SdhA blocks disruption of the Legionella-containing vacuole by hijacking the OCRL phosphatase

Abstract

Legionella pneumophila grows intracellularly within a replication vacuole via action of Icm/Dot-secreted proteins. One such protein, SdhA, maintains the integrity of the vacuolar membrane, thereby preventing cytoplasmic degradation of bacteria. We show here that SdhA binds and blocks the action of OCRL (OculoCerebroRenal syndrome of Lowe), an inositol 5-phosphatase pivotal for controlling endosomal dynamics. OCRL depletion resulted in enhanced vacuole integrity and intracellular growth of a sdhA mutant, consistent with OCRL participating in vacuole disruption. Overexpressed SdhA altered OCRL function, enlarging endosomes, driving endosomal accumulation of PI(4,5)P2, and interfering with endosomal trafficking. SdhA interrupted Rab GTPase-OCRL interactions by binding to the OCRL ASH domain, without directly altering OCRL 5-phosphatase activity. The Legionella vacuole encompassing the sdhA mutant accumulated OCRL and endosomal antigen EEA1, consistent with SdhA blocking accumulation of OCRL-containing endosomal vesicles. Therefore, SdhA hijacking of OCRL is associated with blocking trafficking events that disrupt the pathogen vacuole.