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Bacteria have evolved remarkable strategies to occupy specific niches and evade detection by the host. One mechanism used by many important human and animal pathogens is the versatile type IV secretion system (T4SS). These extraordinary nanomachines are incredibly dynamic, and have the capacity to deliver microbial DNA, protein, and peptidoglycan substrates to target cells. The versatility of T4SS activity contributes to bacterial genome plasticity and survival within distinct host environments. Despite the importance of T4SSs in bacterial pathogenesis and the dissemination of antibiotic resistance determinants, the mechanism by which these translocation machineries deliver cargo across the bacterial envelope is poorly understood.

We have developed chemical scaffolds that prevent translocation of a bacterial oncoprotein and disrupt biogenesis of the T4SS apparatus in the gastric pathogen Helicobacter pylori. In addition to the inhibitory effects observed in H. pylori, these synthetic small molecules can also prevent the dissemination of antibiotic resistance plasmids throughout bacterial populations, and inhibit delivery of harmful DNA to plant cells by the agricultural pathogen Agrobacterium tumefaciens. Our laboratory is using advanced nucleic acid sequencing techniques combined with quantitative mass spectrometry approaches to understand how these molecules perturb the assembly and function of T4SSs. In collaboration with investigators at Umea University (Sweden), we aim to develop and optimize rationally-designed small molecules that target and disarm these important nanomachines in diverse bacterial pathogens.



How do bacteria engineer and erect complex machines on the cell surface? We are interested in understanding the ways in which bacteria sense and dock with target cells to trigger biogenesis of macromolecular complexes and selectively transfer cargo across the host cell membrane. Our laboratory uses genetic and biochemical approaches to understand how components of the T4SS apparatus interact and assemble. In collaboration with investigators at Caltech, we are using electron cryotomography to dissect the architecture of these elaborate machines in vivo. Together, these studies will shed light on how bacteria build the complex T4SS apparatus and orchestrate the transport of molecular substrates across the bacterial envelope. 

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Our laboratory seeks to understand how translocated effector molecules interact with components of the host cell. How do bacteria evade host defenses to remain undetected within protected cellular sites? To address this question, we use in vitro infection models, immunoassays, and biochemical techniques to determine how injected bacterial factors hijack cellular pathways to generate a hospitable environment for invading pathogens. We are particularly interested in defining mechanisms underlying T4SS-mediated pathogenesis, and many projects in the Shaffer Lab focus on understanding the host-pathogen interactions that drive microbial stealth.