Proteasome subunit beta type-6 (PSMB6) and Proteasome subunit beta type-9 (PSMB9) (PSMB6 and PSMB9)

The 26S proteasome is a 2.5 MDa multicatalytic protease complex essential for maintaining cellular protein homeostasis through the ubiquitin-proteasome system [3, 8, 9]. It is composed of a 20S core particle, which contains the proteolytic active sites, and 19S regulatory particles that recognize and unfold ubiquitinated substrates [8, 15]. The beta 1 (PSMB6) and its inducible counterpart beta 1i (PSMB9/LMP2) are key catalytic subunits within the 20S core, primarily responsible for caspase-like or post-acidic cleavage activity [2, 5, 10]. While beta 1 is constitutively expressed in most tissues, beta 1i is induced by pro-inflammatory cytokines like interferon-gamma to form the immunoproteasome, which optimizes peptide generation for MHC class I antigen presentation [1, 10, 19]. These subunits are significant therapeutic targets in oncology, particularly for hematologic malignancies like multiple myeloma, where proteasome inhibitors like bortezomib and carfilzomib induce apoptosis by disrupting protein degradation [4, 6, 11]. Additionally, selective inhibitors of the beta 1i subunit, such as ONX-0914 and KZR-616, are under investigation for treating autoimmune and inflammatory diseases, offering a strategy to modulate the immune system with potentially fewer systemic side effects than broad-spectrum proteasome inhibitors [1, 18, 20].

Other names

26S proteasome beta 1 and beta 1i catalytic subunitsLMP2RING12DeltaYPSMB6i20S proteasome subunit beta-1i20S proteasome subunit beta-6Low molecular mass protein 2

Proteasome inhibition via covalent or non-covalent binding to the N-terminal threonine active site, blocking the caspase-like proteolytic activity [15, 19].