Modulation of DNA and RNA by PNA

Organometallic modification confers oligonucleotides new functionalities

To improve their properties or to introduce entirely new functionalities, the intriguing scaffolds of nucleic acids have been decorated with various modifications, most recently also organometallic ones. While challenging to introduce, organometallic modifications offer the potential of expanding the field of application of metal-dependent functionalities to metal-deficient conditions, notably those of biological media. So far, organometallic moieties have been utilized as probes, labels and catalysts. This Feature Article summarizes recent efforts and predicts likely future developments in each of these lines of research.

Factors Impacting Invader-Mediated Recognition of Double-Stranded DNA

The development of chemically modified oligonucleotides enabling robust, sequence-unrestricted recognition of complementary chromosomal DNA regions has been an aspirational goal for scientists for many decades. While several groove-binding or strand-invading probes have been developed towards this end, most enable recognition of DNA only under limited conditions (e.g., homopurine or short mixed-sequence targets, low ionic strength, fully modified probe strands). Invader probes, i.e., DNA duplexes modified with +1 interstrand zippers of intercalator-functionalized nucleotides, are predisposed to recognize DNA targets due to their labile nature and high affinity towards complementary DNA. Here, we set out to gain further insight into the design parameters that impact the thermal denaturation properties and binding affinities of Invader probes. Towards this end, ten Invader probes were designed, and their biophysical properties and binding to model DNA hairpins and chromosomal DNA targets were studied. A Spearman's rank-order correlation analysis of various parameters was then performed. Densely modified Invader probes were found to result in efficient recognition of chromosomal DNA targets with excellent binding specificity in the context of denaturing or non-denaturing fluorescence in situ hybridization (FISH) experiments. The insight gained from the initial phase of this study informed subsequent probe optimization, which yielded constructs displaying improved recognition of chromosomal DNA targets. The findings from this study will facilitate the design of efficient Invader probes for applications in the life sciences.

Serine-γPNA, Invader probes, and chimeras thereof: three probe chemistries that enable sequence-unrestricted recognition of double-stranded DNA

Three probe chemistries are evaluated with respect to thermal denaturation temperatures, UV-Vis and fluorescence characteristics, recognition of complementary and mismatched DNA hairpin targets, and recognition of chromosomal DNA targets in the context of non-denaturing fluorescence in situ hybridization (nd-FISH) experiments: (i) serine-γPNAs (SγPNAs), i.e., single-stranded peptide nucleic acid (PNA) probes that are modified at the γ-position with (R)-hydroxymethyl moieties, (ii) Invader probes, i.e., DNA duplexes modified with +1 interstrand zippers of 2'-O-(pyren-1-yl)methyl-RNA monomers, a molecular arrangement that results in a violation of the neighbor exclusion principle, and (iii) double-stranded chimeric SγPNAs:Invader probes, i.e., duplexes between complementary SγPNA and Invader strands, which are destabilized due to the poor compatibility between intercalators and PNA:DNA duplexes. Invader probes resulted in efficient, highly specific, albeit comparatively slow recognition of the model DNA hairpin targets. Recognition was equally efficient and faster with the single-stranded SγPNA probes but far less specific, whilst the double-stranded chimeric SγPNAs:Invader probes displayed recognition characteristics that were intermediate of the parent probes. All three probe chemistries demonstrated the capacity to target chromosomal DNA in nd-FISH experiments, with Invader probes resulting in the most favorable and consistent characteristics (signals in >90% of interphase nuclei against a low background and no signal in negative control experiments). These probe chemistries constitute valuable additions to the molecular toolbox needed for DNA-targeting applications.

Novel Small Multilamellar Liposomes Containing Large Quantities of Peptide Nucleic Acid Selectively Kill Breast Cancer Cells

Simple Summary

We present, for the first time, the preparation of small (60–90 nm in diameter) liposomes containing extremely large amounts (~8000 molecules per vesicle) of short, cytosine-rich peptide nucleic acid. The outer surface of liposomes wasfunctionalized with scaffold molecules specific to tumor-associated antigen overexpressing in breast cancer. We have shown that targeted liposomesspecifically interact with cancer cells and reduce their viability in sub-nanomolar concentrations. The results presented here can be widely used in cancer therapy based on cytosine-rich PNA oligonucleotides.

Abstract

Peptide nucleic acid (PNA) may be used in various biomedical applications; however, these are currently limited, due to its low solubility in aqueous solutions. In this study, a methodology to overcome this limitation is demonstrated, as well as the effect of PNA on cell viability. We show that extruding a mixture of natural phospholipids and short (6–22 bases), cytosine-rich PNA through a 100 nm pore size membrane under mild acidic conditions resulted in the formation of small (60–90 nm in diameter) multilamellar vesicles (SMVs) comprising several (3–5) concentric lipid membranes. The PNA molecules, being positively charged under acidic conditions (due to protonation of cytosine bases in the sequence), bind electrostatically to negatively charged phospholipid membranes. The large membrane surface area allowed the encapsulation of thousands of PNA molecules in the vesicle. SMVs were conjugated with the designed ankyrin repeat protein (DARPin_9-29), which interacts with human epidermal growth factor receptor 2 (HER2), overexpressed in human breast cancer. The conjugate was shown to enter HER2-overexpressing cells by receptor-mediated endocytosis. PNA molecules, released from lysosomes, aggregate in the cytoplasm into micron-sized particles, which interfere with normal cell functioning, causing cell death. The ability of DARPin-functionalized SMVs to specifically deliver large quantities of PNA to cancer cells opens a new promising avenue for cancer therapy.

Perspectives on conformationally constrained peptide nucleic acid (PNA): insights into the structural design, properties and applications

Peptide nucleic acid or PNA is a synthetic DNA mimic that contains a sequence of nucleobases attached to a peptide-like backbone derived from N-2-aminoethylglycine. The semi-rigid PNA backbone acts as a scaffold that arranges the nucleobases in a proper orientation and spacing so that they can pair with their complementary bases on another DNA, RNA, or even PNA strand perfectly well through the standard Watson-Crick base-pairing. The electrostatically neutral backbone of PNA contributes to its many unique properties that make PNA an outstanding member of the xeno-nucleic acid family. Not only PNA can recognize its complementary nucleic acid strand with high affinity, but it does so with excellent specificity that surpasses the specificity of natural nucleic acids and their analogs. Nevertheless, there is still room for further improvements of the original PNA in terms of stability and specificity of base-pairing, direction of binding, and selectivity for different types of nucleic acids, among others. This review focuses on attempts towards the rational design of new generation PNAs with superior performance by introducing conformational constraints such as a ring or a chiral substituent in the PNA backbone. A large collection of conformationally rigid PNAs developed during the past three decades are analyzed and compared in terms of molecular design and properties in relation to structural data if available. Applications of selected modified PNA in various areas such as targeting of structured nucleic acid targets, supramolecular scaffold, biosensing and bioimaging, and gene regulation will be highlighted to demonstrate how the conformation constraint can improve the performance of the PNA. Challenges and future of the research in the area of constrained PNA will also be discussed.

Sequence-Specific Recognition of Double-Stranded DNA by Peptide Nucleic Acid Forming Double-Duplex Invasion Complex

Peptide nucleic acid (PNA) is an analog of natural nucleic acids, where the sugar-phosphate backbone of DNA is replaced by an electrostatically neutral N-(2-aminoethyl)glycine backbone. This unique peptide-based backbone enables PNAs to form a very stable duplex with the complementary nucleic acids via Watson–Crick base pairing since there is no electrostatic repulsion between PNA and DNA·RNA. With this high nucleic acid affinity, PNAs have been used in a wide range of fields, from biological applications such as gene targeting, to engineering applications such as probe and sensor developments. In addition to single-stranded DNA, PNA can also recognize double-stranded DNA (dsDNA) through the formation of a double-duplex invasion complex. This double-duplex invasion is hard to achieve with other artificial nucleic acids and is expected to be a promising method to recognize dsDNA in cellula or in vivo since the invasion does not require the prior denaturation of dsDNA. In this paper, we provide basic knowledge of PNA and mainly focus on the research of PNA invasion.

Potential for the Development of a New Generation of Aminoglycoside Antibiotics

The present review summarizes recent publications devoted to aminoglycosides that study the main types of resistance to antibiotics of this class and the main directions of chemical modification aimed at overcoming the resistance or changing the spectrum of biological activity. Conjugates of aminoglycosides with various pharmacophores including amino acids, peptides, peptide nucleic acids, nucleic bases, and several other biologically active molecules and modifications resulting in other types of biological activity of this class of antibiotics are described. It is concluded that a promising research direction aimed at increasing the activity of antibiotics against resistant strains is the search for selective inhibitors of aminoglycoside-modifying enzymes. This would allow renewal of the use of antibiotics already meeting widespread resistance and would increase the potential of a new generation of antibiotics.

Peptide nucleic acid as a template for Taq DNA polymerase

Peptide nucleic acid (PNA), an artificial DNA analog, comprises a purine or pyrimidine base and a pseudo-peptide backbone instead of deoxyribose-phosphate. PNA has been found to have stronger adhesion and higher stability in binding to its complementary DNA than deoxyribose-phosphate. Thus, it could serve as an agent for gene modulation, demonstrating potential in antisense therapy, molecular diagnostics, and nanotechnology. However, the applications of PNA remain limited because its biological activities are not fully known. Here, I demonstrate that a thermostable DNA polymerase, Thermus aquaticus (Taq) polymerase, exhibits transcriptase activity when a PNA oligomer is used as a template and that genetic information of the oligomer can be amplified by PCR using DNA primers. Furthermore, the insertion of a glutamine peptide stretch in the middle part of the PNA template did not interfere with transcription; it was transcribed into a guanosine or adenosine stretch. Intriguingly, this amino acid-to-DNA transcription did not occur when glycine residues were inserted. A synthetic PNA oligomer can, therefore, function as a template for a DNA polymerase, and polyglutamine peptides can be transcribed into guanosine or adenosine. These findings provide a cornerstone to reveal all amino acid genetic codes and transcription activity in the future.

A simple fluorescent assay for the detection of peptide nucleic acid-directed double strand duplex invasion

Peptide nucleic acid (PNA) is a mimic of nucleic acids that is able to bind complementary oligonucleotides with high affinity and excellent selectivity. As such, the use of PNA has been proposed in numerous applications in biochemistry, medicine, and biotechnology. Sequences of pseudo-complementary PNAs containing diaminopurine (D)-2-thiouracil (^S U) base pairs bind to complementary regions within double-stranded DNA targets. This type of binding is termed "double duplex invasion" and involves unwinding of the duplex accompanied by simultaneous hybridization of both DNA strands by the two pseudo-complementary PNAs. In this study, a simple method of assaying DNA strand invasion by pseudo-complementary PNAs was developed. This method is based on the incorporation of a single fluorescent cytidine analog, phenylpyrrolocytidine (PhpC), into the double-stranded DNA target such that upon invasion by PNA, the PhpC is displaced to a single-stranded region resulting in the turn-on of fluorescence emission. This fluorescent assay is applicable to studies both at equilibrium and approach-to-equilibrium (time-dependent) conditions.

Paper-based sensor from pyrrolidinyl peptide nucleic acid for the efficient detection of Bacillus cereus

Bacillus cereus is one of the most common foodborne pathogens found in various kinds of staple foods such as rice and wheat. A rapid and accurate detection method for this pathogen is highly desirable for the sustainable production of relevant food products. While several classical and molecular-based detection methods are available for the identification of B. cereus, they suffered one or more limitations such as the requirement for a tedious and time-consuming process, less than ideal specificity, and the lack of portability. Herein, we developed the first paper-based sensing device that exhibits high species specificity with sufficiently low limit of detection for the visual detection of specific DNA sequences of B. cereus. The success is attributed to the strategic planning of fabrication in various dimensions including thorough bioinformatics search for highly specific genes, the use of the pyrrolidinyl peptide nucleic acid (PNA) probe whose selectivity advantage is well documented, and an effective PNA immobilization and DNA-binding visualization method with an internal cross-checking system for validating the results. Testing in rice matrices indicates that the sensor is capable of detecting and distinguishing B. cereus from other bacterial species. Hence, this paper-based sensor has potential to be adopted as a practical means to detect B. cereus in food industries.

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

Peptide nucleic acid (PNA) is arguably one of the most successful DNA mimics, despite a most dramatic departure from the native structure of DNA. The present review summarizes 30 years of research on PNA's chemistry, optimization of structure and function, applications as probes and diagnostics, and attempts to develop new PNA therapeutics. The discussion starts with a brief review of PNA's binding modes and structural features, followed by the most impactful chemical modifications, PNA enabled assays and diagnostics, and discussion of the current state of development of PNA therapeutics. While many modifications have improved on PNA's binding affinity and specificity, solubility and other biophysical properties, the original PNA is still most frequently used in diagnostic and other in vitro applications. Development of therapeutics and other in vivo applications of PNA has notably lagged behind and is still limited by insufficient bioavailability and difficulties with tissue specific delivery. Relatively high doses are required to overcome poor cellular uptake and endosomal entrapment, which increases the risk of toxicity. These limitations remain unsolved problems waiting for innovative chemistry and biology to unlock the full potential of PNA in biomedical applications.

Peptide nucleic acids and their role in gene regulation and editing

The unique properties of peptide nucleic acid (PNA) makes it a desirable candidate to be used in therapeutic and biotechnological interventions. It has been broadly utilized for numerous applications, with a major focus in regulation of gene expression, and more recently in gene editing. While the classic PNA design has mainly been employed to date, chemical modifications of the PNA backbone and nucleobases provide an avenue to advance the technology further. This review aims to discuss the recent developments in PNA based gene manipulation techniques and the use of novel chemical modifications to improve the current state of PNA mediated gene targeting.

Pyrrolidinyl peptide nucleic acids bearing hydroxy-modified cyclobutane building blocks: Synthesis and binding properties

The conformationally constrained pyrrolidinyl PNA with a dipeptide consisting of an alternating nucleobase-modified D-proline and a cyclic β-amino acid "spacer" exhibited improved nucleic acid binding properties compared to the original PNA. The pyrrolidinyl PNA with the four-membered ring spacer (1S,2S)-2-aminocyclobutanecarboxylic acid (acbcPNA) are among the best performed members of the pyrrolidinyl PNA family. However, these PNA suffer some limitations such as aqueous solubility and non-specific interactions due to their extreme hydrophobicity. In the present work, a hydroxy group is introduced onto the cyclobutane ring spacer of the acbcPNA with the aim of decreasing its hydrophobicity. To this end, a Fmoc/tBu ether-protected 4-hydroxy-2-aminocyclobutanecarboxylic acid building block was synthesized and resolved by chiral HPLC. Each enantiomer was used to synthesize the hydroxy-modified acbcPNA employing Fmoc solid-phase peptide synthesis. DNA/RNA binding studies indicated that the introduction of the hydroxy group to the acbcPNA decreases the binding affinity toward complementary DNA and RNA while maintaining the sequence and directional specificity of unmodified acbcPNA. The hydrophobicity of the hydroxy-modified acbcPNA decreased with the number of hydroxy groups added as indicated by the decrease in the logP values. Only two modifications were sufficient to decrease the logP by an order of magnitude without excessively lowering the binding affinity nor the specificity. This work thus demonstrated that the specific structural modifications for this type of PNA model can be performed in a modular fashion, which paves the way toward the future realization of improving hydrophilicity and nucleic acid binding affinity as well as specificity.

DNA with zwitterionic and negatively charged phosphate modifications: Formation of DNA triplexes, duplexes and cell uptake studies

Two phosphate modifications were introduced into the DNA backbone using the Staudinger reaction between the 3’,5’-dinucleoside β-cyanoethyl phosphite triester formed during DNA synthesis and sulfonyl azides, 4-(azidosulfonyl)-N,N,N-trimethylbutan-1-aminium iodide (N+ azide) or p-toluenesulfonyl (tosyl or Ts) azide, to provide either a zwitterionic phosphoramidate with N+ modification or a negatively charged phosphoramidate for Ts modification in the DNA sequence. The incorporation of these N+ and Ts modifications led to the formation of thermally stable parallel DNA triplexes, regardless of the number of modifications incorporated into the oligodeoxynucleotides (ONs). For both N+ and Ts-modified ONs, the antiparallel duplexes formed with complementary RNA were more stable than those formed with complementary DNA (except for ONs with modification in the middle of the sequence). Additionally, the incorporation of N+ modifications led to the formation of duplexes with a thermal stability that was less dependent on the ionic strength than native DNA duplexes. The thermodynamic analysis of the melting curves revealed that it is the reduction in unfavourable entropy, despite the decrease in favourable enthalpy, which is responsible for the stabilisation of duplexes with N+ modification. N+ONs also demonstrated greater resistance to nuclease digestion by snake venom phosphodiesterase I than the corresponding Ts-ONs. Cell uptake studies showed that Ts-ONs can enter the nucleus of mouse fibroblast NIH3T3 cells without any transfection reagent, whereas, N+ONs remain concentrated in vesicles within the cytoplasm. These results indicate that both N+ and Ts-modified ONs are promising for various in vivo applications.

Isothermal Detection of Canine Blood Parasite (Ehrlichia canis) Utilizing Recombinase Polymerase Amplification Coupled with Graphene Oxide Quenching-Based Pyrrolidinyl Peptide Nucleic Acid

Canine monocytic ehrlichiosis (CME), caused by transmitted Ehrlichia canis infection, is a major disease in dogs with worldwide distribution. Herein, a nucleic acid assay was established for the identification of E. canis infection employing a fluorescently labeled conformationally constrained pyrrolidinyl PNA probe (Flu-acpcPNA) designed to sequence-specifically target the 16S rRNA gene. The sensing principle is based on the excellent quenching ability of graphene oxide (GO) of the free PNA probe, that was diminished upon binding to the DNA target. The addition of DNase I improved the performance of the detection system by eliminating the nonspecific quenching capability of long-chain dsDNA and thus enhancing the fluorescence signaling. The assay was coupled with a recombinase polymerase amplification (RPA) technique, which could be performed under isothermal conditions (37 °C) without DNA denaturation and purification steps. The established method is simple to set up and execute, proving a rapid, specific, and sensitive detection of 16S rRNA gene of E. canis with a limit of detection at least 11.1 pM. This technique shows good potential for the visual detection of double-stranded DNA targets without the need for PCR or complicated instruments, which shows great promise for practical usage in resource limited areas.

Investigation of the Characteristics of NLS-PNA: Influence of NLS Location on Invasion Efficiency

Peptide nucleic acid can recognise sequences in double-stranded DNA (dsDNA) through the formation of a double-duplex invasion complex. This double-duplex invasion is a promising method for the recognition of dsDNA in cellula because peptide nucleic acid (PNA) invasion does not require the prior denaturation of dsDNA. To increase its applicability, we developed PNAs modified with a nuclear localisation signal (NLS) peptide. In this study, the characteristics of NLS-modified PNAs were investigated for the future design of novel peptide-modified PNAs.

Stepwise Strategy for One-Pot Synthesis of Single-Stranded DNA Rings from Multiple Short Fragments

Cyclic rings of single-stranded (ss) DNA have various unique properties, but wider applications have been hampered by their poor availability. This paper reports a convenient one-pot method in which these rings are efficiently synthesized by using T4 DNA ligase through convergent cyclization of easily available short DNA fragments. The key to the present method is to separate all the splint oligonucleotides into several sets, and add each set sequentially at an appropriate interval to the solutions containing all the short DNA fragments. Compared with simple one-pot strategies involving simultaneous addition of all the splints at the beginning of the reaction, both the selectivity and the yields of target ssDNA rings are greatly improved. This convergent method is especially useful for preparing large-sized rings that are otherwise hard to obtain. By starting from six short DNA fragments (71-82 nt), prepared by a DNA synthesizer, a ssDNA ring of 452-nt size was synthesized in 35 mol % yield and in high selectivity. Satisfactorily pure DNA rings were obtainable simply by treating the crude products with exonuclease.

Pyrrolidinyl Peptide Nucleic Acid Probes Capable of Crosslinking with DNA: Effects of Terminal and Internal Modifications on Crosslink Efficiency

In this study, we describe a furan-modified acpcPNA as a probe that can form an interstrand crosslink (ICL) with its DNA target upon activation with N-bromosuccinimide (NBS). To overcome the problem of furan instability under acidic conditions, a simple and versatile post-synthetic methodology for the attachment of the furan group to the PNA probe was developed. Unlike in other designs, the furan was placed at the end of the PNA molecule or tethered to the PNA backbone with all the base pairs in the PNA ⋅ DNA duplexes fully preserved. Hence, the true reactivity of each nucleobase towards the crosslinking could be compared. We show that all DNA bases except T could participate in the crosslinking reaction when the furan was placed at the end of the PNA strand. The crosslinking process was sensitive to mispairing, and lower crosslinking efficiency was observed in the presence of a base-mismatch in the PNA ⋅ DNA duplex. In contrast, when the furan was placed at internal positions of the acpcPNA ⋅ DNA duplex, no ICL was observed; this was explained by the inability of a hydrogen-bonded nucleobase to participate in the crosslinking reaction. The crosslinking efficiency was considerably improved, despite lower duplex stability, when an unpaired base (in the form of C-insertion) was present in the complementary DNA strand close to the furan modification site.

Transport Oligonucleotides-A Novel System for Intracellular Delivery of Antisense Therapeutics

Biological activity of antisense oligonucleotides (asON), especially those with a neutral backbone, is often attenuated by poor cellular accumulation. In the present proof-of-concept study, we propose a novel delivery system for asONs which implies the delivery of modified antisense oligonucleotides by so-called transport oligonucleotides (tON), which are oligodeoxyribonucleotides complementary to asON conjugated with hydrophobic dodecyl moieties. Two types of tONs, bearing at the 5′-end up to three dodecyl residues attached through non-nucleotide inserts (TD series) or anchored directly to internucleotidic phosphate (TP series), were synthesized. tONs with three dodecyl residues efficiently delivered asON to cells without any signs of cytotoxicity and provided a transfection efficacy comparable to that achieved using Lipofectamine 2000. We found that, in the case of tON with three dodecyl residues, some tON/asON duplexes were excreted from the cells within extracellular vesicles at late stages of transfection. We confirmed the high efficacy of the novel and demonstrated that MDR1 mRNA targeted asON delivered by tON with three dodecyl residues significantly reduced the level of P-glycoprotein and increased the sensitivity of KB-8-5 human carcinoma cells to vinblastine. The obtained results demonstrate the efficacy of lipophilic oligonucleotide carriers and shows they are potentially capable of intracellular delivery of any kind of antisense oligonucleotides.

Aminoglycoside Conjugation for RNA Targeting: Antimicrobials and Beyond

Natural aminoglycosides are therapeutically useful antibiotics and very efficient RNA ligands. They are oligosaccharides that contain several ammonium groups able to interfere with the translation process in prokaryotes upon binding to bacterial ribosomal RNA (rRNA), and thus, impairing protein synthesis. Even if aminoglycosides are commonly used in therapy, these RNA binders lack selectivity and are able to bind to a wide number of RNA sequences/structures. This is one of the reasons for their toxicity and limited applications in therapy. At the same time, the ability of aminoglycosides to bind to various RNAs renders them a great source of inspiration for the synthesis of new binders with improved affinity and specificity toward several therapeutically relevant RNA targets. Thus, a number of studies have been performed on these complex and highly functionalized compounds, leading to the development of various synthetic methodologies toward the synthesis of conjugated aminoglycosides. The aim of this review is to highlight recent progress in the field of aminoglycoside conjugation, paying particular attention to modifications performed toward the improvement of affinity and especially to the selectivity of the resulting compounds. This will help readers to understand how to introduce a desired chemical modification for future developments of RNA ligands as antibiotics, antiviral, and anticancer compounds.

Selective Targeting of Guanine-Vacancy-Bearing G-Quadruplexes by G-Quartet Complementation and Stabilization with a Guanine-Peptide Conjugate

Stabilization of G-quadruplexes (G4s) formed in guanine-rich (G-rich) nucleic acids by small-molecule ligands has been extensively explored as a therapeutic approach for diseases such as cancer. Finding ligands with sufficient affinity and specificity toward G4s remains a challenge, and many ligands reported seemed to compromise between the two features. To cope with this challenge, we focused on targeting a particular type of G4s, i.e., the G-vacancy-bearing G-quadruplexes (GVBQs), by taking a structure complementation strategy to enhance both affinity and selectivity. In this approach, a G-quadruplex-binding peptide RHAU23 is guided toward a GVBQ by a guanine moiety covalently linked to the peptide. The filling-in of the vacancy in a GVBQ by the guanine ensures an exclusive recognition of GVBQ. Moreover, the synergy between the RHAU23 and the guanine dramatically improves both the affinity toward and stabilization of the GVBQ. Targeting a GVBQ in DNA by this bifunctional peptide strongly suppresses in vitro replication. This study demonstrates a novel and promising alternative targeting strategy to a distinctive panel of G4s that are as abundant as the canonical ones in the human genome.

Targeting nucleic acids with a G-triplex-to-G-quadruplex transformation and stabilization using a peptide-PNA G-tract conjugate

A dual-functional peptide-PNA (peptide nucleic acid) conjugate consisting of a PNA G3-tract and an RHAU23 peptide is devised to target nucleic acids bearing three tandem guanine tracts (G-tracts). The PNA G3-tract joins the three G-tracts to form a stable bimolecular G-quadruplex (G4) and the resulting G4 is then bound by the RHAU23 moiety to form an extra stable G4-peptide complex. Owing to this synergistic dual structural enforcement, the conjugate accomplished extremely high selectivity and nM to sub-nM affinities towards its targets that are up to 1000 times greater than the small molecule G4 ligands. As a result, the conjugate impacts the tracking activity of motor proteins on DNA with superior selectivity and potency that are rarely seen in other G4-targeting approaches.

Quenching of fluorescently labeled pyrrolidinyl peptide nucleic acid by oligodeoxyguanosine and its application in DNA sensing

Oligodeoxyguanosine effectively quenches the fluorescence of PNA probes via electrostatic interaction, and the signal is restored by the addition of complementary DNA targets.