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OmpR: Outer Membrane Protein Gene Regulator Regulating Xenorhabdus nematophila’s “Appetite for Destruction” MUHS Smart Team: Mohammed Ayesh, Wesley Borden, Alexander Brook, John Day, Mahmoud Elewa, Grant Flesner, Patrick Jordan, Lucas Kuriga, Hector Lopez, Ben Maier, Joseph Radke, Caleb Vogt, Brandon Wolff, and Zeeshan Yacoob Teachers: Keith Klestinski and David Vogt Mentor: Dr. Steven A. Forst, PhD., Department of Molecular Microbiology at the University of Wisconsin-Milwaukee Flagellum Abstract OmpR, a regulator of outer membrane protein genes, is a transcription factor necessary for the nutrition gathering strategy of the bacterium Xenorhabdus nematophila. Bacteria absorb food through membrane pores, which change in size to optimize food intake and to protect themselves from toxins. The bacterium uses pores to absorb food and nutrients. The larger the pores, the more food the bacterium can absorb. However, larger pores also make the bacterium more vulnerable to toxins. X. nematophila has sensor proteins in the inner membrane. When food touches an inner membrane receptor (EnvZ), the receptor transfers phosphate to OmpR forming OmpR-P, which can bind to DNA. When nutrients are abundant, OmpR-P binds to OmpC, a gene promoting formation of a small pore, allowing food uptake yet limiting influx of toxins. When food is scarce, OmpR-P binds OmpF, a gene promoting formation of a large pore, allowing more food intake and growth of a flagellum enabling movement to a nutrient rich location. The OmpR gene is also responsible for production of antibiotic compounds that combat a broad range of microorganisms. X. nematophila often forms a mutualistic relationship with nematodes. The bacterium-nematode pair seek to inhabit and eventually kill certain insects, benefiting from the nutrients provided by the insect’s corpse. Symbiosis in Nature The bacterium Xenorhabdus nematophilia engages in both parasitic and mutualistic relationships. The bacterium is released inside the insect host and produces antibiotics that suppress microbial competition. However, the nematode that also resides in the insect host is immune to the antibiotics. X. nematophila utilizes the OmpR/EnvZ regulatory system to produce toxins that are involved in killing the insect host (pathogenesis). The toxins produced by the bacteria can be employed as natural pesticides to keep crops healthy. Since the toxins are specifically designed to target insects, they can kill pests without harming the plants. DNA binding domain of OmpR showing the central alpha helix (green) containing the amino acids (magenta) that specifically contact DNA The small pore allows less food to diffuse through the cell membrane, but stops toxins from entering the cell. When food is abundant, activated OmpR is more numerous. This lets them bind to the low affinity gene OmpC, which enables small pores to be built. In addition to this, OmpC disables the activation of OmpF, so only one type of pore can be built at a time. When food particles are scarce, OmpR binds to OmpF and launches a two-pronged response. In addition to producing larger pores for increased food intake, OmpR triggers the production of a flagellum. This allows the bacterium to migrate to more fertile terrain. This gene is high affinity, meaning only a few activated OmpR are needed to activate it. When food touches an inner membrane receptor (EnvZ), the receptor transfers phosphate to OmpR forming activated OmpR-P, which can bind to DNA. The amount of food present dictates the response. OmpF OmpC PO43- Photo © 2008 Valdosta State University Nucleoid OmpR OmpR PO43- Primary Citation: Martinez-Hackert E., Stock A.M. The DNA-binding domain of OmpR: Crystal structure of a winged helix transcription factor (1997) Structure, 5 (1), pp. 109-124. PDB File: 1opc.pdb A SMART Team project supported by the National Institutes of Health (NIH) – National Center for Research Resources Science Education Partnership Award (NCRR-SEPA)