RESUMEN
The BvgAS two-component system regulates virulence gene expression in Bordetella pertussis. Although precise three-dimensional structural information is not available for the response regulator BvgA, its sequence conservation with E. coli NarL and previous studies have indicated that it is composed of 3 domains: an N-terminal domain (NTD) containing the phosphorylation site, a linker, and a DNA-binding C-terminal domain (CTD). Previous work has determined how BvgACTD dimers interact with the promoter (P fhaB ) of fhaB, the gene encoding the virulence adhesin filamentous hemagglutinin. Here we use molecular modeling, FeBABE footprinting, and crosslinking to show that within the transcription complex of phosphorylated BvgA (BvgA â¼ P), B. pertussis RNAP, and P fhaB , the NTDs displace from the CTDs and are positioned at specific locations relative to the three BvgA â¼ P binding sites. Our work identifies a patch of the NTD that faces the DNA and suggests that BvgA â¼ P undergoes a conformational rearrangement that relocates the NTD to allow productive interaction of the CTD with the DNA.