Proteasome subunit beta type-5 and Proteasome subunit beta type-1 (PSMB5/PSMB1)

The 20S proteasome is the catalytic core of the 26S proteasome complex, a multi-subunit enzyme essential for maintaining cellular protein homeostasis through the ubiquitin-proteasome pathway (UniProt P28074, P20618). It contains several catalytic subunits, with the β5 (PSMB5) and β1 (PSMB1) subunits providing chymotrypsin-like and caspase-like proteolytic activities, respectively (PubMed: 16169925). These subunits are responsible for the degradation of regulatory proteins that control the cell cycle, DNA repair, and apoptosis. In diseases such as multiple myeloma, cancer cells are highly dependent on proteasome activity to manage the stress of high protein synthesis; inhibiting these subunits leads to lethal proteotoxic stress (NIH: StatPearls). Bortezomib, the first-in-class proteasome inhibitor, targets these subunits by forming a reversible covalent bond with their active-site threonine residues. This interaction disrupts the NF-κB signaling pathway and induces programmed cell death, making it a cornerstone therapy for hematologic malignancies (PubChem CID 191628).

Other names

20S proteasome β5/β1 catalytic subunitsPSMB5PSMB1Proteasome subunit beta type-5Proteasome subunit beta type-120S proteasome catalytic coreMulticatalytic endopeptidase complex

Bortezomib acts as a reversible inhibitor of the 20S proteasome by binding to the N-terminal threonine residues of the β5 (chymotrypsin-like) and β1 (caspase-like) subunits. This inhibition prevents the degradation of polyubiquitinated proteins, leading to the accumulation of misfolded proteins and the stabilization of regulatory proteins such as IκB. The resulting proteotoxic stress and inhibition of the NF-κB pathway trigger cell cycle arrest and apoptosis, particularly in malignant plasma cells (PubMed: 12485808, 16169925).