*Article* **Engineering CatM, a LysR-Type Transcriptional Regulator, to Respond Synergistically to Two E**ff**ectors**

#### **Melissa P. Tumen-Velasquez 1, Nicole S. Laniohan 1,2, Cory Momany 1,2 and Ellen L. Neidle 1,\***


Received: 29 April 2019; Accepted: 30 May 2019; Published: 31 May 2019

**Abstract:** The simultaneous response of one transcriptional regulator to different effectors remains largely unexplored. Nevertheless, such interactions can substantially impact gene expression by rapidly integrating cellular signals and by expanding the range of transcriptional responses. In this study, similarities between paralogs were exploited to engineer novel responses in CatM, a regulator that controls benzoate degradation in *Acinetobacter baylyi* ADP1. One goal was to improve understanding of how its paralog, BenM, activates transcription in response to two compounds (*cis,cis*-muconate and benzoate) at levels significantly greater than with either alone. Despite the overlapping functions of BenM and CatM, which regulate many of the same *ben* and *cat* genes, CatM normally responds only to *cis,cis*-muconate. Using domain swapping and site-directed amino acid replacements, CatM variants were generated and assessed for the ability to activate transcription. To create a variant that responds synergistically to both effectors required alteration of both the effector-binding region and the DNA-binding domain. These studies help define the interconnected roles of protein domains and extend understanding of LysR-type proteins, the largest family of transcriptional regulators in bacteria. Additionally, renewed interest in the modular functionality of transcription factors stems from their potential use as biosensors.

**Keywords:** LysR; transcription factor; *Acinetobacter*; LTTR; benzoate; muconate; synergism; biosensor
