Regulation of dctA and DctA by cAMP-CRP and EIIAGlc at the transcriptional and post-translational levels in E. coli: Consequences for aerobic uptake and metabolism of C4-dicarboxylates

The expression of dctA , encoding the aerobic C 4 -dicarboxylate (C 4 -DC) transporter DctA of Escherichia coli , and its use in the presence of alternative carbon sources was characterized. dctA is regulated by cAMP-CRP and substrates that control cAMP levels, either through the phosphotransferase system (PTS), or through their metabolic link to PEP synthesis. The data indicates that phosphorylation of the regulator EIIA Glc of the glucose-specific PTS represents the mediator for regulation. The dctA promotor region contains a class I CRP-binding site (position -81.5) and a DcuR-binding site (position -105.5). The response regulator DcuR of the C 4 -DC-activated DcuS-DcuR two-component system is known to stimulate expression of dctA , and cAMP-CRP is known to stimulate expression of dcuS-dcuR . Thus, activation of dctA expression by cAMP-CRP and DcuR is organized in a coherent feed-forward loop (FFL) where cAMP-CRP positively regulates the expression of dctA by direct stimulation and by stimulating the expression of dcuR . Stimulation by DcuR is presumed to require DNA bending by cAMP-CRP. In this way, CRP-FFL integrates carbon catabolite control and C 4 -DC-specific regulation. Moreover, EIIA Glc of the glucose-specific PTS strongly interacts with DctA, which could lead to substrate exclusion of C 4 -DCs when preferred carbon substrates such as sugars are present. Since C 4 -DCs are perceived in the periplasmic space by the sensor DcuS, the substrate exclusion is not linked to inducer exclusion, contrasting classical inducer exclusion known for the lactose permease LacY. Thus, aerobic C 4 -DC metabolism is tightly regulated at the transcriptional and post-translational levels, whereas uptake of L-aspartate by DcuA is essentially unaffected. Overall, transcriptional and post-translational regulation of dctA expression and DctA function efficiently fine-tunes C 4 -DC catabolism in response to other preferred carbon sources.