Article

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: 3.96). 09/2009; 393(3):693-703. DOI: 10.1016/j.jmb.2009.08.046
Source: PubMed

ABSTRACT 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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    • "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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