Chymotrypsin-like activity of the 20S proteasome core particle (20S proteasome (chymotrypsin-like activity))

The chymotrypsin-like activity refers specifically to one major catalytic function within the β5 subunit (PSMB5) located inside the barrel-shaped 20S core particle of the eukaryotic proteasome. The 20S core consists structurally of four stacked heptameric rings—two outer α-rings providing structural support/gating, and two inner β-rings containing three main types of active sites: chymotrypsin-like (β5), trypsin-like (β2), and caspase-like/peptidyl-glutamyl-peptide hydrolyzing activities. The chymotrypsin-like site cleaves peptide bonds after hydrophobic residues—a key step in regulated intracellular protein turnover. This enzymatic process is essential for maintaining cellular homeostasis by degrading misfolded/damaged proteins, regulating cell cycle progression through controlled destruction of regulatory factors, generating antigenic peptides for MHC class I presentation during immune responses, and more. Dysregulation or pharmacological inhibition has profound effects on cell survival—making it a validated drug target particularly in oncology but also relevant across neurodegeneration and inflammatory conditions.

Other names

Chymotryptic-like activity of the 20S proteasomeProteasomal chymotrypsin-like siteβ5 subunit (PSMB5) activityProteasome chymotryptic site

Drugs targeting this molecule typically act as proteasome inhibitors, binding covalently or non-covalently to the β5 subunit active site and blocking its chymotrypsin-like catalytic function. This leads to accumulation of ubiquitinated proteins, induction of apoptosis, and disruption of cellular processes critical for rapidly dividing cells such as cancer cells.