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Abstract: A water-soluble selenoxide (DHSox) having a five-membered ring structure enables rapid and selective conversion of cysteinyl SH groups in a polypeptide chain into SS bonds in a wide pH and temperature range. It was previously demonstrated that the second-order rate constants for the SS formation with DHSox would be proportional to the number of the free SH groups present in the substrate if there is no steric congestion around the SH groups. In the present study, kinetics of the SS formation with DHSox was extensively studied at pH 4–10 and 25 °C by using reduced ribonuclease A, recombinant hirudin variant (CX-397), insulin A- and B-chains, and relaxin A-chain, which have two to eight cysteine residues, as polythiol substrates. The obtained rate constants showed stochastic SS formation behaviors under most conditions. However, the rate constants for CX-397 at pH 8.0 and 10.0 were not proportional to the number of the free SH groups, suggesting that the SS intermediate ensembles possess densely packed structures under weakly basic conditions. The high two-electron redox potential of DHSox (375 mV at 25 °C) compared to l-cystine supported the high ability of DHSox for SS formation in a polypeptide chain. Interestingly, the rate constants of the SS formation jumped up at a pH around the pK a value of the cysteinyl SH groups. The SS formation velocity was slightly decreased by addition of a denaturant due probably to the interaction between the denaturant and the peptide. The stochastic behaviors as well as the absolute values of the second-order rate constants in comparison to dithiothreitol (DTTred) are useful to probe the chemical reactivity and conformation, hence the folding, of polypeptide chains. [Copyright &y& Elsevier]

The conformational unfolding kinetics and the equilibrium stability of the C40A, C95A, C65S and C72S mutants of bovine pancreatic ribonuclease A (RNase A), which are analogue of intermediates des[40-95] and des[65-72, were examined via unfolding experiments. The results suggested that local conformational unfolding limits the rate of the reduction of des[65-72]. Moreover, the reduction of the 40-95 disulfide bond in the native protein and in the des[65-72] intermediate may be rate-limited by the isomerization of Pro93.

Management of the gastro-toxicity of non-steroidal anti-inflammatory drugs (NSAIDs) remains a crucial problem, because the commercially available anti-ulcer drugs have side effects and are often expensive. Hence, the potential of a new water-soluble GPx mimic, DL- trans-3,4-dihydroxy-1-selenolane (DHSred) in healing the indomethacin-induced stomach ulceration in mice was examined. Administration of indomethacin (18 mg/kg, p. o.) induced ulceration in the glandular portion of the gastric mucosa, accompanied by increased lipid peroxidation (1.3-fold, p <0.001) and protein oxidation (1.5-fold, p < 0.001), depletion of thiol-defense (42.5%, p < 0.01), plasma total antioxidant status (53.4%, p < 0.001) and mucin (47.5%, p < 0.01), as well as reduced expressions of cyclooxygenases and prostaglandin synthesis (54.7%, p < 0.001) in the gastric tissues of mice. Daily oral administration of DHSred (2.5 mg/kg) or omeprazole (Omez) (3 mg/kg) for 3 days respectively produced ˜74% and 69% ( p < 0.001) healing of the acute gastric ulceration. The test samples also significantly reversed all the adverse effects of indomethacin on the biochemical parameters. Apparently, the gastric ulcer healing action of DHSred and Omez was due to their antioxidant action and their ability to protect mucin and augment PG synthesis by upregulation of the COX isozymes. The results suggested that the non-toxic and inexpensive compound, DHSred, may be a good candidate for further evaluation as a potent anti-ulcer drug. [ABSTRACT FROM AUTHOR]

The one-pot reactions of N-acetylserine methyl ester and N-acetyl-α-methylserine methyl ester with Lawesson's or Woollins' reagent directly produced the corresponding cysteine or selenocysteine derivatives in moderate yields. The transformation would be initiated by phosphorylation of the hydroxy group, rather than chalcogenation of the amide group, and involve the oxazoline as a key intermediate. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT[image omitted] [ABSTRACT FROM AUTHOR]

Weak nonbonded interaction between a divalent selenium and an oxygen atom (i.e., Se&CenterDot;&CenterDot;&CenterDot;O interaction) frequently plays important roles in chemical and biological functions of selenium compounds. To establish that 77 Se NMR is an easy experimental probe to diagnose the strength of an Se&CenterDot;&CenterDot;&CenterDot;O interaction, 3 series of 2-substituted benzeneselenenyl derivatives, which have an intramolecular Se&CenterDot;&CenterDot;&CenterDot;O interaction in solution, were employed. By comparing the 77 Se NMR chemical shifts (d Se ) with those observed for other series of selenium compounds, which have an intramolecular Se&CenterDot;&CenterDot;&CenterDot;Y (Y = N, O, F, Cl, or Br) interaction, approximate linear correlation was found between the d Se values and the strengths of the nonbonded Se&CenterDot;&CenterDot;&CenterDot;Y interactions evaluated by natural bond orbital analysis at the B3LYP level. The correlation will be useful for estimating the strength of an Se&CenterDot;&CenterDot;&CenterDot;O interaction simply from the 77 Se NMR chemical shift. By extending the chemistry of nonbonded Se&CenterDot;&CenterDot;&CenterDot;O interactions to structural biology, analogous S&CenterDot;&CenterDot;&CenterDot;O interactions have been discovered in protein architecture. The directional features were, however, different from those of Se&CenterDot;&CenterDot;&CenterDot;O and S&CenterDot;&CenterDot;&CenterDot;O interactions of small organic compounds. [ABSTRACT FROM AUTHOR]

To investigate the nature of nonbonded Se…O interactions, three series of 2-substituted benzeneselenenyl derivatives [2-(CHO)C6H4SeX (1), 2-(CH2OH)C6H4SeX, (2), 2-(CH2O/Pr)C6H4SeX (3); X = Cl, Br, CN, SPh, SeAr, Me] were synthesized. The 17O NMR absorption observed for 17O-enriched aldehydes 1 appeared upfield relative to benzaldehyde (PhCHO), while the opposite downfield shifts relative to benzyl alcohol (PhCH2OH) were observed for 17O-enriched alcohols 2 and ethers 3. The magnitude of both the upfield and the downfield shifts became larger as the electron-withdrawing ability of a substituent X increased. Quantum chemical calculations at the B3LYP level revealed that for all model compounds the most stable conformer has an intramolecular nonbonded Se…O interaction. Thus, the relative 17O NMR chemical shifts (ΔΣo) for 1-3 would reflect the strengths of the Se…O interactions. The natural bond orbital (NBO) analysis demonstrated that the stabilization energy due to an no → σ*Se-X orbital interaction (ESe…o) correlates with the Se…O atomic distance on a single curve irrespective of the type of the O atom. On the other hand, the atoms in molecules (AIM) analysis showed that the nonbonded Se…O interactions can be characterized by the presence of a bond critical point, the total energy density (HSe…o) of which decreases with strengthening of the interaction. The results suggested that Se…O interactions have a dominant covalent character rather than an electrostatic one. [ABSTRACT FROM AUTHOR]

Presents possible mechanistic roles of amino groups on the glutathione peroxidase (GPX) enzyme activity. Kinetic analysis and 77-selenium nuclear magnetic resonance spectroscopic characterization; Use diselenide as enzyme model; Intermediates of the model reaction; Catalytic cycle; Proximate nitrogen base; Molecular orbit (MO) calculations.

Describes the characterization of areneselenenyl chloride stabilized by the stereoelectronic effect of an intramolecular nitrogen atom. Investigation of the electronic structure around selenium; Consistency of optimized geometries with the results of the X-ray analysis of 4.

ERp57, a member of the protein disulfide isomerase family, is a ubiquitous disulfide catalyst that functions in the oxidative folding of various clients in the mammalian endoplasmic reticulum (ER). In concert with ER lectin-like chaperones calnexin and calreticulin (CNX/CRT), ERp57 functions in virtually all folding stages from co-translation to post-translation, and thus plays a critical role in maintaining protein homeostasis, with direct implication for pathology. Here, we present mechanisms by which Ca2+ regulates the formation of the ERp57-calnexin complex. Biochemical and isothermal titration calorimetry analyses revealed that ERp57 strongly interacts with CNX via a non-covalent bond in the absence of Ca2+. The ERp57-CNX complex not only promoted the oxidative folding of human leukocyte antigen heavy chains, but also inhibited client aggregation. These results suggest that this complex performs both enzymatic and chaperoning functions under abnormal physiological conditions, such as Ca2+ depletion, to effectively guide proper oxidative protein folding. The findings shed light on the molecular mechanisms underpinning crosstalk between the chaperone network and Ca2+. [ABSTRACT FROM AUTHOR]

In this review from literature appearing over about the past 5 years, we focus on selected selenide reports and related chemistry; we aimed for a digestible, relevant, review intended to be usefully interconnected within the realm of fluorescence and selenium chemistry. Tellurium is mentioned where relevant. Topics include selenium in physics and surfaces, nanoscience, sensing and fluorescence, quantum dots and nanoparticles, Au and oxide nanoparticles quantum dot based, coatings and catalyst poisons, thin film, and aspects of solar energy conversion. Chemosensing is covered, whether small molecule or nanoparticle based, relating to metal ion analytes, H2S, as well as analyte sulfane (biothiols—including glutathione). We cover recent reports of probing and fluorescence when they deal with redox biology aspects. Selenium in therapeutics, medicinal chemistry and skeleton cores is covered. Selenium serves as a constituent for some small molecule sensors and probes. Typically, the selenium is part of the reactive, or active site of the probe; in other cases, it is featured as the analyte, either as a reduced or oxidized form of selenium. Free radicals and ROS are also mentioned; aggregation strategies are treated in some places. Also, the relationship between reduced selenium and oxidized selenium is developed. [ABSTRACT FROM AUTHOR]

In the last few decades, development of novel experimental techniques, such as new types of disulfide (SS)-forming reagents and genetic and chemical technologies for synthesizing designed artificial proteins, is opening a new realm of the oxidative folding study where peptides and proteins can be folded under physiologically more relevant conditions. In this review, after a brief overview of the historical and physicochemical background of oxidative protein folding study, recently revealed folding pathways of several representative peptides and proteins are summarized, including those having two, three, or four SS bonds in the native state, as well as those with odd Cys residues or consisting of two peptide chains. Comparison of the updated pathways with those reported in the early years has revealed the flexible nature of the protein folding pathways. The significantly different pathways characterized for hen-egg white lysozyme and bovine milk α-lactalbumin, which belong to the same protein superfamily, suggest that the information of protein folding pathways, not only the native folded structure, is encoded in the amino acid sequence. The application of the flexible pathways of peptides and proteins to the engineering of folded three-dimensional structures is an interesting and important issue in the new realm of the current oxidative protein folding study. [ABSTRACT FROM AUTHOR]

Disulfide bonds play a pivotal role in maintaining the natural structures of proteins to ensure their performance of normal biological functions. Moreover, biological molecular assembly, such as the gluten network, is also largely dependent on the intermolecular crosslinking via disulfide bonds. In eukaryotes, the formation and rearrangement of most intra- and intermolecular disulfide bonds in the endoplasmic reticulum (ER) are mediated by protein disulfide isomerases (PDIs), which consist of multiple thioredoxin-like domains. These domains assist correct folding of proteins, as well as effectively prevent the aggregation of misfolded ones. Protein misfolding often leads to the formation of pathological protein aggregations that cause many diseases. On the other hand, glutenin aggregation and subsequent crosslinking are required for the formation of a rheologically dominating gluten network. Herein, the mechanism of PDI-regulated disulfide bond formation is important for understanding not only protein folding and associated diseases, but also the formation of functional biomolecular assembly. This review systematically illustrated the process of human protein disulfide isomerase (hPDI) mediated disulfide bond formation and complemented this with the current mechanism of wheat protein disulfide isomerase (wPDI) catalyzed formation of gluten networks. [ABSTRACT FROM AUTHOR]

The polypeptide backbone of proteins is held together by two main types of covalent bonds: the peptide bonds that link the amino acid residues and the disulfide bonds that link pairs of cysteine amino acids. Disulfide bonds form as a protein folds in the cell and formation was assumed to be complete when the mature protein emerges. This is not the case for some secreted human blood proteins. The blood clotting protein, fibrinogen, and the protease inhibitor, α2-macroglobulin, exist in multiple disulfide-bonded or covalent states in the circulation. Thousands of different states are predicted assuming no dependencies on disulfide bond formation. In this study, probabilities for disulfide bond formation are employed to estimate numbers of covalent states of a model polypeptide with reference to α2-macroglobulin. When disulfide formation is interdependent in a protein, the number of covalent states is greatly reduced. Theoretical estimates of the number of states will aid the conceptual and experimental challenges of investigating multiple disulfide-bonded states of a protein. [ABSTRACT FROM AUTHOR]

Oxidative protein folding involves the formation of disulfide bonds and the regeneration of native structure (N) from the fully reduced and unfolded protein (R). Oxidative protein folding studies have provided a wealth of information on underlying physico-chemical reactions by which disulfide-bond-containing proteins acquire their catalytically active form. Initially, we review key events underlying oxidative protein folding using bovine pancreatic ribonuclease A (RNase A), bovine pancreatic trypsin inhibitor (BPTI) and hen-egg white lysozyme (HEWL) as model disulfide bond-containing folders and discuss consequential outcomes with regard to their folding trajectories. We re-examine the findings from the same studies to underscore the importance of forming native disulfide bonds and generating a "native-like" structure early on in the oxidative folding pathway. The impact of both these features on the regeneration landscape are highlighted by comparing ideal, albeit hypothetical, regeneration scenarios with those wherein a native-like structure is formed relatively "late" in the R→N trajectory. A special case where the desired characteristics of oxidative folding trajectories can, nevertheless, stall folding is also discussed. The importance of these data from oxidative protein folding studies is projected onto outcomes, including their impact on the regeneration rate, yield, misfolding, misfolded-flux trafficking from the endoplasmic reticulum (ER) to the cytoplasm, and the onset of neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

Background: Relaxin (RLX)-2, produced by the corpus luteum and placenta, is known to be potentially effective in fibrotic diseases of the heart, lungs, kidneys, and bladder; however, its effectiveness in endometriosis has not yet been investigated. In the present study, we conducted a comprehensive study on the effect of RLX-2 on endometriosis. We checked the expressions of LGR-7, a primary receptor of RLX-2, in endometriomas using immunohistochemistry. Endometriotic stromal cells (ESCs) purified from surgical specimens were used in in vitro experiments. The effects of RLX-2 on ESCs were evaluated by quantitative-PCR, ELISA, and Western blotting. Gel contraction assay was used to assess the contraction suppressive effect of RLX-2. The effect of RLX-2 was also examined in the endometriosis mouse model. LGR-7 was expressed in endometriotic lesions. In ESCs, RLX-2 increased the production of cAMP and suppressed the secretion of interleukin-8, an inflammatory cytokine, by 15% and mRNA expression of fibrosis-related molecules, plasminogen activator inhibitor-1 (PAI-1), and collagen-I by approximately 50% (p < 0.05). In the gel contraction assay, RLX-2 significantly suppressed the contraction of ESCs, which was cancelled by removing RLX-2 from the medium or by adding H89, a Protein Kinase A (PKA) inhibitor. In ESCs stimulated with RLX-2, p38 MAPK phosphorylation was significantly suppressed. In the endometriosis mouse model, administration of RLX-2 significantly decreased the area of the endometriotic-like lesion with decreasing fibrotic component compared to non-treated control (p = 0.01). RLX-2 may contribute to the control of endometriotic lesion by suppressing fibrosis, scar formation, and inflammation. [ABSTRACT FROM AUTHOR]

Heat-stable enterotoxin (STa) produced by enterotoxigenic E. coli causes acute diarrhea and also can be used as a specific probe for colorectal cancer cells. STa contains three intra-molecular disulfide bonds (C1–C4, C2–C5, and C3–C6 connectivity). The chemical synthesis of STa provided not only the native type of STa but also a topological isomer that had the native disulfide pairings. Interestingly, the activity of the topological isomer was approximately 1/10–1/2 that of the native STa. To further investigate the bioactive conformation of this molecule and the regulation of disulfide-coupled folding during its chemical syntheses, we examined the folding mechanism of STa that occurs during its chemical synthesis. The folding intermediate of STa with two disulfide bonds (C1–C4 and C3–C6) and two Cys(Acm) residues, the precursor peptide, was treated with iodine to produce a third disulfide bond under several conditions. The topological isomer was predominantly produced under all conditions tested, along with trace amounts of the native type of STa. In addition, NMR measurements indicated that the topological isomer has a left-handed spiral structure similar to that of the precursor peptide, while the native type of STa had a right-handed spiral structure. These results indicate that the order of the regioselective formation of disulfide bonds is important for the regulation of the final conformation of disulfide-rich peptides in chemical synthesis. [ABSTRACT FROM AUTHOR]

The damage caused by oxidative and glycative stress to cells accumulates on a daily basis and accelerates aging. Glutathione (GSH), a major antioxidant molecule in living organisms, plays a crucial role in detoxifying the stress-causing substances inherent in cells, such as H2O2 and methylglyoxal (MG), an important intermediate of advanced glycation end-products (AGEs). In this study, we focused on the enhanced antioxidant capacity of the selenium analog of GSH, i.e., selenoglutathione (GSeH), compared to GSH, and examined its effects on the detoxification of stress-causing substances and improvement in cell viability. In cell-free systems, GSeH (1 mM) generated in situ from GSeSeG in the presence of NADPH and glutathione reductase (GR) rapidly reduced more than 80% of 0.1 mM H2O2, indicating the significant glutathione peroxidase (GPx)-like antioxidant activity of GSeSeG. Similarly, around 50% of 0.5 mM MG was degraded by 0.5 mM GSeH within 30 min through a non-enzymatic mechanism. It was also found that GSeSeG (0.05–0.5 mM) showed glutathione S-transferase (GST)-like activity against 1-chloro-2,4-dinitrobenzene (CDNB), a model substance of oxidative stress-causing toxic materials in cells. Meanwhile, HeLa cells that had been pre-treated with GSeSeG exhibited increased viability against 1.2 mM H2O2 (at [GSeSeG] = 0.5–50 μM) and 4 mM MG (at [GSeSeG] = 3 μM), and the latter effect was maintained for two days. Thus, GSeSeG is a potential antioxidant and antiglycative stress agent for cells. [ABSTRACT FROM AUTHOR]

Cover Feature: Modeling Thioredoxin Reductase-Like Activity with Cyclic Selenenyl Sulfides: Participation of an NH---Se Hydrogen Bond through Stabilization of the Mixed Se-S Intermediate (Chem. Eur. J. 55/2019) Keywords: antioxidants; chalcogens; enzyme models; medicinal chemistry; redox chemistry Antioxidants, chalcogens, enzyme models, medicinal chemistry, redox chemistry. [Extracted from the article]

Until recently the total synthesis of insulin, with its characteristic heterodimeric structure crosslinked by two interchain and one intrachain disulfide (SS) bridge, remained largely an unsolved challenge. By optimizing the synthesis and directed disulfide crosslinking of the two chains, and by applying biomimetic monocomponent proinsulin approaches, efficient insulin syntheses have been realized. Here we report the optimization and characterisation of an alternative strategy, oxidative native chain assembly. In this method unprotected A- and B-chains assemble oxidatively under thermodynamic control to afford bovine pancreatic insulin in 39% yield. Folding is found to proceed predominantly via structured 1SS* and 2SS* intermediates with a common interchain CysA20‒CysB19 disulfide. These results suggest that native chain assembly, long considered inefficient, may represent a reasonable strategy to access insulin variants. This is supported by the synthesis of human insulin and human type-II relaxin in yields of up to 49 and 47%, respectively, although the application to human insulin ValA16 variant is unsuccessful. The synthesis and folding pathways of insulin and related proteins are of wide interest. Here the authors characterise the major two-chain oxidative folding pathways of bovine pancreatic insulin, and develop synthetic conditions applicable to related foldable insulin variants [ABSTRACT FROM AUTHOR]

Seleno-insulin, a class of artificial insulin analogs, in which one of the three disulfide-bonds (S-S's) of wild-type insulin (Ins) is replaced by a diselenide-bond (Se-Se), is attracting attention for its unique chemical and physiological properties that differ from those of Ins. Previously, we pioneered the development of a [C7UA,C7UB] analog of bovine pancreatic insulin (SeIns) as the first example, and demonstrated its high resistance against insulin-degrading enzyme (IDE). In this study, the conditions for the synthesis of SeIns via native chain assembly (NCA) were optimized to attain a maximum yield of 72%, which is comparable to the in vitro folding efficiency for single-chain proinsulin. When the resistance of BPIns to IDE was evaluated in the presence of SeIns, the degradation rate of BPIns became significantly slower than that of BPIns alone. Furthermore, the investigation on the intermolecular association properties of SeIns and BPIns using analytical ultracentrifugation suggested that SeIns readily forms oligomers not only with its own but also with BPIns. The hypoglycemic effect of SeIns on diabetic rats was observed at a dose of 150 μg/300 g rat. The strategy of replacing the solvent-exposed S-S with Se-Se provides new guidance for the design of long-acting insulin formulations. Seleno-insulins (SeIns) are known to exhibit different in vitro properties from wild-type insulin, upon replacement of one of the three disulfide bonds with diselenide bonds; however, the in vivo hypoglycemic effect remains poorly understood. Here, the authors optimize the synthesis of SeIns via native chain assembly and reveal in vitro resistance against the insulin-degrading enzyme, as well as the in vivo hypoglycemic effect in diabetic rats at a dose of 150 μg/300 g rat. [ABSTRACT FROM AUTHOR]