Hiroaki Sawai

Gunma University, Maebashi-shi, Gunma-ken, Japan

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Publications (135)215.5 Total impact

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    ABSTRACT: Short interfering RNA (siRNA) induces specific gene silencing by the RNA interference (RNAi) pathway. Nucleosides in the 3'-overhang regions of siRNAs were replaced with 5-bis(aminoethyl)aminoethylcarbamoylmethyl-2'-deoxyuridine or thymidine. siRNA bearing modified nucleoside was more active in silencing the gene expression of hepatocyte nuclear factor 4α (HNF4α) compared with siRNA bearing thymidine.
    Bioorganic & medicinal chemistry letters 01/2011; 21(2):715-7. · 2.65 Impact Factor
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    ABSTRACT: Recently, KOD and its related DNA polymerases have been used for preparing various modified nucleic acids, including not only base-modified nucleic acids, but also sugar-modified ones, such as bridged/locked nucleic acid (BNA/LNA) which would be promising candidates for nucleic acid drugs. However, thus far, reasons for the effectiveness of KOD DNA polymerase for such purposes have not been clearly elucidated. Therefore, using mutated KOD DNA polymerases, we studied here their catalytic properties upon enzymatic incorporation of nucleotide analogues with base/sugar modifications. Experimental data indicate that their characteristic kinetic properties enabled incorporation of various modified nucleotides. Among those KOD mutants, one achieved efficient successive incorporation of bridged nucleotides with a 2'-ONHCH₂CH₂-4' linkage. In this study, the characteristic kinetic properties of KOD DNA polymerase for modified nucleoside triphosphates were shown, and the effectiveness of genetic engineering in improvement of the enzyme for modified nucleotide polymerization has been demonstrated.
    Molecules 01/2010; 15(11):8229-40. · 2.43 Impact Factor
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    ABSTRACT: The capping of the 3'-ends of thrombin binding aptamers (TBAs) with bridged nucleotides increased the nuclease resistances and the stabilities in human serum. The binding abilities of the aptamers were not affected by the capping. The capping could be simply executed via a one step enzymatic process using 2',4'-bridged nucleoside 5'-triphosphate and terminal deoxynucleotidyl transferase.
    Bioorganic & medicinal chemistry letters 01/2010; 20(5):1626-9. · 2.65 Impact Factor
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    ABSTRACT: An oligodeoxyribonucleotide containing 2 '-O-methoxycarbonylmethyluridine was synthesized and converted into several 2 '-modified oligodeoxyribonucleotides by a postsynthetic modification method. Using this method, oligodeoxyribonucleotides bearing a polyamine at the 2 ' position were easily prepared, which could form duplexes with either complementary DNA or RNA.
    Nucleosides Nucleotides &amp Nucleic Acids 10/2009; 28(10):943-52. · 0.71 Impact Factor
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    ABSTRACT: Oligodeoxyribonucleotides (ODN) where the phosphodiester linkage had been replaced with an amide-type linker [-CH(2)C=ONH-] or an amine-type linker [-CH(2)CH(2)NH-] were synthesized to investigate the effect of these backbone modifications on polymerase reactions. In addition, a triphosphate analogue of thymidine dinucleotide with the amide-type linker was synthesized and enzymatic insertion of the amide linkage into ODN was attempted using this analogue for the polymerase reaction. Primer extension reactions using three types of thermostable DNA polymerases, KOD(exo-), Vent(exo-) and Taq were performed for the assays. Analysis of these data indicate that (i) the polymerase reaction tends to be affected much more by insertion of the cationic flexible amine-type linker than by insertion of the neutral rigid amide-type linker; (ii) the backbone modification has a greater effect on the polymerase reaction when it is adjacent to the 3'-end of a primer as the elongation terminus than when it is on the template, as well as in base or sugar modification; (iii) although the modified linker in the modified DNA template is passed beyond by the polymerase, it still affects the extension reaction several bases downstream from its location; (iv) the modified linker in the template, in some cases, also affects the extension reaction upstream from its location; (v) further improvement of the chemical structure is required for dinucleotide-mimic incorporation.
    Bioorganic & medicinal chemistry 07/2009; 17(11):3782-8. · 2.82 Impact Factor
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    ABSTRACT: Incorporation of 2',4'-bridged nucleotides into the 3'-end of oligodeoxyribonucleotide (ODN) was examined using terminal deoxynucleotidyl transferase (TdT). The three types of 2',4'-bridged nucleoside-5'-triphospates with different bridging structures used were incorporated efficiently into the 3'-end of DNA by TdT, although only single nucleotide incorporation was observed. Nuclease resistance was conferred on DNA, depending on the types of bridging nucleotides added.
    Bioorganic & medicinal chemistry letters 07/2009; 19(11):2941-3. · 2.65 Impact Factor
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    ABSTRACT: Water-soluble neutral cosolutes can be used to quantify biomolecular properties in the particular molecular environment occurring in a cell. We studied the conformation and the thermal stability of DNA and RNA structures in the presence of PEG [poly(ethylene glycol)] and smaller cosolutes of glycerol, ethylene glycol, 1,3-propanediol, 2-methoxyethanol, and 1,2-dimethoxyethane. Although the neutral cosolutes destabilized the oligonucleotide duplex and the hairpin structures, the left-handed Z-form duplex was more energetically favored in the cosolute-containing solutions. These observations were due to the contribution of water molecule on the nucleotide structure formations because the cosolutes act as an osmolyte to reduce the water activity of a solution. Moreover, the sodium ion condensation for the duplex and the hairpin formations was reduced in the presence of PEG, while that for the transition from the B-form to the Z-form was unaltered. The CD (circular dichroism) and EPR (electron paramagnetic resonance) spectra demonstrated that the cosolutes changed the helical conformation of the unstructured oligonucleotides, but not those of the ordered structures. The results of the favorable formation of the noncanonical nucleotide structures, and minimized conformational and thermal perturbations of the ordered nucleotide structures in the cosolute-containing solutions implicate the significance of the intracellular environment on DNA and RNA structures in a cell.
    Molecular BioSystems 07/2008; 4(6):579-88. · 3.35 Impact Factor
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    ABSTRACT: In order to systematically analyze the effects of nucleoside modification of sugar moieties in DNA polymerase reactions, we synthesized 16 modified templates containing 2',4'-bridged nucleotides and three types of 2',4'-bridged nucleoside-5'-triphospates with different bridging structures. Among the five types of thermostable DNA polymerases used, Taq, Phusion HF, Vent(exo-), KOD Dash and KOD(exo-), the KOD Dash and KOD(exo-) DNA polymerases could smoothly read through the modified templates containing 2'-O,4'-C-methylene-linked nucleotides at intervals of a few nucleotides, even at standard enzyme concentrations for 5 min. Although the Vent(exo-) DNA polymerase also read through these modified templates, kinetic study indicates that the KOD(exo-) DNA polymerase was found to be far superior to the Vent(exo-) DNA polymerase in accurate incorporation of nucleotides. When either of the DNA polymerase was used, the presence of 2',4'-bridged nucleotides on a template strand substantially decreased the reaction rates of nucleotide incorporations. The modified templates containing sequences of seven successive 2',4'-bridged nucleotides could not be completely transcribed by any of the DNA polymerases used; yields of longer elongated products decreased in the order of steric bulkiness of the modified sugars. Successive incorporation of 2',4'-bridged nucleotides into extending strands using 2',4'-bridged nucleoside-5'-triphospates was much more difficult. These data indicate that the sugar modification would have a greater effect on the polymerase reaction when it is adjacent to the elongation terminus than when it is on the template as well, as in base modification.
    Nucleic Acids Research 07/2008; 36(13):4257-65. · 8.28 Impact Factor
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    ABSTRACT: Acridone is highly fluorescent and stable against photodegradation, oxidation, and heat. It is also a small molecule with no charge, making it a promising fluorescent agent for use in a DNA probe. Thus, we have prepared 5'-terminal acridone-labeled DNAs by post-modification, and have examined their photophysical properties and their use as donors for a fluorescence resonance energy transfer (FRET) system in combination with a 3'-terminal dabcyl-tagged DNA as an acceptor, which can detect the target DNA by emission-quenching caused by FRET. The FRET with an acridone and dabcyl pair has been found to complement that with fluorescence and dabcyl and other fluorescence-quencher pairs. Significant amounts of quenching of the acridone emissions by guanine in the DNA were observed when guanine was close to acridone, which can be applied as a quencher-free probe for the detection of special sequence of DNA. The DNA bearing acridone at the C5 position of inner thymidine could discriminate the opposite T-T base mismatch, although enhancement of discrimination ability is needed for the practical use of SNP typing.
    Bioorganic & medicinal chemistry 06/2008; 16(14):7013-20. · 2.82 Impact Factor
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    ABSTRACT: Real-time, noninvasive assessment of glomerular filtration rate (GFR) is essential not only for monitoring critically ill patients at the bedside, but also for staging and monitoring patients with chronic kidney disease. In our pursuit to develop exogenous luminescent probes for dynamic optical monitoring of GFR, we have prepared and evaluated Eu(3+) complexes of several diethylenetriamine pentaacetate (DTPA)-monoamide ligands bearing molecular "antennae" to enhance metal fluorescence via intramolecular ligand-metal fluorescence resonance energy transfer process. The results show that Eu-DTPA-monoamide complex 18b, which contains a quinoxanlinyl antenna, exhibits large (ca. 2700-fold) Eu(3+) fluorescence enhancement. Indeed, complex 18b exhibits the highest fluorescent enhancement observed thus far in the DTPA-type metal complexes. The renal clearance property was assessed using the corresponding radioactive (111)In complex 18a, and the data suggest that this complex clears via a complex mechanism that includes glomerular filtration.
    Journal of Medicinal Chemistry 03/2008; 51(4):957-62. · 5.61 Impact Factor
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    ABSTRACT: We have screened glutamic acid-binding aptamers from a modified DNA pool containing arginine residues using the method of systematic evolution of ligands by exponential enrichment (SELEX). Thirty-one modified DNA molecules were obtained from the enriched pool after the 17th round of selection, and their binding affinities for the target were evaluated by binding assays using affinity gels. Three modified DNA molecules having higher affinity were sequenced and we determined their affinity and specificity for the target by surface plasmon resonance (SPR) measurements. The SPR studies indicated that two of these three aptamers distinguished the dicarboxylic acid moiety of the D-isomer from that of the L-isomer; however, the third aptamer did not show enantioselectivity.
    Analytical Sciences 02/2008; 24(1):167-72. · 1.57 Impact Factor
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    ABSTRACT: We synthesized two types of modified DNA templates in which the phosphodiester linkage was replaced with an amide-type linker [-CH(2)C=ONH-] or an amine-type linker [-CH(2)CH(2)NH-]. Primer extension reactions were performed using these modified DNA templates to investigate the effect of backbone modification on polymerase reactions. Our results indicated that the polymerase reaction was affected much more by the insertion of the cationic flexible amine-type linker than by insertion of the neutral rigid amide-type linker.
    Nucleic Acids Symposium Series 02/2008;
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    ABSTRACT: Fluorescent nucleoside analogues were synthesized and derived to protected nucleoside phosphoramidite. The nucleoside analogue bearing 3-aminobenzonitrile was sensitive to the surrounding environment. 3-Aminobenzonitrile is a similar size with pyrimidine base. Therefore, it is expected that the nucleoside little perturbs the formation of duplex. This nucleoside could be incorporated into DNA.
    Nucleic Acids Symposium Series 02/2008;
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    ABSTRACT: The pyrimidine bases of RNA are uracil (U) and cytosine (C), while thymine (T) and C are used for DNA. The C(5) position of C and U is unsubstituted, whereas the C(5) of T is substituted with a Me group. Miller et al. hypothesized that various C(5)-substituted uracil derivatives were formed during chemical evolution, and that C(5)-substituted U derivatives may have played important roles in the transition from an 'RNA world' to a 'DNA-RNA-protein world'. Hyperthermophilic bacteria and archaea are considered to be primitive organisms that are evolutionarily close to the universal ancestor of all life on earth. Thus, we examined the substrate specificity of several C(5)-substituted or C(5)-unsubstituted dUTP and dCTP analogs for several DNA polymerases from hyperthermophilic bacteria, hyperthermophilic archaea, and viruses during PCR or primer extension reaction. The substrate specificity of the C(5)-substituted or C(5)-unsubstituted pyrimidine nucleotides varied greatly depending on the type of DNA polymerase. The significance of this difference in substrate specificity in terms of the origin and evolution of the DNA replication system is discussed briefly.
    Chemistry & Biodiversity 10/2007; 4(9):1979-95. · 1.81 Impact Factor
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    ABSTRACT: Triphosphate of a thymidine analogue bearing acridone was prepared and incorporated as a substrate for PCR using KOD Dash DNA polymerase forming a new fluorescent-labeled DNA that is useful as a DNA probe.
    Bioorganic & Medicinal Chemistry Letters 03/2007; 17(3):776-9. · 2.34 Impact Factor
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    ABSTRACT: A thalidomide-binding aptamer was produced by systematic evolution of ligands by exponential enrichment from a library of non-natural DNA in which thymidine had been replaced with a modified deoxyuridine bearing a cationic functional group via a hydrophobic methylene linker at the C5 position. The additional functional group in the modified DNA aptamer could improve stability against nucleases and increase the binding affinity to thalidomide. The selected aptamer could recognize thalidomide enantioselectively, although a racemic thalidomide-attached gel was used for the selection. Surface plasmon resonance and fluorescence titration studies revealed that the selected modified DNA aptamer and a truncated version bound with an (R)-thalidomide derivative with high enantioselectivity, but not with the (S)-form. The modified group in the DNA aptamer is indispensable for the interaction with thalidomide, as the corresponding natural type DNA bearing the same base sequence showed no binding affinity with (R)- nor (S)-thalidomide. Computational sequence analysis suggested that the selected apatamer (108 mer) could fold into a three-way junction structure; however, truncation of this aptamer (31 mer) revealed that the thalidomide-binding site is a hairpin-bulge region that is a component of one of the arms of the three-way junction structure. The Kd value of the truncated 31 mer aptamer for binding with the (R)-thalidomide derivative was 1.0 microM estimated from fluorescence titration study. The aptamer that can recognize a single enantiomer of thalidomide will be useful as a biochemical tool for the analysis and study of the biological action of thalidomide enantiomers.
    Journal of the American Chemical Society 03/2007; 129(5):1456-64. · 10.68 Impact Factor
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    ABSTRACT: A self-complementary nucleotide sequence can form both a unimolecular hairpin and a bimolecular duplex. In this study, the secondary structures of the self-complementary DNA and RNA oligonucleotides with different sequences and lengths were investigated under various solution conditions by gel electrophoresis, circular dichroism (CD) and electron paramagnetic resonance (EPR) spectroscopy and a ultraviolet (UV) melting analysis. The DNA sequences tended to adopt a hairpin conformation at low cation concentrations, but a bimolecular duplex was preferentially formed at an elevated cationic strength. On the other hand, fully matched RNA sequences adopted a bimolecular duplex regardless of the cation concentration. The thermal melting experiments indicated a greater change in the melting temperature of the bimolecular duplexes (by approximately 20 degrees C) than that of the hairpin (by approximately 10 degrees C) by increasing the NaCl concentration from 10 mM to 1 M. Hairpin formations were also observed for the palindrome DNA sequences derived from Escherichia coli, but association of the complementary palindrome sequences was observed when spermine, one of the major cationic molecules in a cell, existed at the physiological concentration. The results indicate the role of cations for shifting the structural equilibrium toward a nucleotide assembly and implicate nucleotide structures in cells.
    Nucleic Acids Research 02/2007; 35(2):486-94. · 8.28 Impact Factor
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    ABSTRACT: Phenanthroline-polyamine conjugates were synthesized by cross-linking of 1,10-phenanthroline to branched polyamines. The conjugates interacted with DNA strongly, and cleaved plasmid DNA hydrolytically without any metal ions under physiological conditions. The phenanthroline-polyamine conjugates also cleaved linear 30mer DNA at the bulged-out region without metal ions under physiologic conditions.
    Nucleic Acids Symposium Series 02/2007;
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    ABSTRACT: Fluorescent nucleoside analogue bearing 3-amiobenzonitrile, which was a small and sensitive fluoresces probe to the microenvironment, was synthesized by a palladium-mediated Heck-type coupling reaction from iodated 3-aminobenzonitrile derivative and protected glycal. The spectroscopic study of the nucleoside analogue indicated that the fluorescence quenching caused in water and the fluorescent maximum was strongly dependent on the polarity of solvents.
    Nucleic Acids Symposium Series 02/2007;
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    ABSTRACT: We have attempted to synthesise a complimentary strand using oligo-DNA with modified bases, sugars and phosphates as a template strand by polymerase reaction. Analogues bearing C5-substituted uracil, those with amide linkage [-CH2C=ONH-] in place of phospho-diester linkage and those bearing 2'-O, 4'-C-bridged sugar were used. Primer extension reactions were carried out to synthesise complimentary DNA strands. The reactions depended on the thermostable DNA polymerase used, the type of modification or the number of the modified position on the template strand.
    Nucleic Acids Symposium Series 02/2007;

Publication Stats

503 Citations
132 Downloads
215.50 Total Impact Points

Institutions

  • 1988–2011
    • Gunma University
      • • Department of Chemistry and Chemical Biology
      • • Graduate School of Engineering
      • • Faculty of Engineering
      • • Department of Chemistry
      Maebashi-shi, Gunma-ken, Japan
  • 2005–2008
    • Konan University
      • • Frontier Institute for Biomolecular Engineering Research (FIBER)
      • • Faculty of Science and Engineering
      Kōbe-shi, Hyogo-ken, Japan
  • 2002
    • Kumamoto University
      • Department of Child Development
      Kumamoto, Kumamoto Prefecture, Japan