UBC Theses and Dissertations
Proteomic analysis of Salmonella-host interactions reveals novel host targets of SopB Rogers, Lindsay Deborah
Salmonella enterica is an intracellular bacterium causing gastroenteritis and typhoid fever. Virulence is achieved by two type III secretion systems (T3SS) encoded on Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) that translocate effector proteins into host cells where they mimic or block host protein function. Effectors translocated by T3SS-1 facilitate internalization of the bacteria into the Salmonella-containing vacuole (SCV), actively stimulate intracellular signaling cascades, and regulate trafficking of the SCV to avoid degradation. A T3SS-1 effector, SopB has been shown to regulate a vast array of host processes important for pathogenesis, but only a few host proteins have been identified as targets of this effector. Here quantitative mass spectrometry-based proteomics and bioinformatics techniques have been employed to identify novel host targets of SopB. Quantitative immunoprecipitation experiments identified Cell division control protein 42 (Cdc42) as a direct SopB binding partner, and the binding site within SopB was localized to residues 117-168. SopB and active Cdc42 were shown to colocalize at membrane ruffles on the host cell surface, and two SopB monoubiquitylation sites were identified. To globally analyze host protein phosphorylation events regulated by SopB, a phosphoproteomics method employing heat and chaotropic denaturation for phosphatase inactivation, peptide fractionation by in-solution isoelectric focusing, and phosphopeptide enrichment by metal oxide chromatography was developed. Quantitative analysis of host protein phosphorylation during the initial 20 minutes post Salmonella infection identified >9000 phosphorylation sites, >2000 of which were dynamic. Signaling cascades downstream of T3SS-1 were compared to those induced by growth factor simulation, revealing stark differences between these signaling mechanisms. Kinase prediction upstream of dynamic phosphosites revealed protein kinases B and C as master host regulators during Salmonella infection, and phosphorylation dynamics following wild type versus ΔsopB infection were compared to identify novel host targets of SopB. This work has greatly improved our understanding of SopB’s activity within host cells. It has also provided the first global view of host protein phosphorylation dynamics during bacterial infection, and developed several techniques that can be widely applied within the field of pathogen-host interactions.
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