title: Crystal structure of the 20S proteasome from the archaeon T. acidophilum at 3.4 A resolution.
abstract: The three-dimensional structure of the proteasome from the archaebacterium Thermoplasma acidophilum has been elucidated by x-ray crystallographic analysis by means of isomorphous replacement and cyclic averaging. The atomic model was built and refined to a crystallographic R factor of 22.1 percent. The 673-kilodalton protease complex consists of 14 copies of two different subunits, alpha and beta, forming a barrel-shaped structure of four stacked rings. The two inner rings consist of seven beta subunits each, and the two outer rings consist of seven alpha subunits each. A narrow channel controls access to the three inner compartments. The alpha 7 beta 7 beta 7 alpha 7 subunit assembly has 72-point group symmetry. The structures of the alpha and beta subunits are similar, consisting of a core of two antiparallel beta sheets that is flanked by alpha helices on both sides. The binding of a peptide aldehyde inhibitor marks the active site in the central cavity at the amino termini of the beta subunits and suggests a novel proteolytic mechanism.
authors.affiliation: Max-Planck-Institut für Biochemie, Abteilung für Strukturforschung, Martinsried, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Löwe
authors.forename: D
authors.initials: D
authors.lastname: Stock
authors.forename: B
authors.initials: B
authors.lastname: Jap
authors.forename: P
authors.initials: P
authors.lastname: Zwickl
authors.forename: W
authors.initials: W
authors.lastname: Baumeister
authors.forename: R
authors.initials: R
authors.lastname: Huber
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins; D001665:Binding Sites; D018834:Chaperonin 60 / Q000737:chemistry; D003196:Computer Graphics; D018360:Crystallography, X-Ray; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000378:metabolism; D010450:Endopeptidases / Q000737:chemistry* / Q000378:metabolism; D005583:Fourier Analysis; D006860:Hydrogen Bonding; D007976:Leupeptins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism; D011480:Protease Inhibitors / Q000737:chemistry / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000378:metabolism; D013822:Thermoplasma / Q000201:enzymology*
chemical_list: D019843:Archaeal Proteins; D018834:Chaperonin 60; D007976:Leupeptins; D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D011506:Proteins; C063261:acetylleucyl-leucyl-norleucinal; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C093138:proteasome, Thermoplasma