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Journal of Bacteriology, November 2008, p. 7004-7011, Vol. 190, No. 21
0021-9193/08/$08.00+0     doi:10.1128/JB.00458-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

ESAT-6-Like Protein Secretion in Bacillus anthracis{triangledown} ,{dagger}

Gabriella Garufi, Emily Butler, and Dominique Missiakas*

Department of Microbiology, University of Chicago, 920 East 58th Street, Chicago, Illinois 60637

Received 3 April 2008/ Accepted 12 August 2008

Proteins of the WXG100 family represent the prototypical substrates of bacterial type VII secretion systems that typically encompass 100 residues, lack canonical signal peptides, and form helix-turn-helix hairpin structures with WXG positioned in the turn element. Bacillus anthracis encodes six WXG100 proteins, herein referred to as EsxB, EsxL, EsxP, EsxQ, EsxV, and EsxW. With the exception of EsxB, B. anthracis proteins harbor C-terminal extensions that are appended to canonical WXG domains. When cultured in liquid broth, B. anthracis secretes two substrates, EsxB and EsxW, into the extracellular environment. EsxB is required for the stability and secretion of EsxW; however, EsxW is dispensable for EsxB secretion. In agreement with the hypothesis that EsxB binding to substrates promotes recognition and secretion by the type VII pathway, EsxB is reported to interact with EsxB and EsxW. Unlike deletions in mycobacterial EsxB, deletion of five N- or C-terminal residues does not affect the ability of mutant B. anthracis EsxB to travel the type VII pathway and initiate secretion of EsxW. Translational fusion of ubiquitin to the N or C terminus of EsxB also had no effect, while ubiquitin insertion into the center turn abrogated secretion. Anthrax-infected guinea pigs mounted humoral immune responses to EsxB, EsxP, and EsxW, which suggests that B. anthracis activates the type VII secretion pathway during infection.

* Corresponding author. Mailing address: Department of Microbiology, University of Chicago, 920 East 58th St., Chicago, IL 60637. Phone: (773) 834-8161. Fax: (773) 834-8150. E-mail: dmissiak{at}bsd.uchicago.edu

{triangledown} Published ahead of print on 22 August 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, November 2008, p. 7004-7011, Vol. 190, No. 21
0021-9193/08/$08.00+0     doi:10.1128/JB.00458-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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