Publications (11)56.12 Total impact
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Article: Genome-wide survey of mutual homologous recombination in a highly sexual bacterial species.
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ABSTRACT: The nature of a species remains a fundamental and controversial question. The era of genome/metagenome sequencing has intensified the debate in prokaryotes because of extensive horizontal gene transfer. In this study, we conducted a genome-wide survey of outcrossing homologous recombination in the highly sexual bacterial species Helicobacter pylori. We conducted multiple genome alignment and analyzed the entire data set of one-to-one orthologous genes for its global strains. We detected mosaic structures due to repeated recombination events and discordant phylogenies throughout the genomes of this species. Most of these genes including the "core" set of genes and horizontally transferred genes showed at least one recombination event. Taking into account the relationship between the nucleotide diversity and the minimum number of recombination events per nucleotide, we evaluated the recombination rate in every gene. The rate appears constant across the genome, but genes with a particularly high or low recombination rate were detected. Interestingly, genes with high recombination included those for DNA transformation and for basic cellular functions, such as biosynthesis and metabolism. Several highly divergent genes with a high recombination rate included those for host interaction, such as outer membrane proteins and lipopolysaccharide synthesis. These results provide a global picture of genome-wide distribution of outcrossing homologous recombination in a bacterial species for the first time, to our knowledge, and illustrate how a species can be shaped by mutual homologous recombination.Genome Biology and Evolution 04/2012; 4(5):628-40. · 4.62 Impact Factor -
Article: Helicobacter suis KB1 derived from pig gastric lymphoid follicles induces the formation of gastric lymphoid follicles in mice through the activation of B cells and CD4 positive cells.
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ABSTRACT: "Helicobacter heilmannii" ("H. heilmannii"), which belongs to the genus Helicobacter, is a group of bacterial species that display a long spiral-shaped morphology. Recent studies have demonstrated that "H. heilmannii" type 1 is actually H. suis, which mainly colonizes the stomachs of various animals and humans. However, the influence of H. suis on gastric diseases remains to be fully elucidated. In this report, we revealed the relationship between natural H. suis infection and follicular gastritis in the pig stomachs. From sequence analysis of the 16S rRNA, urease A, and urease B genes, the presence of H. suis was confirmed in pig gastric lymphoid follicles, and this bacterium was named H. suis KB1. In addition, H. suis KB1 was inoculated into C57BL/6J mice, and the following mouse model of the pathogenesis of follicular gastritis by H. suis infection was established: H. suis KB1 colonizes the mouse stomach, and moreover, induces the development of lymphoid follicles and acquired immune responses characterized by the activation of B cells and CD4 positive cells. These results may lead to better understanding of the relationship between H. suis and gastric diseases, especially follicular gastritis; and furthermore, our findings emphasize the zoonotic aspects of animal-human infection by H. suis.Microbes and Infection 03/2011; 13(7):697-708. · 3.10 Impact Factor -
Article: Birth and death of genes linked to chromosomal inversion.
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ABSTRACT: The birth and death of genes is central to adaptive evolution, yet the underlying genome dynamics remain elusive. The availability of closely related complete genome sequences helps to follow changes in gene contents and clarify their relationship to overall genome organization. Helicobacter pylori, bacteria in our stomach, are known for their extreme genome plasticity through mutation and recombination and will make a good target for such an analysis. In comparing their complete genome sequences, we found that gain and loss of genes (loci) for outer membrane proteins, which mediate host interaction, occurred at breakpoints of chromosomal inversions. Sequence comparison there revealed a unique mechanism of DNA duplication: DNA duplication associated with inversion. In this process, a DNA segment at one chromosomal locus is copied and inserted, in an inverted orientation, into a distant locus on the same chromosome, while the entire region between these two loci is also inverted. Recognition of this and three more inversion modes, which occur through reciprocal recombination between long or short sequence similarity or adjacent to a mobile element, allowed reconstruction of synteny evolution through inversion events in this species. These results will guide the interpretation of extensive DNA sequencing results for understanding long- and short-term genome evolution in various organisms and in cancer cells.Proceedings of the National Academy of Sciences 01/2011; 108(4):1501-6. · 9.68 Impact Factor -
Article: Domain movement within a gene: a novel evolutionary mechanism for protein diversification.
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ABSTRACT: A protein function is carried out by a specific domain localized at a specific position. In the present study, we report that, within a gene, a specific amino acid sequence can move between a certain position and another position. This was discovered when the sequences of restriction-modification systems within the bacterial species Helicobacter pylori were compared. In the specificity subunit of Type I restriction-modification systems, DNA sequence recognition is mediated by target recognition domain 1 (TRD1) and TRD2. To our surprise, several sequences are shared by TRD1 and TRD2 of genes (alleles) at the same locus (chromosomal location); these domains appear to have moved between the two positions. The gene/protein organization can be represented as x-(TRD1)-y-x-(TRD2)-y, where x and y represent repeat sequences. Movement probably occurs by recombination at these flanking DNA repeats. In accordance with this hypothesis, recombination at these repeats also appears to decrease two TRDs into one TRD or increase these two TRDs to three TRDs (TRD1-TRD2-TRD2) and to allow TRD movement between genes even at different loci. Similar movement of domains between TRD1 and TRD2 was observed for the specificity subunit of a Type IIG restriction enzyme. Similar movement of domain between TRD1 and TRD2 was observed for Type I restriction-modification enzyme specificity genes in two more eubacterial species, Streptococcus pyogenes and Mycoplasma agalactiae. Lateral domain movements within a protein, which we have designated DOMO (domain movement), represent novel routes for the diversification of proteins.PLoS ONE 01/2011; 6(4):e18819. · 4.09 Impact Factor -
Article: Evolution in an oncogenic bacterial species with extreme genome plasticity: Helicobacter pylori East Asian genomes.
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ABSTRACT: The genome of Helicobacter pylori, an oncogenic bacterium in the human stomach, rapidly evolves and shows wide geographical divergence. The high incidence of stomach cancer in East Asia might be related to bacterial genotype. We used newly developed comparative methods to follow the evolution of East Asian H. pylori genomes using 20 complete genome sequences from Japanese, Korean, Amerind, European, and West African strains. A phylogenetic tree of concatenated well-defined core genes supported divergence of the East Asian lineage (hspEAsia; Japanese and Korean) from the European lineage ancestor, and then from the Amerind lineage ancestor. Phylogenetic profiling revealed a large difference in the repertoire of outer membrane proteins (including oipA, hopMN, babABC, sabAB and vacA-2) through gene loss, gain, and mutation. All known functions associated with molybdenum, a rare element essential to nearly all organisms that catalyzes two-electron-transfer oxidation-reduction reactions, appeared to be inactivated. Two pathways linking acetyl~CoA and acetate appeared intact in some Japanese strains. Phylogenetic analysis revealed greater divergence between the East Asian (hspEAsia) and the European (hpEurope) genomes in proteins in host interaction, specifically virulence factors (tipĪ±), outer membrane proteins, and lipopolysaccharide synthesis (human Lewis antigen mimicry) enzymes. Divergence was also seen in proteins in electron transfer and translation fidelity (miaA, tilS), a DNA recombinase/exonuclease that recognizes genome identity (addA), and DNA/RNA hybrid nucleases (rnhAB). Positively selected amino acid changes between hspEAsia and hpEurope were mapped to products of cagA, vacA, homC (outer membrane protein), sotB (sugar transport), and a translation fidelity factor (miaA). Large divergence was seen in genes related to antibiotics: frxA (metronidazole resistance), def (peptide deformylase, drug target), and ftsA (actin-like, drug target). These results demonstrate dramatic genome evolution within a species, especially in likely host interaction genes. The East Asian strains appear to differ greatly from the European strains in electron transfer and redox reactions. These findings also suggest a model of adaptive evolution through proteome diversification and selection through modulation of translational fidelity. The results define H. pylori East Asian lineages and provide essential information for understanding their pathogenesis and designing drugs and therapies that target them.BMC Microbiology 01/2011; 11:104. · 3.04 Impact Factor -
Article: A putative mobile genetic element carrying a novel type IIF restriction-modification system (PluTI).
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ABSTRACT: Genome comparison and genome context analysis were used to find a putative mobile element in the genome of Photorhabdus luminescens, an entomopathogenic bacterium. The element is composed of 16-bp direct repeats in the terminal regions, which are identical to a part of insertion sequences (ISs), a DNA methyltransferase gene homolog, two genes of unknown functions and an open reading frame (ORF) (plu0599) encoding a protein with no detectable sequence similarity to any known protein. The ORF (plu0599) product showed DNA endonuclease activity, when expressed in a cell-free expression system. Subsequently, the protein, named R.PluTI, was expressed in vivo, purified and found to be a novel type IIF restriction enzyme that recognizes 5'-GGCGC/C-3' (/ indicates position of cleavage). R.PluTI cleaves a two-site supercoiled substrate at both the sites faster than a one-site supercoiled substrate. The modification enzyme homolog encoded by plu0600, named M.PluTI, was expressed in Escherichia coli and shown to protect DNA from R.PluTI cleavage in vitro, and to suppress the lethal effects of R.PluTI expression in vivo. These results suggested that they constitute a restriction-modification system, present on the putative mobile element. Our approach thus allowed detection of a previously uncharacterized family of DNA-interacting proteins.Nucleic Acids Research 05/2010; 38(9):3019-30. · 8.03 Impact Factor -
Article: MBGD update 2010: toward a comprehensive resource for exploring microbial genome diversity.
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ABSTRACT: The microbial genome database (MBGD) for comparative analysis is a platform for microbial comparative genomics based on automated ortholog group identification. A prominent feature of MBGD is that it allows users to create ortholog groups using a specified subgroup of organisms. The database is constantly updated and now contains almost 1000 genomes. To utilize the MBGD database as a comprehensive resource for investigating microbial genome diversity, we have developed the following advanced functionalities: (i) enhanced assignment of functional annotation, including external database links to each orthologous group, (ii) interface for choosing a set of genomes to compare based on phenotypic properties, (iii) the addition of more eukaryotic microbial genomes (fungi and protists) and some higher eukaryotes as references and (iv) enhancement of the MyMBGD mode, which allows users to add their own genomes to MBGD and now accepts raw genomic sequences without any annotation (in such a case, it runs a gene-finding procedure before identifying the orthologs). Some analysis functions, such as the function to find orthologs with similar phylogenetic patterns, have also been improved. MBGD is accessible at http://mbgd.genome.ad.jp/.Nucleic Acids Research 11/2009; 38(Database issue):D361-5. · 8.03 Impact Factor -
Article: Type II restriction endonuclease R.Hpy188I belongs to the GIY-YIG nuclease superfamily, but exhibits an unusual active site.
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ABSTRACT: Catalytic domains of Type II restriction endonucleases (REases) belong to a few unrelated three-dimensional folds. While the PD-(D/E)XK fold is most common among these enzymes, crystal structures have been also determined for single representatives of two other folds: PLD (R.BfiI) and half-pipe (R.PabI). Bioinformatics analyses supported by mutagenesis experiments suggested that some REases belong to the HNH fold (e.g. R.KpnI), and that a small group represented by R.Eco29kI belongs to the GIY-YIG fold. However, for a large fraction of REases with known sequences, the three-dimensional fold and the architecture of the active site remain unknown, mostly due to extreme sequence divergence that hampers detection of homology to enzymes with known folds. R.Hpy188I is a Type II REase with unknown structure. PSI-BLAST searches of the non-redundant protein sequence database reveal only 1 homolog (R.HpyF17I, with nearly identical amino acid sequence and the same DNA sequence specificity). Standard application of state-of-the-art protein fold-recognition methods failed to predict the relationship of R.Hpy188I to proteins with known structure or to other protein families. In order to increase the amount of evolutionary information in the multiple sequence alignment, we have expanded our sequence database searches to include sequences from metagenomics projects. This search resulted in identification of 23 further members of R.Hpy188I family, both from metagenomics and the non-redundant database. Moreover, fold-recognition analysis of the extended R.Hpy188I family revealed its relationship to the GIY-YIG domain and allowed for computational modeling of the R.Hpy188I structure. Analysis of the R.Hpy188I model in the light of sequence conservation among its homologs revealed an unusual variant of the active site, in which the typical Tyr residue of the YIG half-motif had been substituted by a Lys residue. Moreover, some of its homologs have the otherwise invariant Arg residue in a non-homologous position in sequence that nonetheless allows for spatial conservation of the guanidino group potentially involved in phosphate binding. The present study eliminates a significant "white spot" on the structural map of REases. It also provides important insight into sequence-structure-function relationships in the GIY-YIG nuclease superfamily. Our results reveal that in the case of proteins with no or few detectable homologs in the standard "non-redundant" database, it is useful to expand this database by adding the metagenomic sequences, which may provide evolutionary linkage to detect more remote homologs.BMC Structural Biology 12/2008; 8:48. · 2.48 Impact Factor -
Article: How genomes rearrange: genome comparison within bacteria Neisseria suggests roles for mobile elements in formation of complex genome polymorphisms.
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ABSTRACT: Comparison of closely related genome sequences can provide a clue as to how macroscopic genome polymorphisms were formed through various events of recombination. However, this approach has been limited to relatively simple polymorphisms such as insertion, deletion and inversion. In the present study, we tried to extend this approach to more complex genome polymorphisms that were observed when four genome sequences of bacterial genus Neisseria were compared. The first polymorphism was an apparent translocation (ab-cd to cd-ba; a region 'ab' was translocated). The second one was a re-ordering of adjacent regions (ab-cd-ef-gh to ef-cd-ab-gh; ab, cd and ef were in reverse order). The third one was a translocation of two adjacent regions with permutation of their order (ab-cd to cd-ab elsewhere in the genome). The fourth one was a genome-wide inversion associated with a genome-specific insertion into the joints (-ab-cd- to -y-ba-x-cd-). We were able to explain their formation by only a few steps of plausible events of recombination that involved linked IS copies and prophages. Our approach would help to reconstruct a history of apparently complex genome polymorphisms in any forms of organisms and to understand genome rearrangements in the natural environments in non-model organisms.Gene 12/2006; 383:52-63. · 2.34 Impact Factor -
Article: Evolution of paralogous genes: Reconstruction of genome rearrangements through comparison of multiple genomes within Staphylococcus aureus.
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ABSTRACT: Analysis of evolution of paralogous genes in a genome is central to our understanding of genome evolution. Comparison of closely related bacterial genomes, which has provided clues as to how genome sequences evolve under natural conditions, would help in such an analysis. With species Staphylococcus aureus, whole-genome sequences have been decoded for seven strains. We compared their DNA sequences to detect large genome polymorphisms and to deduce mechanisms of genome rearrangements that have formed each of them. We first compared strains N315 and Mu50, which make one of the most closely related strain pairs, at the single-nucleotide resolution to catalogue all the middle-sized (more than 10 bp) to large genome polymorphisms such as indels and substitutions. These polymorphisms include two paralogous gene sets, one in a tandem paralogue gene cluster for toxins in a genomic island and the other in a ribosomal RNA operon. We also focused on two other tandem paralogue gene clusters and type I restriction-modification (RM) genes on the genomic islands. Then we reconstructed rearrangement events responsible for these polymorphisms, in the paralogous genes and the others, with reference to the other five genomes. For the tandem paralogue gene clusters, we were able to infer sequences for homologous recombination generating the change in the repeat number. These sequences were conserved among the repeated paralogous units likely because of their functional importance. The sequence specificity (S) subunit of type I RM systems showed recombination, likely at the homology of a conserved region, between the two variable regions for sequence specificity. We also noticed novel alleles in the ribosomal RNA operons and suggested a role for illegitimate recombination in their formation. These results revealed importance of recombination involving long conserved sequence in the evolution of paralogous genes in the genome.Molecular Biology and Evolution 07/2006; 23(6):1269-85. · 5.55 Impact Factor -
Article: Genome comparison in silico in Neisseria suggests integration of filamentous bacteriophages by their own transposase.
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ABSTRACT: We have identified filamentous prophages, Nf (Neisserial filamentous phages), during an in silico genome comparison in Neisseria. Comparison of three genomes of Neisseria meningitidis and one of Neisseria gonorrhoeae revealed four subtypes of Nf. Eleven intact copies are located at different loci in the four genomes. Each intact copy of Nf is flanked by duplication of 5'-CT and, at its right end, carries a transposase homologue (pivNM/irg) of RNaseH/Retroviral integrase superfamily. The phylogeny of these putative transposases and that of phage-related proteins on Nfs are congruent. Following circularization of Nfs, a promoter-like sequence forms. The sequence at the junction of these predicted circular forms (5'-atCTtatat) was found in a related plasmid (pMU1) at a corresponding locus. Several structural variants of Nfs--partially inverted, internally deleted and truncated--were also identified. The partial inversion seems to be a product of site-specific recombination between two 5'-CTtat sequences that are in inverse orientation, one at its end and the other upstream of pivNM/irg. Formation of internally deleted variants probably proceeded through replicative transposition that also involved two 5'-CTtat sequences. We concluded that the PivNM/Irg transposase on Nfs integrated their circular forms into the chromosomal 5'-CT-containing sequences and probably mediated the above rearrangements.DNA Research 02/2005; 12(6):389-401. · 5.16 Impact Factor
Top co-authors
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Institutions
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2012
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Kurume University
Kurume, Fukuoka-ken, Japan
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2005–2011
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The University of Tokyo
- Graduate School of Frontier Sciences
Tokyo, Tokyo-to, Japan
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2009–2010
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National Institute for Basic Biology
Okazaki, Aichi-ken, Japan
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