20S proteasome catalytic core (20S proteasome)

The 20S proteasome catalytic core is a barrel-shaped multi-subunit enzyme complex that serves as the central component of the ubiquitin-proteasome system (UPS). It is responsible for the degradation of polyubiquitinated proteins, which is essential for maintaining cellular proteostasis and regulating key processes such as the cell cycle, signal transduction, and apoptosis (Source: NIH, PubMed). The complex consists of four stacked heptameric rings: two outer alpha-rings that control substrate entry and two inner beta-rings that contain the proteolytic active sites (Source: UniProt). Specifically, the beta-1, beta-2, and beta-5 subunits exhibit caspase-like, trypsin-like, and chymotrypsin-like activities, respectively. In many cancers, particularly multiple myeloma, the 20S proteasome is overactive or essential for the survival of malignant cells that produce high levels of abnormal proteins. Drugs like bortezomib and carfilzomib target the catalytic threonine residues within these subunits to block protein degradation, triggering a proteotoxic stress response that leads to programmed cell death (Source: StatPearls). While highly effective in hematologic malignancies, therapeutic challenges include the development of drug resistance and significant side effects such as peripheral neuropathy and cardiotoxicity (Source: PubMed, PMID: 29113464).

Other names

20S core particleMulticatalytic endopeptidase complexCPProteasome subunit beta type-5PSMB5Proteasome subunit alphaProteasome subunit beta

Inhibition of the proteolytic activity of the beta subunits (primarily the chymotrypsin-like activity of PSMB5) through covalent or non-covalent binding to the N-terminal threonine residue, leading to the accumulation of misfolded proteins and induction of apoptosis.