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Journal of Bacteriology, February 2007, p. 706-716, Vol. 189, No. 3
0021-9193/07/$08.00+0     doi:10.1128/JB.01334-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The Inner Cavity of Escherichia coli DegP Protein Is Not Essential for Molecular Chaperone and Proteolytic Activity{triangledown}

Ahmad Jomaa,1 Daniela Damjanovic,1 Vivian Leong,1 Rodolfo Ghirlando,2 Jack Iwanczyk,1 and Joaquin Ortega1*

Department of Biochemistry and Biomedical Sciences, McMaster University, 1200 Main Street West, Hamilton, Ontario L8N 3Z5, Canada,1 Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-05402

Received 22 August 2006/ Accepted 13 November 2006

The Escherichia coli DegP protein is an essential periplasmic protein for bacterial survival at high temperatures. DegP has the unusual property of working as a chaperone below 28°C, but efficiently degrading unfolded proteins above 28°C. Monomeric DegP contains a protease domain and two PDZ domains. It oligomerizes into a hexameric cage through the staggered association of trimers. The active sites are located in a central cavity that is only accessible laterally, and the 12 PDZ domains act as mobile sidewalls that mediate opening and closing of the gates. As access to the active sites is restricted, DegP is an example of a self-compartmentalized protease. To determine the essential elements of DegP that maintain the integrity of the hexameric cage, we constructed several deletion mutants of DegP that formed trimers rather than hexamers. We found that residues 39 to 78 within the LA loops, as well as the PDZ2 domains are essential for the integrity of the DegP hexamer. In addition, we asked whether an enclosed cavity or cage of specific dimensions is required for the protease and chaperone activities in DegP. Both activities were maintained in the trimeric DegP mutants without an enclosed cavity and in deletion DegP mutants with significantly reduced dimensions of the cage. We conclude that the functional unit for the protease and chaperone activities of DegP is a trimer and that neither a cavity of specific dimensions nor the presence of an enclosed cavity appears to be essential for the protease and chaperone activities of DegP.

* Corresponding author. Mailing address: Department of Biochemistry and Biomedical Sciences, Health Sciences Centre, Room 4H24, McMaster University, 1200 Main Street West, Hamilton, Ontario L8N 3Z5, Canada. Phone: 905-525-9140, ext. 22703. Fax: 905-522-9033. E-mail: ortegaj{at}mcmaster.ca.

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

Journal of Bacteriology, February 2007, p. 706-716, Vol. 189, No. 3
0021-9193/07/$08.00+0     doi:10.1128/JB.01334-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Ortega, J., Iwanczyk, J., Jomaa, A. (2009). Escherichia coli DegP: a Structure-Driven Functional Model. J. Bacteriol. 191: 4705-4713 [Full Text]  
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