Richard C. Stewart
Ph.D., University of Michigan, 1984
Telephone: (301) 405-5475
Research Interests: Signal transduction in microorganisms.
Teaching Interests: Microbial physiology; Microbialgenetics; Introductory microbiology
Microbes live life on the edge: they have little or no ability to change their
environments, and they face fierce competition for limited resources.
So it is not surprising that microorganisms are jam-packed with
fascinating sensory-response systems that enable them to respond
quickly and appropriately when their environments change.
For example, many bacteria can control their swimming movements
in ways that lead them toward more favorable environments: toward
food sources; toward surfaces amebable for colonization; away
from harmful chemicals. Controlling cell movements in response
to gradients of chemicals is called chemotaxis, and in my laboratory
we are investigating how a small set of signal-transducing proteins
(CheA, CheW, CheY, CheZ, CheR, CheB, and receptors) interact to
allow E. coli to respond, with exquisite sensitivity, to
gradients of amino acids, sugars, and oxygen. The responses
mediated by the chemotaxis system are not simple 'knee-jerk' responses,
but rather involve the cell making comparisons of the current environment
to the environment it experienced a few seconds ago.
This is a remarkably sophisticated abilitiy for a 'simple bacterium',
especially when you realize that it makes these comparisons on a
very rapid (sub-second) time scale! Our long term goal is
to understand, at a molecular level, how the combined activities
of the Che proteins generate this sophisticated regulation of swimming
behavior. Current research activities in my laboratory focus
on defining how the activity of the protein kinase (CheA) in this
system is controlled by the cell-surface receptors responsible for
detecting local amino acid and sugar concentrations.
Selected Recent Publications:
Stewart, R.C. and VanBruggen, R. 2004. Association and dissociation kinetics for
CheY interacting with the P2 domain of CheA. J. Molecular Biology
Boukhvalova, M.S., Dahlquist, F.W., and Stewart, R.C. 2002. CheW
binding interactions with CheA and Tar: Importance for chemotaxis
signaling in Escherichia coli. J. Biological Chemistry
Boukhvalova, M.S., VanBruggen, R., and Stewart, R.C. 2002. CheA
kinase and chemoreceptor interaction surfaces on CheW. J. Biological
Chemistry 277, 23596-23603.
Hirschman, A., Boukhvalova, M.S., VanBruggen, R., Wolfe, A.J.,
and Stewart, R.C. 2001. Active site mutations in CheA, the signal-transducing
protein kinase of the chemotaxis system in Escherichia coli.
Biochemistry 40, 13876-13887.