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1.  “Artifactual” arsenate DNA 
Artificial DNA, PNA & XNA  2012;3(1):1-2.
The recent claim by Wolfe-Simon et al. that the Halomonas bacterial strain GFAJ-1 when grown in arsenate-containing medium with limiting phosphate is able to substitute phosphate with arsenate in biomolecules including nucleic acids and in particular DNA1 arose much skepticism, primarily due to the very limited chemical stability of arsenate esters (see ref. 2 and references therein). A major part of the criticisms was concerned with the insufficient (bio)chemical evidence in the Wolfe-Simon study for the actual chemical incorporation of arsenate in DNA (and/or RNA). Redfield et al. now present evidence that the identification of arsenate DNA was artifactual.
doi:10.4161/adna.19672
PMCID: PMC3368811  PMID: 22679526
arsenate; bacteria; DNA; genetic material; life
2.  Templating effect in DNA proximity ligation enables use of non-bioorthogonal chemistry in biological fluids 
Artificial DNA, PNA & XNA  2012;3(3):123-128.
Here we describe the first example of selective reductive amination in biological fluids using split aptamer proximity ligation (StAPL). Utilizing the cocaine split aptamer, we demonstrate small-molecule-dependent ligation that is dose-dependent over a wide range of target concentrations in buffer, human blood serum and artificial urine medium. We explore the substrate binding preferences of the split aptamer and find that the cinchona alkaloids quinine and quinidine bind to the aptamer with higher affinity than cocaine. This increased affinity leads to improved detection limits for these small-molecule targets. We also demonstrate that linker length and hydrophobicity impact the efficiency of split aptamer ligation. The ability to carry out selective chemical transformations using non-bioorthogonal chemistry in media where competing reactive groups are present highlights the power of the increased effective molarity provided by DNA assembly. Obviating the need for bioorthogonal chemistry would dramatically expand the repertoire of chemical transformations available for use in templated reactions such as proximity ligation assays, in turn enabling the development of novel methods for biomolecule detection.
doi:10.4161/adna.23842
PMCID: PMC3581511  PMID: 23370267
DNA; reductive amination; split aptamer; templated reaction; bioorthogonal
3.  DNA display of PNA-tagged ligands 
Artificial DNA, PNA & XNA  2012;3(3):105-108.
Over the past decade, several technologies have emerged to access nucleic acid-tagged libraries and select the fittest compound within such libraries. This perspective focuses on recent development with PNA-tagged small molecules displayed on DNA templates for screening purposes and to probe the optimal geometry in multivalent interactions.
doi:10.4161/adna.21108
PMCID: PMC3581508  PMID: 22871882
DNA display; PNA-encoded synthesis; cooperative binding; inhibitor; multivalent interaction; screen
4.  To DNA, all information is equal 
Artificial DNA, PNA & XNA  2012;3(3):109-111.
Information storage capabilities are key in most aspects of society and the requirement for storage capacity is rapidly expanding. In principle, DNA could be a high-density medium for information storage. Church and coworkers recently demonstrated how binary data can be encoded, stored in, and retrieved from a library of oligonucleotides, increasing by several orders of magnitude the amount and density of manmade information stored in DNA to date. The technology remains in its infancy and important hurdles have yet to be overcome in order to realize its potential. However, DNA may be particularly useful as a storage-medium over long time-scales (centuries), because data-access is compatible with any large-scale DNA-sequencing and -synthesis technology.
doi:10.4161/adna.22671
PMCID: PMC3581509  PMID: 23104084
DNA; information storage in DNA; bit; byte; binary encoding
5.  Peptide nucleic acids in materials science 
Artificial DNA, PNA & XNA  2012;3(3):112-122.
This review highlights the recent methods to prepare PNA-based materials through a combination of self-assembly and self-organization processes. The use of these methods allows easy and versatile preparation of structured hybrid materials showing specific recognition properties and unique physicochemical properties at the nano- and micro-scale levels displaying potential applications in several directions, ranging from sensors and microarrays to nanostructured devices for biochips.
doi:10.4161/adna.21941
PMCID: PMC3581510  PMID: 22925824
PNA; monolayers; nanoparticles; self-assembly; self-organisation; materials; surfaces; sensors; microarrays; biochips; DNA-PNA duplexes; hybridization
6.  Letter from the Editors 
Artificial DNA, PNA & XNA  2012;3(2):29-30.
We are happy to publish this special issue dedicated to Prof. Rosangela Marchelli. This issue not only celebrates her long-standing scientific activity on occasion of her significant anniversary, but it is meant to recognize her contribution to Bioorganic Chemistry in the field of Artificial DNA, and in particular of Peptide Nucleic Acids.
doi:10.4161/adna.21100
PMCID: PMC3429528  PMID: 22777061
7.  Helix control in polymers 
Artificial DNA, PNA & XNA  2012;3(2):31-44.
The helix is a critical conformation exhibited by biological macromolecules and plays a key role in fundamental biological processes. Biological helical polymers exist in a single helical sense arising from the chiral effect of their primary units—for example, DNA and proteins adopt predominantly a right-handed helix conformation in response to the asymmetric conformational propensity of D-sugars and L-amino acids, respectively. In using these homochiral systems, nature blocks our observations of some fascinating aspects of the cooperativity in helical systems, although when useful for a specific purpose, “wrong” enantiomers may be incorporated in specific places. In synthetic helical systems, on the contrary, incorporation of non-racemic chirality is an additional burden, and the findings discussed in this review show that this burden may be considerably alleviated by taking advantage of the amplification of chirality, in which small chiral influences lead to large consequences. Peptide nucleic acid (PNA), which is a non-chiral synthetic DNA mimic, shows a cooperative response to a small chiral effect induced by a chiral amino acid, which is limited, however, due to the highly flexible nature of this oligomeric chimera. The lack of internal stereochemical bias is an important factor which makes PNA an ideal system to understand some cooperative features that are not directly accessible from DNA.
doi:10.4161/adna.20572
PMCID: PMC3429529  PMID: 22772039
helix control; chiral amplification; cooperativity; helical polymers; PNA
8.  Artificial DNA and surface plasmon resonance 
Artificial DNA, PNA & XNA  2012;3(2):45-244.
The combined use of surface plasmon resonance (SPR) and modified or mimic oligonucleotides have expanded diagnostic capabilities of SPR-based biosensors and have allowed detailed studies of molecular recognition processes. This review summarizes the most significant advances made in this area over the past 15 years.
 
Functional and conformationally restricted DNA analogs (e.g., aptamers and PNAs) when used as components of SPR biosensors contribute to enhance the biosensor sensitivity and selectivity. At the same time, the SPR technology brings advantages that allows forbetter exploration of underlying properties of non-natural nucleic acid structures such us DNAzymes, LNA and HNA.
doi:10.4161/adna.21383
PMCID: PMC3429530  PMID: 22821257
DNAzyme; LNA; PNA; SPR; aptamer; biosensors
9.  PNA bearing 5-azidomethyluracil 
Artificial DNA, PNA & XNA  2012;3(2):53-62.
Fmoc- and Boc-protected modified monomers bearing 5-azidomethyluracil nucleobase were synthesized. Four different solid-phase synthetic strategies were tested in order to evaluate the application of this series of monomers for the solid-phase synthesis of modified PNA. The azide was used as masked amine for the introduction of amide-linked functional groups, allowing the production of a library of compounds starting from a single modified monomer. The azide function was also exploited as reactive group for the modification of PNA in solution via azide-alkyne click cycloaddition.
doi:10.4161/adna.20158
PMCID: PMC3429531  PMID: 22772040
modified uracil; peptide nucleic acids; PNA; solid-phase modification; click reaction; orthogonal protection
10.  Selective recognition of DNA from olive leaves and olive oil by PNA and modified-PNA microarrays 
Artificial DNA, PNA & XNA  2012;3(2):63-72.
PNA probes for the specific detection of DNA from olive oil samples by microarray technology were developed. The presence of as low as 5% refined hazelnut (Corylus avellana) oil in extra-virgin olive oil (Olea europaea L.) could be detected by using a PNA microarray. A set of two single nucleotide polymorphisms (SNPs) from the Actin gene of Olive was chosen as a model for evaluating the ability of PNA probes for discriminating olive cultivars. Both unmodified and C2-modified PNAs bearing an arginine side-chain were used, the latter showing higher sequence specificity. DNA extracted from leaves of three different cultivars (Ogliarola leccese, Canino and Frantoio) could be easily discriminated using a microarray with unmodified PNA probes, whereas discrimination of DNA from oil samples was more challenging, and could be obtained only by using chiral PNA probes.
doi:10.4161/adna.20603
PMCID: PMC3429532  PMID: 22772038
PNA; olive oil; hazelnut oil; SNP; cultivar identification; DNA fingerprinting
11.  Introduction of multiphosphonate ligand to peptide nucleic acid for metal ion conjugation 
Artificial DNA, PNA & XNA  2012;3(2):73-79.
Peptide nucleic acid (PNA) is one of the most widely used synthetic DNA analogs. Conjugation of functional molecules to PNA is very effective to further widen its potential applications. For this purpose, here we report the synthesis of several ligand monomers and introduced them to PNA. These ligand-modified PNAs attract cerium ion and are useful for site-selective DNA hydrolysis. It should be noted that these ligands on PNA are also effective even under the conditions of invasion complex.
doi:10.4161/adna.20727
PMCID: PMC3429533  PMID: 22772037
cerium; DNA; hydrolysis; ligand; metal ion; peptide nucleic acid
12.  Peptide nucleic acids tagged with four lysine residues for amperometric genosensors 
Artificial DNA, PNA & XNA  2012;3(2):80-87.
A homothymine PNA decamer bearing four lysine residues has been synthesized as a probe for the development of amperometric sensors. On one hand, the four amino groups introduced make this derivative nine times more soluble than the corresponding homothymine PNA decamer and, on the other hand, allow the stable anchoring of this molecule on Au nanostructured surface through the terminal -NH2 moieties. In particular, XPS and electrochemical investigations performed with hexylamine, as a model molecule, indicate that the stable deposition of primary amine derivatives on such a nanostructured surface is possible and involves the free electron doublet on the nitrogen atom. This finding indicates that this PNA derivative is suitable to act as the probe molecule for the development of amperometric sensors.
 
Thanks to the molecular probe chosen and to the use of a nanostructured surface as the substrate for the sensor assembly, the device proposed makes possible the selective recognition of the target oligonucleotide sequence with very high sensitivity.
doi:10.4161/adna.20777
PMCID: PMC3429534  PMID: 22772036
DNA recognition; PNA; amperometric genosensors; nanostructured surfaces; amine deposition
13.  Targeting pre-miRNA by Peptide Nucleic Acids 
Artificial DNA, PNA & XNA  2012;3(2):88-96.
PNAs conjugated to carrier peptides have been employed for the targeting of miRNA precursor, with the aim to develop molecules able to interfere in the pre-miRNA processing. The capability of the molecules to bind pre-miRNA has been tested in vitro by fluorescence assayes on Thiazole Orange labeled molecules and in vivo, in K562 cells, evaluating the amount of miRNA produced after treatment of cells with two amounts of PNAs.
doi:10.4161/adna.20911
PMCID: PMC3429535  PMID: 22699795
FACS; fluorescence; miR-210; PNA; pre-miR; thiazole orange
14.  Effects of decoy molecules targeting NF-kappaB transcription factors in Cystic fibrosis IB3–1 cells 
Artificial DNA, PNA & XNA  2012;3(2):97-296.
One of the clinical features of cystic fibrosis (CF) is a deep inflammatory process, which is characterized by production and release of cytokines and chemokines, among which interleukin 8 (IL-8) represents one of the most important. Accordingly, there is a growing interest in developing therapies against CF to reduce the excessive inflammatory response in the airways of CF patients. Since transcription factor NF-kappaB plays a critical role in IL-8 expression, the transcription factor decoy (TFD) strategy might be of interest. In order to demonstrate that TFD against NF-kappaB interferes with the NF-kappaB pathway we proved, by chromatin immunoprecipitation (ChIP) that treatment with TFD oligodeoxyribonucleotides of cystic fibrosis IB3–1 cells infected with Pseudomonas aeruginosa leads to a decrease occupancy of the Il-8 gene promoter by NF-kappaB factors. In order to develop more stable therapeutic molecules, peptide nucleic acids (PNAs) based agents were considered. In this respect PNA-DNA-PNA (PDP) chimeras are molecules of great interest from several points of view: (1) they can be complexed with liposomes and microspheres; (2) they are resistant to DNases, serum and cytoplasmic extracts; (3) they are potent decoy molecules. By using electrophoretic mobility shift assay and RT-PCR analysis we have demonstrated that (1) the effects of PDP/PDP NF-kappaB decoy chimera on accumulation of pro-inflammatory mRNAs in P.aeruginosa infected IB3–1 cells reproduce that of decoy oligonucleotides; in particular (2) the PDP/PDP chimera is a strong inhibitor of IL-8 gene expression; (3) the effect of PDP/PDP chimeras, unlike those of ODN-based decoys, are observed even in the absence of protection with lipofectamine. These informations are of great impact, in our opinion, for the development of stable molecules to be used in non-viral gene therapy of cystic fibrosis.
doi:10.4161/adna.21061
PMCID: PMC3429536  PMID: 22772035
NF-kappaB; transcription factor decoy; inflammation; Peptide Nucleic Acids; PNA-DNA chimeras
15.  Enzymatic synthesis of DNA strands containing α-L-LNA (α-L-configured locked nucleic acid) thymine nucleotides 
Artificial DNA, PNA & XNA  2012;3(1):14-21.
We describe the first enzymatic incorporation of an α-L-LNA nucleotide into an oligonucleotide. It was found that the 5′-triphosphate of α-L-LNA is a substrate for the DNA polymerases KOD, 9°Nm, Phusion and HIV RT. Three dispersed α-L-LNA thymine nucleotides can be incorporated into DNA strands by all four polymerases, but they were unable to perform consecutive incorporations of α-L-LNA nucleotides. In addition it was found that primer extension can be achieved using templates containing one α-L-LNA nucleotide.
doi:10.4161/adna.19272
PMCID: PMC3368812  PMID: 22679529
enzymatic synthesis; modified nucleotide; polymerase; triphosphate; α-L-LNA
16.  Cell number and transfection volume dependent peptide nucleic acid antisense activity by cationic delivery methods 
Artificial DNA, PNA & XNA  2012;3(1):22-30.
Efficient intracellular delivery is essential for high activity of nucleic acids based therapeutics, including antisense agents. Several strategies have been developed and practically all rely on auxiliary transfection reagents such as cationic lipids, cationic polymers and cell penetrating peptides as complexing agents and carriers of the nucleic acids. However, uptake mechanisms remain rather poorly understood, and protocols always require optimization of transfection parameters. Considering that cationic transfection complexes bind to and thus may up-concentrate on the cell surface, we have now quantitatively compared the cellular activity (in the pLuc705 HeLa cell splice correction system) of PNA antisense oligomers using lipoplex delivery of cholesterol- and bisphosphonate-PNA conjugates, polyplex delivery via a PNA-polyethyleneimine conjugate and CPP delivery via a PNA-octaarginine conjugate upon varying the cell culture transfection volume (and cell density) at fixed PNA concentration. The results show that for all delivery modalities the cellular antisense activity increases (less than proportionally) with increasing volume (in some cases accompanied with increased toxicity), and that this effect is more pronounced at higher cell densities. These results emphasize that transfection efficacy using cationic carriers is critically dependent on parameters such as transfection volume and cell density, and that these must be taken into account when comparing different delivery regimes.
doi:10.4161/adna.19906
PMCID: PMC3368813  PMID: 22679530
antisense; cellular delivery; lipoplex; octaarginine (CPP); peptide nucleic acid (PNA); polyethyleneimine (PEI)
17.  A DNA nanocapsule with aptamer-controlled open-closure function for targeted delivery 
Artificial DNA, PNA & XNA  2012;3(1):3-4.
A DNA capsule fitted with aptamer controlled target sensing has been “woven” using a 7308-base single-stranded DNA “thread” and 196 staple oligonucleotides. The capsule enables logic-gated molecular cargo delivery to targeted cell surfaces.
doi:10.4161/adna.19843
PMCID: PMC3368814  PMID: 22679527
aptamer; delivery; DNA origami; nanocapsule; nanoscience
18.  (α,α-dimethyl)glycyl (dmg) PNAs 
Artificial DNA, PNA & XNA  2012;3(1):5-13.
The design and facile synthesis of sterically constrained new analogs of PNA having gem-dimethyl substitutions on glycine (dmg-PNA-T) is presented. The PNA oligomers [aminoethyl dimethylglycyl (aedmg) and aminopropyl dimethylglycyl (apdmg)] synthesized from the monomers 6 and 12) effected remarkable stabilization of homothyminePNA2:homoadenine DNA/RNA triplexes and mixed base sequence duplexes with target cDNA or RNA. They show a higher binding to DNA relative to that with isosequential RNA. This may be a structural consequence of the sterically rigid gem-dimethyl group, imposing a pre-organized conformation favorable for complex formation with cDNA. The results complement our previous work that had demonstrated that cyclohexanyl-PNAs favor binding with cRNA compared with cDNA and imply that the biophysical and structural properties of PNAs can be directed by introduction of the right rigidity in PNA backbone devoid of chirality. This approach of tweaking selectivity in binding of PNA constructs by installing gem-dimethyl substitution in PNA backbone can be extended to further fine-tuning by similar substitution in the aminoethyl segment as well either individually or in conjunction with present substitution.
doi:10.4161/adna.19185
PMCID: PMC3368815  PMID: 22679528
(α,α-dimethyl)glycyl PNA; gem-dimethylglycyl PNA; peptide nucleic acid; PNA-DNA binding; sterically constrained PNA analog; α-aminoisobutyric acid PNA

Results 1-18 (18)