20S proteasome chymotrypsin-like β5 subunit (PSMB5) (β5)

The 20S proteasome chymotrypsin-like β5 subunit (PSMB5) is a catalytic component of the 20S core proteasome, a barrel-shaped protease complex essential for intracellular protein degradation. Located in the inner β-rings, β5 provides the chymotrypsin-like activity by cleaving peptide bonds after large hydrophobic residues using its N-terminal threonine as the nucleophile, working alongside β1 (caspase-like) and β2 (trypsin-like) subunits for selective proteolysis. This subunit enables ubiquitin-dependent breakdown of regulatory proteins, removal of misfolded aggregates, and MHC class I antigen presentation, with its gate-regulated access preventing non-specific degradation. In disease, dysregulated β5 activity contributes to cancer cell survival through rapid protein turnover, while inhibition triggers apoptosis in malignant cells; it also plays roles in neurodegeneration via aggregate clearance and inflammation through immunoproteasome forms like LMP7. Approved inhibitors such as bortezomib covalently target β5's active site, forming the basis of multiple myeloma therapies, though challenges include neuropathy from broad proteasome blockade and variable efficacy across tumor types.

Other names

PSMB5Proteasome subunit beta type 5Proteasome catalytic subunit β5LMP7 (immunoproteasome form)Chymotrypsin-like subunit of 20S proteasome

Reversible or irreversible inhibition of the N-terminal threonine active site, preventing cleavage after hydrophobic residues Accumulation of ubiquitinated proteins, leading to cell cycle arrest and apoptosis