Characterizing L. pneumophila effector protein interactions using GST pull-down assays

Legionella pneumophila, the causative agent of Legionnaire’s disease, is a Gram-negative bacterium that invades and replicates inside alveolar macrophages of humans with compromised immune systems. Legionella is a natural occurring intracellular bacterium found in freshwater amoeba that can be aerosolized and inhaled during human transmission. L. pneumophila uses a type IV secretion system called the Dot/Icm apparatus to release effector proteins into the host cell cytoplasm. Although many effector proteins of Legionella pneumophila have been identified, individual functions of effectors remain largely unknown. Legionella resides in a distinctive compartment called the Legionella-containing vacuole (LCV), characterized by the presence of smooth vesicles and ribosomes derived from the host cell endoplasmic reticulum. Previous experiments involving L. pneumophila effector proteins have suggested a possible interaction between the effector protein SdhB and an endogenous macrophage SNARE protein present during regulation of vesicle trafficking between the ER and the Golgi. The primary aim of my research is to establish binding interactions and effector functions of the Legionella effector proteins SidH, SdhA, and SdhB. Through the use of conventional PCR, gene cloning, and protein expression, the ultimate goal of our research is to identify interactions of L. pneumophila effector proteins with endogenous macrophage proteins playing a role in intracellular transport. GST-SidH/SdhA/SdhB fusion proteins will be utilized in GST-pulldown assays, in which interactions between host cell proteins and SidH paralogs can be observed by Western blot analyses. Binding information will provide insight into the molecular interactions that occur between host and pathogen during Legionella pathogenesis.