Small host GTPases: Direct targets of Vibrio vulnificus MARTX toxin effectors

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Project Summary/Abstract Gastrointestinal and wound infections caused by the Gram-negative bacterium Vibrio vulnificus (Vv) can be exceptionally life-threatening resulting in death in approximately 50% of cases. These infections progress within days and must be identified and treated quickly to decrease mortality and morbidity. While antibiotics are used to treat Vv infections, they are often ineffective as the disease progresses rapidly, especially in immunocompromised individuals. This disease is of particular concern now as the incidence of the disease is increasing due to climate change. The Multifunctional Autoprocessing Repeats in Toxin (MARTX) toxin is a large protein toxin that is secreted by Vv and is essential to cause infections. The MARTX toxin functions to deliver up to five different toxic effectors as a single bolus directly into the eukaryotic host cytoplasm. There are ten known unique effectors, and each is capable of causing cytotoxic effects. Determining the mechanism by which the effectors encoded within the MARTX toxin function will reveal a novel mechanisms related to bacterial toxin function that could impact our understanding of host-microbe interactions across many diverse systems. The Makes Caterpillars Floppy-like (MCF) toxin is the most common Vv MARTX effector. MCF is linked to Golgi dispersion, inhibition of cell proliferation, and apoptosis. In preliminary studies, MCF is observed to be stimulated to autoprocess via binding to ADP-ribosylation factors resulting in its absolute release as an individual effector domain within the host cell and activation. However, how MCF functions within the eukaryotic host once individually released and activated that results in its toxicity is unclear. The goal of this proposal is to investigate the hypothesis that, once activated, MCF moves on to bind and target another class of small GTPases, Rabs, resulting in a disruption of proper cell functions. To test this hypothesis, we will determine: 1) Which subset of Rabs are the target of MCF; 2) How MCF gains access to these Rabs; 3) How this interaction alters proper Rab functioning and localization; 4) The manner in which these two proteins interact; and 5) The function of the different domains of MCF. In addition, these studies will involve training to utilize novel techniques and concepts. The results from this work have the potential to develop into several independent research projects. The proposed fellowship will involve collaborations, which are facilitated and encouraged in the Department of Microbiology-Immunology at Northwestern.