Molecular characterization of PrpR, the transcriptional activator of propionate catabolism in Corynebacterium glutamicum.

The 2-methylcitrate cycle is used to metabolize propionate in Corynebacterium glutamicum. The regulator, PrpR (Cg0800), of the prpDBC2 operon was identified and characterized. The regulator has no similarities to the up to now known PrpR regulators from other organisms. Growth of a ΔprpR mutant revealed severe growth deficits and a prolonged lag phase if propionate was present in the medium. Transcriptome analyses demonstrated the inability of the ΔprpR strain to induce the prpDBC2 genes in the presence of propionate indicating that PrpR represents a transcriptional activator. They also provided evidence that PrpR controls only the prpDBC2 operon while transcription of the prpR gene was found to be independent of the used carbon source. GC-MS based metabolic profiling of the wild type and the ΔprpR strain grown with propionate revealed smaller pool sizes of the metabolites of the 2-methylcitrate cycle in the mutant strain. The transcriptional start sites and their putative promoters of the prpDBC2 operon and the prpR gene were identified by RACE-PCR. Analyses of promoter test vector constructs led to the identification of a 121bp operator region upstream of prpDBC2, which is essential for a propionate-induced transcription by PrpR. Finally, EMSA studies revealed that 2-methylcitrate most probably acts as co-activator of PrpR.