A Legionella pneumophila T4SS effector protein (Ravl) triggers mitochondrial fragmentation through phosphoinositide...

Upon ingestion by macrophages, Legionella pneumophila hijacks host membrane trafficking by decorating Legionella-containing vacuoles (LCV), thereby escaping lysosomal degradation. L. pneumophila is dependent on the T4SS effector proteins to recruit mitochondria or promote mitochondria association with the LCV, which induces mitochondrial fragmentation and ultimately alters mitochondrial metabolism. However, a T4SS effector protein implicated in mitochondrial recruitment and fragmentation has yet to be identified. Here, we report the crystal structure of RavL, a L. pneumophila T4SS effector protein. The RavL N-terminus has a canonical mitochondrial targeting sequence. We show that RavL localizes to the mitochondrial membrane and induces fragmentation to disrupt mitochondrial function, ultimately triggering apoptosis in THP-1 macrophages. Further biochemical analysis reveals that RavL is a phosphatidylinositol polyphosphate 5-phosphatase that specifically hydrolyzes the D5 phosphate of PtdIns(4)P, which is derived from PtdIns(4,5)P₂. Taken together, our study has identified a novel atypical phosphoinositide phosphatase, RavL, which actively exploits phosphoinositide metabolism to disturb mitochondrial function, thereby promoting bacterial infection.