Positive Effects of ATP on G-Quadruplex-Hemin DNAzyme-Mediated Reactions

Some G-quadruplex-hemin complexes can be used as peroxidase-mimicking DNAzymes, catalyzing H2O2-mediated reactions such as the oxidation of 2,2′-azinobis (3-ethylbenzothiozoline)-6-sulfonic acid (ABTS) by H2O2. However, some challenges, for example, the relatively low catalytic activity and the disproportionation of the reaction product ABTS·+, may seriously restrict further development and applications of these complexes. Here, we demonstrated the positive effect of adenosine triphosphate (ATP) on G-quadruplex-hemin DNAzyme-mediated catalytic reactions. The presence of ATP not only improved the catalytic activity of G-quadruplex-hemin DNAzymes, but also inhibited the disproportionation of ABTS·+. These observations may improve the performance of existing G-quadruplex-hemin DNAzyme-based chemical sensors, for example, the Ag+-detection method that uses G-quadruplex-hemin DNAzymes, and widen the application range of G-quadruplex-hemin DNAzymes. We also demonstrated that the phosphate groups, nucleobase, and sugar of ATP determine the reaction-promoting ability of ATP. These observations may be helpful in the design of highly efficient enhancers for G-quadruplex-hemin DNAzymes

Ag⁺ and Cysteine Quantitation Based on G-Quadruplex−Hemin DNAzymes Disruption by Ag⁺

Some G-quadruplex−hemin complexes are DNAzyme peroxidases that efficiently catalyze H2O2-mediated reactions, such as the oxidation of ABTS (2,2′-azinobis(3-ethylbenzothiozoline)-6-sulfonic acid) by H2O2. Since Ag+ chelates guanine bases at the binding sites are involved in G-quadruplex formation, the presence of Ag+ may disrupt these structures and inhibit the peroxidase activity of G-quadruplex−hemin DNAzymes. On the basis of this principle, a highly sensitive and selective Ag+-detection method was developed. The method allows simple detection of aqueous Ag+ with a detection limit of 64 nM and a linear range of 50−3000 nM. Cysteine (Cys) is a strong Ag+-binder and competes with quadruplex-forming G-rich oligonucleotides for Ag+-binding, promoting the reformation of G-quadruplexes and increasing their peroxidase activity. Therefore, the Ag+-sensing system was also developed as a Cys-sensing system. This “turn-on” process allowed the detection of Cys at concentrations as low as 50 nM using a simple colorimetric technique. The Cys-sensing system could also be used for the detection of reduced glutathione (GSH). Neither the Ag+-sensing nor the Cys-sensing systems required labeled oligonucleotides. In addition, both gave large changes in absorbance signal that could be observed by the naked eye. Thus, a simple visual method for Ag+- or Cys-detection was developed

Highly Integrated, Biostable, and Self-Powered DNA Motor Enabling Autonomous Operation in Living Bodies

An ultimate goal of synthetic DNA motor studies is to mimic natural protein motors in biological systems. Here, we rationally designed a highly integrated and biostable DNA motor system with high potential for living body operation, through simple assembly of a Mn2+-dependent DNAzyme-powered DNA motor with a degradable MnO2 nanosheet. The motor system shows outstanding high integration and improved biostability. High integration confers the motor system with the ability to deliver all the core components to the target sites as a whole, thus, enabling precise control of the spatiotemporal distribution of these components and achieving high local concentrations. At the target sites, reduction of the MnO2 nanosheet by intracellular glutathione (GSH) not only releases the DNA motor, which can then be initiated by the intracellular target, but also produces Mn2+ in situ to power the autonomous and progressive operation of the DNA motor. Interestingly, the resultant consumption of GSH in turn protects the DNA motor from destruction by physiological GSH, thus, conferring our motor system with improved biostability, reduced false-positive outputs, and consequently, an increased potential to be applied in a living body. As a proof of concept, the highly integrated DNA motor system was demonstrated to work well for amplified imaging detection of survivin mRNA (mRNA), an important tumor biomarker, in both living cancer cells and living tumor-bearing mice. This work reveals concepts and strategies promoting synthetic DNA motor applications in biological systems

Asymmetric Cationic Porphyrin as a New G‑Quadruplex Probe with Wash-Free Cancer-Targeted Imaging Ability Under Acidic Microenvironments

Porphyrins are promising candidates for nucleic acid G-quadruplex-specific optical recognition. We previously demonstrated that G-quadruplex recognition specificity of porphyrins could be improved by introducing bulky side arm substituents, but the enhanced protonation tendency limits their applications in some cases, such as under acidic conditions. Here, we demonstrated that the protonation tendency of porphyrin derivatives could be efficiently overcome by increasing molecular asymmetry. To validate this, an asymmetric, water-soluble, cationic porphyrin FA-TMPipEOPP (5-{4-[2-[[(2<i>E</i>)-3-[3-methoxy-4-[2-(1-methyl-1-piperidinyl)­ethoxy]­phenyl]-1-oxo-2-propenyl]­oxy]­ethoxy]­phenyl},10,15,20-tri­{4-[2-(1-methyl-1-piperidinyl)­ethoxy]-phenyl}­porphyrin) was synthesized by introducing a ferulic acid (FA) unit at one side arm, and its structure was well-characterized. Unlike its symmetric counterpart TMPipEOPP that has a tendency to protonate under acidic conditions, FA-TMPipEOPP remained in the unprotonated monomeric form under the pH range of 2.0–8.0. Correspondingly, FA-TMPipEOPP showed better G-quadruplex recognition specificity than TMPipEOPP and thus might be used as a specific optical probe for colorimetric and fluorescent recognition of G-quadruplexes under acidic conditions. The feasibility was demonstrated by two proof-of-concept studies: probing structural competition between G-quadruplexes and duplexes and label-free and wash-free cancer cell-targeted bioimaging under an acidic tumor microenvironment. As G-quadruplex optical probes, FA-TMPipEOPP works well under acidic conditions, whereas TMPipEOPP works well under neutral conditions. This finding provides useful information for G-quadruplex probe research. That is, porphyrin-based G-quadruplex probes suitable for different pH conditions might be obtained by adjusting the molecular symmetry

Fluorescent Sensor for Monitoring Structural Changes of G-Quadruplexes and Detection of Potassium Ion

G-rich sequences with the potential for quadruplex formation are common in genomic DNA. Considering that the biological functions of G-quadruplexes may well depend on their structures, the development of a sensitive structural probe for distinguishing different types of quadruplexes has received great attention. Crystal violet (CV) is a triphenylmethane dye, which can stack onto the two external G-quartets of a G-quadruplex. The ability of CV to discriminate G-quadruplexes from duplex and single-stranded DNAs has been reported by us. Herein, the ability of CV to discriminate parallel from antiparallel structures of a G-quadruplex was studied. The binding of CV to an antiparallel G-quadruplex can make its fluorescence intensity increase to a high level because of the protection of bound CV from the solvent by quadruplex end loops. The presence of side loops in parallel G-quadruplexes cannot provide bound CV such protection, causing the fluorescence intensity of CV/G-quadruplex mixture to be obviously weaker when the G-quadruplex adopts a parallel structure than that when the G-quadruplex adopts an antiparallel structure. Therefore, CV can be developed as a sensitive fluorescent biosensor for the discrimination of antiparallel G-quadruplexes from parallel G-quadruplexes and for monitoring the structural interconversion of G-quadruplexes. In addition, considering that some G-rich DNA sequences can adopt different G-quadruplex structures under Na+ or K+ ion conditions, a novel, cheap and simple K+ ion detection method was developed. This method displays a high K+ ion selectivity against Na+ ion, the change of 200 mM in Na+ ion concentration only causes a similar fluorescent signal change to 0.3 mM K+ ion

Excitation spectra of TMPipEOPP in the absence or presence of different DNAs when the emission wavelength is held at 726 nm.

<p>[TMPipEOPP] = 5 µM. [DNA] = 10 µM (strand concentration). [CtDNA] = 240 µM (base concentration).</p

Absorption titration of TMPipEOPP with Hum24.

<p>[TMPipEOPP] = 5 µM. The Hum24 concentration increases from 0 to 50 µM.</p

Fluorescence spectra of TMPipEOPP in the absence or presence of different DNAs when excited at 422 nm.

<p>[TMPipEOPP] = 5 µM. [DNA] = 10 µM (strand concentration). [CtDNA] = 240 µM (base concentration).</p

Fluorescence spectra of TMPipEOPP in the absence or presence of different DNAs when excited at 464 nm.

<p>[TMPipEOPP] = 5 µM. [DNA] = 10 µM (strand concentration). [CtDNA] = 240 µM (base concentration).</p

Lignin-Based Hydrogen-Bonded Covalent Organic Polymers as Functional “Switches” of Modified Atmosphere Packaging Membranes for Preservation of Perishable Foods

To reduce poverty and hunger in economically backward countries and regions, increasing demand for addressing severe worldwide food deterioration and wastage has triggered intensive research efforts toward modified atmosphere packaging (MAP) technology. Herein, we demonstrate that natural lignin can be used as a cheap and green monomer for preparation of hydrogen-bonded covalent organic polymers (HCOPs) with good crystallinity, permanent porosity, and high thermostability. The optimal lignin-based HCOPs (named LT-HCOPs) are synthesized by using tetrafluoroterephthalonitrile as the cross-linker, ethanol/water (7/3, v/v) as the reaction solvent, 120 °C as the reaction temperature, and ammonium persulphate and anhydrous potassium carbonate as catalysts. As-prepared LT-HCOPs can be used as promising “switches” for regulating gas permeability in the passive MAP membranes. The LT-HCOP-based passive MAP membrane, which is prepared by a simple mixing and solvent evaporation process, shows good biocompatibility, antimicrobial and antioxidant activities, improved ultraviolet light barrier property, high CO2/O2 selectivity, and suitable H2O permeation and thus is demonstrated to work well in prolonging the shelf life of perishable foods such as strawberries, waxberries, cherries, cherry tomatoes, and mangoes. This work provides a feasible way to use cheap and green natural materials to construct advanced functional materials for practical applications