Biology and Genetics of Bacterial Cell Wall - INSERM Avenir Group  


  HEADDr. Ivo Gomperts Boneca / ivo.gomperts-boneca@pasteur.fr
  MEMBERSMathilde Bonis (PhD student) / Chantal Ecobichon (Technician) / Meriem El Ghachi (Post-doctoral fellow) / Martine Fanton d’Andon Klimz (Technician) / Sophie Roure (PhD student) / Catherine Werts (Staff senior scientist)


  Annual Report

The research of our group is focused on the bacterial cell wall and in particular around peptidoglycan (PGN) metabolism with two main aims being pursued: 1) use Helicobacter pylori has an alternative model to study PGN assembly, 2) study how bacteria adapt their PGN metabolism to modulate host-microbe interactions and their consequences on the host innate response mediated by the Nod proteins.

a) peptidoglycan assembly

We focus on the enzymes required for PGN assembly and maturation in the periplasmic space. These include the PGN synthetases or also known as penicillin-binding proteins (PBPs) and the PGN hydrolases. H. pylorihas the advantage to have a minimal set of those enzymes (3 PBPs and 3 hydrolases) clearly identified from the genome analysis. All three PBPs were shown to be essential. Hence, the last couple of years, we developed the first inducible system adapted to H. pylori to allow construction of conditional mutants. Now, we have been addressing the role of the PBPs in cell morphology and division in H. pylori and aim to characterize their protein partners, in particular, the PGN hydrolases.

We have characterized the three clearly identified PGN hydrolases, the lytic transglycosylases Slt and MltD, and a predicted amidase AmiA. We have shown that Slt and MltD perform distinct non-redundant functions in H. pylori as Slt is a exo enzyme and MltD is an endo-lytic transglysosylase. We also showed that AmiA is required for the cell daughter separation and morphological transition of H. pylorifrom rod/spiral shape to coccoïd bacteria.

The lytic transglycosylases have also an important role in the functionality/assembly of surface appendices such as flagella and type 4 secretion systems. Usually, there are dedicated lytic transglycosylases for the assembly of these surface structures. However, H. pyloridoes not have any PGN hydrolase dedicated for the flagellum. We are addressing the role of Slt and MltD in the assembly and functionality of H. pyloriflagellum.

b) host-microbe interactions

PGN is a major pathogen-associated molecular pattern (PAMP) that is sensed by the host innate immune system. In mammals, PGN detection occurs by the intracellular pattern recognition receptors (PRRs) Nod1 and Nod2. These proteins detect degradation fragments of PGN that are generated by the endogenous bacterial PGN hydrolases or host PGN hydrolases. We have been studying several mechanisms that bacteria use to modulate either their own PGN metabolism or the host PGN hydrolases as an innate immune stealth mechanism. Hence, we have shown that H. pylori uses its morphological transformation into coccoïd bacteria to escape Nod1 detection by gastric epithelial cells. Alternatively, we have shown that Listeria monocytogenes modifies its PGN by deacetylating the N-acetylglucosamine moieties to confer resistance to host lysozyme and modulate Nod response.

The Nod proteins have a central role in detecting bacteria particularly in the gut. The first evidence for a central role of Nod proteins in the gut physiology came from epidemiological studies that clearly established Nod2 as involved in the development of Crohn’s disease. In collaboration with the group of Gérard Eberl (Institut Pasteur), we have shown that Nod1 is essential for the homeostasis of the instestinal lymphoid tissue. In fact, the homeastasis can be recapitulated in germ-free mice by feeding them with pure Nod1 ligand. This highlights the importance for better understanding the Nod proteins and Nod signaling during interactions of bacteria and the host. For example, we have shown that ubiquitin-editing enzyme A20, a general negative regulator of the TNF and NF-kB pathways, is needed to regulate Nod signaling.

Keywords: Peptidoglycan – antibiotics - penicillin-binding proteins – autolysins -peptidoglycan hydrolases – inflammation – Helicobacter – ulcer – gastric carcinoma – MALT – Nod1 – Nod2 – innate immunity – Toll-like receptor



  Publications

Bouskra D, Brézillon C, Bérard MWerts C, Varona R, Boneca IG, Eberl G. 2008. Lymphoid tissue genesis induced by commensals through NOD1 regulates intestinal homeostasis.Nature.456(7221):507-10. (PMID: 18987631).

Hitotsumatsu O, Ahmad RC, Tavares R, Wang M, Philpott D, Turer EE, Lee BL, Shiffin N, Advincula R, Malynn BA,Werts C, Ma A. 2008. The ubiquitin-editing enzyme A20 restricts nucleotide-binding oligomerization domain containing 2-triggered signals.Immunity.28.(3):381-90. (PMID: 18342009).

Boneca IG, Ecobichon C, Chaput C, Mathieu A, Guadagnini S,Prévost MC, Labigne A and de Reuse H. 2008. Development of inducible systems to engineer conditional mutants of essential genes of Helicobacter pylori. Applied Environm. Microbiol. 74.(7):2095-2102. (PMID: 18245237).

Boneca IG, Dussurget O, Cabanes D, Nahori MA, Sousa S, Lecuit M, Psylinakis E, Bouriotis V, Giovannini M, Hugot JP, Coyle A, Bertin J, Namane A, Rousselle JC, Cayet N, Prévost MC, Balloy V, Chignard M, Philpott DJ, Cossart P and Girardin SE. 2007. A critical role for peptidoglycan N-deacetylationin Listeria evasion from the host innate immune system. Proc Natl Acad Sci U S A.104.(3):997-1002. (PMID: 17215377).

Chaput C, Ecobichon C, Cayet N, Girardin SE, Werts C, Guadagnini S, Prévost MC, Mengin-Lecreulx D, Labigne A and Boneca IG. 2006. Role of the AmiA amidase in the morphological transition of Helicobacter pylori and in immune escape. PLOS pathog.2. (9): 844-52. (PMID: 17002496)





Activity Reports 2009 - Institut Pasteur
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