Roles of LysP and CadC in mediating the lysine requirement for acid induction of the Escherichia coli cad operon

Abstract

Expression of the Escherichia col cadBA operon, Encoding functions required for the conversion of lysine to cadaverine and for cadaverine excretion, requires at least two extracellular signals: low pH and a high concentration of lysine. To better understand the nature of the lysine-dependent signal, mutants were isolated which expressed a cad4-lacZ transciription fusion in the absence of lysine while retaining pH regulation. The responsible mutation in one of these isolates (EP310) was in cadC, a gene encoding a function necessary for transcriptional activation of cadB4. This mutation (cadC310) is in a part of the gene encoding the periplasmic domain of CadC and results in an Arg-to-Cys chane at position 265, indicating that this part of the protein is involved in responding to the presence of lysine. Three other mutants had mutations mapping in or near lysP (cadR), a gene encoding a lysine transport protein that has previously been shown to regulate cad4 expression. One of these mutations is an insertion in the lysP coding regiw. Thus, in the absence of exogenous lysine, LysP is a negative regulator ofcadB4 expression. Negative regulation b$fysP was further demonstrated by showing that lysP expression from a hi-opy-number plasmid rendered cad4-lacZ uninducible. Expression of cad4-lacZ in a strain carrying the cadC310 allele, however, was not affected by the plasmid-expressed IsP. Cadaverine was shown to inhibit expression of the cad4-lacZ fusion in cadC' cells but not in a cadC310 background.Bacteria respond to changes in external pH by altering their pattern of gene expression as well as other physiological processes (1, 3, 9, 14, 15, 18-20, 28-30, 39, 41). In many cases the responsible pH change does not alter internal pH, suggesting that bacteria possess transmembrane signaling systems which ultimately influence the transcription and translation machineries. Despite the important role that this physicochemical parameter plays in cell physiology, the components and operation of these signaling systems are poorly understood. One of the first observations concerning the alteration of enzymatic functions in bacteria as a consequence of low external pH was of increased levels of amino acid decarboxylases (13). These decarboxylation reactions result in excretion of the decarboxylated amino acid, release of C02, and an increase in external pH. The exact physiological role of each of these reactants and products in growth and survival of the cell at low pH has not been thoroughly examined. An adaptation response occurs when Escherichia coli and Salmonella typhimurium are exposed to moderate acid conditions, which serves to protect them from a more severe drop in external pH (8-12, 33, 36). E. coli mutants defective in lysine decarboxylase carry out a normal adaptation response, suggesting that these systems for responding to low external pH are distinct (35).To better understand how bacteria sense and respond to changes in external pH, we have been studying the genetic elements involved in acid induction of the E. ...

Regulation of Vibrio cholerae Genes Required for Acid Tolerance by a Member of the “ToxR-Like” Family of Transcriptional Regulators

“…Together, these results suggest that our previous demonstration of low-pH induction of cadA transcription (25) occurs at the level of increased bicistronic cadBA and monocistronic cadA mRNA. pH-regulated induction of cadBA in E. coli is completely dependent on CadC in that a cadC null mutant does not express cadBA under any conditions tested (28). Unlike the case for E. coli, though, V. cholerae shows basal-level expression of cadBA transcript at neutral pH.…”

Sequencing, characterization and transcriptional analysis of the histidine decarboxylase operon of Lactobacillus buchneri

“…It can therefore be concluded that in all clusters, the permease and decarboxylase genes are present. Aminoacyl-tRNA synthetase was located in some clusters only (Neely et al, 1994;Lucas et al, 2003;Connil et al, 2002;Fernández et al, 2004).…”

The Escherichia coli ldcC gene encodes another lysine decarboxylase, probably a constitutive enzyme.

“…The cadA gene mapped at 93.7 min is co-transcribed with the preceding cadB gene that encodes a lysine/cadaverine antiporter. The cadA and cadB genes constitute an acidinducible operon under a dual control: a positive regulation by the product of cadC located immediately upstream of cadBA and a negative regulation by the product of cadR (= lysP) located at 46.5 min (Neely et al, 1994). The absence of any homologous sequence between the PcadBA and PldcC promoters suggests that ldcC is under a regulation different from that of cadBA.…”