Paradoxical enhancement of chemoreceptor detection sensitivity by a sensory adaptation enzyme

Abstract

A sensory adaptation system that tunes chemoreceptor sensitivity enables motile Escherichia coli cells to track chemical gradients with high sensitivity over a wide dynamic range. Sensory adaptation involves feedback control of covalent receptor modifications by two enzymes: CheR, a methyltransferase, and CheB, a methylesterase. This study describes a CheR function that opposes the signaling consequences of its catalytic activity. In the presence of CheR, a variety of mutant serine chemoreceptors displayed up to 40-fold enhanced detection sensitivity to chemoeffector stimuli. This response enhancement effect did not require the known catalytic activity of CheR, but did involve a binding interaction between CheR and receptor molecules. Response enhancement was maximal at low CheR:receptor stoichiometry and quantitative analyses argued against a reversible binding interaction that simply shifts the ON-OFF equilibrium of receptor signaling complexes. Rather, a short-lived CheR binding interaction appears to promote a long-lasting change in receptor molecules, either a covalent modification or conformation that enhances their response to attractant ligands.bacterial chemotaxis | receptor methyltransferase | dynamic-bundle model | signaling conformation | nonequilibrium mechanism M otile bacteria, despite their small size and simple cellular architecture, track chemical gradients in their living environments with extraordinary precision (see refs. 1 and 2 for reviews). They do so with only a handful of different proteins organized in a sensory signaling network that has stimulus integration, amplification, and memory capabilities. The extensively studied chemotaxis machinery of Escherichia coli has provided the molecular paradigm for transmembrane and intracellular signaling mechanisms in microbial chemosensory systems. This report describes a long-unrecognized activity of a central component of the E. coli chemotaxis machinery, suggesting that there are important new molecular lessons to learn from this structurally simple, yet functionally sophisticated, signaling system. E. coli senses attractant and repellent chemicals with transmembrane chemoreceptors known as methyl-accepting chemotaxis proteins (MCPs) (3). MCPs form networked arrays of signaling complexes, typically at the cell poles, that produce highly sensitive and cooperative responses to small chemoeffector concentration changes. The four MCPs of E. coli (Tsr, Tar, Tap, and Trg) have a common functional architecture comprising a periplasmic sensing domain and a cytoplasmic signaling domain (Fig. 1). An interposed HAMP domain communicates conformational changes between the sensing and signaling domains through an extended four-helix coiled-coil that contains sites for sensory adaptation adjustments of receptor signal output (4). The chemoreceptors modulate the activity of a histidine autokinase (CheA), which is stably coupled to receptors by a scaffolding protein (CheW). CheA donates its phosphoryl groups to CheY, a response regulator that in its phosphory...

Spatial control of sensory adaptation modulates mechanosensing inPseudomonas aeruginosa

“…We detected two differentially migrating species of PilJ during liquid and surface growth (Suppl Fig 3A). By analogy to the migration of E. coli MCPs in methylation immunoblots 40–45 , the slower migrating band is predicted to represent the unmethylated PilJ state, and the faster migrating band is predicted to represent a methylated form of PilJ (which we validate below). By calculating the fraction of methylated PilJ, we demonstrated that methylated PilJ was significantly increased after 2 h of surface growth compared to liquid growth (p=0.002; Fig 1D), suggesting that PilJ methylation increases in response to mechanical stimuli generated during surface contact.…”

“…In ∆chpB, the faster-migrating 3xFlag-PilJ band was the most abundant species, likely corresponding to methylated PilJ, with a corresponding increase in the fraction of methylated PilJ. Thus, like the migration behavior of E. coli MCPs [40][41][42][43][44][45] , methylated PilJ migrates faster than unmethylated PilJ in this experimental setup.…”

“…The chromosomally integrated 3xFlag-PilJ is functional, as demonstrated by near wild-type (WT) levels of subsurface twitching motility (Suppl Fig 1A) and cAMP production (Suppl Fig 1C). We used a well-established low-bis SDS-PAGE separation protocol to detect and quantify MCP methylation in vivo (hereafter referred to as methylation immunoblots) [40][41][42][43][44][45] . We detected two differentially migrating species of PilJ during liquid and surface growth (Suppl Fig 3A).…”

“…We detected two differentially migrating species of PilJ during liquid and surface growth (Suppl Fig 3A). By analogy to the migration of E. coli MCPs in methylation immunoblots [40][41][42][43][44][45] , the slower migrating band is predicted to represent the unmethylated PilJ state, and the faster migrating band is predicted to Since surface contact promotes cAMP synthesis 26,29 (Fig 1C), and many TFP and Pil-Chp genes are positively regulated by cAMP 38 , we assessed whether the increase in PilJ methylation after surface growth was a secondary consequence of increased cAMP levels. The fraction of methylated PilJ did not significantly change in strains with low cAMP levels (∆cyaB) or with high cAMP levels (∆cpdA; Suppl Fig 3B,C).…”

Mutations in surface‐sensing receptor WspA lock the Wsp signal transduction system into a constitutively active state

“…Much evidence indicates that methylation modulates the packing stability of the cytoplasmic methylation helix (MH) bundles in MCPs (Parkinson, 2010; Lai et al ., 2017). The predicted secondary structure of WspA is shown in Fig.…”