Institut de Biologie StructuraleGrenoble / France

Contact person(s) related to this article / VERNET Thierry

Presentation of the Pneumococcus Group

Group leader : Thierry Vernet

Group members : Laure Bellard, Anne Marie Di Guilmi, Claire Durmort, Cécile Morlot, Anne-Marie Villard, André Zapun.


Cell surface, cell wall and morphogenesis of pneumococcus

Our group is interested in the biology of pneumococcus (Streptococcus pneumoniae), an important human pathogen. We are particularly interested in topics related to the cell surface physiology, the cell wall metabolism and morphogenesis, as well as the resistance to beta-lactam antibiotics.

Pneumococcal infections are responsible for more than a million deaths per year worldwide. Pneumococcus is a Gram positive ovoid coccus that asymptomatically colonizes the naso-pharynx, but causes diverse diseases when it invades other sites: otitis, sinusitis, pneumonia, meningitis and bacteremia. Today in France, nearly half of the clinical isolates are resistant to several antibiotics, in particular to beta-lactams (penicillins). Available vaccines are efficient but do not cover all virulent serotypes, and are progressively loosing their efficacy through the selection of strains that are not covered.

[bleu marine]Thin-section electron micrograph of S. pneumoniae (B. Gallet, IBS).[/bleu marine]

Research themes

[rouge]Cell surface physiology : functions and properties[/rouge]
The cell surface is the site of numerous proteic and saccharidic virulence factors that mediate interactions between the pneumococcus and human tissues. These surface molecules can participate to the adhesion and the invasion of human cells, or to the evasion of the immune system. Understanding the role of surface proteins is fundamental to understand the origin of pneumococcal diseases. Virulence factors can also constitute promising vaccinal antigens or targets for novel antibiotics. More specifically, we have studied the formation of the pili, proteinaceous filaments that extend from the cell wall, as well as other proteins involved in adhesion to and invasion of the human host.
The surface is also the site of communication between the medium and the cell, and we have recently studied factors involved in zinc homeostasis, and transporters contributing to antibiotic resistance.

[rouge]Cell wall metabolism and morphogenesis[/rouge]
Peptidoglycan is the main component of the cell wall, it is a polymer of disaccharides and peptides that surrounds entirely the cell, confers its shape and protects it from its internal osmotic pressure. Several antibiotics, such as the beta-lactams (penicillins…), act by preventing synthesis of the peptidoglycan. Enzymes responsible for the peptidoglycan assembly are targets of the beta-lactams: the Penicillin-Binding Proteins (PBPs). The mechanism of the PBPs, as well as the architecture of the peptidoglycan itself, or its degradation, remains mysterious.

We are studying the assembly and degradation of the cell wall by reconstituting these processes in vitro, as well as the function, regulation and localization in vivo of the protein complexes involved.

Key words
ABC transporter, bacterial cell wall, bacterial division, bacterial morphogenesis, beta-lactams, choline-binding protein (CBP), host-pathogen interaction, murein, penicillin-binding protein (PBP), peptidoglycan, peptidoglycan hydrolase, pilin, pilus, pneumococcus, protein secretion, sortase, Streptococcus pneumoniae, teichoic acids, virulence, virulence factors, zinc homeostasis.

Specialized techniques
Molecular biology
Protein biochemistry (membrane and soluble)
Pneumococcal genetic
Protein engineering
High-throughput gene cloning (RoBioMol)
High-throughput site-directed mutagenesis (RoBioMol)
High-throughput recombinant protein expression (RoBioMol)
« Thermal Shift Assay » (RoBioMol)
Quantitative PCR
Immunofluorescence microscopy and GFP-fusion proteins
Super-resolution photonic microscopy (PALM)
Electron microscopy of thin section
Protein crystallization

Available services
High-throughput gene cloning (RoBioMol)
High-throughput site-directed mutagenesis (RoBioMol)
« Thermal Shift Assay » (RoBioMol)
Detergent screening for membrane protein solubilization (RoBioMol)

Major recent publications

Philippe J, Gallet B, Morlot C, Denapaite D, Hakenbeck R, Chen Y, Vernet T and Zapun A.
Mechanism of β-lactam action in Streptococcus pneumoniae: the piperacillin paradox.
Antimicrob Agents Chemother (2015) 59(1):609-21.

Terrasse R, Amoroso A, Vernet T and Di Guilmi AM
Streptococcus pneumoniae GAPDH Is Released by Cell Lysis and Interacts with Peptidoglycan.
PLoS One (2015) 10(4):e0125377.

Vassal-Stermann E, Lacroix M, Gout E, Lafly E, Pedersen CM, Martin L, Amoroso A, Schmidt RR, Zähringer U, Gaboriaud C, Di Guilmi AM and Thielens NM. Moieties of Pneumococcal Teichoic Acid Human L-Ficolin Recognizes Phosphocholine.
J Immunol (2014) 193:5699-5708.

Morlot C, Bayle L, Jacq M, Fleurie A, Tourcier G, Galisson F, Vernet T, Grangeasse C and Di Guilmi AM
Interaction of Penicillin-Binding Protein 2x and Ser/Thr protein kinase StkP, two key players in Streptococcus pneumoniae R6 morphogenesis.
Mol Microbiol (2013) 90(1):88-102.

Bersch B, Bougault C, Roux L, Favier A, Vernet T and Durmort C
New insights into histidine triad proteins: solution structure of a Streptococcus pneumoniae PhtD domain and zinc transfer to AdcAII.
PLoS One (2013) 8(11):e81168.

Zapun A, Philippe J, Abrahams KA, Signor L, Roper DI, Breukink E and Vernet T
In vitro reconstitution of peptidoglycan assembly from the Gram-positive pathogen Streptococcus pneumoniae.
ACS Chem Biol (2013) 8(12):2688-96.

Terrasse R, Tacnet-Delorme P, Moriscot C, Pérard J, Schoehn G, Vernet T, Thielens NM, Di Guilmi AM, Frachet P.
Human and pneumococcal cell surface glyceraldehyde-3-phosphate dehydrogenase (GAPDH) proteins are both ligands of human C1q protein.
J Biol Chem (2012) 287(51):42620-33.

Boncoeur E, Durmort C, Bernay B, Ebel C, Di Guilmi AM, Croizé J, Vernet T and Jault JM
PatA and PatB form a functional heterodimeric ABC multidrug efflux transporter responsible for the resistance of Streptococcus pneumoniae to fluoroquinolones.
Biochemistry (2012) 51(39):7755-65.

El Mortaji L, Contreras-Martel C, Moschioni M, Ferlenghi I, Manzano C, Vernet T, Dessen A and Di Guilmi AM
The full-length Streptococcus pneumoniae major pilin RrgB crystallizes in a fibre-like structure, which presents the D1 isopeptide bond and provides details on the mechanism of pilus polymerization.
Biochem J (2012) 441(3):833-41.

The complete list of the Pneumococcus group publications is available here.