180 research outputs found
Triplex inducer-directed self-assembly of single-walled carbon nanotubes: a triplex DNA-based approach for controlled manipulation of nanostructures
As a promising strategy for artificially control of gene expression, reversible assembly of nanomaterials and DNA nanomachine, DNA triplex formation has received much attention. Carbon nanotubes as gene and drug delivery vector or as ābuilding blocksā in nano/microelectronic devices have been successfully explored. Therefore, studies on triplex DNA-based carbon nanotube hybrid materials are important for development of smart nanomaterials and for gene therapy. In this report, a small molecule directed single-walled carbon nanotubes (SWNTs) self-assembly assay has been developed by disproportionation of SWNTsādT22Ā·dA22 duplex into triplex dT22Ā·dA22Ā·dT22 and dA22 by a triplex formation inducer, coralyne. This has been studied by circular dichroism, light scattering (LS) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), electrophoretic mobility shift assay and supported by using DNA random sequence. In contrast, SWNTs do not aggregate under the same experimental conditions when the small molecules used can not induce dT22Ā·dA22Ā·dT22 triplex formation. Therefore, this novel small molecule-directed SWNTs self-assembly assay has also been used for screening of triplex inducers in our studies
Chiral metallo-supramolecular complexes selectively recognize human telomeric G-quadruplex DNA
Here, we report the first example that one enantiomer of a supramolecular cylinder can selectively stabilize human telomeric G-quadruplex DNA. The P-enantiomer of this cylinder has a strong preference for G-quadruplex over duplex DNA and, in the presence of sodium, can convert G-quadruplexes from an antiparallel to a hybrid structure. The compound's chiral selectivity and its ability to discriminate quadruplex DNA have been studied by DNA melting, circular dichroism, gel electrophoresis, fluorescence spectroscopy and S1 nuclease cleavage. The chiral supramolecular complex has both small molecular chemical features and the large size of a zinc-finger-like DNA-binding motif. The complex is also convenient to synthesize and separate enantiomers. These results provide new insights into the development of chiral anticancer agents for targeting G-quadruplex DNA
Designed Arginine-Rich RNA-Binding Peptides with Picomolar Affinity
Arginine-rich peptide motifs (ARMs) capable of binding unique RNA structures play critical roles in transcription, translation, RNA trafficking, and RNA packaging. Bacteriophage ARMs necessary for transcription antitermination bind to distinct boxB RNA hairpin sequences with a characteristic induced Ī±-helical structure. Characterization of ARMs from lambdoid phages reveals that the dissociation constant of the P22 bacteriophage modelāantitermination complex (P22_(N21)āP22boxB) is 200 Ā± 56 pM in free solution at physiologic concentrations of monovalent cation, significantly stronger than previously determined by gel mobility shift and polyacrylamide gel coelectophoresis, and 2 orders of magnitude stronger than the tightest known native ARMāRNA interaction at physiological salt. Here, we use a reciprocal design approach to enhance the binding affinity of two separate Ī±-helical ARMāRNA interactions; one derived from the native Ī» phage antitermination complex and a second isolated using mRNA display selection experiments targeting boxB RNA
Chiral metallohelices enantioselectively target hybrid human telomeric G-quadruplex DNA
The design and synthesis of metal complexes that can specifically target DNA secondary structure has attracted considerable attention. Chiral metallosupramolecular complexes (e.g. helicates) in particular display unique DNA-binding behavior, however until recently few examples which are both water-compatible and enantiomerically pure have been reported. Herein we report that one metallohelix enantiomer , available from a diastereoselective synthesis with no need for resolution, can enantioselectively stabilize human telomeric hybrid G-quadruplex and strongly inhibit telomerase activity with IC 50 of 600 nM. In contrast, no such a preference is observed for the mirror image complex . More intriguingly, neither of the two enantiomers binds specifically to human telomeric antiparallel G-quadruplex. To the best of our knowledge, this is the first example of one pair of enantiomers with contrasting selectivity for human telomeric hybrid G-quadruplex. Further studies show that can discriminate human telomeric G-quadruplex from other telomeric G-quadruplexes
Mirror-image dependence : targeting enantiomeric G-quadruplex DNA using triplex metallohelices
Natural dāDNA and lāDNA are mirrorāimage counterparts. However, because of the inherent flexibility and conformation diversity of DNA, it is still not clear how enantiomeric compounds recognize dāDNA and lāDNA. Herein, taking Gāquadruplex (G4) DNA as an example that has diverse conformations and distinct biofunctions, the binding of ten pairs of iron triplex metallohelices to dā and lāG4 DNA were evaluated. The Īāenantiomer binds to dāDNA and the Īāenantiomer binds to lāDNA, exhibiting almost the same stabilization effect and binding affinity. The binding affinity of the Īāmetallohelix with dāG4 is nearly 70āfold higher than that of Īāmetallohelix binding dāG4. ĪāMetallohelix binding to dāG4 follows a twoāstep binding process driven by a favorable enthalpy contribution to compensate for the associated unfavorable entropy
Stereochemistry and amyloid inhibition : asymmetric triplex metallohelices enantioselectively bind to AĪ² peptide
Stereochemistry is vital for pharmaceutical development and can determine drug efficacy. Herein, 10 pairs of asymmetric triplex metallohelix enantiomers as a library were used to screen inhibitors of amyloid Ī² (AĪ²) aggregation via a fluorescent cellābased high-throughput method. Intriguingly, Ī enantiomers show a stronger inhibition effect than Ī enantiomers. In addition, the metallohelices with aromatic substituents are more effective than those without, revealing that these groups play a key role in the AĪ² interaction. Fluorescence stopped-flow kinetic studies indicate that binding of the Ī enantiomer to AĪ² is much faster than that of the Ī enantiomer. Furthermore, studies in enzyme digestion, isothermal titration calorimetry, nuclear magnetic resonance, and computational docking demonstrate that the enantiomers bind to the central hydrophobic Ī±-helical region of AĪ²13ā23, although with different modes for the Ī and Ī enantiomers. Finally, an in vivo study showed that these metallohelices extend the life span of the Caenorhabditis elegans CL2006 strain by attenuating AĪ²-induced toxicity. Our work will shed light on the design and screening of a metal complex as an amyloid inhibitor against Alzheimerās disease
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