| 2000 |
PI31 is a proline-rich inhibitor of the 20S proteasome; its C-terminal proline-rich domain confers inhibition by forming a proteasome-PI31 complex and blocking hydrolysis of both protein and peptide substrates. PI31 also inhibits activation of the proteasome by regulatory proteins PA700 and PA28. |
Recombinant protein expression in E. coli, truncation mutant analysis, in vitro proteasome activity assays |
The Journal of biological chemistry |
High |
10764772
|
| 2008 |
PI31 interacts with Fbxo7·Skp1 through a conserved N-terminal FP (Fbxo7/PI31) domain that mediates both homodimerization of PI31 and heterodimerization with Fbxo7. The crystal structure of the PI31 FP domain reveals a novel α/β-fold. Knockdown of Fbxo7 does not affect PI31 levels, arguing against PI31 being an SCF(Fbxo7) substrate. |
Crystal structure determination, biophysical analysis (SEC, ITC), site-directed mutagenesis, co-immunoprecipitation, RNAi knockdown |
The Journal of biological chemistry |
High |
18495667
|
| 2014 |
PI31 contains a C-terminal HbYX motif; peptides corresponding to this motif bind to and activate the 20S proteasome in an HbYX-dependent manner, but intact PI31 inhibits 20S activity. PI31 blocks ATP-dependent in vitro assembly of 26S proteasome from 20S and PA700 subcomplexes but has no effect on activity of intact 26S proteasome. Ectopic overexpression or RNAi knockdown of PI31 in cells produced no detectable change in overall cellular proteasome content or function. |
In vitro proteasome activity assays with truncation and point mutants, 26S assembly assay, RNAi knockdown, ectopic overexpression |
The Journal of biological chemistry |
High |
24770418
|
| 2014 |
In yeast (S. cerevisiae), the PI31 ortholog Fub1 is essential when the CP assembly chaperone Pba4 is deleted. Deletion of the N-terminus of α7 (α7ΔN), but not α3ΔN, suppresses the lethality of Δfub1 Δpba4, indicating that Fub1 functionally antagonizes a specific gate-opening role of the α7 N-terminus in CP activation. |
Yeast genetic epistasis (double-mutant analysis), suppressor screen with α-subunit N-terminal deletions |
Molecular and cellular biology |
Medium |
25332237
|
| 2015 |
VCP (type II AAA-ATPase) directly interacts with PSMF1/PI31 and the two proteins antagonistically regulate proteasomal activity. |
Direct interaction assay (co-immunoprecipitation/pull-down implied), proteasome activity measurements |
Biochemical and biophysical research communications |
Medium |
26086101
|
| 2019 |
PI31 serves as an adaptor to couple proteasomes with dynein light chain proteins DYNLL1/2, enabling microtubule-dependent transport of proteasomes in axons. Phosphorylation of PI31 by p38 MAPK enhances PI31 binding to DYNLL1/2 and promotes directional movement of proteasomes in axons. Inactivation of PI31 inhibited proteasome motility in axons and disrupted synaptic proteostasis, structure, and function. |
Co-immunoprecipitation, live-cell axonal transport imaging, phosphorylation assays, PI31 inactivation in Drosophila and mouse neurons, synaptic structure/function readouts |
Developmental cell |
High |
31327739
|
| 2019 |
PI31 interacts with TBK1 and Sec16A at endoplasmic reticulum exit sites (ERES); NOD2/TLR2 signaling causes TBK1 to phosphorylate PI31 in dendritic cells, which positively regulates MHC class I peptide loading and immunoproteasome stability. Depletion of PI31 impairs DC cross-presentation and CD8+ T cell activation. |
Co-immunoprecipitation of PI31 with TBK1 and Sec16A, phosphorylation assay, PI31 depletion in dendritic cells, cross-presentation assay, in vivo CD8+ T cell activation |
Frontiers in immunology |
Medium |
31114588
|
| 2019 |
Conditional knockout of PI31 in mouse spinal motor neurons and cerebellar Purkinje cells causes markers of proteotoxic stress followed by axon degeneration, neuronal loss, and progressive motor dysfunction, establishing PI31 as essential for neuronal protein homeostasis in vivo. |
Conditional knockout mouse model, histological and behavioral analysis, proteotoxic stress markers |
Proceedings of the National Academy of Sciences of the United States of America |
High |
31754024
|
| 2022 |
Cryo-EM structure of S. cerevisiae PI31 (Fub1) inside the proteasome core particle shows that the conserved C-terminal domain simultaneously interacts with all six active sites. Targeted mutations disrupt inhibition at individual active sites independently. Fub1 evades degradation through distinct mechanisms at each active site. The proteasome gate is constitutively closed when Fub1 is bound, and Fub1 is enriched in mutant CPs with an abnormally open gate, suggesting Fub1 neutralizes aberrant proteasomes. |
Cryo-EM structure determination, site-directed mutagenesis of active-site contacts, biochemical proteasome inhibition assays |
Nature structural & molecular biology |
High |
35927584
|
| 2023 |
High-resolution cryo-EM structure of the mammalian 20S proteasome–PI31 complex shows that two copies of the intrinsically disordered C-terminus of PI31 enter the central cavity from opposite ends of the 20S cylinder and interact with catalytic sites in a closed-gate conformation, blocking proteolysis while resisting their own degradation. PI31 can inhibit proteasome activity in mammalian cells. |
Cryo-EM structure determination, cellular proteasome activity assays |
The Journal of biological chemistry |
High |
37236357
|
| 2024 |
PI31 inhibits the constitutive 20S proteasome (20Sc) more strongly than the immunoproteasome (20Si). Unlike 20Sc, 20Si hydrolyzes the C-terminus of PI31, contributing to reduced PI31 inhibitory activity toward 20Si. PI31 point mutants that lose inhibition of 20Sc are degraded by 20Sc. |
In vitro proteasome activity assays with purified 20Sc and 20Si, PI31 point mutant analysis, proteolytic degradation assays |
Biochemistry |
High |
38577872
|
| 2024 |
An FBXO7 L250P patient mutation selectively ablates the Fbxo7–PI31 interaction and causes reduced Fbxo7 and PI31 levels in patient fibroblasts, reduced proteasome activity and proteasome subunit levels. PI31 interacts with mitochondrial fission adaptors MiD49/51 and facilitates SCF(Fbxo7)-mediated ubiquitination of MiD49. |
Patient fibroblast analysis, co-immunoprecipitation, proteasome activity assay, ubiquitination assay, L250P mutant structural validation |
The FEBS journal |
Medium |
38466799
|
| 2024 |
The INF2 R218Q mutation disrupts sequestration of Dynll1 by INF2, freeing Dynll1 to interact with PI31 and promoting dynein-mediated transport of nephrin to the proteasome for degradation. Knockdown of Dynll1 or PI31, dynein inactivation, or proteasome inhibition each restores nephrin proteostasis in R218Q podocytes. |
Genetic knockdown (Dynll1, PI31), dynein inactivation, proteasome inhibition, nephrin stability assays in R218Q KI mouse podocytes, in vivo mouse model |
Kidney360 |
Medium |
39621430
|
| 2025 |
Genetic ablation of PI31 in mammalian cells had no effect on constitutive proteasome content or activity but reduced the cellular content and activity of interferon-γ-induced immunoproteasomes (20Si) due to impaired 20Si assembly, evidenced by accumulation of 20Si assembly intermediates. PI31 thus plays a chaperone-like role specifically in 20Si assembly. |
CRISPR/Cas9 genetic ablation in mammalian cells, immunoproteasome induction by IFN-γ, proteasome activity assays, analysis of assembly intermediates |
Journal of cell science |
High |
39868238 40337847
|
| 2025 |
Restoring PI31 levels in Fbxo7 mutant flies and mice prevents neuronal degeneration and improves neuronal function and lifespan. Fbxo7 inactivation in mouse neurons causes tau hyperphosphorylation, which is suppressed by transgenic PI31 expression, establishing PI31 as the key downstream effector of Fbxo7 in neuroprotection. |
Transgenic PI31 expression in Fbxo7 mutant Drosophila and mouse models, neuronal survival assays, tau phosphorylation analysis, lifespan and locomotor assays |
Proceedings of the National Academy of Sciences of the United States of America |
High |
40956890
|
| 2025 |
Biallelic PSMF1 loss-of-function variants in patients impair mitochondrial membrane potential, dynamics, and mitophagy, and reduce proteasomal abundance and assembly in patient-derived fibroblasts. PI31 loss-of-function in Drosophila causes dopaminergic neurodegeneration and mitochondrial depolarization. |
Patient-derived fibroblast functional assays (mitochondrial membrane potential, dynamics, mitophagy, proteasome assembly), Drosophila and mouse loss-of-function models |
Nature communications |
Medium |
39148840 41986367
|