Caspase-3 cleavage of Salmonella type III secreted effector protein SifA is required for localization of functional domains and bacterial dissemination

Patel, S., Wall, D. M. , Castillo, A. and McCormick, B. A. (2019) Caspase-3 cleavage of Salmonella type III secreted effector protein SifA is required for localization of functional domains and bacterial dissemination. Gut Microbes, 10(2), pp. 172-187. (doi: 10.1080/19490976.2018.1506668) (PMID:30727836) (PMCID:PMC6546311)

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SifA is a bi-functional Type III Secretion System (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. Our work demonstrates 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 type-III secretion system (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.

Item Type:Articles
Additional Information:This work was supported by National Institutes of Health Grants R01DK056754 and R01DK109677 to B.A. McCormick.
Glasgow Author(s) Enlighten ID:Wall, Dr Daniel
Authors: Patel, S., Wall, D. M., Castillo, A., and McCormick, B. A.
College/School:College of Medical Veterinary and Life Sciences > School of Infection & Immunity
Journal Name:Gut Microbes
Publisher:Taylor and Francis
ISSN (Online):1949-0984
Published Online:06 February 2019
Copyright Holders:Copyright © 2019 The Authors
First Published:First published in Gut Microbes 10(2):172-187
Publisher Policy:Reproduced under a Creative Commons License

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