The protein interaction network of a taxis signal transduction system in a Halophilic Archaeon

Abstract

BackgroundThe taxis signaling system of the extreme halophilic archaeon Halobacterium (Hbt.) salinarum differs in several aspects from its model bacterial counterparts Escherichia coli and Bacillus subtilis. We studied the protein interactions in the Hbt. salinarum taxis signaling system to gain an understanding of its structure, to gain knowledge about its known components and to search for new members.ResultsThe interaction analysis revealed that the core signaling proteins are involved in different protein complexes and our data provide evidence for dynamic interchanges between them. Fifteen of the eighteen taxis receptors (halobacterial transducers, Htrs) can be assigned to four different groups depending on their interactions with the core signaling proteins. Only one of these groups, which contains six of the eight Htrs with known signals, shows the composition expected for signaling complexes (receptor, kinase CheA, adaptor CheW, response regulator CheY). From the two Hbt. salinarum CheW proteins, only CheW1 is engaged in signaling complexes with Htrs and CheA, whereas CheW2 interacts with Htrs but not with CheA. CheY connects the core signaling structure to a subnetwork consisting of the two CheF proteins (which build a link to the flagellar apparatus), CheD (the hub of the subnetwork), two CheC complexes and the receptor methylesterase CheB.ConclusionsBased on our findings, we propose two hypotheses. First, Hbt. salinarum might have the capability to dynamically adjust the impact of certain Htrs or Htr clusters depending on its current needs or environmental conditions. Secondly, we propose a hypothetical feedback loop from the response regulator to Htr methylation made from the CheC proteins, CheD and CheB, which might contribute to adaptation analogous to the CheC/CheD system of B. subtilis.

Screening of a Haloferax volcanii Transposon Library Reveals Novel Motility and Adhesion Mutants

“…volcanii , chemotaxis plays an important role in both adhesion and motility. Although the connection between these chemotaxis genes and motility had already been established in archaea [10,34,35,36], to the best of our knowledge, this is the first indication in any archaeon that chemotaxis is also required for adhesion. This is particularly intriguing since we have previously shown that, unlike for bacterial adhesion, flagella-dependent motility is not required for Hfx.…”

Transmembrane Signal Transduction in Two‐Component Systems: Piston, Scissoring, or Helical Rotation?

“…The sensory rhodopsin is a seven‐helical retinal‐binding photoactive membrane protein. Upon illumination, it undergoes conformational changes, which are then passed to the transducer and then, as in chemotaxis systems, to class II HK CheA . Sensory rhodopsin transducers are 2TM membrane proteins similar to chemoreceptors.…”

Mechanism and Role of Globin-Coupled Sensor Signalling

“…HemAT- Hs is essential for aerotaxis in H. salinarium and controls an aerophobic response. In addition, HemAT- Hs is methylated by CheR in vivo , thereby enhancing CheA activation and downstream aerotactic signaling, but direct interaction partners of HemAT- Hs are still unknown (Hou et al, 2000; Schlesner et al, 2012). Both HemAT- Hs and HemAT- Bh exhibit similar ligand binding properties and reasonable amino acid similarity to HemAT- Bs (HemAT- Bs vs. HemAT- Bh = 56% similarity; HemAT- Bs vs. HemAT- Hs = 38% similarity), suggesting that the proteins may utilize similar sensing mechanisms (Hou, Belisle, et al, 2001; Hou, Freitas, et al, 2001; Hou et al, 2000).…”