title: Structure of the mature Streptococcal cysteine protease exotoxin mSpeB in its active dimeric form.
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.
authors.affiliation: Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Ole Maaloes Vej 5, Copenhagen, Denmark.
authors.forename: Johan G
authors.initials: JG
authors.lastname: Olsen
authors.forename: Robert
authors.initials: R
authors.lastname: Dagil
authors.forename: Louise Meinert
authors.initials: LM
authors.lastname: Niclasen
authors.forename: Ole E
authors.initials: OE
authors.lastname: Sørensen
authors.forename: Birthe B
authors.initials: BB
authors.lastname: Kragelund
mesh_terms: D000215:Acylation; D001426:Bacterial Proteins / Q000737:chemistry*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003546:Cysteine Endopeptidases / Q000737:chemistry*; D005098:Exotoxins / Q000737:chemistry*; D008958:Models, Molecular; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D013297:Streptococcus pyogenes / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D005098:Exotoxins; C027951:erythrogenic toxin; D003546:Cysteine Endopeptidases