Legionella employs the multimodal ubiquitination of Sec22b to modulate SNARE pairing

<i>Legionella pneumophila</i> establishes its replicative niche through the deployment of multiple effector proteins. During this process, the host v-SNARE Sec22b is recruited from the endoplasmic reticulum to bacterial phagosomes and engages in non-canonical pairings with plasma membrane syntaxins. We previously reported that Sec22b undergoes polyubiquitination at early stages of infection and that the <i>Legionella</i> deubiquitinase LotB cleaves polyubiquitin chains from Sec22b, resulting in Sec22b dissociating from syntaxin 3. The current study investigates the molecular mechanisms underlying Sec22b ubiquitination and its physiological function during <i>L. pneumophila</i> infection. SdeA, a <i>Legionella</i> ubiquitin ligase, is identified as a crucial factor in promoting Sec22b polyubiquitination. SdeA catalyzes the conjugation of phosphoribosyl-linked ubiquitin to serine 137 of Sec22b; subsequently, the canonical ubiquitin system appears to polyubiquitinate Sec22b. Additionally, multimodal ubiquitination of Sec22b facilitates non-canonical SNARE pairing during early infection. This research outlines a bacterial strategy for modulating SNARE protein dynamics via reversible post-translational modifications.