Proteasome

Proteasome inhibitors block the 26S proteasome, the protease complex that degrades ubiquitin-tagged proteins. Its 20S core carries caspase-like, trypsin-like and chymotrypsin-like active sites on β subunits with an N-terminal threonine. In 1994, peptide aldehydes including MG-132 were shown to block degradation of most cell proteins. The same inhibitors prevented generation of peptides for major histocompatibility complex (MHC) class I molecules. Lactacystin, a Streptomyces metabolite, modifies the catalytic threonine of specific subunits. Later chemotypes include the boronates bortezomib and ixazomib and the epoxyketones carfilzomib and epoxomicin, which bind irreversibly. ONX-0914 prefers low molecular mass polypeptide 7 (LMP7), a subunit of the immunoproteasome.