Reversed Signaling Flow of a Bacterial Pseudokinase

Bacteria respond to environmental and cellular cues both through isolated signaling events between one sensor histidine kinase and its response regulator, and through more interconnected arrays. Caulobacter crescentus achieves asymmetric division through a network of histidine kinases, and here we interrogate a novel DivL pseudokinase reverse signaling mechanism that enables productive cross-talk across the network. A leucine zipper fusion method was used to synthetically stimulate reverse signaling between the sensor and kinase domains and directly test if reverse signaling could modulate the signaling network in vivo. Stimulation of sensor-kinase helix conformational changes resulted in changes in C. crescentus motility and DivL accumulation at the cell poles. The repurposed roles of the sensor domain in these processes were evaluated. We demonstrate that a domain of unknown function that binds to two scaffolding proteins, and two conserved signaling domains are employed as modulators of an active kinase. We propose that reversed signaling may be widely used across signaling enzymes.