[Editors] EMBARGOED: MIT unravels bacteria communication pathways

[Teresa Herbert]

EMBARGOED for 12 P.M., ET Thursday, JUNE 12, 2008

Contact: Teresa Herbert, MIT News Office -- Phone: 617-258-5403 /  
Email: therbert at mit.edu

Image available upon request

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MIT researchers unravel bacteria communication pathways
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CAMBRIDGE, Mass. -- MIT researchers have figured out how bacteria  
ensure that they respond correctly to hundreds of incoming signals  
from their environment.

The researchers also successfully rewired the cellular communications  
pathways that control those responses, raising the possibility of  
engineering bacteria that can serve as biosensors to detect chemical  
pollutants. The work is reported in the June 13 issue of Cell.

Led by MIT biology professor Michael Laub, the team studied genomes of  
nearly 200 bacteria, which can have hundreds of different pathways  
that respond to different types of external stimuli. Nutrients,  
antibiotics, temperature or light can evoke a variety of responses,  
including transcription of particular genes.

In most cases, the pathways involve two proteins. The first protein,  
an enzyme known as a histidine kinase, receives the external signal  
and then activates the second protein, known as a response regulator.

It’s critical that each histidine kinase activate only the appropriate  
response regulator. Different histidine kinases are often very  
structurally similar, as are the response regulator proteins, so  
scientists have wondered how cells prevent signals from getting crossed.

“If an organism has tons of this class of signaling pathway, why do we  
not get a lot of crosstalk?” said Laub. “How does the kinase pick out  
the right target?”

Based on earlier studies, the MIT researchers theorized that the  
specificity of the interaction is determined by a subset of amino  
acids on the histidine kinase and a corresponding subset of amino  
acids on the response regulator.

To confirm their theory, they looked for patterns of amino acid co- 
evolution in pairs of histidine kinases and their target response  
regulators.

Co-evolution occurs when a mutation in one of the two proteins is  
followed by a secondary mutation in the corresponding amino acid on  
the other protein, allowing the protein pair to maintain their  
interaction.

After searching a vast database of nearly 1,300 protein pairs, they  
identified a small set of co-evolved amino acids. They then confirmed  
that these amino acids govern signaling specificity by successfully  
rewiring five of the pathways by mutating the target amino acids.

Such manipulation could allow scientists to engineer bacteria that  
exhibit novel behavior such as glowing when they detect the presence  
of a pollutant such as toluene, said Laub.

Lead author of the paper is Jeffrey Skerker, a former MIT postdoctoral  
associate now at the Broad Institute. Other MIT authors are Barrett  
Perchuk, technical associate in the Department of Biology, and  
graduate students Emma Lubin and Orr Ashenberg.

The research was funded by the U.S. Department of Energy and the  
National Institutes of Health.

By Anne Trafton, News Office

# # #
Teresa Herbert
Media Specialist
Massachusetts Institute of Technology
News Office, Room 11-400
Cambridge, MA 02139-4307

Phone: 617-258-5403
Fax: 617-258-8762

therbert at mit.edu




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