An O2-sensing stressosome from a Gram-negative bacterium

Abstract

Bacteria have evolved numerous pathways to sense and respond to changing environmental conditions, including, within Gram-positive bacteria, the stressosome complex that regulates transcription of general stress response genes. However, the signalling molecules recognized by Gram-positive stressosomes have yet to be identified, hindering our understanding of the signal transduction mechanism within the complex. Furthermore, an analogous pathway has yet to be described in Gram-negative bacteria. Here we characterize a putative stressosome from the Gram-negative bacterium Vibrio brasiliensis. The sensor protein RsbR binds haem and exhibits ligand-dependent control of the stressosome complex activity. Oxygen binding to the haem decreases activity, while ferrous RsbR results in increased activity, suggesting that the V. brasiliensis stressosome may be activated when the bacterium enters anaerobic growth conditions. The findings provide a model system for investigating ligand-dependent signalling within stressosome complexes, as well as insights into potential pathways controlled by oxygen-dependent signalling within Vibrio species.

Mechanism and Role of Globin-Coupled Sensor Signalling

“…In addition, O 2 dissociation from Vb RsbR was affected by formation of the Vb RsbR/S/T complex; however, in contrast to Bpe GReg and Pcc GCS, the amplitudes of each rate were altered upon complex formation (Table 1) but the dissociation rates were not affected. While the molecular details behind these differences are unknown, these data further support the roles of subtle differences between sensor globin domains, as well as the middle and output domains of GCS proteins, in affecting globin ligand binding kinetics and affinity (Jia et al, 2016). …”

“…As phosphorylation of both RsbR and RsbS was absolutely required for activation of the B. subtilis Rsb signaling pathway (Gaidenko & Price, 2014; Kim et al, 2004a), these studies suggest that Vb RsbR controls O 2 -dependent stressosome signaling in V. brasiliensis (Figure 13). These data also suggest that the conformational changes that occur in Vb RsbR upon O 2 association/dissociation are sufficient for signal propagation to multiple binding partners (Jia et al, 2016). …”

“…Expression of the RsbR protein from V. brasiliensis ( Vb RsbR), a non-pathogenic relative, found that the protein was heme bound and able to bind diatomic ligands (Jia et al, 2016). When Vb RsbR was incubated with Vb RsbS and Vb RsbT, the other components of the stressosome complex, the proteins were able to associate, although complex formation did not depend on heme ligation state.…”

“…Phosphorylation activity of Vb RsbT was demonstrated to be controlled by ligation/oxidation state of Vb RsbR; Fe II -O 2 and Fe III Vb RsbR inhibited Vb RsbT phosphoryl transfer to Vb RsbR and Vb RsbS, while inclusion of Vb RsbR Fe II -CO and Fe II -NO exhibited intermediate activity, and Vb RsbR Fe II resulted in maximum phosphoryl transfer (Jia et al, 2016). As phosphorylation of both RsbR and RsbS was absolutely required for activation of the B. subtilis Rsb signaling pathway (Gaidenko & Price, 2014; Kim et al, 2004a), these studies suggest that Vb RsbR controls O 2 -dependent stressosome signaling in V. brasiliensis (Figure 13).…”

“…Fw109-5 (Kitanishi et al, 2011); adenylate cyclase-containing GCS from Leishmania major (Sen Santara et al, 2013); putative gene-regulating GCS from Vibrio brasiliensis (Jia et al, 2016), and GCS of unknown function from Geobacter sulfureducens (Pesce et al, 2009). Through a compilation of biochemical, spectroscopic, and physiological studies, the importance of these proteins in sensing the gaseous environment and regulating key organismal phenotypes is being elucidated.…”