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RESEARCH INTERESTS
Bioenergetics; mechanism of flagellar rotation; transmembrane proton conduction
Molecular mechanism of bacterial motility
Biological energy conversions at membranes
Structure-function of membrane proteins
PUBLICATIONS
Many species of bacteria swim by means of flagella, thin
helical propellers driven by rotary motors in the cell
membrane. The flagellar rotary motors can turn at speeds as
high as 1,000 revolutions per second, obtaining the energy
for rotation from the membrane proton gradient (or the
sodium-ion gradient in some species). In most species the
motors can turn either clockwise or counterclockwise. By
controlling the direction of motor rotation in response to
environmental cues (esp. chemicals and temperature), cells
can move toward environments that favor their survival. Our
goal is to understand the structure and molecular mechanism
of the flagellar motor.
About 50 proteins are needed for the assembly and operation
of the flagellar motor. Genetic studies have shown that
only three of these- FliG, MotA, and MotB-are directly
involved in torque generation. MotA and MotB are integral
membrane proteins that function as a proton channel and that
form the stator, or nonrotating part, of the motor. FliG
is a component of the rotor. Mutational studies have
identified the functionally important amino-acid residues of
FliG, MotA, and MotB. These include charged residues of
FliG and MotA that interact at the rotor-stator interface,
proline residues of MotAthat are hypothesized to function in
regulating conformational changes, and an aspartic acid
residue of MotB that functions in proton transfer.
Recently, in collaboration with the Hill group in the
Biochemistry Dept., we have determined the structure of the
part of FliG that contains the key charged residues.
Together, the structure and the mutational studies suggest
a model for the orientation of FliG subunits within the
flagellum, and thus a structural model for the part of the
rotor that interacts with the stator (see Figure).
Future studies will continue to utilize a combination of
biochemical, physiological, biophysical, and genetic
approaches. Specific goals include detailed physiological
studies to determine the precise role of each residue
involved in torque generation; further structural studies
of the key proteins and protein domains; and EM studies
to determine the location of each protein within the motor.
These studies should provide the experimental information
needed to ground a detailed, chemically explicit hypothesis
for torque generation by the flagellar motor.
Our studies of the flagellar motor are motivated by
curiosity regarding a fundamental biochemical process--the
conversion of one form of energy into another. Most
biological energy conversion involves the movement of
protons, so lessons learned from the flagellar motor are
of general interest. Studies of bacterial motility may have
medical applications as well, because motility is known to
play a role in infection by several bacterial pathogens, and
the flagellum is closely related to a large, multi-subunit
apparatus that functions in the secretion of virulence
factors in many pathogenic species.
Selected Publications
Lloyd, S.A., F.G. Whitby, D.F. Blair and C.P. Hill. 1999.
Structure of the C-terminal domain of FliG, a component of
the rotor in the bacterial flagellar motor. Nature
400:472-75.
Braun, T.F., S. Poulson, J.B. Gully, C.C. Empey, S. Van Way,
A. Putnam and D.F. Blair. 1999. Function of proline
residues of MotA in torque generation by the flagellar
motor of Escherichia coli. J. Bacteriol.181:3542-51.
Mathews, M.A.A., H.L. Tang and D.F. Blair. 1998. Domain
analysis of the FliM protein of Escherichia coli.
J. Bacteriol. 180:5580-90.
Zhou, J., S.A. Lloyd and D.F. Blair. 1998. Electrostatic
interactions between rotor and stator in the bacterial
flagellar motor. Proc. Natl. Acad. Sci.
USA 95:6436-6441.
Zhou, J., L. Sharp, H. Tang, S.A. Lloyd, S. Billings, T.F.
Braun and D.F. Blair. 1998. Function of protonatable
residues in the flagellar motor of Escherichia coli:
A critical role for Asp 32 of MotB. J. Bacteriol.
180:2729-2735.
Zhou, J. and D.F. Blair. 1997. Residues of the cytoplasmic
domain of MotA essential for torque generation in the
flagellar motor. J. Mol. Biol.
273:428-439.
Lloyd, S.A. and D.F. Blair. 1997. Charged residues of the
rotor protein FliG essential for torque generation in the
flagellar motor of Escherichia coli. J. Mol. Biol.
266:733-744.
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