Leptospira interrogans Aer2: an Unusual Membrane-Bound PAS-Heme Oxygen Sensor

Abstract

Leptospira interrogans , the cause of the zoonotic infection leptospirosis, is found in soil and water contaminated with animal urine. L. interrogans survives in complex environments with the aid of 12 chemoreceptors, none of which has been explicitly studied. In this study, we characterized the first L. interrogans chemoreceptor, Li Aer2, and reported its unique characteristics. Li Aer2 is membrane-bound, has three cytoplasmic PAS-heme domains that each bound hexacoordinate b -type heme and O 2 turned Li Aer2 signaling off.

The Aer2 chemoreceptor from Vibrio vulnificus is a tri‐PAS‐heme oxygen sensor

“…After 1 mM IPTG induction, the tumbling bias and response of Vv Aer2 410‐807 remained the same (data not shown). Overall, these results are analogous to what we previously observed for Li Aer2, which has three PAS domains and can reversibly signal with just its PAS3 domain (Orillard & Watts, 2022 ).…”

“…Like PAS1 38‐157 , PAS1 1‐157 also eluted as a brown‐colored protein with a Q‐band at ~628 nm, and it also oxidized readily during O 2 titrations (data not shown). Similar to Vv PAS1, the PAS2 domain of Li Aer2 had a high O 2 affinity and unstable O 2 binding (Orillard & Watts, 2022 ).…”

“…By expressing N‐terminally truncated Vv Aer2 proteins, we determined that Vv Aer2 can signal reversibly through PAS3 alone connected to the C‐terminal di‐HAMP and kinase control domains (Figure 3b ). Li Aer2 can likewise signal with just its PAS3 domain connected to its C‐terminal di‐HAMP and kinase control domains, even though Li Aer2 is ordinarily membrane‐embedded (Orillard & Watts, 2022 ). In contrast, neither Pa Aer2 nor Vc Aer2 can signal reversibly through a single PAS domain in the absence of additional N‐terminal domains (Greer‐Phillips et al, 2018 , Watts et al, 2011 ).…”

“…In any event, all three PAS domains bound pentacoordinate b‐ type heme via Eη‐His residues in their proximal heme cleft (Figures 4 , 5 , 6 ). Heme coordination via Eη‐His appears to be a defining feature of Aer2‐containing PAS‐heme domains, as the PAS domains of Pa Aer2, Vc Aer2, Li Aer2 and Vv Aer2 all employ this residue for heme coordination (Garcia et al, 2017 ; Greer‐Phillips et al, 2018 ; Orillard & Watts, 2022 ). Similarly, the Iβ‐Trp that stabilizes O 2 binding in Aer2‐PAS domains is universally conserved (Garcia et al, 2017 ), although it is not an absolute requirement for O 2 binding.…”

“…Although the roles of the individual Li Aer2 PAS domains have not been determined, a truncated Li Aer2 functions well with just its PAS3 domain connected to its di‐HAMP and kinase control domains. Moreover, the three Li Aer2 PAS domains bind hexacoordinate heme in the deoxy state (Orillard & Watts, 2022 ). This is unprecedented for Aer2 receptors, which typically bind pentacoordinate heme.…”