Redox-modulated bacterial deubiquitinase ElaD: Target recognition and suppression of K63-linked polyubiquitin accumulation in yeast.

Bacterial deubiquitinases (DUBs) are important virulence effectors that manipulate host ubiquitin signaling during infection. ElaD, a CE-clan DUB expressed by enterohemorrhagic Escherichia coli, preferentially cleaves K63-linked ubiquitin chains, yet its effects on conserved cellular stress responses remain poorly understood. We demonstrate that ElaD exhibits redox-dependent DUB activity in vitro. In addition, we identified the molecular basis underlying the selective recognition of substrate proteins, ubiquitin and NEDD8 by ElaD. Structural and mutational analyses reveal that, beyond the conserved catalytic site, ElaD engages ubiquitin through a combination of electrostatic and hydrophobic interactions. Using Saccharomyces cerevisiae as a heterologous model system, we show that wild-type ElaD rescues the proteotoxic stress phenotype of ubp2{Delta} yeast cells, whereas specific ElaD mutants fail to confer a similar response. Furthermore, expression of ElaD suppresses oxidative stress-induced accumulation of K63-linked polyubiquitin and may perturb stress-associated translational regulation linked to K63 ubiquitin signaling. Consequently, cells expressing ElaD exhibit altered stress adaptation and diminished fitness during prolonged oxidative stress. Collectively, these findings indicate that ElaD perturbs ubiquitin-mediated stress signaling by counteracting K63-linked ubiquitination events that support adaptive cellular responses. Our study highlights how a bacterial DUB can reprogram conserved ubiquitin-dependent pathways and exploit host ubiquitin signaling networks to modulate cellular stress responses and protein homeostasis. These findings further suggest potential host targets of bacterial DUBs during infection.