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  • I2BC

    • Mardi 2 octobre 2018 11:00-12:00 - Thierry Touzé - Département Microbiologie, I2BC

      Insights into biogenesis of bacterial cell-wall and recycling of bactoprenol, the peptidoglycan subunit carrier lipid

      Lieu : Auditorium I2BC - Bât. 21, Campis Gif


    • Mardi 2 octobre 2018 14:00-15:30 - Jinwei Zhang - National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, USA

      Feast or famine - amino acid sensing on the tRNA by a mRNA

      Résumé : Amino acids are among the most ubiquitous and essential nutrients. T-box riboswitches are bacterial cis-regulatory noncoding RNAs that regulate amino acid-metabolic genes through multipartite interactions with tRNAs [1]. T-boxes share a phylogenetically conserved architecture comprised of two domains — a 5’ Stem I and 3’ antiterminator domain and a linker. Stem I selectively docks a cognate tRNA via sequence- and structure-specific interactions [2-4]. The antiterminator probes the molecular volume of the docked tRNA 3’ end to sense aminoacylation [5]. This readout dictates the formation of either an intrinsic transcription terminator or antiterminator. The architecture of a full-length T-box complex and detailed interactions between the tRNA 3’ region and the antiterminator remain poorly understood.
      We define a minimal region of the T-box both necessary and sufficient to selectively bind an uncharged tRNA, and report a 2.7 Å co-crystal structure of the complex. The structure reveals how tRNA 3’ end is buried inside the antiterminator such that a conserved G•U wobble pair at the base of helix A2 abuts the ribose 3’-OH of the tRNA terminal adenosine. This juxtaposition creates steric clash between the universal amino group of the esterified amino acid and the uridine nucleobase, thus providing a general mechanism to reject any aminoacyl-tRNA. Interestingly, the clash is exasperated by the outward shift of the wobble uridine into the major groove. We compare this RNA-based steric device to ribosome-bound RelA, which positions a beta strand to reject aminoacyl-tRNA in stringent response [6-7].
      Further, we report a cryo-EM structure of a full-length T-box riboswitch-tRNA complex, which reveals a surprisingly ordered inter- domain linker. Together, the structures show that extensive intermolecular stacking allows Stem I and antiterminator domains of the T-box to sandwich the uncharged tRNA to form a 30-bp continuous stack, to stabilize the antiterminator to transcribe downstream genes.
      1. Grundy & Henkin, Cell 1993 ; 2. Grigg & Ke, Structure 2013 ; 3. Zhang & Ferré-D’Amaré, Nature 2013 ; 4. Zhang & Ferré-D’Amaré, Structure 2014 ; 5. Zhang & Ferré-D’Amaré, Mol Cell 2014 ; 6. Brown et al., Nature 2016 ; 7. Loveland et al., eLife 2016. Supported in part by the intramural research program of NIDDK, NIH.

      Lieu : Auditorium I2BC - Bât. 21, Campus Gif


    • Jeudi 25 octobre 2018 14:30-15:30 - Marek Basler - University of Basel

      Type VI secretion system : from the discovery to the mode of action of a dynamic bacterial nanomachine

      Résumé : Bacteria have evolved several nanomachines to deliver proteins from their cytosol to target cells. These nanomachines differ in their structure, regulation, secreted substrates and are essential for bacterial survival in different environments. In my talk, I will describe the journey from the discovery of the Type VI secretion system (T6SS) to the current understanding of its structure, dynamics and mode of action. I will explain how we used a combination of live-cell imaging, cryo-electron microscopy and genetics to show that T6SS works as a powerful speargun to force large proteins across cell envelopes of both eukaryotic and bacterial cells. I will provide evidence that T6SS structure is evolutionarily related to contractile phage tails and show that subcellular localization of T6SS assembly is in many bacteria regulated with a remarkable precision with implications for its function. I will discuss how T6SS influences bacterial pathogenesis, competition and horizontal gene transfer and thus impacts human health.

      Lieu : Auditorium I2BC - CNRS Bat. 21, Campus de Gif-sur-Yvette


  • I2BC

    • Vendredi 12 octobre 2018 14:00-15:00 - Guillaume Lenoir - Département B3S, I2BC

      Organization, structure, and dynamics of biological membranes

      Résumé : Membrane proteins (MPs) are involved in numerous functions such as cell signaling, membrane trafficking, metabolite/ion/lipid transport, and cell detoxification. Hence, MPs are implicated in many pathophysiological conditions, being as well the target of more than 50% of the currently used drugs. In that context, researchers at the Laboratory of Membrane Proteins and Membrane Systems (LPSM) have worked in the past five years at deciphering the mechanism of primary active transport processes, at the elucidation of protein-protein and protein-lipid interaction and significance, and at understanding the regulatory mechanism of mitochondrial energy-transducing complexes. Due to the upcoming retirement of Francis Haraux, the actual head of the LPSM, we propose José Luis Vázquez-Ibar and Guillaume Lenoir to take over the shared responsibility of the LPSM. In the next years, we will focus on projects related to the role of MPs in the dynamic organization and structure of biological membranes. During this seminar, we will present some of the work we achieved in the recent years and outline our projects for the coming years.

      Lieu : Auditorium I2BC - Campus Gif, Bâtiment 21


  • cytoskeleton club

    • Mardi 9 octobre 2018 11:30-13:00 - Julien Pernier - Institut Curie, UMR CNRS 168, Paris - A new actin depolymerase : a catch bond Myosin 1 motor

      Cytoskeleton club

      Lieu : Bibliothèque - bât. 34


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