Small RNA‐binding protein RapZ mediates cell envelope precursor sensing and signaling in Escherichia coli

摘要

The ‐binding protein RapZ cooperates with small s ( s) GlmY and GlmZ to regulate the in . Enzyme GlmS synthesizes glucosamine‐6‐phosphate (GlcN6P), initiating cell envelope biosynthesis. GlmZ activates expression by base‐pairing. When GlcN6P is ample, GlmZ is bound by RapZ and degraded through ribonuclease recruitment. Upon GlcN6P depletion, the decoy GlmY accumulates through a previously unknown mechanism and sequesters RapZ, suppressing GlmZ decay. This circuit ensures GlcN6P homeostasis and thereby envelope integrity. In this work, we identify RapZ as GlcN6P receptor. GlcN6P‐free RapZ stimulates phosphorylation of the two‐component system QseE/QseF by interaction, which in turn activates expression. Elevated GlmY levels sequester RapZ into stable complexes, which prevents GlmZ decay, promoting expression. Binding of GlmY also prevents RapZ from activating QseE/QseF, generating a negative feedback loop limiting the response. When GlcN6P is replenished, GlmY is released from RapZ and rapidly degraded. We reveal a multifunctional ‐binding protein that dynamically engages into higher‐order complexes for metabolite signaling.