Abstract
A significant part of bacterial two-component system response regulators contains effector domains predicted to be involved in metabolism of bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP), a second messenger that plays a key role in many physiological processes. The intracellular level of c-di-GMP is controlled by diguanylate cyclase and phosphodiesterases activities associated with GGDEF and EAL domains, respectively. The Legionella pneumophila Lens genome displays 22 GGDEF/EAL domain-encoding genes. One of them, lpl0329, encodes a protein containing a two-component system receiver domain and both GGDEF and EAL domains. Here, we demonstrated that the GGDEF and EAL domains of Lpl0329 are both functional and lead to simultaneous synthesis and hydrolysis of c-di-GMP. Moreover, these two opposite activities are finely regulated by Lpl0329 phosphorylation due to the atypical histidine kinase Lpl0330. Indeed, Lpl0330 was found to autophosphorylate on a histidine residue in an atypical H box, which is conserved in various bacteria species and thus defines a new histidine kinase subfamily. Lpl0330 also catalyzes the phosphotransferase to Lpl0329, which results in a diguanylate cyclase activity decrease whereas phosphodiesterase activity remains efficient. Altogether, these data present (i) a new histidine kinase subfamily based on the conservation of an original H box that we named HGN H box, and (ii) the first example of a bifunctional enzyme that modulates synthesis and turnover of c-di-GMP in response to phosphorylation of its receiver domain.
Highlights
Systems couple a broad range of external or internal signals to regulation of diverse fundamental processes, such as metabolism, motility, and virulence [1,2,3]
Lpl0330 was found to autophosphorylate on a histidine residue in an atypical H box, which is conserved in various bacteria species and defines a new histidine kinase subfamily
Proteins involved in the metabolism of c-diGMP exhibit GGDEF and/or EAL domains responsible for the synthesis and hydrolysis of this secondary metabolite, via their diguanylate cyclase (DGC) and phosphodiesterase (PDE) activities, respectively
Summary
Systems couple a broad range of external or internal signals to regulation of diverse fundamental processes, such as metabolism, motility, and virulence [1,2,3]. Typical TCSs are composed of a sensor histidine kinase (HK) and a response regulator protein (RR) usually encoded by a pair of adjacent genes. Both the HK and the RR are multidomain proteins. Proteins involved in the metabolism of c-diGMP exhibit GGDEF and/or EAL domains responsible for the synthesis and hydrolysis of this secondary metabolite, via their diguanylate cyclase (DGC) and phosphodiesterase (PDE) activities, respectively. Lpl0329 has been characterized as a RR with two opposite activities: GGDEF and EAL domains of Lpl0329 are both functional in vitro and lead to simultaneous synthesis and hydrolysis of c-di-GMP. We observed for the first time that DGC activity depends on the phosphorylation state of a DGC/PDE enzyme, suggesting a “molecular switch” that favors one of the two-enzymatic activities and affects the production rate of c-di-GMP
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