Dynamic polarity control by a tunable protein oscillator in bacteria

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Structural asymmetry in a conserved signaling system that regulates division, replication, and virulence of an intracellular pathogen

We have functionally and structurally defined an essential protein phosphorelay that regulates expression of genes required for growth, division, and intracellular survival of the global zoonotic pathogen Brucella abortus. Our study delineates phosphoryl transfer through this molecular pathway, which initiates from the sensor kinase CckA and proceeds through the ChpT phosphotransferase to two regulatory substrates: CtrA and CpdR. Genetic perturbation of this system results in defects in cell growth and division site selection, and a specific viability deficit inside human phagocytic cells. Thus, proper control of B. abortus division site polarity is necessary for survival in the intracellular niche. We further define the structural foundations of signaling from the central phosphotransferase, ChpT, to its response regulator substrate, CtrA, and provide evidence that there are at least two modes of interaction between ChpT and CtrA, only one of which is competent to catalyze phosphoryltransfer. The structure and dynamics of the active site on each side of the ChpT homodimer are distinct, supporting a model in which quaternary structure of the 2:2 ChpT–CtrA complex enforces an asymmetric mechanism of phosphoryl transfer between ChpT and CtrA. Our study provides mechanistic understanding, from the cellular to the atomic scale, of a conserved transcriptional regulatory system that controls the cellular and infection biology of B. abortus. More generally, our results provide insight into the structural basis of two-component signal transduction, which is broadly conserved in bacteria, plants, and fungi

Molecular Evolution of the Two-Component System BvgAS Involved in Virulence Regulation in Bordetella

The whooping cough agent Bordetella pertussis is closely related to Bordetella bronchiseptica, which is responsible for chronic respiratory infections in various mammals and is occasionally found in humans, and to Bordetella parapertussis, one lineage of which causes mild whooping cough in humans and the other ovine respiratory infections. All three species produce similar sets of virulence factors that are co-regulated by the two-component system BvgAS. We characterized the molecular diversity of BvgAS in Bordetella by sequencing the two genes from a large number of diverse isolates. The response regulator BvgA is virtually invariant, indicating strong functional constraints. In contrast, the multi-domain sensor kinase BvgS has evolved into two different types. The pertussis type is found in B. pertussis and in a lineage of essentially human-associated B. bronchiseptica, while the bronchiseptica type is associated with the majority of B. bronchiseptica and both ovine and human B. parapertussis. BvgS is monomorphic in B. pertussis, suggesting optimal adaptation or a recent population bottleneck. The degree of diversity of the bronchiseptica type BvgS is markedly different between domains, indicating distinct evolutionary pressures. Thus, absolute conservation of the putative solute-binding cavities of the two periplasmic Venus Fly Trap (VFT) domains suggests that common signals are perceived in all three species, while the external surfaces of these domains vary more extensively. Co-evolution of the surfaces of the two VFT domains in each type and domain swapping experiments indicate that signal transduction in the periplasmic region may be type-specific. The two distinct evolutionary solutions for BvgS confirm that B. pertussis has emerged from a specific B. bronchiseptica lineage. The invariant regions of BvgS point to essential parts for its molecular mechanism, while the variable regions may indicate adaptations to different lifestyles. The repertoire of BvgS sequences will pave the way for functional analyses of this prototypic system

Gear up! An overview of the molecular equipment used by Myxococcus to move, kill, and divide in prey colonies

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Etude du régulateur central de la virulence, BvgA/S, chez Bordetella pertussis, l'agent de la coqueluche

La régulation de la virulence chez Bordetella pertussis, l'agent de la coqueluche, est sous la dépendance d'un système à deux composants complexe appelé BvgA/S. Ce système est composé d'une protéine senseur membranaire appelée BvgS et d'un régulateur transcriptionnel cytoplasmique, BvgA. En présence d'activateurs de la virulence (non encore définis), BvgS s'autophosphoryle, l'accepteur terminal du phosphate étant BvgA qui est alors actif et va réguler la transcription des gènes impliqués dans la virulence. Par contre, lorsque la bactérie est en présence d'inhibiteurs de la virulence, comme l'acide nicotinique ou le MgSO4, il y a absence d'autophosphorylation de BvgS, BvgA n'est plus activé et les gènes réprimés lors de la virulence sont actifs. Malgré toutes ces informations, nous ne connaissons pas encore les domaines de BvgS impliqués dans la perception des signaux environnementaux activateurs ou inhibiteurs de la virulence. Nous nous sommes donc intéressés à deux domaines de BvgS qui pourraient être impliqués dans ce mécanisme. Le premier domaine est le domaine périplasmique de BvgS homologue à des PBP (Periplasmic Binding Protein). Il pourrait intervenir dans la fixation de ligands activateurs ou inhibiteurs de la virulence. Le deuxième domaine, cytoplasmique, est appelé domaine PAS. Il est très répandu chez les eucaryotes et procaryotes et est impliqué dans l'adaptation du métabolisme de la cellule à des variations de conditions environnementales (comme des variations de potentiel redox, de luminosité ou à la en présence d'oxygène ou de fer...). Ce domaine pourrait intervenir dans la fixation d'inhibiteur ou d'activateur de la virulence. Ce travail permettra donc d'avoir une meilleure compréhension du fonctionnement du complexe BvgAS dans la régulation de la virulence, d'identifier les domaines impliqués dans la perception des signaux positifs ou négatifs de la virulence, et de connaître l'identité de ces différents signauxLILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF

Do vegans have a higher fracture risk?

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Linking single-cell decisions to collective behaviours in social bacteria

International audienceSocial bacteria display complex behaviours whereby thousands of cells collectively and dramatically change their form and function in response to nutrient availability and changing environmental conditions. In this review, we focus on Myxococcus xanthus motility, which supports spectacular transitions based on prey availability across its life cycle. A large body of work suggests that these behaviours require sensory capacity implemented at the single-cell level. Focusing on recent genetic work on a core cellular pathway required for single-cell directional decisions, we argue that signal integration, multi-modal sensing and memory are at the root of decision making leading to multicellular behaviours. Hence, Myxococcus may be a powerful biological system to elucidate how cellular building blocks cooperate to form sensory multicellular assemblages, a possible origin of cognitive mechanisms in biological systems. This article is part of the theme issue ‘Basal cognition: conceptual tools and the view from the single cell’

BvgS of Pathogenic Bordetellae: a Paradigm for Sensor-kinases with Venus Flytrap Perception Domains

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Characterization of the PAS domain in the sensor-kinase BvgS: mechanical role in signal transmission.

International audienceBACKGROUND: In bacteria, signal-transduction two-component systems are major players for adaptation to environmental stimuli. The perception of a chemical or physical signal by a sensor-kinase triggers its autophosphorylation. The phosphoryl group is then transferred to the cognate response regulator, which mediates the appropriate adaptive response. Virulence of the whooping cough agent Bordetella pertussis is controlled by the two-component system BvgAS. Atypically, the sensor-kinase BvgS is active without specific stimuli at 37[degree sign]C in laboratory conditions and is inactivated by the addition of negative chemical modulators. The structure of BvgS is complex, with two tandem periplasmic Venus flytrap domains and a cytoplasmic PAS domain that precedes the kinase domain, which is followed by additional phosphotransfer domains. PAS domains are small, ubiquitous sensing or regulatory domains. The function of the PAS domain in BvgS remains unknown. RESULTS: We showed that recombinant BvgS PAS proteins form dimers that are stabilized by alpha helical regions flanking the PAS core. A structural model of the PAS domain dimer was built and probed by site-directed mutagenesis and by biochemical and functional analyses. Although we found no ligands for the PAS domain cavity, its integrity is required for signaling. We also showed that the structural stability of the PAS core and its proper coupling to its flanking N- and C-terminal alpha helices are crucial for BvgS activity. CONCLUSIONS: We propose that a major function of the BvgS PAS domain is to maintain conformational signals arising from mechanical strain generated by the periplasmic domain. The tight structure of the PAS core and its connections with the upstream and downstream helices ensure signaling to the kinase domain, which determines BvgS activity. Many mild substitutions that map to the PAS domain keep BvgS active but make it unresponsive to negative modulators, supporting that modulation increases conformational strain in the protein