Characterization of the caspase-3 cleavage motif of the Salmonella Typhimurium effector protein SifA and its role in pathogenesis
Authors
Patel, SamirFaculty Advisor
Dr. Beth A. McCormickAcademic Program
Immunology and MicrobiologyUMass Chan Affiliations
Infectious Diseases and ImmunologyDocument Type
Doctoral DissertationPublication Date
2018-11-16Keywords
SalmonellaType III Secretion System
Effector Proteins
Bacterial Dissemination
Bacterial Infections and Mycoses
Immunology and Infectious Disease
Microbiology
Metadata
Show full item recordAbstract
Salmonella enterica serovar Typhimurium (S. Typhimurium) is a Gram-negative facultative anaerobe that induces severe inflammation resulting in gastroenteritis. In the case of S. Typhimurium infection, induction of an inflammatory response has been linked to its primary virulence mechanism, the type III secretion system (T3SS). The T3SS secretes protein effectors that exploit the host’s cell biology to facilitate bacterial entry and intracellular survival, and to modulate the host immune response. One such effector, SifA, is a bi-functional T3SS effector protein that plays an important role in Salmonella virulence. The N-terminal domain of SifA binds SifA-Kinesin-Interacting-Protein (SKIP), and via an interaction with kinesin, forms tubular membrane extensions called Sif filaments (Sifs) that emanate from the Salmonella Containing Vacuole (SCV). The C-terminal domain of SifA harbors a WxxxE motif that functions to mimic active host cell GTPases. Taken together, SifA functions in inducing endosomal tubulation in order to maintain the integrity of the SCV and promote bacterial dissemination. Since SifA performs multiple, unrelated functions, the objective of this study was to determine how each functional domain of SifA becomes processed. In the present study, we demonstrate that a linker region containing a caspase-3 cleavage motif separates the two functional domains of SifA. To test the hypothesis that processing of SifA by caspase-3 at this particular site is required for function and proper localization of the effector protein domains, we developed two tracking methods to analyze the intracellular localization of SifA. We first adapted a fluorescent tag called phiLOV that allowed for T3SS mediated delivery of SifA and observation of its intracellular colocalization with caspase-3. Additionally, we created a dual-tagging strategy that permitted tracking of each of the SifA functional domains following caspase-3 cleavage to different subcellular locations. The results of this study reveal that caspase-3 cleavage of SifA is required for the proper localization of functional domains and bacterial dissemination. Considering the importance of these events in Salmonella pathogenesis, we conclude that caspase-3 cleavage of effector proteins is a more broadly applicable effector processing mechanism utilized by Salmonella to invade and persist during infection.DOI
10.13028/7M0M-BX53Permanent Link to this Item
http://hdl.handle.net/20.500.14038/31219Rights
Copyright is held by the author, with all rights reserved.ae974a485f413a2113503eed53cd6c53
10.13028/7M0M-BX53