A cAMP-independent carbohydrate-driven mechanism inhibits tnaA expression and TnaA enzyme activity in Escherichia coli
Abstract
WhenEscherichia coliis grown in a medium lacking glucose or another preferred carbohydrate, the concentration of cAMP–cAMP receptor protein (cAMP–CRP) increases, and this latter complex regulates the expression of more than 180 genes. To respond rapidly to changes in carbohydrate availability,E. colimust maintain a suitable intracellular concentration of cAMP by either exporting or degrading excess cAMP. Currently, cAMP export via the TolC protein is thought to be more efficient at reducing these levels than is CpdA-mediated degradation of cAMP. Here, we compared the contributions of TolC and CpdA by measuring the expression of cAMP-regulated genes that encode tryptophanase (TnaA) and β-galactosidase. In the presence of exogenous cAMP, atolCmutant produced intermediate levels of these enzymes, suggesting that cAMP levels were held in check by CpdA. Conversely, acpdAmutant produced much higher amounts of these enzymes, indicating that CpdA was more efficient than TolC at reducing cAMP levels. Surprisingly, expression of thetnaAgene halted rapidly when glucose was added to cells lacking both TolC and CpdA, even though under these conditions cAMP could not be removed by either pathway andtnaAexpression should have remained high. This result suggests the existence of an additional mechanism that eliminates intracellular cAMP or terminates expression of some cAMP–CRP-regulated genes. In addition, adding glucose and other carbohydrates rapidly inhibited the function of pre-formed TnaA, indicating that TnaA is regulated by a previously unknown carbohydrate-dependent post-translational mechanism.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 01, 2014
- Source ID
- 10.1099/mic.0.080705-0
Entities
People
- Gang Li
- Kevin D. Young
Organizations
- Army Research Office
- Federal Government of the United States
- University of Arkansas for Medical Sciences