THE FUNCTIONAL CONSEQUENCES OF TYROSINE RESIDUE MODIFICATIONS ON CEST-CSRA BINDING AND DOWNSTREAM EFFECTOR EXPRESSION

Candidate: Jocelyne Mendez Guzman
Supervisor: Dr. Dustin Little

ABSTRACT

Enteropathogenic E. coli use the type III secretion system to hierarchically inject effectors into host cells to manipulate cellular pathways and promote colonization of host cells. Currently, the precise mechanism behind differential effector secretion remains poorly understood at the molecular level. Here, we characterize the role of tyrosine phosphorylation in modulating effector secretion. Pull-down assays showed that the secretion system chaperone, CesT, requires residue Y152 to bind the regulatory protein CsrA. Through SPR, we found that CsrA binds CesT with varying affinities depending on different CesT phosphosite mutations. To assess which kinase regulates CesT, BY-kinase deletion strains were used to test their effect on NleA_GFP expression. HeLa Cell infections showed that deleting cesT reduces NleA expression and that YjiL is implicated as a putative CesT kinase. These findings highlight the critical role of tyrosine phosphorylation in regulating effector trafficking and suggest a mechanism for temporal control of secretion during infection.