Reversible Disulfide Bond Research Articles

Reversible Disulfide Bond Cross-Links as Tunable Levers of Phase Separation in Designer Biomolecular Condensates.

Biomolecular condensates (BCs) are membraneless hubs enriched with proteins and nucleic acids that have emerged as important players in many cellular functions. Uncovering the sequence determinants of proteins for phase separation is essential in understanding the biophysical and biochemical properties of BCs. Despite significant discoveries in the past decade, the role of cysteine residues in BC formation and dissolution has remained unknown. Here, to uncover the involvement of disulfide cross-links and their redox sensitivity in BCs, we designed a "stickers and spacers" model of phase-separating peptides interspersed with cysteines. Through biophysical investigations, we learned that cysteines promote liquid-liquid phase separation in oxidizing conditions and perpetuate liquid condensates through disulfide cross-links, which can be reversibly tuned with redox chemistry. By varying the composition of cysteines, subtle but distinct changes in the viscoelastic behavior of the condensates were observed. Empirically, we conclude that cysteines function neither as stickers nor spacers but as covalent nodes to lower the effective concentrations for sticker interactions and inhibit system-spanning percolation networks. Together, we unmask the possible role of cysteines in the formation of biomolecular condensates and their potential use as tunable covalent cross-linkers in developing redox-sensitive viscoelastic materials.

Reversible disulfide bond crosslinks as tunable levers of phase separation in designer biomolecular condensates.

Biomolecular condensates (BCs) are membraneless hubs enriched in proteins and nucleic acids that have become important players in many cellular functions. Uncovering the sequence determinants of proteins for phase separation is important in understanding the biophysical and biochemical properties of BCs. Despite significant discoveries in the last decade, the role of cysteine residues in BC formation and dissolution has remained unknown. Here, to determine the involvement of disulfide crosslinks and their redox sensitivity in BCs, we designed a 'stickers and spacers' model of phase-separating peptides interspersed with cysteines. Through biophysical investigations, we learned that cysteines promote liquid-liquid phase separation in oxidizing conditions and perpetuate liquid condensates through disulfide crosslinks, which can be reversibly tuned with redox chemistry. By varying the composition of cysteines, subtle but distinct changes in the viscoelastic behavior of the condensates were observed. Empirically, we conclude that cysteines are neither stickers nor spacers but function as covalent nodes to lower the effective concentrations for sticker interactions and inhibit system-spanning percolation networks. Together, we unmask the role of cysteines in protein phase behavior and the potential to develop tunable, redox-sensitive viscoelastic materials.

Synthesis of PDMS Chain Structure with Introduced Dynamic Covalent Bonding for High‐Performance Rehealable Tactile Sensor Application

AbstractIn addressing the increasing demand for wearable sensing systems, the performance and lifespan of such devices must be improved by enhancing their sensitivity and healing capabilities. The present work introduces an innovative method for synthesizing a healable disulfide bond contained in a polydimethylsiloxane network (PDMS−SS) that incorporates ionic salts, which is designed to serve as a highly effective dielectric layer for capacitive tactile sensors. Within the polymer network structure, the cross‐linking agent pentaerythritol tetrakis 3‐mercaptopropionate (PTKPM) forms reversible disulfide bonds while simultaneously increasing polymer softness and the dielectric constant. The incorporation of dioctyl sulfosuccinate sodium salt (DOSS) significantly improves the capacitance and sensing properties by forming an electrical double‐layer through interactions between the electrode charge and salt ions at the contact interface. The developed polymer material‐based tactile sensor shows a strong response signal at low pressure (0.1 kPa) and maintains high sensitivity (0.175 kPa−1) over a wide pressure range (0.1–10 kPa). It also maintains the same sensitivity over 10 000 repeated applications of external pressure and is easily self‐healed against mechanical deformation due to the dynamic disulfide covalent bonding, restoring ≈95% of its detection capacity.

Light- and heat-induced shape deformation polyurethane actuators that combine self-healing capabilities

Materials commonly experience physical damage during regular usage, and the implementation of self-healing materials can effectively repair this damage, thereby prolonging the lifespan of the materials. We have successfully synthesized a polyurethane material, S-PU, by introducing azobenzene and reversible disulfide bonds through co-polymerization. The S-PU film not only exhibits light-induced bending, heat-induced recovery ability, but also good self-healing properties. The disulfide bonds in S-PU accelerate the dynamic exchange as the polymer chains flow under heated conditions, enabling self-repairing without affecting the mechanical properties of the material. S-PU is a self-repairing material that can repair damage in a variety of ways. By combining dual-stimulus response characteristics with self-healing properties, this work provides a new idea for self-healing materials and opens more directions for the practical application of the material.

Engineering bio-brick protein scaffolds for organizing enzyme assemblies.

Enzyme scaffolding is an emerging approach for enhancing the catalytic efficiency of multi-enzymatic cascades by controlling their spatial organization and stoichiometry. This study introduces a novel family of engineered SCAffolding Bricks, named SCABs, utilizing the consensus tetratricopeptide repeat (CTPR) domain for organized multi-enzyme systems. Two SCAB systems are developed, one employing head-to-tail interactions with reversible covalent disulfide bonds, the other relying on non-covalent metal-driven assembly via engineered metal coordinating interfaces. Enzymes are directly fused to SCAB modules, triggering assembly in a non-reducing environment or by metal presence. A proof-of-concept with formate dehydrogenase (FDH) and L-alanine dehydrogenase (AlaDH) shows enhanced specific productivity by 3.6-fold compared to free enzymes, with the covalent stapling outperforming the metal-driven assembly. This enhancement likely stems from higher-order supramolecular assembly and improved NADH cofactor regeneration, resulting in more efficient cascades. This study underscores the potential of protein engineering to tailor scaffolds, leveraging supramolecular spatial-organizing tools, for more efficient enzymatic cascade reactions.

Co-ordinated polyhedral oligomeric silsesquioxane and cyclodextrin on polyurethane elastomer with network topology for simultaneously improved fatigue-resistant and self-healable properties

Long-term usage can induce cracks on the surface or inside the polyurethane (PU) and cause fatigue damage, thus reducing the performance and lifetime of PU. It is therefore of great practical importance to impart fatigue resistance and self-healing ability to PU. However, the conventional covalent cross-linked network design with irreversible and rigid properties limits their fatigue resistance. Here, we have designed a highly ductile, fatigue-resistant and self-healing PU enabled by the synergistic effect of covalent network topology, dynamic reversible disulfide bonds and multiple hydrogen bond stacking. This judicious design yields excellent mechanical properties such as high tensile strength (7.38 MPa), high elongation at break (1159%) and high toughness (42.91 MJ·m−3). Notably, the PU successfully combines fatigue resistance with self-healing behavior. During 1000 cycles of stretch-release processes at 100% strain, the stress retention of the PU almost unchanged. Moreover, the PU achieves a high self-healing efficiency of 98% after self-healing at 80 ℃ for 2 h. The above-mentioned superiority enables the PU-based strain sensors to have a timely and stable output signal as well as excellent self-healing performance. Such a judicious strategy will facilitate the practical application of durable flexible electronics.

Itaconic acid-based sustainable polyurethane covalent adaptable networks with robust mechanical, reshaping and UV-resistant properties based on reversible disulfide bond

Thermoset polymer materials are widely used in various fields due to their excellent performance brought by their permanently cross-linked structures. However, their inability to be recycled also leads to a serious waste of resources. The emergence of covalent adaptable networks (CANs) has solved the problem perfectly that thermoset materials are difficult to recycle. Meanwhile, with the increasing concern for resources and the environment, bio-based materials have sparked a research boom. Itaconic acid is a biomass feedstock with great prospects for development. In this study, itaconic acid, 1,6-hexanediol, 6-mercapto-1-hexanol, isocyanate, and 4,4′-dithiodiphenylamine were used as raw materials. Itaconic acid-based polyols were first synthesized by thiol-ene click reaction, and a series of itaconic acid-based polyurethane (PU) materials containing dynamic covalent networks were synthesized by varying the ratios between the amino and hydroxyl groups. The obtained material has good mechanical properties with a maximum tensile strength of 31.5 MPa and a modulus of 717 MPa. The presence of disulfide bonds allows the material to be recycled by remodeling, and the recovery efficiency of tensile strength after three remodeling cycles is 85.1 %. The material also has excellent solvent resistance and UV-blocking resistance. In conclusion, this work provides possible ideas for the high-value utilization of itaconic acid in polyurethanes.

Preparation of Oxidized and Reduced PTP4A1 for Structural and Functional Studies.

The formation of a reversible disulfide bond between the catalytic cysteine and a spatially neighboring cysteine (backdoor) in protein tyrosine phosphatases (PTPs) serves as a critical regulatory mechanism for maintaining the activity of protein tyrosine phosphatases. The failure of such protection results in the formation of irreversibly oxidized cysteines into sulfonic acid in a highly oxidative cellular environment in the presence of free radicals. Hence, it is important to develop methods to interconvert PTPs into reduced and oxidized forms to understand their catalytic function in vitro. Protein tyrosine phosphatase 4A type 1 (PTP4A1), a dual-specificity phosphatase, is catalytically active in the reduced form. Unexpectedly, also its oxidized form performs a key biological function in systemic sclerosis (SSc) by forming a kinase-phosphatase complex with Src kinases. Thus, we developed simple and efficient protocols for producing oxidized and reduced PTP4A1 to elucidate their biological function, which can be extended to study other protein tyrosine phosphatases and other recombinantly produced proteins.

Photo-cured phase change energy storage material with photo-thermal conversion, self-cleaning and electromagnetic shielding performances via the lamellar structure strengthened by segment rearrangement of dynamic disulfide bond

At present, phase change materials (PCMs) with single function hardly meet the needs of advanced intelligent materials in practical applications, and the multifunction integration is the current trend. However, photo-cured multifunctional PCMs are hampered by insufficient transparency due to adding functional fillers, such as carbon and metal materials. The novel strategy is necessary to overcome this limitation. Here, a photo-cured multifunctional PCM is prepared by using the design of a lamellar structure composing the photo-cured phase change polymer layer and the functional fillers layer. The curing of the phase change polymer is realized by the photo-induced "thiol-ene" click reaction, and reversible dynamic disulfide bonds are introduced into the PCM, which not only gives the phase change crosslinked network reprocessability, but also strengthens the interface layer by the chain rearrangement to form a stable composite structure. The carboxylated multiwalled carbon nanotubes (CCNTs) and silver nanowires (AgNWs), as functional fillers, give the PCM photo-thermal conversion, self-cleaning and electromagnetic shielding (EMI SE) performances. Its phase change latent heat and photo-thermal conversion can reach 105.2 J/g and 78.5%, and the water contact angle is 142° with self-cleaning performance. In addition, due to the dense and well-developed conductive path formed by AgNWs layer on the PCM surface, the EMI SE effect can reach 39 dB with only 6.3% (in mass) filler content and 7.2% phase change latent heat loss. As far as we know, this is the first report about photo-cured PCMs with self-cleaning, photo-thermal conversion and EMI SE performances.

Dynamic reversible disulfide bonds hydrogel of thiolated galactoglucomannan/cellulose nanofibril with self-healing property for protein release

In the context of sustainability transition to effectively utilize renewable biopolymers in building functional materials, we report a dynamic reversible nanocomposite hydrogel via thiolated galactoglucomannan (GGMSH) and TEMPO-oxidized cellulose nanofibrils (T-CNF) by deploying a UV-triggered thiol-disulfide exchange reaction. By adjusting the compositional content of GGMSH, the viscoelastic properties of the hydrogel precursors are tuneable and the crosslinking degree of disulfide bonds in these hydrogels dictates their mechanical properties upon UV irradiation. The nanocomposite hydrogels of GGMSH/T-CNF demonstrate robust self-healing properties, attributed to the dynamically reversible disulfide bonds and strong hydrogen bonds between T-CNF and GGMSH. For the hydrogel system of GGMSH/T-CNF/bovine serum albumin (BSA), the swelling behaviour of nanocomposite hydrogels largely dominated the release of BSA out of the hydrogels, suppressing the effect of redox-responsive stimuli with the addition of glutathione. Still, the cytotoxicity test proved a low cytotoxicity of the nanocomposite hydrogel and provided promising reference value to exploit this class of natural polymer-based hydrogel systems in biomedical applications.

Self-healing polyurethane composite films loaded with Ni@C nanoparticles

Widely employed as polymers, polyurethanes also struggle to strike a balance between mechanical and self-healing qualities. Extrinsic self-healing can readily result in the production of material defects and stress concentration, which can result in the loss of mechanical property. In this study, self-healing and mechanical properties were combined to create a self-healing polyurethane nanocomposite film (PUHN) with good fatigue resistance. Reversible hydrogen and disulfide bonds were introduced to the polyurethane film, meanwhile, carbon-coated nickel nanoparticles were dispersed into the matrix as fillers during the early stage of polymerization. The results showed that PUHN combines outstanding mechanical properties with excellent self-healing properties, while the tensile strength of PUHN was increased by 38 % to 2.32 MPa due to the small-size effect caused by the introduction of nanoparticles. The introduction of reversible disulfide bonding and the presence of abundant hydrogen bonding give PUHN excellent self-healing properties, which can reach 91.2 % self-healing efficiency after 3 h in an oven at 80℃. Meanwhile, the fatigue resistance of the composite material also shows considerable application potential for use in packaging.

Structural Insight into the Catalytic Mechanisms of an L-Sorbosone Dehydrogenase.

L-Sorbosone dehydrogenase (SNDH) is a key enzyme involved in the biosynthesis of 2-keto-L-gulonic acid , which is a direct precursor for the industrial scale production of vitamin C. Elucidating the structure and the catalytic mechanism is essential for improving SNDH performance. By solving the crystal structures of SNDH from Gluconobacter oxydans WSH-004, a reversible disulfide bond between Cys295 and the catalytic Cys296 residues is discovered. It allowed SNDH to switch between oxidation and reduction states, resulting in opening or closing the substrate pocket. Moreover, the Cys296 is found to affect the NADP+ binding pose with SNDH. Combining the in vitro biochemical and site-directed mutagenesis studies, the redox-based dynamic regulation and the catalytic mechanisms of SNDH are proposed. Moreover, the mutants with enhanced activity are obtained by extending substrate channels. This study not only elucidates the physiological control mechanism of the dehydrogenase, but also provides a theoretical basis for engineering similar enzymes.

Self-healing icephobic coating with UV shielding and removability based on biobased epoxy and reversible disulfide bonds

Icephobic coatings have attracted wide attention due to low energy consumption, low cost, and high efficiency. However, the icephobic coating is vulnerable to external damage due to long-term exposure, which can result in icephobic properties loss and limit its industrial application. Herein, the novel amphiphilic epoxy self-healing icephobic coating was designed by a compound with multiple hydrophilic groups, polydimethylsiloxane (PDMS) with hydrophobic groups and 4, 4′-diaminodiphenyldisulfide (APD) with reversible bonds. Moreover, considering the resource crisis, the biobased epoxy (GTE) was selected as the compound containing hydrophilic groups. In this study, the GTE will form hydrogen bonds with water molecules to achieve an anti-icing effect, while PDMS mainly play a deicing effect due to low surface energy. Due to the reasonable design, the icephobic coating showed good comprehensive icephobic properties: a 12.5-fold increase in icing delay time (802 s) and a 6.6-fold decrease in ice adhesion strength (32.6 kPa) compared with bare aluminum. Furthermore, the crystallization temperature of water was reduced by about 11 °C. More importantly, the APD with reversible disulfide bonds provides the icephobic coating with self-healing performance, removability, and excellent UV shielding performance. The coating provides a new idea for the preparation of sustainable and durable coatings with comprehensive icephobic performance.

Bioengineered Bovine Papillomavirus L1 Protein Virus-like Particle (VLP) Vaccines for Enhanced Induction of CD8 T Cell Responses through Cross-Priming.

Safe and effective T cell vaccines are needed for the treatment or prevention of cancers as well as infectious agents where vaccines for neutralizing antibodies have performed poorly. Recent research highlights an important role for tissue-resident memory T cells (TRM cells) in protective immunity and the role of a subset of dendritic cells that are capable of cross-priming for the induction of TRM cells. However, efficient vaccine technologies that operate through cross-priming and induce robust CD8+ T cell responses are lacking. We developed a platform technology by genetically engineering the bovine papillomavirus L1 major capsid protein to insert a polyglutamic acid/cysteine motif in place of wild-type amino acids in the HI loop. Virus-like particles (VLPs) are formed by self-assembly in insect cells infected with a recombinant baculovirus. Polyarginine/cysteine-tagged antigens are linked to the VLP by a reversible disulfide bond. The VLP possesses self-adjuvanting properties due to the immunostimulatory activity of papillomavirus VLPs. Polyionic VLP vaccines induce robust CD8+ T cell responses in peripheral blood and tumor tissues. A prostate cancer polyionic VLP vaccine was more efficacious than other vaccines and immunotherapies for the treatment of prostate cancer in a physiologically relevant murine model and successfully treated more advanced diseases than the less efficacious technologies. The immunogenicity of polyionic VLP vaccines is dependent on particle size, reversible linkage of the antigen to the VLP, and an interferon type 1 and Toll-like receptor (TLR)3/7-dependent mechanism.

Biobased epoxidized natural rubber/sodium carboxymethyl cellulose composites with enhanced strength and healing ability

Conventional vulcanized rubbers cause a non-negligible waste of resources due to the formation of 3D irreversible covalently cross-linked networks. The introduction of reversible covalent bonds, such as reversible disulfide bonds, into the rubber network, is an available solution to the above problem. However, the mechanical properties of rubber with only reversible disulfide bonds cannot meet most practical applications. In this paper, a strengthened bio-based epoxidized natural rubber (ENR) composite reinforced by sodium carboxymethyl cellulose (SCMC) was prepared. SCMC forms a mass of hydrogen bonds between its hydroxyl groups and the hydrophilic groups of ENR chain, which gives the ENR/2,2′-Dithiodibenzoic acid (DTSA)/SCMC composites an enhanced mechanical performance. With 20 phr SCMC, the tensile strength of the composite increases from 3.0 to 10.4 MPa, which is almost 3.5 times that of the ENR/DTSA composite without SCMC. Simultaneously, DTSA covalently cross-linked ENR with the introduction of reversible disulfide bonds, which enables the cross-linked network to rearrange its topology at low temperatures and thus endows the ENR/DTSA/SCMC composites with healing properties. The ENR/DTSA/SCMC-10 composite has a considerable healing efficiency of about 96 % after healing at 80 °C for 12 h.

Light responsive self-healable carbon nanotube/polyurethane smart networks with precisely remote-controlled shape-changing properties

Smart materials can dynamically react to environmental stimuli and thus change at the micro or macro scale. However, when exposed to harsh conditions, damage can occur to them to varying degrees, thus affecting their performance and service life. In this study, a recyclable shape memory polyurethane material with self-healing properties was prepared using polycaprolactone (PCL) and polytetrahydrofuran diol (PTMG) as raw materials and isofuranone diisocyanate (IPDI) as a cross-linking agent. Dynamic cross-linking networks are constructed by introducing reversible disulfide bonds to enhance the self-healing and recyclable properties of the materials. Hydroxylated multiwalled carbon nanotubes (MWCNTs-OH), as photothermal particles, impart a remote response ability to the material, making the material temperature variable under near-infrared radiation (NIR). The shape memory recovery of CNT-PCL-PTMG can be triggered remotely and precisely controlled the irradiated NIR area. The results of tensile tests, scanning electron microscopy (SEM) and optical microscopy (OM) show that 3%CNT-5PCL-5PTMG can achieve efficient and rapid self-healing. Additionally, the synergistic effect of transesterification and the dynamic exchange of disulfide bonds gives materials reprocessability for recycling use. The material is promising as an alternative material for soft robotics and smart sensors.

Self‐Healing Photochromic Elastomer Composites for Wearable UV‐Sensors

AbstractPhotochromic materials have recently received strong interest for the development of wearable ultraviolet (UV) detection technologies because they do not require electronic components, resulting in systems and devices that change color upon irradiation. However, their implementation in wearable technology has lightweight, compliance, and durability (especially under mechanical stress) requirements that are limited by the materials’ properties. Here, a self‐healing photochromic elastomer composite (photoPUSH) consisting of phosphomolybdic acid (PMA) in a self‐healing polyurethane dynamic network with reversible disulfide bonds (PUSH) is presented. The unique properties of the dynamic polymer matrix enable multiple complementary functions in the UV‐sensing composite: i) photochromism via electron donor groups without requiring additional dopants, ii) stretchability and durability via elastomeric properties, iii) healing of extreme mechanical damage via dynamic bonds, and iv) multimaterial integration via adhesive properties. PhotoPUSH composites exhibit excellent durability, tunable sensing range, and no loss of performance under mechanical stress and severe damage, as well as in underwater environments (waterproof). Leveraging these properties, soft, portable, multimaterial photoPUSH‐based UV‐sensing devices are developed for applications in environmental monitoring, packaging, and healthcare wearable technology (including skin‐mounted, textile‐mounted, and wristband devices) in challenging environments and tunable to different skin types.

Liquid Metal‐Based Self‐Healable and Elastic Conductive Fiber in Complex Operating Conditions

Flexible conductive fibers are essential for wearable electronics and smart electronic textiles. However, in complex operating conditions, conductive fibers will inevitably fracture or damage. Herein, we have developed an elastic conductive self‐healable fiber (C‐SHF), of which the electrical and mechanical properties can efficiently heal in a wide operating range, including room temperature, underwater, and low temperature. This advantage can be owed to the combination of reversible covalent imine bond and disulfide bond, as well as the instantaneous self‐healing ability of liquid metal. The C‐SHF, with stretchability, conductivity stability, and universal self‐healing properties, can be used as an electrical signal transmission line at high strain and under different operating conditions. Besides, C‐SHF was assembled into a double‐layer capacitor structure to construct a self‐healable sensor, which can effectively respond to pressure as a wearable motion detector.

Biomimetic supramolecular polyurethane with sliding polyrotaxane and disulfide bonds for strain sensors with wide sensing range and self-healing capability.

To prolong the service life of flexible electronic materials, polymeric matrixes with excellent self-healing capability and integrated mechanical properties are highly desirable, but the balance between the self-healing capability and mechanical properties is a grand challenge. Here, polyrotaxanes as sliding crosslinkers and dynamic disulfide bonds are incorporated into the main chains of polyurethane (PU) via one-pot synthesis, which endows the PU with polydisperse hard/soft segments, high density of self-healing points and energy dissipation. Based on this judicious molecular design, the PU elastomers exhibit exceptional mechanical properties, such as high stretchability (1167% with a tensile strength of 3.49MPa), high fracture energy (20,775Jm-2) and high puncture energy (200.70mJ). Moreover, due to the presence of dynamic reversible hydrogen and disulfide bonds, the elastomer could achieve stress and strain repair efficiencies of 93.98% and 99.21% at 100 ℃ within 1h, respectively. The above-mentioned superiorities enable the bioinspired strain sensors to possess a large sensing range (∼596%), high sensitivity (∼79.98), short response time (∼128ms), along with excellent reliability and self-healing ability. Besides, the strain sensor exhibits remarkable recyclability and prominent reprocessability, which nicely solves the pollution by discarded electronics.

Bio-Based Healable 2K PU Textile Coating for Durable Applications.

A biobased healable 2K polyurethane (PU) coating incorporating a Schiff base was synthesized and applied as a thin coating on textiles. The Schiff base, made out of cystine and vanillin, contained reversible imine and disulfide bonds and was used as a chain extender in PU synthesis. The FT-IR analysis indicated the successful incorporation of the Schiff base in the PU backbone. Compared with control PU coatings, the healable bio-based PU coating with the Schiff base showed very good healing properties using heat as external stimuli: a healing recovery of 75% was obtained after applying a 2 N scratch and complete recovery of the resistance to hydrostatic pressure. SEM analysis revealed complete closure of the scratch after healing for 30 min at 90 °C. The healing properties are attributed to the synergy of the dual-dynamic metatheses of the imine and disulfide bonds.