Oxygen-Induced Conformational Changes in the PAS-Heme Domain of the Pseudomonas aeruginosa Aer2 Receptor

Biochemistry. 2021 Aug 31;60(34):2610-2622. doi: 10.1021/acs.biochem.1c00452. Epub 2021 Aug 12.


The Aer2 receptor from Pseudomonas aeruginosa has an O2-binding PAS-heme domain that stabilizes O2 via a Trp residue in the distal heme pocket. Trp rotates ∼90° to bond with the ligand and initiate signaling. Although the isolated PAS domain is monomeric, both in solution and in a cyanide-bound crystal structure, an unliganded structure forms a dimer. An overlay of the two structures suggests possible signaling motions but also predicts implausible clashes at the dimer interface when the ligand is bound. Moreover, in a full-length Aer2 dimer, PAS is sandwiched between multiple N- and C-terminal HAMP domains, which would feasibly restrict PAS motions. To explore the PAS dimer interface and signal-induced motions in full-length Aer2, we introduced Cys substitutions and used thiol-reactive probes to examine in vivo accessibility and residue proximities under both aerobic and anaerobic conditions. In vivo, PAS dimers were retained in full-length Aer2 in the presence and absence of O2, and the dimer interface was consistent with the isolated PAS dimer structure. O2-mediated changes were also consistent with structural predictions in which the PAS N-terminal caps move apart and the C-terminal DxT region moves closer together. The DxT motif links PAS to the C-terminal HAMP domains and was critical for PAS-HAMP signaling. Removing the N-terminal HAMP domains altered the distal PAS dimer interface and prevented signaling, even after signal-on lesions were introduced into PAS. The N-terminal HAMP domains thus facilitate the O2-dependent shift of PAS to the signal-on conformation, clarifying their role upstream of the PAS-sensing domain.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / metabolism
  • Heme / metabolism*
  • Heme-Binding Proteins / chemistry*
  • Heme-Binding Proteins / metabolism
  • Models, Molecular
  • Oxygen / metabolism*
  • Protein Domains
  • Protein Structure, Tertiary
  • Pseudomonas Infections / metabolism*
  • Pseudomonas Infections / microbiology
  • Pseudomonas Infections / pathology
  • Pseudomonas aeruginosa / isolation & purification
  • Pseudomonas aeruginosa / metabolism*
  • Signal Transduction
  • Structure-Activity Relationship
  • Type III Secretion Systems / chemistry*
  • Type III Secretion Systems / metabolism


  • Bacterial Proteins
  • Escherichia coli Proteins
  • Heme-Binding Proteins
  • PAS protein, E coli
  • Type III Secretion Systems
  • heme protein, bacteria
  • Heme
  • Oxygen