As suggested by the detected interactions, CheB could be regulated by CheD and/or by CheC1. In analogy to the B.subtilis CheC, the receptor part of the feedback circuit would be CheC2 and/or CheC3 which sense either CheY-P or, more likely, CheY. These ”receptors”

interact with the control center CheD and with CheC1 in the case of CheC2. Finally, the receptor demethylation and/or deamidation activities of CheB would respond to changes in CheY-P or CheY levels and thus regulate CheA activity. If CheD itself also acts as effector in Hbt.salinarum (by receptor deamidation and/or CheA regulation) remains to be investigated. Conclusions In this study we analyzed the protein interaction network of an archaeal taxis signaling system. For the core signaling structure, the interaction analysis revealed: (1) the Htrs can be assigned to different groups according to A-1210477 cell line their interactions with the core signaling proteins; (2) under the tested conditions, only CheW1 is engaged in signaling complexes with Htrs and CheA, whereas CheW2 builds complexes with Htrs but

without CheA; and (3) the core signaling proteins are involved in different protein complexes and we have evidence for dynamic changes. Together, these findings indicate that basic properties of the archaeal core signaling structure are still not understood, possibly because they are not present in the best-studied taxis signaling system, the streamlined system of E.coli. We propose that Hbt.salinarum has the capability to selectively adjust the impact of certain MCC950 cost Htrs or Htr clusters depending on its current needs or environmental conditions. For the other Che proteins, our results show: (1) different interactions of the three CheC proteins indicating different functional

roles; (2) a central role in the Che protein interaction network for CheD; and (3) interactions of CheB with CheC1 and with CheD. On the basis of these interactions we hypothesize that the CheCs, CheD and CheB build a feedback loop from the response regulator to Htr methylation. Follow-up experiments are needed to assess the biological relevance of the interactions detected Inositol monophosphatase 1 in this study and to test the hypotheses derived from the interactions. It will be interesting to see if the here described findings are restricted to archaeal taxis signaling systems or if they occur in bacterial systems as well. Methods Materials Unless C188-9 molecular weight indicated otherwise all chemicals were purchased from Sigma-Aldrich (St. Louis, MO, USA), Merck (Darmstadt, Germany), or Fluka (Buchs, Switzerland) at the highest purity grade available. Restriction enzymes were purchased from New England Biolabs (Frankfurt, Germany). U-13C6-leucine was from Cambridge Isotope Laboratories (MA, USA). Strains and growth conditions Hbt.salinarum strain R1 (DSM 671) was grown aerobically in the dark either in complex medium or in synthetic medium as described previously [115, 116].