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Mol Microbiol. 2008 Oct;70(1):89-99. doi: 10.1111/j.1365-2958.2008.06391.x. Epub 2008 Aug 19.

Structural basis of specific TraD-TraM recognition during F plasmid-mediated bacterial conjugation.

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Departments of Biochemistry, University of Alberta, Edmonton, Alberta, Canada.


F plasmid-mediated bacterial conjugation requires interactions between a relaxosome component, TraM, and the coupling protein TraD, a hexameric ring ATPase that forms the cytoplasmic face of the conjugative pore. Here we present the crystal structure of the C-terminal tail of TraD bound to the TraM tetramerization domain, the first structural evidence of relaxosome-coupling protein interactions. The structure reveals the TraD C-terminal peptide bound to each of four symmetry-related grooves on the surface of the TraM tetramer. Extensive protein-protein interactions were observed between the two proteins. Mutational analysis indicates that these interactions are specific and required for efficient F conjugation in vivo. Our results suggest that specific interactions between the C-terminal tail of TraD and the TraM tetramerization domain might lead to more generalized interactions that stabilize the relaxosome-coupling protein complex in preparation for conjugative DNA transfer.

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