Legionella effector RavH is a tandem WH2-like domain-containing PI(3)P-dependent actin nucleator

Legionella pneumophila infects and replicates within protozoa and macrophages in a specialized compartment termed the Legionella-containing vacuole. To establish this niche, the bacterium delivers more than 350 effector proteins through its type IV secretion system to modulate host pathways and prevent phagolysosome fusion. Here, we identify the effector Lpg0733/RavH as a tandem WH2 domain-containing actin nucleator. RavH localizes to endosomal membranes via its N-terminal lipid-binding domain and promotes actin polymerization when expressed in yeast or mammalian cells. We further demonstrate that RavH functions as a membrane-dependent pointed-end actin nucleator, requiring both its lipid-binding domain and multiple C-terminal WH2-like domains to drive robust actin assembly on PI(3)P-containing membranes. Although dispensable for Legionella intracellular replication in Acanthamoeba castellanii amoeba cells, RavH is recruited to the Legionella-containing vacuole during the early stages of infection in macrophages, where it may contribute to vacuole positioning and motility.