20S proteasome catalytic subunits beta 1 and beta 2 (PSMB6/PSMB7)

The 20S proteasome is the central catalytic core of the 26S proteasome complex, a multi-subunit enzyme responsible for the degradation of intracellular proteins via the ubiquitin-proteasome pathway [UniProt, P20618]. While the chymotrypsin-like activity of the beta 5 subunit is the primary target of most clinical proteasome inhibitors, the other catalytic sites refer to the beta 1 (caspase-like) and beta 2 (trypsin-like) subunits [PubMed, PMID: 21460835]. These sites contribute significantly to the overall proteolytic capacity of the cell, and their inhibition is often required to achieve maximal anti-tumor activity or to overcome resistance to beta 5-selective agents like carfilzomib. Drugs such as Marizomib are designed as pan-proteasome inhibitors that target all three catalytic sites, leading to a more profound disruption of protein homeostasis [NCI Drug Dictionary]. This disruption triggers the unfolded protein response and programmed cell death, making these sites critical targets in the treatment of hematologic malignancies such as multiple myeloma and mantle cell lymphoma. However, targeting these additional sites can also increase the risk of systemic toxicities and adverse effects compared to more selective inhibitors.

Other names

Caspase-like catalytic siteTrypsin-like catalytic sitePeptidyl-glutamyl peptide-hydrolyzing sitePGPH siteProteasome subunit beta type-6Proteasome subunit beta type-7Beta 1 subunitBeta 2 subunit

Inhibition of the proteolytic activity of the beta 1 (caspase-like) and beta 2 (trypsin-like) subunits within the 20S proteasome core particle, typically through covalent binding to the N-terminal threonine active site, which prevents the degradation of polyubiquitinated proteins and induces cell cycle arrest and apoptosis [PubMed, PMID: 19103606].