26S proteasome beta 5, beta 1, and beta 1i subunits (PSMB5, PSMB6, and PSMB9)

The 26S proteasome is a multi-subunit enzyme complex responsible for the degradation of ubiquitinated proteins, a process essential for maintaining cellular homeostasis (UniProt P28074). The catalytic core, known as the 20S proteasome, contains specific beta subunits—β5 (PSMB5), β1 (PSMB6), and the inducible β1i (PSMB9)—which exhibit chymotrypsin-like and caspase-like proteolytic activities (PubMed: 21685913). These subunits play a critical role in regulating the cell cycle, signal transduction, and the immune response by processing antigens for MHC class I presentation (UniProt P28065). In many cancers, particularly hematological malignancies like multiple myeloma, the proteasome is overactive, helping malignant cells survive high protein synthesis rates and evade apoptosis (StatPearls: Proteasome Inhibitors). Drugs targeting these subunits, such as bortezomib, inhibit their enzymatic activity, causing a buildup of misfolded proteins that triggers the unfolded protein response and leads to programmed cell death (PubChem CID 387447). While highly effective in treating certain cancers, targeting these subunits can lead to systemic side effects like peripheral neuropathy due to the proteasome's broad role in healthy tissues (PubMed: 19147771).

Other names

Proteasome subunit beta type-5Proteasome subunit beta type-6Proteasome subunit beta type-9LMP2PSMB5PSMB6PSMB920S proteasome catalytic subunitsMulticatalytic endopeptidase complex subunits

Inhibition of the chymotrypsin-like (β5) and caspase-like (β1/β1i) proteolytic activities of the proteasome, leading to the accumulation of ubiquitinated proteins, induction of the unfolded protein response, and subsequent apoptosis.