Characterization of FerC, a MarR-type transcriptional regulator, involved in transcriptional regulation of the ferulate catabolic operon in Sphingobium sp. strain SYK-6

Sphingobium sp. strain SYK-6 is able to degrade various lignin-derived aromatic compounds including ferulate, vanillate, and syringate. In the SYK-6 cells, ferulate is converted to vanillin and acetyl-coenzyme A (acetyl-CoA) through the reactions catalyzed by feruloyl-CoA synthetase and feruloyl-CoA hydratase/lyase encoded by ferA and ferB, respectively. Here, we characterized the transcriptional regulation of ferBA controlled by a MarR-type transcriptional regulator, FerC. The ferC gene is located upstream of ferB. Reverse transcription (RT)-PCR analysis suggested that the ferBA genes form an operon. Quantitative RT-PCR analyses of SYK-6 and its mutant cells revealed that the transcription of the ferBA operon is negatively regulated by FerC, and feruloyl-CoA was identified as an inducer. The transcription start site of ferB was mapped at 30 nucleotides upstream from the ferB initiation codon. Purified His-tagged FerC bound to the ferC-ferB intergenic region. This region contains an inverted repeat sequence, which overlaps with a part of the -10 sequence and the transcriptional start site of ferB. The binding of FerC to the operator sequence was inhibited by the addition of feruloyl-CoA, indicating that FerC interacts with feruloyl-CoA as an effector molecule. Furthermore, hydroxycinnamoyl-CoAs, including p-coumaroyl-CoA, caffeoyl-CoA, and sinapoyl-CoA also acted as effector.