Biomedical subjects

Akitsugu Takasu

Publications and source records attributed to Akitsugu Takasu.

5 recordsLinked to original sources

PubMed2004

Analysis of local convergence in NMR structure calculation for RNA by a classification system for nucleic acid structure (CSNA).

We are developing a program system, CSNA, to classify a set of structures into groups sharing similar structural characters. In the present study, CSNA was applied to the analysis of NMR structures obtained by the simulated annealing calculation to elucidate local convergences. A 34-mer RNA, U6-34, having a bulge-out region that is derived from the human U6 snRNA is used as a target molecule in the present study. Although the structure calculation was not converged with the conventional method, it was found by the CSNA analysis that the two stem regions in the molecule were converged well. Furthermore, one strand of the bulge-out region (A7-A11) was found to form a continuously stacked structure in two-thirds of calculated structures. In conclusion, CSNA can be a novel tool to elucidate the local convergence of the NMR structure calculations.

Base Sequence↗

PubMed2003

NMR study on the photoresponsive DNA tethering an azobenzene. Assignment of the absolute configuration of two diastereomers and structure determination of their duplexes in the trans-form.

Two diastereomers of a photoresponsive oligodeoxyribonucleotide tethering a trans-azobenzene, based on the chirality of the central carbon of a diol linker, were separated by reversed-phase HPLC. On the basis of 2D NMR analysis, absolute configurations of the diastereomers alpha and beta (tentatively designated from differences in their retention time) were determined as R- and S-forms, respectively. For both diastereomers, their NMR-determined duplex structure showed that trans-azobenzene intercalates between base pairs, because distinct NOEs were observed between the protons of azobenzene and those of the adjacent base pairs, such as with the imino protons and methyl protons of thymine. The melting temperatures of both duplexes were higher than that of the corresponding native duplex, which contained no azobenzene residue, due to the intercalated trans-azobenzene stabilizing the duplex by a stacking interaction. Between these two diastereomers, differences in T(m) were also found: the melting temperature of the R-form duplex (alpha-isomer) was higher than that of the S-form (beta-isomer). On the basis of the NMR-determined structure, this difference was attributed to the fact that the S-form (beta isomer) causes more stress forming the duplex than does the R-form (alpha isomer) due to disturbances of the right-hand helix.

Azo Compounds↗

PubMed2003

Application of the RNA structure classification system, CSNA, to NMR structure determination.

CSNA is a computer system which classifies a set of RNA structures based on their structural characters; hydrogen bond and base-base stacking. CSNA has been applied to the RNA structure determination by NMR and it was found that CSNA could provide well converged groups as the lowest energy structures. Here, we further applied CSNA to the structure determination of a 31mer RNA forming a psuedoknot structure. It was demonstrated that CSNA is a useful tool for the RNA structure determination by NMR.

Base Sequence↗

PubMed2002

Classification of RNA structures based on hydrogen bond and base-base stacking patterns: application for NMR structures.

A computational system, CSNA, for classifying RNA structures according to structural characters was developed. CSNA lists up all the hydrogen bonds and base-base stackings in the structures, and classifies the structures into sub-groups based on their patterns as the first step grouping. The frequency of each hydrogen bond or base-base stacking is calculated, the frequency score being defined as the sum of the frequency of existing hydrogen bonds or base-base stackings for each sub-group. Finally, the sub-groups are further classified into groups based on the frequency score defined in this study and the difference between the patterns. According to the frequency score, CSNA suggests a group that shares most frequently appearing hydrogen bonds and base-base stackings. CSNA was applied to the classification of the results of two individual simulated annealing calculations based on NMR information. It was found that CSNA could extract structures with lower energy without checking any energy term and could provide well converged groups as the lowest energy structures. Thus, CSNA could be a new tool for structural determination of nucleic acids.

Algorithms↗

PubMedDate not supplied

Analysis of relative positions of ribonucleotide bases in a crystal structure of ribosome.

Relative positions of bases to bases in a crystal structure of ribosome were analyzed extensively. It was found that there is no clear relation between bases apart more than 15 A and, thus, the relative location of bases can be analyzed within 15 A of the reference bases. As for base pairing, major positioning was found to be due to the Watson-Crick type base pairs. Some other positions corresponding to non-Watson-Crick type base pairs were also found in some extents. As for base-base stacking, it was observed that the bases stacked to adenine base are dispersive. It was found that less non-Watson-Crick base pairs was found close to the protein binding site, suggesting that the protein components have a tendency to bind to the regular stem structures. The database of relative location of bases must be useful for improvement of structural determination and structural modeling systems.

Algorithms↗