Legionella Manipulates Non-canonical SNARE Pairing Using a Bacterial Deubiquitinase.

The intracellular bacterial pathogen Legionella pneumophila uses many effector proteins delivered by the bacterial type IV secretion system (T4SS) to hijack the early secretory pathway to establish its replicative niche, known as the Legionella-containing vacuole (LCV). On LCV biogenesis, the endoplasmic reticulum (ER) vesicular soluble N-ethylmaleimide-sensitive factor attachment protein receptors (v-SNARE) Sec22b is recruited to the bacterial phagosome and forms non-canonical pairings with target membrane SNAREs (t-SNAREs) from the plasma membrane. Here, we identify a Legionella deubiquitinase (DUB), LotB, that can modulate the early secretory pathway by interacting with coatomer protein complex I (COPI) vesicles when ectopically expressed. We show that Sec22b is ubiquitinated upon L. pneumophila infection in a T4SS-dependent manner and that, subsequently, LotB deconjugates K63-linked ubiquitins from Sec22b. The DUB activity of LotB stimulates dissociation of the t-SNARE syntaxin 3 (Stx3) from Sec22b, which resides on the LCV. Our study highlights a bacterial strategy manipulating the dynamics of infection-induced SNARE pairing using a bacterial DUB.