Eukaryotic 20S proteasome catalytic beta subunits (20S proteasome)

The eukaryotic 20S proteasome catalytic beta subunits are the enzymatic components of the 20S core particle, which forms the central part of the 26S proteasome complex responsible for ATP-dependent protein degradation [1]. The 20S core is a barrel-shaped structure composed of four stacked heptameric rings: two outer alpha rings and two inner beta rings. Within the beta rings, three subunits—beta-1 (PSMB6), beta-2 (PSMB7), and beta-5 (PSMB5)—contain N-terminal threonine residues that act as nucleophiles for proteolytic cleavage, providing caspase-like, trypsin-like, and chymotrypsin-like activities, respectively [2][3]. This system is essential for maintaining cellular proteostasis by degrading misfolded, damaged, or regulatory proteins such as cyclins and IkappaB [4]. In diseases like multiple myeloma, malignant plasma cells are hypersensitive to proteasome inhibition due to their high rate of immunoglobulin production, which leads to lethal proteotoxic stress when degradation is blocked [5]. Therapeutic agents like bortezomib and carfilzomib specifically target these beta subunits to treat hematological malignancies, though resistance can develop through mutations in the PSMB5 subunit [6].

Other names

Proteasome subunit beta20S core particleMulticatalytic endopeptidase complexPSMB subunitsThreonine-type endopeptidase complex

Inhibition of the N-terminal threonine active sites within the beta subunits, primarily targeting the chymotrypsin-like activity of the beta-5 subunit, leading to the accumulation of misfolded proteins and induction of apoptosis.