-dimensional structural modeling and folding pattern further suggested that SSP411 is identifiable as a member of thioredoxin family. In summary, we have identified a new rat spermatid protein gene, ssp411, and its orthologs in human and mouse and demonstrated that SSP411 might belong to a testis-specific thioredoxin family. This suggests that SSP411 may play a role in sperm maturation, fertilization, and/or embryo development, as has been shown in thioredoxin family.

Solution structure of At3g04780.1-des15, an Arabidopsis thaliana ortholog of the C-terminal domain of human thioredoxin-like protein

The structure of At3g04780.1-des15, an Arabidopsis thaliana ortholog of the C-terminal domain of human thioredoxin-like protein, was determined by NMR spectroscopy. The structure is dominated by a beta-barrel sandwich. A two-stranded anti-parallel beta-sheet, which seals off one end of the beta-barrel, is flanked by two flexible loops rich in acidic amino acids. Although this fold often provides a ligand binding site, the structure did not reveal an appreciable cavity inside the beta-barrel. The three-dimensional structure of At3g04780.1-des15 provides an entry point for understanding its functional role and those of its mammalian homologs.