Fig 1.

Schematic of HTCS regulation. (A) Domain organization of HTCSs. Activation of HTCSs by polysaccharides is through the functional dimer of histidine kinase domains. The DNA-binding activities need to be regulated within the dimer and further mediated by phosphorylation of the REC domain. (B) Effects of interdomain interaction on phosphorylation kinetics and DNA binding activities. Inhibitory interaction shifts the conformational equilibrium, increases the free energy barrier, and slows down phosphorylation kinetics. Isolated REC domains or RR variants with disrupted interaction (brown line) will have a smaller energy barrier for phosphorylation than RRs with the inhibitory interaction (black line).