Crystal Structure of the 20S Proteasome from the Archaeon T. acidophilum at 3.4 Å 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, α and β, forming a barrel-shaped structure of four stacked rings. The two inner rings consist of seven β subunits each, and the two outer rings consist of seven α subunits each. A narrow channel controls access to the three inner compartments. The α_7β_7β_7α_7 subunit assembly has 72-point group symmetry. The structures of the α and β subunits are similar, consisting of a core of two antiparallel β sheets that is flanked by α 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 β subunits and suggests a novel proteolytic mechanism.
- Publication:
-
Science
- Pub Date:
- April 1995
- DOI:
- 10.1126/science.7725097
- Bibcode:
- 1995Sci...268..533L