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Journal of Bacteriology, January 2009, p. 375-387, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00578-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Conserved Residues in the HAMP Domain Define a New Family of Proposed Bipartite Energy Taxis Receptors{triangledown}

Kathryn T. Elliott,1,{dagger} Igor B. Zhulin,2,3 Jeanne A. Stuckey,4 and Victor J. DiRita1,5*

Department of Microbiology and Immunology,1 Life Sciences Institute,4 Unit for Lab Animal Medicine, University of Michigan, Ann Arbor, Michigan,5 Department of Microbiology, University of Tennessee, Knoxville,2 Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee3

Received 25 April 2008/ Accepted 14 October 2008

HAMP domains, found in many bacterial signal transduction proteins, generally transmit an intramolecular signal between an extracellular sensory domain and an intracellular signaling domain. Studies of HAMP domains in proteins where both the input and output signals occur intracellularly are limited to those of the Aer energy taxis receptor of Escherichia coli, which has both a HAMP domain and a sensory PAS domain. Campylobacter jejuni has an energy taxis system consisting of the domains of Aer divided between two proteins, CetA (HAMP domain containing) and CetB (PAS domain containing). In this study, we found that the CetA HAMP domain differs significantly from that of Aer in the predicted secondary structure. Using similarity searches, we identified 55 pairs of HAMP/PAS proteins encoded by adjacent genes in a diverse group of microorganisms. We propose that these HAMP/PAS pairs form a new family of bipartite energy taxis receptors. Within these proteins, we identified nine residues in the HAMP domain and proximal signaling domain that are highly conserved, at least three of which are required for CetA function. Additionally, we demonstrated that CetA contributes to the invasion of human epithelial cells by C. jejuni, while CetB does not. This finding supports the hypothesis that members of HAMP/PAS pairs possess the capacity to act independently of each other in cellular traits other than energy taxis.

* Corresponding author. Mailing address: 5641 Medical Science Building II, 1150 West Medical Center Dr., Ann Arbor, MI 48109-5620. Phone: (734) 936-3084. Fax: (734) 936-3235. E-mail: vdirita{at}umich.edu

{triangledown} Published ahead of print on 24 October 2008.

{dagger} Present address: Department of Microbiology, University of Georgia, Athens, GA.

Journal of Bacteriology, January 2009, p. 375-387, Vol. 191, No. 1
0021-9193/09/$08.00+0     doi:10.1128/JB.00578-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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