Molecular Genetics - CNRS URA2172  

  HEADProf Anthony P.Pugsley /
  MEMBERSActuel: Mlle BERAUD Mélanie / Dr BUDDELMEIJER Nienke / M. CAMPOS Manuel / M. CISNEROS David A. / Mlle COLLIN Séverine / Dr. DANOT Olivier / Dr FRANCETIC Olivera / Mme GUILVOUT Ingrid / Dr KOLB Annie / Mme LAVENIR Armelle / M. LE CHEVALIER Fabien / Mme LEGAT Geneviève / Mme NADEAU Nathalie / Dr. NICKERSON Nicholas / Dr NOREL-BOZOUKLIAN / M. PAILLER Jérémy / Prof. PUGSLEY Anthony / Mlle REYNGOUD Maria / Dr RICHET Evelyne / Mme ROBBE-SAULE Véronique
Ex members: Dr KREHENBRINK Martin / Dr MARQUENET Evelyne / Prof YOUNG Ry

  Annual Report

The Molecular Genetics Unit focuses on two fundamentally important aspects of bacterial physiology: how they regulate gene expression in order to adapt to changing environments and nutrients, and how they construct their cellular envelope and secrete proteins into the surrounding environment. All of the studies conducted in the unit are designed to reveal new molecular and mechanistic insights into microbial life. They use astute combinations of biochemical, biophysical, structural and genetic approaches that involve a wide variety of sophisticated technologies.

Several years ago, the Molecular Genetics Unit uncovered the molecular basis for the now extensively characterized type II secretion system (the secreton) in Gram-negative bacteria. Our work now focuses on the specific roles of individual components of the system. For example, the team led by Tony Pugsley is investigating the dodecameric outer membrane protein (secretin) that allows the secreted proteins (exoproteins) to cross the outer membrane (how is it targeted to the outer membrane, how does it assemble, and how does it insert?), and its specific chaperone (pilotin) that guides it through the periplasm. Olivera Francetic’s team focuses on the analysis of another secreton component, the periplasmic filament called the pseudopilus. The elongation of this filament from the inner membrane either drives exoproteins though the secretin channel in a piston-like manner, or promotes channel gating. The Francetic team is also trying to identify the signals in the exoprotein that allows it to be recognized and secreted. These studies are revealing radically new principals in the mechanisms of protein translocation through membranes.

A second aspect of membrane function studied in this unit is the biogenesis of bacterial lipoproteins. Members of this relatively abundant (Escherichia coli has about 100)but poorly characterized family of membrane-anchored proteins play important roles in bacterial physiology, from membrane architecture to virulence and nutrient uptake. Nienke Buddelmeijer and her team are characterizing two fatty acyl transferases involved in lipoprotein biogenesis. They have recently uncovered a novel enzyme intermediate in which the fatty acid is covalently bound to the enzyme before it is transferred to the recipient apolipoprotein.

Evelyne Richet’s team is studying MalT, a signal transducing transcription regulator that responds to the presence of maltodextrins in the environment. MalT is the prototype of a large family of so-called STAND ATPases. We are trying to understand how positive (ATP and maltotriose) and negative (the proteins MalK, Aes and MalY) effectors affect the ability of MalT to oligomerize and bind to its specific recognitions sites in the cognate promoters of the operons it controls. In particular, we are identifying the sites at which the different effectors bind and studying the conformational changes that these interactions induce in MalT, and their consequences thereof. These studies contribute substantially to understanding the mechanism of signal transduction in other STAND ATPases, key components in major signaling cascades in eukaryotes.

The team led by Annie Kolb and Françoise Norel is examining how the Salmonellaadapt to their environment. In particular, we are characterizing the functions and mode of action of the stationary phase sigma factor component of RNA polymerase and its chaperone Crl, which affect the expression of over 10% of the genome when the bacteria cease to grow at exponential rates because of nutrient limitation, for example.

Keywords: Signal transduction, gene expression, protein secretion, membrane biogenesis, lipoproteins, membrane protein assembly


Fluorescence of a secreton-fluorescent protein chimera in the outer membrane of E. coli reveals its tendency to form clusters (from Buddelmeijer et al (2009) J Bacteriol 191: 161-168).


England, P., Westblade, L.F., Karimova, G., Robbe-Saule, V., Norel, F., and Kolb, A. (2008) Binding of the unorthodox transcription activator, Crl, to the components of the transcription machinery. J Biol Chem 283: 33455-33464.

Guilvout, I., Chami, M., Engel, A., Pugsley, A.P., and Bayan, N. (2006) Bacterial outer membrane secretin PulD assembles and inserts into the inner membrane in the absence of its pilotin. EMBO J 25: 5241-5249.

Guilvout, I., Chami, M., Berrier, C., Ghazi, A., Engel, A., Pugsley, A.P., and Bayan, N. (2008) Secretin multimers insert into liposome membranes in vitro. J Mol Biol 382: 13-23.

Marquenet, E., and Richet, E. (2007) How integration of positive and negative regulatory signals by a STAND signaling protein depends on ATP hydrolysis. Mol Cell 28: 187-199.

Vidal-Ingigliardi, D., Lewenza, S., and Buddelmeijer, N. (2007) Identification of essential residues in apolipoprotein N-acyl transferase, a member of the CN hydrolase family. J Bacteriol 189: 4456-4464.

Activity Reports 2009 - Institut Pasteur
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