AUTOPHOSPHORYLATION AND PHOSPHOTRANSFER IN THE BORDETELLA-PERTUSSIS BVGAS SIGNAL-TRANSDUCTION CASCADE

Expression of adhesins, toxins, and other virulence factors of Bordete lla pertussis is under control of the BvgA and BvgS proteins, members of a bacterial two-component signal transduction family. BvgA bears se quence similarity to regulator components, whereas BvgS shows similari ty to both sensor and regulator components. BvgA and the cytoplasmic p ortion of BvgS ('BvgS) were over''pressed and purified. 'BvgS autophos phorylated with the gamma-phosphate from [gamma-P-32]ATP and phosphory lated BvgA. Kinetic analysis indicated that BvgA receives its phosphat e from 'BvgS. Mutations in the transmitter, receiver, and C-terminal d omains of BvgS were tested for activation of a BvgAS-dependent fhaB=la cZ reporter fusion in vivo and for autophosphorylation and phosphotran sfer to BvgA in vitro. All mutations abolished activation of the fhaB= lacZ fusion. A point mutation in the transmitter (H729Q) prevented aut ophosphorylation of 'BvgS. In contrast to other characterized sensor p roteins, autophosphorylation also required sequences in the 'BvgS rece iver and C-terminal domains. A 'BvgS receiver point mutation (D1023N) had the novel phenotype of being able to autophosphorylate but unable to transfer the phosphate to BvgA. Autophosphorylation activity of the D1023N mutant protein was kinetically and chemically indistinguishabl e from wild-type 'BvgS despite an uncoupling of phosphotransfer from a utophosphorylation. 'BvgS was shown to contain primarily amidyl phosph ate and BvgA an acyl phosphate linkage. We present a model for a phosp horelay controlling virulence gene expression in B. pertussis.