A divergent CheW stabilizes nucleoid-associated chemosensory arrays

Chemosensory systems are highly organized signaling pathways allowing bacteria to adapt to environmental changes. The Frz chemosensory system from M. xanthus possesses, in addition to its core CheW, FrzA, a second CheW homologue, FrzB. We found that this protein does not interact with the cognate CheA, FrzE, as it lacks the amino acid region responsible of this interaction. FrzB, instead, acts upstream of FrzCD in the regulation of M. xanthus chemotaxis behaviors and activates the Frz pathway by allowing the formation and distribution of multiple chemosensory clusters on the nucleoid. These results, together, show that the lack of the CheA-interacting region in FrzB confers new functions to this small protein.