Signal Integration by the Two-Component Signal Transduction Response Regulator CpxR

Abstract

The CpxAR two-component signal transduction system in Escherichia coli and other pathogens senses diverse envelope stresses and promotes the transcription of a variety of genes that remedy these stresses. An important member of the CpxAR regulon is cpxP. The CpxA-dependent transcription of cpxP has been linked to stresses such as misfolded proteins and alkaline pH. It also has been proposed that acetyl phosphate, the intermediate of the phosphotransacetylase (Pta)-acetate kinase (AckA) pathway, can activate the transcription of cpxP in a CpxA-independent manner by donating its phosphoryl group to CpxR. We tested this hypothesis by measuring the transcription of cpxP using mutants with mutations in the CpxAR pathway, mutants with mutations in the Pta-AckA pathway, and mutants with a combination of both types of mutations. From this epistasis analysis, we learned that CpxR integrates diverse stimuli. The stimuli that originate in the envelope depend on CpxA, while those associated with growth and central metabolism depend on the Pta-AckA pathway. While CpxR could receive a phosphoryl group from acetyl phosphate, this global signal was not the primary trigger for CpxR activation associated with the Pta-AckA pathway. On the strength of these results, we contend that the interactions between central metabolism and signal transduction can be quite complex and that successful investigations of such interactions must include a complete epistatic analysis.

Inhibition of Acetyl Phosphate-dependent Transcription by an Acetylatable Lysine on RNA Polymerase

“…This inhibition is thought to be accomplished by the removal of phosphoryl groups from phospho-CpxR (Fig. 1B) (7,8), an activity that has been demonstrated in vitro (9,10). In vivo, the existence of this activity is supported by the apparent accumulation of phosphoCpxR by cpxA mutants of Yersinia pseudotuberculosis (11).…”

“…Thus, if glucose-induced cpxP transcription depended strictly on AcP, then an ackA mutant should respond more robustly to glucose than its wild-type (WT) parent, whereas the pta (or pta ackA) mutant should respond more poorly. Although the latter is true (14), the former is not (8); ackA mutants do not elicit the predicted robust response, even though purified CpxR readily autophosphorylates in the presence of AcP (6,11). This puz-zling observation could mean that AcP is not the in vivo phosphoryl donor to CpxR.…”

“…12). One such behavior is the CpxA-independent induction of cpxP transcription that occurs when glucose is added to tryptone-based growth media (8,14,15). If a behavior strictly depends on AcP to donate its phosphoryl group to a response regulator, then an ackA mutant, which accumulates AcP (16), should elicit behavior opposite to that exhibited by a pta mutant, which cannot synthesize AcP (16).…”

A pivotal role for the response regulator DegU in controlling multicellular behaviour

“…Alternatively, phosphorylation of DegU could be mediated via a small molecular phosphate donor such as acetyl phosphate. This is becoming increasingly recognized as a global regulator of gene transcription (Wolfe et al, 2003(Wolfe et al, , 2008. The presence of an 'orphan' response regulator, or sensor kinase that also has phosphatase activity, suggests that acetyl phosphate may play a role in the signal transduction system (Wolfe, 2005).…”

Deletion analysis of RcsC reveals a novel signalling pathway controlling poly-N-acetylglucosamine synthesis and biofilm formation in Escherichia coli

“…cpxR, ompR, phoR, uvrY) from the Keio collection were analysed for biofilm formation (Fredericks et al, 2006;Matsubara & Mizuno, 1999;McCleary & Stock, 1994;Tomenius et al, 2005;Wolfe et al, 2008). Each mutant was transformed with the pMPMABD plasmid, grown in the presence of glucose or L-arabinose and evaluated in the microtitre dish assay.…”