A cell cycle kinase with tandem sensory PAS domains integrates cell fate cues

Abstract

All cells must integrate sensory information to coordinate developmental events in space and time. The bacterium Caulobacter crescentus uses two-component phospho-signalling to regulate spatially distinct cell cycle events through the master regulator CtrA. Here, we report that CckA, the histidine kinase upstream of CtrA, employs a tandem-PAS domain sensor to integrate two distinct spatiotemporal signals. Using CckA reconstituted on liposomes, we show that one PAS domain modulates kinase activity in a CckA density-dependent manner, mimicking the stimulation of CckA kinase activity that occurs on its transition from diffuse to densely packed at the cell poles. The second PAS domain interacts with the asymmetrically partitioned second messenger cyclic-di-GMP, inhibiting kinase activity while stimulating phosphatase activity, consistent with the selective inactivation of CtrA in the incipient stalked cell compartment. The integration of these spatially and temporally regulated signalling events within a single signalling receptor enables robust orchestration of cell-type-specific gene regulation.

A Kinase-Phosphatase Switch Transduces Environmental Information into a Bacterial Cell Cycle Circuit

“…It is well established that under optimal conditions CckA drives oscillations of the master cell cycle regulator CtrA through dynamically switching between its kinase and phosphatase activities [16,22,34,37]. Our new data suggest that environmental stress locks CckA in its phosphatase mode leading to the rapid inactivation of CtrA, its elimination through the protease ClpXP and consequently a block of CtrA regulated functions including cell division (Fig 8B).…”

“…Under non-stress conditions CckA dynamically switches between its kinase and phosphatase activities [16,34]. We reasoned that the observed inactivation of CtrA could either be due to complete loss of CckA function or to a more active mechanism, in which CckA switches from a kinase into a phosphatase.…”

“…CckA has two PAS (Per Arnt Sim) domains, PAS-A and PAS-B, which sense distinct spatiotemporal signals and thereby mediate the cell cycle-dependent regulation of CckA activity [34]. These PAS domains might also perceive information about the environment, for example by binding molecules that are present under certain conditions.…”

An intracellular compass spatially coordinates cell cycle modules in Caulobacter crescentus

“…First, CckA is primarily delocalized in swarmer cells, is localized to the stalked pole in some stalked cells, and subsequently localized either to both poles or only at the swarmer pole in predivisional cells [35,36]. Accumulation of CckA at the new cell pole, mediated by the pseudokinase DivL, promotes kinase activity in the swarmer compartment [37 • ,38] (Figure 2a). Second, DivK, when phosphorylated, binds to DivL, and this DivL–DivK~P complex can inhibit CckA kinase activity [39,40 • ].…”

“…Second, DivK, when phosphorylated, binds to DivL, and this DivL–DivK~P complex can inhibit CckA kinase activity [39,40 • ]. PleD, when phosphorylated, synthesizes cyclic-di-GMP (cdG), which can bind CckA and inhibit its kinase activity [37 • ,41 • ]. The levels of DivK~P and PleD~P are modulated by the swarmer fate determinant PleC and the stalked fate determinant DivJ (Figure 2a).…”