proteasome core complex

GO:0005839 · Other · Multiprotein complex · Proposed

A barrel-shaped self-compartmentalized protease core of proteasomes, built from stacked alpha- and beta-subunit rings that sequester threonine protease active sites in an internal chamber for protein degradation. [GO:0005839]

Synonyms: 20S proteasome; 20S proteasome core particle

Part of: proteasome complex (GO:0000502)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
proteasome alpha-type subunits	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	prcA	two outer heptameric rings	ESSENTIAL	Forms the two outer rings of the 20S barrel and gates substrate entry into the internal proteolytic chamber. `DOI:10.1042/ETLS20180025` Maupin-Furlow 2018 reviews archaeal 20S proteasome core particles as alpha- and beta-subunit barrels. `DOI:10.1038/emboj.2010.95` Li et al. 2010 structurally analyzed assembly and gate closure of the Mycobacterium tuberculosis 20S proteasome alpha ring. `DOI:10.1146/annurev-biochem-060410-150257` Tomko and Hochstrasser 2013 review the eukaryotic 20S core as a barrel-shaped protease with alpha-subunit outer rings.
proteasome beta-type subunits	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	prcB	two inner heptameric rings	ESSENTIAL	Forms the two inner rings of the 20S core and provides the N-terminal threonine protease active sites in the chamber. `DOI:10.1042/ETLS20180025` Maupin-Furlow 2018 reviews archaeal proteasome beta subunits as the catalytic subunits of the 20S core. `DOI:10.1111/j.1365-2958.2005.05036.x` Hu et al. 2006 solved the Mycobacterium tuberculosis 20S proteasome structure and localized active-site chemistry to the beta subunits. `DOI:10.1146/annurev-biochem-060410-150257` Tomko and Hochstrasser 2013 review the eukaryotic 20S core as a barrel-shaped protease with beta-subunit inner rings.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

proteasome alpha-type subunits

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P9WHU1`	Proteasome subunit alpha	prcA	Mycobacterium tuberculosis H37Rv (`NCBITaxon:83332`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene prcA in Mycobacterium tuberculosis H37Rv, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `https://www.uniprot.org/uniprotkb/P9WHU1` UniProtKB reviewed (Swiss-Prot) entry P9WHU1, the single reviewed entry for gene prcA in Mycobacterium tuberculosis H37Rv. Establishes the accession and gene identity only; the component's membership in this structure rests on the record's own sources.

proteasome beta-type subunits

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P9WHT9`	Proteasome subunit beta	prcB	Mycobacterium tuberculosis H37Rv (`NCBITaxon:83332`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene prcB in Mycobacterium tuberculosis H37Rv, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `https://www.uniprot.org/uniprotkb/P9WHT9` UniProtKB reviewed (Swiss-Prot) entry P9WHT9, the single reviewed entry for gene prcB in Mycobacterium tuberculosis H37Rv. Establishes the accession and gene identity only; the component's membership in this structure rests on the record's own sources.

Taxonomic distribution

NCBITaxon:2157 Archaea — COMMON: 20S proteasomes are broadly conserved archaeal self-compartmentalized proteases. [DOI:10.1042/ETLS20180025]
NCBITaxon:201174 Actinomycetota — VARIABLE: Bacterial 20S proteasomes are best characterized in actinobacteria, including mycobacteria, but are not universal across bacteria. [DOI:10.3389/fmolb.2019.00023]
NCBITaxon:2759 Eukaryota — COMMON: The 20S core is the proteolytic barrel of eukaryotic proteasomes and is conserved in microbial eukaryotes as part of the ubiquitin-proteasome system. [DOI:10.1146/annurev-biochem-060410-150257]

Canonical examples

NCBITaxon:83332 Mycobacterium tuberculosis H37Rv — Mycobacterial strain whose 20S core structure and gate-closure mechanism were solved crystallographically. [DOI:10.1038/emboj.2010.95]

Functions

proteasomal protein catabolic process GO:0010498 — The core complex degrades unfolded proteins or peptides inside its enclosed proteolytic chamber.
- DOI:10.1042/ETLS20180025 Maupin-Furlow 2018 reviews archaeal protein degradation by proteasomes associated with AAA-ATPases.
- DOI:10.3389/fmolb.2019.00023 Muller et al. 2019 review bacterial proteasome core particles and activators in Mycobacterium tuberculosis.
threonine-type endopeptidase activity GO:0004298 — Beta subunit N-terminal threonines catalyze peptide-bond hydrolysis inside the 20S core.
- DOI:10.1111/j.1365-2958.2005.05036.x Hu et al. 2006 captured the Mycobacterium tuberculosis proteasome active site and inhibitor interactions.

Mechanism graphs

Stacked alpha and beta rings form a gated proteolytic barrel (FUNCTION)

Proteasome alpha subunits form the two outer rings of a gated barrel, beta subunits form the two inner proteolytic rings, and unfolded substrate entering the internal chamber is cleaved by beta-subunit threonine protease sites.

Subject	Predicate	Object	Evidence
proteasome alpha-type subunits	form outer rings of	proteasome core complex	`DOI:10.1038/emboj.2010.95` Li et al. 2010 structurally analyzed the Mycobacterium tuberculosis 20S proteasome alpha rings.
proteasome beta-type subunits	form inner rings of	proteasome core complex	`DOI:10.1111/j.1365-2958.2005.05036.x` Hu et al. 2006 solved the Mycobacterium tuberculosis 20S proteasome core structure.
proteasome alpha-type subunits	gate	alpha-ring axial gate	`DOI:10.1038/emboj.2010.95` Li et al. 2010 model Mycobacterium tuberculosis 20S gate closure by alpha-ring N termini.
alpha-ring axial gate	controls entry to	proteasome proteolytic chamber	`DOI:10.1038/emboj.2010.95` Li et al. 2010 connect M. tuberculosis alpha-ring gate closure to substrate entry into the proteolytic core.
proteasome beta-type subunits	cleave	unfolded protein substrate	`DOI:10.1111/j.1365-2958.2005.05036.x` Hu et al. 2006 structurally localized the mycobacterial 20S proteasome catalytic sites to beta subunits.
unfolded protein substrate	is converted to	peptide products	`DOI:10.3389/fmolb.2019.00023` Muller et al. 2019 review degradation of proteins by the bacterial 20S core and associated activator complexes.
proteasome core complex	carries out	proteasomal protein catabolic process	`DOI:10.1042/ETLS20180025` Maupin-Furlow 2018 reviews archaeal proteasomes as self-compartmentalized proteases involved in targeted proteolysis.

Evidence

DOI:10.1042/ETLS20180025 Maupin-Furlow 2018, Proteolytic systems of archaea: slicing, dicing, and mincing in the extreme, Emerging Topics in Life Sciences.
DOI:10.3389/fmolb.2019.00023 Muller et al. 2019, The bacterial proteasome at the core of diverse degradation pathways, Frontiers in Molecular Biosciences.
DOI:10.1038/emboj.2010.95 Li et al. 2010, Structural basis for the assembly and gate closure mechanisms of the Mycobacterium tuberculosis 20S proteasome, The EMBO Journal.
DOI:10.1111/j.1365-2958.2005.05036.x Hu et al. 2006, Structure of the Mycobacterium tuberculosis proteasome and mechanism of inhibition by a peptidyl boronate, Molecular Microbiology.
DOI:10.1146/annurev-biochem-060410-150257 Tomko and Hochstrasser 2013, Molecular Architecture and Assembly of the Eukaryotic Proteasome, Annual Review of Biochemistry.

Curation history

2026-09-06T12:53:45Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-06T12:56:44Z claude · EXPANDED_RECORD — Added 20S proteasome synonyms, proteasome-complex parthood, alpha and beta core subunits, archaeal and actinobacterial taxonomy, an M. tuberculosis H37Rv example, protein-catabolism functions, record evidence, and a gated-barrel proteolysis graph.
2026-09-06T13:55:03Z claude · EXPANDED_TAXONOMIC_SCOPE — #205: added eukaryotic 20S proteasome scope and eukaryotic architecture evidence to keep the taxonomic distribution aligned with the cross-domain alpha and beta subunit model.
2026-09-08T07:40:07Z uniprot_genes · SEED_PROTEIN_EXAMPLES — #183: added 2 protein example(s) by resolving each of the component's declared gene symbols to the single reviewed UniProtKB entry for that symbol in a taxon this record names, deduplicated by accession. Symbols resolving to more than one reviewed entry were skipped rather than chosen between.

Source: data/structures/other/proteasome_core_complex.yaml