Protein SgpR of Pseudomonas putida strain AK5 is a LysR-type regulator of salicylate degradation through gentisate

Abstract

Pseudomonas putida strain AK5 was the first characterized natural strain containing the 'classical' nah1 operon and nahR gene along with genes whose products are responsible for the less explored pathway of salicylate degradation through gentisate (the sgp operon). The sgp operon was found to be preceded by the divergently directed sgpR gene. The amino acid sequence of the sgpR product qualifies it as a LysR-type transcriptional regulator (LTTR) and suggests its potential function as an sgp operon transcriptional regulator. This study focused on verification of SgpR's involvement in regulation of transcription of the operon genes and characterization of its interaction with the sgp promoter. We determined the transcription start for sgpAIKGHB and identified the SgpR binding site. The equilibrium dissociation constant (KD) of the SgpR-DNA complex determined in the presence and absence of the inducer salicylate appeared to be, on the whole, at the lower end of the range for KD values reported for LTTRs. RT-qPCR showed that in the presence of salicylate, efficiency of transcription of the sgpAIKGHB operon increased by three orders of magnitude and reached the highest values so far observed for LTTR-controlled operons, thus holding much promise for further studies of the mechanism of transcriptional regulation that involves SgpR.