title: Size matters for the tripeptidylpeptidase II complex from Drosophila: The 6-MDa spindle form stabilizes the activated state.
abstract: Tripeptidylpeptidase II (TPP II) is an exopeptidase of the subtilisin type of serine proteases, a key component of the protein degradation cascade in many eukaryotes, which cleaves tripeptides from the N terminus of proteasome-released products. The Drosophila TPP II is a large homooligomeric complex (approximately 6 MDa) that is organized in a unique repetitive structure with two strands each composed of ten stacked homodimers; two strands intertwine to form a spindle-shaped structure. We report a novel procedure of preparing an active, structurally homogeneous TPP II holo-complex overexpressed in Escherichia coli. Assembly studies revealed that the specific activity of TPP II increases with oligomer size, which in turn is strongly concentration-dependent. At a TPP II concentration such as prevailing in Drosophila, equilibration of size and activity proceeds on a time scale of hours and leads to spindle formation at a TPP II concentration of > or =0.03 mg/ml. Before equilibrium is reached, activation lags behind assembly, suggesting that activation occurs in a two-step process consisting of (i) assembly and (ii) a subsequent conformational change leading to a switch from basal to full activity. We propose a model consistent with the hyperbolic increase of activity with oligomer size. Spindle formation by strand pairing causes both significant thermodynamic and kinetic stabilization. The strands inherently heterogeneous in length are thus locked into a discrete oligomeric state. Our data indicate that the unique spindle form of the holo-complex represents an assembly motif stabilizing a highly active state.
authors.affiliation: Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany.
authors.forename: Gönül
authors.initials: G
authors.lastname: Seyit
authors.forename: Beate
authors.initials: B
authors.lastname: Rockel
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Baumeister
authors.forename: Jürgen
authors.initials: J
authors.lastname: Peters
mesh_terms: D000626:Aminopeptidases; D000818:Animals; D003001:Cloning, Molecular; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003720:Densitometry; D019281:Dimerization; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D004305:Dose-Response Relationship, Drug; D004330:Drosophila / Q000201:enzymology*; D004926:Escherichia coli / Q000201:enzymology; D007700:Kinetics; D010447:Peptide Hydrolases / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D012697:Serine Endopeptidases / Q000737:chemistry*; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D003432:Cross-Linking Reagents; D011994:Recombinant Proteins; D010447:Peptide Hydrolases; D000626:Aminopeptidases; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; C048001:tripeptidyl-peptidase 2; D012697:Serine Endopeptidases