Download Signal Transduction in Bacterial Chemotaxis

Victor Sourjik
Signal Transduction in Bacterial Chemotaxis
Introduction
Chemotaxis in Escherichia coli is one of the moststudied model systems for signal transduction.
E. coli can respond to a variety of amino acids,
sugars, and dipeptides, as well as pH, temperature, and redox state, by adjusting its swimming
behaviour. The signalling pathway in chemotaxis
is relatively simple (Fig. 1) but noted for its high
sensitivity, integration of multiple stimuli, wide dynamic range, and robustness. Signalling involves
stimulus-dependent autophosphorylation of the
histidine kinase CheA and subsequent phosphorylation of the response regulator CheY. The
pathway also includes CheZ, a phosphatase of
CheY-P, and an adaptation system that consists
of the methyltransferase, CheR, and the methylesterase, CheB.
Our goal is a quantitative description of signal
processing in chemotaxis. We apply several fluorescence microscopy techniques to study dynamics of the pathway in the cell. We also investigate
cross-talk between chemotaxis and other cellular
networks and study effects of the natural cell-tocell variation in protein levels on signal transduction. In collaboration with computer modelling
groups, we integrate our results with available
biochemical data to reproduce pathway behaviour in silico.
Fig. 1: Signal transduction pathway in chemotaxis of E. coli
FRET-based measurement of signal processing
D. Kentner, S. Schulmeister
We developed an assay, based on fluorescence
resonance energy transfer (FRET), to study in
vivo interactions of E. coli chemotaxis proteins
expressed as fusions to cyan fluorescent protein,
CFP, and yellow fluorescent protein, YFP (Fig.
2). So far, we used FRET to probe phosphorylation-dependent interactions of the response
regulator CheY with CheZ, CheA, and the motor
protein FliM. We are now extending these studies
to map all pairwise interactions between chemotaxis proteins. FRET enables us to measure the
amplitudes and kinetics of changes in interaction
upon stimulation and to estimate protein binding
constants in vivo.
We use FRET between CheY and CheZ as a
reporter assay to monitor output of the receptorCheW-CheA sensory complex and to quantify
amplification and integration of different stimuli.
Another part of the project is to analyze the amaz-
Victor Sourjik
[email protected]
1997
PhD (Dr. rer. nat.) at the University of Regensburg
1998-2003 Postdoctoral work at the Department of Molecular and Cellular Biology,
Harvard University, USA
since 2003 Group leader at the ZMBH
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Fig. 2: FRET as a reporter of
pathway activity. Stimulation-induced changes in FRET between
CheY-YFP and CheZ-CFP are
shown on the right.
ing dynamic range of the chemotaxis system - its
ability to respond and perfectly adapt to over five
orders of magnitude of chemoeffector concentrations.
Formation and dynamics of chemoreceptor cluster
S. Röhrig
Sensory complexes are organized in polar receptor clusters that are essential for signal processing and include thousands of proteins (Fig. 3). The
goal of this project is to investigate the assembly
and positioning of the receptor cluster. We use
time-lapse fluorescence microscopy to study the
formation of the new clusters during cell division,
and fluorescence recovery after photobleaching
(FRAP) to measure association dynamics of the
proteins that constitute the sensory complex.
External funding
During a part of the period reported our research
was supported by a project grant (SO 421/3-1)
from the Deutsche Forschungsgemeinschaft.
PUBLICATIONS 2002 - 2004
Sourjik, V. and Berg, H. C. (2002a). Receptor sensitivity in
bacterial chemotaxis. Proc. Natl. Acad. Sci. USA 99, 123127.
Sourjik, V. and Berg, H. C. (2002b). Binding of the Escherichia
coli response regulator CheY to its target measured in vivo
by fluorescence resonance energy transfer. Proc. Natl. Acad.
Sci. USA 99, 12669-12674.
Sourjik, V. and Berg, H. C. (2004). Functional interactions
between receptors in bacterial chemotaxis. Nature 428, 437441.
Liberman, L., Berg, H. C., and Sourjik, V. (2004). Effect of
chemoreceptor modification on assembly and activity of the
receptor-kinase complex in Escherichia coli. J. Bacteriol. 186,
6643-6646.
Sourjik, V. (2004). Receptor clustering and signal processing
in E. coli chemotaxis. Trends Microbiol. 12, 569-576.
THESES
Diploma
Løvdok, Linda (2004): Cell-to-cell variation in gene expression in Escherichia coli and its effect on signal transduction
in chemotaxis.
Contact:
ZMBH, Im Neuenheimer Feld 282
69120 Heidelberg, Germany
Fig. 3: Chemoreceptor clustering in bacteria. Overlay
of receptor clusters (labeled by CheR-YFP; green) and cell
division ring (labeled by FtsZ-CFP; blue) with a bright-field
image of the cell.
Phone:
+49 6221 546858
Fax:
+49 6221 545894
[email protected]
http://www.zmbh.uni-heidelberg.de/Sourjik/default.html
SOURJIK GROUP
Group Leader
Sourjik, Victor, Dr.
PhD Students
Kentner, David, Dipl. Biol.
Röhrig, Sebastian, Dipl. Biol.
Schulmeister, Sonja, Dipl. Biol.*
*only part of the time reported
Diploma Student
Løvdok, Linda*
Techn. Assistants
Müller, Anette*
Schwarz, Gabi
Liberman, Louisa*
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