title: 26S proteasome structure revealed by three-dimensional electron microscopy.
abstract: In 26S proteasomes, "19S cap complexes" associate with either one or both ends of the barrel-shaped 20S core complex. These regulatory complexes which comprise about 20 different subunits, including 6 ATPases of the AAA family, are thought to recognize ubiquitinated substrate proteins, to dissociate and unfold them before threading them into the 20S core where they are degraded. Here, we examine the structure of 26S proteasomes from Drosophila embryos and Xenopus oocytes by electron microscopy. Image analysis reveals a rather flexible linkage between the 19S caps and the 20S core, with a peculiar wagging-type movement of the caps relative to the core. At this stage of the analysis, it is not clear whether this movement is relevant in terms of function. Three-dimensional reconstructions, taking this into account, provide first insights into the remarkably complex structure of the 19S caps and allows us to put forward a composite model of the entire 26S complex.
authors.affiliation: Department of Structural Biology, Max-Planck-Institut für Biochemie, Martinsried, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Walz
authors.forename: A
authors.initials: A
authors.lastname: Erdmann
authors.forename: M
authors.initials: M
authors.lastname: Kania
authors.forename: D
authors.initials: D
authors.lastname: Typke
authors.forename: A J
authors.initials: AJ
authors.lastname: Koster
authors.forename: W
authors.initials: W
authors.lastname: Baumeister
mesh_terms: D000818:Animals; D004331:Drosophila melanogaster / Q000201:enzymology; D005260:Female; D007091:Image Processing, Computer-Assisted; D046911:Macromolecular Substances; D008854:Microscopy, Electron / Q000379:methods*; D008958:Models, Molecular; D009865:Oocytes / Q000201:enzymology; D010447:Peptide Hydrolases / Q000737:chemistry* / Q000648:ultrastructure*; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D014981:Xenopus
chemical_list: D046911:Macromolecular Substances; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease