Affinage

PAAF1

Proteasomal ATPase-associated factor 1 · UniProt Q9BRP4

Length
392 aa
Mass
42.2 kDa
Annotated
2026-06-10
16 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PAAF1 (mammalian ortholog of yeast Rpn14) is a dedicated chaperone for assembly of the 19S regulatory particle (RP) base of the 26S proteasome (PMID:19412159, PMID:19490896). It binds the C-terminal domain of the ATPase subunit Rpt6 (PSMC5) through complementary charge interactions—an acidic surface on the PAAF1 seven-bladed beta-propeller engaging the basic Rpt6 C-terminus—and acts within a p28-Rpt3-Rpt6-PAAF1 module that nucleates base subcomplex formation (PMID:19490896, PMID:20236927). PAAF1 promotes incorporation of Rpt6 into the heterohexameric Rpt ring (arrangement Rpt1-Rpt2-Rpt6-Rpt3-Rpt4-Rpt5), facilitating contacts with adjacent Rpt dimers, and dissociates before the 26S holoenzyme is completed, consistent with a role in restricting Rpt C-terminal access to the core particle during assembly (PMID:19412159, PMID:20471945, PMID:22275368). When present in excess, PAAF1 negatively regulates 26S assembly: overexpression reduces 20S-19S association and proteasomal degradation, while its depletion enhances proteasome activity (PMID:15831487). Because PAAF1 remains bound to PSMC5 until assembly completes, it serves as an adaptor by which the HERC1 ubiquitin ligase detects and degrades unassembled Rpt intermediates, a process disrupted by a neurodegeneration-causing HERC1 missense mutation (PMID:34446601). Beyond its assembly role, PAAF1 coactivates HIV-1 LTR transcription by driving dissociation of the 26S proteasome into 19S particles recruited to the viral promoter and by physically binding and protecting the elongation factor Spt6 from proteolysis (PMID:17289585, PMID:22316138), and it mediates inhibition of 26S proteasome activity by phospho-S129 α-synuclein through a direct interaction (PMID:38415292).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2005 High

    Established that PAAF1 physically associates with 19S proteasomal ATPases and that its abundance bidirectionally controls 26S assembly and degradation activity, defining it as a regulator of the proteasome.

    Evidence Co-IP and affinity purification of the 19S complex plus overexpression/siRNA with GFP degradation reporters in HeLa cells

    PMID:15831487

    Open questions at the time
    • Did not identify which specific Rpt subunit PAAF1 binds
    • Did not distinguish a role in assembly versus disassembly
    • No structural basis for the interaction
  2. 2007 Medium

    Showed that PAAF1 can be co-opted by HIV-1 Tat to drive 26S dissociation into 19S particles that are recruited to the viral promoter, linking proteasome remodeling to transcriptional elongation.

    Evidence Gel filtration of nuclear extracts, ChIP, transcription reporter assays, and Co-IP

    PMID:17289585

    Open questions at the time
    • Mechanism by which the 19S particle promotes elongation not fully resolved
    • Did not identify the 19S elongation targets at the promoter
    • Single-lab study
  3. 2009 High

    Defined the ortholog Rpn14/PAAF1 as a dedicated 19S RP assembly chaperone that binds the Rpt6 C-terminal domain, associates with RP but not mature holoenzyme, and acts in a discrete base-assembly module.

    Evidence Yeast genetics and biochemical fractionation/Co-IP (PMID 19412159); modular assembly intermediate purification in mammalian cells identifying the p28-Rpt3-Rpt6-Rpn14 module (PMID 19490896)

    PMID:19412159 PMID:19490896

    Open questions at the time
    • Atomic basis of the Rpt6 interaction not yet resolved
    • Trigger for chaperone dissociation during maturation unclear
    • Order of all module incorporation steps incompletely defined
  4. 2010 High

    Provided the structural and topological basis for PAAF1 function: an atomic-resolution structure revealing the beta-propeller and the acidic Rpt6-binding surface, and disulfide mapping placing Rpn14 on a defined four-ATPase assembly intermediate.

    Evidence X-ray crystallography of yeast Rpn14 at 2.0 Å with interface-residue mutagenesis (PMID 20236927); disulfide engineering establishing the Rpt ring order and chaperone-bound intermediate (PMID 20471945)

    PMID:20236927 PMID:20471945

    Open questions at the time
    • Function of the N-terminal domain unknown
    • No structure of the full assembly intermediate
    • Dynamics of chaperone release not captured
  5. 2012 Medium

    Extended PAAF1 mechanism to nucleotide-dependent ring assembly and to a transcriptional protective function, showing it relieves assembly blocks from Rpt6 nucleotide-binding mutants and shields Spt6 from proteolysis.

    Evidence Chaperone/Walker-mutant Rpt coexpression with Co-IP and ATPase assays (PMID 22275368); a 1.6 Å Rpn14 structure (PMID 22691779); siRNA, Co-IP, ChIP, profiling and rescue of HIV-1 transcription via Spt6 (PMID 22316138)

    PMID:22275368 PMID:22316138 PMID:22691779

    Open questions at the time
    • Generality of Spt6 protection across cellular gene programs not established
    • Whether nucleotide-state sensing is direct unresolved
    • Single-lab transcription data
  6. 2018 Medium

    Positioned Rpn14/PAAF1 within an assembly checkpoint in which chaperone occupancy of Rpt sites must yield to an E3 ligase to license ring maturation.

    Evidence Cocrystal analysis, ubiquitination assays, Co-IP, and genetic epistasis in yeast showing Not4 competes with Rpn14 for Rpt access

    PMID:30530678

    Open questions at the time
    • Rpn14's role inferred from a competition model rather than direct kinetics
    • Mammalian conservation of the Not4 checkpoint not tested here
    • Temporal coupling of dissociation and ubiquitination unresolved
  7. 2019 Medium

    Revealed a stress-responsive layer regulating chaperone-mediated assembly, in which excess Rpt subunits relative to chaperones including Rpn14/PAAF1 are sequestered into puncta and chaperone-independent assembly can occur.

    Evidence Fluorescence microscopy of puncta, genetic manipulation of chaperone/Rpt levels, and proteasome activity assays in yeast

    PMID:30814255

    Open questions at the time
    • Specific contribution of PAAF1 versus other chaperones not isolated
    • Whether mammalian PAAF1 behaves identically untested
    • Composition of the sequestration puncta undefined
  8. 2021 High

    Established PAAF1 as an adaptor for HERC1-mediated quality control, with persistent PAAF1 binding to PSMC5 marking unassembled intermediates for ubiquitination and degradation, and linked this to neurodegeneration via a HERC1 mutation.

    Evidence Co-IP, ubiquitination and degradation assays in mammalian cells, plus a HERC1 missense mutant and mouse neurodegeneration model

    PMID:34446601

    Open questions at the time
    • Signal that releases PAAF1 upon successful assembly not defined
    • Whether HERC1 directly contacts PAAF1 or PSMC5 not fully resolved
    • Human disease relevance beyond the mouse model untested
  9. 2024 Medium

    Connected PAAF1 to α-synuclein proteotoxicity, showing it binds and stabilizes pS129 α-synuclein and mediates its inhibition of 26S proteasome activity across species.

    Evidence tFT reporter genome-wide screen, Co-IP, and proteasome activity assays in yeast and human cells with overexpression

    PMID:38415292

    Open questions at the time
    • Structural basis of the PAAF1–α-synuclein interaction unknown
    • Whether the interaction occurs at endogenous expression levels untested
    • Mechanistic link to neurodegenerative disease in vivo not established

Open questions

Synthesis pass · forward-looking unresolved questions
  • The signal that triggers PAAF1 release from Rpt6/PSMC5 upon successful ring maturation, and how its assembly-chaperone, transcriptional, and proteotoxic-stress roles are coordinated, remain undefined.
  • No defined trigger for chaperone dissociation during maturation
  • Function of the PAAF1 N-terminal domain uncharacterized
  • Integration of assembly versus transcription/disease roles unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 3 GO:0098772 molecular function regulator activity 2 GO:0140110 transcription regulator activity 2 GO:0060090 molecular adaptor activity 1
Localization
GO:0005829 cytosol 2 GO:0005634 nucleus 1
Pathway
R-HSA-392499 Metabolism of proteins 4 R-HSA-1852241 Organelle biogenesis and maintenance 3 R-HSA-74160 Gene expression (Transcription) 2
Partners
HERC1PSMC4PSMC5RPT3RPT6SNCASPT6
Complex memberships
19S regulatory particle base26S proteasomep28-Rpt3-Rpt6-PAAF1 assembly module

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 PAAF1 (proteasomal ATPase-associated factor 1) specifically interacts with proteasomal ATPases of the 19S regulatory complex. Overexpression of PAAF1 in HeLa cells decreased the level of 20S core associated with the 19S complex in a dose-dependent manner, inhibiting 26S proteasome assembly and reducing proteasomal degradation activity in vivo. Conversely, siRNA-mediated suppression of PAAF1 enhanced proteasome activity, establishing PAAF1 as a negative regulator of proteasome assembly/disassembly. Affinity purification of 19S regulatory complex, immunoprecipitation, immunoaffinity purification of PAAF1, overexpression and siRNA knockdown with GFP-based proteasomal degradation reporters in HeLa cells Molecular and cellular biology High 15831487
2007 PAAF1 is recruited by HIV-1 Tat to the proteasome and promotes dissociation of the 26S proteasome into 19S and 20S particles. Co-expression of Tat and PAAF1 enhanced the abundance of a 19S-like complex in nuclear extracts (gel filtration chromatography). The 19S complex (but not 20S) was recruited to the HIV-1 promoter in the presence of Tat and PAAF1, and coactivated Tat-dependent transcription by facilitating transcriptional elongation. Gel filtration chromatography of nuclear extracts, chromatin immunoprecipitation (ChIP), transcriptional reporter assays, co-immunoprecipitation Molecular cell Medium 17289585
2009 Yeast Rpn14 (ortholog of PAAF1) is a dedicated chaperone for 19S regulatory particle (RP) assembly that associates with RP but not with the mature RP-CP holoenzyme. Rpn14 binds to the C-terminal domain of a specific Rpt ATPase subunit (Rpt6). Mutations in RPN14 confer proteasome loss-of-function phenotypes due to deficient RP assembly, not degradation of Rpn14 itself. Rpn14 dissociates from RP as proteasomes mature, consistent with a role in restricting Rpt C-terminal accessibility to the CP during assembly. Genetic (mutant analysis, loss-of-function phenotypes), biochemical fractionation, co-immunoprecipitation, identification of chaperone-RP but not holoenzyme association in yeast Nature High 19412159
2009 In mammalian cells, PAAF1 (Rpn14) participates in base subcomplex assembly as part of a p28-Rpt3-Rpt6-Rpn14 module. Base assembly initiates with association of this module with the S5b-Rpt1-Rpt2-Rpn1 complex, followed by incorporation of the p27-Rpt5-Rpt4 module and Rpn2. PAAF1/Rpn14 and the other chaperones (p28, S5b, p27) dissociate before completion of 26S proteasome formation. Affinity purification, co-immunoprecipitation, identification of modular assembly intermediates in mammalian cells Cell High 19490896
2010 Crystal structure of yeast Rpn14 (PAAF1 ortholog) determined at 2.0 Å resolution, revealing an N-terminal domain of unknown function and a C-terminal seven-bladed beta-propeller fold. Structural comparison with the Nas6-Rpt3-C complex predicted the Rpt6-binding site on Rpn14; the top face exhibits a highly acidic surface complementary to the basic surface of Rpt6-C. Specific residues of Rpn14 and Rpt6 mediating complementary charge interactions required for 19S RP assembly were identified. X-ray crystallography (2.0 Å resolution), structural comparison, genetic and biochemical validation of predicted binding interface residues The Journal of biological chemistry High 20236927
2010 Disulfide engineering in yeast established the Rpt ring arrangement as Rpt1-Rpt2-Rpt6-Rpt3-Rpt4-Rpt5 in fully assembled proteasomes. This arrangement, together with cognate chaperone (Rpn14/Nas6/Nas2) binding specificities, led to identification of a four-ATPase assembly intermediate containing Rpt6-Rpt3-Rpt4-Rpt5 together with their chaperones Rpn14, Nas6, and Nas2. Disulfide engineering, biochemical fractionation, identification of assembly intermediates in yeast Molecular cell High 20471945
2012 PAAF1 coactivates HIV-1 LTR transcription partly by protecting the transcription elongation factor Spt6 from proteasomal degradation. PAAF1 physically interacts with the N-terminus of Spt6, shielding it from proteolysis. Depletion of PAAF1 reduced histone occupancy at the HIV-1 promoter and induced aberrant transcripts; ectopic Spt6 expression or proteasome inhibitor treatment partially rescued the transcription defect caused by PAAF1 loss. A subset of cellular genes (including BRCA1, BARD1) are co-regulated by PAAF1 and Spt6. siRNA knockdown, co-immunoprecipitation (PAAF1-Spt6 interaction), chromatin immunoprecipitation (ChIP), transcriptional profiling, ectopic overexpression rescue assays Retrovirology Medium 22316138
2012 PAAF1 facilitates incorporation of mutant Rpt6 (Walker A motif mutation, nucleotide-binding deficient) into the assembling Rpt ring by facilitating interactions with adjacent Rpt dimers. Nucleotide binding (but not ATP hydrolysis) is required for stable Rpt ring assembly, and PAAF1 (together with S5b for Rpt1) can relieve the assembly block imposed by nucleotide-binding mutations. Coexpression of chaperones with Walker A/B mutant Rpt subunits in human cells, co-immunoprecipitation, ATPase activity assays The Journal of biological chemistry Medium 22275368
2012 Improved crystal structure of Rpn14 (PAAF1 ortholog) with E384A mutation determined at 1.6 Å resolution in space group P2(1), providing higher-resolution framework for understanding proteasome assembly mechanism. X-ray crystallography (1.6 Å resolution) Acta crystallographica. Section F, Structural biology and crystallization communications Medium 22691779
2018 In yeast, the chaperone Rpn14 (PAAF1 ortholog) occupies the Rpt6 binding site on the assembling Rpt ring, and the E3 ligase Not4 must compete with Rpn14 (and other chaperones) to access and ubiquitinate Rpt5. Not4-mediated ubiquitination sites in Rpt5 are obstructed by Nas2 and Hsm3 chaperones, defining an assembly checkpoint where chaperone dissociation allows Not4 to monitor ring maturation. Cocrystal structure analysis, ubiquitination assays, co-immunoprecipitation, genetic epistasis in yeast Proceedings of the National Academy of Sciences of the United States of America Medium 30530678
2019 During stressed conditions (heat), excess Rpt subunits relative to their chaperones (including Rpn14/PAAF1) are sequestered into cytoplasmic puncta, providing an alternative mechanism to regulate onset of chaperone-mediated Rpt ring assembly. When the free Rpt pool is limiting, Rpt subunits can assemble without cognate chaperones. Once sufficient holoenzyme is formed, the proteasome itself degrades excess Rpt subunits, creating a self-regulatory loop. Fluorescence microscopy (puncta formation), genetic manipulation of chaperone and Rpt subunit levels, proteasome activity assays in yeast The Journal of biological chemistry Medium 30814255
2021 PAAF1 serves as an adaptor for the HERC1 ubiquitin ligase to target unassembled PSMC5 (Rpt8/Rpt6 equivalent) for degradation in mammalian cells. PAAF1 remains bound to PSMC5 until assembly is complete, so HERC1 uses PAAF1 as a proxy to detect unassembled intermediates, including the PSMC4-PSMC5-PAAF1 complex. A disease-causing missense mutation in HERC1 (causing neurodegeneration in mice) impairs recognition and ubiquitination of the PSMC5-PAAF1 complex. Co-immunoprecipitation, ubiquitination assays, mammalian cell degradation assays, mouse neurodegeneration model, HERC1 missense mutant analysis Science (New York, N.Y.) High 34446601
2024 Rpn14/PAAF1 physically interacts with α-synuclein (α-syn) and stabilizes the phospho-S129 (pS129) form of α-syn. Elevated levels of Rpn14 enhanced α-syn-mediated growth inhibition and accumulation of ubiquitin conjugates. Co-expression of α-syn with elevated Rpn14 or its human counterpart PAAF1 reduced 26S proteasome activity in both yeast and human cells, establishing that pS129 α-syn inhibits proteasome activity through Rpn14/PAAF1. Tandem fluorescent protein timer (tFT) reporter genome-wide screen, co-immunoprecipitation (Rpn14-α-syn interaction), proteasome activity assays in yeast and human cells, genetic overexpression Aging cell Medium 38415292

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2009 Assembly pathway of the Mammalian proteasome base subcomplex is mediated by multiple specific chaperones. Cell 178 19490896
2009 Chaperone-mediated pathway of proteasome regulatory particle assembly. Nature 153 19412159
2010 Heterohexameric ring arrangement of the eukaryotic proteasomal ATPases: implications for proteasome structure and assembly. Molecular cell 125 20471945
2007 The proteasome regulates HIV-1 transcription by both proteolytic and nonproteolytic mechanisms. Molecular cell 72 17289585
2005 Proteasomal ATPase-associated factor 1 negatively regulates proteasome activity by interacting with proteasomal ATPases. Molecular and cellular biology 42 15831487
2021 Identification of a quality-control factor that monitors failures during proteasome assembly. Science (New York, N.Y.) 36 34446601
2019 Genome-scale CRISPR activation screening identifies a role of ELAVL2-CDKN1A axis in paclitaxel resistance in esophageal squamous cell carcinoma. American journal of cancer research 30 31285951
2007 Lower expression of catalytic and structural subunits of the proteasome contributes to decreased proteolysis in peripheral blood T lymphocytes during aging. The international journal of biochemistry & cell biology 24 17317272
2010 Crystal structure of yeast rpn14, a chaperone of the 19 S regulatory particle of the proteasome. The Journal of biological chemistry 19 20236927
2012 Stable incorporation of ATPase subunits into 19 S regulatory particle of human proteasome requires nucleotide binding and C-terminal tails. The Journal of biological chemistry 17 22275368
2012 Spt6 levels are modulated by PAAF1 and proteasome to regulate the HIV-1 LTR. Retrovirology 15 22316138
2018 Ubiquitin-dependent switch during assembly of the proteasomal ATPases mediated by Not4 ubiquitin ligase. Proceedings of the National Academy of Sciences of the United States of America 13 30530678
2024 HMZDupFinder: a robust computational approach for detecting intragenic homozygous duplications from exome sequencing data. Nucleic acids research 11 38153174
2019 Two alternative mechanisms regulate the onset of chaperone-mediated assembly of the proteasomal ATPases. The Journal of biological chemistry 11 30814255
2024 Inhibition of 26S proteasome activity by α-synuclein is mediated by the proteasomal chaperone Rpn14/PAAF1. Aging cell 9 38415292
2012 New crystal structure of the proteasome-dedicated chaperone Rpn14 at 1.6 Å resolution. Acta crystallographica. Section F, Structural biology and crystallization communications 3 22691779

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