Abstract
Intracellular bacterial pathogens inject effector proteins to hijack host cellular processes and promote their survival and proliferation. To systematically map effector-host protein-protein interactions (PPIs) during infection, we generated a library of 32 Salmonella enterica serovar Typhimurium (STm) strains expressing chromosomally encoded affinity-tagged effectors and quantified PPIs in macrophages and epithelial cells. We identified 446 effector-host PPIs, 25 of which were previously described, and validated 13 by reciprocal co-immunoprecipitation. While effectors converged on the same host cellular processes, most had multiple targets, which often differed between cell types. We demonstrate that SseJ, SseL, and SifA modulate cholesterol accumulation at the Salmonella-containing vacuole (SCV) partially via the cholesterol transporter Niemann-Pick C1 protein. PipB recruits the organelle contact site protein PDZD8 to the SCV, and SteC promotes actin bundling by phosphorylating formin-like proteins. This study provides a method for probing host-pathogen PPIs during infection and a resource for interrogating STm effector mechanisms.
Highlights
To usurp host defenses, intracellular pathogens secrete effector proteins to intercept and modify the host cell, aiming to evade detection by host innate immune receptors and establish a hospitable intracellular niche (Cunha and Zamboni, 2013)
Mapping the host targets of Salmonella effectors during infection We built a library of 32 tagged-effector serovar Typhimurium (STm) 14028s strains, i.e., most known effectors translocated by T3SS1 and T3SS2 (Table S1)
We used immunoprecipitation and antibodies directed against host targets we identified in the original cell line screen and included non-cognate STm effectors of a similar translocation level to evaluate specificity (Figure 4B)
Summary
Intracellular pathogens secrete effector proteins to intercept and modify the host cell, aiming to evade detection by host innate immune receptors and establish a hospitable intracellular niche (Cunha and Zamboni, 2013). The host has mechanisms to overcome such molecular insults. This evolutionary arms race has driven pathogens to develop remarkably diverse arsenals of effector proteins, as in the case of the bacterium Legionella pneumophila, which secretes >300 effectors (Schroeder, 2017). As methods and data analysis advanced, large-scale studies helped to resolve the picture of relevant host-pathogen PPIs. Yet, as methods and data analysis advanced, large-scale studies helped to resolve the picture of relevant host-pathogen PPIs This is the case for HIV, where systematic AP-MS uncovered the strong and relevant PPIs (Ja€ger et al, 2011a) out of more than a thousand PPIs reported from just a handful of viral proteins by targeted approaches (Ja€ger et al, 2011b), thereby fueling new mechanistic insights into HIV biology
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