Domain communications within the global bacterial Rcs signaling network

The inner membrane assocciated protein signaling complex Rcs including the sensor proteins RcsC and RcsD, the central transcription factor RcsB and the accessorial proteins RcsA and RcsF, belongs to one of the most remarkable signal transduction systems in enterobacteriaceae. It is involved in exopolysaccharide synthesis, cell division, biofilm formation and virulence by multiplex transcriptional network. The activity of RcsB is controlled by its phosphorylation state. By studying DNA binding we could identify a binding motif of a RcsAB complex. To illuminate the Rcs network and the factors affecting the phosphotransfer we have focused to investigate protein/DNA and protein/protein interactions in more detail by using NMR. We have solved the important structures of the Rcs phosphorelay and have mapped their interactions in dependence of phosphorylation state. A novel domain type integrated in Rcs signal transduction cascade is the ABL (alpha-beta-loop) domain. The domain RcsC-ABL is located in the membrane associated hybrid sensor kinase RcsC connecting the histidine kinase (HK) domain and the phosphor receiver (PR) domain. The other domain, RcsD-ABL, is located in the RcsD sensor kinase forming a heterodimer with RcsC, and connects the histidine kinase (HK) domain and the histidine phospho transferase (HPt) domain. Interestingly on the in-vitro level using NMR titration experiments we could detect a strong interaction between RcsD-ABL and the global transcription regulator RcsB. We confirmed the interaction by calorimetry and functional studies. Characterisation of the obtained protein complexes result in a very illuminating hint how the Rcs phosphorelay is regulated by the transcription factor RcsB.