ER remodeling by the large GTPase atlastin promotes vacuolar growth of .

The pathogenic bacterium replicates in host cells within a distinct ER-associated compartment termed the -containing vacuole (LCV). How the dynamic ER network contributes to pathogen proliferation within the nascent LCV remains elusive. A proteomic analysis of purified LCVs identified the ER tubule-resident large GTPase atlastin3 (Atl3, yeast Sey1p) and the reticulon protein Rtn4 as conserved LCV host components. Here, we report that Sey1/Atl3 and Rtn4 localize to early LCVs and are critical for pathogen vacuole formation. Sey1 overproduction promotes intracellular growth of , whereas a catalytically inactive, dominant-negative GTPase mutant protein, or Atl3 depletion, restricts pathogen replication and impairs LCV maturation. Sey1 is not required for initial recruitment of ER to PtdIns(4)-positive LCVs but for subsequent pathogen vacuole expansion. GTP (but not GDP) catalyzes the Sey1-dependent aggregation of purified, ER-positive LCVs Thus, Sey1/Atl3-dependent ER remodeling contributes to LCV maturation and intracellular replication of .