M Protein Is Dispensable for Maturation of Streptococcal Cysteine Protease SpeB

• Published in: Infection and Immunity 2005-02, Vol.73 (2), p.859-864
• Main Authors: Zimmerlein, Björn, Park, Hae-Sun, Li, Shaoying, Podbielski, Andreas, Cleary, P. Patrick
• Format: Article
• Language: English
• Subjects: Antigens, Bacterial - genetics; Antigens, Bacterial - metabolism; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Culture Techniques; Cysteine Endopeptidases - metabolism; Exotoxins - metabolism; Fundamental and applied biological sciences. Psychology; Microbiology; Miscellaneous; Molecular Pathogenesis; Mutation; Streptococcus; Streptococcus pyogenes - genetics; Streptococcus pyogenes - metabolism
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.73.2.859-864.2005

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.