Significance GabR is a member of the MocR/GabR subfamily of the GntR family of bacterial transcription regulators. It regulates the metabolism of γ-aminobutyric acid, an important nitrogen and carbon source in many bacteria. The crystal structures reported here show that this protein has evolved from the fusion of a type I aminotransferase and a winged helix-turn-helix DNA-binding protein to form a chimeric protein that adopts a dimeric head-to-tail configuration. The pyridoxal 5′-phosphate–binding regulatory domain of GabR is therefore an example of a coenzyme playing a role in transcription regulation rather than in enzymatic catalysis. Our structural and biochemical studies lay the mechanistic foundation for understanding the regulatory functions of the MocR/GabR subfamily of transcription regulators.

No abstract