Structure-function analysis of pathogen sensors binding plant-tumor compounds – sensor

Determination of protein structures

Structures of Atu4342 with and without GABA

work on NocT and OccJ

1- Planamente S, Mondy S, Hommais F, Vigouroux A, Moréra S, Faure D.(2012) Structural basis for selective GABA binding in bacterial pathogens. Mol Microbiol. 86:1085-99.


2- Planamente S, Moréra S, Faure D. (2013). In planta fitness-cost of the Atu4232-regulon encoding for a selective GABA-binding sensor in Agrobacterium.Commun Integr Biol. 1;6:e23692.

The project SENSOR groups 3 teams with expertise in chemistry (Team 3), molecular and structural biology (Team 2 and 1 respectively) in an integrative structure-function study of 4 key-sensors which belong to the large family of periplasmic binding proteins (PBP) and are involved in the perception of plant-derived compounds such as GABA and opines (resulting from condensation of amino acids, organic acids or sugars). These 4 PBPs and their ligands are in turn involved, or potentially involved, in quorum sensing and virulence of the plant pathogen Agrobacterium tumefaciens strains C58 and B6. A. tumefaciens B6 and C58 are model strains of which the complete genome sequence is available. The bacterial pathogen A. tumefaciens genetically engineers the plant host by transferring a piece of DNA (the T-DNA) from its tumor inducing (Ti) plasmid to the nuclear genome of plants. Proliferation of the transformed plant cells results in formation of a tumor (crown gall disease) in numerous plants of agronomical (poplar, tomato plant) and horticultural (rose) interest. In plant tumors, expression of the T-DNA redirects the metabolism of plant cells towards the production of opines, which are used by the pathogen as nutrients (C and N sources) and signals to control the expression of some virulence functions. In bacterial cells, opines stimulate the synthesis of a quorum-sensing (QS) signal which increases aggressiveness of Agrobacterium and activates the dissemination of the virulence Ti plasmid by horizontal transfer (by conjugation). In 2009, Team 1 and Team 2 joined their expertises (co-direction of a PhD, Sara Planamente 2009-2011) to understand how the A. tumefaciens C58 solves the paradox between opine-induced biosynthesis and GABA-induced biodegradation of quorum-sensing signals by studying a PBP (Atu2422) which binds GABA but also some other amino-acids. They demonstrated that free proline (Pro), which accumulates in the plant tumour, binds Atu2422, antagonizes import of GABA and consequently prevents the GABA-induced degradation of the bacterial quorum-sensing signal. In A. tumefaciens, other PBPs are involved in the perception and importation via ABC transporters of plant-derived signals including opines and GABA. Surprisingly, none PBP structure has been solved in complex with opines so far and a unique PBP structure in complex with GABA (but this PBP Atu2422 is not specific to GABA) was recently published by the teams implicated in the proposed SENSOR project. The three PBPs involved in opine binding are NocT and AccA in A. tumefaciens C58 and OccJ in A. tumefaciens B6. That involves in GABA binding only is Atu4243 from A. tumefaciens C58. Moreover, bacterial genome databases reveal that putative orthologs of these 4 PBPs are present in several animal- and plant-interacting bacteria including Pseudomonas, Burkholderia and Rhizobium. SENSOR project will (1) solve and compare the molecular structure and affinity of these 4 PBPs-sensors involved in the binding of opines and GABA, (2) evaluate their roles in quorum-sensing and virulence of Agrobacterium using appropriate KO-mutants and transcriptomics, and (3) will use them as references for defining structural-functional clusters among PBPs that are present in databases. This project will improve our basic knowledge on the structure-function relationship and virulence regulation of one the most abundant families of ligand-binding protein (PBP) in pathogenic and symbiotic bacteria. In addition, several actions for dissemination of these data to scientific and non-scientific communities are proposed.