The Staphostatin-staphopain complex: a forward binding inhibitor in complex with its target cysteine protease

• Published in: The Journal of biological chemistry Vol. 278; no. 42; pp. 40959 - 40966
• Main Authors: Filipek, Renata, Rzychon, Malgorzata, Oleksy, Aneta, Gruca, Milosz, Dubin, Adam, Potempa, Jan, Bochtler, Matthias
• Format: Journal Article
• Language: English
• Published: United States 17.10.2003
• Subjects: Bacterial Proteins; Carrier Proteins - chemistry; Carrier Proteins - pharmacology; Cysteine Endopeptidases - chemistry; Cysteine Endopeptidases - pharmacology; Dose-Response Relationship, Drug; Escherichia coli - metabolism; Humans; Intracellular Signaling Peptides and Proteins; Kinetics; Models, Molecular; Mutation; Peptides - chemistry; Protein Binding; Protein Conformation; Protein Structure, Secondary; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; staphopain; staphostatin; Staphylococcus aureus; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M302926200

Staphostatins are the endogenous inhibitors of the major secreted cysteine proteases of Staphylococcus aureus, the staphopains. Our recent crystal structure of staphostatin B has shown that this inhibitor forms a mixed, eight-stranded beta-barrel with statistically significant similarity to lipocalins, but not to cystatins. We now present the 1.8-A crystal structure of staphostatin B in complex with an inactive mutant of its target protease. The complex is held together through extensive interactions and buries a total surface area of 2300 A2. Unexpectedly for a cysteine protease inhibitor, staphostatin B binds to staphopain B in an almost substrate-like manner. The inhibitor polypeptide chain runs through the protease active site cleft in the forward direction, with residues IG-TS in P2 to P2' positions. Both in the free and complexed forms, the P1 glycine residue of the inhibitor is in a main chain conformation only accessible to glycines. Mutations in this residue lead to a loss of affinity of the inhibitor for protease and convert the inhibitor into a substrate.