Institut de Biologie StructuraleGrenoble / France

Contact person(s) related to this article / DI GUILMI Anne-Marie / DURMORT Claire

Cell surface physiology

Surface proteins of Streptococcus pneumoniae are key players in the interactions with tissues of the human host, including during the colonization of respiratory mucosa, the crossing of epithelial and endothelial barriers, and in various mechanisms of escape from the innate immune system.

Molecular mechanisms of pilus biogenesis in S. pneumoniae

Proteinaceous pili have been identified at the surface of pneumococcus. These pili play an important role in the first steps of colonizing host tissues. Six genes are involved in pilus assembly. Three genes encode structural proteins termed pilins that form the pilus. Pilins are LPxTG proteins. Three other genes encode sortase enzymes that catalyze the covalent linkage of pilins to generate a multi-protein fiber. We have described the molecular processes of the pilus biogenesis through functional and structural studies (El Mortaji et al. 2010; 2012) in collaboration with the Bacterial Pathogenesis Group (Andrea Dessen, IBS). Unusual intramolecular isopeptide bonds within the pilin structures have been exploited in the BioMolecular Welding (BMW) patented technique (patent).

[bleu marine]Structural scheme of the pneumococcal pilus composed of three different types of pilin, attached to the peptidoglycan.[/bleu marine]

Molecular mechanisms of S. pneumoniae escape from the innate immune system

We have studied virulence mechanisms of the pneumococcus by analyzing how it escapes the human innate immune system. In collaboration with the IRPAS Group (P. Frachet, IBS), we have shown that the presence of the enzyme GAPDH at the pneumococcal surface mediates the binding of the C1q from the complement (Terrasse et al. 2012). GAPDH is a cytoplasmic enzyme that appears to be used at the pneumococcal cell surface to mediate interaction with the human host. We have demonstrated that GAPDH is recruited at the bacterial surface following release by lysis of neighbor cells (Terrasse et al. 2015).
Human L-ficolin is a soluble protein of the innate immune system able to sense pathogens through its fibrinogen (FBG) recognition domains and to trigger activation of the lectin complement pathway through associated serine proteases. We have recently showed that L-ficolin is involved in host antipneumococcal defense through recognition of cell wall teichoic acids components (Vassal et al. 2014, collab. IRPAS Group, N. Thielens).

Molecular mechanisms of Zinc homeostasis in S. pneumoniae

Zinc homeostasis is a critical factor during the pneumococcal infectious process as the bacteria must cope with important variations of the zinc concentration in the various host tissues. The pneumococcus finely tune zinc import through ATP-binding cassette (ABC) transporters, such as AdcA. To fully understand zinc transport in pneumococcus, we have characterized AdcAII, a protein with 34% of similarity to AdcA, and PhtD, another zinc binding protein. PhtD was shown to transfer zinc to AdcAII and its structure was solved by NMR (Bersch et al. 2013), in collaboration with the Biomolecular NMR Group at IBS.

[bleu marine]Structure of pneumococcal PhtD zinc-binding domain[/bleu marine]

ABC transporters and antibiotic resistance

Efflux pumps are used to export toxic compounds from the cell. We are studying two types of ABC transporters from S. pneumoniae that confer resistance to antibiotics. PatA/PatB expels fluoroquinolones as a heterodimer (Boncoeur et al. 2012) and hydrolyzes GTP preferentially to ATP. Spr0812/0813 is an exporter of drugs that target cell wall metabolism. We are investigating its regulation by the two-component system, His-kinase response regulator Spr1473/1474 (collab. J.-M. Jault, BMSSI, Lyon).