Orillard E, Anaya S, Johnson MS, Watts KJ. Oxygen-Induced Conformational Changes in the PAS-Heme Domain of the
Pseudomonas aeruginosa Aer2 Receptor.
Biochemistry 2021;
60:2610-2622. [PMID:
34383467 DOI:
10.1021/acs.biochem.1c00452]
[Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
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.
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