Mechanisms of Host Cell Modulation By Bacterial Effector Proteins

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In environmental, agricultural and domestic settings, bacteria form symbiotic relationships with plants, animals, and humans. From the perspective of the bacteria, this is often mediated by a specialized class of proteins called effectors, which are secreted from the microbe to interact with proteins in neighbouring organisms and affect their biological function. Bacterial effectors play important ecological roles, such as their contribution to nodule formation in plants. In agricultural and domestic settings, bacterial effectors play intrinsic roles in infection of animals and humans, ultimately contributing to the survival of the bacterium in the host organism. Identifying the host targets of bacterial effectors, and consequently determining their mechanisms of action, has proven to be challenging. Effectors typically function in a dynamic and transient manner against their targets. However, traditional interaction--based approaches to identify the underlying protein--protein interactions require the interaction to maintain intact throughout the lengthy experimental process. We recently adapted a strategy that involves irreversible enzymatic labeling of proximal proteins (BioID) for the study of host--microbe interactions, and performed a systematic analysis in comparison to the traditional interaction--based approach. Our research revealed that BioID represents an exceptional complementary tool for the study of host--microbe interactions, and is capable of identifying new and complex functioning targets. We have established a streamlined approach to study host--microbe interactions that we will extend to the investigation of diverse microbes. Currently, our focus is the environmental pathogen Salmonella enterica serovar Typhimurium, which has a broad host range that includes humans, livestock, rodents, birds and domestic animals. We will use our new approach to perform a complete BioID screen of Salmonella's 64 predicted effectors. A series of downstream strategies will be employed to identify and dissect the molecular mechanisms of the newly identified effector functions. To accomplish these goals, we will use genetic, biochemical, and cell biological approaches. In addition, fluorescence microscopy will allow us to monitor both host and microbe over time. Collectively, this research program will provide new mechanistic insights into our understanding of host--microbe relationships, and provide new tools to study host cell biology. Additionally, this research may uncover new fundamental biological processes that contribute to the host cellular immune response.