Regulation of Aerobic Succinate Transporter dctA of E. coli by cAMP-CRP, DcuS-DcuR, and EIIA[sup.Glc]: Succinate as a Carbon Substrate and Signaling Molecule

• Published in: Microbial Physiology Vol. 34; no. 1; p. 108
• Main Authors: Schubert, Christopher, Unden, Gottfried
• Format: Journal Article
• Language: English
• Published: S. Karger AG 01.01.2024
• Subjects: Cyclic adenylic acid; Dextrose; Escherichia coli; Glucose; Lactose; Physiological aspects
• ISSN: 2673-1665
• DOI: 10.1159/000538095

Introduction: C4-dicarboxylates (C4-DC) have emerged as significant growth substrates and signaling molecules for various Enterobacteriaceae during their colonization of mammalian hosts. Particularly noteworthy is the essential role of fumarate respiration during colonization of pathogenic bacteria. To investigate the regulation of aerobic C4-DC metabolism, the study explored the transcriptional control of the main aerobic C4-DC transporter, dctA, under different carbohydrate conditions. In addition, mutants related to carbon catabolite repression (CCR) and C4-DC regulation (DcuS-DcuR) were examined to better understand the regulatory integration of aerobic C4-DC metabolism into CCR. For initial insight into posttranslational regulation, the interaction between the aerobic C4-DC transporter DctA and EIIA[sup.Glc] from the glucose-specific phosphotransferase system was investigated. Methods: The expression of dctA was characterized in the presence of various carbohydrates and regulatory mutants affecting CCR. This was accomplished by fusing the dctA promoter (P[sub.dctA]) to the lacZ reporter gene. Additionally, the interaction between DctA and EIIA[sup.Glc] of the glucose-specific phosphotransferase system was examined in vivo using a bacterial two-hybrid system. Results: The dctA promoter region contains a class I cAMP-CRP-binding site at position 81.5 and a DcuR-binding site at position 105.5. DcuR, the response regulator of the C4-DC-activated DcuS-DcuR two-component system, and cAMP-CRP stimulate dctA expression. The expression of dctA is subject to the influence of various carbohydrates via cAMP-CRP, which differently modulate cAMP levels. Here we show that EIIA[sup.Glc] of the glucose-specific phosphotransferase system strongly interacts with DctA, potentially resulting in the exclusion of C4-DCs when preferred carbon substrates, such as sugars, are present. In contrast to the classical inducer exclusion known for lactose permease LacY, inhibition of C4-DC uptake into the cytoplasm affects only its role as a substrate, but not as an inducer since DcuS detects C4-DCs in the periplasmic space ("substrate exclusion"). The work shows an interplay between cAMP-CRP and the DcuS-DcuR regulatory system for the regulation of dctA at both transcriptional and posttranslational levels. Conclusion: The study highlights a hierarchical interplay between global (cAMP-CRP) and specific (DcuS-DcuR) regulation of dctA at the transcriptional and posttranslational levels. The integration of global and specific transcriptional regulation of dctA, along with the influence of EIIA[sup.Glc] on DctA, fine-tunes C4-DC catabolism in response to the availability of other preferred carbon sources. It attributes DctA a central role in the control of aerobic C4-DC catabolism and suggests a new role to EIIA[sup.Glc] on transporters (control of substrate uptake by substrate exclusion). Keywords: Carbon catabolite repression, Aerobic C4-dicarboxylate metabolism, Succinate, Hierarchical carbon utilization, C4-dicarboxylate transporter DctA, Escherichia coli