Proteomic Profiling Reveals RisR as a Novel Regulatory Element in the Virulence Network of Bordetella pertussis

Bordetella pertussis,
the causative
agent of whooping cough, regulates its virulence through the BvgAS
two-component system, which controls the transition between virulent
(Bvg+) and avirulent (Bvg–) phases. In
the virulent phase, virulence-activated genes (vags) are expressed, while in the avirulent phase, these are repressed.
Virulence-repressed genes (vrgs) are induced under
the control of the response regulator RisA. Phosphorylation of RisA
by the nonoperonic kinase RisK is essential for vrgs expression. Adjacent to risK lies risR, a gene encoding a putative response regulator, whose function remained
unexplored. To investigate the RisR’s role in B. pertussis biology, we performed comparative proteomic
analyses between wild-type and an isogenic risR-deficient
strain, grown under both virulent and avirulent conditions. Our data
show that RisR modulates the abundance of proteins encoded by vags and vrgs, suggesting a previously
unrecognized interplay between RisR and the BvgAS–RisAK regulatory
network. Moreover, RisR regulates the abundance of proteins important
for bacterial fitness, including those involved in iron acquisition
and intracellular adaptation. Functional assays further support the
role of RisR in promoting intracellular survival. This study provides
the first proteome-wide characterization of the RisR regulon and identifies
it as a novel regulator of B. pertussis virulence and adaptation.