Our studies focus on molecular understanding of fundamental processes of protein traffic and transcription regulation in Gram-negative bacteria. The unit is divided into five teams, two of which work on the type II secretion system or secreton.

The “Secretin” team studies the structure-function of the outer membrane component of the secreton, the secretin PulD, with particular emphasis on regions of PulD required for its assembly into a multimer composed of 12 subunits and for interaction with its dedicated chaperone/pilot protein, the lipoprotein PulS that is required for outer membrane targeting of PulD. The crystal structure of the chaperone has been solved and details of its interaction with its specific binding site in PulD have been elucidated. Mutations affecting the folding and assembly of PulD have recently led to the identification of two potentially novel assembly intermediates.

The “Pseudopilus” team focuses on the structure function analysis of another secreton component, the periplasmic filament called the pseudopilus. The elongation of this filament from the inner membrane somehow facilitates the movement of exoproteins across the outer membrane. The high-resolution structure of the pseudopilus core composed of the major pilin PulG has been extended to the minor pseudopilins and their role in pseudopilus assembly control.

The “Lipoprotein” team is the third group studying membrane functions. They are examining the steps leading to the maturation of bacterial lipoproteins, which are important components of the cell envelopes of all bacteria. This team has recently identified a novel stable intermediate in which a fatty acid is linked to an enzyme that will transfer it to the target lipoprotein. These studies provide much-needed insight into this poorly characterized but important process.

The “SigmaS” team studies the sigmaS network, involved in stationary phase survival and stress resistance in many Gram-negative bacteria. They investigate several aspects regarding the molecular and physiological mechanisms of action of sigmaS : (1) modulation of sigmaS activity by Crl, a unique chaperone-like protein that helps sigmaS to bind the core RNA polymerase ; (2) negative regulation of gene expression by sigmaS and its contribution to bacterial fitness; (3) characterization of downstream effectors of sigmaS in the adaptation of Salmonella to the environment. This team has recently identified a domain of sigmaS that interacts with Crl and residues in Crl important for the interaction.

The "Maltose" team studies the ins and outs of signal transduction by STAND (Signalling ATPases with Numerous Domains) proteins by using MalT, the transcriptional activator of the E. colimaltose regulon, as a model system. They mainly focus on the conformational changes underlying the inducer-promoted conversion of the ADP-bound, monomeric form (the dormant form) into the multimeric, ATP-bound form, which is competent for downstream signalling.

All of these studies rely on a combination of bioinformatics, genetics, molecular biology, fluorescence, confocal and electron microscopy, biochemistry, biophysics and X-ray crystallography to gain insight into the mechanisms involved.

Keywords: Secretion, pili, lipoproteins, cell envelope, transcription factors ATPase, sigma factors, stress

Beraud, M., Kolb, A., Monteil, V., D'Alayer, J., and Norel, F. (2010) A proteomic analysis reveals differential regulation of the sigma(S)-dependent yciGFE(katN) locus by YncC and H-NS in Salmonella and Escherichia coli K-12. Mol Cell Proteomics 9: 2601-2616.

Buddelmeijer, N., and Young, R. (2010) The essential Escherichia coli apolipoprotein N-acyltransferase (Lnt) exists as an extracytoplasmic thioester acyl-enzyme intermediate. Biochemistry 49: 341-346.

Campos, M., Nilges, M., Cisneros, D.A., and Francetic, O. (2010) Detailed structural and assembly model of the type II secretion pilus from sparse data. Proc Natl Acad Sci U S A 107: 13081-13086.

Danot, O. (2010) The inducer maltotriose binds in the central cavity of the tetratricopeptide-like sensor domain of MalT, a bacterial STAND transcription factor. Mol Microbiol 77: 628-641.

Monteil, V., Kolb, A., Mayer, C., Hoos, S., England, P., and Norel, F. (2010b) Crl binds to domain 2 of sigma(S) and confers a competitive advantage on a natural rpoS mutant of Salmonella enterica serovar Typhi. J Bacteriol 192: 6401-6410.