The spoke model was used to derive binary interactions from the copurification data. Only proteins discussed in the text are shown. The complete network is depicted in Additional file 6. The prefixes “Che” and

“Htr” were omitted from the protein labels. The core signaling proteins CheA, CheW1 and CheY are highlighted by red shading. The weak binding of CheW2 to the core signaling complexes (see text) is indicated by red and white stripes. The gray areas delineate different groups of Htrs that can be distinguished by their interactions with CheA, CheR, CheW1, CheW2 and GW-572016 in vivo CheY (see text). For clarity, interactions identified with these baits are shown in different colors. The interactions detected in this study were compared to interactions between the Che proteins in other prokaryotic organisms (Additional file 7). However, the comparability of the datasets is rather low because the only other protein-protein interaction (PPI) study in an archaeal organism (P.horikoshii, [66]) reported just one interaction between Che proteins (CheC-CheD). The large-scale studies in bacteria (Escherichia coli[67, 68], Helicobacter pylori[69], Campylobacter jejuni[70], Treponema pallidum[71]) as well as a dedicated PPI YAP-TEAD Inhibitor 1 study of the E.coli taxis signaling

system [72] were performed in organisms with quite different taxis signaling systems compared to that of Hbt.salinarum. For example, none of these organisms contains CheC and CheD proteins, which together account for a substantial part of the interactions described in the present study. Figure 4 presents a general interaction network for enough prokaryotic taxis signaling systems. Figure 4 Physical and functional interactions in prokaryotic taxis signaling systems. The interactions of the core signaling

proteins are generally in agreement between Hbt.salinarum and the data of the other organisms. The Hbt.salinarum dataset probably contains indirect interactions (e. g. CheY-CheW, CheY-Htr) because it was generated by AP-MS. The interactions of the other Che proteins have, with the exception of CheC-CheD, not been described in other organisms. References for literature data are given in Additional file 7. The core signaling structure The centerpiece of the chemotaxis signal transduction system is the histidine kinase CheA, which is bound to the Htrs together with the coupling protein CheW. It check details phosphorylates the response regulator CheY to generate the output signal CheY-P [19, 73]. Bait fishing experiments with the core signaling proteins confirmed this assumed organization of the core structure (Figure 3) and also led to the identification of novel protein complexes around the core signaling proteins (described below). CheA was found to strongly interact with CheW1, and 6 of the 18 Htrs were found to interact with both CheA and CheW1.