Molecular control of gene expression byBrucellaBaaR, an IclR-family repressor

Abstract

The Brucella abortus general stress response sigma factor, σE1, directly and indirectly regulates the transcription of dozens of genes that influence stress survival and host infection. Characterizing the functions of σE1 regulated genes therefore contributes to understanding of B. abortus physiology and infection biology. Transcription of the IclR family regulator, Bab2_0215, is indirectly activated by σE1 but its function remains undefined. We present a structural and functional characterization of Bab2_0215, which we have named Brucellaadipic acid activated regulator (BaaR). BaaR adopts a classic IclR-family fold and directly regulates the transcription of two operons with predicted roles in carboxylic acid oxidation. BaaR binds two sites on chromosome II between baaR and a divergently transcribed hydratase/dehydrogenase (acaD2), and represses transcription. We identified three carboxylic acids (adipic acid tetradecanedioic acid, ε-aminocaproic acid) and a lactone (ε-caprolactone) that enhance transcription from the baaR and acaD2 promoters. However, neither the activating acids nor caprolactone enhance transcription by binding directly to BaaR. Induction of baaR transcription by adipic acid requires the gene bab2_0213, which encodes a major facilitator superfamily transporter, suggesting that Bab2_0213 transports adipic acid across the inner membrane. We conclude that a set of structurally related organic molecules activate transcription of genes repressed by BaaR. Our study provides molecular-level understanding of a gene expression program regulated downstream of σE1.

The Phospholipid N-Methyltransferase and Phosphatidylcholine Synthase Pathways and the ChoXWV Choline Uptake System Involved in Phosphatidylcholine Synthesis Are Widely Conserved in Most, but Not All Brucella Species

“…Sequencing of the choX1 and choX2 orthologs showed that all the above-summarized characteristics of B. suis bv2 Thomsen were reproduced in Bs2WT. In contrast with ChoX1 and ChoX2, the BSUIS_A0222 encoded protein does not show any of the relevant features described in ChoX of S. meliloti and A. tumefaciens, in accordance with the results presented by Herrou et al (2017) describing the B. abortus BSUIS_A0222 ortholog.…”

“…Similarly, the ChoX1 homolog in B. abortus shows dissociation constants of 7 ± 2 nM for choline and 350 ± 30 µM for betaine, and no specific L-carnitine or L-proline binding (Herrmann et al, 2013). While these types of experiments have not been conducted with B. abortus ChoX2, ligand binding assays performed with B. abortus YehZ (the protein encoded by the homolog of BSUIS_A0222) showed no interaction with glycine betaine, choline, ectoine, or carnitine at low ligand concentration, and only low affinity for glycine betaine (Herrou et al, 2017).…”