Abstact

We show that the monomeric form of Shigella IpaH9.8 E3 ligase catalyses the ubiquitination of human U2AF35 in vitro, providing a molecular mechanism for the observed in vivo effect. We further discover that under non-reducing conditions IpaH9.8 undergoes a domain swap driven by the formation of a disulfide bridge involving the catalytic cysteine and that this dimer is unable to catalyse the ubiquitination of U2AF35. The crystal structure of the domain-swapped dimer is presented. The redox inactivation of IpaH9.8 could be a mechanism of regulating the activity of the IpaH9.8 E3 ligase in response to cell damage so that the host cell in which the bacteria resides is maintained in a benign state suitable for bacterial survival.