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Journal of Bacteriology, December 2006, p. 8244-8251, Vol. 188, No. 23
0021-9193/06/$08.00+0     doi:10.1128/JB.00954-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Crystal Structure and Mechanism of TraM2, a Second Quorum-Sensing Antiactivator of Agrobacterium tumefaciens Strain A6{triangledown}

Guozhou Chen,1 Chao Wang,2 Clay Fuqua,1 Lian-Hui Zhang,2 and Lingling Chen1*

Department of Biology, 915 E. 3rd St., Indiana University, Bloomington, Indiana 47405,1 Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 1386732

Received 30 June 2006/ Accepted 8 September 2006

Quorum sensing is a community behavior that bacteria utilize to coordinate a variety of population density-dependent biological functions. In Agrobacterium tumefaciens, quorum sensing regulates the replication and conjugative transfer of the tumor-inducing (Ti) plasmid from pathogenic strains to nonpathogenic derivatives. Most of the quorum-sensing regulatory proteins are encoded within the Ti plasmid. Among these, TraR is a LuxR-type transcription factor playing a key role as the quorum-sensing signal receptor, and TraM is an antiactivator that antagonizes TraR through the formation of a stable oligomeric complex. Recently, a second TraM homologue called TraM2, not encoded on the Ti plasmid of A. tumefaciens A6, was identified, in addition to a copy on the Ti plasmid. In this report, we have characterized TraM2 and its interaction with TraR and solved its crystal structure to 2.1 Å. Like TraM, TraM2 folds into a helical bundle and exists as homodimer. TraM2 forms a stable complex (Kd = 8.6 nM) with TraR in a 1:1 binding ratio, a weaker affinity than that of TraM for TraR. Structural analysis and biochemical studies suggest that protein stability may account for the difference between TraM2 and TraM in their binding affinities to TraR and provide a structural basis for L54 in promoting structural stability of TraM.

* Corresponding author. Mailing address: Indiana University, Department of Biology, 915 E. 3rd St., Myers Hall 216B, Bloomington, IN 47405. Phone: (812) 855-0491. Fax: (812) 855-6082. E-mail: linchen{at}indiana.edu.

{triangledown} Published ahead of print on 22 September 2006.

Journal of Bacteriology, December 2006, p. 8244-8251, Vol. 188, No. 23
0021-9193/06/$08.00+0     doi:10.1128/JB.00954-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Chen, G., Jeffrey, P. D., Fuqua, C., Shi, Y., Chen, L. (2007). Structural basis for antiactivation in bacterial quorum sensing. Proc. Natl. Acad. Sci. USA 104: 16474-16479 [Abstract] [Full Text]  
  • Qin, Y., Su, S., Farrand, S. K. (2007). Molecular Basis of Transcriptional Antiactivation: TraM DISRUPTS THE TraR-DNA COMPLEX THROUGH STEPWISE INTERACTIONS. J. Biol. Chem. 282: 19979-19991 [Abstract] [Full Text]  


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