Abstact

Pathogens have evolved diverse strategies to counteract host immunity. Ubiquitylation of lipopolysaccharide (LPS) on cytosol-invading bacteria by the E3 ligase RNF213 creates 'eat me' signals for antibacterial autophagy, but whether and how cytosol-adapted bacteria avoid LPS ubiquitylation remains poorly understood. Here, we show that the enterobacterium Shigella flexneri actively antagonizes LPS ubiquitylation through IpaH1.4, a secreted effector protein with ubiquitin E3 ligase activity. IpaH1.4 binds to RNF213, ubiquitylates it and targets it for proteasomal degradation, thus counteracting host-protective LPS ubiquitylation. To understand how IpaH1.4 recognizes RNF213, we determined the cryogenic electron microscopy structure of the IpaH1.4-RNF213 complex. The specificity of the interaction is achieved through the leucine-rich repeat of IpaH1.4, which binds the RING domain of RNF213 by hijacking the conserved RING interface required for binding to ubiquitin-charged E2 enzymes. IpaH1.4 also targets other E3 ligases involved in inflammation and immunity through binding to the E2-interacting face of their RING domains, including the E3 ligase LUBAC that is required for the synthesis of M1-linked ubiquitin chains on cytosol-invading bacteria downstream of RNF213. We conclude that IpaH1.4 has evolved to antagonize multiple antibacterial and proinflammatory host E3 ligases.