We report here a Green method for the synthesis of fluorescent gold nanoclusters using dithiothreitol (DTT) as both a capping agent and reducing agent at 22 °C and pH 8. The physical and chemical properties of the synthesized AuNCs@DTT were studied by TEM and UV-vis absorption, fluorescence, and X-ray photoelectron spectroscopy. AuNCs@DTT recognizes cupric ions with high selectivity and sensitivity, which allows this material to act as a copper(II) sensor in aqueous solution. A linear relationship was observed between the fluorescence intensity of the DTT capped gold nanoclusters and the concentration of copper(II) ions, in the range of 0-60 ?M with a detection limit of 80 nM. The copper content in serum was also analyzed by using this copper sensor. It was shown that data obtained using the proposed method was comparable to values obtained by the traditional colorimetric method. This technique represents an alternative method for the determination of serum copper in clinical diagnosis especially for those laboratories which lack expensive analytical facilities.
To explore the disassembly mechanism of tobacco mosaic virus (TMV), a model system for virus study, during infection, we have used single-molecule force spectroscopy to mimic and follow the process of RNA disassembly from the protein coat of TMV by the replisome (molecular motor) in vivo, under different pH and Ca(2+) concentrations. Dynamic force spectroscopy revealed the unbinding free-energy landscapes as that at pH 4.7 the disassembly process is dominated by one free-energy barrier, whereas at pH 7.0 the process is dominated by one barrier and that there exists a second barrier. The additional free-energy barrier at longer distance has been attributed to the hindrance of disordered loops within the inner channel of TMV, and the biological function of those protein loops was discussed. The combination of pH increase and Ca(2+) concentration drop could weaken RNA-protein interactions so much that the molecular motor replisome would be able to pull and disassemble the rest of the genetic RNA from the protein coat in vivo. All these facts provide supporting evidence at the single-molecule level, to our knowledge for the first time, for the cotranslational disassembly mechanism during TMV infection under physiological conditions.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces cell death in various types of cancer cells but has little or no effects on normal cells. Unfortunately, not all cancer cells respond to TRAIL; therefore, TRAIL sensitizing agents are currently being explored. Here, we reported that 6-(4-N,N-dimethylaminophenyltelluro)-6-deoxy-?-cyclodextrin (DTCD), a cyclodextrin-derived diorganyl telluride which has been identified as an excellent inhibitor of thioredoxin reductase (TrxR), could sensitize TRAIL resistant human ovarian cancer cells to undergo apoptosis. In vitro, DTCD enhanced TRAIL-induced cytotoxicity in human ovarian cancer cells through up-regulation of DR5. Luciferase analysis and CHIP assays showed that DTCD increased DR5 promoter activity via Sp1 activation. Additionally, DTCD stimulated extracellular signal-regulated kinase (ERK) activation, while the ERK inhibitor PD98059 blocked DTCD-induced DR5 expression and suppressed binding of Sp1 to the DR5 promoter. We further demonstrated that DTCD could induce the release of ASK1 from its complex with Trx-1, and recovered its kinase activity. Meanwhile, suppression of ASK1 by RNA interference led to decreased ERK phosphorylation induced by DTCD. The underlying mechanisms reveal that Trx-1 is heavily oxidized in response to DTCD treatment, in accordance with the fact that DTCD could inhibit the activity of TrxR that reduces oxidized Trx-1. Moreover, using an A2780 xenograft model, DTCD plus TRAIL significantly inhibited the growth of tumor in vivo. Our results suggest that Trx/TrxR system inhibition may play a critical role in apoptosis by combined treatment with DTCD and TRAIL, and raise the possibility that their combination may be a promising strategy for ovarian carcinoma treatment.
In this article, interactions between Bacillus subtilis single-stranded DNA binding proteins (BsSSB) and single-stranded DNA (ssDNA) were systematically studied. The effect of different molar ratios between BsSSB and ssDNA on their binding modes was first investigated by electrophoretic mobility shift assays (EMSAs). It is found that a high molar ratio of BsSSB to ssDNA can produce BsSSB-ssDNA complexes formed in the mode of two proteins binding one 65-nt (nucleotide) ssDNA whereas a low molar ratio facilitates the formation of BsSSB-ssDNA complexes in the mode of one protein binding one 65-nt ssDNA. Furthermore, two binding modes are in dynamic equilibrium. The unbinding force of BsSSB-ssDNA complexes was measured quantitatively in solutions with different salt concentrations by using AFM-based single-molecule force spectroscopy (SMFS). Our results show that the unbinding force is about 10 pN higher at high salt concentration (0.5 M NaCl) than at low salt concentration (0.1 M NaCl) and the lifetime of BsSSB-ssDNA complexes at high salt concentration is twice as long as that at low salt concentration. These results indicate that more tightly packed BsSSB-ssDNA complexes can form at high salt (0.5 M NaCl) concentration. In addition, the results of EMSA show that ssDNA, which is bound to BsSSB, can dissociate from BsSSB in the presence of the cDNA strand, indicating the dynamic nature of BsSSB-ssDNA interactions.
Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits potent antitumour activity via membrane receptors on cancer cells without deleterious side-effects for normal tissue. Unfortunately, like many other cancer types, breast cancer cells develop resistance to TRAIL; therefore, TRAIL-sensitising agents are currently being explored. In this study, we report that seleno-cyclodextrin (2-selenium-bridged ?-cyclodextrin, 2-SeCD), a seleno-organic compound with glutathione peroxidase (GPx)-mimetic activity, sensitises TRAIL-resistant human breast cancer cells and xenograft tumours to undergo apoptosis. In vitro, 2-SeCD reduces the viability of cancer cells by inducing cell cycle arrest in G(2)/M phase. Furthermore, 2-SeCD efficiently sensitises MDA-MB-468 and T47D cells but not untransformed human mammary epithelial cells to TRAIL-mediated apoptosis, as evidenced by enhanced caspase activity and poly-ADP-ribose-polymerase (PARP) cleavage. From a mechanistic standpoint, we show that 2-SeCD induces the expression of TRAIL receptors DR5 but not DR4 on both mRNA and protein levels in a dose-dependent manner. Moreover, 2-SeCD treatment also suppresses TRAIL-induced nuclear factor-?B (NF-?B) pro-survival pathways by preventing cytosolic I?B? degradation and p65 nuclear translocation. Consequently, the combined administration suppresses anti-apoptotic proteins transcriptionally regulated by NF-?B. In vivo, 2-SeCD and TRAIL are well tolerated in mice, and their combination significantly inhibits the growth of MDA-MB-468 xenografts and promotes apoptosis. Up-regulation of DR5 and down-regulation of NF-?B by dual treatment were also observed in tumour tissues. Overall, 2-SeCD sensitises resistant breast cancer cells to TRAIL-based apoptosis in vitro and in vivo. These findings provide strong evidence for the therapeutic potential of this combination against breast cancers.
Reactive oxygen species (ROS) are involved in cell growth, differentiation, and death. Excessive amounts of ROS (e.g., O(2)(-), H(2)O(2), and HO) play a role in aging as well as in many human diseases. Superoxide dismutase (SOD) and glutathione peroxidase (GPx) are critical antioxidant enzymes in living organisms. SOD catalyzes the dismutation of O(2)(-) to H(2)O(2), and GPx catalyzes the reduction of H(2)O(2) and other harmful peroxides by glutathione (GSH). They not only function in catalytic processes but also protect each other, resulting in more efficient removal of ROS, protection of cells against injury, and maintenance of the normal metabolism of ROS. To imitate the synergism of SOD and GPx, a 65-mer peptide (65P), containing sequences that form the domains of the active center of SOD and the catalytic triad of GPx upon the incorporation of some metals, was designed on the basis of native enzyme structural models; 65P was expressed in the cysteine auxotrophic expression system to obtain Se-65P. Se-65P was converted into Se-CuZn-65P by incorporating Cu(2+) and Zn(2+). Se-CuZn-65P exhibited high SOD and GPx activities because it has a delicate dual-activity center. The synergism of the enzyme mimic was evaluated by using an in vitro model and a xanthine/xanthine oxidase/Fe(2+)-induced mitochondrial damage model system. We anticipate that the peptide enzyme mimic with synergism is promising for the treatment of human diseases and has potential applications in medicine as a potent antioxidant.
Enzymes, highly evolved machinery developed by nature, catalyse reactions with formidable efficiency and specificity under mild conditions. Considerable efforts have been devoted for several decades on the development of enzyme-like catalysts with tailored properties by rationally manipulating natural and artificially synthesized host molecules. One of the great challenges is to design artificial systems with catalytic efficiencies and specificities rivalling natural components. Although most of the designed artificial enzymes present mild rate promotion, the high efficiency and specificity rivalling natural ones by artificially designed system appears. In this tutorial review, we recount the methods and strategies of design and redesign of artificial selenoenzymes on synthesized and natural hosts, with emphasis on construction of the active sites of antioxidative glutathione peroxidase (GPx) by the concept of synergy between recognition and catalysis (66 references).
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits potent antitumor activity via membrane receptors on cancer cells without deleterious side effects for normal tissue. Unfortunately, breast cancer cells, as many other cancer types, develop resistance to TRAIL; therefore, TRAIL sensitizing agents are currently being explored. 2-Tellurium-bridged ?-cyclodextrin (2-TeCD) is a synthetic organotellurium compound, with both glutathione peroxidase-like catalytic ability and thioredoxin reductase inhibitor activity. In the present study, we reported that 2-TeCD sensitized TRAIL-resistant human breast cancer cells and xenograft tumors to undergo apoptosis. In vitro, 2-TeCD efficiently sensitized MDA-MB-468 and T47D cells, but not untransformed human mammary epithelial cells, to TRAIL-mediated apoptosis, as evidenced by enhanced caspase activity and poly (adenosine diphosphate-ribose) polymerase cleavage. From a mechanistic standpoint, we showed that 2-TeCD treatment of breast cancer cells significantly upregulated the messenger RNA and protein levels of TRAIL receptor, death receptor (DR) 5, in a transcription factor Sp1-dependent manner. 2-TeCD treatment also suppressed TRAIL-induced nuclear factor-?B (NF-?B) prosurvival pathways by preventing cytosolic I?B? degradation, as well as p65 nuclear translocation. Consequently, the combined administration suppressed anti-apoptotic molecules that are transcriptionally regulated by NF-?B. In vivo, 2-TeCD and TRAIL were well tolerated in mice and their combination significantly inhibited growth of MDA-MB-468 xenografts and promoted apoptosis. Upregulation of DR5 and downregulation of NF-?B by the dual treatment were also observed in tumor tissues. Overall, 2-TeCD sensitizes resistant breast cancer cells to TRAIL-based apoptosis in vitro and in vivo. These findings provide strong evidence for the therapeutic potential of this combination against breast cancers.
RNA-coat protein interactions in intact tobacco mosaic virus have been investigated for the first time directly on the single-molecule level by pulling the genetic RNA step by step out of the helical groove formed by its protein coat. The effects of pulling speed and pH on RNA-protein interactions are presented. In addition, the rebinding behavior of the detached RNA with the protein coat is discussed. Our results demonstrate the possibility of studying nucleic acid-protein interactions in more complicated systems using AFM-based single-molecule force spectroscopy.
The antioxidant enzymes, such as superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase contribute dominatingly to enhance cellular antioxidant defense against oxidative stress. They act cooperatively to scavenge reactive oxygen species, and not one of them can singlehandedly clear all forms of reactive oxygen species. On the basis of the structural understanding for these natural enzymes, many mimics with multifunctional activities had been obtained by chemical synthesis, biosynthesis, and protein fusion techniques. Some of them display remarkable antioxidant cooperative effect in living model which possess potential application in medicine as potent antioxidants. This review summarizes aspects of some multifunctional mimics which have been reported so far.
A convenient approach to synthesize patterned carbon nanotubes (CNTs) of three morphologies on printed substrates by combination of microcontact printing (microCP) and a plasma-enhanced chemical vapor deposition (PECVD) process is presented. Micelles of polystyrene-block-poly-(2-vinylpyridine) (PS-b-P2VP) in toluene were used as nanoreactors to fabricate FeCl3 in the core domains, and the complex solution was used as an ink to print films with polydimethylsiloxane (PDMS) stamps, different morphologies (porous, dots and stripes patterns) of the FeCl3-loaded micellar films were left onto silicon substrates after printed. After removing the polymer by thermal decomposition, the left iron oxide cluster arrays on the substrate were used as catalysts for the growth of CNTs by the process of PECVD, where the CNTs uniformly distributed on the substrates according to the morphologies of patterned catalysts arrays.
Single-stranded DNA binding proteins (SSB) interact with single-stranded DNA (ssDNA) specifically. Taking advantage of this character, we have employed Bacillus subtilis SSB protein to investigate the nature of force-induced conformation transition of double-stranded DNA (dsDNA) by using AFM-based single molecule force spectroscopy (SMFS) technique. Our results show that, when a dsDNA is stretched beyond its contour length, the dsDNA is partially melted, producing some ssDNA segments which can be captured by SSB proteins. We have also systematically investigated the effects of stretching length, waiting time, and salt concentration on the conformation transition of dsDNA and SSB-ssDNA interactions, respectively. Furthermore, the effect of proflavine, a DNA intercalator, on the SSB-DNA interactions has been investigated, and the results indicate that the proflavine-saturated dsDNA can be stabilized to the extent that the dsDNA will no longer melt into ssDNA under the mechanical force even up to 150 pN, and no SSB-DNA interactions are detectable.
A facile layer-by-layer (LbL) assembly method for the fabrication of matrix films capable of coloading and simultaneous release of oppositely charged molecules has been established by using polyampholyte microgels as building blocks. Polyampholyte microgels (named PAH-D-CO(2)) containing amine and carbamate groups were LbL assembled with polyanion poly(sodium 4-styrenesulfonate) (PSS) to produce PAH-D-CO(2)/PSS multilayer films. The successful fabrication of PAH-D-CO(2)/PSS multilayer films was verified by quartz crystal microbalance measurements and cross-sectional scanning electron microscopy. Anionic methyl orange and cationic rhodamine 6G were coloaded into PAH-D-CO(2)/PSS multilayer films because of the electrostatic interaction of these dyes with amine and carbamate groups in the PAH-D-CO(2)/PSS microgel films. The abundance of amine and carbamate groups as well as the swelling capacity of PAH-D-CO(2) microgels guarantees the high loading capacity of the PAH-D-CO(2)/PSS multilayer films toward the anionic and cationic dyes. Methyl orange and rhodamine 6G were simultaneously released from PAH-D-CO(2)/PSS multilayer films when immersing the dye-loaded films into 0.9% normal saline. The releasing behaviors of the polyampholyte microgel films can be tailored by capping the PAH-D-CO(2)/PSS films with barrier layers. The polyampholyte microgel films of PAH-D-CO(2)/PSS are expected to be widely useful as matrixes for coloading oppositely charged functional guest materials such as drugs and even for their controlled release.
For constructing a bifunctional antioxidative enzyme with both superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities, a supramolecular artificial enzyme was successfully constructed by the self-assembly of the Mn(III)meso-tetra[1-(1-adamantyl methyl ketone)-4-pyridyl] porphyrin (MnTPyP-M-Ad) and cyclodextrin-based telluronic acid (2-CD-TeO(3)H) through host-guest interaction in aqueous solution. The self-assembly of the adamantyl moieties of Mn(III) porphyrin and the beta-CD cavities of 2-CD-TeO(3)H was demonstrated by the NMR spectra. In this supramolecular enzyme model, the Mn(III) porphyrin center acted as an efficient active site of SOD and tellurol moiety endowed GPx activity. The SOD-like activity (IC(50)) of the new catalyst was found to be 0.116 microM and equals to 2.56% of the activity of the native SOD. Besides this, supramolecular enzyme model also showed a high GPx activity, and a remarkable rate enhancement of 27-fold compared to the well-known GPx mimic ebselen was observed. More importantly, the supramolecular artificial enzyme showed good thermal stability.
A temperature-sensitive block copolymer (PAAm-b-PNIPAAm-Te) with a glutathione peroxidase-like active site was synthesized via ATRP. As a new glutathione peroxidase (GPx) mimic, it displays typical saturation kinetic behaviors and high catalytic activity. More importantly, the catalytic activity of the polymer can be well modulated by changing the temperature. The experiments proved that a change in the self-assembly structure of the polymer plays a key role for the modulation of catalytic activity. As a contrast, another block copolymer, PAAm-Te-b-PNIPAAm, was synthesized. In comparison with PAAm-b-PNIPAAm-Te, the different temperature dependent catalytic behavior seen further indicates that the micellar structure plays an important role in modulating the catalytic activity of the smart enzyme model.
Insertion of selenocysteine (Sec) into protein scaffolds provides an opportunity for designing enzymes with improved and unusual catalytic properties. The use of a common thioredoxin fold with a high affinity for glutathione in glutaredoxin (Grx) and glutathione peroxidase (GPx) suggests a possibility of engineering Grx into GPx and vice versa. Here, we engineered a Grx domain of mouse thioredoxin/glutathione reductase (TGR) into a selenium-containing enzyme by substituting the active site cysteine (Cys) with selenocysteine (Sec) in a Cys auxotrophic system. The resulting selenoenzyme displayed an unusually high GPx catalytic activity rivaling that of several native GPxs. The engineered seleno-Grx was characterized by mass spectrometry and kinetic analyses. It showed a typical ping-pong kinetic mechanism, and its catalytic properties were similar to those of naturally occurring GPxs. For example, its second rate constant (k(cat)/K(mH2O2)) was as high as 1.55x10(7) M(-1) min(-1). It appears that glutathione-dependent Grx, GPx and glutathione transferase (GST) evolved from a common thioredoxin-like ancestor to accommodate related glutathione-dependent functions and can be interconverted by targeted Sec insertion.
Poly[(D,L-lactide)-co-glycolide] nanoparticles coated with polyethyleneimine on their surface were prepared by an emulsification-solvent evaporation method and subsequently surface modified by LBL assembly. The assembly of poly(acrylic acid) and polyethyleneimine on a planar substrate and on the PLGA nanoparticles was monitored by QCM-D, zeta-potential, flow cytometry and TEM. Carboxylic and amino groups in the multilayers were crosslinked by carbodiimide condensation, which was also later used to graft poly(ethylene glycol) (PEG). Rhodamine 6G, 5(6)-carboxyfluorescein and fluorescein were incorporated into the nanoparticles and their release profiles were recorded at 60 degrees C and at 37 degrees C for rhodamine 6G, for nanoparticles with a multilayer coating, and those that were crosslinked and grafted with PEG.
Layer-by-layer (LbL) assembled organic-inorganic poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH)/ Au nanoparticle hybrid films are patterned by using Norland Optical Adhesive 63 (NOA 63) polymer molds. Depending on the rigidity of the hybrid films, their patterning can be realized by a room-temperature imprinting or lift-off process. For [(PAA/PAH)1-(Au nanoparticle/PAH)3]*10 and [(PAA/PAH)3-(Au nanoparticle/PAH)3]*5 films which have a low content of Au nanoparticles, the films can be imprinted at room temperature to form patterned films with large areas because of the compressibility and fluidity of the films under high pressure. The Au nanoparticle/PAH films, which have an extremely high content of Au nanoparticles and are fragile, can be patterned by a lift-off process during which the film contacted with the NOA 63 mold was peeled off because of the strong adhesion between the film and the mold and the fragility of the film. The complementary room-temperature imprinting and lift-off methods with polymer NOA 63 molds provide facile and general ways to pattern LbL assembled organic-inorganic films with various film compositions.
A composite scaffold of poly(L-lactic-co-glycolic acid) (PLGA) microspheres and fibrin gel was fabricated by blending fibrinogen-immobilized PLGA microspheres with fibrinogen and thrombin solution. The PLGA microspheres with a size of 70 approximately 100 microm were aminolyzed in a hexanediamine/n-propanol solution to introduce free amino groups on their surface. The fibrinogen immobilization was achieved by glutaraldehyde coupling. When the --NH(2) content on the microsphere surface was increased from approximately 2 x 10(-8) mol/mg to approximately 4 x 10(-8) mol/mg, the fibrinogen amount was correspondingly increased from approximately 35 microg/mg to approximately 70 microg/mg. Measured by UV-VIS spectroscopy, the clotting time of the composite was less influenced by the microsphere amount, but mainly controlled by the thrombin concentration. When the thrombin concentration was higher than 15 U/mL, the gelation could be finished within 1 min and yielded a composite with evenly suspended and distributed PLGA microspheres. Blending with the microspheres could significantly improve the elastic modulus of the hydrogel as well, whereas less influence on the chondrocyte proliferation and extracellular matrix production.
Adhesion molecules play an important role in the pathogenesis of atherogenesis. They are expressed on endothelial cells surface in response to various inflammatory stimuli. In this paper, we examined the effect of 2-tellurium-bridged beta-cyclodextrin (2-TeCD), a GPx mimic, on the expression of adhesion molecules in human umbilical vein endothelial cells (HUVECs) under tumor necrosis factor-alpha (TNF-alpha) stimulation. Experimental results indicated that 2-TeCD suppressed the TNF-alpha-induced the expression of vascular adhesion molecule-1 (VCAM-1) and intercellular cell adhesion molecule-1 (ICAM-1) on HUVECs surface in a dose-dependent manner. 2-TeCD also reduced the level of mRNA expression of VCAM-1 and ICAM-1. Furthermore, 2-TeCD inhibited THP-1 monocyte adhesion to HUVECs stimulated by TNF-alpha. Nuclear factor-kappaB (NF-kappaB) could regulate transcription of VCAM-1 and ICAM-1 genes. Western blot analysis showed that 2-TeCD inhibited the translocation of the p65 subunit of NF-kappaB into the nucleus. In short, these results indicated that 2-TeCD inhibits TNF-alpha-stimulated VCAM-1 and ICAM-1 expression in HUVECs partly due to suppressing translocation of NF-kappaB.
A composite scaffold for cartilage tissue engineering was fabricated by filling a porous poly (L: -lactide) (PLLA) scaffold with fibrin gel. The porous PLLA scaffold prepared by a method of thermally induced phase separation has an average pore diameter of 200 microm and a porosity of 93%. Incorporation of fibrin gel into the scaffold was achieved by dropping a fibrinogen and thrombin mixture solution onto the scaffold. For a couple of minutes the fibrin gel was in situ formed within the scaffold. The filling efficiency was decreased along with the increase of the fibrinogen concentration. After fibrin gel filling, the compressive modulus and the yield stress increased from 5.94 MPa and 0.37 MPa (control PLLA scaffold in a hydrated state) to 7.21 MPa and 0.53 MPa, respectively. While the fibrin gel lost its weight in phosphate buffered saline up to approximately 50% within 3 days, 85% and 70% of the fibrin gel weight in the composite scaffold was remained within 3 and 35 days, respectively. A consistent significant higher level of rabbit auricular chondrocyte viability, cell number and glycosaminoglycan was measured in the composite scaffold than that in the control PLLA scaffold. Rabbit auricular chondrocytes with round morphology were also observed in the composite scaffold by confocal microscopy and scanning electron microscopy. Altogether with the features of better strength and cytocompatibility, this type of composite scaffold may have better performance as a matrix for cartilage tissue engineering.
Angiogenesis of an implanted construct is one of the most important issues in tissue engineering and regenerative medicine, and can often take as long as several weeks. The vascular endothelial growth factor (VEGF) shows a positive effect on enhancing angiogenesis in vivo. But the incorporation of growth factors has many limitations, since they typically have half-lives only on the order of minutes. Therefore, in this work the DNA encoding VEGF was applied to enhance the angiogenesis of a collagen scaffold. A cationic gene delivery vector, N,N,N-trimethyl chitosan chloride (TMC), was used to form complexes with the plasmid DNA encoding VEGF. The complexes were then incorporated into the collagen scaffold, the loading being mediated by the feeding concentration and release in a sustained manner. In vitro cell culture demonstrated a significant improvement in the VEGF expression level from the TMC/DNA complexes containing scaffolds, in particular with a large amount of DNA. The scaffolds containing the TMC/DNA complexes were subcutaneously implanted into Sprague-Dawley mice to study their angiogenesis via macroscopic observation, hematoxylin-eosin staining and immunohistochemical staining. The results demonstrated that the incorporation of TMC/DNA complexes could effectively enhance the in vivo VEGF expression and thereby the angiogenesis of implanted scaffolds.
A rival to native peroxidase! An existing binding site for glutathione was combined with the catalytic residue tellurocysteine by using an auxotrophic expression system to create an engineered enzyme that functions as a glutathione peroxidase from the scaffold of a glutathione transferase (see picture). The catalytic activity of the telluroenzyme in the reduction of hydroperoxides by glutathione is comparable to that of native glutathione peroxidase.
Water-soluble Au nanocrystal (NC) micelles with an inserted catalytic Cu(II) center that act as excellent nanoenzyme models for imitating ribonuclease were constructed by supramolecular self-assembly. The dodecane-1-thiol-based Au NC was constructed first, and subsequently the cationic surfactant hexadecyltrimethylammonium bromide and the catalytic ligand (N1,N1-bis(2-aminoethyl)-N2-dodecylethane-1,2-diamine) copper(II) were installed on the surface of the Au NC via hydrophobic interaction. The catalytic capability of the Au NC micelles designed was estimated by the cleavage of a typical RNA analogue, 2-hydroxypropyl p-nitrophenyl phosphate (HPNP). The study of the catalytic behavior of Au NC micelle catalysis showed that the Au NC micelles exhibited dramatic ribonuclease-like activity: a high rate acceleration of k(cat)/k(uncat) = 1.10 x 10(5) for the cleavage of HPNP in comparison with the spontaneous cleavage of HPNP (k(uncat)) was observed. The catalytic capability for HPNP cleavage by these functionalized Au NC micelles can be compared with that of covalent Au nanoparticles reported previously as nanozymes under comparable conditions. A detailed investigation of enzymatic kinetics was carried out and a possible mechanism was suggested.
Hollow polyphosphazene microcapsules have been fabricated by the covalent layer-by-layer assembly of polydichlorophosphazene (PDCP) and hexamethylenediamine (HDA) on aminosilanized silica particles, followed by core removal in a HF/NH(4) F solution. The hollow and intact microcapsules in both wet and dry states have been characterized by transmission electron microscopy and confocal laser scanning microscopy. The chemical structure of the microcapsules has been verified by FT-IR spectroscopy. The microcapsules could be hydrolytically degraded in a phosphate buffer at biological pH.
We report a direct method to amplify the exponential growth of multilayers significantly by the alternating deposition of polyethylenimine (PEI) at high pH and poly(acrylic acid) (PAA) at low pH. The alternating pH switches the degree of ionization of the polyelectrolytes in the multilayers, which enhances the diffusion of PEI into and out of the film and hence increases the deposited mass per cycle. The synergetic action of the pH-tunable charge density and diffusivity of the weak polyelectrolytes provides a new method for the enhanced growth of multilayers with hierarchal micro- and nanostructured surfaces.
Glutathione peroxidase (GPx, EC 188.8.131.52) is a key enzyme involved in scavenging of reactive oxygen species in biological system. For developing an efficient GPx-like antioxidant, catalytically necessary amino acid derivatives which located near the GPx active center were prepared as functional monomers. Via predetermined imprinting with substrate glutathione (GSH), a polymer-based GPx mimic with a similar structure of catalytic center of natural GPx was developed, and it demonstrated high-catalytic efficiency and substrate specificity. The imprinting polymer (I-PEM) exhibits GPx-like activity about three times higher than that of 2-SeCD, a cyclodextrin-based GPx mimic. The detailed studies on kinetics revealed that not only the substrate binding but also positional arrangement of reacting groups contribute significantly to the catalytic efficiency of the peroxidase model.
"Micelle-enhanced" polyelectrolyte capsules were fabricated via a layer-by-layer technique, templated on hybrid calcium carbonate particles with built-in polymeric micelles based on polystyrene-b-poly(acrylic acid). Due to the presence of a large number of negatively charged micelles inside the polyelectrolyte capsule, which were liberated from templates, the capsule wall was reconstructed and had properties different to those of conventional polyelectrolyte capsules. This type of capsule could selectively entrap positively charged water-soluble substances. The encapsulation efficiency of positively charged substances was dependent on their molecular weight or size. For some positively charged compounds, such as rhodamine B and lysozyme, the concentration in the capsules was orders of magnitude higher than that in the incubation solution. In addition, in vitro release study suggested that the encapsulated compounds could be released through a sustained manner to a certain degree. All these results point to the fact that these capsules might be used as novel delivery systems for some water-soluble compounds.
Thermosensitive nanocables consisting of Au nanowire cores and poly(N-isopropylacrylamide) sheaths (denoted as Au/PNIPAAm) were synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP). The formation of PNIPAAm sheath was verified by Fourier transform infrared (FTIR) and hydrogen nuclear magnetic resonance ((1)H NMR) spectroscopy. Transmission electron microscope (TEM) results confirmed the core/shell structure of nanohybrids. The thickness and density of PNIPAAm sheaths can be adjusted by controlling the amount of cross-linker during the polymerization. Signature temperature response was observed from Au/cross-linked-PNIPAAm nanocables. Such smart nanocables show immense potentials as building blocks for novel thermosensitive nanodevices in future.
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