Affinage

PSMD5

26S proteasome non-ATPase regulatory subunit 5 · UniProt Q16401

Round 2 corrected
Length
504 aa
Mass
56.2 kDa
Annotated
2026-04-28
44 papers in source corpus 7 papers cited in narrative 6 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PSMD5 (S5b) is a dedicated assembly chaperone and negative regulator of the 26S proteasome that transiently associates with the 19S regulatory particle (RP) base subcomplex during its biogenesis but is excluded from the mature 26S holoenzyme. It forms a specific tetramer with the ATPase subunits PSMC1 (S4) and PSMC2 (S7) and the non-ATPase subunit PSMD1 (S2), and its C-terminus inserts into the RP ATPase pore to physically block docking of the 20S core particle (PMID:10625621, PMID:19217412). When PSMD5 expression is elevated—for example by TNF-α/NF-κB signaling—it sequesters PSMC2 in non-proteasome complexes, inhibiting 26S assembly and overall proteasome activity; conversely, PSMD5 loss in intestinal tumors enhances 26S proteasome assembly, and re-expression restores assembly inhibition with concomitant accumulation of polyubiquitinated substrates (PMID:22921402, PMID:29716915). Transgenic mice overexpressing PSMD5 exhibit reduced proteasome activity and premature aging, while PSMD5 deficiency in Drosophila ameliorates tauopathy and extends lifespan (PMID:22921402).

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 2000 High

    Identifying that PSMD5 associates specifically with the PSMC1/PSMC2 ATPase pair within a defined tetramer established its binding specificity within the 19S base and distinguished it from other RP sub-assemblies.

    Evidence In vitro co-translation, co-immunoprecipitation, sedimentation, and chimeric domain-swap experiments in reticulocyte lysate

    PMID:10625621

    Open questions at the time
    • Whether PSMD5 is a stoichiometric subunit of the mature 26S or a transient factor was unresolved
    • No in vivo functional consequence of PSMD5 binding was demonstrated
    • Structural basis of the PSMD5–ATPase interaction was unknown
  2. 2009 High

    Demonstrating that yeast Hsm3 (PSMD5 ortholog) is absent from the mature 26S proteasome and functions as a transient base-assembly chaperone resolved the long-standing question of whether PSMD5 is a true proteasome subunit or a biogenesis factor.

    Evidence Reciprocal co-immunoprecipitation, sucrose gradient sedimentation, and yeast deletion genetics

    PMID:19217412 PMID:19250902

    Open questions at the time
    • Functional consequences of PSMD5 overexpression or depletion in mammalian cells were not yet tested
    • Signal-regulated control of PSMD5 expression was unknown
    • Mechanism by which PSMD5 prevents premature RP–CP association was undefined
  3. 2012 High

    Revealing that TNF-α/NF-κB signaling upregulates PSMD5 to inhibit 26S proteasome assembly—and that overexpression causes aging phenotypes in mice while loss ameliorates tauopathy in Drosophila—established PSMD5 as a physiologically regulated negative regulator of proteasome activity with in vivo consequences.

    Evidence Genome-wide cDNA screen, co-immunoprecipitation, siRNA knockdown, proteasome activity assays, transgenic mouse overexpression, and Drosophila knockout

    PMID:22921402

    Open questions at the time
    • Structural mechanism by which excess PSMD5 blocks 20S CP docking was not resolved
    • Whether PSMD5 regulation is relevant in human disease contexts beyond aging models was unclear
    • Quantitative stoichiometry of PSMD5 versus assembled proteasomes in vivo was not determined
  4. 2018 High

    Finding that PSMD5 expression is lost during intestinal tumor progression and that its re-expression restores assembly inhibition linked the PSMD5 regulatory axis to cancer biology and showed that enhanced proteasome assembly in tumors is not merely a consequence of increased subunit production.

    Evidence Native gel proteasome activity assays, PSMD5 rescue experiments, polyubiquitin accumulation assays in transformed vs. non-transformed cells

    PMID:29716915

    Open questions at the time
    • Causal role of PSMD5 loss in tumor initiation or progression was not genetically tested
    • Mechanism of PSMD5 downregulation in tumors was not identified
    • Whether restoring PSMD5 has therapeutic potential was not explored
  5. 2025 Medium

    Cryo-EM and crosslinking mass spectrometry showed that the PSMD5 C-terminus inserts into the RP ATPase pore, directly occluding the 20S CP binding interface and providing the first structural explanation for assembly inhibition.

    Evidence Cryo-electron microscopy, PhIX-MS in-cell crosslinking, and AlphaFold modeling (preprint)

    PMID:bio_10.1101_2025.07.31.667872

    Open questions at the time
    • Preprint not yet peer-reviewed
    • Dynamic steps of PSMD5 insertion and ejection during normal assembly are uncharacterized
    • Whether specific post-translational modifications regulate C-terminal pore insertion is unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the precise trigger for PSMD5 release during normal RP maturation, the mechanism of PSMD5 downregulation in cancer, and whether pharmacological modulation of PSMD5 levels can tune proteasome activity therapeutically.
  • Release mechanism from the maturing RP base is structurally undefined
  • Transcriptional or post-translational regulation of PSMD5 beyond NF-κB is unexplored
  • No genetic study has tested whether PSMD5 loss is causally tumorigenic

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0044183 protein folding chaperone 2
Localization
GO:0005829 cytosol 2
Pathway
R-HSA-392499 Metabolism of proteins 4 R-HSA-168256 Immune System 1
Partners
PSMC1PSMC2PSMD1
Complex memberships
19S regulatory particle base assembly intermediate

Evidence

Reading pass · 6 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2000 PSMD5 (S5b) forms a tetramer with ATPase subunits S4 (PSMC1) and S7 (PSMC2) and the non-ATPase subunit S2 (PSMD1) within the 19S regulatory complex. Using in vitro co-translation, immunoprecipitation, and sedimentation, S5b was shown to bind the C-terminal two-thirds of S4 and the N-terminal region of S7, while S2 binds the N-terminal region of S4 and the C-terminal two-thirds of S7, forming a defined S2-S4-S7-S5b tetramer. S5b did not associate with the S6-S8 or S6'-S10b ATPase dimers, indicating specificity for the S4/S7 pair. In vitro co-translation in reticulocyte lysate with [35S]methionine, co-immunoprecipitation, sedimentation analysis, chimeric ATPase domain-swap experiments The Journal of biological chemistry High 10625621
2009 Yeast Hsm3 is a dedicated assembly chaperone for the 19S regulatory particle base subcomplex and is the functional homolog of mammalian S5b/PSMD5. Hsm3 associates with 19S base subcomplexes via the C-terminal domain of the Rpt1 (base) ATPase subunit but is absent from the final mature 26S proteasome, demonstrating that it acts transiently during assembly and is not a stoichiometric subunit of the final complex. Hsm3 is specifically required for base subcomplex assembly. Co-immunoprecipitation, sucrose gradient sedimentation, yeast genetics (deletion mutants), structural/sequence homology analysis between Hsm3 and human S5b/PSMD5 Molecular cell High 19217412 19250902
2012 PSMD5 (S5b) acts as a negative regulator of 26S proteasome assembly and activity. TNF-α increases PSMD5 expression via NFκB activation, and surplus PSMD5 directly inhibits 26S proteasome assembly and activity. Mechanistically, TNF-α enhances the interaction of PSMD5 with the ATPase subunit S7/PSMC2 in non-proteasome complexes (i.e., free PSMD5-PSMC2 complexes outside the assembled proteasome), and interfering with this interaction rescues TNF-α-induced proteasome inhibition. Downregulation of PSMD5 abolished TNF-α-induced proteasome inhibition. Transgenic mice overexpressing PSMD5 show reduced proteasome activity and premature aging phenotypes, while PSMD5 deficiency in Drosophila ameliorates tauopathy and extends lifespan. Genome-wide cDNA screen (5,500 cDNAs), co-immunoprecipitation, proteasome activity assays, siRNA knockdown, transgenic mouse overexpression, Drosophila genetic knockout, in vivo proteasome activity measurements in tissues Cell reports High 22921402
2018 PSMD5 expression is reduced during intestinal tumor progression, and this loss promotes enhanced 26S proteasome assembly in malignant cells. Re-expression of PSMD5 in tumor cells decreased 26S proteasome assembly and caused accumulation of polyubiquitinated proteins, confirming PSMD5 as an inhibitor of 26S proteasome assembly in cancer cells. Enhanced proteasome assembly was observed specifically in transformed cells but not in other rapidly dividing cells, and occurred without changes in levels of individual proteasome subunits. 26S proteasome native gel activity assays, PSMD5 re-expression (rescue experiments), polyubiquitinated protein accumulation assays, comparison of transformed vs. non-transformed dividing cells Cancer research High 29716915
2025 Cryo-EM and PhIX-MS (Photo-induced In situ Crosslinking-Mass Spectrometry) resolved PSMD5 bound to the 19S regulatory particle (RP) in the absence of the 20S catalytic core particle (CP). The C-terminus of PSMD5 inserts into the ATPase pore of the RP, physically blocking CP binding. This provides a structural explanation for how PSMD5 acts as an assembly chaperone/inhibitor that prevents premature or aberrant association of the RP with the CP. PhIX-MS (UV-activated in-cell crosslinking mass spectrometry), cryo-electron microscopy, AlphaFold structural modeling bioRxivpreprint Medium bio_10.1101_2025.07.31.667872
2025 BAG3 physically interacts with PSMD5 (along with PSMF1) in human iPSC-derived astrocytes, as identified by co-immunoprecipitation. BAG3 loss reduces proteasome function in astrocytes, placing PSMD5 within the BAG3 astrocytic proteostasis network. Co-immunoprecipitation of BAG3 in human astrocytes followed by mass spectrometry interactome mapping; western blot validation bioRxivpreprint Low bio_10.1101_2025.09.20.677505

Source papers

Stage 0 corpus · 44 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1996 Structure and functions of the 20S and 26S proteasomes. Annual review of biochemistry 2108 8811196
2005 Towards a proteome-scale map of the human protein-protein interaction network. Nature 2090 16189514
2002 Isolation of a human gene that inhibits HIV-1 infection and is suppressed by the viral Vif protein. Nature 1924 12167863
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2003 Broad antiretroviral defence by human APOBEC3G through lethal editing of nascent reverse transcripts. Nature 1236 12808466
2003 DNA deamination mediates innate immunity to retroviral infection. Cell 1150 12809610
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2003 Induction of APOBEC3G ubiquitination and degradation by an HIV-1 Vif-Cul5-SCF complex. Science (New York, N.Y.) 1006 14564014
2014 A proteome-scale map of the human interactome network. Cell 977 25416956
2003 The cytidine deaminase CEM15 induces hypermutation in newly synthesized HIV-1 DNA. Nature 912 12808465
2013 Landscape of the PARKIN-dependent ubiquitylome in response to mitochondrial depolarization. Nature 870 23503661
2020 A reference map of the human binary protein interactome. Nature 849 32296183
2018 VIRMA mediates preferential m6A mRNA methylation in 3'UTR and near stop codon and associates with alternative polyadenylation. Cell discovery 829 29507755
2003 The antiretroviral enzyme APOBEC3G is degraded by the proteasome in response to HIV-1 Vif. Nature medicine 798 14528300
2003 Species-specific exclusion of APOBEC3G from HIV-1 virions by Vif. Cell 763 12859895
2003 Complete sequencing and characterization of 21,243 full-length human cDNAs. Nature genetics 754 14702039
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2012 A census of human soluble protein complexes. Cell 689 22939629
2003 HIV-1 Vif protein binds the editing enzyme APOBEC3G and induces its degradation. Nature medicine 679 14528301
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2003 HIV-1 Vif blocks the antiviral activity of APOBEC3G by impairing both its translation and intracellular stability. Molecular cell 607 14527406
1994 A 26 S protease subunit that binds ubiquitin conjugates. The Journal of biological chemistry 584 8125911
2003 Hypermutation of HIV-1 DNA in the absence of the Vif protein. Science (New York, N.Y.) 570 12750511
2003 Exploring proteomes and analyzing protein processing by mass spectrometric identification of sorted N-terminal peptides. Nature biotechnology 485 12665801
2007 Dioxin receptor is a ligand-dependent E3 ubiquitin ligase. Nature 464 17392787
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
2003 The Vif protein of HIV triggers degradation of the human antiretroviral DNA deaminase APOBEC3G. Current biology : CB 405 14614829
2001 Anaphase-promoting complex/cyclosome-dependent proteolysis of human cyclin A starts at the beginning of mitosis and is not subject to the spindle assembly checkpoint. The Journal of cell biology 372 11285280
2009 Hsm3/S5b participates in the assembly pathway of the 19S regulatory particle of the proteasome. Molecular cell 93 19217412
2000 Differential expression of leptin receptor in high- and low-fat-fed Osborne-Mendel and S5B/Pl rats. Obesity research 54 11011914
2000 Mapping subunit contacts in the regulatory complex of the 26 S proteasome. S2 and S5b form a tetramer with ATPase subunits S4 and S7. The Journal of biological chemistry 53 10625621
2012 Role of S5b/PSMD5 in proteasome inhibition caused by TNF-α/NFκB in higher eukaryotes. Cell reports 41 22921402
2018 PSMD5 Inactivation Promotes 26S Proteasome Assembly during Colorectal Tumor Progression. Cancer research 32 29716915
2010 Obesity-resistant S5B rats showed greater cocaine conditioned place preference than the obesity-prone OM rats. Physiology & behavior 24 20801137
2010 Sensitivity to the satiating effects of exendin 4 is decreased in obesity-prone Osborne-Mendel rats compared to obesity-resistant S5B/Pl rats. International journal of obesity (2005) 23 20404826
1997 Feeding response to mercaptoacetate in Osborne-Mendel and S5B/PL rats. Obesity research 22 9449144
2005 Effect of a high or low ambient perinatal temperature on adult obesity in Osborne-Mendel and S5B/Pl rats. American journal of physiology. Regulatory, integrative and comparative physiology 15 15677528
2021 Sex differences in markers of metabolic syndrome and adipose tissue inflammation in obesity-prone, Osborne-Mendel and obesity-resistant, S5B/Pl rats. Life sciences 12 33662430
2000 Effect of a serotonin 1-A agonist on food intake of Osborne-Mendel and S5B/P1 rats. Physiology & behavior 11 10764902
2015 High-fat diet differentially regulates metabolic parameters in obesity-resistant S5B/Pl rats and obesity-prone Osborne-Mendel rats. Canadian journal of physiology and pharmacology 9 26641537
2009 Hsm3/S5b joins the ranks of 26S proteasome assembly chaperones. Molecular cell 8 19250902
2019 The prevalence of cardio-metabolic risk factors is differentially elevated in obesity-prone Osborne-Mendel and obesity-resistant S5B/Pl rats. Life sciences 7 30872180