title: Proteasome from Thermoplasma acidophilum: a threonine protease.
abstract: The catalytic mechanism of the 20S proteasome from the archaebacterium Thermoplasma acidophilum has been analyzed by site-directed mutagenesis of the beta subunit and by inhibitor studies. Deletion of the amino-terminal threonine or its mutation to alanine led to inactivation of the enzyme. Mutation of the residue to serine led to a fully active enzyme, which was over ten times more sensitive to the serine protease inhibitor 3,4-dichloroisocoumarin. In combination with the crystal structure of a proteasome-inhibitor complex, the data show that the nucleophilic attack is mediated by the amino-terminal threonine of processed beta subunits. The conservation pattern of this residue in eukaryotic sequences suggests that at least three of the seven eukaryotic beta-type subunit branches should be proteolytically inactive.
authors.affiliation: Abteilung für Strukturbiologie Max-Planck Institut für Biochemie, Martinsried, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Seemüller
authors.forename: A
authors.initials: A
authors.lastname: Lupas
authors.forename: D
authors.initials: D
authors.lastname: Stock
authors.forename: J
authors.initials: J
authors.lastname: Löwe
authors.forename: R
authors.initials: R
authors.lastname: Huber
authors.forename: W
authors.initials: W
authors.lastname: Baumeister
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins; D001665:Binding Sites; D003374:Coumarins / Q000494:pharmacology; D010450:Endopeptidases / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D049934:Isocoumarins; D008969:Molecular Sequence Data; D016296:Mutagenesis; D017510:Protein Folding; D016415:Sequence Alignment; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013822:Thermoplasma / Q000201:enzymology*
chemical_list: D019843:Archaeal Proteins; D003374:Coumarins; D049934:Isocoumarins; D015842:Serine Proteinase Inhibitors; C046235:3,4-dichloroisocoumarin; D010450:Endopeptidases; C093138:proteasome, Thermoplasma