Journal article
Self-trimerization of ExsD limits inhibition of the Pseudomonas aeruginosa transcriptional activator ExsA in vitro
The FEBS journal, Vol.280(4), pp.1084-1094
02/2013
DOI: 10.1111/febs.12103
PMCID: PMC3621117
PMID: 23279839
Abstract
The opportunistic pathogen
Pseudomonas aeruginosa
ranks among leading causes of nosocomial infections. The type III secretion system (T3SS) aids acute
P. aeruginosa
infections by injecting potent cytotoxins into host cells to suppress the host's innate immune response. Expression of all T3SS-related genes is strictly dependent upon the transcription factor ExsA. Consequently, ExsA and the biological processes that regulate ExsA function are of great biomedical interest. The presented work focuses on the ExsA-ExsC-ExsD-ExsE signaling cascade that ties host cell contact to the up-regulation of T3SS gene expression. Prior to T3SS induction, the anti-activator protein ExsD binds to ExsA and blocks ExsA-dependent transcription by interfering with ExsA dimerization and promoter interactions. Upon host cell contact, ExsD is sequestered by the T3SS chaperone ExsC resulting in the release of ExsA and an up-regulation of the T3SS. Previous studies have shown that the ExsD-ExsA interactions are not freely reversible. Because independently folded ExsD and ExsA were not found to interact, it has been hypothesized that folding intermediates of the two proteins form the complex. Here we demonstrate for the first time that ExsD alone is sufficient to inhibit ExsA-dependent transcription
in vitro
and that no other cellular factors are required. More significantly, we show that independently folded ExsD and ExsA are capable of interacting, but only at 37°C and not at 30°C. Guided by the crystal structure of ExsD, we designed a monomeric variant of the protein and demonstrate that ExsD trimerization prevents ExsD from inhibiting ExsA-dependent transcription at 30°C. We propose that this unique mechanism plays an important role in T3SS regulation.
Details
- Title: Subtitle
- Self-trimerization of ExsD limits inhibition of the Pseudomonas aeruginosa transcriptional activator ExsA in vitro
- Creators
- Robert C Bernhards - University of Iowa Department of Microbiology 540B Eckstein Medical Research Building Iowa City, IA 52242-1101Anne E Marsden - University of Iowa Department of Microbiology 540B Eckstein Medical Research Building Iowa City, IA 52242-1101Shannon K Esher - University of Iowa Department of Microbiology 540B Eckstein Medical Research Building Iowa City, IA 52242-1101Timothy L Yahr - University of Iowa Department of Microbiology 540B Eckstein Medical Research Building Iowa City, IA 52242-1101Florian D Schubot - University of Iowa Department of Microbiology 540B Eckstein Medical Research Building Iowa City, IA 52242-1101
- Resource Type
- Journal article
- Publication Details
- The FEBS journal, Vol.280(4), pp.1084-1094
- DOI
- 10.1111/febs.12103
- PMID
- 23279839
- PMCID
- PMC3621117
- ISSN
- 1742-464X
- eISSN
- 1742-4658
- Language
- English
- Date published
- 02/2013
- Academic Unit
- Microbiology and Immunology
- Record Identifier
- 9984001150402771
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