Dithiothreitol reduces oxidative stress and necrosis caused by ultraviolet A radiation in L929 fibroblasts.

Ultraviolet A (UVA) radiation, present in sunlight, can induce cell redox imbalance leading to cellular damage and even cell death, compromising skin health. Here, we evaluated the in vitro antioxidant and photochemoprotective effect of dithiothreitol (DTT). DTT neutralized the free radicals 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS·+), 2,2-diphenyl-1-picrylhydrazyl (DPPH·), and superoxide anion (O2·-) in in vitro assays, as well as the ferric ion (Fe3+) in the ferric reducing antioxidant power (FRAP) assay. We also evaluated the effect of DTT pre-treatment in L929 dermal fibroblasts and DTT (50 and 100 µM) led to greater cell viability following UVA-irradiation compared to cells that were untreated. Furthermore, the pre-treatment of cells with DTT prevented the increase of intracellular reactive oxygen species (ROS) production, including hydrogen peroxide (H2O2), lipid peroxidation, and DNA condensation, as well as the decrease in mitochondrial membrane potential (Δψm), that occurred following irradiation in untreated cells. The endogenous antioxidant system of cells was also improved in irradiated cells that were DTT pre-treated compared to the untreated cells, as the activity of the superoxide dismutase (SOD) and catalase (CAT) enzymes remained as high as non-irradiated cells, while the activity levels were depleted in the untreated irradiated cells. Furthermore, DTT reduced necrosis in UVA-irradiated fibroblasts. Together, these results showed that DTT may have promising use in the prevention of skin photoaging and photodamage induced by UVA, as it provided photochemoprotection against the harmful effects of this radiation, reducing oxidative stress and cell death, due mainly to its antioxidant capacity.

Dithiothreitol Affects the Fertilization Response in Immature and Maturing Starfish Oocytes.

Immature starfish oocytes isolated from the ovary are susceptible to polyspermy due to the structural organization of the vitelline layer covering the oocyte plasma membrane, as well as the distribution and biochemical properties of the actin cytoskeleton of the oocyte cortex. After the resumption of the meiotic cycle of the oocyte triggered by the hormone 1-methyladenine, the maturing oocyte reaches fertilizable conditions to be stimulated by only one sperm with a normal Ca2+ response and cortical reaction. This cytoplasmic ripening of the oocyte, resulting in normal fertilization and development, is due to the remodeling of the cortical actin cytoskeleton and germinal vesicle breakdown (GVBD). Since disulfide-reducing agents such as dithiothreitol (DTT) are known to induce the maturation and GVBD of oocytes in many species of starfish, we analyzed the pattern of the fertilization response displayed by Astropecten aranciacus oocytes pre-exposed to DTT with or without 1-MA stimulation. Short treatment of A. aranciacus immature oocytes with DTT reduced the rate of polyspermic fertilization and altered the sperm-induced Ca2+ response by changing the morphology of microvilli, cortical granules, and biochemical properties of the cortical F-actin. At variance with 1-MA, the DTT treatment of immature starfish oocytes for 70 min did not induce GVBD. On the other hand, the DTT treatment caused an alteration in microvilli morphology and a drastic depolymerization of the cortical F-actin, which impaired the sperm-induced Ca2+ response at fertilization and the subsequent embryonic development.

Long-term storage protocol of reagent red blood cells treated with 0.01M dithiothreitol (DTT) for pre-transfusion testing of patients receiving anti-CD38 therapy, daratumumab.

OBJECTIVE: Use red blood cell stabilizer to store the antibody screening and antibody identification reagent red blood cells (RBCs) treated with 0.01 mol/L DTT and investigate its value in the pre-transfusion examinations of patients treated with daratumumab. METHOD: Determined the optimal incubation time for the 0.01 mol/L DTT-treated RBCs method by evaluating the effect of treatment at different time points. Added ID-CellStab to store DTT-treated RBCs, determined the maximum shelf life of reagent RBCs by monitoring the hemolysis index, and assessed changes in the antigenicity of blood group antigens on the surface of RBCs during storage with antibody reagents. RESULT: A protocol for long-term storage of reagent red blood cells treated with the 0.01 mol/L DTT method was established. The optimal incubation time was 40-50 min. RBCs could be stored stably for 18 days after adding ID-CellStab. The protocol was able to eliminate pan-agglutination caused by daratumumab, with no significant changes in the antigens of most blood group systems, except for some attenuation of K antigen and Duffy blood group system antigens during the storage period. CONCLUSION: The storage protocol of reagent RBCs based on the 0.01 mol/L DTT method does not affect the detection of most blood group antibodies and retains a certain degree of detection ability for anti-K antibodies, allowing patients treated with daratumumab to quickly perform pre-transfusion examinations, making up for the shortcomings of currently commercial reagent RBCs.

[Dithiothreitol promotes apoptosis in rat hepatocytes by inhibiting family with sequence similarity 134 member B (FAM134B)-mediated endoplasmic reticulophagy].

Objective To investigate the effect of family with sequence similarity 134 member B (FAM134B)-mediated endoplasmic reticulophagy on apoptosis of hepatocytes induced by endoplasmic reticulum stress (ERS) and identify its potential regulatory mechanism. Methods BRL-3A cells were treated with 0, 0.5, 1.0, 2.0, 4.0, 6.0 mmol/L dithiothreitol (DTT) for 48 hours. The effect of DTT treatment on the proliferation and apoptosis was analyzed using real time cellular dynamic analysis (RTCA) and flow cytometry. The level of proteins related to ERS, endoplasmic reticulophagy, mitochondria-endoplasmic reticulum contact sites (MERCs), and mitochondrial apoptosis pathway were determined using Western blot analysis. Co-localization of ER and lysosomes were detected using ER and lysosomal fluorescence probes. A Ca2+ fluorescence probe was used to detect the level of Ca2+ in mitochondria. Results DTT treatment significantly inhibited cell proliferation and promoted apoptosis in hepatocytes. The levels of proteins related to ERS and endoplasmic reticulophagy, MERCs and the mitochondrial apoptosis pathway significantly increased in BRL-3A cells treated with DTT. DTT treatment decreased the ER-lysosome co-localization and enhanced the fluorescence intensity of Ca2+ in mitochondria. Conclusion DTT aggravates hepatocyte apoptosis by inhibiting FAM134B-mediated endoplasmic reticulophagy and enhancing the level of mitochondrial Ca2+.

Metal binding and oligomerization properties of FurC (PerR) from Anabaena sp. PCC7120: an additional layer of regulation?

Metal and redox homeostasis in cyanobacteria is tightly controlled to preserve the photosynthetic machinery from mismetallation and minimize cell damage. This control is mainly taken by FUR (ferric uptake regulation) proteins. FurC works as the PerR (peroxide response) paralog in Anabaena sp. PCC7120. Despite its importance, this regulator remained poorly characterized. Although FurC lacks the typical CXXC motifs present in FUR proteins, it contains a tightly bound zinc per subunit. FurC: Zn stoichiometrically binds zinc and manganese in a second site, manganese being more efficient in the binding of FurC: Zn to its DNA target PprxA. Oligomerization analyses of FurC: Zn evidence the occurrence of different aggregates ranging from dimers to octamers. Notably, intermolecular disulfide bonds are not involved in FurC: Zn dimerization, dimer being the most reduced form of the protein. Oligomerization of dimers occurs upon oxidation of thiols by H2O2 or diamide and can be reversed by 1,4-Dithiothreitol (DTT). Irreversible inactivation of the regulator occurs by metal catalyzed oxidation promoted by ferrous iron. However, inactivation upon oxidation with H2O2 in the absence of iron was reverted by addition of DTT. Comparison of models for FurC: Zn dimers and tetramers obtained using AlphaFold Colab and SWISS-MODEL allowed to infer the residues forming both metal-binding sites and to propose the involvement of Cys86 in reversible tetramer formation. Our results decipher the existence of two levels of inactivation of FurC: Zn of Anabaena sp. PCC7120, a reversible one through disulfide-formed FurC: Zn tetramers and the irreversible metal catalyzed oxidation. This additional reversible regulation may be specific of cyanobacteria.

Dietary-derived vitamin B12 protects Caenorhabditis elegans from thiol-reducing agents.

BACKGROUND: One-carbon metabolism, which includes the folate and methionine cycles, involves the transfer of methyl groups which are then utilised as a part of multiple physiological processes including redox defence. During the methionine cycle, the vitamin B12-dependent enzyme methionine synthetase converts homocysteine to methionine. The enzyme S-adenosylmethionine (SAM) synthetase then uses methionine in the production of the reactive methyl carrier SAM. SAM-binding methyltransferases then utilise SAM as a cofactor to methylate proteins, small molecules, lipids, and nucleic acids. RESULTS: We describe a novel SAM methyltransferase, RIPS-1, which was the single gene identified from forward genetic screens in Caenorhabditis elegans looking for resistance to lethal concentrations of the thiol-reducing agent dithiothreitol (DTT). As well as RIPS-1 mutation, we show that in wild-type worms, DTT toxicity can be overcome by modulating vitamin B12 levels, either by using growth media and/or bacterial food that provide higher levels of vitamin B12 or by vitamin B12 supplementation. We show that active methionine synthetase is required for vitamin B12-mediated DTT resistance in wild types but is not required for resistance resulting from RIPS-1 mutation and that susceptibility to DTT is partially suppressed by methionine supplementation. A targeted RNAi modifier screen identified the mitochondrial enzyme methylmalonyl-CoA epimerase as a strong genetic enhancer of DTT resistance in a RIPS-1 mutant. We show that RIPS-1 is expressed in the intestinal and hypodermal tissues of the nematode and that treating with DTT, ß-mercaptoethanol, or hydrogen sulfide induces RIPS-1 expression. We demonstrate that RIPS-1 expression is controlled by the hypoxia-inducible factor pathway and that homologues of RIPS-1 are found in a small subset of eukaryotes and bacteria, many of which can adapt to fluctuations in environmental oxygen levels. CONCLUSIONS: This work highlights the central importance of dietary vitamin B12 in normal metabolic processes in C. elegans, defines a new role for this vitamin in countering reductive stress, and identifies RIPS-1 as a novel methyltransferase in the methionine cycle.

Preparations of Terminal Oxidase Cytochrome bd-II Isolated from Escherichia coli Reveal Significant Hydrogen Peroxide Scavenging Activity.

Cytochrome bd-II is one of the three terminal quinol oxidases of the aerobic respiratory chain of Escherichia coli. Preparations of the detergent-solubilized untagged bd-II oxidase isolated from the bacterium were shown to scavenge hydrogen peroxide (H2O2) with high rate producing molecular oxygen (O2). Addition of H2O2 to the same buffer that does not contain enzyme or contains thermally denatured cytochrome bd-II does not lead to any O2 production. The latter observation rules out involvement of adventitious transition metals bound to the protein. The H2O2-induced O2 production is not susceptible to inhibition by N-ethylmaleimide (the sulfhydryl binding compound), antimycin A (the compound that binds specifically to a quinol binding site), and CO (diatomic gas that binds specifically to the reduced heme d). However, O2 formation is inhibited by cyanide (IC50 = 4.5 ± 0.5 µM) and azide. Addition of H2O2 in the presence of dithiothreitol and ubiquinone-1 does not inactivate cytochrome bd-II and apparently does not affect the O2 reductase activity of the enzyme. The ability of cytochrome bd-II to detoxify H2O2 could play a role in bacterial physiology by conferring resistance to the peroxide-mediated stress.

Biotransformation of Dec-604 and potential effect on thyroid deiodinase activity in highly flame retardant-exposed gulls.

Several halogenated flame retardants (HFRs) have been identified as thyroid disruptors in birds including the polybrominated diphenyl ether (PBDE) mixtures, which have been replaced with other HFRs such as Dechlorane-604 (Dec-604). Dec-604 Component B (Dec-604 CB), a putative debrominated product of Dec-604, has been frequently reported in urban-adapted ring-billed gulls (Larus delawarensis) breeding in the Montreal area (QC, Canada). The metabolic pathways of Dec-604 are yet to be characterized, although the occurrence of Dec-604 CB in gulls may suggest that enzyme-mediated dehalogenation may occur, potentially involving the thyroid deiodinases. The objective of this study was to investigate the effect of Dec-604 on type 1 deiodinase (DIO1) in the presence of thyroxine (T4) in an in vitro DIO1 assay using liver microsomes of ring-billed gulls that are highly exposed to HFRs in the Montreal area, and to determine whether DIO1 is involved in the in vitro debromination of Dec-604. We tested the in vitro activity of DIO1 in gull liver microsomes in the presence of five concentrations of Dec-604 ranging from 0.86 to 86.21 nM. HFR concentrations (Σ40HFR) were also determined in liver samples of gulls. Results showed that total DIO1 activity in gull liver microsomes was increased by three of the five concentrations of Dec-604. No relationship between liver Σ40HFR concentrations and DIO1 activity was observed, except for T2 formation rates that significantly decreased with increasing liver HFR concentrations. Moreover, greater Dec-604 CB to Dec-604 concentration ratios in activated gull microsomes (with the DIO1 cofactor dithiothreitol) were found at the intermediate Dec-604 concentration compared to controls. These results suggested that liver microsome DIO1 activity may be perturbed in ring-billed gulls exposed to Dec-604, and be involved at least in part, in the debromination of Dec-604 leading to the formation of Dec-604 CB.

Comparative metabolomics and transcriptomics analyses provide insights into the high-yield mechanism of phenazines biosynthesis in Pseudomonas chlororaphis GP72.

AIMS: Phenazines, such as phenazine-1-carboxylic acid (PCA), phenazine-1-carboxamide (PCN), 2-hydroxyphenazine-1-carboxylic acid (2-OH-PCA), 2-hydroxyphenazine (2-OH-PHZ), are a class of secondary metabolites secreted by plant-beneficial Pseudomonas. Ps. chlororaphis GP72 utilizes glycerol to synthesize PCA, 2-OH-PCA and 2-OH-PHZ, exhibiting broad-spectrum antifungal activity. Previous studies showed that the addition of dithiothreitol (DTT) could increase the phenazines production in Ps. chlororaphis GP72AN. However, the mechanism of high yield of phenazine by adding DTT is still unclear. METHODS AND RESULTS: In this study, untargeted and targeted metabolomic analysis were adopted to determine the content of metabolites. The results showed that the addition of DTT to GP72AN affected the content of metabolites of central carbon metabolism, shikimate pathway and phenazine competitive pathway. Transcriptome analysis was conducted to investigate the changed cellular process, and the result indicated that the addition of DTT affected the expression of genes involved in phenazine biosynthetic cluster and genes involved in phenazine competitive pathway, driving more carbon flux into phenazine biosynthetic pathway. Furthermore, genes involved in antioxidative stress, phosphate transport system and mexGHI-opmD efflux pump were also affected by adding DTT. CONCLUSION: This study demonstrated that the addition of DTT altered the expression of genes related to phenazine biosynthesis, resulting in the change of metabolites involved in central carbon metabolism, shikimate pathway and phenazine competitive pathway. SIGNIFICANCE AND IMPACT OF THE STUDY: This work expands the understanding of high yield of phenazine by the addition of DTT and provides several targets for increasing phenazine production.

Dithiothreitol causes toxicity in C. elegans by modulating the methionine-homocysteine cycle.

The redox reagent dithiothreitol (DTT) causes stress in the endoplasmic reticulum (ER) by disrupting its oxidative protein folding environment, which results in the accumulation and misfolding of the newly synthesized proteins. DTT may potentially impact cellular physiology by ER-independent mechanisms; however, such mechanisms remain poorly characterized. Using the nematode model Caenorhabditis elegans, here we show that DTT toxicity is modulated by the bacterial diet. Specifically, the dietary component vitamin B12 alleviates DTT toxicity in a methionine synthase-dependent manner. Using a forward genetic screen, we discover that loss-of-function of R08E5.3, an S-adenosylmethionine (SAM)-dependent methyltransferase, confers DTT resistance. DTT upregulates R08E5.3 expression and modulates the activity of the methionine-homocysteine cycle. Employing genetic and biochemical studies, we establish that DTT toxicity is a result of the depletion of SAM. Finally, we show that a functional IRE-1/XBP-1 unfolded protein response pathway is required to counteract toxicity at high, but not low, DTT concentrations.

Animal and plant cells synthesize a significant fraction of their proteins on a structure known as the endoplasmic reticulum. Researchers often use the molecule dithiothreitol to specifically target this compartment and learn more about its role. The toxin works by disturbing the complex chemical environment present in the reticulum, which is required for the proteins to assemble properly. However, it is important to clarify whether dithiothreitol could also affect other parts of the cell, as this could give rise to misleading results. To explore this possibility, Gokul G and Jogender Singh studied the effects of dithiothreitol on the millimetre-long roundworm Caenorhabditis elegans. Their experiments revealed that vitamin B12 could protect against dithiothreitol toxicity via a complex cascade of molecular events which reduced the levels of an important regulatory molecule known as S-adenosylmethionine. Crucially, the chemical reactions that dithiothreitol targeted took place outside the reticulum, suggesting that the toxin impairs processes in the wider cell. These results suggest that dithiothreitol should be reconsidered for use in endoplasmic reticulum studies. However, they also imply that this toxin could be beneficial in small doses, as a reduced concentration of S-adenosylmethionine increases lifespan and health in a variety of organisms.

Synthesis of functionalised organochalcogenides and in vitro evaluation of their antioxidant activity.

Differently substituted ß-hydroxy- and ß-amino dialkyl and alkyl-aryl tellurides and selenides have been prepared through ring-opening reactions of epoxides and aziridines with selenium- or tellurium-centered nucleophiles. The antioxidant properties and the cytotoxicity of such compounds have been investigated on normal human dermal fibroblasts. Most of the studied compounds exhibited a low cytotoxicity and a number of them proved to be non-toxic, not showing any effect on cell viability even at the highest concentration used (100 µM). The obtained results showed a significant antioxidant potential of the selected organotellurium compounds, particularly evident under conditions of exogenously induced oxidative stress. The antioxidant activity of selenium-containing analogues of active tellurides has also been evaluated on cells, highlighting that the replacement of Se with Te brought about a significant increase in the peroxidase activity.

Structural basis of catalysis and substrate recognition by the NAD(H)-dependent α-d-glucuronidase from the glycoside hydrolase family 4.

Members of the glycoside hydrolase family 4 (GH4) employ an unusual glycosidic bond cleavage mechanism utilizing NAD(H) and a divalent metal ion, under reducing conditions. These enzymes act upon a diverse range of glycosides, and unlike most other GH families, homologs here are known to accommodate both α- and ß-anomeric specificities within the same active site. Here, we report the catalytic properties and the crystal structures of TmAgu4B, an α-d-glucuronidase from the hyperthermophile Thermotoga maritima. The structures in three different states include the apo form, the NADH bound holo form, and the ternary complex with NADH and the reaction product d-glucuronic acid, at 2.15, 1.97 and 1.85 Šresolutions, respectively. These structures reveal the step-wise route of conformational changes required in the active site to achieve the catalytically competent state, and illustrate the direct role of residues that determine the reaction mechanism. Furthermore, a structural transition of a helical region in the active site to a turn geometry resulting in the rearrangement of a unique arginine residue governs the exclusive glucopyranosiduronic acid recognition in TmAgu4B. Mutational studies show that modifications of the glycone binding site geometry lead to catalytic failure and indicate overlapping roles of specific residues in catalysis and substrate recognition. The data highlight hitherto unreported molecular features and associated active site dynamics that determine the structure-function relationships within the unique GH4 family.

In tube immunocytochemistry for fluorescence-activated cell sorting that prevents RNA degradation in sorted cells.

Fluorescence-activated cell sorting (FACS) is a powerful tool for analyzing stem cells. When using fixed cells, however, it is sometimes difficult to analyze RNA extracted from sorted cells due to RNA degradation. We established a protocol for immunocytochemistry before FACS to prevent RNA degradation. Cells were fixed with a methanol-based fixative (UM-Fix), then subjected to immunocytochemistry. The addition of RNase inhibitor and dithiothreitol (DTT) to some buffers used for immunocytochemistry increased RNA integrity after cell recovery. We found increased copy numbers of mRNA in recovered cells using quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. When RNase inhibitor and DTT were added, amplification of mRNA using T7 promoter was possible with RNA extracted from recovered cells after FACS. Our protocol ensures high quality RNA in cells recovered by FACS; therefore, gene expression analysis with a smaller number of cells is possible using pre-amplification of mRNAs. Our protocol for immunocytochemistry also might be applicable to RNA recovery after immunostaining.

Understanding the role of electron donors in the reaction catalyzed by Tsrm, a cobalamin-dependent radical S-adenosylmethionine methylase.

The cobalamin-dependent radical S-adenosylmethionine (SAM) enzyme TsrM catalyzes the methylation of C2 of L-tryptophan to form 2-methyltryptophan during the biosynthesis of thiostrepton A. Although TsrM is a member of the radical SAM superfamily, unlike all other annotated members, it does not catalyze a reductive cleavage of SAM to a 5'-deoxyadenosyl 5'-radical intermediate. In fact, it has been proposed that TsrM catalyzes its reaction through two polar nucleophilic displacements, with its cobalamin cofactor cycling directly between methylcobalamin (MeCbl) and cob(I)alamin. Nevertheless, the enzyme has been stated to require the action of a reductant, which can be satisfied by dithiothreitol. By contrast, all other annotated RS enzymes require a reductant that exhibits a much lower reduction potential, which is necessary for the reductive cleavage of SAM. Herein, we show that TsrM can catalyze multiple turnovers in the absence of any reducing agent, but only when it is pre-loaded with MeCbl. When hydroxocobalamin (OHCbl) or cob(II)alamin is bound to TsrM, a reductant is required to convert it to cob(I)alamin, which can acquire a methyl group directly from SAM. Our studies suggest that TsrM uses an external reductant to prime its reaction by converting bound OHCbl or cob(II)alamin to MeCbl, and to regenerate the MeCbl form of the cofactor upon adventitious oxidation of the cob(I)alamin intermediate to cob(II)alamin.

Structural analysis of Cytochrome P450 BM3 mutant M11 in complex with dithiothreitol.

The bacterial Cytochrome P450 (CYP) BM3 (CYP102A1) is one of the most active CYP isoforms. BM3 mutants can serve as a model for human drug-metabolizing CYPs and/or as biocatalyst for selective formation of drug metabolites. Hence, molecular and computational biologists have in the last two decades shown strong interest in the discovery and design of novel BM3 variants with optimized activity and selectivity for substrate conversion. This led e.g. to the discovery of mutant M11 that is able to metabolize a variety of drugs and drug-like compounds with relatively high activity. In order to further improve our understanding of CYP binding and reactions, we performed a co-crystallization study of mutant M11 and report here the three-dimensional structure M11 in complex with dithiothreitol (DTT) at a resolution of 2.16 Å. The structure shows that DTT can coordinate to the Fe atom in the heme group. UV/Vis spectroscopy and molecular dynamics simulation studies underline this finding and as first structure of the CYP BM3 mutant M11 in complex with a ligand, it offers a basis for structure-based design of novel mutants.

Crystal structure of yeast xylose reductase in complex with a novel NADP-DTT adduct provides insights into substrate recognition and catalysis.

Aldose reductases (ARs) belonging to the aldo-keto reductase (AKR) superfamily catalyze the conversion of carbonyl substrates into their respective alcohols. Here we report the crystal structures of the yeast Debaryomyces nepalensis xylose reductase (DnXR, AKR2B10) in the apo form and as a ternary complex with a novel NADP-DTT adduct. Xylose reductase, a key enzyme in the conversion of xylose to xylitol, has several industrial applications. The enzyme displayed the highest catalytic efficiency for l-threose (138 ± 7 mm-1 ·s-1 ) followed by d-erythrose (30 ± 3 mm-1 ·s-1 ). The crystal structure of the complex reveals a covalent linkage between the C4N atom of the nicotinamide ring of the cosubstrate and the S1 sulfur atom of DTT and provides the first structural evidence for a protein mediated NADP-low-molecular-mass thiol adduct. We hypothesize that the formation of the adduct is facilitated by an in-crystallo Michael addition of the DTT thiolate to the specific conformation of bound NADPH in the active site of DnXR. The interactions between DTT, a four-carbon sugar alcohol analog, and the enzyme are representative of a near-cognate product ternary complex and provide significant insights into the structural basis of aldose binding and specificity and the catalytic mechanism of ARs. DATABASE: Structural data are available in the PDB under the accession numbers 5ZCI and 5ZCM.

Dimeric Structure of the Blue Light Sensor Protein Photozipper in the Active State.

The light oxygen voltage-sensing (LOV) domain plays a crucial role in blue light (BL) sensing in plants and microorganisms. LOV domains are usually associated with the effector domains and regulate the activities of effector domains in a BL-dependent manner. Photozipper (PZ) is monomeric in the dark state. BL induces reversible dimerization of PZ and subsequently increases its affinity for the target DNA sequence. In this study, we report the analyses of PZ by pulsed electron-electron double resonance (PELDOR). The neutral flavin radical was formed by BL illumination in the presence of dithiothreitol in the LOV-C254S (without the bZIP domain) and PZ-C254S mutants, where the cysteine residue responsible for adduct formation was replaced with serine. The magnetic dipole interactions of 3 MHz between the neutral radicals were detected in both LOV-C254S and PZ-C254S, indicating that these mutants are dimeric in the radical state. The PELDOR simulation showed that the distance between the radical pair is close to that estimated from the dimeric crystal structure in the "light state" [Heintz, U., and Schlichting, I. (2016) eLife 5, e11860], suggesting that in the radical state, LOV domains in PZ-C254S form a dimer similar to that of LOV-C254S, which lacks the bZIP domain.

Cysteine perthiosulfenic acid (Cys-SSOH): A novel intermediate in thiol-based redox signaling?

The reversible oxidation of protein cysteine residues (Cys-SH) is a key reaction in cellular redox signaling involving initial formation of sulfenic acids (Cys-SOH), which are commonly detected using selective dimedone-based probes. Here, we report that significant portions of dimedone-tagged proteins are susceptible to cleavage by DTT reflecting the presence of perthiosulfenic acid species (Cys-SSOH) due to similar oxidation of hydropersulfides (Cys-SSH), since Cys-S-dimedone adducts are stable toward DTT. Combined studies using molecular modeling, mass spectrometry, and cell-based experiments indicate that Cys-SSH are readily oxidized to Cys-SSOH, which forms stable adducts with dimedone-based probes. We additionally confirm the presence of Cys-SSH within protein tyrosine kinases such as EGFR, and their apparent oxidation to Cys-SSOH in response NADPH oxidase activation, suggesting that such Cys-SSH oxidation may represent a novel, as yet uncharacterized, event in redox-based signaling.

Comprehensive assessment for serum treatment for single antigen test for detection of HLA antibodies.

The single antigen test is widely used in the field of transplantation to determine the specificity of HLA antibodies. It will be beneficial to standardize the procedure of the single antigen test among HLA laboratories. It is not uncommon that single antigen testing on native sera fails to detect antibodies with very high concentrations. It has been shown that cleavage products of activated complement components may mask strongly binding antibodies in single antigen testing. To overcome inhibition by the activated complement products, sera are pretreated with ethylenediaminetetraacetic acid (EDTA), dithiothreitol (DTT), or heat inactivation before single antigen testing. However, no studies have been published to systemically compare the impact of these treatments on single antigen testing. The aim of this study is to understand the different effects these treatments may have on single antigen test results. We found that mean fluorescence intensity (MFI) obtained from sera treated with EDTA and heat inactivation were nearly identical, while DTT treatment was less potent to remove the inhibition. In addition, sera dilution did not further increase MFI of antibodies after EDTA treatment. Our results provide guidance to choose a pretreatment reagent for single antigen testing, and to compare studies obtained from laboratories using different treatments.

Heme-thiolate sulfenylation of human cytochrome P450 4A11 functions as a redox switch for catalytic inhibition.

Cytochrome P450 (P450, CYP) 4A11 is a human fatty acid ω-hydroxylase that catalyzes the oxidation of arachidonic acid to the eicosanoid 20-hydroxyeicosatetraenoic acid (20-HETE), which plays important roles in regulating blood pressure regulation. Variants of P450 4A11 have been associated with high blood pressure and resistance to anti-hypertensive drugs, and 20-HETE has both pro- and antihypertensive properties relating to increased vasoconstriction and natriuresis, respectively. These physiological activities are likely influenced by the redox environment, but the mechanisms are unclear. Here, we found that reducing agents (e.g. dithiothreitol and tris(2-carboxyethyl)phosphine) strongly enhanced the catalytic activity of P450 4A11, but not of 10 other human P450s tested. Conversely, added H2O2 attenuated P450 4A11 catalytic activity. Catalytic roles of five of the potentially eight implicated Cys residues of P450 4A11 were eliminated by site-directed mutagenesis. Using an isotope-coded dimedone/iododimedone-labeling strategy and mass spectrometry of peptides, we demonstrated that the heme-thiolate cysteine (Cys-457) is selectively sulfenylated in an H2O2 concentration-dependent manner. This sulfenylation could be reversed by reducing agents, including dithiothreitol and dithionite. Of note, we observed heme ligand cysteine sulfenylation of P450 4A11 ex vivo in kidneys and livers derived from CYP4A11 transgenic mice. We also detected sulfenylation of murine P450 4a12 and 4b1 heme peptides in kidneys. To our knowledge, reversible oxidation of the heme thiolate has not previously been observed in P450s and may have relevance for 20-HETE-mediated functions.