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 O . 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 O -sensor [K , 19 μM], utilizing the same Iβ Trp (W276) as PaAer2 to stabilize O . 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 O [K 12 μM], although O binding was stabilized by either a Trp or Tyr residue. Moreover, PAS1 appeared to function as a signal modulator, regulating O -mediated signaling from PAS2, and resulting in activation of the cluster III chemosensory pathway. This article is protected by copyright. All rights reserved.

Repurposing a chemosensory macromolecular machine

“…The P. aeruginosa Aer2 receptor is well characterized: it consists of three N-terminal HAMP domains, followed by a PAS domain, two additional HAMP domains and a cytoplasmic signaling domain 22,23 . The V. cholerae Aer2 receptor is also well characterized: it consists of two N-terminal PAS domains, two HAMP domains and a cytoplasmic signaling domain 24 . We used CD-VIST 25 to predict the domain architecture of the related receptor in the two remaining species.…”

Deciphering the Che2 chemosensory pathway and the roles of individual Che2 proteins from Pseudomonas aeruginosa

“…Q414 appears to be the only deamidation site in WT Aer2 (Figure 5a), and this site is not shared by all other Aer2 receptors. For example, V. cholerae Aer2 lacks this adaptation site and the surrounding CheD consensus binding sequence (Greer-Phillips et al, 2018). Moreover, deamidation assays and behavioral assays did not support a role for CheD-mediated deamidation of Aer2 (Figures 5 and 6).…”

“…This motif is necessary for CheC to bind to CheY-P in B. subtilis (Muff and Ordal, 2007). However, the CheD proteins from some other Aer2-containing systems, for example, from V. cholerae (Greer-Phillips et al, 2018) or Vibrio vulnificus, do not have the CheC-like motif, so their CheY proteins may not directly interact with CheD. Rather, their genomes encode CheX, which contains the CheC-like motif.…”

Repurposing a macromolecular machine: Architecture and evolution of the F7 chemosensory system

“…While we did not test different growth conditions for M. alcaliphilum, we did observe that formation of F7 arrays in S. oneidensis was dependent on culture conditions. Another clue is that both P. aeruginosa and V. cholerae are capable of sensing oxygen, which binds to the PAS-heme domains of Aer2 receptors to activate signaling (24,45). We therefore favor the working model that the older F7 systems are part of an emergency response system activated by stress conditions, perhaps related to the availability of oxygen.…”