Thesis

Identification of Legionella pneumophila effector proteins that interact with human endocytic rabs

Legionella pneumophila are intracellular bacteria that cause pneumonia by infecting alveolar macrophages. Normally, bacteria internalized by macrophages travel down the endocytic pathway to the lysosome where they are degraded. The endocytic pathway is regulated by Rab GTPases that facilitate movement of vesicles. Legionella escape degradation in the lysosome by secreting effector proteins into host cells. Several effector proteins have been shown to interact with host GTPases ofthe exocytic pathway, Rabl and Arfl. This project has identified for the first time an interaction between a Legionella pneumophila effector protein and a human endocytic Rab protein using a yeast two-hybrid screen. Rab4a, Rab5aQ79L and Rab22a proteins have been used as bait in the 2-hybrid screen. Sequences containing Legionella genes have been sequenced from the positives ofthe yeast two-hybrid screen. Seven positives have been screened for Rab4a; ten for Rab5aQ79L and twelve positives were screened for Rab22a. Two Legionella proteins that bind to Rab4a have been identified. The identified protein, Lpg2229, is annotated as a saframycin MXl synthetase B and Lpg2336 as a peptide chain release factor-1. Four proteins that bound to Rab5aQ79L were identified. These proteins include LegC7, a Legionella effector protein that is thought to affect endocytic transport. Other proteins binding to Rab5aQ79L include a sensory box protein Lpgll68, a transposase Lpg2120 and an unknown protein Lpg2576. Finally, a protein of unknown function, Lpg1644, was found to interact with Rab22a. The data obtained in this thesis may aid in identifying the molecular mechanism by which Legionella avoids destruction in host cells.

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