Use of Proteasome Inhibitors to Examine Processing of Antigens for Major Histocompatibility Complex

Proteasomes are multicatalytic proteases present in the nucleus and cytosol of eukaryotic cells. The central catalytic core, the 20S proteasome, consists of four heptameric rings, the central two of which contain the catalytic β-sub- units, members of a new family of threonine (Thr)-proteases. The outer rings, made of α-subunits, bind the regulators that control the substrate specificity of the proteasome. The binding of a 19S regulator to each end of the 20S core creates the 26S proteasome, which degrades ubiquitinated substrates in an adenosine triphosphate-dependent manner (1 ,2 ).