Effector-stimulated single molecule protein-DNA
interactions of a quorum sensing system in Sinorhizobium
meliloti
Frank Wilco Bartels 1, Matthew McIntosh 1, Alexander Fuhrmann 1, Christoph Metzendorf 1, Patrik Plattner 1, Norbert Sewald 1, Dario Anselmetti 1, Robert Ros 2* and Anke Becker 1
1 Bielefeld University
2 Bielefeld University, Faculty of Physics
* To whom correspondence should be addressed. E-mail: robert.ros{at}physik.uni-bielefeld.de.
Submitted on January 25, 2006
Revised on May 25, 2006
Accepted on 26 January 2007
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Abstract |
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Intercellular communication by means of small signal molecules coordinates gene expression among bacteria. This population density-dependent regulation is known as quorum sensing (QS). The symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti Rm1021 possesses the Sin QS system based on N-acyl homoserine lactones (AHL) as signal molecules. Here, we demonstrate that the LuxR-type regulator ExpR binds specifically to a target sequence in the sinRI locus in the presence of different AHLs with acyl side chains from 8 to 20 carbons. Dynamic force spectroscopy (DFS) based on the atomic force microscope (AFM) provided detailed information about the molecular mechanism of binding upon activation by six different AHLs. These single molecule experiments revealed that the mean lifetime of the bound protein-DNA complex varies depending on the specific effector molecule. The small differences between individual AHLs also had a pronounced influence on the structure of protein-DNA interaction: The reaction length of dissociation varied from 2.6 to 5.8 Å. In addition, DFS experiments indicate that N-heptanoyl-DL-homoserine lactone binds to ExpR but is not able to stimulate protein-DNA interaction.
Key Words:
atomic force microscopy (AFM), protein-DNA interaction, quorum sensing, single molecule force spectroscopy, transcriptional regulation
