Host SNAREs mediate fusion of vacuoles containing Legionella pneumophila with vesicles exiting the endoplasmic reticulum

Abstract

Legionella pneumophila is an intracellular pathogen that initially resides in a plasma membrane‐derived vacuole that fuses with endoplasmic reticulum‐derived vesicles to create a specialized organelle that supports bacterial replication. Host SNARE proteins were examined to determine the mechanism of fusion of this vacuole with early secretory vesicles. Localization studies determined that plasma membrane t‐SNARES are associated with vacuoles containing Legionella shortly after bacterial uptake into mammalian cells. Syntaxin‐2, Syntaxin‐3, Syntaxin‐4, and SNAP23 were all localized to vacuoles containing Legionella. The v‐SNARE Sec22b was rapidly recruited to vacuoles containing Legionella after internalization. Reducing production of Syntaxins by RNAi inhibited the recruitment of Sec22b to vacuoles containing Legionella. Infection by Legionella induced the formation of SNARE complexes containing plasma membrane Syntaxins, SNAP23, and Sec22b. Syntaxin, SNAP23, and Sec22b complexes formed during infection were dissociated upon the addition of NSF/α‐SNAP, indicating that these are functional SNARE complexes. Thus, Legionella has the ability to manipulate the pairing of host SNARE proteins to efficiently promote fusion of a plasma membrane‐derived vacuole with early secretory vesicles. NIH grant R01 AI041699 supported this work.