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The Brucella abortus virulence regulator, LovhK, is a sensor kinase in the general stress response signalling pathway.

ABSTRACT: In the intracellular pathogen Brucella abortus, the general stress response (GSR) signalling system determines survival under acute stress conditions in vitro, and is required for long-term residence in a mammalian host. To date, the identity of the Brucella sensor kinase(s) that function to perceive stress and directly activate GSR signalling have remained undefined. We demonstrate that the flavin-binding sensor histidine kinase, LovhK (bab2_0652), functions as a primary B. abortus?GSR sensor. LovhK rapidly and specifically phosphorylates the central GSR regulator, PhyR, and activates transcription of a set of genes that closely overlaps the known B. abortus?GSR regulon. Deletion of lovhK severely compromises cell survival under defined oxidative and acid stress conditions. We further show that lovhK is required for cell survival during the early phase of mammalian cell infection and for establishment of long-term residence in a mouse infection model. Finally, we present evidence that particular regions of primary structure within the two N-terminal PAS domains of LovhK have distinct sensory roles under specific environmental conditions. This study elucidates new molecular components of a conserved signalling pathway that regulates B. abortus stress physiology and infection biology.

SUBMITTER: Kim HS

PROVIDER: S-EPMC4227936 | biostudies-literature | 2014 Nov

REPOSITORIES: biostudies-literature

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The Brucella abortus virulence regulator, LovhK, is a sensor kinase in the general stress response signalling pathway.

Kim Hye-Sook HS Willett Jonathan W JW Jain-Gupta Neeta N Fiebig Aretha A Crosson Sean S

Molecular microbiology 20141019 4

In the intracellular pathogen Brucella abortus, the general stress response (GSR) signalling system determines survival under acute stress conditions in vitro, and is required for long-term residence in a mammalian host. To date, the identity of the Brucella sensor kinase(s) that function to perceive stress and directly activate GSR signalling have remained undefined. We demonstrate that the flavin-binding sensor histidine kinase, LovhK (bab2_0652), functions as a primary B. abortus GSR sensor. ...[more]

PMID: 25257300

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Project description:The general stress response (GSR) system of the intracellular pathogen Brucella abortus controls the transcription of approximately 100 genes in response to a range of stress cues. The core genetic regulatory components of the GSR are required for B. abortus survival under nonoptimal growth conditions in vitro and for maintenance of chronic infection in an in vivo mouse model. The functions of the majority of the genes in the GSR transcriptional regulon remain undefined. bab1_1070 is among the most highly regulated genes in this regulon: its transcription is activated 20- to 30-fold by the GSR system under oxidative conditions in vitro. We have solved crystal structures of Bab1_1070 and demonstrate that it forms a homotetrameric complex that resembles those of WrbA-type NADH:quinone oxidoreductases, which are members of the flavodoxin protein family. However, B. abortus WrbA-related protein (WrpA) does not bind flavin cofactors with a high affinity and does not function as an NADH:quinone oxidoreductase in vitro. Soaking crystals with flavin mononucleotide (FMN) revealed a likely low-affinity binding site adjacent to the canonical WrbA flavin binding site. Deletion of wrpA (?wrpA) does not compromise cell survival under acute oxidative stress in vitro or attenuate infection in cell-based or mouse models. However, a ?wrpA strain does elicit increased splenomegaly in a mouse model, suggesting that WrpA modulates B. abortus interaction with its mammalian host. Despite high structural homology with canonical WrbA proteins, we propose that B. abortus WrpA represents a functionally distinct member of the diverse flavodoxin family.Brucella abortus is an etiological agent of brucellosis, which is among the most common zoonotic diseases worldwide. The general stress response (GSR) regulatory system of B. abortus controls the transcription of approximately 100 genes and is required for maintenance of chronic infection in a murine model; the majority of GSR-regulated genes remain uncharacterized. We present in vitro and in vivo functional and structural analyses of WrpA, whose expression is strongly induced by GSR under oxidative conditions. Though WrpA is structurally related to NADH:quinone oxidoreductases, it does not bind redox cofactors in solution, nor does it exhibit oxidoreductase activity in vitro. However, WrpA does affect spleen inflammation in a murine infection model. Our data provide evidence that WrpA forms a new functional class of WrbA/flavodoxin family proteins.

Project description:Virulence of pathogenic bacteria is often determined by their ability to adapt to stress.The Brucella abortus general stress response (GSR) system is required for chronic mammalian infection and is regulated by phosphorylation and proteolysis.The B. abortus GSR signaling pathway has multiple layers of post-translational control and is a determinant of chronic infection.This study provides new, molecular level insight into chronic Brucella infection. Brucella spp. are adept at establishing a chronic infection in mammals. We demonstrate that core components of the ?-proteobacterial general stress response (GSR) system, PhyR and ?(E1), are required for Brucella abortus stress survival in vitro and maintenance of chronic murine infection in vivo. ?phyR and ?rpoE1 null mutants exhibit decreased survival under acute oxidative and acid stress but are not defective in infection of primary murine macrophages or in initial colonization of BALB/c mouse spleens. However, ?phyR and ?rpoE1 mutants are attenuated in spleens beginning 1 month postinfection. Thus, the B. abortus GSR system is dispensable for colonization but is required to maintain chronic infection. A genome-scale analysis of the B. abortus GSR regulon identified stress response genes previously linked to virulence and genes that affect immunomodulatory components of the cell envelope. These data support a model in which the GSR system affects both stress survival and the interface between B. abortus and the host immune system. We further demonstrate that PhyR proteolysis is a unique feature of GSR control in B. abortus. Proteolysis of PhyR provides a mechanism to avoid spurious PhyR protein interactions that inappropriately activate GSR-dependent transcription. We conclude that the B. abortus GSR system regulates acute stress adaptation and long term survival within a mammalian host and that PhyR proteolysis is a novel regulatory feature in B. abortus that ensures proper control of GSR transcription.

Dataset Information

The Brucella abortus virulence regulator, LovhK, is a sensor kinase in the general stress response signalling pathway.

Publications

The Brucella abortus virulence regulator, LovhK, is a sensor kinase in the general stress response signalling pathway.

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