© STEVE GRAEPEL
The proteasome can be divided into two main components: the core particle, four stacked rings that form the proteasome’s barrel structure, and the regulatory particles that form “lids” on either end of the barrel. At the junction of the lids and bases of the regulatory particles is Rpn10, which binds the polyubiquitins on targeted proteins. Other subunits in the regulatory particle release the ubiquitin and help unfold the proteins. Inside the core particle, the proteolytic β rings, each of which have seven subunits, degrade the protein chain into short peptides of just 3 to 15 amino acids.
Proteasomes cut the carboxyl side of basic, acidic, and bulky hydrophobic amino acids.THE SCIENTIST STAFFIn contrast to cellular proteases, which cleave proteins at specific sequences, the proteasome hydrolyzes targeted proteins at certain types of individual amino acids. Threonine residues in three separate β subunits of the core particle attack the peptide bond of its target amino acid (colored arrows).
• Chymotrypsin-like (blue ...
