Reductive Cleavage Of Disulfide Bonds Research Articles

UV-C light promotes the reductive cleavage of disulfide bonds in β-Lactoglobulin and improves in vitro gastric digestion

β-Lactoglobulin (β-Lg) is the main protein in whey and is known for its allergenicity and resistance to the digestion of pepsin and trypsin. The UV-C photoinduced cleavage of disulfide bonds in β-Lactoglobulin, as promoted by excitation of tryptophan residues (Trp), is shown to induce changes in the protein's secondary structure, significantly reducing the protein's resistance to pepsin digestion. The UV-C light-induced changes in the protein secondary structure are marked by an increase in the contribution of β-sheet and α-helix structures with a concomitantly smaller contribution of the β-turn structural motif. The photoinduced cleavage of disulfide bonds in β-Lg has an apparent quantum yield of ф = 0.0015 ± 0.0003 and was shown by transient absorption laser flash photolysis to arise by two different pathways: a) the reduction of the disulfide bond Cys66Cys160 occurs by direct electron transfer from the triplet-excited 3Trp to the disulfide bond due to the existence of a CysCys/Trp triad (Cys66Cys160/Trp61) and b) the reduction of the buried Cys106Cys119 disulfide bond involves a reaction with a solvated electron originated by the photoejection of electrons from the triplet-excited 3Trp decay. The in vitro gastric digestion index for UV-C-treated β-Lg is revealed to have increased significantly by 36 ± 4 % and 9 ± 2 % under simulated elderly and young adult digestive conditions, respectively. When compared to the native protein, the peptide mass fingerprint profile of digested UV-C-treated β-Lg shows a higher content and variety of peptides, including the production of some exclusive bioactive peptides such as PMHIRL and EKFDKALKALPMH.

Novel octanuclear copper(I) clusters [Cu8{(N)-(μ4-S)}4(μ3-I)2I2(PPh3)2] produced via reductive S-S bond cleavage of disulfide Schiff base ligands and their use as efficient heterogeneous catalysts in CuAAC click reaction

Thiol/disulfide interconversion, catalyzed by metal ions and enzymes, is a fundamental transformation and plays important roles in biological systems. The thiolates, produced in these reactions, are particularly versatile sulfur-containing ligands that can bind to metals or group of metals via a variety of modes and this versatility can lead to the formation of polymeric chains and metal clusters with high nuclearity. Herein, we report the facile one pot synthesis of novel octanuclear copper(I) complexes, [Cu8{(N)-(μ4-S)}4(μ3-I)2I2(PPh3)2] (1–5), by the reaction of copper(I) iodide and disulfide Schiff base molecules (R-CHN˗Ph˗S˗S˗Ph-NCH-R, RMePh = 4-MePh (SB1), RMeOPh = 4-MeOPh (SB2), RMeSPh = 4-MeSPh (SB3), RBrPh = 4-BrPh (SB4), and RFur = 2-furan (SB5)) in the presence of PPh3 in dichloromethane-acetonitrile or chloroform-acetonitrile solution under ambient conditions. Single-crystal X-ray structure analyses of these clusters confirm the presence of Cu8S4I4 core stabilized by the chelating Schiff base thiolate fragment R-CHN˗Ph˗Sˉ produced by the reductive cleavage of disulfide bond, Iˉ, and PPh3. DFT calculations have been performed to describe a speculative mechanism of cluster formation. The octanuclear clusters [Cu8{(N)-(μ4-S)}4(μ3-I)2I2(PPh3)2] (1–5) have been exploited as efficient heterogeneous catalysts for the green synthesis of 1,2,3-triazoles from NaN3, alkyl halides, and alkyne derivatives (CuAAC reaction) under mild conditions.

Comments on some chemical properties of diphenyl disulfide and its derivatives: II.Correlating the studies of reductive cleavage of disulfide bonds with the studies of anti‐human immunodeficiency virus activity with lowest unoccupied molecular orbital properties

AbstractThe higher anti‐human immunodeficiency virus activity of a symmetrical 2,2′‐disubstitued derivative of diphenyl disulfide (DPDS) has been explained by the lower energy of the lowest unoccupied molecular orbital (LUMO), resulted from a better hydrogen bond stabilization of the σ*SS bond orbital (BO). This conclusion entails the participation of σ*SS BO in constructing the LUMO. The higher content of σ*SS BO, compared to π*CC BOs of phenyl groups, in LUMO of DPDS has been found through analysis of the LUMO of DPDS expanded in the BO space. The high content of σ*SS BO (%σ*SS) in the LUMO of DPDS has laid the foundation for the formation of σ‐type radical anion intermediate in the stepwise reductive cleavage of disulfide bond in the symmetrical 4,4′‐disubstitued DPDS derivatives. For the nine 4,4′‐disubstituted DPDS‐derivatives under reductive cleavage studies, the increasing %σ*SS in the LUMOs is parallel to the increasing value of inner reorganization energy.

Dual-targeting nanoparticles with core-crosslinked and pH/redox-bioresponsive properties for enhanced intracellular drug delivery

Multifunctional nanoparticles (NPs) with high blood-stability, tumor-targeting ability, and stimuli-bioresponsive drug release behaviors are urgently demanded. Herein, folic acid (FA) and galactose (GAL) functionalized, core-crosslinked NPs (CC NPs) with dual-targeting and pH/redox-bioresponsive properties were developed based on amphiphilic FA-poly(6-O-methacryloyl-d-galactopyranose)-b-poly[2-(diisopropylamino) ethyl methacrylate-co-pyridyl disulfide methylacrylate] [FA-PMAgGP-b-P(DPA-co-PDEMA), termed as FA-PMgDP] block copolymers, and then investigated for facilitated hepatoma-targeting delivery of doxorubicin (DOX). A series of PMgDP copolymers were synthesized though two-step RAFT copolymerization followed by acid-induced acetal deprotection reaction. Their well-defined chemical structures and compositions were characterized by 1H NMR and gel permeation chromatography. Nano-sized, non-crosslinked PMgDP NPs (PMgDP NC NPs) with sizes of less than 25 nm in aqueous solution were self-assembled via the solvent exchange method, and PMgDP CC NPs were readily prepared in the presence of dithiothreitol. The drug-loading content of PMgDP CC NPs was up to 15.8% and its entrapment efficiency was 89.0%. In normal physiological conditions, 11.6% of DOX was released from DOX-loaded PMgDP CC NPs at 25 h, whereas in analogous intracellular microenvironment, 95.5% was released at 11 h owing to the acid-induced protonation of tertiary amine and reductive cleavage of disulfide bond in the hydrophobic core. In a cellular uptake study, FA and GAL-mediated, active, dual-targeted DOX-loaded FA-PMgDP CC NPs showed a 3.54-fold increase in cellular uptake efficiency to HepG2 cells compared to that of shown by single GAL-targeted, DOX-loaded PMgDP NC NPs. Results of in vitro cytotoxicity study showed that blank FA-PMgDP CC NPs exhibited good biocompatibility, whereas dual-targeting DOX-loaded FA-PMgDP CC NPs increased cell apoptosis. Therefore, the above results indicated that the well-constructed FA-PMgDP CC NPs with multi-synergistic effect may serve as new nanocarriers in the field of precise hepatoma-targeting drug delivery.

Enzymatic PEG-Poly(amine-co-disulfide ester) Nanoparticles as pH- and Redox-Responsive Drug Nanocarriers for Efficient Antitumor Treatment.

We have designed and constructed novel multifunctional nanoparticle drug-delivery systems that are stable under physiological conditions and responsive to tumor-relevant pH and intracellular reduction potential. The nanoparticles were fabricated from enzymatically synthesized poly(ethylene glycol) (PEG)-poly(ω-pentadecalactone-co-N-methyldiethyleneamine-co-3,3'-dithiodipropionate) (PEG-PPMD) and PEG-poly(ε-caprolactone-co-N-methyldiethyleneamine-co-3,3'-dithiodipropionate) (PEG-PCMD) block copolymers via self-assembly processes in aqueous solution. At acidic pH and in the presence of a reductant (e.g., d,l-dithiothreitol or glutathione), the nanosized micelle particles rapidly swell and disintegrate due to the protonation of amino groups and reductive cleavage of disulfide bonds in the micelle cores. Consistently, docetaxel (DTX)-loaded PEG-PPMD and PEG-PCMD micelles can be triggered synergistically by acidic endosomal pH and a high intracellular reduction potential to rapidly release the drug for efficient killing of cancer cells. The drug formulations based on PEG-PPMD and PEG-PCMD copolymers exhibited a substantially higher potency than free DTX in inhibiting tumor growth in mice, whereas their therapeutic effects on important organ tissues were minimal. These results demonstrate that PEG-PPMD and PEG-PCMD nanoparticles have a great potential to serve as site-specific, controlled drug-delivery vehicles for safe and efficient antitumor treatment.

Two New Devices for Identifying Electrochemical Reaction Intermediates with Desorption Electrospray Ionization Mass Spectrometry.

Desorption electrospray ionization mass spectrometry (DESI-MS) previously has been used to capture and identify transient intermediates in electrochemical redox reactions on a platinum-covered rotating waterwheel. We present here two different setups that use a flat surface with porous carbon tape as the working electrode, where analyte-containing microdroplets from the DESI probe contacted with electrolyte supplied onto the surface. One setup had the conducting carbon tape in the form of a grooved inclined plane; the other one was in the form of a flat plane that had the conducting carbon tape as its front surface. Both these setups, which were relatively robust and easy to operate, overcame interference from the electrospray sheath gas that disturbs and dries the flowing electrolyte. By using the inclined-plane device, we observed radical cations and dimer species generated in the electrochemical oxidation of triphenylamine, diimine and imine alcohol in the electrochemical oxidation of uric acid, and the reductive cleavage of disulfide bonds in glutathione disulfide. By using the device with the flat carbon tape, we detected nitrenium ions generated in the electrochemical oxidation of N,N'-dimethyoxydiphenylamine and di-p-tolylamine. Our experience suggests that the flat porous carbon tape surface might be preferable over the inclined plane because of its ease of setup.

Environmental biodegradation control of polymers by cleavage of disulfide bonds

Ideal biodegradable polymers have high durability during use and high degradability in the natural environment it enters after use. A trigger system that uses external stimuli to change the chemical properties of a polymer or directly degrade the polymer to low molecular weight compounds is suitable for controlling the biodegradability of a polymer. In this study, we adopted the reductive cleavage of disulfide bonds as a trigger to control the biodegradability of polymers. We synthesized polyesters with disulfide bonds and demonstrated that the environmental biodegradability of these polymers could be triggered by cleavage of the disulfide bonds in a reductive environment.

Selective Enrichment of Cysteine-Containing Phosphopeptides for Subphosphoproteome Analysis.

Among the natural amino acids, cysteine is unique since it can form a disulfide bond through oxidation and reduction of sulfhydryl and thus plays a pervasive role in modulation of proteins activities and structures. Crosstalk between phosphorylation and other post-translational modifications has become a recurrent theme in cell signaling regulation. However, the crosstalk between the phosphorylation and the formation and reductive cleavage of disulfide bond has not been investigated so far. To facilitate the study of this crosstalk, it is important to explore the subset of phosphoproteome where phosphorylations are occurred near to cysteine in the protein sequences. In this study, we developed a straightforward sequential enrichment method by combining the thiol affinity chromatography with the immobilized titanium ion affinity chromatography to selectively enrich cysteine-containing phosphopeptides. The high specificity and high sensitivity of this method were demonstrated by analyzing the samples of Jurkat cells. This "divide and conquer" strategy by specific analysis of a subphosphoproteome enables identification of more low abundant phosphosites than the conventional global phosphoproteome approach. Interestingly, amino acid residues surrounding the identified phosphosites were enriched with buried residues (L, V, A, C) while depleted with exposed residues (D, E, R, K). Also, the phosphosites identified by this approach showed a dramatic decrease in locating in disorder regions compared to that identified by conventional global phosphoproteome. Further analysis showed that more proline directed kinases and fewer acidophilic kinases were responsible for the phosphorylation sites of this subphosphoproteome.

Tris(3-hydroxypropyl)phosphine (THPP): A mild, air-stable reagent for the rapid, reductive cleavage of small-molecule disulfides.

Tris(3-hydroxypropyl)phosphine (THPP) is demonstrated to be a versatile, water-soluble and air-stable reducing agent, allowing for the rapid, irreversible reductive cleavage of disulfide bonds in both aqueous and buffered aqueous-organic media. The reagent shows exceptional stability at biological pH under which condition it permits the rapid reduction of a wide range of differentially functionalized small-molecule disulfides.

Cancer wars: significance of protein unfolding in cancer and its inhibition with natural amphiphilic substances.

OPINION article Front. Oncol., 11 July 2014 | https://doi.org/10.3389/fonc.2014.00183

Intramolecular Electron Transfer in Bipyridinium Disulfides

Reductive cleavage of disulfide bonds is an important step in many biological and chemical processes. Whether cleavage occurs stepwise or concertedly with electron transfer is of interest. Also of interest is whether the disulfide bond is reduced directly by intermolecular electron transfer from an external reducing agent or mediated intramolecularly by internal electron transfer from another redox-active moiety elsewhere within the molecule. The electrochemical reductions of 4,4'-bipyridyl-3,3'-disulfide (1) and the di-N-methylated derivative (2(2+)) have been studied in acetonitrile. Simulations of the cyclic voltammograms in combination with DFT (density functional theory) computations provide a consistent model of the reductive processes. Compound 1 undergoes reduction directly at the disulfide moiety with a substantially more negative potential for the first electron than for the second electron, resulting in an overall two-electron reduction and rapid cleavage of the S-S bond to form the dithiolate. In contrast, compound 2(2+) is reduced at less negative potential than 1 and at the dimethyl bipyridinium moiety rather than at the disulfide moiety. Most interesting, the second reduction of the bipyridinium moiety results in a fast and reversible intramolecular two-electron transfer to reduce the disulfide moiety and form the dithiolate. Thus, the redox-active bipyridinium moiety provides a low energy pathway for reductive cleavage of the S-S bond that avoids the highly negative potential for the first direct electron reduction. Following the intramolecular two-electron transfer and cleavage of the S-S bond the bipyridinium undergoes two additional reversible reductions at more negative potentials.

Self-Assembled Stimuli-Responsive Polyrotaxane Core–Shell Particles

Thermodynamically assembled core-shell nanocarriers are potential candidates for drug delivery applications due to their submicrometer size and the ability to load drugs into their hydrophobic core. Herein, we describe the formation of core-shell particles that consist of noncovalent polymers, that is, polyrotaxanes (PRXs), that form an α-cyclodextrin (αCD) core surrounded by a corona of low-fouling poly(ethylene glycol) (PEG). The PRX core-shell particles are able to sequester small organic molecules, such as pyrene and calcein, releasing these small molecules during degradation. The small, cellular peptide, glutathione, was used to degrade the particles through the reductive cleavage of disulfide bonds that stabilize the individual PRX polymers. Cleavage of a single bond allows for the degradation of the supramolecular-polymer, making these PRX core-shell particles highly responsive. Furthermore, these particles demonstrate negligible cytotoxicity in mammalian cells, making them promising carriers for future drug delivery research.

Acid-Denatured Green Fluorescent Protein (GFP) as Model Substrate to Study the Chaperone Activity of Protein Disulfide Isomerase

Green fluorescent protein (GFP) has been widely used in several molecular and cellular biology applications, since it is remarkably stable in vitro and in vivo. Interestingly, native GFP is resistant to the most common chemical denaturants; however, a low fluorescence signal has been observed after acid-induced denaturation. Furthermore, this acid-denatured GFP has been used as substrate in studies of the folding activity of some bacterial chaperones and other chaperone-like molecules. Protein disulfide isomerase enzymes, a family of eukaryotic oxidoreductases that catalyze the oxidation and isomerization of disulfide bonds in nascent polypeptides, play a key role in protein folding and it could display chaperone activity. However, contrasting results have been reported using different proteins as model substrates. Here, we report the further application of GFP as a model substrate to study the chaperone activity of protein disulfide isomerase (PDI) enzymes. Since refolding of acid-denatured GFP can be easily and directly monitored, a simple micro-assay was used to study the effect of the molecular participants in protein refolding assisted by PDI. Additionally, the effect of a well-known inhibitor of PDI chaperone activity was also analyzed. Because of the diversity their functional activities, PDI enzymes are potentially interesting drug targets. Since PDI may be implicated in the protection of cells against ER stress, including cancer cells, inhibitors of PDI might be able to enhance the efficacy of cancer chemotherapy; furthermore, it has been demonstrated that blocking the reductive cleavage of disulfide bonds of proteins associated with the cell surface markedly reduces the infectivity of the human immunodeficiency virus. Although several high-throughput screening (HTS) assays to test PDI reductase activity have been described, we report here a novel and simple micro-assay to test the chaperone activity of PDI enzymes, which is amenable for HTS of PDI inhibitors.

Discovery of a Small Molecule PDI Inhibitor That Inhibits Reduction of HIV-1 Envelope Glycoprotein gp120

Protein disulfide isomerase (PDI) is a promiscuous protein with multifunctional properties. PDI mediates proper protein folding by oxidation or isomerization and disrupts disulfide bonds by reduction. The entry of HIV-1 into cells is facilitated by the PDI-catalyzed reductive cleavage of disulfide bonds in gp120. PDI is regarded as a potential drug target because of its reduction activity. We screened a chemical library of natural products for PDI-specific inhibitors in a high-throughput fashion and identified the natural compound juniferdin as the most potent inhibitor of PDI. Derivatives of juniferdin were synthesized, with compound 13 showing inhibitory activities comparable to those of juniferdin but reduced cytotoxicity. Both juniferdin and compound 13 inhibited PDI reductase activity in a dose-dependent manner, with IC(50) values of 156 and 167 nM, respectively. Our results also indicated that juniferdin and compound 13 exert their inhibitory activities specifically on PDI but do not significantly inhibit homologues of this protein family. Moreover, we found that both compounds can inhibit PDI-mediated reduction of HIV-1 envelope glycoprotein gp120.

Snap-Top Nanocarriers

An approach to the design and fabrication of mechanized mesoporous silica nanoparticles is demonstrated at the proof of principle level. It relies on the reductive cleavage of disulfide bonds within an integrated nanosystem, wherein surface-bound rotaxanes incorporate disulfide bonds in their stalks, which are encircled by cucurbit[6]uril or alpha-cyclodextrin rings, until reductive chemistry is performed, resulting in the snapping of the stalks of the rotaxanes, leading to cargo release from the inside of the nanoparticles.

Online Coupling of Electrochemical Reactions with Liquid Sample Desorption Electrospray Ionization-Mass Spectrometry

The combination of electrochemistry (EC) and mass spectrometry (MS) is a powerful analytical tool to study redox reactions. This work reports the online coupling of a thin-layer electrochemical flow cell with liquid sample desorption electrospray ionization mass spectrometry (DESI-MS) and its applications in investigating various electrochemical reactions of biological molecules such as oxidative formation and reductive cleavage of disulfide bonds and online derivatization of peptides/proteins. As a result of the direct sampling nature of DESI, several useful features of such a coupling have been found, including simple instrumentation, fast response time (e.g., 3.6 s in the case of dopamine oxidation), freedom to choose a favorable ionization mode of DESI or traditional electrolysis solvent systems, and the absence of background signal possibly resulting from ionization when the cell is off (e.g., in the case of dopamine oxidation). More importantly, with the use of this new coupling apparatus, three disulfide bonds of insulin were fully cleaved by electrolytic reduction and both the A and B chains of the protein were successfully detected online by DESI-MS. In addition, online tagging of free cysteine residues of peptides/proteins employing electrogenerated dopamine o-quinone can be performed. These revealed characteristics of the coupling along with examined electrochemical reactions suggest that EC/DESI-MS has good potential in bioanalysis.

Synthesis of Staudinger-type Molecular Probe for Catch-and-release Purification of the Binding Protein for Potassium Isolespedezate, a Leaf-closing Substance of Leguminous Plant

Abstract We synthesized azide-containing photoaffinity probe 1 based on the structure of potassium isolespedezate. This probe can be used for catch-and-release-mechanism purification of binding protein for 1: photo-crosslinking with 1 gave azide-labeled receptor which can be captured by phosphane-linked gel matrix by the Staudinger ligation. After washing the gel, the caught binding protein can be released by the reductive cleavage of disulfide bond in 1. This process can be used as a convenient method for the purification of binding protein for bioactive natural product.

Degradable gene carriers based on oligomerized polyamines

The focus of this work was to develop potentially biodegradable, polycationic gene carriers possessing high efficiency for gene delivery and being essentially non-toxic. A library of 37 soluble polycations was synthesized by oligomerization of low molecular weight oligoamines with three different crosslinkers, dithiobis-succinimidyl proprionate, dimethyl dithiobis-propionamidate, and hexanediol diacrylate. The types of oligoamine and crosslinker influenced biophysical properties such as DNA binding, hemolytic and endosomolytic membrane activity, transfection efficiency and cytotoxicity of the gene carrier. Degradability of polymers based on reductive cleavage of disulfide bonds or ester hydrolysis was demonstrated. Within the library, oligoethylenimine (800 Da)-based polymers showed the highest gene transfer efficiencies and exceeded the golden standard linear polyethylenimine (22 kDa) in terms of activity/toxicity profile.

Impact of Reductive Cleavage of an Intramolecular Disulfide Bond Containing Cationic Gemini Surfactant in Monolayers and Bilayers

The properties of a novel disulfide-bond-containing gemini surfactant bis[N,N-dimethyl-N-hexadecyl-N-(2-mercaptoethyl)ammonium bromide] disulfide (DSP) were studied using a Langmuir balance, supported monolayers, differential scanning calorimetry, giant vesicles, and LUVs. In 150 mM NaCl the cmc for DSP was 7.5 microM whereas that of the monomer N,N-dimethyl-N-hexadecyl-N-(2-mercaptoethyl)ammonium bromide (MSP) was 12.1 microM. Both surfactants exhibited single endotherms upon DSC, with peak temperatures Tm at 21.7 and 20.1 degrees C for DSP and MSP, respectively. The endotherm for MSP was significantly broader indicating less cooperative melting. Both in monolayers and in vesicles reductive cleavage of the disulfide bond of DSP could be obtained by glutathione (GSH). For Langmuir films of DSP the addition of GSH into the subphase led to a decrease in surface pressure pi as well as surface dipole potential psi. Although the cleavage by GSH was significantly slower in the presence of a charge saturating concentration of DNA, it did not prevent the reaction. The resulting monomers detached from supported monolayers, leading to loss of affinity of the surface for DNA. Disruption of giant vesicles containing DSP within approximately 30 s following a local injection of GSH was observed, revealing membrane destabilization.

1106. Development and Testing of Ternary Peptide Copolymerized Gene Delivery Systems

In a previous study we reported the biodistribution, hepatocyte targeting and gene transfer efficiency of DNA condensates prepared by template polymerization of sulfhydryl cross-linking peptides to form a copolymer composed of polyethylene glycol (PEG)-peptide and glycopeptide 1. In the present study, we demonstrate a significant advancement of this concept through the generation of ternary peptide copolymers composed of a sulfhydryl cross-linking melittin fusogenic peptide, a PEG-peptide and a glycopeptide. We also demonstrate a means to prepare ternary peptide polymers of precise composition without the necessity of DNA template polymerization. Purified ternary peptide copolymers (TPC) were characterized for peptide monomer composition by RP-HPLC following reduction. The molecular weight of TPCs were estimated from a ladder of bands revealed by SDS-PAGE. TPCs were optimized to form small DNA condensates that target to liver hepatocytes in mice via asialoglycoprotein recognition of the glycopeptide. Once internalized TPCs undergo reductive cleavage of disulfide bonds to trigger the release of melittin which functions to lyse endosomes and facilitate DNA release into the cytosol. To prove this hypothesis in vivo, we have analyzed TPC/DNA condensate mediated SEAP expression in mice following i.v. dosing. The results indicate a relationship between the level of gene expression and the amount of melittin delivered to hepatocytes. This new delivery system, based on a pre-polymerized sulfhydryl cross-linked PEG-peptides, glycopeptides and melittin, can circulate in mice, target hepatocytes and trigger the release of a fusogenic peptide inside the target cell.