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Akihiko Ueno

Publications and source records attributed to Akihiko Ueno.

15 recordsLinked to original sources
PubMed2006

Chiral recognition by fluorescent chemosensors based on N-dansyl-amino acid-modified cyclodextrins.

Four kinds of N-dansyl-amino acid-modified beta-cyclodextrins (beta-CDs) were prepared as fluorescent chemosensors for chiral discrimination. The use of an amino acid as a spacer improved binding affinities and chiral discrimination abilities of the chemosensors. N-dansyl-l-Phe-modified beta-CD showed high d-selectivity for norbornane derivatives and N-dansyl-d-Phe-modified beta-CD showed high l-selectivity for menthol. Microcalorimetric titration results indicate that the chemosensors selectively accommodate the enantiomer that induces the least unfavorable entropy change on making an inclusion complex.

Amino Acids↗
PubMed2006

Direct assay for alpha-amylase using fluorophore-modified cyclodextrins.

A simple assay method for alpha-amylase was developed based on fluorophore-modified cyclodextrins (CDs). Four kinds of CD derivatives bearing a 4-amino-7-nitrobenz-2-oxa-1,3-diazole (NBD-amine) moiety were prepared as artificial substrates for the assay method. The fluorescence intensity of all the NBD-amine-modified CDs decreased upon addition of Aspergillus oryzae alpha-amylase, indicating a reduction in hydrophobicity near the NBD-amine moiety induced by hydrolysis of the CD ring. NC4gammaCD, having a gamma-CD and an amino-tetramethylene spacer, was the most sensitive substrate for the alpha-amylase assay. The initial rate of hydrolysis of NC4gammaCD displayed a liner correlation to the concentration of the alpha-amylase. NC4gammaCD was sensitive to the alpha-amylase but was not sensitive to guest compounds that were accommodated by the native CDs.

Aspergillus oryzae↗
PubMed2005

Skeleton-selective fluorescent chemosensor based on cyclodextrin bearing a 4-amino-7-nitrobenz-2-oxa-1,3-diazole moiety.

A new type of fluorescent chemosensor, based on modified cyclodextrins bearing the fluorophore unit NBD-amine, was prepared. One of these new chemosensors, NC0betaCD, is sensitive to adamantane and borneol derivatives, which have a comparatively spherical shape that fits the beta-CD cavity, but is not sensitive to bile acids, which are strongly bound by the native beta-CD. Even in the presence of a bile acid, NC0betaCD can detect 1-adamantanol. Another of this new type of chemosensors, NC0gammaCD, is sensitive to bile acids but not to adamantane derivatives. The response of the new type of chemosensors to a guest was an increase in the fluorescence intensity.

Adamantane↗
PubMed2005

Template-assisted stereoselective photocyclodimerization of 2-anthracenecarboxylic acid by bispyridinio-appended gamma-cyclodextrin.

[reaction: see text] Four kinds of bispyridinio-appended gamma-cyclodextrin (gamma-CD) were prepared to make a molecular flask for controlling the stereoselectivity of photocyclodimerization of 2-anthracenecarboxylate. When the photocyclodimerization of 2-anthracenecarboxylate was carried out in the presence of A,E-bispyridinio-appended gamma-CD, the relative yield of one of the configurational isomers, the head-to-head/anti-isomer, was increased 1.8-fold compared to the corresponding yield in the presence of unmodified gamma-CD or in the absence of any gamma-CD. The optical yields of the photocyclodimerization reaction products also increased more than 10-fold by the addition of bispyridinio-appended gamma-CD compared with unmodified gamma-CD.

Anthracenes↗
PubMed2004

Cyclodextrin trimers as receptors for arranging ester and catalyst at optimized location to achieve enhancement of hydrolytic activity.

Two novel trimer receptor molecules (AC and AD trimers) consisting of two alpha-cyclodextrins (alpha-CDs) and one beta-cyclodextrin (beta-CD) have been designed and synthesized in order to make an optimum arrangement between a substrate and a catalyst. In the reaction systems that use trimer receptors as host molecules, the substrate and the catalyst are thought to be accommodated by two alpha-CDs and one beta-CD, respectively. The rate for the hydrolytic reaction of a long-shaped ester was largely increased, when the trimer receptors were used as receptor molecules or molecular flasks, which provided optimum location between the substrate and the catalyst.

Catalysis↗
PubMed2004

Enantioselective ester hydrolysis catalyzed by beta-cyclodextrin conjugated with beta-hairpin peptides.

Designed cyclodextrin-peptide conjugates, which have one or two beta-hairpin peptides, have been synthesized as catalysts for ester hydrolysis. One or two beta-hairpin peptides were located at the primary hydroxyl group side of beta-cyclodextrin so as to arrange two histidine residues that act as a general acid and a general base catalysts and provide the substrate recognition subsite. Kinetic studies revealed that the two-beta-hairpin peptide was more effective than that of the one-beta-hairpin peptide for substrate recognition.

Carcinogens↗
PubMed2003

Fluorescence resonance energy transfer in a novel cyclodextrin-peptide conjugate for detecting steroid molecules.

A novel cyclodextrin conjugated peptide, 1, having two different fluorophores, coumarin and pyrene, in the side chains has been designed and synthesized. The circular dichroism study reveals that 1 shows typical alpha-helix pattern, and forms intramolecular inclusion complex with coumarin. The fluorescence emission study shows that the peptide exhibits intramolecular fluorescence resonance energy transfer (FRET) without quenching of two fluorophores. We have determined the binding constants of 1 for various biologically important steroid molecules as guests using the guest-responsive variation in the fluorescence emission intensity of coumarin.

Circular Dichroism↗
PubMed2003

Efficient transport of saccharides through a liquid membrane mediated by a cyclodextrin dimer.

A new efficient system for transporting saccharides through a liquid membrane has been constructed. The transport rates of saccharides were accelerated greatly by the cyclodextrin dimer 2; by contrast, the corresponding cyclodextrin monomer 1 was not effective at mediating saccharide transport. The transport rate of D-ribose through a chloroform liquid membrane was 17 times faster when the cyclodextrin dimer 2 was used as the transporter than when the cyclodextrin monomer 1 was used. Similarly the transport rate of methyl D-galactopyranoside was 16 times faster by 2 than by 1.

Biological Transport↗
PubMed2003

Complementary nucleobase interaction enhances peptide-peptide recognition and self-replicating catalysis.

The availability of the complementary interaction of nucleobases for influencing the formation of peptide architectures was explored. Nucleobases were incorporated as additional recognition elements in coiled-coil peptides by employing nucleobase amino acids (NBAs), which are artificial L-alpha-amino gamma-nucleobase-butyric acids. The effect of the base-pair interaction on intermolecular recognition between peptides was evaluated through a self-replication reaction. The self-replication reactions of the peptides with complementary base pairs such as thymine-adenine or guanine-cytosine at the g-g' heptad positions were accelerated in comparison with those of the peptides with mismatched base pairs or without nucleobases. However, thymine-adenine pairs at the e-e' positions did not enhance the self-replication. In the presence of a denaturant, the enhancement effects of complementary base pairs on the reaction disappeared. Thermal denaturation studies showed that the thymine-adenine pairs contributed to stabilization of the coiled-coil structure and that the pairs at the g-g' positions were more effective than those at the e-e' positions. The peptide-peptide interaction was reinforced by complementary nucleobase interactions appropriately arranged in the peptide structure; these led to acceleration of the self-replication reactions.

Amino Acid Sequence↗
PubMed2003

Novel peptides bearing pyrene and coumarin units with or without beta-cyclodextrin in their side chains exhibit intramolecular fluorescence resonance energy transfer.

Novel peptides bearing the pyrene/coumarin FRET pair in their side chains have been designed and synthesized. Peptide 1 having endogenous beta-cyclodextrin (beta-CD) in the side chain exhibits FRET in aqueous solution, indicating that coumarin, being accommodated into the CD cavity, is separated from pyrene. Guest-induced quenching of the fluorophores in 1 indicates that coumarin, being excluded from the CD cavity, comes into close contact with pyrene. Peptide 2 shows FRET only after addition of external beta-CD that again reflects the idea that beta-CD surely caps the coumarin unit in its hydrophobic cavity, and, therefore, quenching of the fluorophores can be prevented in FRET peptide probes. With this strategy, various peptide-based FRET probes can be developed that would be useful for studying biological phenomena in living cells.

Circular Dichroism↗
PubMed2002

Amyloid architecture: complementary assembly of heterogeneous combinations of three or four peptides into amyloid fibrils.

The amyloid fibril is a misfolded and undesirable state for proteins that has been proposed to be a causative agent for a variety of fatal diseases known as amyloid diseases, such as Alzheimer's and prion diseases. However, the fibril has a highly ordered tertiary structure in which numerous beta-strand polypeptide chains align in a regular pattern. Thus, this kind of fibril has the potential to be engineered into proteinaceous materials. Amyloid fibrils of misfolded proteins primarily comprise a single polypeptide species, that is, the self-assembly is homogeneous. We here found that three or four designed peptides can assemble heterogeneously and cooperatively into amyloid fibrils, a process accompanied by a drastic secondary structural transition from alpha helix to beta sheet. Heterogeneous assembly into fibrils is accomplished by complementary electrostatic interactions between three or four peptide species, each of which is not able to self-assemble homogeneously. These findings will lead to a novel way to study the molecular details of amyloid formation and also to design beta-sheet peptidyl materials.

Amino Acid Sequence↗
PubMed2002

Nucleobase amino acids incorporated into the HIV-1 nucleocapsid protein increased the binding affinity and specificity for a hairpin RNA.

L-alpha-amino acids with a nucleobase in the side chain (nucleobase amino acids; NBAs) were used to enhance the function of RNA-binding proteins that recognize structured RNA. These NBAs were utilized in the three-dimensional structure of the protein to enhance RNA binding affinity and specificity as a result of selective recognition of NBAs by RNA bases. NBA units were incorporated at various positions into the HIV-1 nucleocapsid protein NCp7 (residues 1-55), which contains two CCHC-type (Cys-X(2)-Cys-X(4)-His-X(4)-Cys-type; X=an amino acid residue) zinc knuckle domains. The binding ability was evaluated by using the stem-loop (SL)3 region of HIV-1 Psi-RNA. Visible light absorption measurements revealed that two zinc ions bound strongly and quantitatively to the NBA-NCp7 molecule and to the wild-type NCp7 protein. This result indicates that the incorporation of NBA units composed of L-alpha-amino acids did not influence the formation of the specific structure of NCp7. Binding analysis with fluorescein-labeled SL3 RNA revealed that incorporation of NBA units into the NCp7 protein at appropriate positions increased its RNA binding affinity and specificity. An NBA-NCp7 protein that possessed cytosine and guanine NBA units at positions 13 and 46, respectively, showed a binding affinity for SL3 RNA ninefold higher than that of wild-type NCp7 as a result of the specific and cooperative interaction of the NBA units with RNA bases. These results clearly demonstrate that inclusion of NBA units in the three-dimensional structure of an RNA-binding protein is a useful strategy for enhancing the function of the protein.

Amino Acid Sequence↗
PubMed2002

Construction of the novel conformationally-restricted peptide library for screening of peptides that control the interaction between nucleobases.

A unique conformationally-restricted peptide library was constructed using a loop structure as a structural scaffold. This library was used for the screening of the amino acid sequences that control the interaction between nucleobase triplets. The peptides have PNAs at the C-terminus as the recognition site and the random amino acid sequence at the N-terminus as the effector for the interaction between PNA and its complementary DNA triplets. From the peptide libraries constructed by the positional scanning method, the sequences that affect the interaction between PNA and complementary DNA were selected. The difference in the characteristic results by using A-T and G-C pairs was presented. This study would also give us some useful information about interaction between peptides and nucleic acids, such as relevances between these biomolecules in a prebiotic era.

Animals↗
PubMed2002

Heterodimerization of dye-modified cyclodextrins with native cyclodextrins.

The heterodimerization behavior of dye-modified beta-cyclodextrins (1-6) with native cyclodextrins (CDs) was investigated by means of absorption and induced circular dichroism spectroscopy in an aqueous solution. Three types of azo dye-modified beta-CDs (1-3) show different association behaviors, depending on the positional difference and the electronic character of substituent connected to the CD unit in the dye moiety. p-Methyl red-modified beta-CD (1), which has a 4-(dimethylamino)azobenzene moiety connected to the CD unit at the 4' position by an amido linkage, forms an intramolecular self-complex, inserting the dye moiety in its beta-CD cavity. It also associates with the native alpha-CD by inserting the moiety of 1 into the alpha-CD cavity. The association constants for such heterodimerization are 198 M(-1) at pH 1.00 and 305 M(-1) at pH 6.59, which are larger than the association constant of 1 for beta-CD (43 M(-1) at pH 1.00). Methyl red-modified 2, which has the same dye moiety as that for 1 although its substituent position is different from that of 1, does not associate even with alpha-CD due to the stable self-intramolecular complex, in which the dye moiety is deeply included in its own cavity of beta-CD. Alizarin yellow-modified CD (3), which has an azo dye moiety different from that of 1 and 2, caused a slight spectral variation upon addition of alpha-CD, suggesting that the interaction between 3 and alpha-CD is weak. On the other hand, phenolphthalein-modified beta-CD (4), which forms an intermolecular association complex in its higher concentrations, binds with beta-CD with an association constant of 787 M(-1) at pH 10.80, where 4 exists as the dianion monomer in the absence of beta-CD. p-Nitorophenol-modified beta-CDs (5 and 6), each having p-nitorophenol moieties with a different connecting part with an amido and amidophenyl group, respectively, associated with alpha-CD with association constants of 66 and 16 M(-1) for 5 and 6, respectively. The phenyl unit in the connecting part of 6 may prevent the smooth binding with alpha-CD. All these results suggest that the dye-modified CDs, in which the dye part is not tightly included in its CD cavity, associate with the native CD to form heterodimer composed of two different CD units by inserting the dye moiety into the native CD unit. The resulting heterodimers have a cavity that can bind another appending moiety of host molecules. On this basis, more ordered molecular arrays or the supramolecular hereropolymers can be constructed.

Journal Article↗