CatM Regulation of the benABCDE Operon: Functional Divergence of Two LysR-Type Paralogs in Acinetobacter baylyi ADP1

Abstract

Two LysR-type transcriptional regulators, BenM and CatM, control benzoate consumption by the soil bacterium Acinetobacter baylyi ADP1. These homologs play overlapping roles in the expression of multiple genes. This study focuses on the benABCDE operon, which initiates benzoate catabolism. At this locus, BenM and CatM each activate transcription in response to the catabolite cis,cis-muconate. BenM, but not CatM, additionally responds to benzoate as an effector. Regulation by CatM alone is insufficient for growth on benzoate as the sole carbon source. However, three point mutations independently increased CatM-activated benA transcription and enabled growth on benzoate without BenM. Two mutations generate variants with one amino acid change in the 303-residue CatM, CatM(V158M) and CatM(R156H). These substitutions affected regulation of benA differently than that of catB, another CatM-regulated gene involved in benzoate catabolism. In relation to CatM, CatM(V158M) increased cis,cis-muconate-dependent transcription of benA but decreased that of catB. CatM(R156H) increased effector-independent expression of catB compared to CatM. In contrast, cis,cis-muconate was required with CatM(R156H) to activate unusually high benA expression. Thus, induction by cis,cis-muconate depends on both the sequence of CatM and the promoter. A point mutation at position ؊40 of the benA promoter enhanced CatM-activated gene expression and altered regulation by CatM(R156H). BenM and CatM bound to the same locations on ben region DNA. The frequency with which spontaneous mutations allow CatM to substitute for BenM might predict that one regulator would be sufficient for controlling benzoate consumption. This prediction is discussed in light of current and previous studies of the BenM-CatM regulon.

Structure and function of the LysR-type transcriptional regulator (LTTR) family proteins

“…It was later reclassified as a transcriptional activator and found to be part of a more complex regulatory network involving BenM. Both CatM and BenM activate the transcription of catBCIJFD but BenM additionally regulates expression of the benABCDE operon, which encodes proteins necessary for benzoate degradation (Collier et al, 1998;Ezezika et al, 2006Ezezika et al, , 2007. A larger subgroup of LTTRs that are associated with degradation of catechols and chlorinated aromatics has emerged in which CatM and BenM are classified.…”

Biochemical and Genetic Bases of Indole-3-Acetic Acid (Auxin Phytohormone) Degradation by the Plant-Growth-Promoting Rhizobacterium Paraburkholderia phytofirmans PsJN

“…On the other hand, the LTTR family is a well-characterized group of transcriptional regulators, highly conserved and ubiquitous among bacteria (51), which have been involved in control of metabolism, cell division, quorum sensing, virulence, motility, and nitrogen fixation, among others (51)(52)(53)(54). A larger subgroup of LTTRs is associated with degradation of aromatic compounds, in which regulators CatM and BenM of Bz catabolism are quite well studied (55,56). It is reported here that the iacR1 and iacR2 genes are essential for P. phytofirmans IAA catabolism, whereas the lack of the iacS gene decreased catabolism of IAA.…”

The Transcription Factor AlsR Binds and Regulates the Promoter of the alsSD Operon Responsible for Acetoin Formation in Bacillus subtilis

“…This effector binding domain has been well defined for both CatM and BenM, which represent paralogous LTTRs found in Acinetobacter subspecies, activating the transcription of the catBCIJFD genes, encoding the catabolic degradation of catechol. BenM additionally regulates the expression of the benABCDE operon, which encodes proteins necessary for benzoate degradation (3,7,8). BenM has the distinctive feature of activating transcription in response to two effectors, benzoate and cis,cis-muconate (2).…”