Switchback RNA.

Intricately designed DNA and RNA motifs guide the assembly of robust and functional nucleic acid nanostructures. In this work, we present a globally left-handed RNA motif with two parallel strands called switchback RNA and report its assembly, biophysical, and biochemical characterization. Switchback RNA can be assembled in buffers without Mg, with improved thermal stability in buffers containing Mg, Na, or K.

The unusual structural properties and potential biological relevance of switchback DNA.

Synthetic DNA motifs form the basis of nucleic acid nanotechnology. The biochemical and biophysical properties of these motifs determine their applications. Here, we present a detailed characterization of switchback DNA, a globally left-handed structure composed of two parallel DNA strands.

Barium Concentration-Dependent Anomalous Electrophoresis of Synthetic DNA Motifs.

The structural integrity, assembly yield, and biostability of DNA nanostructures are influenced by the metal ions used to construct them. Although high (>10 mM) concentrations of divalent ions are often preferred for assembling DNA nanostructures, the range of ion concentrations and the composition of the assembly products vary for different assembly conditions. Here, we examined the unique ability of Ba to retard double crossover DNA motifs by forming a low mobility species, whose mobility on the gel is determined by the concentration ratio of DNA and Ba.

The unusual structural properties and potential biological relevance of switchback DNA.

Synthetic DNA motifs form the basis of nucleic acid nanotechnology, and their biochemical and biophysical properties determine their applications. Here, we present a detailed characterization of switchback DNA, a globally left-handed structure composed of two parallel DNA strands. Compared to a conventional duplex, switchback DNA shows lower thermodynamic stability and requires higher magnesium concentration for assembly but exhibits enhanced biostability against some nucleases.

Self-Assembly of DNA Nanostructures in Different Cations.

The programmable nature of DNA allows the construction of custom-designed static and dynamic nanostructures, and assembly conditions typically require high concentrations of magnesium ions that restricts their applications. In other solution conditions tested for DNA nanostructure assembly, only a limited set of divalent and monovalent ions are used so far (typically Mg and Na ). Here, we investigate the assembly of DNA nanostructures in a wide variety of ions using nanostructures of different sizes: a double-crossover motif (76 bp), a three-point-star motif (~134 bp), a DNA tetrahedron (534 bp) and a DNA origami triangle (7221 bp).

Fluorometric Determination of DNA Nanostructure Biostability.

The analysis and improvement of DNA nanostructure biostability is one of the keys areas of progress needed in DNA nanotechnology applications. Here, we present a plate-compatible fluorometric assay for measuring DNA nanostructure biostability using the common intercalator ethidium bromide. We demonstrate the assay by testing the biostability of duplex DNA, a double crossover DNA motif, and a DNA origami nanostructure against different nucleases and in fetal bovine serum.

Caffeine-induced release of small molecules from DNA nanostructures.

Several planar aromatic molecules are known to intercalate between base pairs of double-stranded DNA. This mode of interaction has been used to stain DNA as well as to load drug molecules onto DNA-based nanostructures. Some small molecules are also known to induce deintercalation in double-stranded DNA, one such molecule being caffeine.

Self-assembly of DNA nanostructures in different cations.

The programmable nature of DNA allows the construction of custom-designed static and dynamic nanostructures, and assembly conditions typically require high concentrations of magnesium ions which restricts their applications. In other solution conditions tested for DNA nanostructure assembly, only a limited set of divalent and monovalent ions have been used so far (typically Mg and Na ). Here, we investigate the assembly of DNA nanostructures in a wide variety of ions using nanostructures of different sizes: a double-crossover motif (76 bp), a three-point-star motif (∼134 bp), a DNA tetrahedron (534 bp) and a DNA origami triangle (7221 bp).

Peptide Nucleic Acid with Double Face: Homothymine-Homocytosine Bimodal Cα-PNA (-Cα-PNA) Forms a Double Duplex of the -PNA:DNA Triplex.

Cα-bimodal peptide nucleic acids (-Cα-PNA) are PNAs with two faces and are designed homologues of PNAs in which each aminoethylglycine () repeating unit in the standard PNA backbone hosts a second nucleobase at Cα through a spacer chain with a triazole linker. Such -Cα-PNA with mixed sequences can form double duplexes by simultaneous binding to two complementary DNAs, one to the base sequence on t-amide side and the other to the bases on the Cα side chain. The synthesis of -Cα-PNA with homothymine (T) on the t-amide face and homocytosine (C) on the Cα side chain through the triazole linker was achieved by solid phase synthesis with the global click reaction.

Silver assisted stereo-directed assembly of branched peptide nucleic acids into four-point nanostars.

Branched chiral peptide nucleic acids br(4S/R)-PNA with three arms of PNA-C4 strands were constructed on a central chiral core of 4(R/S)-aminoproline as the branching center. The addition of Ag+ triggered the self-assembly of branched PNAs through the formation of C-Ag+-C metallo base pairing of the three PNA C4 arms leading to non-covalent dendrimers, whose architecture is directed by the C4(R/S)-stereocenter of core 4-aminoproline. The 4S-aminoprolyl core enabled the precise formation of four-pointed nanostars that was not realised with 4R-aminoprolyl or acyclic, achiral aminoethyl glycyl PNA cores.

Cγ(/)-Bimodal Peptide Nucleic Acids (Cγ--PNA) Form Coupled Double Duplexes by Synchronous Binding to Two Complementary DNA Strands.

Peptide nucleic acids (PNAs) are linear equivalents of DNA with a neutral acyclic polyamide backbone that has nucleobases attached via -amide link on repeating units of aminoethylglycine. They bind complementary DNA or RNA with sequence specificity to form hybrids that are more stable than the corresponding DNA/RNA self-duplexes. A new type of PNA termed bimodal PNA [Cγ(/)--PNA] is designed to have a second nucleobase attached via amide spacer to a side chain at Cγ on the repeating units of PNA oligomer.

Conformation and Morphology of 4-(NH/OH)-Substituted l/d-Prolyl Polypeptides: Effect of Homo- and Heterochiral Backbones on Formation of β-Structures and Nanofibers.

The relative stereochemistry of C2 and C4 in 4-substituted prolyl polypeptides plays an important role in defining the derived conformation in solution. -(2,4)-Amino/hydroxy-l-prolyl polypeptide (l- /l- ) shows a PPII conformation in phosphate buffer and a β-structure in a relatively hydrophobic solvent, trifluoroethanol (TFE). It is now demonstrated that the homochiral enantiomeric cis-substituted d-prolyl polypeptide (d- /d- ) exhibits mirror image β-structures in TFE.

Structural Design and Synthesis of Bimodal PNA That Simultaneously Binds Two Complementary DNAs To Form Fused Double Duplexes.

Bimodal PNAs are new PNA constructs designed to bind two different cDNA sequences synchronously to form double duplexes. They are synthesized on solid phase using sequential coupling and click reaction to introduce a second base in each monomer at C via alkyltriazole linker. The ternary bimodal PNA:DNA complexes show stability higher than that of individual duplexes.

Receptor-Specific Delivery of Peptide Nucleic Acids Conjugated to Three Sequentially Linked -Acetyl Galactosamine Moieties into Hepatocytes.

Peptide nucleic acids (PNAs) are DNA analogs that bind with high affinity to DNA and RNA in a sequence-specific manner but have poor cell permeability, limiting use as therapeutic agents. The work described here is motivated by recent reports of efficient gene silencing specifically in hepatocytes by small interfering RNAs conjugated to triantennary -acetyl galactosamine (GalNAc), the ligand recognized by the asialoglycoprotein receptor (ASGPR). PNAs conjugated to either triantennary GalNAc at the N-terminus (the branched architecture) or monomeric GalNAc moieties anchored at C of three consecutive PNA monomers of -(2-aminoethyl)glycine () scaffolds (the sequential architecture) were synthesized on the solid phase.

DNA Nanocarriers: Programmed to Deliver.

Simple base-pairing rules of complementarity, perfected by evolution for encoding genetic information, provide unprecedented control over the process of DNA self-assembly. These rules allow us to build exquisite nanostructures and rationally design their morphology, fine-tune their chemical properties, and program their response to environmental stimuli. DNA nanostructures have emerged as promising candidates for transporting drugs across various physiological barriers of the body.