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Infection and Immunity, October 2006, p. 5595-5601, Vol. 74, No. 10
0019-9567/06/$08.00+0     doi:10.1128/IAI.00135-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The C-Terminal Region of Bacteroides fragilis Toxin Is Essential to Its Biological Activity

Cynthia L. Sears,1,2 Simy L. Buckwold,1 Jai W. Shin,1 and Augusto A. Franco1*

Divisions of Infectious Diseases,1 Gastroenterology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 212052

Received 26 January 2006/ Returned for modification 20 February 2006/ Accepted 26 June 2006

To evaluate the role of the C-terminal region in Bacteroides fragilis toxin (BFT) activity, processing, and secretion, sequential C-terminal truncation and point mutations were created by site-directed mutagenesis. Determination of BFT activity on HT29/C1 cells, cleavage of E-cadherin, and the capacity to induce interleukin-8 secretion by wild-type BFT and C-terminal deletion mutants showed that deletion of only 2 amino acid residues at the C terminus significantly reduced BFT biological activity and deletion of eight or more amino acid residues obliterated BFT biologic activity. Western blot and reverse transcription-PCR analyses indicated that BFT mutants lacking seven or fewer amino acid residues in the C-terminal region are processed and expressed similar to wild-type BFT. However, BFT mutants lacking eight or more amino acids at the C terminus are expressed similar to wild-type BFT but are unstable. We concluded that the C terminus of BFT is not tolerant of modest amino acid deletions, suggesting that it is biologically important for BFT activity.

* Corresponding author. Mailing address: Division of Infectious Diseases, Johns Hopkins University School of Medicine, Cancer Research Building II, 1550 Orleans Street, Loading Dock, Room 1M04, Baltimore, MD 21205. Phone: (410) 502-8240. Fax: (410) 502-5741. E-mail: afranco{at}jhem.jhmi.edu.

Editor: W. A. Petri, Jr.

Infection and Immunity, October 2006, p. 5595-5601, Vol. 74, No. 10
0019-9567/06/$08.00+0     doi:10.1128/IAI.00135-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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