title: Rearrangement of the 16S precursor subunits is essential for the formation of the active 20S proteasome.
abstract: Proteasome-dependent proteolysis is essential for a number of key cellular processes and requires a sophisticated biogenesis pathway to function. Here, we have arrested the assembly process in its dynamic progression at the short-lived 16S state. Structural analysis of the 16S proteasome precursor intermediates by electron microscopy, and single particle analysis reveals major conformational changes in the structure of the beta-ring in comparison with one-half of the 20S proteasome. The individual beta-subunits in the 16S precursor complex rotate with respect to their positions in the x-ray crystallographic structure of the fully assembled 20S. This rearrangement results in a movement of the catalytic residue threonine-1 from the protected location in 16S precursor complexes to a more exposed position in the 20S structure. Thereby, our findings provide a molecular explanation for the structural rearrangements necessary for the dimerization of two 16S precursor complexes and the subsequent final maturation to active 20S proteasomes.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Texas-Houston Medical School, Houston, Texas 77030, USA.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Mullapudi
authors.forename: Lee
authors.initials: L
authors.lastname: Pullan
authors.forename: Ozlem T
authors.initials: OT
authors.lastname: Bishop
authors.forename: Hassan
authors.initials: H
authors.lastname: Khalil
authors.forename: James K
authors.initials: JK
authors.lastname: Stoops
authors.forename: Roland
authors.initials: R
authors.lastname: Beckmann
authors.forename: Peter M
authors.initials: PM
authors.lastname: Kloetzel
authors.forename: Elke
authors.initials: E
authors.lastname: Krüger
authors.forename: Pawel A
authors.initials: PA
authors.lastname: Penczek
mesh_terms: D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D003461:Crystallography / Q000379:methods; D019281:Dimerization; D004789:Enzyme Activation; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008956:Models, Chemical; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry; D046988:Proteasome Endopeptidase Complex / Q000138:chemical synthesis* / Q000648:ultrastructure*; D011487:Protein Conformation; D021122:Protein Subunits; D012336:RNA, Ribosomal, 16S / Q000737:chemistry* / Q000648:ultrastructure*; D013329:Structure-Activity Relationship
chemical_list: D046912:Multiprotein Complexes; D021122:Protein Subunits; D012336:RNA, Ribosomal, 16S; D046988:Proteasome Endopeptidase Complex