26S-Proteasome (26S-PSM)

The 26S proteasome is a biological macromolecule consisting of a variety of different subunits. The complex is ubiquitous in eukaryotic cells, working as natural machinery for degradation of proteins. Regarding the structure as well as the function of the 26S proteasome, the macromolecule can be subdivided into two parts. Four ring-like structures form the 20S proteasome, a cylindrically shaped molecule with a length of 15 nm and a diameter of 11 nm, enclosing three cavities. The central cavity contains the active sites of the proteasome, where peptide chains are cleaved into oligomers. Attached to the 20S core particle are one or two so-called 19S complexes, resulting in a length of 30 nm or 44 nm for the entire particle. It is assumed, that it contains the substrate binding site, recognizing proteins subjected to degradation. Additionally, a protein has to be unfolded prior to cleavage, because only the unfolded peptide chain can enter the reaction compartment of the 20S core.