Molecular characterization of the BvgA response regulator of Bordetella holmesii

Summary: The BvgAS system controls the expression of most virulence factors in Bordetella pertussis. Recently, we identified an orthologous system in the related human pathogen Bordetella holmesii. However, while we found that the orthologous histidine kinases BvgS could be functionally exchanged between the two species, the B. holmesii response regulator BvgABH could not substitute for its B. pertussis counterpart in vivo and, accordingly, was not able to bind to B. pertussis virulence promoters in vitro. Here we show that a hybrid response regulator consisting of the B. pertussis derived DNA-binding output domain of BvgABP combined with the B. holmesii receiver domain binds to BvgABP regulated virulence promoters of B. pertussis in vitro and is functional in B. pertussis in vivo. This shows that the inability of BvgABH to complement BvgABP in B. pertussis is due to the small number of sequence variations present in its output domain. However, by mutation analysis we show that four amino acid exchanges present in the helix-turn-helix motif of BvgABH as compared to BvgABP are not the only reason for its inability to substitute for BvgABP but additional mutations present in the output domain must play a role. [Copyright &y& Elsevier]