Search

Cooperativity is a feature many multimeric proteins use to control activity. Here we show that the bacterial heptose isomerase GmhA displays homotropic positive and negative cooperativity among its four protomers. Most similar proteins achieve this through conformational changes: GmhA instead employs a delicate network of hydrogen bonds, and couples pairs of active sites controlled by a unique water channel. This network apparently raises the Lewis acidity of the catalytic zinc, thus increasing the activity at one active site at the cost of preventing substrate from adopting a reactive conformation at the paired negatively cooperative site – a “half-site” behavior. Our study establishes the principle that multimeric enzymes can exploit this cooperativity without conformational changes to maximize their catalytic power and control. More broadly, this subtlety by which enzymes regulate functions could be used to explore new inhibitor design strategies.

Highlights • Upon wounding, Woronin bodies seal hyphal septa in filamentous ascomycetes. • Little is known about the mechanism underpinning Woronin body translocation. • Passive bulk flow of cytoplasm may move Woronin bodies into the septal pore. • Mechanisms that involve Lah proteins are likely to support Woronin body based sealing. • ATP is required to prevent Woronin bodies from closing pores in healthy cells., In ascomycete fungi, hyphal cells are separated by perforate septa, which allow cell-to-cell communication. To protect against extensive wound-induced damage, septal pores are sealed by peroxisome-derived Woronin bodies (WBs). The mechanism underpinning WB movement is unknown, but cytoplasmic bulk flow may “flush” WBs into the pore. However, some studies suggest a controlled and active mechanism of WB movement. Indeed, in the wheat pathogen Zymoseptoria tritici cellular ATP prevents WBs from pore sealing in unwounded cells. Thus, cells appear to exert active control over WB closure. Here, we summarize our current understanding of WB-based pore sealing in ascomycete fungi.

One Health is an effective approach for the management of zoonotic disease in humans, animals and environments. Examples of the management of bacterial zoonoses in Europe and across the globe demonstrate that One Health approaches of international surveillance, information-sharing and appropriate intervention methods are required to successfully prevent and control disease outbreaks in both endemic and non-endemic regions. Additionally, a One Health approach enables effective preparation and response to bioterrorism threats.

International audience; There is now ample evidence that bacterial virulence is modulated by eukaryotic messengers including hormones. We have shown previously that the C-type Natriuretic Peptide (CNP), a peptide produced by lung, enhances Pseudomonas virulence. In the present work, we studied the effect of CNP on bacterial biofilm formation and we looked for a putative P. aeruginosa protein that could explain the effect of CNP on bacteria. We used in silico and in vitro approaches to identify a bacterial sensor for CNP. Additionally, pharmacological tools were used as an innovative strategy to characterize the binding site in P. aeruginosa. We observed that CNP inhibits P. aeruginosa biofilm formation. This effect is totally prevented by Isatin, an antagonist of natriuretic peptide receptors in eukaryotic cells. The actions of CNP on P. aeruginosa virulence are mimicked by the eukaryotic receptor NPR-C agonist cANF4-23. Screening and comparing 3D structures of human natriuretic peptides receptors and Pseudomonas proteins revealed that the bacterial protein AmiC shows significant homology with the human C-type eukaryotic natriuretic peptide receptor (hNPR-C) and that both CNP and Isatin can interact with AmiC using the same amino acids as in hNPR-C. Finally, recombinant protein AmiC was purified and the protein interactions assessed using MicroScale Thermophoresis. The results showed that both CNP and hNPR-C agonist bind AmiC protein with a KD of 2 µM and less than 100 nM respectively, whereas hNPR-A agonist has poor affinity for AmiC. Using an amiC- mutant strain and its complemented derivative, we definitively validated the crucial role of AmiC protein on CNP’s effect on P. aeruginosa biofilm formation. As observed for hNPR-C in mammals, AmiC is highly selective and can discriminate between the different natriuretic peptides, since another natriuretic peptide (brain natriuretic peptide, BNP) has no affinity with AmiC. In conclusion, our work provides the first demonstration that the bacterial protein AmiC may be an ortholog of the eukaryotic receptor hNPR-C, acting as a CNP sensor in P. aeruginosa. AmiC appears to modulate a switch between chronic and acute infection phenotypes depending on exposition to host factors. The observation that CNP strongly decreases bacterial biofilm formation should have major consequences for cystic fibrosis treatment.

How is information communicated both within and between cells of living systems with high signal to noise? We discuss transmembrane signaling models involving two receptor tyrosine kinases: the fibroblast growth factor receptor (FGFR) and the MET receptor. We suggest that simple dimerization models might occur opportunistically giving rise to noise but cooperative clustering of the receptor tyrosine kinases observed in these systems is likely to be important for signal transduction. We propose that this may be a more general prerequisite for high signal to noise in transmembrane receptor signaling.

International audience