Summary auto-generated
This study demonstrates that the Cra (catabolite repressor/activator) protein indirectly regulates adenylate cyclase (AC) activity in Escherichia coli by controlling expression of the fructose operon. When cra mutant strains were grown on fructose, they synthesized 10-fold less cAMP than wild-type strains. The researchers found that IIAglc, the glucose-specific phosphotransferase system protein that activates AC when phosphorylated, became largely dephosphorylated in cra mutant strains. This dephosphorylation resulted from increased fructose operon transcription and uptake, as cra mutants showed 2.5-fold higher fructose-1-phosphate kinase activity than wild-type cells. By artificially increasing fructose operon expression using an inducible plasmid, the authors demonstrated that higher fructose metabolism directly reduced AC activity. The mechanism involves competition between the fructose transport protein FruB and the glucose phosphotransferase system for phosphorylated Enzyme I, thereby limiting IIAglc phosphorylation and AC activation. These findings reveal how Cra-mediated transcriptional control of metabolic genes indirectly influences cAMP levels during fructose utilization.
Key findings
- cra mutants grown on fructose produce 10-fold less cAMP than wild-type strains, while cAMP levels are comparable with other carbon sources
- IIAglc remains largely dephosphorylated in fructose-grown cra strains, preventing activation of adenylate cyclase
- cra mutants show 2.5-fold higher fructose-1-phosphate kinase activity due to derepression of the fructose operon
- Increased fructose operon expression directly decreases cAMP levels by competing for the phosphoryl donor needed to phosphorylate IIAglc
- Cra indirectly regulates AC activity without affecting cya or crr gene transcription or IIAglc protein levels
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
In Escherichia coli, expression of certain genes and operons, including the fructose operon, is controlled by Cra, the pleiotropic catabolite repressor/activator protein formerly known as FruR. In this study we have demonstrated that cra mutant strains synthesize 10-fold less cAMP than isogenic wild-type strains, specifically when grown in fructose- containing minimal media. The glucose-specific IIA protein (IIAglc) of the phosphotransferase system, which activates adenylate cyclase when phosphorylated, is largely dephosphorylated in cra but not wild-type strains growing under these conditions. Dephosphorylation of IIAglc in cra strains apparently results from enhanced fructose operon transcription and fructose uptake. These conclusions were supported by showing that fructose-grown cra strains possess 2.5-fold higher fructose-1-phosphate kinase activity than fructose-grown wild-type strains. Moreover, artificially increasing fructose operon expression in cells transporting fructose dramatically decreased the activity of adenylate cyclase. The results establish that Cra indirectly regulates the activity of adenylate cyclase by controlling the expression of the fructose operon in cells growing with fructose as the sole carbon source.