Structure of the Mature Streptococcal Cysteine Protease Exotoxin mSpeB in Its Active Dimeric Form

Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaloes Vej 5, Copenhagen, Denmark.
Journal of Molecular Biology (Impact Factor: 4.33). 09/2009; 393(3):693-703. DOI: 10.1016/j.jmb.2009.08.046
Source: PubMed


Invasive infections of Streptococcus pyogenes are dependent on the cysteine protease streptococcal pyrogenic exotoxin B. Previous structures of the enzyme have not disclosed the proper active-site configuration. Here, the crystal structure of the mature enzyme is presented to 1.55 A, disclosing a homodimer. A serine from one subunit inserts into the active site of the other to donate to the oxyanion hole and coordinates the ligand proximal to the active-site cysteine. Dimerization is unique to the mature form and is clearly a prerequisite for catalysis. The present structure supports a tripartite switch system that is triggered upon dimerization and substrate binding: (1) liberation of the active-site histidine from an inactive configuration, (2) relocation of residues blocking the substrate binding pockets and (3) repositioning of two active-site tryptophans to settle in the active configuration. Based on the present structure, the active site of clan CA cysteine proteases is expanded and a detailed mechanism of the deacylation mechanism is proposed. The results may have applications for the development of protease inhibitors specific to bacterial cysteine proteases.

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    • "Several groups have solved the crystal structure of SpeBz and SpeBm, revealing a papain-like fold despite very low primary sequence similarity. Furthermore, there is evidence that the fl exible carboxy-terminal domain is important for the broad substrate specifi city and the active form of SpeBm is actually a dimer (Kagawa et al. , 2000 ; Olsen et al. , 2009 ; Wang et al. , 2009 ). To protect itself from intracellular SpeB activity, S. pyogenes cotranscribes a cognate inhibitor, Spi, which is a structural homologue to the SpeB propeptide (Kagawa et al. , 2005 ). "
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    ABSTRACT: Group A streptococcus (Streptococcus pyogenes) is an exclusively human pathogen that causes a wide spectrum of diseases ranging from pharyngitis, to impetigo, to toxic shock, to necrotizing fasciitis. The diversity of these disease states necessitates that S. pyogenes possess the ability to modulate both the innate and adaptive immune responses. SpeB, a cysteine proteinase, is the predominant secreted protein from S. pyogenes. Because of its relatively indiscriminant specificity, this enzyme has been shown to degrade the extracellular matrix, cytokines, chemokines, complement components, immunoglobulins, and serum protease inhibitors, to name but a few of the known substrates. Additionally, SpeB regulates other streptococcal proteins by degrading them or releasing them from the bacterial surface. Despite the wealth of literature on putative SpeB functions, there remains much controversy about this enzyme because many of reported activities would produce contradictory physiological results. Here we review all known host and bacterial protein substrates for SpeB, their cleavage sites, and discuss the role of this enzyme in streptococcal pathogenesis based on the current literature.
    Full-text · Article · Dec 2011 · Biological Chemistry
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    • "Several interesting features of the active SpeBm protease were revealed in the crystal structure. SpeBm crystallized as a homodimer (Olsen et al., 2009b). In the dimeric form, S182 undergoes trans-cis isomerization and reaches into the adjacent subunit forming part of the active site. "
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    ABSTRACT: Streptococcal pyrogenic exotoxin B (SpeB) is a protease secreted by group A streptococci and known to degrade a wide range of host and GAS proteins in vitro. Although the role of SpeB in GAS infection is debated, recent evidence has conclusively demonstrated that SpeB is critical for the pathogenesis of severe invasive disease caused by GAS. Genetic inactivation of the speB gene results in significantly decreased virulence in a necrotizing fasciitis model of infection. Production of fully active SpeB by GAS is extremely complex. Following transcription and translation the SpeB protein is secreted as an inactive zymogen, which is autocatalytically processed through a series of intermediates to form an active protease. Each step from transcription to protease activation is tightly controlled and regulated by the bacterial cell reflecting the critical role played by this virulence factor in GAS infection. Here we review the molecular aspects of SpeB production by GAS from transcription to activation and the multiple layers of control involved.
    Preview · Article · Jun 2011 · Molecular Microbiology
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