Prokaryotic Signal Transduction

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Prokaryotic Signal Transduction
Michael Caparon
Recommended for Review
Browning, D. F. and S. J. W. Busby. 2004. The
regulation of bacterial transcription
initiation. Nature Rev. Microbiol. 257-65.
Galperin, M. Y. and Gomelsky, M. 2005. Bacterial
signal transduction modules from Genomics to
Biology. ASM News. 71326-333.
Required Reading
Strecker, J. M., B. S. Perchuk, A. Siryaporn, E.
A. Lubin, O. Asenberg, M. Goulian, and M. T.
Laub. 2008. Rewiring the specificity of
two-component signal transduction systems. Cell.
1331043-1054.
Fox, K. A., A. Ramesh, J. E. Stearns, A.
Bourgogne, A. Reyes-Jara, W. C. Winkler, and D.
A. Garsin. 2009. Feb. 25. epub ahead of print.
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Objectives

• Stress application of concepts over details of
  the examples given.
• Understand and recognize the basic paradigms of
  bacterial signal transduction
• When presented with a regulation scenario, be
  able to propose and test a hypothesis to explain
  the mechanism of regulation.

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virulence factors
Host
Pathogenesis
Pathophysiology
Symptomatology
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What is a Virulence Factor?
Operational Definition
the product of a gene, which when mutated
results in a measurable decrease in virulence
Challenge
Determine the molecular basis of how that gene
product interacts with the host to promote
pathogenesis
Objective
How does understanding how bacteria make
decisions help us understand the function of a
virulence factor?
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Common Steps in Pathogenesis
1. Encounter2. Entry3. Spread4.
Multiplication5. Damage6. Outcome
Require adaptation
Aspects of a developmental process?
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IP
Skin (mouse)
Muscle (zebrafish)
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Analysis of regulation 1. in vitro models of
in vivo behavior. 2. The important role of
mutants
Control
pH 7.5
0.15 M NaCl
0.15 M Glucose
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Becauseall actions have consequences
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Prokaryotic Gene Structure
Polycistronic messages
No processing
No splice, no CAP, no polyA tail
Transcription and translation are coupled
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Control activity of regulators in response to an
environmental cue
Signal Transduction
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The Payoff
Bacteria sense simple cues to make sophisticated
decisions about how to regulate expression of
virulence genes
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What does this list tell us about E. colis
lifestyle and the decisions it must make?
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Questions
What regulates these responses?
What is the molecular basis of sensing stress?
What is the molecular basis of discrimination
between related stresses?
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katG catalase
Bla beta lactamase
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Cysteine is a versatile sensor of Redox
Can coordinate metal ions
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Changes in monomers and structure of dimers
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Direct oxidation? What reduces OxyR or once
activated, is it always on?
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Direct oxidation?
Signal pathway a sensor of the GSH pool
Oxidative stress
GR glutathione reductase
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Many genes are unique to each response
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4 Cys metal?
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2Fe-2S
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Levels, is not modified
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SoxR senses oxidation state of coordinated Fe ion
SoxR also binds DNA in Red or Ox forms
(True for most regulators is affinity that is
altered)
Practical application can footprint in absence
of signal
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Bacteria sense the Exterior Environment
Regulate virulence genes
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H
Cat
Sensor most often both kinase and phosphatase
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D
receiver
output
Single flexible linker
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Questions

• Docking?
• Dimerization?
• Specificity?
• Cross-talk?

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M. T. Laub and M. Goulain. 2007. Ann Rev.
Genet. 41121-145
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Strecker et al. 2008. Cell. 1331043-1054.
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A simple example
Osmotic stress
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Balance between Phosphatase and Kinase altered
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A complicated Example
Chemotaxis
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Chemotaxis Issues
10-20 cell lengths per sec
Cells are small Brownian motion a problem
Cells are too small to sense a chemical gradient
Do sense very small differences in concentrations
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Counterclockwise (CCW) default bacteria swim
Clockwise (CW) requires signaling. Bacteria
tumble
Mechanism of signal transduction Sensory
adaptation
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Biased random walk
Key concepts
Direction is random
Duration of movement under control of sensory
adaptation
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Sensory Adaptation
Time, not space
ME occurs at constant rate. It is absence of a
signal from MCP to CheA that removes ME
Default CCW move
key concept
No signal tumble
Signal no tumble
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Bacteria Sense the presence of other bacteria
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Two Teardrops
Two teardrops were floatin down the river One
teardrop says to the other Im from the soft
blue eyes of a woman in love Im a tear of joy
she couldnt carry She was so happy, shed just
gotten married I was on her cheek when she
wiped me away with her glove From the look on
her face I could see that she didnt need
me So, I drifted on down and caught me a ride
to the sea
The other teardrop said Weve a connection Im
a tear of sorrow, born of rejection Im from
the sad brown eyes of her old flame She told
them they would be life-long companions She
left him questions and not any answers I was on
his cheek as he stood there calling her name I
could tell that he had lots of my friends for
company So, I drifted on down, and caught me a
ride to the sea
Oh, the ocean is a little bit bigger tonight Two
more teardrops that somebody cried One of them
happy, One of them bluer than blue The tide goes
out and the tide goes in And someday theyll be
teardrops again Released in a moment of pleasure,
or a moment of pain And, theyll drift on down
and ride to the sea again
Steve Wariner 1999 Capitol Records
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Lessons

• We are not alone
• Decisions have consequences
• Importance of small molecules in signaling
  interactions

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Bacteria sense each other
Community behavior
Cells closely packed (form a community
Intracellular (IBC)
Tissue communities
microcolonies
Other?
Differentiation
structure
biofilm
specialization
Regional and temporal gene expression
Mechanism of control?
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LuxI (traI) is AI synthase
LuxR is sensor and activator
Different species use a different lipid
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Quorum sensing in community behavior?
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Mut AI
WT
Mut
Pseudomonas aeruginosa
LasI LuxI