Quantitative real-time PCR analyses showed significantly reduced dsbD expression in all misR/S mutants, which was rescued by genetic complementation.
The direct and specific interaction of MisR with the upstream region of the dsbD promoter was demonstrated by electrophoretic mobility shift assay, and the MisR binding sequences were mapped. Further, the expression of dsbD was found to be induced by dithiothrietol (DTT), through the MisR/S regulatory system. Surprisingly, we revealed that inactivation of dsbD can only be achieved in a strain carrying an ectopically located dsbD, in the dsbA1A2 double mutant or in the dsbA1A2A3 triple mutant, thus DsbD is indispensable for DsbA-catalysed oxidative protein folding in N. meningitidis.
The defects of the meningococcal dsbA1A2 mutant in transformation and resistance to oxidative stress were more severe in the absence of dsbD.