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The Aer2 receptor from Vibrio cholerae is a dual PAS-heme oxygen sensor.

ABSTRACT: The diarrheal pathogen Vibrio cholerae navigates complex environments using three chemosensory systems and 44-45 chemoreceptors. Chemosensory cluster II modulates chemotaxis, whereas clusters I and III have unknown functions. Ligands have been identified for only five V. cholerae chemoreceptors. Here, we report that the cluster III receptor, VcAer2, binds and responds to O₂ . VcAer2 is an ortholog of Pseudomonas aeruginosa Aer2 (PaAer2) but differs in that VcAer2 has two, rather than one, N-terminal PAS domain. We have determined that both PAS1 and PAS2 form homodimers and bind penta-coordinate b-type heme via an Eη-His residue. Heme binding to PAS1 required the entire PAS core, but receptor function also required the N-terminal cap. PAS2 functioned as an O₂ -sensor [ Kd(O2) , 19 μM], utilizing the same Iβ Trp (W276) as PaAer2 to stabilize O₂ . The crystal structure of PAS2-W276L was similar to that of PaAer2-PAS but resided in an active conformation mimicking the ligand-bound state, consistent with its signal-on phenotype. PAS1 also bound O₂ [ Kd(O2) , 12 μM], although O₂ binding was stabilized by either a Trp residue or Tyr residue. Moreover, PAS1 appeared to function as a signal modulator, regulating O₂ -mediated signaling from PAS2 and resulting in activation of the cluster III chemosensory pathway.

SUBMITTER: Greer-Phillips SE

PROVIDER: S-EPMC6214802 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Periodontal disease (PD) results from a shift in the composition of the microbial community of the subgingival crevice. As the bacterial population transitions from Gram-positive bacteria to predominantly Gram-negative anaerobes and spirochetes, dramatic changes occur in the physiological and immunological environment at diseased sites. Treponema denticola thrives in periodontal pockets, indicating that it has a unique ability to adapt to changing environmental conditions. Hpk2 (tde1970), a Per-Arnt-Sim motif (PAS) domain-containing histidine kinase (HK), is part of the T. denticola Hpk2-Rrp2 (tde1969) two-component regulatory (TCR) system. This TCR system is growth phase regulated and has been postulated to play a key role in adaptive responses. In this study, we employ predictive structural analyses and site-directed mutagenesis to investigate the functional role of specific amino acid residues located within the Hpk2 PAS domain. Specific substitutions impacted autophosphorylation (AP), phosphotransfer (PT), oligomerization, and hemin binding. The AP, PT, hemin binding, and oligomerization potential of some mutated Hpk2 proteins differed under aerobic versus anaerobic reaction conditions. The data presented here suggest that the regulatory activity of Hpk2 is linked to diatomic gas levels. In a broader sense, this study highlights the importance of studying proteins produced by anaerobes under conditions that approximate the environment in which they thrive.IMPORTANCE Periodontal disease affects nearly 60% of the global adult population. Its costs to individuals, and to society as a whole, are enormous. As periodontal disease develops, there is a shift in the composition of the oral microbial community. The bacteria that become dominant are able to cause significant damage to the tissues that support the teeth, leading to tooth loss. Treponema denticola is one of the keystone pathogens associated with periodontal disease. An earlier study demonstrated that the Hpk2 and Rrp2 proteins play an important role in adaptive responses. Here, we explore the role of specific Hpk2 amino acids in environmental sensing and function, using structural analyses and site-directed mutagenesis.

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The Aer2 receptor from Vibrio cholerae is a dual PAS-heme oxygen sensor.

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