le 2 avril 2015 à 14 h
Laurent Terradot, Institut de Biologie et Chimie des Protéines, Université Lyon 1

Helicobacter pylori is one of the most successful bacterial pathogen, infecting the stomach of about half of the world population and causing peptic ulcer or gastric cancer. Our group is interested in the structural biology of DNA replication initiation proteins from H. pylori. Bacterial DNA replication initiation requires the DnaA protein that directly binds to the chromosomal origin of replication oriC. DnaA multimerises, forms a nucleoprotein complex (orisome) and unwinds double stranded DNA at a nearby AT rich region. The orisome then serves as a docking platform to load the ring-shape hexameric helicase DnaB, enzyme that unwinds dsDNA in the 5’ to 3’ direction. Because of this polarity, two hexamers of DnaB must be positioned in opposite directions on each of the DNA forks for replication to proceed bi-directionally. Deposition of two helicase rings (helicase loading) onto the DUE is assisted in some bacteria by dedicated loaders. Loaded DnaB anchors the DnaG primase forming the primosome, responsible for RNA primers synthesis.

If the hallmarks of DNA replication are conserved in H. pylori, this bacterium has features that deviate from the “model” systems. To study these systems we have developed different strategies based on protein purification, Biochemistry and hybrid methods in Structural Biology (Multi-angle laser light scattering MALS, X-ray crystallography, Small Angle X-ray Scattering and Electron Microscopy). We have studied the replicative helicase DnaB from Helicobacter pylori (HpDnaB) and found that the protein forms four-layered double hexamers in electron microscopy 1. We have recently solved the crystal structure of the HpDnaB dodecamer which reveals a novel helicase organisation where two hexamers assemble via the NTD-rings in a stack-twisted mode. We have then studied the interaction of DnaB with the primase DnaG by several biophysical and biochemical methods. Together with our current knowledge of H. pylori replication machinery, the results obtained suggest a new mechanism for DNA replication initiation in this bacteria and possibly others.

1. Stelter M, et al. Architecture of a dodecameric bacterial replicative helicase. Structure 20, 554-564 (2012).

Lieu(x) :         Amphithéatre Curie, Ecole Polytechnique

Contact :       Hannu Myllykallio
                      hannu.myllykallio at polytechnique.edu

À télécharger :       Séminaire TERRADOT.pdf - PDF