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Research

Many medically relevant bacterial pathogens engage their hosts in an intricate biochemical cross-talk. My laboratory is interested in using the tools of biochemistry, structural and cell biology to examine the targeting of host machineries by bacterial virulence factors.

Virulence Factor Delivery into Host Cells

Virulence Factor Delivery into Host CellsBacterial pathogens achieve the internalization of a multitude of virulence factors into eukaryotic cells. Some secrete extracellular toxins which bring about their own entry, usually by hijacking cell surface receptors and endocytic pathways. Others possess specialized secretion and translocation systems to directly inject bacterial proteins into the host cytosol. We are studying both mechanisms, focusing primarily on delivery by the specialized protein Type III secretion system of Gram negative bacterial pathogens, their substrates, and the machinery in the bacterial cell (e.g., chaperones) that allow them to function.

Sample Project 1: Type III Secretion System Chaperones
Sample Project 2: Type III Secretion System Protein InvA
Sample Project 3: “Classical” AB Toxin

Modulation of the Eukaryotic Cytoskeleton

A very common theme in bacterial pathogenesis is that of manipulation of the host cell structure, and in particular, by modulating the eukaryotic cytoskeleton. By altering the structure of cells, bacteria are able to induce their uptake into normally non-phagocytic host cells, or prevent their uptake into professional phagocytes. In some cases, internalized bacteria remodel elements of the actin cytoskeleton and microtubule networks for purposes ranging from the creation and maintenance of a specialized intracellular vacuole to the propulsion within and between cells. In the least sophisticated instances, bacteria can use toxins to irreversibly alter host cytoskeletal structure, often with death of the eukaryotic cell.

Sample Project 1: Actin polymerization by SipA
Sample Project 2: RhoGDI Factor YpkA
Sample Project 3: Inhibition of Actin polymerization by SpvB
Sample Project 4: The CagA Toxin of Helicobacter pylori

Modulation of the Eukaryotic Cell Cycle

Bacteria have been found to both directly and indirectly target the eukaryotic cell cycle, leading to both stimulatory (pro-cell cycle progressing) and inhibitory (cell cycle arrest) effects. The bacterial proteins achieving cell cycle deregulation are termed “cyclomodulins,” and possess fascinating biological activities that are only now just beginning to be elucidated.  Examples we have studied include toxins that are literally “genotoxins” that damage DNA, and cause the cell cycle controls to arrest progression as the damage is repaired, to factors that specifically target regulatory elements central to cell cycle progression.  These effects are thought to aid in bacterial dissemination as well as suppress proliferative-dependent processes in the innate and acquired immune system.

Sample Project 1: The CDT Genotoxin
Sample Project  2: Cycle Inhibiting Factor, Cif

Modulation of Eukaryotic Programmed Cell Death

Bacteria have been found to modulate host programmed cell death pathways through a variety of factors. This has been especially true for bacterial pathogens of plants, as plants utilize a defense mechanism, the Hypersensitive Response, a key component of which is programmed cell death localized to the infection site. Animal pathogens are also known to modulate host programmed cell death for their own benefit, targeting, for example, caspases and the mitochondria.  Understanding how bacteria modulate programmed cell death in eukaryotic cells not only reveals their mechanisms of virulence, but also, in many cases, gives important insight into the host cell death pathways that are of great interest for their relation to human health (e.g., developmental programs and cancer). 

Sample Project : AvrPtoB, a Bacterial RING finger E3 Ligase 

Modulation of Host Ubiquitin Pathways

The ubiquitination of proteins is a central eukaryotic regulatory mechanism controlling multiple biological processes, such as programmed cell death, cell cycle progression, and signal transduction, which, when defective, can lead to cancer and neurodegenerative disorders. The ubiquitination system regulates many biological processes through the covalent conjugation of either a single or multiple subunit(s) of ubiquitin to a target protein. The structural form of the ubiquitin modification can result in distinct functional signals. For example, the conjugation of a single ubiquitin molecule can alter protein trafficking, whereas polyubiquitination of proteins can regulate protein function by both proteasome-dependent and independent mechanisms. Bacterial factors have recently been identified that exploit these pathways, functioning as E3 ubiquitin ligases, possessing sequences conveying differential half-lives in the host, or serving themselves as substrates for monoubiquitination for purposes such as localization within the eukaryotic cell.

Sample Project 1: A Host-like Bacterial Ubiquitin Ligase that Inhibits Programmed Cell Death Defenses
Sample Project 2: A Bacterial Ubiquitin Ligase of Novel Structure
Sample Project 3: A Bacterial Cyclomodulin that Inhibits Host Ubiquitin Ligases

Antibiotic Development

Bacteria have and are constantly evolving and exchanging mechanisms to resist the activity of antibiotics. This has led to a crisis in medical care, in which many pathogens are multi-drug resistant, and the specter is raised of a "post-antibiotic" world. There is a great need for novel pharmacological interventions in bacterial infection, and modern pharmaceutical companies are currently scaling back such efforts or closing them down completely. Academic groups, therefore, have an important role to play in contributing to the next generation of anti-bacterial drugs. We are interested in the possibility of virulence inhibitors serving as therapeutic agents, and are using computational and chemical screening to identify such compounds.

Sample Project 1: Virulence Inhibitors
Sample Project 2: Novel Antibiotic Targets