A Developmentally Regulated Two-component Signal Transduction System in Chlamydia

Richard S. Stephens,Ingrid Chou Koo

doi:10.1074/jbc.m212170200

Richard S. Stephens, Ingrid Chou Koo

Open Access

https://doi.org/10.1074/jbc.m212170200

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Abstract

Two-component systems allow bacteria to adapt to changing environmental conditions and may induce developmental changes necessary for survival. Chlamydia trachomatis alternates between two distinct developmental forms, each optimized for survival in a separate niche. Transcriptional regulation of development is not understood. The C. trachomatis genome sequence revealed a single pair of genes (ctcB-ctcC) predicted to encode proteins with sequence conservation to bacterial two-component systems. Sequence analysis revealed that the sensor kinase, CtcB, possessed an energy-sensing PAS domain and phosphorylation site. The response regulator, CtcC, had homology to sigma(54) activators, possessing conserved receiver and ATPase domains and phosphorylation site, but lacked the C-terminal DNA-binding domain. ctcB and ctcC were expressed late in the developmental cycle, and both proteins were detected in EB lysates. Recombinant CtcB and CtcC were purified from denatured Escherichia coli inclusion bodies and refolded. CtcC was found to aggregate as dimers and tetramers in solution. In vitro phosphorylation assays showed that CtcB autophosphorylated in the presence of Mg(2+), Mn(2+), and Fe(2+) and transferred the phosphoryl group in the presence of CtcC. Collectively, these results show that CtcB and CtcC function as a two-component system and are likely responsible for transcriptional regulation by sigma(54) holoenzyme during late-stage chlamydial development.

Highlights

Two-component signal transduction systems are ubiquitous in bacteria, representing the primary mechanism of sensing and adapting to environmental changes such as pH, temperature, and osmolarity
Chlamydiae are obligate, intracellular bacterial pathogens that adapt morphologically and metabolically according to two distinct environments, extracellular and intracellular. Their unique, biphasic developmental cycle consists of the infectious elementary body (EB)1 and the vegetative reticulate body (RB)
Because only one sensor kinase response regulator pair has been identified in the genome, we hypothesized that the chlamydial two-component system is functional and, together

Summary

Several bacterial species with unique developmental stages

Have been shown to require two-component systems and minor ␴ factors for regulation of stage-specific gene expression. Chlamydiae are obligate, intracellular bacterial pathogens that adapt morphologically and metabolically according to two distinct environments, extracellular and intracellular. Their unique, biphasic developmental cycle consists of the infectious elementary body (EB) and the vegetative reticulate body (RB). The genome sequence of C. trachomatis [11] revealed several genes whose predicted protein products had sequence conservation to bacterial transcription factors These included a pair of proteins with similarity to the histidine kinase response regulator pairs of two-component systems, as well as the sigma factor (␴54) it is predicted to activate. That function has been demonstrated, we have named these genes ctcB and ctcC for chlamydial two-component system

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