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28 février 2020: 4 événements

  • Département Biologie des Génomes

    Vendredi 28 février 10:00-11:00 - Tomio TAKAHASHI - Microbiology Department, I2BC

    Advances in understanding Topoisomerase I molecular mechanisms

    Résumé : Abstract :
    Chromosome structure and dynamics, DNA repair, DNA replication and transcription are all mechanisms that involve changes in the topology of DNA, requiring a set of enzyme called DNA topoisomerases. In particular, human topoisomerase IB (Top1) removes torsional stresses associated with DNA replication and transcription, and is important for the regulation of gene expression. Top1 activity involves one step of DNA cleavage and one step of DNA ligation. The current structural data suggests that Top1 clamps the DNA molecule during these two steps. However, there is little data concerning the mechanisms underlying the entry and the exit of the DNA molecule inside this toroidal structure.
    The topoisomerase IB from one hyperthermophilic archaeon, Caldiarchaeum subterraneum was recently found to be highly similar to the eukaryotic enzyme (1). This highly thermostable enzyme allowed me recently to solve the first structure of Top1 in an open conformation in the absence of DNA. This novel structure reveals that Top1 is a bimodular enzyme, in which one catalytic domain and one core domain are linked with one flexible hinge loop, which allows the opening/closing of the enzyme. Top1 dynamics raises question about the specificity of the enzyme towards specific DNA structures including supercoiled DNA and non-canonical DNA structures such as G-quadruplexes.
    I will also briefly introduce a new family of proteins, homologous with Topoisomerase IIB and Spo11, which are found exclusively in viruses (2).
    References :
    1. Dahmane N, Gadelle D, Delmas S, Criscuolo A, Eberhard S, Desnoues N, et al. TopIb, a phylogenetic hallmark gene of Thaumarchaeota encodes a functional eukaryote-like topoisomerase IB. Nucleic Acids Res. 2016 ;44(6):2795–805.
    2. Takahashi, T.S., Da Cunha, V., Krupovic, M., Mayer, C., Forterre, P., and Gadelle, D. Expanding the type IIB DNA topoisomerase family : identification of new topoisomerase and topoisomerase-like proteins in mobile genetic elements. NAR Genomics and Bioinformatics 2(1) (2020)
    Contact : Yoshi Yamaichi <Yoshiharu.YAMAICHI>

    Lieu : Bibliothèque- bâtiment 34 - Campus CNRS de Gif-sur-Yvette

    En savoir plus : Département Biologie des Génomes
  • Département Biochimie, Biophysique et Biologie Structurale

    Vendredi 28 février 11:00-12:00 - Diego F. GAUTO - Institut de Biologie Structurale (IBS), Grenoble

    Atomic-Resolution structure determination and dynamic studies on big macromolecular protein assemblies : Joining strenghts between NMR, CryoEM and Computational Simulations

    Lieu : Auditorium I2BC - Bâtiment 21, Campus de Gif-sur-Yvette

    En savoir plus : Département Biochimie, Biophysique et Biologie Structurale
  • Département Microbiologie

    Vendredi 28 février 11:30-12:30 - Daisuke NAKANE - Gakushuin University, Dpt of Physics, Japan

    How bacteria move ? Pulling, crawling, and drilling

    Résumé : Many bacteria swim freely in a fluid with a rotation of flagella filament. On the other hand, some tiny organisms also develop several varieties of cell motility without flagella. These mysterious movements are widespread in bacteria, and have been very attractive to many researchers for long time. But it had remained unclear how bacteria move without flagella, and what is the machinery for cell propulsion. Recent advance on the visualization techniques of optical microscopy provides us dynamic behaviors of molecular machineries at a single cellular level in detail, and the current understanding of this field have dramatically jumped in the last 10-20 years. In this seminar, I would like to introduce our recent study about a surprising new world of biological movements in the smallest life forms such as Spider-man like motion by the repeated cycles of extension and retraction, a caterpillar like motion by the surface flow along cell membrane, and a corkscrew like motion by mechanical drilling in high viscous environments.

    References :
    - Nakane & Miyata (2007) PNAS 104 : 19518-23
    - Nakane et al. (2013) PNAS 110 : 11145-50
    - Kinosita, Nakane et al. (2014) PNAS 111 : 8601-6
    - Nakane & Nishizaka (2017) PNAS 114 : 6593-98

    Lieu : Bibliothèque - Bâtiment 34, Campus de Gif-sur-Yvette

    En savoir plus : Département Microbiologie
  • Département Biochimie, Biophysique et Biologie Structurale

    Vendredi 28 février 14:00-15:00 - Volker LOHMANN - University of Heidelberg

    Shaping the lipid composition of viral replication organelles by Hepatitis C virus

    Résumé : Chronic Hepatitis C virus (HCV) infections affect 71 million people worldwide, often resulting in severe liver damage. Since 2014 highly efficient therapies based on direct acting antivirals (DAAs) are available, offering cure rates of almost 100%, if the infection is diagnosed in time. It took more than a decade to discover HCV in 1989 and another decade to establish the first cell culture model, which was essential for therapy development, from drug screening to understanding of mode of action and resistance. More recently we are beginning to understand the molecular basis for efficient HCV replication in cell culture, which is highly dependent on the shaping of the lipid composition of the membranous viral replication organelle, mediated by host factors like PI4KA and SEC14L2. This presentation will summarize our current knowledge on the mechanism of action of host factors contributing to HCV RNA synthesis and provide an outlook on future opportunities based on our increasing understanding of molecular mechanisms governing HCV replication.

    Lieu : Bibliothèque - Bâtiment 34, Campus de Gif-sur-Yvette

    En savoir plus : Département Biochimie, Biophysique et Biologie Structurale