Affinage

IST1

IST1 homolog · UniProt P53990

Length
364 aa
Mass
39.8 kDa
Annotated
2026-04-28
24 papers in source corpus 17 papers cited in narrative 17 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

IST1 is a divergent ESCRT-III family member that functions as a central adaptor coordinating membrane scission, VPS4 ATPase regulation, and effector recruitment across multiple ESCRT-dependent processes including multivesicular body biogenesis, endosomal recycling, autophagosome–lysosome fusion, and cytokinetic abscission. Its N-terminal domain adopts an ESCRT-III-like fold that binds CHMP1B/Did2, while its C-terminal MIM1 and MIM2 motifs recruit MIT domain–containing partners—VPS4, LIP5, Spartin, Calpain-7, and SNX15—using structurally distinguishable MIM1 versus MIM3 binding modes (PMID:25657007, PMID:18032582, PMID:19129479). IST1 cooperates with CHMP1B to drive scission of endosomal recycling carriers directing transferrin receptor and mannose-6-phosphate receptor trafficking, and pharmacological disruption of the IST1–CHMP1B interaction selectively stalls sorting endosomes and triggers noncanonical LC3 lipidation (PMID:37926552, PMID:38635626). At the midbody, IST1 recruits VPS4 and Calpain-7 whose proteolytic activity is required for both abscission completion and NoCut checkpoint maintenance (PMID:19129479, PMID:37772788).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2007 High

    The fundamental question of how Vps4 is regulated at endosomes was answered by demonstrating that Ist1 dually modulates Vps4—positively via Did2-dependent recruitment and negatively through direct Ist1–Vps4 heterodimerization—establishing Ist1 as a switch-like regulator of ESCRT disassembly.

    Evidence Genetic epistasis, co-immunoprecipitation, and functional MVB sorting assays in S. cerevisiae across two companion studies

    PMID:18032582 PMID:18032584

    Open questions at the time
    • Mechanism of conformational switch between inhibitory and stimulatory states was not resolved
    • Whether Ist1 dual regulation is conserved in mammals was untested
  2. 2009 High

    Translating yeast findings to human biology, IST1 was shown to be required for cytokinetic abscission through MIM1/MIM2-mediated co-recruitment of VPS4 with CHMP1 to midbodies, and its N-terminal domain was crystallized revealing an ESCRT-III-like fold—answering whether IST1 is a bona fide ESCRT-III family member.

    Evidence NMR of MIT–MIM complexes, X-ray crystallography of Ist1 NTD and Ist1–Did2 co-crystal, siRNA depletion with midbody imaging in HeLa cells

    PMID:19129479 PMID:19477918

    Open questions at the time
    • Identity of downstream effectors recruited by IST1 at the midbody beyond VPS4 was unknown
    • Structural basis for autoinhibition inferred from crystal packing was not directly validated
  3. 2010 High

    IST1 was established as a recruitment platform for MIT domain–containing effectors at midbodies, binding both Spartin and Calpain-7 through its MIM motifs—Spartin recruitment is required for normal cytokinesis, and IST1 MIM peptides directly stimulate Calpain-7 catalytic autolysis in vitro.

    Evidence SPR binding kinetics for Spartin–IST1, structure-based mutagenesis blocking midbody localization, reconstituted in vitro Calpain-7 autolysis assays with purified proteins

    PMID:20719964 PMID:20849418

    Open questions at the time
    • Physiological substrates of Calpain-7 activated by IST1 were unknown
    • Whether Spartin and Calpain-7 act in the same or distinct abscission sub-pathways was unclear
  4. 2015 High

    Structural and biochemical work resolved how IST1 discriminates among its multiple MIT-domain partners: crystal structures of IST1 MIM bound to VPS4, LIP5, and Spartin MIT domains revealed that two phenylalanine residues toggle between MIM1 and MIM3 binding modes, and in vitro reconstitution showed that Did2 binding converts Ist1 from a Vps4 inhibitor to a stimulator by altering Ist1 conformation.

    Evidence X-ray crystallography of three MIT–MIM complexes with mutagenesis; ATPase activity assays and ESCRT-III disassembly reconstitution in yeast

    PMID:25657007 PMID:26515066

    Open questions at the time
    • No full-length IST1 structure in active versus autoinhibited state
    • Whether conformational switching occurs in vivo was not demonstrated
  5. 2019 Medium

    IST1's role was extended beyond endosomal sorting and cytokinesis to autophagy: IST1 facilitates CHMP2B–CHMP4B ESCRT-III complex assembly required for autophagosome–lysosome fusion, and tau accumulation pathologically suppresses IST1 transcription via an ANP32A–INHAT histone acetylation mechanism.

    Evidence AAV-mediated IST1 overexpression/knockdown in mouse brain, co-immunoprecipitation of ESCRT-III components, autophagy flux assays

    PMID:31223056

    Open questions at the time
    • Whether IST1 acts directly in membrane fusion or indirectly through ESCRT-III assembly is unresolved
    • Relevance to human tauopathy was not confirmed with patient-derived material
  6. 2022 Medium

    A previously unrecognized post-translational input was identified: IST1 ubiquitination is required for its proper endosomal recruitment and for cargo recycling from endosomes to the plasma membrane, with the AAA-ATPase Cdc48/Npl4 acting in this pathway.

    Evidence Ubiquitination assays, genetic analysis, and live-cell imaging of cargo recycling in yeast

    PMID:36125415

    Open questions at the time
    • The E3 ligase responsible for IST1 ubiquitination was not identified
    • Whether Cdc48 acts directly on ubiquitinated IST1 or indirectly was not resolved
    • Conservation in mammalian cells was not tested
  7. 2023 High

    IST1–CHMP1B was shown to be required for scission of endosomal recycling carriers, with IST1 recruited to distinct endosomal subdomains by alternating partners SNX15 and CHMP1B; concurrently, CAPN7 tandem MIT domains were shown to simultaneously engage two IST1 MIM motifs, and this interaction is required for both abscission and NoCut checkpoint maintenance through CAPN7 proteolytic activity.

    Evidence siRNA depletion with kinetic trafficking assays and live-cell microscopy for recycling; crystallography, mutagenesis, and depletion/rescue with abscission timing for CAPN7–IST1

    PMID:37772788 PMID:37926552

    Open questions at the time
    • Substrates of CAPN7 protease at the midbody remain unidentified
    • How SNX15 versus CHMP1B pools of IST1 are coordinated on the same endosome is unclear
  8. 2024 Medium

    Pharmacological disruption of the IST1–CHMP1B interaction with a specific chemical inhibitor demonstrated that this copolymer is selectively required for endosomal recycling carrier scission but dispensable for cytokinesis, MVB sorting, and extracellular vesicle biogenesis, and that stalled endosomes trigger noncanonical LC3 lipidation.

    Evidence Pseudonatural product inhibitor treatment with transferrin recycling assays, LC3 lipidation assays, and live-cell imaging in mammalian cells

    PMID:38635626

    Open questions at the time
    • Off-target effects of the compound cannot be fully excluded
    • Molecular mechanism linking stalled IST1–CHMP1B endosomes to LC3 lipidation is unknown
  9. 2025 Medium

    IST1 dynamics and neuronal function were characterized: endogenous IST1 exists in distinct stable and transient endosomal pools modulated by growth factor signaling, and in neurons IST1 mediates Spastin-dependent AMPA receptor endosomal recycling required for synaptic transmission.

    Evidence CRISPR-tagged endogenous IST1 live-cell imaging with FRAP-like analysis; co-IP, siRNA knockdown with mEPSC electrophysiology and surface biotinylation in neurons

    PMID:41060239 PMID:41296224

    Open questions at the time
    • How the two endosomal IST1 pools relate to distinct partner complexes is unresolved
    • Whether IST1-dependent AMPAR recycling is relevant to hereditary spastic paraplegia pathology is untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key open questions include the identity of CAPN7 proteolytic substrates at midbodies, the E3 ligase(s) responsible for IST1 ubiquitination, the structural basis for full-length IST1 autoinhibition and activation, and how IST1's multiple partner interactions are spatiotemporally coordinated on endosomal membranes.
  • No full-length IST1 structure in autoinhibited or active conformation
  • CAPN7 substrates at the midbody remain unidentified
  • E3 ligase for IST1 ubiquitination unknown
  • Spatiotemporal coordination of IST1 partner switching on endosomes not resolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 8 GO:0008092 cytoskeletal protein binding 3 GO:0098772 molecular function regulator activity 2
Localization
GO:0005768 endosome 5 GO:0005856 cytoskeleton 3 GO:0005829 cytosol 2
Pathway
R-HSA-5653656 Vesicle-mediated transport 5 R-HSA-1640170 Cell Cycle 3 R-HSA-9609507 Protein localization 3 R-HSA-9612973 Autophagy 1
Partners
CAPN7CHMP1BLIP5PDCD6SNX15SPASTSPG20VPS4
Complex memberships
ESCRT-IIIIST1-CHMP1B copolymerIST1-Did2 complex

Evidence

Reading pass · 17 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2007 Yeast Ist1 localizes to the ESCRT machinery via Did2 and positively regulates recruitment of Vps4, while also forming an Ist1-Vps4 heterodimer that negatively regulates Vps4 by preventing its binding to the ESCRT machinery, thus dually regulating Vps4 activity in MVB vesicle formation. Genetic and biochemical analyses in yeast, including interaction studies and functional assays Molecular biology of the cell High 18032582
2007 Yeast Ist1 forms a physical complex with Did2 (Ist1-Did2 complex) that functions as a positive modulator of late-step MVB sorting; Ist1 is recruited to endosomes in an ESCRT-III-dependent manner and binds the AAA-ATPase Vps4; synthetic genetic interactions place Ist1-Did2 and Vta1-Vps60 as two independent functional units modulating Vps4 and MVB sorting. Synthetic genetic analysis, co-immunoprecipitation, epistasis with vps2/did4 mutations Molecular biology of the cell High 18032584
2009 Human IST1 functions in the ESCRT pathway and is required for efficient cytokinetic abscission in HeLa cells; IST1 contains two distinct MIT-interacting motifs (MIM1 and MIM2) in its C-terminus that bind to different grooves of the VPS4 MIT helical bundle; IST1 and CHMP1 co-recruit VPS4 to midbodies, and depletion of either IST1 or CHMP1 blocks VPS4 recruitment and abscission; IST1 depletion does not inhibit HIV-1 budding. NMR spectroscopy, mutagenesis, siRNA depletion, immunofluorescence microscopy of midbodies, HIV budding assay Molecular biology of the cell High 19129479
2009 The crystal structure of the N-terminal domain of Ist1 reveals an ESCRT-III subunit-like fold, identifying Ist1 as a divergent ESCRT-III family member; co-crystallization with a Did2 fragment shows Ist1NTD binds the Did2 C-terminal MIM1 via a novel MIM-binding structural motif, revealing a mechanism for intermolecular ESCRT-III subunit association and potential intramolecular autoinhibition. X-ray crystallography, co-crystallization of Ist1NTD with Did2 fragment Molecular biology of the cell High 19477918
2010 The SPG20 protein spartin is recruited to midbodies by IST1 via direct MIT-MIM interaction; spartin MIT domain binds IST1 (but not CHMP1-7) with micromolar affinity measured by surface plasmon resonance; a structure-based F24D mutation in spartin MIT domain blocks spartin-IST1 interaction, prevents spartin midbody localization, and acts dominantly to impair cytokinesis. Yeast two-hybrid, surface plasmon resonance, siRNA depletion, structure-based mutagenesis, immunofluorescence Molecular biology of the cell High 20719964
2010 Human IST1 binds to the tandem MIT domains of calpain-7 via MIM1 and MIM2 motifs; the IST1 MIM peptide directly stimulates autolytic activity of purified calpain-7 in vitro, and this autolysis requires the catalytic Cys290 residue; IST1 together with CHMP1B increases calpain-7 membrane/organelle association. GST pulldown, co-immunoprecipitation, in vitro autolysis assay with purified proteins, mutagenesis The FEBS journal High 20849418
2011 Calpain-7 binds to the second α-helical region (not canonical C-terminal MIM1) of CHMP1B via its MIT domains; IST1 and CHMP1B together form a ternary complex with calpain-7, and co-expression of both CHMP1B and IST1 further enhances calpain-7 autolysis in HEK293T cells. In vitro pulldown with purified proteins, co-immunoprecipitation, subcellular fractionation, cell-based autolysis assay Journal of biochemistry Medium 21616915
2013 Mammalian IST1 interacts with the Ca2+-binding protein ALG-2 in a Ca2+-dependent manner; the distinctive Met-Pro repeat sequence in IST1's proline-rich region is essential for this interaction; co-expression with CHMP1 proteins enhances ALG-2 binding to IST1. Far-Western analysis with biotinylated ALG-2, GST pulldown assays with deletion and point mutants Bioscience, biotechnology, and biochemistry Medium 23649269
2015 Crystal structures of IST1 MIM bound to the MIT domains of VPS4, LIP5, and Spartin reveal that IST1 uses two distinct binding mechanisms (MIM1 mode vs. MIM3 mode) depending on the partner; two phenylalanine residues within IST1 MIM discriminate between MIM1 and MIM3 binding modes. X-ray crystallography of three MIT-MIM complexes, structure-guided mutagenesis The Journal of biological chemistry High 25657007
2015 Yeast Ist1 inhibits Vps4 ATPase activity via two elements: its MIM and a surface containing a conserved ELYC sequence; a more open conformation of Ist1 core converts Ist1 from inhibitor to stimulator of Vps4; binding of Did2 to Ist1 also converts Ist1 from inhibitor to stimulator of Vps4 ATPase activity and alters ESCRT-III disassembly in vitro. ATPase activity assays, in vitro ESCRT-III disassembly assay, mutagenesis The Journal of biological chemistry High 26515066
2019 IST1 is a positive modulator for ESCRT-III complex formation required for autophagosome-lysosome fusion; IST1 facilitates association of CHMP2B and CHMP4B to form ESCRT-III complex; MAPT/tau accumulation suppresses IST1 transcription through an ANP32A-INHAT-mediated histone acetylation mechanism; downregulation of IST1 impedes ESCRT-III complex formation and blocks autophagosome-lysosome fusion. AAV-mediated IST1 overexpression/knockdown in mice, co-immunoprecipitation, autophagy flux assays (LC3-II, p62, autophagosome accumulation) Autophagy Medium 31223056
2022 In yeast, IST1 is ubiquitinated and this ubiquitination is required for proper endosomal recruitment of IST1 and for cargo recycling from endosomes to the plasma membrane; the AAA-ATPase Cdc48 and its adaptor Npl4 are required for this recycling pathway, potentially via regulation of ubiquitinated IST1. Genetic analysis, live-cell imaging, ubiquitination assays in yeast The Journal of cell biology Medium 36125415
2023 Human IST1, together with its binding partner CHMP1B, contributes to scission of early endosomal carriers; IST1 depletion impairs transferrin receptor delivery from early/sorting endosomes to the endocytic recycling compartment and mannose-6-phosphate receptor export; IST1 interacts with the MIT domain-containing sorting nexin SNX15 on endosomes; SNX15 and CHMP1B alternately recruit IST1 to distinct endosomal subdomains (clathrin-containing subdomain vs. base of endosomal tubules). siRNA depletion, live-cell microscopy, co-immunoprecipitation, kinetic trafficking assays Traffic (Copenhagen, Denmark) Medium 37926552
2023 CAPN7 (Calpain-7) tandem MIT domains bind simultaneously to two distinct MIM motifs on IST1; structure-guided point mutations in either CAPN7 MIT domain disrupt IST1 binding in vitro and in cells; the CAPN7-IST1 interaction is required for CAPN7 recruitment to midbodies, efficient cytokinetic abscission, and NoCut checkpoint arrest; CAPN7 proteolytic activity (not just binding) is also required for abscission and checkpoint maintenance. Crystallography, in vitro binding assays, mutagenesis, depletion/rescue experiments, live-cell imaging of abscission eLife High 37772788
2024 A pseudonatural product chemical inhibitor specifically disrupts the IST1-CHMP1B interaction, inhibiting formation of IST1-CHMP1B copolymers required for normal-topology membrane scission; inhibition rapidly blocks transferrin receptor recycling causing accumulation in stalled sorting endosomes; stalled endosomes become decorated with lipidated LC3, linking IST1-CHMP1B function to noncanonical LC3 lipidation; the compound does not affect cytokinesis, MVB sorting, or extracellular vesicle biogenesis. Chemical inhibitor treatment, transferrin recycling assay, LC3 lipidation assay, live-cell imaging Proceedings of the National Academy of Sciences of the United States of America Medium 38635626
2025 Endogenous IST1 exists in at least two distinct pools on endosomes in mammalian cells: one transient and one relatively stable; upon growth factor stimulation, the stable pool becomes more mobile and the transient pool accumulates more rapidly; ESCRT-III dynamics are distinct from other ESCRT complexes. High-speed live-cell imaging of endogenous IST1 (CRISPR-tagged), FRAP-like dynamics analysis The Journal of cell biology Medium 41060239
2025 DeSUMOylated Spastin (K427R mutant) shows enhanced binding to IST1 compared to wild-type Spastin; IST1 co-overexpression with Spastin enhances synaptic transmission and spine maturation; IST1 knockdown reduces GluA1 (AMPAR) surface levels and abolishes Spastin's effects on AMPAR recycling, placing IST1 as a mediator of Spastin-dependent AMPAR endosomal sorting. Co-immunoprecipitation, siRNA knockdown, electrophysiology (mEPSC), surface biotinylation, confocal imaging Molecular neurobiology Medium 41296224

Source papers

Stage 0 corpus · 24 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2019 MAPT/Tau accumulation represses autophagy flux by disrupting IST1-regulated ESCRT-III complex formation: a vicious cycle in Alzheimer neurodegeneration. Autophagy 159 31223056
2007 Ist1 regulates Vps4 localization and assembly. Molecular biology of the cell 116 18032582
2009 Biochemical analyses of human IST1 and its function in cytokinesis. Molecular biology of the cell 114 19129479
2007 Novel Ist1-Did2 complex functions at a late step in multivesicular body sorting. Molecular biology of the cell 109 18032584
2009 Structural basis of Ist1 function and Ist1-Did2 interaction in the multivesicular body pathway and cytokinesis. Molecular biology of the cell 78 19477918
2010 SPG20 protein spartin is recruited to midbodies by ESCRT-III protein Ist1 and participates in cytokinesis. Molecular biology of the cell 67 20719964
2016 Role of SKD1 Regulators LIP5 and IST1-LIKE1 in Endosomal Sorting and Plant Development. Plant physiology 58 26983994
1998 Expression of Mel-CAM in implantation site intermediate trophoblastic cell line, IST-1, limits its migration on uterine smooth muscle cells. Journal of cell science 51 9701564
2015 Distinct mechanisms of recognizing endosomal sorting complex required for transport III (ESCRT-III) protein IST1 by different microtubule interacting and trafficking (MIT) domains. The Journal of biological chemistry 34 25657007
2010 Autolytic activity of human calpain 7 is enhanced by ESCRT-III-related protein IST1 through MIT-MIM interaction. The FEBS journal 34 20849418
1999 IST1 insertional inactivation of the resB gene: implications for phenotypic switching in Thiobacillus ferrooxidans. FEMS microbiology letters 22 10386372
2022 Recycling of cell surface membrane proteins from yeast endosomes is regulated by ubiquitinated Ist1. The Journal of cell biology 19 36125415
2015 Conformational Changes in the Endosomal Sorting Complex Required for the Transport III Subunit Ist1 Lead to Distinct Modes of ATPase Vps4 Regulation. The Journal of biological chemistry 17 26515066
2024 A chemical inhibitor of IST1-CHMP1B interaction impairs endosomal recycling and induces noncanonical LC3 lipidation. Proceedings of the National Academy of Sciences of the United States of America 11 38635626
2011 Calpain-7 binds to CHMP1B at its second α-helical region and forms a ternary complex with IST1. Journal of biochemistry 11 21616915
2023 IST1 regulates select recycling pathways. Traffic (Copenhagen, Denmark) 10 37926552
2023 The Calpain-7 protease functions together with the ESCRT-III protein IST1 within the midbody to regulate the timing and completion of abscission. eLife 9 37772788
2013 Mammalian ESCRT-III-related protein IST1 has a distinctive met-pro repeat sequence that is essential for interaction with ALG-2 in the presence of Ca2+. Bioscience, biotechnology, and biochemistry 9 23649269
2024 Reduced circ_lrrc49 in trigeminal ganglion contributes to neuropathic pain in mice by downregulating Ist1 and impairing autophagy. Journal of neurochemistry 5 38348636
2025 DeSUMOylation of Spastin Enhances AMPA Receptor Recycling and Synaptic Plasticity via IST1-Dependent Endosomal Sorting. Molecular neurobiology 1 41296224
2025 Insulin receptor substrate family member IST-1 regulates the development of Caenorhabditis elegans age-1 and aap-1 mutants. microPublication biology 0 40642152
2025 Analysis of native Ist1 dynamics reveals multiple pools of ESCRT-III on endosomes. The Journal of cell biology 0 41060239
2025 IST1 alleviated acrylamide-induced apoptosis and cognitive impairment through regulating autophagy flux blockage in SH-SY5Y cells and C57BL/6J mice. Ecotoxicology and environmental safety 0 41187541
2023 IST1 regulates select endosomal recycling pathways. bioRxiv : the preprint server for biology 0 37577466