Evaluation of single-base substitution rate in DNA by affinity capillary electrophoresis

Thermodynamics-based rational design of DNA block copolymers for quantitative detection of single-nucleotide polymorphisms by affinity capillary electrophoresis

Diblock copolymers composed of allele-specific oligodeoxyribonucleotide (ODN) and poly(ethylene glycol) (PEG) are used as an affinity probe of free-solution capillary electrophoresis to quantitatively detect single-base substitutions in genetic samples. During electrophoresis, the probe binds strongly to a wild-type single-stranded DNA analyte (WT) through hybridization, while it binds weakly to its single-base-mutated DNA analyte (MT) due to a mismatch. Complex formation with the probe augments the hydrodynamic friction of either analyte, thereby retarding its migration. The difference in affinity strength leads to separation of the WT, MT, and contaminants, including the PCR primers used for sample preparation. The optimal sequence of the probe's ODN segment is rationally determined in such a way that the binding constant between the ODN segment and MT at the capillary temperature is on the order of 10(6) M(-1). The validity of this guideline is verified using various chemically synthesized DNA analytes, as well as those derived from a bacterial genome. The peak area ratio of MT agrees well with its feed ratio, suggesting the prospective use of the present method in SNP allele frequency estimation.

Dumbbell-shaped DNA analytes amplified by polymerase chain reaction for robust single-nucleotide polymorphism genotyping by affinity capillary electrophoresis

A sample preparation method was developed for single-nucleotide polymorphism (SNP) genotyping based on hybridization between a single-stranded DNA (ssDNA) analyte and an allele-specific oligonucleotide (ASO) probe. When the SNP site is located in the stable secondary structure, the folding of this analyte imposes kinetic penalties on the hybridization with the ASO probe. To address this issue, the sequence of the ssDNA analyte was converted from the original one so that the analyte exhibited a clear dumbbell-shaped structure composed of two stem-loop moieties and an unfolded probe-binding site. The as-prepared analyte was structurally favorable for hybridization with the ASO probe, irrespective of the original sequence and secondary structure of the analyte. The sequence conversion was easily achieved by polymerase chain reaction using forward and reverse primers having an additional sequence at the 5'-terminus. These ssDNA analytes were subjected to affinity capillary electrophoresis using a diblock copolymer probe composed of an ASO segment and a poly(ethylene glycol) segment. The 70-base dumbbell-shaped analytes with a single-base difference were clearly separated within 12 min, although the original ones exhibited almost no separation due to the undesired folding of the probe-binding site. This sample preparation method should open up a wide range of applications for the ASO probes in genetic analysis.

Quantitative SNP genotyping by affinity capillary electrophoresis using PEG-oligodeoxyribonucleotide block copolymers with electroosmotic flow

Quantitative SNP detection was demonstrated with an ACE using a PEG-oligodeoxyribonucleotide block copolymer (PEG-b-ODN) as a probe in the presence of an EOF. The probe's PEG segment with large molecular weight and small polydispersity yielded a high resolution in the separation of a chemically synthesized 60-base ssDNA (WT) and its single-base-substituted mutant (MT). A mixture of WT and MT was clearly separated within 10 min by simultaneously using two types of PEG-b-ODN probes whose ODN segments were complementary to WT and MT and whose PEG segments were of different lengths. The peak area ratio between WT and MT was in good agreement with the feed ratio. The averaged difference between the feed and observed ratio of MT was determined to be 0.23%, which is lower than that of any other methods. The ACE using the PEG-b-ODN probes in the presence of EOF could be utilized as a facile method for estimating SNP allele frequency in various research fields.

Estimation of binding constants of peptide nucleic acid and secondary-structured DNA by affinity capillary electrophoresis

An affinity capillary electrophoresis method was developed to determine a binding constant between a peptide nucleic acid (PNA) and a hairpin-structured DNA. A diblock copolymer composed of PNA and polyethylene glycol (PEG) was synthesized as a novel affinity probe. The base sequence of the probe's PNA segment was complementary to a hairpin-structured region of a 60-base single-stranded DNA (ssDNA). Upon applying a voltage, the DNA hairpin migrated slowly compared to a random sequence ssDNA in the presence of the PNA probe. This retardation was induced by strand invasion of the PNA into the DNA hairpin to form a hybridized complex, where the PEG segment received a large amount of hydrodynamic friction during electrophoresis. The binding constant between the PNA probe and the DNA hairpin was easily determined by mobility analysis. This simple method would be potentially beneficial in studying binding behaviors of various artificial nucleotides to natural DNA or RNA.

Electrochemical and spectroscopic study on the interaction between isoprenaline and DNA using multivariate curve resolution-alternating least squares

Interaction of isoprenaline (ISO) with calf-thymus DNA was studied by spectroscopic and electrochemical methods. The behavior of ISO was investigated at a glassy carbon electrode (GCE) by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV); ISO was oxidized and an irreversible oxidation peak was observed. The binding constant K and the stoichiometric coefficient m of ISO with DNA were evaluated. Also, with the addition of DNA, hyperchromicity of the UV-vis absorption spectra of ISO was noted, while the fluorescence intensity decreased significantly. Multivariate curve resolution-alternating least squares (MCR-ALS) chemometrics method was applied to resolve the combined spectroscopic data matrix, which was obtained by the UV-vis and fluorescence methods. Pure spectra of ISO, DNA and ISO-DNA complex, and their concentration profiles were then successfully obtained. The results indicated that the ISO molecule intercalated into the base-pairs of DNA, and the complex of ISO-DNA was formed.

DNA-functionalized nanochannels for SNP detection

We have developed ultrahigh density array of functionalized nanochannels by using a block copolymer having end di-COOH group. This approach provides a facile route for direct functionalization of wall surface of the nanochannels and immobilization site for molecular recognition agents (MRAs). By using overhanging single-stranded DNA as MRAs, the DNA-functionalized nanochannels showed high resolution to detect a single-base mismatch as well as to discriminate single-mismatched sequence at various locations by hybridization preference with MRAs.

RAFT-generated polyacrylamide-DNA block copolymers for single-nucleotide polymorphism genotyping by affinity capillary electrophoresis

Capillary electrophoretic separation of a mixture of 5'-fluorescein isothiocyanate-labeled single-stranded DNA (normal ssDNA) and its single-base-substituted one (mutant ssDNA) was achieved by using a RAFT-generated polyacrylamide-oligodeoxyribonucleotide block copolymer (PAAm-b-ODN) as an affinity polymeric probe. PAAm-b-ODN was synthesized through the Michael addition of thiol-terminated PAAm (PAAm-SH) to 5'-maleimide-modified ODN. PAAm-SH was derived from dithiobenzoate-terminated PAAm prepared via RAFT polymerization. The number-averaged molecular weight (M(n)) and the molecular weight distribution were determined by aqueous size exclusion chromatography. After a capillary tube was filled with the running buffer solution of PAAm-b-ODN, a mixture of normal and mutant ssDNA was subjected to electrophoresis and detected by a laser-induced fluorescent detector. Because the base sequence of PAAm-b-ODN was complementary to part of the mutant ssDNA, including a single-base substitution site, the electrophoretic migration of mutant ssDNA was retarded due to the formation of the equilibrium complex with PAAm-b-ODN. Increasing M(n) of the PAAm segment enhanced this retardation. On the other hand, normal ssDNA was unable to form the complex owing to a single-base mismatch, which was proved by melting curve measurements. The Lineweaver-Burk-type analysis of the mobility of mutant ssDNA revealed that the binding constants for the complexes with different PAAm-b-ODN probes were almost identical to each other. The analysis also demonstrated that the ratio of the hydrodynamic radius of the complex to that of the free mutant ssDNA increased with increasing M(n) of the affinity polymeric probe's PAAm segment. This means that the PAAm segment indirectly provides mutant ssDNA with an additional hydrodynamic friction force via the affinity interaction of the ODN segment. Optimization of the salt concentration of the running buffer and the capillary temperature improved the resolution of the separation. This affinity polymeric probe will be useful for developing a simple and highly reliable single-nucleotide polymorphism genotyping method.