Phosphomimetic Tyrosine Mutations in Spa47 Inhibit Type Three Secretion ATPase Activity and Shigella Virulence Phenotype

is a highly infectious human pathogen responsible for 269 million infections and 200,000 deaths per year. virulence is absolutely reliant on the injection of effector proteins into the host cell cytoplasm via its type three secretion system (T3SS). The protein Spa47 is a T3SS ATPase whose activity is essential for the proper function of the T3SS needle-like apparatus through which effectors are secreted. A phosphoproteomics study recently found several T3SS proteins, including Spa47, to be tyrosine phosphorylated, suggesting a means of regulating Spa47 enzymatic activity, T3SS function, and overall virulence. The work presented here employs phosphomimetic mutations in Spa47 to probe the effects of phosphorylation at these targeted tyrosines through in vitro radiometric ATPase assays and circular dichroism as well as in vivo characterization of T3SS secretion activity, erythrocyte hemolysis, and cellular invasion. Results presented here demonstrate a direct correlation between Spa47 tyrosine phosphorylation state, Spa47 ATPase activity, T3SS function, and virulence. Together, these findings provide a strong foundation that leads the way to uncovering the specific pathway(s) that employ to mitigate wasteful ATP hydrolysis and effector protein secretion when not required as well as T3SS activation in preparation for host infection and immune evasion.