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.

A divergent CheW confers plasticity to nucleoid-associated chemosensory arrays

“…Interestingly, the FrzCD receptor does not contain an obvious ligand-binding domain. Instead, it contains an N-terminal region that has been recently shown to be involved in DNA binding [28]. Thus, FrzB could also function to deliver signals to the Frz pathway.…”

“…To verify whether FrzB was part of the Frz clusters, we constructed a mCherry-frzB fusion that replaced frzB at the endogenous locus and encoded a functional protein (S2 and S3 Figs). mCherry-FrzB formed multiple nucleoid-associated clusters that resembled those formed by FrzCD-GFP and FrzE-mCherry ( Fig 4A) [28]. Then, we decided to check how the absence of FrzA and FrzB affected the formation of these complexes.…”

“…It has been previously shown that Frz proteins form nucleoid-associated signaling complexes [27,28]. To verify whether FrzB was part of the Frz clusters, we constructed a mCherry-frzB fusion that replaced frzB at the endogenous locus and encoded a functional protein (S2 and S3 Figs).…”

“…Then, we decided to check how the absence of FrzA and FrzB affected the formation of these complexes. For that, we transferred a frzCD-gfp gene fusion [28] into ΔfrzA and ΔfrzB mutants. M. xanthus cells of the resulting strains were then imaged by fluorescence microscopy.…”

“…This would explain the lack of clusters in a small population of cells. In the wild type, the multiple Frz clusters would be expected to be distributed to both daughter cells [28]. Finally, we wanted to verify if FrzB β4-β5 could mediate FrzCD-GFP cluster formation like FrzA.…”