Search

Thioredoxin reductase 1 (TXNRD1) has been identified as one of the promising chemotherapeutic targets in cancer cells. Therefore, a novel TXNRD1 inhibitor could accelerate chemotherapy in clinical anticancer research. In this study, glaucocalyxin A (GlauA), a natural diterpene extracted from Rabdosia japonica var. glaucocalyx, was identified as a novel inhibitor of TXNRD1. We found that GlauA effectively inhibited recombinant TXNRD1 and reduced its activity in gastric cancer cells without affecting the enzyme's expression level. Mechanistically, the selenocysteine residue (U498) of TXNRD1 was irreversibly modified by GlauA through a Michael addition. Additionally, GlauA formed a covalent adduct with glutathione (GSH) and disrupted cellular redox balance by depleting cellular GSH. The inhibition of TXNRD1 and depletion of GSH by GlauA conferred its cytotoxic effects in spheroid culture and Transwell assays in AGS cells. The disulfide stress induced cytotoxicity of GlauA could be mitigated by adding reducing agents, such as DTT and β‐ME. Furthermore, the FDA‐approval drug auranofin, a TXNRD1 inhibitor, triggered oligomerization of the cytoskeletal protein Talin‐1 in AGS cells, indicating that inhibiting TXNRD1 triggered disulfide stress. In conclusion, this study uncovered GlauA as an efficient inhibitor of TXNRD1 and demonstrated the potential of TXNRD1 inhibition as an effective anticancer strategy by disrupting redox homeostasis and inducing disulfide stress. [ABSTRACT FROM AUTHOR]

In this study, the transcriptome analysis was practiced to identify potential genes of probiotic Bacillus subtilis BSN313 involved in selenium (Se) enrichment metabolism. The transcriptomic variation of the strain was deliberated in presence of three different sodium selenite concentrations (0, 3, and 20 μg/mL). The samples were taken at 1 and 13 h subsequent to inoculation of selenite and gene expression profiles in Se metabolism were analyzed through RNA sequencing. The gene expression levels of the pre log phase were lower than the stationary phase. It is because, the bacteria has maximum grown with high concentration of Se (enriched with organic Se), at stationary phase. Bacterial culture containing 3 μg/mL concentration of inorganic Se (sodium selenite) has shown highest gene expression as compared to no or high concentration of Se. This concentration (3 μg/mL) of sodium selenite (as Se) in the medium promoted the upregulation of thioredoxin reductase expression, whereas its higher Se concentration inhibited the formation of selenomethionine (SeMet). The result of 5 L bioreactor fermentation showed that SeMet was also detected in the fermentation supernatant as the growth entered in the late stationary phase and reached up to 857.3 ng/mL. The overall intracellular SeMet enriched content in BSN313 was extended up to 23.4 μg/g dry cell weight. The other two selenoamino acids (Se‐AAs), methyl‐selenocysteine, and selenocysteine were hardly detected in medium supernatant. From this study, it was concluded that SeMet was the highest content of organic Se byproduct biosynthesized by B. subtilis BSN313 strain in Se‐enriched medium during stationary phase. Thus, B. subtilis BSN313 can be considered a commercial probiotic strain that can be used in the food and pharmaceutical industries. This is because it can meet the commercial demand for Se‐AAs (SeMet) in both industries. [ABSTRACT FROM AUTHOR]

Mild strategies for the selective modification of peptides and proteins are in demand for applications in therapeutic peptide and protein discovery, and in the study of fundamental biomolecular processes. Herein, we describe the development of an electrochemical selenoetherification (e‐SE) platform for the efficient site‐selective functionalization of polypeptides. This methodology utilizes the unique reactivity of the 21st amino acid, selenocysteine, to effect formation of valuable bioconjugates through stable selenoether linkages under mild electrochemical conditions. The power of e‐SE is highlighted through late‐stage C‐terminal modification of the FDA‐approved cancer drug leuprolide and assembly of a library of anti‐HER2 affibody conjugates bearing complex cargoes. Following assembly by e‐SE, the utility of functionalized affibodies for in vitro imaging and targeting of HER2 positive breast and lung cancer cell lines is also demonstrated. [ABSTRACT FROM AUTHOR]

Ferroptosis has emerged as an attractive strategy in cancer therapy. Understanding the operational networks regulating ferroptosis may unravel vulnerabilities that could be harnessed for therapeutic benefit. Using CRISPR‐activation screens in ferroptosis hypersensitive cells, we identify the selenoprotein P (SELENOP) receptor, LRP8, as a key determinant protecting MYCN‐amplified neuroblastoma cells from ferroptosis. Genetic deletion of LRP8 leads to ferroptosis as a result of an insufficient supply of selenocysteine, which is required for the translation of the antiferroptotic selenoprotein GPX4. This dependency is caused by low expression of alternative selenium uptake pathways such as system Xc−. The identification of LRP8 as a specific vulnerability of MYCN‐amplified neuroblastoma cells was confirmed in constitutive and inducible LRP8 knockout orthotopic xenografts. These findings disclose a yet‐unaccounted mechanism of selective ferroptosis induction that might be explored as a therapeutic strategy for high‐risk neuroblastoma and potentially other MYCN‐amplified entities. Synopsis: The low‐density lipoprotein receptor (LRP8) was identified as a critical suppressor of ferroptosis in MYCN‐amplified neuroblastoma. Blocking selenium/selenocysteine uptake mechanisms via LRP8 offers a selective strategy to induce ferroptosis and disrupt GPX4 function. Ferroptosis, a cell death modality, is gaining interest as a therapeutic approach against challenging tumors.GPX4 is crucial for suppressing ferroptosis, but suitable in vivo inhibitors are lacking, limiting translation to cancer therapies.Genome‐wide and single‐cell CRISPR‐activation screens reveal LRP8 as a critical ferroptosis suppressor in MYCN‐amplified neuroblastoma.Blocking selenium/selenocysteine uptake via LRP8 disrupts GPX4 function and selectively induces ferroptotic cell death.LRP8 dependency emerges as the result of the low system Xc− activity suggesting that targeting LRP8 could be explore in other entities such as AML and lymphoma. [ABSTRACT FROM AUTHOR]

Human seleno‐epidermal growth factor (seleno‐EGF), a 53‐residue peptide where all six cysteine residues of the parent human EGF sequence were replaced by selenocysteines, was synthesized and the oxidative folding of a polypeptide containing three diselenide bonds was compared to that of the parent cysteine peptide. The crude high performance liquid chromatography (HPLC) profiles clearly showed that both the native EGF and its selenocysteine‐analogue fold smoothly, yielding a single sharp peak, proving that even in the case of three disulfide‐bonded polypeptides the disulfide‐to‐diselenide bond substitution is highly isomorphous, as confirmed by conformational circular dichroism measurements and particularly by the biological assays. [ABSTRACT FROM AUTHOR]

AuI‐carbene and PtIV−AuI‐carbene prodrugs display low to sub‐μM activity against several cancer cell lines and overcome cisplatin (cisPt) resistance. Linking a cisPt‐derived PtIV(phenylbutyrate) complex to a AuI‐phenylimidazolylidene complex 2, yielded the most potent prodrug. While in vivo tests against Lewis Lung Carcinoma showed that the prodrug PtIV(phenylbutyrate)‐AuI‐carbene (7) and the 1 : 1 : 1 co‐administration of cisPt: phenylbutyrate:2 efficiently inhibited tumor growth (≈95 %), much better than 2 (75 %) or cisPt (84 %), 7 exhibited only 5 % body weight loss compared to 14 % for 2, 20 % for cisPt and >30 % for the co‐administration. 7 was much more efficient than 2 at inhibiting TrxR activity in the isolated enzyme, in cells and in the tumor, even though it was much less efficient than 2 at binding to selenocysteine peptides modeling the active site of TrxR. Organ distribution and laser‐ablation (LA)‐ICP‐TOFMS imaging suggest that 7 arrives intact at the tumor and is activated there. [ABSTRACT FROM AUTHOR]

Granulocyte colony stimulating factor (G‐CSF) is a cytokine used to treat neutropenia. Different glycosylated and non‐glycosylated variants of G‐CSF for therapeutic application are currently generated by recombinant expression. Here, we describe our approaches to establish a first semisynthesis strategy to access the aglycone and O‐glycoforms of G‐CSF, thereby enabling the preparation of selectively and homogeneously post‐translationally modified variants of this important cytokine. Eventually, we succeeded by combining selenocysteine ligation of a recombinantly produced N‐terminal segment with a synthetic C‐terminal part, transiently equipped with a side‐chain‐linked, photocleavable PEG moiety, at low concentration. The transient PEGylation enabled quantitative enzymatic elongation of the carbohydrate at Thr133. Overall, we were able to significantly reduce the problems related to the low solubility and the tendency to aggregate of the two protein segments, which allowed the preparation of four G‐CSF variants that were successfully folded and demonstrated biological activity in cell proliferation assays. [ABSTRACT FROM AUTHOR]

Human SELENOF is an endoplasmic reticulum (ER) selenoprotein that contains the redox active motif CXU (C is cysteine and U is selenocysteine), resembling the redox motif of thiol‐disulfide oxidoreductases (CXXC). Like other selenoproteins, the challenge in accessing SELENOF has somewhat limited its full biological characterization thus far. Here we present the one‐pot chemical synthesis of the thioredoxin‐like domain of SELENOF, highlighted by the use of Fmoc‐protected selenazolidine, native chemical ligations and deselenization reactions. The redox potential of the CXU motif, together with insulin turbidimetric assay suggested that SELENOF may catalyze the reduction of disulfides in misfolded proteins. Furthermore, we demonstrate that SELENOF is not a protein disulfide isomerase (PDI)‐like enzyme, as it did not enhance the folding of the two protein models; bovine pancreatic trypsin inhibitor and hirudin. These studies suggest that SELENOF may be responsible for reducing the non‐native disulfide bonds of misfolded glycoproteins as part of the quality control system in the ER. [ABSTRACT FROM AUTHOR]

Ferrocene (Fc) conjugated selenopeptides were synthesized using a new modified solid‐phase peptide synthesis (SPSS) protocol and their self‐assembled nanostructure formation into spheres, nanofibers, and nanotubes studied. Four selenopeptide conjugates have been successfully prepared: two containing both selenocysteine (Sec) and Fc, the other two have either one of these units. These compounds were well‐characterized with various spectroscopic techniques, including 1D and 2D NMR. The importance of the Fc unit, aromatic moieties, and weak intermolecular interactions on the self‐assembled process was revealed by systematic morphological studies. [ABSTRACT FROM AUTHOR]

This work is devoted to investigations of the influence of O–H···Se(–) hydrogen bonds on the electronic shells of selenolate R–Se(–) fragment (R═CH3). The geometric, energetic and nuclear magnetic resonance (NMR) spectral parameters for various conformers of CH3Se(–)⋯(H2O)n clusters with n = 0–6 were calculated at CCSD/aug‐cc‐pVDZ level of theory. For selenolate anion CH3Se(–) solvation free energy was calculated, and for water media it is equal to −71.41 kcal/mol. For O–H···Se(–) hydrogen bonds the proportionality coefficients between QTAIM parameters at (3; −1) bond critical point and the strength of an individual hydrogen bond ∆E were proposed. It was shown, that despite a relative weakness of O–H···Se(–) hydrogen bonds, the outer electronic shell of the selenium atom changes significantly upon formation of each hydrogen bond. This, in turn, cause the dramatic change of NMR parameters of selenium nuclei. [ABSTRACT FROM AUTHOR]

The controlled oxidation reaction of L‐selenocystine under neutral pH conditions affords selenocysteine seleninic acid (3‐selenino‐L‐alanine) which is characterized also by means of single‐crystal X‐ray diffraction. This technique shows that selenium forms three chalcogen bonds (ChBs), one of them being outstandingly short. A survey of seleninic acid derivatives in the Cambridge Structural Database (CSD) confirms that the C−Se(=O)O− functionality tends to act as a ChB donor robust enough to systematically influence the interactional landscape in the solid. Quantum Theory of Atom in Molecules (QTAIM) analysis proves the attractive nature of the short contacts observed in crystals containing the seleninic functionality and calculation of surface molecular electrostatic potential (MEP) reveals that remarkably positive σ‐holes can frequently be found opposite to the covalent bonds at selenium. Both CSD searches and QTAIM and MEP approaches show that also the sulfinic acid moiety can function as a ChB donor, albeit less frequently than the seleninic acid one. These findings may contribute to a better understanding, at the atomic level, of the mechanism of action of the enzymes that control oxidative stress and ROS deactivation and that contain selenocysteine seleninic acid and cysteine sulfinic acid in the active site. [ABSTRACT FROM AUTHOR]

A visible light‐initiated method has been developed for preparation of Se−S bond‐containing peptides. The method is based on generation of sulfur‐centered radical employing organic dye. The protocol is tolerant to unprotected peptides with "sensitive" amino acids. The stability of Se−S bond is evaluated in buffers at different pH (3.0–10.0) and also in the presence of oxidants and reducing agents. Additionally, the ability of Se−S bond to serve as an oxidation sensitive linker in biocompatible materials has been confirmed. [ABSTRACT FROM AUTHOR]

A straightforward and atom‐economic method for the functionalization of short selenocystine‐containing peptides is presented. This method is shown to be tolerant to unprotected peptides. The detailed protocol is based on the generation of a selenium radical via visible light‐initiated reaction in the presence of transition metal‐free photocatalyst. The selenium radical is further oxidized to an electrophile and trapped by N‐heterocycles. The mechanism is confirmed by NMR, HRMS, UV, EPR and cyclic voltammetry (CV) experiments and photocatalyst emission quenching studies. A visible light‐initiated reaction is employed for the synthesis of selenocysteine‐containing indole‐based macrocycles via intramolecular Se−C bond formation. [ABSTRACT FROM AUTHOR]

α‐Diazo homophotalimides were reacted with various propiolic acids on Rh2(esp)2 catalysis. The resulting propiolate esters were transformed into novel, heterocyclic Δα,β‐spirobutenolides in good to excellent product yields. The approach represents a fundamentally novel entry into natural‐like Δα,β‐spirobutenolides present in many biologically active natural products as well as fully synthetic compounds endowed with diverse biological activities. The Δα,β‐spirobutenolides thus obtained were shown to inhibit thioredoxin reductase, a selenocysteine enzyme target for cancer. Moreover, for the best compound in the series (TrxR IC50 1.49±0.08 μM), by using MALDI‐TOF mass‐spectrometry it was shown that it selectively binds selenocysteine in the presence of a 10‐fold excess of cysteine. This validates the new compound as a promising lead for anticancer therapy development. [ABSTRACT FROM AUTHOR]

Essential trace element selenium in association with selenoproteins, which is found in almost all organisms except higher plants and fungi, is involved in various biological functions. Advancement in the field of whole genome sequencing and data analyzing bioinformatic tools led to the accumulation of genome information of organisms. However, selenoproteins are unique and it needs specialized genomics tool for its identification as well as characterization. In this study, the presence of selenoprotein T (SelT) from Scenedesmus quadricauda was shown for the first time with experimental evidence and compared with SelT of marine microalgae Nannochloropsis oceanica. Along with SelT, all the associated machineries required to synthesize the selenoproteins were also identified. Also, the present study tried to explicate the evolutionary relatedness of SelT of these two organisms with other known bacteria and eukaryotes. Transcript level analysis in S. quadricauda under endoplasmic reticulum stress showed a 1.2 ± 0.28‐fold increase in SelT expression. Thus, it provided the first experimental evidence on SelT expression from microalgae. [ABSTRACT FROM AUTHOR]

The so‐called peroxidatic cysteines and selenocysteines in proteins reduce hydroperoxides through a dual attack to the peroxide bond in a two‐step mechanism. First, a proton dislocation from the thiol/selenol to a close residue of the enzymatic pocket occurs. Then, a nucleophilic attack of the anionic cysteine/selenocysteine to one O atom takes place, while the proton is shuttled back to the second O atom, promoting the formation of a water molecule. In this computational study, we use a molecular model of GPx to demonstrate that the enzymatic environment significantly lowers the barrier of the latter SN2 step. Particularly, in our Se‐based model the energy barriers for the two steps are 29.82 and 2.83 kcal mol−1, both higher than the corresponding barriers computed in the enzymatic cluster, i. e., 21.60 and null, respectively. Our results, obtained at SMD‐B3LYP‐D3(BJ)/6‐311+G(d,p), cc‐pVTZ//B3LYP‐D3(BJ)/6‐311G(d,p), cc‐pVTZ level of theory, show that the mechanistic details can be well reproduced using an oversimplified model, but the energetics is definitively more favorable in the GPx active site. In addition, we pinpoint the role of the chalcogen in the peroxide reduction process, rooting the advantages of the presence of selenium in its acidic and nucleophilic properties. [ABSTRACT FROM AUTHOR]

Copyright of Nachrichten aus der Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wild‐type human glutathione peroxidase 4 (GPX4) was co‐expressed with SBP2 (selenocysteine insertion sequence‐binding protein 2) in human HEK cells to achieve efficient production of this selenocysteine‐containing enzyme on a preparative scale for structural biology. The protein was purified and crystallized, and the crystal structure of the wild‐type form of GPX4 was determined at 1.0 Å resolution. The overall fold and the active site are conserved compared with previously determined crystal structures of mutated forms of GPX4. A mass‐spectrometry‐based approach was developed to monitor the reaction of the active‐site selenocysteine Sec46 with covalent inhibitors. This, together with the introduction of a surface mutant (Cys66Ser), enabled the crystal structure determination of GPX4 in complex with the covalent inhibitor ML162 [(S)‐enantiomer]. The mass‐spectrometry‐based approach described here opens the path to further co‐complex crystal structures of this potential cancer drug target in complex with covalent inhibitors. [ABSTRACT FROM AUTHOR]

Selenocysteine (Sec) is a crucial component of mammalian thioredoxin reductase (TrxR) where it serves as a nucleophile for disulfide bond rupture in thioredoxin (Trx). Generation of the reduced state of Sec in TrxR requires consecutive two electron transfer steps, namely: (i) from NADPH to flavin adenine dinucleotide, (ii) from reduced flavin to the disulfide bond Cys59‐S‐S‐Cys64, and finally (iii) from Cys59 and Cys64 to the selenosulfide bond Cys497‐S‐Se‐Sec498. In this work, we studied the reaction between reduced riboflavin (RibH2) and selenocystine (Sec‐Sec), an oxidized form of Sec. The interaction between RibH2 and Sec‐Sec proceeded relatively slowly in comparison with its reverse reaction, that is, reduction of riboflavin (Rib) by Sec. The rate constant for the reaction between RibH2 and Sec‐Sec was (7.9 ± 0.1) × 10−2 M−1 s−1 (pH 7.0, 25.0°C). The reaction between Rib and Sec proceeded via two steps, namely, a rapid reversible binding of Rib to Sec having a protonated selenol group to form a Sec‐Rib complex, followed by nucleophilic attack of Sec‐Rib by a second Sec molecule harboring a deprotonated selenol group. The equilibrium constant for the overall reduction process of Rib by Sec is (1.2 ± 0.1) × 106 M−1 (25.0°C). The finding that the interaction of RibH2 with oxidized selenol is reversible with its equilibrium favored toward the reverse reaction provides an additional explanation for the exceptional mechanism of the mammalian Trx/TrxR system involving transient reduction of a disulfide bond. [ABSTRACT FROM AUTHOR]

The development of site‐selective chemistry targeting the canonical amino acids enables the controlled installation of desired functionalities into native peptides and proteins. Such techniques facilitate the development of polypeptide conjugates to advance therapeutics, diagnostics, and fundamental science. We report a versatile and selective method to functionalize peptides and proteins through free‐radical‐mediated dechalcogenation. By exploiting phosphine‐induced homolysis of the C−Se and C−S bonds of selenocysteine and cysteine, respectively, we demonstrate the site‐selective installation of groups appended to a persistent radical trap. The reaction is rapid, operationally simple, and chemoselective. The resulting aminooxy linker is stable under a variety of conditions and selectively cleavable in the presence of a low‐oxidation‐state transition metal. We have explored the full scope of this reaction using complex peptide systems and a recombinantly expressed protein. [ABSTRACT FROM AUTHOR]

Long‐acting insulin analogues represent the most prescribed class of therapeutic proteins. An innovative design strategy was recently proposed: diselenide substitution of an external disulfide bridge. This approach exploited the distinctive physicochemical properties of selenocysteine (U). Relative to wild type (WT), Se‐insulin[C7UA, C7UB] was reported to be protected from proteolysis by insulin‐degrading enzyme (IDE), predicting prolonged activity. Because of this strategy's novelty and potential clinical importance, we sought to validate these findings and test their therapeutic utility in an animal model of diabetes mellitus. Surprisingly, the analogue did not exhibit enhanced stability, and its susceptibility to cleavage by either IDE or a canonical serine protease (glutamyl endopeptidase Glu‐C) was similar to WT. Moreover, the analogue's pharmacodynamic profile in rats was not prolonged relative to a rapid‐acting clinical analogue (insulin lispro). Although [C7UA, C7UB] does not confer protracted action, nonetheless its comparison to internal diselenide bridges promises to provide broad biophysical insight. [ABSTRACT FROM AUTHOR]

Herein, we present methods for the generation of selenocysteinyl electrophile by weak Lewis acids or oxidants. The electrophilic selenium species were further utilized in 5‐endo‐dig cyclization reactions with 2‐ethynyl phenols, anisoles, and anilines, yielding substituted benzo[b]furans and indoles bearing short selenocysteine‐containing peptides. Copper(II) bromide promoted 5‐endo‐dig cyclization can be successfully applied for protected and unprotected peptides in high yields. Elaborated protocol allows the construction of phenylindeno[1,2‐c]chromene moiety in 5‐endo‐dig/6‐endo‐dig cascade reactions. [ABSTRACT FROM AUTHOR]

Sulfoxide synthases are non‐heme iron enzymes that participate in the biosynthesis of thiohistidines, such as ergothioneine and ovothiol A. The sulfoxide synthase EgtB from Chloracidobacterium thermophilum (CthEgtB) catalyzes oxidative coupling between the side chains of N‐α‐trimethyl histidine (TMH) and cysteine (Cys) in a reaction that entails complete reduction of molecular oxygen, carbon–sulfur (C−S) and sulfur–oxygen (S−O) bond formation as well as carbon–hydrogen (C−H) bond cleavage. In this report, we show that CthEgtB and other bacterial sulfoxide synthases cannot efficiently accept selenocysteine (SeCys) as a substrate in place of cysteine. In contrast, the sulfoxide synthase from the filamentous fungus Chaetomium thermophilum (CthEgt1) catalyzes C−S and C−Se bond formation at almost equal efficiency. We discuss evidence suggesting that this functional difference between bacterial and fungal sulfoxide synthases emerges from different modes of oxygen activation. [ABSTRACT FROM AUTHOR]

This article, titled "Cover Feature: Highly Electrophilic Intermediates in the Bypass Mechanism of Glutathione Peroxidase: Synthesis, Reactivity, and Structures of Selenocysteine-Derived Cyclic Selenenyl Amides," explores the role of selenocysteine cyclic selenenyl amides in the catalytic cycle of the antioxidant enzyme glutathione peroxidase (GPx). The study reveals that these intermediates, previously overlooked, have dual functionality. They not only prevent the inactivation of GPx but also act as highly electrophilic intermediates in selenoprotein reactions. The researchers compare the roles of these intermediates to a chess king, dynamically adapting to their application. [Extracted from the article]

While chemical protein synthesis has granted access to challenging proteins, the synthesis of longer proteins is often limited by low abundance or non‐strategic placement of cysteine residues, which are essential for native chemical ligations, as well as multiple purification and isolation steps. We describe the one‐pot total synthesis of human thiosulfate:glutathione sulfurtransferase (TSTD1). WT‐TSTD1 was synthesized in a C‐to‐N synthetic approach involving multiple NCL reactions, CuII‐mediated deprotection of selenazolidine (Sez), and chemoselective deselenization. The seleno‐analog Se‐TSTD1, in which the active site Cys is replaced with selenocysteine, was also synthesized with a kinetically controlled ligation with an N‐to‐C synthetic approach. The catalytic activity of the two proteins indicated that Se‐TSTD1 possessed only four‐fold lower activity than WT‐TSTD1, thus suggesting that selenoproteins can have physiologically comparable sulfutransferase activity to their cysteine counterparts. [ABSTRACT FROM AUTHOR]

Herein we report the first example of a strategy for peptide functionalization through the generation of selenocysteine electrophile in 5‐ and 6‐endo‐dig cyclization reactions. This simple approach allows bio‐conjugation of selenocystine‐based peptides. The developed protocol is based on copper(II) bromide mediated reactions of selenocystine with either 2‐propargyl N‐heterocycles through 5‐endo‐dig closure or with 2‐ethynylbiaryls through 6‐endo‐dig closure. It allows construction of indolizinium moiety on selenocysteine residue as well as formation of polyaromatic fragment bonded to selenium in a simple one‐pot process under mild reaction conditions. [ABSTRACT FROM AUTHOR]

A simple and efficient strategy for the selective modification of the peptide N terminus with an unnatural amino acid is described. A peptide having a SUMO‐HisTag‐TEV sequence (SUMO: small ubiquitin‐related modifier, TEV: tobacco etch virus) preceding the N terminus of the target peptide was designed. Recombinant expression in E. coli and subsequent SUMO protease cleavage yielded the HisTag‐TEV‐target peptide. Partial protection of the lysine side chains of this peptide with d‐glucopyranosyloxycarbonyl and removal of the HisTag‐TEV sequence by TEV protease yielded the partially protected peptide with a free N‐terminal amine. Coupling of selenocysteine selectively at the N terminus and subsequent acidic deprotection of the carbohydrate protecting groups yielded a modified peptide that can be used for native chemical ligation (NCL). As a proof of concept, the modification of a longer recombinant peptide with selenocysteinylserine (GalNAc) at the N terminus was demonstrated. [ABSTRACT FROM AUTHOR]

Small molecule‐based electrophilic compounds such as 1‐chloro‐2,4‐dinitrobenzene (CDNB) and 1‐chloro‐4‐nitrobenzene (CNB) are currently being used as inhibitors of cysteine‐ and selenocysteine‐containing proteins. CDNB has been used extensively to determine the activity of glutathione S‐transferase and to deplete glutathione (GSH) in mammalian cells. Also, CDNB has been shown to irreversibly inhibit thioredoxin reductase (TrxR), a selenoenzyme that catalyses the reduction of thioredoxin (Trx). Mammalian TrxR has a C‐terminal active site motif, Gly‐Cys‐Sec‐Gly, and both the cysteine and selenocysteine residues could be the targets of the electrophilic reagents. In this paper we report on the stability of a series of cysteine and selenocysteine derivatives that can be considered as models for the selenoenzyme–inhibitor complexes. We show that these derivatives react with H2O2 to generate the corresponding selenoxides, which undergo spontaneous elimination to produce dehydroalanine. In contrast, the cysteine derivatives are stable towards such elimination reactions. We also demonstrate, for the first time, that the arylselenium species eliminated from the selenocysteine derivatives exhibit significant redox activity by catalysing the reduction of H2O2 in the presence of GSH (GPx (glutathione peroxidase)‐like activity), which suggests that such redox modulatory activity of selenium compounds may have a significant effect on the cellular redox state during the inhibition of selenoproteins. [ABSTRACT FROM AUTHOR]

Insulin analogues, mainstays in the modern treatment of diabetes mellitus, exemplify the utility of protein engineering in molecular pharmacology. Whereas chemical syntheses of the individual A and B chains were accomplished in the early 1960s, their combination to form native insulin remains inefficient because of competing disulfide pairing and aggregation. To overcome these limitations, we envisioned an alternative approach: pairwise substitution of cysteine residues with selenocysteine (Sec, U). To this end, CysA6 and CysA11 (which form the internal intrachain A6–A11 disulfide bridge) were each replaced with Sec. The A chain[C6U, C11U] variant was prepared by solid‐phase peptide synthesis; while sulfitolysis of biosynthetic human insulin provided wild‐type B chain‐di‐S‐sulfonate. The presence of selenium atoms at these sites markedly enhanced the rate and fidelity of chain combination, thus solving a long‐standing challenge in chemical insulin synthesis. The affinity of the Se‐insulin analogue for the lectin‐purified insulin receptor was indistinguishable from that of WT‐insulin. Remarkably, the thermodynamic stability of the analogue at 25 °C, as inferred from guanidine denaturation studies, was augmented (ΔΔGu ≈0.8 kcal mol−1). In accordance with such enhanced stability, reductive unfolding of the Se‐insulin analogue and resistance to enzymatic cleavage by Glu‐C protease occurred four times more slowly than that of WT‐insulin. 2D‐NMR and X‐ray crystallographic studies demonstrated a native‐like three‐dimensional structure in which the diselenide bridge was accommodated in the hydrophobic core without steric clash. [ABSTRACT FROM AUTHOR]

Bicyclic and tricyclic peptides have emerged as promising candidates for the development of protein binders and new therapeutics. However, convenient and efficient strategies that can generate topologically controlled bicyclic and tricyclic peptide scaffolds from fully‐unprotected peptides are still much in demand, particularly for those amenable to the design of biosynthetic libraries. In this work, we report a reliable chemical and ribosomal synthesis of topologically controlled bicyclic and tricyclic peptide scaffolds. Our strategy involves the combination of selenoether cyclization followed by disulfide or thioether cyclization, yielding desirable bicyclic and tricyclic peptides. This work thus lays the foundation for developing peptide libraries with controlled topology of multicyclic scaffolds for in vitro display techniques. You'd better shape up: A reliable chemical and ribosomal synthesis of topologically controlled bicyclic and tricyclic peptide scaffolds was developed. Selenoether cyclization was combined with disulfide or thioether cyclization to yield desirable bicyclic and tricyclic peptides. This work lays the foundation for developing peptide libraries with multicyclic scaffolds of controlled topology for in vitro display techniques. [ABSTRACT FROM AUTHOR]

Selenocysteine (Sec) is the 21st amino acid in the genetic code and it is present in a small number of proteins where it replaces the much more commonly used amino acid cysteine (Cys). It is both more complicated and bioenergetically costly to insert Sec into a protein in comparison to Cys, and this cost is most likely compensated by a gain of function to the enzyme/protein in which it is incorporated. Here we investigate one such gain of function, the enhancement of one‐electron transfer catalysis. We compared the ability of Sec‐containing mouse mitochondrial thioredoxin reductase (mTrxR2) to catalyze the reduction of bovine cytochrome c, ascorbyl radical, and dehydroascorbate in comparison to Cys‐containing thioredoxin reductases from D. melanogaster (DmTrxR) and P. falciparum (PfTrxR). The Sec‐containing mTrxR2 was able to reduce all three substrates, while the Cys‐containing enzymes had little or no activity. In addition, we constructed Cys➔Sec mutants of DmTrxR and PfTrxR and found that this substitution resulted in a gain of function, as these mutant enzymes were now able to catalyze the reduction of these substrates. We also found that in the case of PfTrxR, reduction of cytochrome c was enhanced five‐fold in a truncated PfTrxR in which the C‐terminal redox center was removed. This shows that some of the ability of thioredoxin reductase to reduce this substrate comes from the flavin coenzyme. We also discuss a possible mechanism by which Sec‐containing thioredoxin reductase reduces dehydroascorbate to ascorbate by two sequential, one‐electron reductions, in part catalyzed by Sec. [ABSTRACT FROM AUTHOR]

Dimedone is a widely used reagent to assess the redox state of cysteine‐containing proteins as it will alkylate sulfenic acid residues, but not sulfinic acid residues. While it has been reported that dimedone can label selenenic acid residues in selenoproteins, we investigated the stability, and reversibility of this label in a model peptide system. We also wondered whether dimedone could be used to detect seleninic acid residues. We used benzenesulfinic acid, benzeneseleninic acid, and model selenocysteine‐containing peptides to investigate possible reactions with dimedone. These peptides were incubated with H2O2 in the presence of dimedone and then the reactions were followed by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS). The native peptide, H‐PTVTGCUG‐OH (corresponding to the native amino acid sequence of the C‐terminus of mammalian thioredoxin reductase), could not be alkylated by dimedone, but could be carboxymethylated with iodoacetic acid. However the "mutant peptide," H‐PTVTGAUG‐OH, could be labeled with dimedone at low concentrations of H2O2, but the reaction was reversible by addition of thiol. Due to the reversible nature of this alkylation, we conclude that dimedone is not a good reagent for detecting selenenic acids in selenoproteins. At high concentrations of H2O2, selenium was eliminated from the peptide and a dimeric form of dimedone could be detected using LCMS and 1H NMR. The dimeric dimedone product forms as a result of a seleno‐Pummerer reaction with Sec‐seleninic acid. Overall our results show that the reaction of dimedone with oxidized cysteine residues is quite different from the same reaction with oxidized selenocysteine residues. [ABSTRACT FROM AUTHOR]

Mammalian thioredoxin reductase (TrxR) enzymes are homodimeric flavin proteins sharing a unique yet essential selenocysteine residue at their C‐terminus. TrxRs, together with their endogenous substrate thioredoxins, play a crucial role in regulating diverse cellular redox events. A wealth of evidence from both clinic observations and bench studies supports that overactivation/dysfunction of TrxRs has a close link to the onset and development of various diseases, such as cancer and neurodegeneration. Thus, an increasing interest has been attracted to find small molecule modulators of TrxRs during the past years. Herein, we briefly discussed the relevance of targeting TrxRs inhibition for cancer treatment, and presented the small molecule inhibitors of mammalian TrxRs published in the nonpatent literatures from 2011 to 2016. The mechanisms of inhibition by different classes of molecules were summarized, and some inhibitors with promising anticancer activity were further discussed. We expect this work would be a comprehensive reference in the medicinal chemistry, and have a broad audience across multiple disciplines. [ABSTRACT FROM AUTHOR]

Selenocysteine (Sec) lacks a cognate aminoacyl‐tRNA synthetase. Instead, seryl‐tRNA synthetase (SerRS) produces Ser‐tRNASec, which is subsequently converted by selenocysteine synthase to Sec‐tRNASec. Escherichia coli SerRS serylates tRNASec poorly; this may hinder efficient production of designer selenoproteins in vivo. Guided by structural modelling and selection for chloramphenicol acetyltransferase activity, we evolved three SerRS variants capable of improved Ser‐tRNASec synthesis. They display 10‐, 8‐, and 4‐fold increased kcat/KM values compared to wild‐type SerRS using synthetic tRNASec species as substrates. The enzyme variants also facilitate in vivo read‐through of a UAG codon in the position of the critical serine146 of chloramphenicol acetyltransferase. These results indicate that the naturally evolved SerRS is capable of further evolution for increased recognition of a specific tRNA isoacceptor. [ABSTRACT FROM AUTHOR]

SUMMARY: A complete open reading frame (ORF) encoding a glutathione peroxidase (ICE‐LGPx) was determined from Antarctic Chlamydomonas sp. ICE‐L by the molecular biological methods. The transcriptional expression patterns of ICE‐LGPx under different salinity and temperature stresses were determined by the real‐time polymerase chain reaction, and the activities of ICE‐LGPx were assayed under salinity stress as well. The full‐length cDNA sequence of ICE‐LGPx mRNA was 1956 bp including an ORF of 765 bp. Molecular structure analysis revealed that ICE‐LGPx was a selenium‐dependent glutathione peroxidase (Se‐GPx) containing a form‐2 SECIS (SelenoCysteine Insertion Sequence) element. Phylogenetic analysis showed that ICE‐LGPx displayed parallel evolution with those of Volvox carteri, Chlorella variabilis, Micromonas sp. RCC299 and Micromonas pusilla. The expression analysis results indicated that transcription of ICE‐LGPx was induced by the changes of the salinity and temperature. The change tendency of enzyme activities was similar to that of ICE‐LGPx mRNA level. Time‐ and dose‐dependent effects were observed in the salinity treatments and time‐dependent effects were found in the temperature treatments as well. These results suggested that ICE‐LGPx might play an important role in the acclimatization of Chlamydomonas sp. ICE‐L to salt and low temperature stresses. Furthermore, the results of this investigation may help to clarify the acclimatization and stress response mechanisms of Antarctic ice alga. [ABSTRACT FROM AUTHOR]

Abstract: Ein einfacher Ansatz nutzt einen erweiterten genetischen Code von Escherichia coli zur Biosynthese von Selenoproteinen mit zahlreichen Sec‐Resten. Kürzlich wurden so genannte allo‐tRNAs entdeckt. Diese verfügen über eine ungewöhnliche Struktur, sind genauso effiziente Serinakzeptoren wie die normale tRNASer aus E. coli und werden von der Aeromonas‐salmonicida‐Selenocysteinsynthase (SelA) von Ser‐allo‐tRNA zu Sec‐allo‐tRNA umgesetzt. Anschließend ermöglicht es Sec‐allo‐tRNA, fünf UAG‐Stop‐Codons auf der fdhF‐mRNA für E.‐coli‐Formatdehydrogenase H als Sec zu translatieren und katalytisch aktive E.‐coli‐Formatdehydrogenase mit fünf Sec‐Resten in E. coli zu produzieren. Weiterhin konnte gezeigt werden, dass sich in E. coli durch Kombination genetischer Varianten von allo‐tRNA und SelA mit einem modifizierten Selenstoffwechsel das humane Selenoenzym GPx1 mit über 80 % Sec‐Einbaurate rekombinant produzieren lässt. Beide Beispiele belegen den Wert von allo‐tRNAUTu als molekulare Plattform zur Entwicklung neuartiger Selenoproteine. [ABSTRACT FROM AUTHOR]

Abstract: Selenocysteine (Sec, U) confers new chemical properties on proteins. Improved tools are thus required that enable Sec insertion into any desired position of a protein. We report a facile method for synthesizing selenoproteins with multiple Sec residues by expanding the genetic code of Escherichia coli. We recently discovered allo‐tRNAs, tRNA species with unusual structure, that are as efficient serine acceptors as E. coli tRNASer. Ser‐allo‐tRNA was converted into Sec‐allo‐tRNA by Aeromonas salmonicida selenocysteine synthase (SelA). Sec‐allo‐tRNA variants were able to read through five UAG codons in the fdhF mRNA coding for E. coli formate dehydrogenase H, and produced active FDHH with five Sec residues in E. coli. Engineering of the E. coli selenium metabolism along with mutational changes in allo‐tRNA and SelA improved the yield and purity of recombinant human glutathione peroxidase 1 (to over 80 %). Thus, our allo‐tRNAUTu system offers a new selenoprotein engineering platform. [ABSTRACT FROM AUTHOR]

Abstract: Osteosarcoma represents the most common primary malignant bone tumor in children and adolescents, which shows severe resistance toward standard chemotherapy because of high invasive capacity and growing incidence. Selenocysteine (SeC) is a naturally available Se‐containing amino acid that displays splendid anticancer activities against several human tumors. However, little information about SeC‐induced growth inhibition against human osteosarcoma is available. Herein, the anticancer efficiency and underlying mechanism of SeC against human osteosarcoma were evaluated in vitro and in vivo. The results revealed that SeC significantly inhibited MG‐63 human osteosarcoma cells growth in vitro through induction of S‐phase arrest and apoptosis, as reflected by the decrease of cyclin A and CDK‐2, PARP cleavage, and caspases activation. SeC treatment also resulted in mitochondrial dysfunction through affecting Bcl‐2 family expression. Moreover, SeC triggered p53 phosphorylation by inducing reactive oxygen species (ROS) overproduction. ROS inhibition effectively blocked SeC‐induced cytotoxicity and p53 phosphorylation. Importantly, MG‐63 human osteosarcoma xenograft growth in nude mice was significantly suppressed in vivo through triggering apoptosis and p53 phosphorylation. These results indicated that SeC had the potential to inhibit human osteosarcoma cells growth in vitro and in vivo through triggering mitochondrial dysfunction and ROS‐mediated p53 phosphorylation, which validated the potential application of Se‐containing compounds in treatment of human osteosarcoma. [ABSTRACT FROM AUTHOR]

Selenocysteine, the selenium-containing analogue of cysteine, is the twenty-first proteinogenic amino acid. Since its discovery almost fifty years ago, it has been exploited in unnatural systems even more often than in natural systems. Selenocysteine chemistry has attracted the attention of many chemists in the field of chemical biology owing to its high reactivity and resulting potential for various applications such as chemical modification, chemical protein (semi)synthesis, and protein folding, to name a few. In this Minireview, we will focus on the chemistry of selenium and selenocysteine and their utility in protein chemistry. [ABSTRACT FROM AUTHOR]

We studied the reaction between aquacobalamin (H2OCbl) and selenocysteine (Sec), a selenium-containing analogue of cysteine, using conventional UV/Vis spectroscopy. This reaction leads to the formation of cob(II)alamin [Cbl(II)] without any detectable intermediate complexation of Cbl(III) with selenocysteine, whereas the interaction between H2OCbl and cysteine proceeds distinctly through the coordination of Cys onto the CoIII ion with further reduction of the CoIII-Cys complex to Cbl(II). The latter is slower than the reaction with Sec. We also showed that selenocystine is capable of accelerating the reduction of H2OCbl to Cbl(II) by cysteine. [ABSTRACT FROM AUTHOR]

Glutathione peroxidase-like enzymes (GPXLs) constitute a family of eight peroxidases in Arabidopsis thaliana. In contrast to the eponymous selenocysteine glutathione peroxidases in mammalian cells that use glutathione as electron donor, GPXLs rely on cysteine instead of selenocysteine for activity and depend on the thioredoxin system for reduction. Although plant GPXLs have been implicated in important agronomic traits such as drought tolerance, photooxidative tolerance and immune responses, there remain major ambiguities regarding their subcellular localization. Because their site of action is a prerequisite for an understanding of their function, we investigated the localization of all eight GPXLs in stable Arabidopsis lines expressing N-terminal and C-terminal fusions with redox-sensitive green fluorescent protein 2 (roGFP2) using confocal microscopy. GPXL1 and GPXL7 were found in plastids, while GPXL2 and GPXL8 are cytosolic nuclear. The N-terminal target peptide of GPXL6 is sufficient to direct roGFP2 into mitochondria. Interestingly, GPXL3, GPXL4 and GPXL5 all appear to be membrane bound. GPXL3 was found exclusively in the secretory pathway where it is anchored by a single N-terminal transmembrane domain. GPXL4 and GPXL5 are anchored to the plasma membrane. Presence of an N-terminal myristoylation motif and genetic disruption of membrane association through targeted mutagenesis point to myristoylation as essential for membrane localization. [ABSTRACT FROM AUTHOR]

Selenocysteine (Sec) is a primary kind of reactive selenium species in cells whose antioxidant roles in a series of liver diseases have been featured. However, it is difficult to determine Sec in living cells and in vivo due to its high reactivity and instability. This work reports a ratiometric near-infrared fluorescent probe (Cy-SS) for qualitative and quantitative determination of Sec in living cells and in vivo. The probe is composed of heptamethine cyanine fluorophore, the response unit bis(2-hydroxyethyl) disulfide, and the liver-targeting moiety d-galactose. Based on a detection mechanism of selenium-sulfur exchange reaction, the concentrations of Sec in HepG2, HL-7702 cells, and primary mouse hepatocytes is determined as 3.08 ± 0.11 × 10−6 m, 4.03 ± 0.16 × 10−6 m and 4.34 ± 0.30 × 10−6 m, respectively. The probe can selectively accumulate in liver. The ratio fluorescence signal of the probe can be employed to quantitatively analyze the fluctuation of Sec concentrations in cells and mice models of acute hepatitis. The experimental results demonstrate that Sec plays important antioxidant and anti-inflammatory roles during inflammatory process. And the levels of intracellular Sec have a close relationship with the degree of liver inflammation. The above imaging detections make this new probe a potential candidate for the accurate diagnosis of inflammation. [ABSTRACT FROM AUTHOR]

Synthetic insulin analogues with a long lifetime are current drug targets for the therapy of diabetic patients. The replacement of the interchain disulfide with a diselenide bridge, which is more resistant to reduction and internal bond rotation, can enhance the lifetime of insulin in the presence of the insulin-degrading enzyme (IDE) without impairing the hormonal function. The [C7UA,C7UB] variant of bovine pancreatic insulin (BPIns) was successfully prepared by using two selenocysteine peptides (i.e., the C7U analogues of A- and B-chains, respectively). In a buffer solution at pH 10 they spontaneously assembled under thermodynamic control to the correct insulin fold. The selenoinsulin (Se-Ins) exhibited a bioactivity comparable to that of BPIns. Interestingly, degradation of Se-Ins with IDE was significantly decelerated ( τ1/2≈8 h vs. ≈1 h for BPIns). The lifetime enhancement could be due to both the intrinsic stability of the diselenide bond and local conformational changes induced by the substitution. [ABSTRACT FROM AUTHOR]

The reduction of seleno-L-cystine is examined on gold and platinum electrodes in aqueous solution. The voltammetric behavior is indicative of a two-step process, in which the metallic substrate is modified by the diselenide analyte prior to observation of diffusionally controlled, proton-coupled electron transfer. X-ray photoelectron spectroscopy confirms the presence of selenium on gold foil samples that have been reductively cycled in selenocystine solution. The selenium-based surface modification, which is accessible through multiple preparation routes, can be removed by anodic stripping and fully restored through subsequent cycling. The described electrochemical approach allows for the analysis of redox-active chalcogen-containing species under physiologically relevant conditions. [ABSTRACT FROM AUTHOR]

The use of native chemical ligation at selenocysteine (Sec) residues with peptide thioesters and additive-free selenocystine ligation with peptides bearing phenyl selenoesters, in concert with one-pot oxidative deselenization chemistry, is described. These approaches provide a simple and rapid method for accessing native peptides with serine in place of Sec at the ligation junction. The efficiency of both variants of the one-pot ligation-oxidative deselenization chemistry is probed through the synthesis of a MUC5AC-derived glycopeptide. [ABSTRACT FROM AUTHOR]

We previously reported on a method for the facile removal of 4-methoxybenzyl and acetamidomethyl protecting groups from cysteine (Cys) and selenocysteine (Sec) using 2,2′-dithiobis-5-nitropyridine dissolved in trifluoroacetic acid, with or without thioanisole. The use of this reaction mixture removes the protecting group and replaces it with a 2-thio(5-nitropyridyl) (5-Npys) group. This results in either a mixed selenosulfide bond or disulfide bond (depending on the use of Sec or Cys), which can subsequently be reduced by thiolysis. A major disadvantage of thiolysis is that excess thiol must be used to drive the reaction to completion and then removed before using the Cys-containing or Sec-containing peptide in further applications. Here, we report a further advancement of this method as we have found that ascorbate at pH 4.5 and 25 °C will reduce the selenosulfide to the selenol. Ascorbolysis of the mixed disulfide between Cys and 5-Npys is much less efficient but can be accomplished at higher concentrations of ascorbate at pH 7 and 37 °C with extended reaction times. We envision that our improved method will allow for in situ reactions with alkylating agents and electrophiles without the need for further purification, as well as a number of other applications. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Selenocysteine (Sec or U) is encoded by UGA, a stop codon reassigned by a Sec-specific elongation factor and a distinctive RNA structure. To discover possible code variations in extant organisms we analyzed 6.4 trillion base pairs of metagenomic sequences and 24 903 microbial genomes for tRNASec species. As expected, UGA is the predominant Sec codon in use. We also found tRNASec species that recognize the stop codons UAG and UAA, and ten sense codons. Selenoprotein synthesis programmed by UAG in Geodermatophilus and Blastococcus, and by the Cys codon UGU in Aeromonas salmonicida was confirmed by metabolic labeling with 75Se or mass spectrometry. Other tRNASec species with different anticodons enabled E. coli to synthesize active formate dehydrogenase H, a selenoenzyme. This illustrates the ease by which the genetic code may evolve new coding schemes, possibly aiding organisms to adapt to changing environments, and show the genetic code is much more flexible than previously thought. [ABSTRACT FROM AUTHOR]

Although native chemical ligation has enabled the synthesis of hundreds of proteins, not all proteins are accessible through typical ligation conditions. The challenging protein, 125-residue human phosphohistidine phosphatase 1 (PHPT1), has three cysteines near the C-terminus, which are not strategically placed for ligation. Herein, we report the first sequential native chemical ligation/deselenization reaction. PHPT1 was prepared from three unprotected peptide segments using two ligation reactions at cysteine and alanine junctions. Selenazolidine was utilized as a masked precursor for N-terminal selenocysteine in the middle segment, and, following ligation, deselenization provided the native alanine residue. This approach was used to synthesize both the wild-type PHPT1 and an analogue in which the active-site histidine was substituted with the unnatural and isosteric amino acid β-thienyl- l-alanine. The activity of both proteins was studied and compared, providing insights into the enzyme active site. [ABSTRACT FROM AUTHOR]

Despite the unique chemical properties of selenocysteine (Sec), ligation at Sec is an under-utilized methodology for protein synthesis. We describe herein an unprecedented protocol for the conversion of Sec to serine (Ser) in a single, high-yielding step. When coupled with ligation at Sec, this transformation provides a new approach to programmed ligations at Ser residues. This new reaction is compatible with a wide range of functionality, including the presence of unprotected amino acid side chains and appended glycans. The utility of the methodology is demonstrated in the rapid synthesis of complex glycopeptide fragments of the epithelial glycoproteins MUC5AC and MUC4 and through the total synthesis of the structured, cysteine (Cys)-free protein eglin C. [ABSTRACT FROM AUTHOR]

As selenocysteine (Sec) carries out the majority of the functions of the various Se-containing species in vivo, it is of high importance to develop reliable and rapid assays with biocompatibility to detect Sec. Herein, an NIR fluorescent turn-on probe for highly selective detection of selenol was designed and synthesized. The probe exhibits large turn-on signal upon treatment with selenocysteine (R-SeH), and it was further demonstrated that the new NIR fluorescent probe can be employed to image selenol in living animals. [ABSTRACT FROM AUTHOR]