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Structural basis of transcriptional activation by the OmpR/PhoB-family response regulator PmrA

Yuan-Chao Lou1, Hsuan-Yu Huang2, Hsin-Hong Yeh3

  • 1Biomedical Translation Research Center, Academia Sinica, Taipei 11529, Taiwan.

Nucleic Acids Research
|September 4, 2023
PubMed

Insights

PmrA, a bacterial regulator, activates polymyxin resistance genes by binding to specific DNA sequences. A cryo-EM structure reveals how PmrA interacts with RNA polymerase, influencing transcription and bacterial defense mechanisms.

Area of Science:

  • Microbiology
  • Structural Biology
  • Molecular Biology

Background:

  • PmrA is a response regulator controlling polymyxin resistance in bacteria.
  • It recognizes a specific DNA sequence (pmra-box) replacing the canonical -35 promoter element.
  • Understanding the PmrA-dependent transcription activation complex (TAC) is crucial for bacterial resistance mechanisms.

Purpose of the Study:

  • To determine the structural basis of PmrA-dependent transcription activation.
  • To elucidate the interactions between PmrA, RNA polymerase, and promoter DNA.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) was used to obtain the structure of the TAC.
  • In vivo assays were performed to validate the functional significance of observed interactions.

Main Results:

  • The cryo-EM structure revealed a dynamic TAC conformation with PmrA dimer and RNA polymerase σ70 holoenzyme bound to promoter DNA.
  • RNA polymerase interacts electrostatically with PmrA's DNA-binding domain, reorienting it upstream of the pmra-box.
  • Mutational analysis confirmed the importance of DNA-recognition and RNAPH-interacting residues for transcriptional activity.

Conclusions:

  • PmrA recognition induces DNA distortion, and PmrA facilitates promoter escape, both critical for transcriptional activation.
  • The findings provide insights into the mechanism of polymyxin resistance gene regulation.

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