AccR Is a Master Regulator Involved in Carbon Catabolite Repression of the Anaerobic Catabolism of Aromatic Compounds in Azoarcus sp. CIB

J Andrés Valderrama,Victoria Shingler,Manuel Carmona,Eduardo Díaz

doi:10.1074/jbc.m113.517714

Abstract

Here we characterized the first known transcriptional regulator that accounts for carbon catabolite repression (CCR) control of the anaerobic catabolism of aromatic compounds in bacteria. The AccR response regulator of Azoarcus sp. CIB controls succinate-responsive CCR of the central pathways for the anaerobic catabolism of aromatics by this strain. Phosphorylation of AccR to AccR-P triggers a monomer-to-dimer transition as well as the ability to bind to the target promoter and causes repression both in vivo and in vitro. Substitution of the Asp(60) phosphorylation target residue of the N-terminal receiver motif of AccR to a phosphomimic Glu residue generates a constitutively active derivative that behaves as a superrepressor of the target genes. AccR-P binds in vitro to a conserved inverted repeat (ATGCA-N6-TGCAT) present at two different locations within the PN promoter of the bzd genes for anaerobic benzoate degradation. Because the DNA binding-proficient C-terminal domain of AccR is monomeric, we propose an activation mechanism in which phosphorylation of Asp(60) of AccR alleviates interdomain repression mediated by the N-terminal domain. The presence of AccR-like proteins encoded in the genomes of other β-proteobacteria of the Azoarcus/Thauera group further suggests that AccR constitutes a master regulator that controls anaerobic CCR in these bacteria.

Highlights

Mechanisms underlying carbon catabolite repression (CCR) control of the anaerobic degradation of aromatic compounds have previously remained elusive
In our previous work [20], we found that anaerobic expression of the bzd genes from the PN promoter is subject to CCR control in response to organic acids, such as succinate, malate, and acetate, the mechanism(s) underlying this level of control was not determined
The utilization of preferred carbon sources is controlled by global regulatory mechanisms, termed CCR, which depend on the energy status of the cell

Summary

Background

Mechanisms underlying carbon catabolite repression (CCR) control of the anaerobic degradation of aromatic compounds have previously remained elusive. Elucidating the molecular mechanism(s) underlying CCR is important for both basic understanding of how metabolism is regulated in the environment and for potential biotechnological applications, such as optimizing bioremediation strategies and the design of tailor-made biocatalysts/biosensors [4] This is relevant for aromatic compounds that are difficult to degrade and tend to accumulate in the environment under both aerobic and anaerobic conditions. Activity of the PN promoter strictly requires the AcpR transcriptional activator, an ortholog of the E. coli Fnr global regulator, which drives expression of the bzd catabolic operon in an oxygen-dependent manner [25] In addition to this dual repressor/activator control, the PN promoter is subject to control by the benzoyl-CoA dependent BoxR repressor, a BzdR paralog that regulates the expression of the box genes, indicating the existence of cross-regulation between the aerobic and anaerobic benzoate degradation pathways of Azoarcus sp. Because of the existence of AccR orthologs within the genomes of closely related Azoarcus/Thauera strains, we suggest that AccR is probably the global mediator of CCR control for anaerobic assimilation of aromatic compounds in this group of ␤-proteobacteria

EXPERIMENTAL PROCEDURES

20 This work

RESULTS

DISCUSSION