Salmonella Translocated Effectors Recruit OSBP1 to the Phagosome to Promote Vacuolar Membrane Integrity

Abstract

Intracellular Salmonella use a type III secretion system (TTSS) to translocate effector proteins across the phagosome membrane to promote vacuole membrane tubulation, resulting in intracellular survival. This work demonstrates that the effector SseJ binds the eukaryotic lipid transporter oxysterol binding protein 1 (OSBP1). SseJ directs OSBP1 to the endosomal compartment in a manner dependent on the TTSS located on Salmonella pathogenicity island 2 (SPI2) and is mediated by both SseJ and another OSBP1-binding SPI2 translocated effector, the deubiquitinase SseL. Only deletion of both SseJ and SseL reduced vacuolar integrity with increased bacteria released into the eukaryotic cytoplasm, indicating that their combined activities are necessary for vacuole membrane stability. Cells deleted for the OSBP1-binding proteins VAPA/B also demonstrate loss of vacuole integrity, consistent with the hypothesis that OSBP1 recruitment is required to provide membrane for a vacuole undergoing endosomal tubulation, cholesterol esterification, and other SPI2-mediated alterations that promote Salmonellae intracellular survival.