Legionella longbeachae effector protein RavZ inhibits autophagy and regulates phagosome ubiquitination during infection

Abstract

Legionellaorganisms are ubiquitous environmental bacteria that are responsible for human Legionnaires’ disease, a fatal form of severe pneumonia. These bacteria replicate intracellularly in a wide spectrum of host cells within a distinct compartment termed theLegionella-containingvacuole (LCV). Effector proteins translocated by the Dot/Icm apparatus extensively modulate host cellular functions to aid in the biogenesis of the LCV and intracellular proliferation. RavZ is anL.pneumophilaeffector that functions as a cysteine protease to hydrolyze lipidated LC3, thereby compromising the host autophagic response to bacterial infection. In this study, we characterized the RavZ (RavZLP) ortholog inL.longbeachae(RavZLLO), the second leading cause ofLegionellainfections in the world. RavZLLOand RavZLPshare approximately 60% sequence identity and a conserved His-Asp-Cys catalytic triad. RavZLLOis recognized by the Dot/Icm systems of bothL.pneumophilaandL.longbeachae. Upon translocation into the host, it suppresses autophagy signaling in cells challenged with both species, indicating the functional redundancy of RavZLLOand RavZLP. Additionally, ectopic expression of RavZLLObut not RavZLPin mammalian cells reduces the levels of cellular polyubiquitinated and polyneddylated proteins. Consistent with this process, RavZLLOregulates the accumulation of polyubiquitinated species on the LCV duringL.longbeachaeinfection.