Activation of Rho through a cross-link with polyamines catalyzed by Bordetella dermonecrotizing toxin

The small GTPase Rho, which regulates a variety of cell functions, also ser ves as a specific substrate for bacterial toxins. Here we demonstrate that Bordetella dermonecrotizing toxin (DNT) catalyzes cross-linking of Rho with ubiquitous polyamines such as putrescine, spermidine and spermine. Mass sp ectrometric analyses revealed that the cross-link occurred at Gln63, which had been reported to be deamidated by DNT in the absence of polyamines. Rad and Cdc42, other members of the Rho family GTPases, were also polyaminated by DNT. The polyamination, like the deamidation, markedly reduced the GTPa se activity of Rho without affecting its GTP-binding activity, indicating t hat polyaminated Rho behaves as a constitutively active analog. Moreover, p olyamine-linked Rho, even in the GDP-bound form, associated more effectivel y with its effector ROCK than deamidated Rho in the GTP-bound form and, whe n microinjected into cells, induced the anomalous formation of stress fiber s indistinguishable from those seen in DNT-treated cells. The results imply that the polyamine-linked Rho, transducing signals to downstream ROCK in a novel GTP-independent manner; plays an important role in DNT cell toxicity .