title: In situ structural studies of tripeptidyl peptidase II (TPPII) reveal spatial association with proteasomes.
abstract: Tripeptidyl peptidase II (TPPII) is a eukaryotic protease acting downstream of the 26S proteasome; it removes tripeptides from the degradation products released by the proteasome. Structural studies in vitro have revealed the basic architecture of TPPII, a two-stranded linear polymer that assembles to form a spindle-shaped complex of ∼6 MDa. Dependent on protein concentration, TPPII has a distinct tendency for polymorphism. Therefore, its structure in vivo has remained unclear. To resolve this issue, we have scrutinized cryo-electron tomograms of rat hippocampal neurons for the occurrence and spatial distribution of TPPII by template matching. The quality of the tomograms recorded with the Volta phase plate enabled a detailed structural analysis of TPPII despite its low abundance. Two different assembly states (36-mers and 32-mers) coexist as well as occasional extended forms with longer strands. A distance analysis of the relative locations of TPPII and 26S proteasomes confirmed the visual impression that these two complexes spatially associate in agreement with TPPII's role in postproteasomal degradation.
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Fukuda
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Beck
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Jürgen M
authors.initials: JM
authors.lastname: Plitzko
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany baumeist@biochem.mpg.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Baumeister
mesh_terms: D000626:Aminopeptidases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000626:Aminopeptidases; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; C048001:tripeptidyl-peptidase 2; D012697:Serine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease
keywords: 26S proteasome; Volta phase plate; cryo-electron tomography; primary cultured neuronal cell; subtomogram averaging