The nucleoid as a scaffold for the assembly of bacterial signaling complexes

Abstract

The FrzCD chemoreceptor from the gliding bacterium Myxococcus xanthus forms cytoplasmic clusters that occupy a large central region of the cell body also occupied by the nucleoid. In this work, we show that FrzCD directly binds to the nucleoid with its N-terminal positively charged tail and recruits active signaling complexes at this location. The FrzCD binding to the nucleoid occur in a DNA-sequence independent manner and leads to the formation of multiple distributed clusters that explore constrained areas. This organization might be required for cooperative interactions between clustered receptors as observed in membrane-bound chemosensory arrays.AUTHOR SUMMARYIn this work, we show that the cytoplasmic chemoreceptor of the Frz chemosensory system, FrzCD, does not bind the cytoplasmic membrane like most MCPs but bind the bacterial nucleoid directly, thus forming distributed protein clusters also containing the Frz kinase. In vitro and in vivo experiments show that DNA-binding is not sequence-specific and is mediated by a basic aminoacid sequence of the FrzCD N-terminal domain. The deletion of this motif abolishes FrzCD DNA-binding and cooperativity in the response to signals. This work shows the importance of the nucleoid in the organization and functioning of cytoplasmic signaling systems in bacteria.

Linking single-cell decisions to collective behaviours in social bacteria

“…Unlike paradigmatic Che receptors, FrzCD does not assemble as a receptor protein array in the bacterial membrane, but rather uniquely forms signalling complexes by directly associating with the bacterial chromosome [27,32]. This unusual signalling complex-chromosomal association is mediated by a N-terminal DNA-binding domain in FrzCD and direct interaction with the coupling protein FrzB, which organizes potential signalling arrays directly at the surface of the chromosome (figure 3 a ).…”

“…Bearing these limitations in mind, the cognitive features of the Myxococcus sensory apparatus become apparent. First, the FrzCD receptor's dose-dependent response curve to IAA has a sigmoidal shape, suggesting signal amplification [30,32]. Cooperativity depends on the formation of receptor complexes on the nucleoid [32], which suggests that, similar to membrane-bound chemoreceptors, Frz receptor organization promotes signal integration and nonlinear responses to stimulation.…”

“…First, the FrzCD receptor's dose-dependent response curve to IAA has a sigmoidal shape, suggesting signal amplification [30,32]. Cooperativity depends on the formation of receptor complexes on the nucleoid [32], which suggests that, similar to membrane-bound chemoreceptors, Frz receptor organization promotes signal integration and nonlinear responses to stimulation. This property leads to sharp transitions from slow reversals to fast reversals triggered by relatively narrow signal fluctuations.…”

Dynamic polarity control by a tunable protein oscillator in bacteria

“…The molecular signals that activate the Frz pathway remain unidentified which largely complicates this analysis. Remarkably, the Frz receptor-kinase complex is not assembled in the bacterial inner membrane, as most receptors do, but it localizes to the cytoplasm, interacting directly with the nucleoid [45]. The cognate response regulators (FrzX and FrzZ) thus act as diffusible messengers between the bacterial chromosome and the cell poles.…”