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Home > Research teams > Membrane Trafficking and Signaling in Bacteria > Secretion and virulence factors

Molecular mechanisms of protein secretion and targeting

Protein transport across membranes is an essential function in all living cells. In Gram negative bacteria, several highly specialized systems are dedicated to the secretion of various proteins implicated in nutrient acquisition, competition and pathogenesis. Among them, the Type 2 Secretion System (T2SS) is a sophisticated multiprotein machine that spans the two bacterial membranes and allows secretion of large folded proteins from the periplasm to the cell exterior. The proteins secreted by T2SS play a wide range of life-sustaining functions and are involved in biopolymer degradation, metal reduction and depollution. Furthermore, lytic enzymes and toxins secreted by T2SS are major virulence determinants in many human, animal and plant pathogens.

The plant pathogenic bacterium Dickeya dadantii utilizes this versatile machine to secrete plant cell wall degrading enzymes, mainly pectinases. We use this bacterium as a model to elucidate the molecular mechanisms of protein recruitment and secretion by T2SS. To gain this knowledge, we employ an integrative approach combining biochemical, proteomics and genetic studies with structural biology and bioinformatics analyses. For instance, to capture transient protein interactions in the course of secretion and characterize their contacts we use site-specific photo-crosslinking coupled to mass spectrometry. Comprehensive mapping of the interacting epitopes is pursued by peptide array. To establish the molecular basis of these protein-protein interactions, a series of structural analysis is carried out in collaboration with partner labs. Combined with extensive functional analyses, these studies will allow us to decipher the nature of the secretion signals that target the proteins to the T2SS, the T2SS components involved in their recognition and the molecular basis of these protein-protein interactions.

Recently, we were interested in an emerging species, Dickeya solani, which causes serious losses in the potato production in Europe. Preliminary results revealed a close similarity between this species and D. dadantii in their set of virulence factors and their regulation. In collaboration with French and European partners, our objective is to characterize the virulence functions leading to the emergence of these Dickeya strains.

Global methods such as transcriptomics, proteomics or metabolomics should lead to a complete vision of the adaptive capacities of Dickeya, especially in functions governing the Plant interaction. Comparative genomics and functional genomics approaches are used to predict and verify the metabolic capabilities of the bacteria. Various experimental approaches allow to screen the metabolic pathways implemented by bacteria to multiply on host-derived resources. Furthermore, we are identifying plant and bacterial signals that allow the adaptation of bacterial metabolism during pathogenesis, triggering the expression of functions required at each stage of infection.