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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)