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author:("Kono, hitoshi")
1.  Local Conformational Changes in the DNA Interfaces of Proteins 
PLoS ONE  2013;8(2):e56080.
When a protein binds to DNA, a conformational change is often induced so that the protein will fit into the DNA structure. Therefore, quantitative analyses were conducted to understand the conformational changes in proteins. The results showed that conformational changes in DNA interfaces are more frequent than in non-interfaces, and DNA interfaces have more conformational variations in the DNA-free form. As expected, the former indicates that interaction with DNA has some influence on protein structure. The latter suggests that the intrinsic conformational flexibility of DNA interfaces is important for adjusting their conformation for DNA. The amino acid propensities of the conformationally changed regions in DNA interfaces indicate that hydrophilic residues are preferred over the amino acids that appear in the conformationally unchanged regions. This trend is true for disordered regions, suggesting again that intrinsic flexibility is of importance not only for DNA binding but also for interactions with other molecules. These results demonstrate that fragments destined to be DNA interfaces have an intrinsic flexibility and are composed of amino acids with the capability of binding to DNA. This information suggests that the prediction of DNA binding sites may be improved by the integration of amino acid preference for DNA and one for disordered regions.
doi:10.1371/journal.pone.0056080
PMCID: PMC3571985  PMID: 23418514
2.  Molecular Structure of Isolated MvspI, a Variable Surface Protein of the Fish Pathogen Mycoplasma mobile 
Journal of Bacteriology  2012;194(12):3050-3057.
Mycoplasma mobile is a parasitic bacterium that causes necrosis in the gills of freshwater fishes. This study examines the molecular structure of its variable surface protein, MvspI, whose open reading frame encodes 2,002 amino acids. MvspI was isolated from mycoplasma cells by a biochemical procedure to 92% homogeneity. Gel filtration and analytical ultracentrifugation suggested that this protein is a cylinder-shaped monomer with axes of 66 and 2.7 nm. Rotary shadowing transmission electron microscopy of MvspI showed that the molecule is composed of two rods 30 and 45 nm long; the latter rod occasionally features a bulge. Immuno-electron microscopy and epitope mapping showed that the bulge end of the molecular image corresponds to the C terminus of the amino acid sequence. Partial digestion by various proteases suggested that the N-terminal part, comprised of 697 amino acids, is flexible. Analysis of the predicted amino acid sequence showed that the molecule features a lipoprotein and 16 repeats of about 90 residues; 15 positions exist between residues 88 and 1479, and the other position is between residues 1725 and 1807. The amino acid sequence of MvspI was mapped onto a molecular image obtained by electron microscopy. The present study is the first to elucidate the molecular shape of a variable surface protein of mycoplasma.
doi:10.1128/JB.00208-12
PMCID: PMC3370835  PMID: 22447898
3.  A new method for evaluating the specificity of indirect readout in protein–DNA recognition 
Nucleic Acids Research  2012;40(17):e129.
Proteins recognize a specific DNA sequence not only through direct contact (direct readout) with base pairs but also through sequence-dependent conformation and/or flexibility of DNA (indirect readout). However, it is difficult to assess the contribution of indirect readout to the sequence specificity. What is needed is a straightforward method for quantifying its contributions to specificity. Using Bayesian statistics, we derived the probability of a particular sequence for a given DNA structure from the trajectories of molecular dynamics (MD) simulations of DNAs containing all possible tetramer sequences. Then, we quantified the specificity of indirect readout based on the information entropy associated with the probability. We tested this method with known structures of protein–DNA complexes. This method enabled us to correctly predict those regions where experiments suggested the involvement of indirect readout. The results also indicated new regions where the indirect readout mechanism makes major contributions to the recognition. The present method can be used to estimate the contribution of indirect readout without approximations to the distributions in the conformational ensembles of DNA, and would serve as a powerful tool to study the mechanism of protein–DNA recognition.
doi:10.1093/nar/gks462
PMCID: PMC3458528  PMID: 22618872
4.  Classifying and assembling two-dimensional X-ray laser diffraction patterns of a single particle to reconstruct the three-dimensional diffraction intensity function: resolution limit due to the quantum noise 
A new algorithm is developed for reconstructing the high-resolution three-dimensional diffraction intensity function of a globular biological macromolecule from many quantum-noise-limited two-dimensional X-ray laser diffraction patterns, each for an unknown orientation. The structural resolution is expressed as a function of the incident X-ray intensity and quantities characterizing the target molecule.
A new two-step algorithm is developed for reconstructing the three-dimensional diffraction intensity of a globular biological macromolecule from many experimentally measured quantum-noise-limited two-dimensional X-ray laser diffraction patterns, each for an unknown orientation. The first step is classification of the two-dimensional patterns into groups according to the similarity of direction of the incident X-rays with respect to the molecule and an averaging within each group to reduce the noise. The second step is detection of common intersecting circles between the signal-enhanced two-dimensional patterns to identify their mutual location in the three-dimensional wavenumber space. The newly developed algorithm enables one to detect a signal for classification in noisy experimental photon-count data with as low as ∼0.1 photons per effective pixel. The wavenumber of such a limiting pixel determines the attainable structural resolution. From this fact, the resolution limit due to the quantum noise attainable by this new method of analysis as well as two important experimental parameters, the number of two-dimensional patterns to be measured (the load for the detector) and the number of pairs of two-dimensional patterns to be analysed (the load for the computer), are derived as a function of the incident X-ray intensity and quantities characterizing the target molecule.
doi:10.1107/S010876731200493X
PMCID: PMC3329770  PMID: 22514069
biological macromolecules; classification of two-dimensional diffraction patterns; common intersecting circles; attainable structural resolution
5.  A generalized conformational energy function of DNA derived from molecular dynamics simulations 
Nucleic Acids Research  2009;37(20):e135.
Proteins recognize DNA sequences by two different mechanisms. The first is direct readout, in which recognition is mediated by direct interactions between the protein and the DNA bases. The second is indirect readout, which is caused by the dependence of conformation and the deformability of the DNA structure on the sequence. Various energy functions have been proposed to evaluate the contribution of indirect readout to the free-energy changes in complex formations. We developed a new generalized energy function to estimate the dependence of the deformability of DNA on the sequence. This function was derived from molecular dynamics simulations previously conducted on B-DNA dodecamers, each of which had one possible tetramer sequence embedded at its center. By taking the logarithm of the probability distribution function (PDF) for the base-step parameters of the central base-pair step of the tetramer, its ability to distinguish the native sequence from random ones was superior to that with the previous method that approximated the energy function in harmonic form. From a comparison of the energy profiles calculated with these two methods, we found that the harmonic approximation caused significant errors in the conformational energies of the tetramers that adopted multiple stable conformations.
doi:10.1093/nar/gkp718
PMCID: PMC2777435  PMID: 19729512
6.  coliSNP database server mapping nsSNPs on protein structures 
Nucleic Acids Research  2007;36(Database issue):D409-D413.
We have developed coliSNP, a database server (http://yayoi.kansai.jaea.go.jp/colisnp) that maps non-synonymous single nucleotide polymorphisms (nsSNPs) on the three-dimensional (3D) structure of proteins. Once a week, the SNP data from the dbSNP database and the protein structure data from the Protein Data Bank (PDB) are downloaded, and the correspondence of the two data sets is automatically tabulated in the coliSNP database. Given an amino acid sequence, protein name or PDB ID, the server will immediately provide known nsSNP information, including the amino acid mutation caused by the nsSNP, the solvent accessibility, the secondary structure and the flanking residues of the mutated residue in a single page. The position of the nsSNP within the amino acid sequence and on the 3D structure of the protein can also be observed. The database provides key information with which to judge whether an observed nsSNP critically affects protein function and/or stability. As far as we know, this is the only web-based nsSNP database that automatically compiles SNP and protein information in a concise manner.
doi:10.1093/nar/gkm801
PMCID: PMC2238833  PMID: 17921498
7.  Sequence-dependent DNA deformability studied using molecular dynamics simulations 
Nucleic Acids Research  2007;35(18):6063-6074.
Proteins recognize specific DNA sequences not only through direct contact between amino acids and bases, but also indirectly based on the sequence-dependent conformation and deformability of the DNA (indirect readout). We used molecular dynamics simulations to analyze the sequence-dependent DNA conformations of all 136 possible tetrameric sequences sandwiched between CGCG sequences. The deformability of dimeric steps obtained by the simulations is consistent with that by the crystal structures. The simulation results further showed that the conformation and deformability of the tetramers can highly depend on the flanking base pairs. The conformations of xATx tetramers show the most rigidity and are not affected by the flanking base pairs and the xYRx show by contrast the greatest flexibility and change their conformations depending on the base pairs at both ends, suggesting tetramers with the same central dimer can show different deformabilities. These results suggest that analysis of dimeric steps alone may overlook some conformational features of DNA and provide insight into the mechanism of indirect readout during protein–DNA recognition. Moreover, the sequence dependence of DNA conformation and deformability may be used to estimate the contribution of indirect readout to the specificity of protein–DNA recognition as well as nucleosome positioning and large-scale behavior of nucleic acids.
doi:10.1093/nar/gkm627
PMCID: PMC2094071  PMID: 17766249
8.  ReadOut: structure-based calculation of direct and indirect readout energies and specificities for protein–DNA recognition 
Nucleic Acids Research  2006;34(Web Server issue):W124-W127.
Protein–DNA interactions play a central role in regulatory processes at the genetic level. DNA-binding proteins recognize their targets by direct base–amino acid interactions and indirect conformational energy contribution from DNA deformations and elasticity. Knowledge-based approach based on the statistical analysis of protein–DNA complex structures has been successfully used to calculate interaction energies and specificities of direct and indirect readouts in protein–DNA recognition. Here, we have implemented the method as a webserver, which calculates direct and indirect readout energies and Z-scores, as a measure of specificity, using atomic coordinates of protein–DNA complexes. This server is freely available at . The only input to this webserver is the Protein Data Bank (PDB) style coordinate data of atoms or the PDB code itself. The server returns total energy Z-scores, which estimate the degree of sequence specificity of the protein–DNA complex. This webserver is expected to be useful for estimating interaction energy and DNA conformation energy, and relative contributions to the specificity from direct and indirect readout. It may also be useful for checking the quality of protein–DNA complex structures, and for engineering proteins and target DNAs.
doi:10.1093/nar/gkl104
PMCID: PMC1538882  PMID: 16844974
9.  ProTherm, version 2.0: thermodynamic database for proteins and mutants 
Nucleic Acids Research  2000;28(1):283-285.
ProTherm 2.0 is the second release of the Thermodynamic Database for Proteins and Mutants that includes numerical data for several thermodynamic parameters, structural information, experimental methods and conditions, functional and literature information. The present release contains >5500 entries, an ~67% increase over the previous version. In addition, we have included information about reversibility of data, details about buffer and ion concentrations and the surrounding residues in space for all mutants. A WWW interface enables users to search data based on various conditions with different sorting options for outputs. Further, ProTherm has links with other structural and literature databases, and the mutation sites and surrounding residues are automatically mapped on the structures and can be directly viewed through 3DinSight developed in our laboratory. The ProTherm database is freely available through the WWW at http://www.rtc.riken.go.jp/protherm.html
PMCID: PMC102403  PMID: 10592247

Results 1-9 (9)