Nanopore Analysis of the 5-Guanidinohydantoin to Iminoallantoin Isomerization in Duplex DNA

Simultaneous Dual-Site Identification of 5mC/8oG in DNA Triplex Using a Nanopore Sensor

DNA triplex participates in delivering site-specific epigenetic modifications critical for the regulation of gene expression. Among these marks, 5mC with 8oG functions comprehensively on gene expression. Recently, few research studies have emphasized the necessity of incorporation detection of 5mC with 8oG using one DNA triplex at the same time. Herein, DNA triplex structure was designed and tailored for the site-specific identification of 5mC with 8oG by means of nanopore electroanalysis. The identification was associated with the distinguishable current modulation types caused by DNA unzipping through the nanopore in an electrical field. Results demonstrated that the epigenetic modification proximity to the latch zone or constriction area of the nanopore enables differentiation of modification series at single nucleotide resolution in one DNA triplex, at both physiological and mildly acidic environment. In addition, our nanopore method enables the kinetic and thermodynamic studies to calculate the free energy of modified DNA triplex with applied potentials. Gibbs' energy provided the direct evidence that the DNA triplex with these epigenetic modifications is more stable in acidic environment. Considering modified DNA functions significantly in gene expression, the presented method may provide future opportunities to understand incorporating epigenetic mechanisms of many dysregulated biological processes on the basis of accurate detection.

Current and Future Methodology for Quantitation and Site-Specific Mapping the Location of DNA Adducts

Formation of DNA adducts is a key event for a genotoxic mode of action, and their presence is often used as a surrogate for mutation and increased cancer risk. Interest in DNA adducts are twofold: first, to demonstrate exposure, and second, to link DNA adduct location to subsequent mutations or altered gene regulation. Methods have been established to quantitate DNA adducts with high chemical specificity and to visualize the location of DNA adducts, and elegant bio-analytical methods have been devised utilizing enzymes, various chemistries, and molecular biology methods. Traditionally, these highly specific methods cannot be combined, and the results are incomparable. Initially developed for single-molecule DNA sequencing, nanopore-type technologies are expected to enable simultaneous quantitation and location of DNA adducts across the genome. Herein, we briefly summarize the current methodologies for state-of-the-art quantitation of DNA adduct levels and mapping of DNA adducts and describe novel single-molecule DNA sequencing technologies to achieve both measures. Emerging technologies are expected to soon provide a comprehensive picture of the exposome and identify gene regions susceptible to DNA adduct formation.

Recent advances in biological nanopores for nanopore sequencing, sensing and comparison of functional variations in MspA mutants

Biological nanopores are revolutionizing human health by the great myriad of detection and diagnostic skills. Their nano-confined area and ingenious shape are suitable to investigate a diverse range of molecules that were difficult to identify with the previous techniques. Additionally, high throughput and label-free detection of target analytes instigated the exploration of new bacterial channel proteins such as Fragaceatoxin C (FraC), Cytolysin A (ClyA), Ferric hydroxamate uptake component A (FhuA) and Curli specific gene G (CsgG) along with the former ones, like α-hemolysin (αHL), Mycobacterium smegmatis porin A (MspA), aerolysin, bacteriophage phi 29 and Outer membrane porin G (OmpG). Herein, we discuss some well-known biological nanopores but emphasize on MspA and compare the effects of site-directed mutagenesis on the detection ability of its mutants in view of the surface charge distribution, voltage threshold and pore-analyte interaction. We also discuss illustrious and latest advances in biological nanopores for past 2-3 years due to limited space. Last but not the least, we elucidate our perspective for selecting a biological nanopore and propose some future directions to design a customized nanopore that would be suitable for DNA sequencing and sensing of other nontrivial molecules in question.

Detection and Discrimination of DNA Adducts Differing in Size, Regiochemistry, and Functional Group by Nanopore Sequencing

Chemically induced DNA adducts can lead to mutations and cancer. Unfortunately, because common analytical methods (e.g., liquid chromatography-mass spectrometry) require adducts to be digested or liberated from DNA before quantification, information about their positions within the DNA sequence is lost. Advances in nanopore sequencing technologies allow individual DNA molecules to be analyzed at single-nucleobase resolution, enabling us to study the dynamic of epigenetic modifications and exposure-induced DNA adducts in their native forms on the DNA strand. We applied and evaluated the commercially available Oxford Nanopore Technology (ONT) sequencing platform for site-specific detection of DNA adducts and for distinguishing individual alkylated DNA adducts. Using ONT and the publicly available ELIGOS software, we analyzed a library of 15 plasmids containing site-specifically inserted O⁶- or N²-alkyl-2'-deoxyguanosine lesions differing in sizes and regiochemistries. Positions of DNA adducts were correctly located, and individual DNA adducts were clearly distinguished from each other.

γ-Hemolysin Nanopore Is Sensitive to Guanine-to-Inosine Substitutions in Double-Stranded DNA at the Single-Molecule Level

Biological nanopores provide a unique single-molecule sensing platform to detect target molecules based on their specific electrical signatures. The γ-hemolysin (γ-HL) protein produced by Staphylococcus aureus is able to assemble into an octamer nanopore with a ∼2.3 nm diameter β-barrel. Herein, we demonstrate the first application of γ-HL nanopore for DNA structural analysis. To optimize conditions for ion-channel recording, the properties of the γ-HL pore (e.g., conductance, voltage-dependent gating, and ion-selectivity) were characterized at different pH, temperature, and electrolyte concentrations. The optimal condition for DNA analysis using γ-HL corresponds to 3 M KCl, pH 5, and T = 20 °C. The γ-HL protein nanopore is able to translocate dsDNA at about ∼20 bp/ms, and the unique current-signature of captured dsDNA can directly distinguish guanine-to-inosine substitutions at the single-molecule level with ∼99% accuracy. The slow dsDNA threading and translocation processes indicate this wild-type γ-HL channel has potential to detect other base modifications in dsDNA.