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Infection and Immunity, February 2005, p. 859-864, Vol. 73, No. 2
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.2.859-864.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

The M Protein Is Dispensable for Maturation of Streptococcal Cysteine Protease SpeB

Björn Zimmerlein,¹ Hae-Sun Park,² Shaoying Li,² Andreas Podbielski,¹ and P. Patrick Cleary^2*

Department of Medical Microbiology and Hospital Hygiene, University Hospital, Rostock, Germany,¹ Department of Microbiology, University of Minnesota Medical School, Minneapolis, Minnesota²

Received 4 June 2004/ Returned for modification 23 September 2004/ Accepted 6 October 2004

The streptococcal pyrogenic exotoxin B (SpeB) is an important virulence factor of group A streptococci (GAS) with cysteine protease activity. Maturation of SpeB to a proteolytically active form was suggested to be dependent on cell-wall-anchored M1 protein, the major surface protein of GAS (M. Collin and A. Olsén, Mol. Microbiol. 36:1306-1318, 2000). Collin and Olsén showed that mutant GAS strains expressing truncated M protein secrete a conformationally different form of unprocessed SpeB with no proteolytic activity. Alternatively, we hypothesized that a truncated M protein may interfere with processing of this secreted protease, and therefore we tested cysteine protease activity in genetically defined mutant strains that express either no M protein or membrane-anchored M protein with an in-frame deletion of the AB repeat region. Measurements of SpeB activity by cleavage of a substrate n-benzoyl-Pro-Phe-Arg-p-nitroanilide hydrochloride showed that the proteolytic activities in culture supernatants of both mutants were similar to those from the wild-type strain. In addition, Western blot analysis of culture supernatants showed that SpeB expression and processing to a mature form was unaffected by either deletion mutation. Therefore, we conclude that M protein is not required for maturation of the streptococcal cysteine protease SpeB.

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* Corresponding author. Mailing address: Department of Microbiology, University of Minnesota Medical School, 1460 Mayo Bldg., MMC196, 420 Delaware St. SE, Minneapolis, MN 55455. Phone: (612) 624-3932. Fax: (612) 626-0623. E-mail: cleary{at}mail.ahc.umn.edu.

Editor: V. J. DiRita

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Infection and Immunity, February 2005, p. 859-864, Vol. 73, No. 2
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.2.859-864.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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