A tale of two giant proteases.
The 26S proteasome and tripeptidyl peptidase II (TPPII) are two exceptionally large eukaryotic protein complexes involved in intracellular proteolysis, where they exert their function sequentially: the proteasome, a multisubunit complex of 2.5 MDa, acts at the downstream end of the ubiquitin pathway and degrades ubiquitinylated proteins into small oligopeptides. Such oligopeptides are substrates for TPPII, a 6-MDa homooligomer, which releases tripeptides from their free N-terminus. Both 26S and TPPII are very fragile complexes refractory to crystallization and in their fully assembled native form have been visualized only by electron microscopy. Here, we will discuss the structural features of the two complexes and their functional implications.
Rockel
B
B
Department of Molecular Structural Biology, Max-Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany. rockel@biochem.mpg.de
Baumeister
W
W
D000818:Animals; D004789:Enzyme Activation; D006801:Humans; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization
D010447:Peptide Hydrolases