{"gene":"ATG4B","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2009,"finding":"Crystal structures of catalytically inert human ATG4B in complex with processed and unprocessed LC3 reveal the mechanism of substrate recognition and catalysis: the regulatory loop masking the active site entrance is lifted by LC3 Phe119, forming a groove for the LC3 tail to enter the active site, while the N-terminal tail masking the active site exit is detached, exposing a flat surface that may enable access to membrane-bound LC3-PE.","method":"X-ray crystallography of ATG4B–LC3 complex (catalytically inert mutant); structural analysis of conformational changes upon substrate binding","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional interpretation, direct structural evidence for mechanism, published in high-impact journal with extensive subsequent citation and validation","pmids":["19322194"],"is_preprint":false},{"year":2005,"finding":"Crystal structure of human ATG4B at 2.0 Å resolution shows it is a cysteine protease with a catalytic triad of Cys74, His280, and Asp278, comprising a 'protease domain' resembling papain superfamily cysteine proteinases and an 'auxiliary domain' of unknown function; residues R229 and W142 are specifically essential for substrate recognition and catalysis of both precursor processing and de-conjugation.","method":"X-ray crystallography; site-directed mutagenesis of active-site residues","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with mutagenesis validation of catalytic residues, independently replicated in subsequent structural studies","pmids":["16325851"],"is_preprint":false},{"year":2003,"finding":"A single protease, ATG4B (Apg4B/autophagin-1), is the processing and deconjugating enzyme for all four mammalian ATG8 homologues: GATE-16, GABARAP, MAP1-LC3, and Apg8L, as demonstrated by electrophilic activity-based probes that form specific adducts in crude cell lysates.","method":"Activity-based protein profiling with electrophilic ubiquitin-like probes; adduct formation in cell lysates","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — chemical biology (activity-based probes) directly identifying the enzyme, replicated by subsequent biochemical and genetic studies across multiple labs","pmids":["14530254"],"is_preprint":false},{"year":2017,"finding":"MST4 (STK26) kinase phosphorylates ATG4B at serine residue 383, which stimulates ATG4B protease activity and increases autophagic flux; radiation induces MST4 expression, ATG4B phosphorylation, and autophagy; inhibition of MST4 or ATG4B suppresses autophagy and glioblastoma tumorigenicity.","method":"In vitro kinase assay; phospho-specific antibodies; genetic knockdown/overexpression; xenograft mouse models","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro kinase assay plus multiple orthogonal cellular and in vivo genetic approaches across multiple conditions","pmids":["29232556"],"is_preprint":false},{"year":2017,"finding":"ULK1 phosphorylates ATG4B at serine 316, resulting in inhibition of its catalytic activity both in vitro and in vivo; the phosphatase PP2A-PP2R3B removes this inhibitory phosphorylation, providing a reversible phospho-switch that regulates ATG4B activity to coordinate LC3 processing during autophagy.","method":"In vitro kinase assay; phospho-mimetic and phospho-deficient mutants; co-immunoprecipitation; cell-based autophagy assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay plus mutagenesis plus phosphatase identification, single lab with multiple orthogonal methods","pmids":["28821708"],"is_preprint":false},{"year":2015,"finding":"Phosphorylation of ATG4B at Ser-383 and Ser-392 increases its hydrolase activity toward LC3 substrate; phosphorylation-deficient ATG4B shows reduced interactions with lipid-conjugated LC3 (but not unconjugated LC3), and reconstitution of atg4b−/− cells with phospho-deficient ATG4B demonstrates a role for these sites in LC3 delipidation and autophagic flux.","method":"In vitro biochemical hydrolase assay; reconstitution of atg4b−/− cells; co-immunoprecipitation; flow cytometry","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro activity assay, reconstitution in knockout cells, and multiple orthogonal readouts, single lab","pmids":["26378241"],"is_preprint":false},{"year":2015,"finding":"A REDD1/TXNIP pro-oxidant complex regulates ATG4B activity through reactive oxygen species: stress conditions induce ROS via REDD1/TXNIP, which suppresses the redox-sensitive ATG4B cysteine endopeptidase activity, thereby reducing LC3B delipidation and activating autophagy; loss of REDD1 or TXNIP increases ATG4B catalytic activity and causes failed autophagy in vivo.","method":"ATG4B catalytic activity assays; REDD1−/− and TXNIP knockout cells/mice; ROS measurement; mitochondrial function assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — enzymatic activity assays plus genetic knockout models plus in vivo phenotypic validation, multiple orthogonal methods","pmids":["25916556"],"is_preprint":false},{"year":2012,"finding":"The membrane-associated E3 ubiquitin ligase RNF5 ubiquitinates ATG4B and controls its stability, specifically regulating the membranal fraction of ATG4B and thereby limiting LC3 processing, phagophore formation, and basal autophagy levels; RNF5 mutants retaining E3 ligase activity but unable to associate with ATG4B no longer affect LC3 puncta.","method":"Co-immunoprecipitation; ubiquitination assays; RNF5−/− MEFs; LC3 puncta quantification; bacterial infection models","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, knockout cell lines, domain-mapping mutants, and in vivo infection model providing multiple independent lines of evidence","pmids":["23093945"],"is_preprint":false},{"year":2017,"finding":"ATG4B S-nitrosation at Cys189 and Cys292 (induced by high glucose/NO) compromises both its pro-LC3 processing and LC3-PE deconjugation activities, suppressing autophagosome biogenesis and causing neurotoxicity; GABARAPL1 processing is least affected by this modification compared to other substrates.","method":"LC-MS/MS-based quantitative S-nitrosation proteomics; site-directed mutagenesis (Cys189, Cys292); ATG4B activity assays; mRFP-GFP-LC3 flux analysis; neuronal cell culture models","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — proteomics identification plus mutagenesis validation plus activity assays plus cellular phenotype in single study with multiple orthogonal methods","pmids":["28633005"],"is_preprint":false},{"year":2018,"finding":"AKT phosphorylates ATG4B at Ser34, which has little effect on autophagic flux but promotes the Warburg effect (increased lactate, glucose consumption, decreased oxygen consumption) in HCC cells by impairing mitochondrial function including F1Fo-ATP synthase activity; Ser34 phosphorylation enhances ATG4B mitochondrial localization and co-localization with F1Fo-ATP synthase.","method":"In vitro kinase assay; phospho-site mutagenesis; metabolic assays; subcellular fractionation; co-immunoprecipitation; submitochondrial particle reconstitution assay","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro kinase assay plus multiple functional readouts, single lab","pmids":["29165041"],"is_preprint":false},{"year":2021,"finding":"PFKP (phosphofructokinase 1 platelet isoform) acts as a protein kinase that phosphorylates ATG4B at Ser34 under amino acid deprivation; this phosphorylation enhances ATG4B protease activity and autophagic flux; amino acid deprivation strengthens the ATG4B–PFKP interaction, and PFKP loss reduces LC3-II degradation.","method":"Tandem affinity purification/mass spectrometry; co-immunoprecipitation; in vitro kinase assay; CRISPR/Cas9 knockout; phospho-site mutagenesis; autophagy flux assays","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay plus CRISPR knockout plus mutagenesis, single lab","pmids":["33607258"],"is_preprint":false},{"year":2024,"finding":"UBE3C is an E3 ubiquitin ligase of ATG4B that assembles K33-branched ubiquitin chains on ATG4B at Lys119 without causing ATG4B degradation; K33-ubiquitination reduces ATG4B protease activity and ATG4B–LC3 interaction, inhibiting autophagic flux; under starvation, the ATG4B–UBE3C interaction decreases and K33-linked ubiquitin chains are removed.","method":"Mass spectrometry identification of interactors; co-immunoprecipitation; ubiquitin chain-type analysis; ATG4B activity assays; site-directed mutagenesis (K119R); overexpression/knockout experiments","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — MS-based identification plus IP-based chain typing plus activity assays plus mutagenesis, single lab","pmids":["38146933"],"is_preprint":false},{"year":2022,"finding":"SIRT2 deacetylates ATG4B at lysine 39 (K39), enhancing ATG4B protease activity and autophagic flux; EP300/p300 acetylates ATG4B K39, antagonizing SIRT2; starvation reduces the CCNE-CDK2 complex, decreases SIRT2 Ser331 phosphorylation, activates SIRT2, promotes ATG4B K39 deacetylation, and initiates autophagy; validated in sirt2−/− mice.","method":"Co-immunoprecipitation; ATG4B activity assays; site-directed mutagenesis (K39); sirt2−/− mouse model; phosphorylation/deacetylation biochemical assays","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — enzymatic activity assays, mutagenesis, and in vivo knockout model, single lab","pmids":["36056541"],"is_preprint":false},{"year":2019,"finding":"TMED10 directly binds to ATG4B and negatively regulates its proteolytic activity for LC3 cleavage; this interaction is diminished under autophagy-activating conditions (rapamycin, serum deprivation); in Alzheimer disease, reduced TMED10 expression increases ATG4B activity and autophagy.","method":"Bimolecular fluorescence complementation (BiFC); co-immunoprecipitation; ATG4B protease activity assays; siRNA knockdown; amyloid-β treatment experiments","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — direct protein-protein interaction by BiFC and co-IP plus activity assays, single lab","pmids":["30821607"],"is_preprint":false},{"year":2017,"finding":"The small GTPase Rab7b interacts and co-localizes with ATG4B on vesicles; Rab7b depletion increases autophagic flux, and Rab7b regulates LC3 processing by modulating ATG4B activity, identifying Rab7b as a negative regulator of autophagy through its interaction with ATG4B.","method":"Co-immunoprecipitation; co-localization by fluorescence microscopy; autophagic flux assays; Rab7b knockdown","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — co-IP plus co-localization plus functional assays, single lab","pmids":["28835545"],"is_preprint":false},{"year":2006,"finding":"Human ATG4B (but not ATG4A or ATG4C) cleaves the C-terminus of Atg8L in vitro, and Atg8L undergoes E1 (ATG7) and E2 (ATG3) conjugation reactions, identifying it as the fourth mammalian ATG8-conjugation modifier processed by ATG4B.","method":"In vitro cleavage assay; E1/E2 intermediate trapping with catalytic mutants; subcellular fractionation; fluorescence co-localization","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution of cleavage and conjugation reactions, single lab","pmids":["16704426"],"is_preprint":false},{"year":2006,"finding":"ATG4B knockdown in PC12 cells suppresses the in vitro cleavage of recombinant proLC3 to LC3-I, confirming ATG4B plays a major role in LC3 processing; ATG4B protein and mRNA are ubiquitously expressed across rat tissues with highest levels in brain (particularly neurons of cerebellum and olfactory bulb) and testis.","method":"RNA interference; recombinant proLC3 cleavage assay; Western blot; immunohistochemistry; in situ hybridization","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi knockdown with in vitro activity assay readout, single lab","pmids":["16874114"],"is_preprint":false},{"year":2009,"finding":"Overexpression of catalytically inactive ATG4B(C74A) mutant sequesters LC3 paralogues, blocks formation of the ATG7–LC3 intermediate, causes accumulation of ATG5-positive autophagic structures, and prevents autophagosome closure, demonstrating that excess ATG4B mutant inhibits autophagy at the level of LC3 lipidation and autophagosome sealing.","method":"Overexpression of dominant-negative mutant; immunofluorescence of autophagic structures; biochemical intermediate trapping assays","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic analysis using dominant-negative approach with multiple cellular readouts, single lab","pmids":["19104152"],"is_preprint":false},{"year":2013,"finding":"C/EBPβ transcriptionally activates Atg4b expression by directly binding to its promoter, which is required for autophagy induction during adipocyte differentiation; Atg4b-dependent autophagy mediates degradation of Klf2 and Klf3 (negative regulators of adipogenesis) via the adaptor protein p62/SQSTM1.","method":"ChIP assay; promoter reporter assays; ATG4B knockdown/overexpression in 3T3-L1 cells; mouse models; p62 interaction studies","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP validation of direct promoter binding plus functional rescue experiments plus in vivo confirmation, single lab","pmids":["23754749"],"is_preprint":false},{"year":2017,"finding":"Egr-1 transcription factor binds to the ATG4B promoter upon ionizing radiation and upregulates ATG4B expression in HCC cells, thereby inducing protective autophagy and radioresistance; dominant-negative Egr-1 suppresses radiation-induced ATG4B expression, autophagy, and cell migration.","method":"Luciferase reporter assay; chromatin immunoprecipitation (ChIP); dominant-negative Egr-1 overexpression; autophagy and clonogenic survival assays","journal":"Oncogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and reporter assay demonstrating direct promoter binding plus functional consequence, single lab","pmids":["28134935"],"is_preprint":false},{"year":2017,"finding":"ATG4B and LC3B mediate melanosome trafficking on cytoskeletal tracks: LC3B labels melanosomes and enables assembly of a microtubule translocon complex for intracellular positioning; ATG4B enzymatically delipidates LC3B from melanosomal membranes at the microtubule-actin crossover junction; melanosomes transferred to keratinocytes lack melanocyte-specific LC3B.","method":"Live-cell fluorescence imaging; enzymatic ATG4B activity assays; cytoskeletal co-localization; keratinocyte transfer assays","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — live imaging plus enzymatic activity evidence for delipidation at specific cellular location, single lab","pmids":["28598240"],"is_preprint":false},{"year":2022,"finding":"ATG4B localizes to early autophagic membranes in an LC3B-dependent manner; during autophagy, ATG4B and LC3B undergo rapid cytosol/isolation membrane exchange but not at completed autophagosomes; ATG4B activity controls the efficiency of autophagosome formation by impacting LC3B membrane binding/dissociation.","method":"Fluorescence recovery after photobleaching (FRAP) of GFP-tagged ATG4B and LC3B in living cells; autophagy inhibitor experiments","journal":"Journal of molecular cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct live-cell FRAP measurements linking localization dynamics to functional consequence, single lab","pmids":["34562084"],"is_preprint":false},{"year":2013,"finding":"ATG4B interacts with Bcl-2 by co-immunoprecipitation, and ATG4B upregulation promotes disassociation of the Bcl-2–Beclin1 complex, releasing Beclin1 to activate the autophagic pathway in cadmium-treated A549 cells.","method":"Co-immunoprecipitation; ATG4B knockdown/overexpression; Bcl-2–Beclin1 interaction assays; autophagy flux measurements","journal":"Free radical biology & medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP experiment in one cell line under one treatment condition, single lab","pmids":["30458278"],"is_preprint":false},{"year":2015,"finding":"SLC27A4 directly interacts with ATG4B (by co-IP and GST pull-down) in lung cancer cells, maintains ATG4B protein stability and intracellular concentration, and thereby facilitates autophagy induction in response to nutrient deprivation or chemotherapy stress.","method":"Tandem affinity purification/mass spectrometry; co-immunoprecipitation; GST pull-down assay; siRNA knockdown; autophagic flux assays","journal":"Tumour biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — co-IP and pull-down with functional follow-up, single lab, limited mechanistic detail in abstract","pmids":["26662804"],"is_preprint":false},{"year":2022,"finding":"Copper ion (but not other metal ions) directly inhibits ATG4B protease activity and induces ATG4B cysteine oxidation-dependent oligomer formation; copper promotes formation of insoluble ATG4B aggregates along with p62- and ubiquitin-positive aggregates; ATG4B overexpression partially reduces Mallory body formation and rescues impaired autophagy in Wilson disease cell models.","method":"In vitro ATG4B activity assay with copper; cysteine oxidation/oligomerization assays; cell-based autophagy flux assays; Wilson disease cell model","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro enzyme inhibition assay plus cellular mechanistic follow-up, single lab with multiple orthogonal methods","pmids":["35349929"],"is_preprint":false},{"year":2020,"finding":"ATG4B cleaves LC3-PE using a molecular ruler mechanism dependent on the LC3 C-terminal motif (residues Gln116, Phe119, Gly120); the C-terminal tail of ATG4B is required for LC3 binding and proteolysis (contributing ≥1000-fold to binding affinity) but not for cleavage of a short peptide substrate; distinct from the Legionella effector RavZ which lacks this molecular ruler mechanism.","method":"Semisynthetic LC3-PE proteins with C-terminal mutations; molecular docking; biochemical cleavage assays; ATG4B truncation mutants","journal":"Chembiochem","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and structural modeling, single lab","pmids":["32686895"],"is_preprint":false},{"year":2022,"finding":"Biochemical and biophysical characterization shows the ubiquitin-like core of LC3B (residues 1–115, lacking the C-terminal cleavage site) binds full-length ATG4B with a KD in the low nanomolar range (10–30-fold tighter than pro-LC3B substrate); the C-terminal tail of ATG4B contributes ≥1000-fold higher binding affinity; binding of LC3B-115 does not alter the ATG4B active-site conformation, supporting a bipartite binding model.","method":"Biochemical binding assays (KD measurement); inhibition assays (IC50); ATG4B truncation mutants; peptide substrate cleavage assays","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — rigorous in vitro biochemical characterization with mutants defining binding domains, single lab","pmids":["36264309"],"is_preprint":false},{"year":2023,"finding":"ATG4B promotes GABARAP-directed selective autophagic degradation of TBK1, thereby antagonizing antiviral type-I interferon signaling; ATG4B knockdown enhances IFN signaling and antiviral immunity.","method":"siRNA knockdown; co-immunoprecipitation; autophagic flux assays; IFN reporter assays; viral replication assays","journal":"Autophagy","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, limited mechanistic detail in abstract, co-IP and knockdown only","pmids":["37434364"],"is_preprint":false},{"year":2019,"finding":"ATG4B host cysteine protease can hydrolyze the substrate of EV71 3C protease with comparable activity, and genetic disruption of ATG4B reduces EV71 viral proliferation in vivo, identifying ATG4B as indispensable for EV71 replication.","method":"Activity-based protein profiling (ABP); in vitro substrate cleavage assays; ATG4B genetic disruption; viral titer assays","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — activity-based profiling plus in vitro enzymatic assay plus genetic disruption in vivo, single lab","pmids":["31554687"],"is_preprint":false},{"year":2021,"finding":"SIRT3 deacetylates ATG4B, and DHM (dihydromyricetin) increases SIRT3 expression leading to SIRT3-mediated ATG4B deacetylation, upregulating ATG4B protein levels and inducing autophagy to attenuate palmitic acid-induced oxidative stress in hepatocytes; the protective effect is abolished in SIRT3-inhibited or ATG4B heterozygous knockout cells.","method":"Western blot for ATG4B acetylation; SIRT3 inhibitor treatment; ATG4B+/− heterozygous knockout cells; ROS and mitochondrial function assays","journal":"Nutrition & metabolism","confidence":"Low","confidence_rationale":"Tier 3 / Weak — indirect evidence for deacetylation (no direct deacetylation assay described in abstract), single lab","pmids":["34503544"],"is_preprint":false},{"year":2023,"finding":"ATG4B accumulates in pancreatic acinar cells after ethanol treatment, directly inhibits autophagosome formation by reducing LC3-II levels through enhanced ATG4B enzymatic activity and strengthened interaction with LC3-II; adenoviral ATG4B overexpression inhibits autophagy and aggravates trypsinogen activation and necrosis; shRNA ATG4B knockdown enhances autophagosome formation and alleviates ethanol-induced acinar cell damage.","method":"Mouse model of alcoholic pancreatitis; adenoviral overexpression; shRNA knockdown; ATG4B activity assays; LC3-II quantification; trypsinogen activation assays","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo model plus gain- and loss-of-function with enzymatic activity measurement, single lab","pmids":["37431575"],"is_preprint":false},{"year":2017,"finding":"HSF1 transcription factor upregulates ATG4B expression by directly binding to the ATG4B gene promoter at position −1429 to −1417, thereby enhancing epirubicin-induced protective autophagy and reducing HCC cell sensitivity to chemotherapy.","method":"Luciferase reporter assay; chromatin immunoprecipitation (ChIP); HSF1/ATG4B knockdown; xenograft mouse models","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and reporter assay demonstrating direct promoter binding with functional consequence, single lab","pmids":["28889000"],"is_preprint":false},{"year":2023,"finding":"Pro-LC3B accumulated aberrantly at the centrosome upon ATG4B knockout, with concomitant increases in centrosomal proteins PCM1 and CEP131; this was rescued by exogenous ATG4B, revealing a role for ATG4B in processing LC3B at the centrosome to permit normal cell cycle progression; ATG4B and ATG4A double knockout causes delays in both G1-S phase transition and mitosis.","method":"CRISPR/Cas9 ATG4B/ATG4A single and double knockout; immunofluorescence; rescue experiments; cell cycle analysis","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR knockout with rescue experiments and centrosomal localization phenotype, single lab","pmids":["37701987"],"is_preprint":false}],"current_model":"ATG4B is a cysteine protease (catalytic triad Cys74-His280-Asp278) that acts as the sole processing and deconjugating enzyme for all mammalian ATG8 homologues (LC3, GABARAP, GATE-16, Apg8L/ATG8L); substrate recognition involves LC3 Phe119 lifting a regulatory loop and engagement of the ATG4B C-terminal tail in a bipartite interaction; its activity is tightly regulated by multiple post-translational modifications including stimulatory phosphorylation at Ser383/392 by MST4 and AKT, inhibitory phosphorylation at Ser316 by ULK1 (reversed by PP2A-PP2R3B), inhibitory K33-ubiquitination at Lys119 by UBE3C, inhibitory acetylation at Lys39 by EP300 (reversed by SIRT2 deacetylation), inhibitory S-nitrosation at Cys189/Cys292, redox-dependent inhibition by ROS via the REDD1/TXNIP complex, and stability control through RNF5-mediated ubiquitination of the membrane-associated pool; transcriptional regulation by C/EBPβ, Egr-1, and HSF1 links ATG4B expression to adipogenesis, radiation stress, and chemoresistance; ATG4B additionally mediates melanosome trafficking by delipidating LC3B from melanosomal membranes, interacts with Rab7b on vesicles to modulate autophagic flux, participates in centrosomal LC3 processing for cell cycle progression, and promotes selective autophagic degradation of TBK1 to antagonize innate immune signaling."},"narrative":{"mechanistic_narrative":"ATG4B is the cysteine protease that processes and deconjugates all four mammalian ATG8 homologues (LC3, GABARAP, GATE-16, Apg8L/ATG8L), positioning it as a central enzymatic node in the autophagy machinery [PMID:14530254, PMID:16704426]. It is a papain-superfamily cysteine protease with a Cys74-His280-Asp278 catalytic triad whose active-site entrance is masked by a regulatory loop; substrate engagement is driven by LC3 Phe119 lifting this loop to admit the LC3 tail, while the N-terminal tail detaches to expose a flat surface compatible with access to membrane-bound LC3-PE [PMID:19322194, PMID:16325851]. Recognition is bipartite and exquisitely sequence-specific: the LC3 ubiquitin-like core binds full-length ATG4B with low-nanomolar affinity and the ATG4B C-terminal tail contributes a ≥1000-fold affinity gain, while a 'molecular ruler' mechanism reading the LC3 C-terminal motif (Gln116/Phe119/Gly120) confers cleavage-site fidelity [PMID:32686895, PMID:36264309]. ATG4B performs both pro-LC3 priming and LC3-PE delipidation, and its catalytic level must be balanced—dominant-negative ATG4B(C74A) sequesters LC3 and blocks autophagosome closure, whereas its delipidation activity controls LC3 membrane binding/dissociation dynamics and the efficiency of autophagosome formation at early autophagic membranes [PMID:19104152, PMID:34562084]. ATG4B activity is governed by a dense layer of post-translational control: stimulatory phosphorylation at Ser383/Ser392 by MST4 and at Ser34 by PFKP enhances protease activity and flux, ULK1 phosphorylation at Ser316 inhibits it (reversed by PP2A-PP2R3B), and additional inhibitory inputs include UBE3C-mediated K33 ubiquitination at Lys119, EP300 acetylation at Lys39 (antagonized by SIRT2 deacetylation), S-nitrosation at Cys189/Cys292, and ROS/REDD1-TXNIP redox suppression; RNF5 ubiquitination controls the stability of the membrane-associated pool [PMID:29232556, PMID:33607258, PMID:28821708, PMID:38146933, PMID:36056541, PMID:25916556, PMID:23093945, PMID:28633005]. At the transcriptional level, C/EBPβ, Egr-1, and HSF1 link ATG4B expression to adipogenesis and to radiation- and chemotherapy-induced protective autophagy [PMID:23754749, PMID:28134935, PMID:28889000]. Beyond bulk autophagy, ATG4B delipidates LC3B from melanosomal membranes during melanosome trafficking, processes centrosomal LC3B to permit normal cell cycle progression, and promotes GABARAP-directed selective degradation of TBK1 to dampen type-I interferon signaling [PMID:28598240, PMID:37701987, PMID:37434364].","teleology":[{"year":2003,"claim":"Establishing which enzyme processes the mammalian ATG8 family was prerequisite to understanding LC3 lipidation; activity-based profiling identified ATG4B as the single protease handling all four homologues.","evidence":"Activity-based protein profiling with electrophilic ubiquitin-like probes in cell lysates","pmids":["14530254"],"confidence":"High","gaps":["Did not resolve substrate-specific kinetic differences among the four ATG8 homologues","No structural basis for recognition yet"]},{"year":2005,"claim":"Defining the catalytic machinery showed ATG4B is a papain-like cysteine protease, identifying the residues required for both precursor processing and deconjugation.","evidence":"X-ray crystallography at 2.0 Å plus active-site mutagenesis (Cys74, His280, Asp278; R229, W142)","pmids":["16325851"],"confidence":"High","gaps":["Function of the auxiliary domain unresolved","No substrate-bound structure to explain selectivity"]},{"year":2006,"claim":"Genetic and reconstitution work confirmed ATG4B as the dominant LC3-processing enzyme and added Atg8L as a bona fide substrate, completing the substrate roster.","evidence":"In vitro cleavage and E1/E2 conjugation reconstitution; RNAi in PC12 cells; tissue expression profiling","pmids":["16704426","16874114"],"confidence":"Medium","gaps":["Relative contributions of ATG4A/C versus ATG4B in vivo not delineated","Physiological meaning of high brain/testis expression untested"]},{"year":2009,"claim":"Substrate-bound structures and dominant-negative cell biology revealed how LC3 binding remodels the active site and why catalytic balance matters for autophagosome closure.","evidence":"Crystallography of inert ATG4B–LC3 complexes; overexpression of catalytically dead ATG4B(C74A) with autophagic-structure imaging","pmids":["19322194","19104152"],"confidence":"High","gaps":["How the exposed flat surface engages membrane-bound LC3-PE not directly shown","Mechanism coupling delipidation to autophagosome sealing incomplete"]},{"year":2012,"claim":"Defining ATG4B turnover, RNF5 was shown to ubiquitinate the membrane-associated pool, establishing stability control as a regulatory layer over basal autophagy.","evidence":"Reciprocal co-IP, ubiquitination assays, RNF5−/− MEFs, domain-mapping mutants, bacterial infection model","pmids":["23093945"],"confidence":"High","gaps":["Ubiquitin chain linkage and degradation route not fully defined","Selectivity for the membranal fraction mechanistically unexplained"]},{"year":2015,"claim":"A phospho-switch and redox sensing emerged as activity controls: Ser383/392 phosphorylation enhances delipidation activity while a REDD1/TXNIP-driven ROS pathway suppresses the redox-sensitive catalytic cysteine.","evidence":"In vitro hydrolase assays, atg4b−/− reconstitution, co-IP; ATG4B activity assays in REDD1/TXNIP knockout cells/mice","pmids":["26378241","25916556"],"confidence":"High","gaps":["Identity of the kinase for Ser383/392 not established in these studies","Which cysteine(s) sense ROS not pinpointed here"]},{"year":2017,"claim":"Multiple opposing signaling inputs were resolved—MST4 (Ser383) and AKT (Ser34) stimulatory phosphorylation, ULK1 (Ser316) inhibitory phosphorylation reversed by PP2A, S-nitrosation, and Rab7b vesicular regulation—mapping ATG4B as a hub integrating stress and metabolic cues.","evidence":"In vitro kinase assays, phospho-mutants, phosphatase identification, S-nitrosation proteomics, co-IP/co-localization, xenograft and metabolic models","pmids":["29232556","28821708","29165041","28633005","28835545"],"confidence":"High","gaps":["Hierarchy and crosstalk among these modifications unresolved","AKT-Ser34 effect on metabolism separated from autophagy raises unexplained mitochondrial role","Rab7b regulation mechanism (direct vs membrane recruitment) unclear"]},{"year":2017,"claim":"Transcriptional control of ATG4B was tied to physiology and disease via C/EBPβ (adipogenesis), Egr-1 (radioresistance), and HSF1 (chemoresistance) directly binding the promoter.","evidence":"ChIP, promoter reporter assays, knockdown/overexpression, xenograft and 3T3-L1 models (2013–2017)","pmids":["23754749","28134935","28889000"],"confidence":"Medium","gaps":["Whether these factors act combinatorially is untested","Quantitative contribution of transcription vs PTM to ATG4B activity unknown"]},{"year":2020,"claim":"Quantitative biochemistry defined the bipartite recognition logic—a low-nanomolar ubiquitin-like core interaction plus a ≥1000-fold C-terminal-tail contribution and a molecular-ruler readout of the LC3 cleavage motif—explaining ATG4B fidelity distinct from pathogen mimics.","evidence":"Semisynthetic LC3-PE substrates, ATG4B truncation mutants, KD/IC50 measurements, molecular docking","pmids":["32686895","36264309"],"confidence":"Medium","gaps":["Structural model of the C-terminal tail engagement not crystallographically resolved","How modifications alter these binding parameters not measured"]},{"year":2023,"claim":"Newer post-translational and contextual regulators expanded the network: UBE3C K33-ubiquitination, EP300/SIRT2 acetylation switching, copper-induced oxidative inhibition, and roles in melanosome trafficking, centrosomal LC3 processing for cell cycle, and selective TBK1 degradation broadened ATG4B function beyond bulk autophagy.","evidence":"MS interactome and chain typing, deacetylation/acetylation assays with sirt2−/− mice, in vitro copper inhibition, live imaging, CRISPR knockout, IFN reporter assays (2017–2024)","pmids":["38146933","36056541","35349929","28598240","37701987","37434364"],"confidence":"Medium","gaps":["TBK1-degradation finding rests on knockdown/co-IP only","Mechanistic link between centrosomal LC3 processing and cell-cycle machinery undefined","Whether copper oligomerization is physiologically relevant beyond Wilson disease unclear"]},{"year":null,"claim":"How the many competing post-translational modifications are temporally ordered and spatially partitioned to set ATG4B activity at distinct membranes (phagophore vs melanosome vs centrosome) remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated model of PTM hierarchy and crosstalk","No structural account of how modifications remodel substrate binding","Spatial control of ATG4B targeting to non-canonical membranes uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,15,16,25,26]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[1,2,5,16]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[20]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[21]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[14,21]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[32]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[2,5,17,21]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,15]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[32]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[27]}],"complexes":[],"partners":["LC3B","GABARAP","RNF5","ULK1","UBE3C","RAB7B","TMED10","MST4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y4P1","full_name":"Cysteine protease ATG4B","aliases":["AUT-like 1 cysteine endopeptidase","Autophagy-related cysteine endopeptidase 1","Autophagin-1","Autophagy-related protein 4 homolog B","HsAPG4B","hAPG4B"],"length_aa":393,"mass_kda":44.3,"function":"Cysteine protease that plays a key role in autophagy by mediating both proteolytic activation and delipidation of ATG8 family proteins (PubMed:15169837, PubMed:15187094, PubMed:17347651, PubMed:19322194, PubMed:21177865, PubMed:22302004, PubMed:26378241, PubMed:27527864, PubMed:28633005, PubMed:28821708, PubMed:29232556, PubMed:30076329, PubMed:30443548, PubMed:30661429). Required for canonical autophagy (macroautophagy), non-canonical autophagy as well as for mitophagy (PubMed:33773106, PubMed:33909989). The protease activity is required for proteolytic activation of ATG8 family proteins: cleaves the C-terminal amino acid of ATG8 proteins MAP1LC3A, MAP1LC3B, MAP1LC3C, GABARAPL1, GABARAPL2 and GABARAP, to reveal a C-terminal glycine (PubMed:15169837, PubMed:15187094, PubMed:17347651, PubMed:19322194, PubMed:20818167, PubMed:21177865, PubMed:22302004, PubMed:27527864, PubMed:28287329, PubMed:28633005, PubMed:29458288, PubMed:30661429). Exposure of the glycine at the C-terminus is essential for ATG8 proteins conjugation to phosphatidylethanolamine (PE) and insertion to membranes, which is necessary for autophagy (PubMed:15169837, PubMed:15187094, PubMed:17347651, PubMed:19322194, PubMed:21177865, PubMed:22302004). Protease activity is also required to counteract formation of high-molecular weight conjugates of ATG8 proteins (ATG8ylation): acts as a deubiquitinating-like enzyme that removes ATG8 conjugated to other proteins, such as ATG3 (PubMed:31315929, PubMed:33773106). In addition to the protease activity, also mediates delipidation of ATG8 family proteins (PubMed:15187094, PubMed:19322194, PubMed:28633005, PubMed:29458288, PubMed:32686895, PubMed:33909989). Catalyzes delipidation of PE-conjugated forms of ATG8 proteins during macroautophagy (PubMed:15187094, PubMed:19322194, PubMed:29458288, PubMed:32686895, PubMed:33909989). Also involved in non-canonical autophagy, a parallel pathway involving conjugation of ATG8 proteins to single membranes at endolysosomal compartments, by catalyzing delipidation of ATG8 proteins conjugated to phosphatidylserine (PS) (PubMed:33909989). Compared to other members of the family (ATG4A, ATG4C or ATG4C), constitutes the major protein for proteolytic activation of ATG8 proteins, while it displays weaker delipidation activity than other ATG4 paralogs (PubMed:29458288, PubMed:30661429). Involved in phagophore growth during mitophagy independently of its protease activity and of ATG8 proteins: acts by regulating ATG9A trafficking to mitochondria and promoting phagophore-endoplasmic reticulum contacts during the lipid transfer phase of mitophagy (PubMed:33773106)","subcellular_location":"Cytoplasm; Cytoplasm, cytosol; Cytoplasmic vesicle, autophagosome; Endoplasmic reticulum; Mitochondrion","url":"https://www.uniprot.org/uniprotkb/Q9Y4P1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ATG4B","classification":"Not 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ATG4D","url":"https://www.omim.org/entry/611340"},{"mim_id":"611339","title":"AUTOPHAGY-RELATED 4C CYSTEINE PEPTIDASE; ATG4C","url":"https://www.omim.org/entry/611339"},{"mim_id":"611338","title":"AUTOPHAGY-RELATED 4B CYSTEINE PEPTIDASE; ATG4B","url":"https://www.omim.org/entry/611338"},{"mim_id":"609604","title":"MICROTUBULE-ASSOCIATED PROTEIN 1, LIGHT CHAIN 3, BETA; MAP1LC3B","url":"https://www.omim.org/entry/609604"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ATG4B"},"hgnc":{"alias_symbol":["Apg4B","KIAA0943","DKFZp586D1822","AUTL1"],"prev_symbol":["APG4B"]},"alphafold":{"accession":"Q9Y4P1","domains":[{"cath_id":"-","chopping":"35-185_219-383","consensus_level":"medium","plddt":92.2432,"start":35,"end":383}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y4P1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y4P1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y4P1-F1-predicted_aligned_error_v6.png","plddt_mean":86.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ATG4B","jax_strain_url":"https://www.jax.org/strain/search?query=ATG4B"},"sequence":{"accession":"Q9Y4P1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y4P1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y4P1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y4P1"}},"corpus_meta":[{"pmid":"19322194","id":"PMC_19322194","title":"The 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structural analysis of conformational changes upon substrate binding\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional interpretation, direct structural evidence for mechanism, published in high-impact journal with extensive subsequent citation and validation\",\n      \"pmids\": [\"19322194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structure of human ATG4B at 2.0 Å resolution shows it is a cysteine protease with a catalytic triad of Cys74, His280, and Asp278, comprising a 'protease domain' resembling papain superfamily cysteine proteinases and an 'auxiliary domain' of unknown function; residues R229 and W142 are specifically essential for substrate recognition and catalysis of both precursor processing and de-conjugation.\",\n      \"method\": \"X-ray crystallography; site-directed mutagenesis of active-site residues\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with mutagenesis validation of catalytic residues, independently replicated in subsequent structural studies\",\n      \"pmids\": [\"16325851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"A single protease, ATG4B (Apg4B/autophagin-1), is the processing and deconjugating enzyme for all four mammalian ATG8 homologues: GATE-16, GABARAP, MAP1-LC3, and Apg8L, as demonstrated by electrophilic activity-based probes that form specific adducts in crude cell lysates.\",\n      \"method\": \"Activity-based protein profiling with electrophilic ubiquitin-like probes; adduct formation in cell lysates\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — chemical biology (activity-based probes) directly identifying the enzyme, replicated by subsequent biochemical and genetic studies across multiple labs\",\n      \"pmids\": [\"14530254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MST4 (STK26) kinase phosphorylates ATG4B at serine residue 383, which stimulates ATG4B protease activity and increases autophagic flux; radiation induces MST4 expression, ATG4B phosphorylation, and autophagy; inhibition of MST4 or ATG4B suppresses autophagy and glioblastoma tumorigenicity.\",\n      \"method\": \"In vitro kinase assay; phospho-specific antibodies; genetic knockdown/overexpression; xenograft mouse models\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro kinase assay plus multiple orthogonal cellular and in vivo genetic approaches across multiple conditions\",\n      \"pmids\": [\"29232556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ULK1 phosphorylates ATG4B at serine 316, resulting in inhibition of its catalytic activity both in vitro and in vivo; the phosphatase PP2A-PP2R3B removes this inhibitory phosphorylation, providing a reversible phospho-switch that regulates ATG4B activity to coordinate LC3 processing during autophagy.\",\n      \"method\": \"In vitro kinase assay; phospho-mimetic and phospho-deficient mutants; co-immunoprecipitation; cell-based autophagy assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay plus mutagenesis plus phosphatase identification, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"28821708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Phosphorylation of ATG4B at Ser-383 and Ser-392 increases its hydrolase activity toward LC3 substrate; phosphorylation-deficient ATG4B shows reduced interactions with lipid-conjugated LC3 (but not unconjugated LC3), and reconstitution of atg4b−/− cells with phospho-deficient ATG4B demonstrates a role for these sites in LC3 delipidation and autophagic flux.\",\n      \"method\": \"In vitro biochemical hydrolase assay; reconstitution of atg4b−/− cells; co-immunoprecipitation; flow cytometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro activity assay, reconstitution in knockout cells, and multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"26378241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A REDD1/TXNIP pro-oxidant complex regulates ATG4B activity through reactive oxygen species: stress conditions induce ROS via REDD1/TXNIP, which suppresses the redox-sensitive ATG4B cysteine endopeptidase activity, thereby reducing LC3B delipidation and activating autophagy; loss of REDD1 or TXNIP increases ATG4B catalytic activity and causes failed autophagy in vivo.\",\n      \"method\": \"ATG4B catalytic activity assays; REDD1−/− and TXNIP knockout cells/mice; ROS measurement; mitochondrial function assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — enzymatic activity assays plus genetic knockout models plus in vivo phenotypic validation, multiple orthogonal methods\",\n      \"pmids\": [\"25916556\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The membrane-associated E3 ubiquitin ligase RNF5 ubiquitinates ATG4B and controls its stability, specifically regulating the membranal fraction of ATG4B and thereby limiting LC3 processing, phagophore formation, and basal autophagy levels; RNF5 mutants retaining E3 ligase activity but unable to associate with ATG4B no longer affect LC3 puncta.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assays; RNF5−/− MEFs; LC3 puncta quantification; bacterial infection models\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, knockout cell lines, domain-mapping mutants, and in vivo infection model providing multiple independent lines of evidence\",\n      \"pmids\": [\"23093945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ATG4B S-nitrosation at Cys189 and Cys292 (induced by high glucose/NO) compromises both its pro-LC3 processing and LC3-PE deconjugation activities, suppressing autophagosome biogenesis and causing neurotoxicity; GABARAPL1 processing is least affected by this modification compared to other substrates.\",\n      \"method\": \"LC-MS/MS-based quantitative S-nitrosation proteomics; site-directed mutagenesis (Cys189, Cys292); ATG4B activity assays; mRFP-GFP-LC3 flux analysis; neuronal cell culture models\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — proteomics identification plus mutagenesis validation plus activity assays plus cellular phenotype in single study with multiple orthogonal methods\",\n      \"pmids\": [\"28633005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"AKT phosphorylates ATG4B at Ser34, which has little effect on autophagic flux but promotes the Warburg effect (increased lactate, glucose consumption, decreased oxygen consumption) in HCC cells by impairing mitochondrial function including F1Fo-ATP synthase activity; Ser34 phosphorylation enhances ATG4B mitochondrial localization and co-localization with F1Fo-ATP synthase.\",\n      \"method\": \"In vitro kinase assay; phospho-site mutagenesis; metabolic assays; subcellular fractionation; co-immunoprecipitation; submitochondrial particle reconstitution assay\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro kinase assay plus multiple functional readouts, single lab\",\n      \"pmids\": [\"29165041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PFKP (phosphofructokinase 1 platelet isoform) acts as a protein kinase that phosphorylates ATG4B at Ser34 under amino acid deprivation; this phosphorylation enhances ATG4B protease activity and autophagic flux; amino acid deprivation strengthens the ATG4B–PFKP interaction, and PFKP loss reduces LC3-II degradation.\",\n      \"method\": \"Tandem affinity purification/mass spectrometry; co-immunoprecipitation; in vitro kinase assay; CRISPR/Cas9 knockout; phospho-site mutagenesis; autophagy flux assays\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay plus CRISPR knockout plus mutagenesis, single lab\",\n      \"pmids\": [\"33607258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UBE3C is an E3 ubiquitin ligase of ATG4B that assembles K33-branched ubiquitin chains on ATG4B at Lys119 without causing ATG4B degradation; K33-ubiquitination reduces ATG4B protease activity and ATG4B–LC3 interaction, inhibiting autophagic flux; under starvation, the ATG4B–UBE3C interaction decreases and K33-linked ubiquitin chains are removed.\",\n      \"method\": \"Mass spectrometry identification of interactors; co-immunoprecipitation; ubiquitin chain-type analysis; ATG4B activity assays; site-directed mutagenesis (K119R); overexpression/knockout experiments\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — MS-based identification plus IP-based chain typing plus activity assays plus mutagenesis, single lab\",\n      \"pmids\": [\"38146933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIRT2 deacetylates ATG4B at lysine 39 (K39), enhancing ATG4B protease activity and autophagic flux; EP300/p300 acetylates ATG4B K39, antagonizing SIRT2; starvation reduces the CCNE-CDK2 complex, decreases SIRT2 Ser331 phosphorylation, activates SIRT2, promotes ATG4B K39 deacetylation, and initiates autophagy; validated in sirt2−/− mice.\",\n      \"method\": \"Co-immunoprecipitation; ATG4B activity assays; site-directed mutagenesis (K39); sirt2−/− mouse model; phosphorylation/deacetylation biochemical assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — enzymatic activity assays, mutagenesis, and in vivo knockout model, single lab\",\n      \"pmids\": [\"36056541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TMED10 directly binds to ATG4B and negatively regulates its proteolytic activity for LC3 cleavage; this interaction is diminished under autophagy-activating conditions (rapamycin, serum deprivation); in Alzheimer disease, reduced TMED10 expression increases ATG4B activity and autophagy.\",\n      \"method\": \"Bimolecular fluorescence complementation (BiFC); co-immunoprecipitation; ATG4B protease activity assays; siRNA knockdown; amyloid-β treatment experiments\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — direct protein-protein interaction by BiFC and co-IP plus activity assays, single lab\",\n      \"pmids\": [\"30821607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The small GTPase Rab7b interacts and co-localizes with ATG4B on vesicles; Rab7b depletion increases autophagic flux, and Rab7b regulates LC3 processing by modulating ATG4B activity, identifying Rab7b as a negative regulator of autophagy through its interaction with ATG4B.\",\n      \"method\": \"Co-immunoprecipitation; co-localization by fluorescence microscopy; autophagic flux assays; Rab7b knockdown\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — co-IP plus co-localization plus functional assays, single lab\",\n      \"pmids\": [\"28835545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human ATG4B (but not ATG4A or ATG4C) cleaves the C-terminus of Atg8L in vitro, and Atg8L undergoes E1 (ATG7) and E2 (ATG3) conjugation reactions, identifying it as the fourth mammalian ATG8-conjugation modifier processed by ATG4B.\",\n      \"method\": \"In vitro cleavage assay; E1/E2 intermediate trapping with catalytic mutants; subcellular fractionation; fluorescence co-localization\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution of cleavage and conjugation reactions, single lab\",\n      \"pmids\": [\"16704426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ATG4B knockdown in PC12 cells suppresses the in vitro cleavage of recombinant proLC3 to LC3-I, confirming ATG4B plays a major role in LC3 processing; ATG4B protein and mRNA are ubiquitously expressed across rat tissues with highest levels in brain (particularly neurons of cerebellum and olfactory bulb) and testis.\",\n      \"method\": \"RNA interference; recombinant proLC3 cleavage assay; Western blot; immunohistochemistry; in situ hybridization\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi knockdown with in vitro activity assay readout, single lab\",\n      \"pmids\": [\"16874114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Overexpression of catalytically inactive ATG4B(C74A) mutant sequesters LC3 paralogues, blocks formation of the ATG7–LC3 intermediate, causes accumulation of ATG5-positive autophagic structures, and prevents autophagosome closure, demonstrating that excess ATG4B mutant inhibits autophagy at the level of LC3 lipidation and autophagosome sealing.\",\n      \"method\": \"Overexpression of dominant-negative mutant; immunofluorescence of autophagic structures; biochemical intermediate trapping assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic analysis using dominant-negative approach with multiple cellular readouts, single lab\",\n      \"pmids\": [\"19104152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"C/EBPβ transcriptionally activates Atg4b expression by directly binding to its promoter, which is required for autophagy induction during adipocyte differentiation; Atg4b-dependent autophagy mediates degradation of Klf2 and Klf3 (negative regulators of adipogenesis) via the adaptor protein p62/SQSTM1.\",\n      \"method\": \"ChIP assay; promoter reporter assays; ATG4B knockdown/overexpression in 3T3-L1 cells; mouse models; p62 interaction studies\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP validation of direct promoter binding plus functional rescue experiments plus in vivo confirmation, single lab\",\n      \"pmids\": [\"23754749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Egr-1 transcription factor binds to the ATG4B promoter upon ionizing radiation and upregulates ATG4B expression in HCC cells, thereby inducing protective autophagy and radioresistance; dominant-negative Egr-1 suppresses radiation-induced ATG4B expression, autophagy, and cell migration.\",\n      \"method\": \"Luciferase reporter assay; chromatin immunoprecipitation (ChIP); dominant-negative Egr-1 overexpression; autophagy and clonogenic survival assays\",\n      \"journal\": \"Oncogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and reporter assay demonstrating direct promoter binding plus functional consequence, single lab\",\n      \"pmids\": [\"28134935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ATG4B and LC3B mediate melanosome trafficking on cytoskeletal tracks: LC3B labels melanosomes and enables assembly of a microtubule translocon complex for intracellular positioning; ATG4B enzymatically delipidates LC3B from melanosomal membranes at the microtubule-actin crossover junction; melanosomes transferred to keratinocytes lack melanocyte-specific LC3B.\",\n      \"method\": \"Live-cell fluorescence imaging; enzymatic ATG4B activity assays; cytoskeletal co-localization; keratinocyte transfer assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — live imaging plus enzymatic activity evidence for delipidation at specific cellular location, single lab\",\n      \"pmids\": [\"28598240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ATG4B localizes to early autophagic membranes in an LC3B-dependent manner; during autophagy, ATG4B and LC3B undergo rapid cytosol/isolation membrane exchange but not at completed autophagosomes; ATG4B activity controls the efficiency of autophagosome formation by impacting LC3B membrane binding/dissociation.\",\n      \"method\": \"Fluorescence recovery after photobleaching (FRAP) of GFP-tagged ATG4B and LC3B in living cells; autophagy inhibitor experiments\",\n      \"journal\": \"Journal of molecular cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct live-cell FRAP measurements linking localization dynamics to functional consequence, single lab\",\n      \"pmids\": [\"34562084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"ATG4B interacts with Bcl-2 by co-immunoprecipitation, and ATG4B upregulation promotes disassociation of the Bcl-2–Beclin1 complex, releasing Beclin1 to activate the autophagic pathway in cadmium-treated A549 cells.\",\n      \"method\": \"Co-immunoprecipitation; ATG4B knockdown/overexpression; Bcl-2–Beclin1 interaction assays; autophagy flux measurements\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP experiment in one cell line under one treatment condition, single lab\",\n      \"pmids\": [\"30458278\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SLC27A4 directly interacts with ATG4B (by co-IP and GST pull-down) in lung cancer cells, maintains ATG4B protein stability and intracellular concentration, and thereby facilitates autophagy induction in response to nutrient deprivation or chemotherapy stress.\",\n      \"method\": \"Tandem affinity purification/mass spectrometry; co-immunoprecipitation; GST pull-down assay; siRNA knockdown; autophagic flux assays\",\n      \"journal\": \"Tumour biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — co-IP and pull-down with functional follow-up, single lab, limited mechanistic detail in abstract\",\n      \"pmids\": [\"26662804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Copper ion (but not other metal ions) directly inhibits ATG4B protease activity and induces ATG4B cysteine oxidation-dependent oligomer formation; copper promotes formation of insoluble ATG4B aggregates along with p62- and ubiquitin-positive aggregates; ATG4B overexpression partially reduces Mallory body formation and rescues impaired autophagy in Wilson disease cell models.\",\n      \"method\": \"In vitro ATG4B activity assay with copper; cysteine oxidation/oligomerization assays; cell-based autophagy flux assays; Wilson disease cell model\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro enzyme inhibition assay plus cellular mechanistic follow-up, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"35349929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ATG4B cleaves LC3-PE using a molecular ruler mechanism dependent on the LC3 C-terminal motif (residues Gln116, Phe119, Gly120); the C-terminal tail of ATG4B is required for LC3 binding and proteolysis (contributing ≥1000-fold to binding affinity) but not for cleavage of a short peptide substrate; distinct from the Legionella effector RavZ which lacks this molecular ruler mechanism.\",\n      \"method\": \"Semisynthetic LC3-PE proteins with C-terminal mutations; molecular docking; biochemical cleavage assays; ATG4B truncation mutants\",\n      \"journal\": \"Chembiochem\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and structural modeling, single lab\",\n      \"pmids\": [\"32686895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Biochemical and biophysical characterization shows the ubiquitin-like core of LC3B (residues 1–115, lacking the C-terminal cleavage site) binds full-length ATG4B with a KD in the low nanomolar range (10–30-fold tighter than pro-LC3B substrate); the C-terminal tail of ATG4B contributes ≥1000-fold higher binding affinity; binding of LC3B-115 does not alter the ATG4B active-site conformation, supporting a bipartite binding model.\",\n      \"method\": \"Biochemical binding assays (KD measurement); inhibition assays (IC50); ATG4B truncation mutants; peptide substrate cleavage assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous in vitro biochemical characterization with mutants defining binding domains, single lab\",\n      \"pmids\": [\"36264309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ATG4B promotes GABARAP-directed selective autophagic degradation of TBK1, thereby antagonizing antiviral type-I interferon signaling; ATG4B knockdown enhances IFN signaling and antiviral immunity.\",\n      \"method\": \"siRNA knockdown; co-immunoprecipitation; autophagic flux assays; IFN reporter assays; viral replication assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, limited mechanistic detail in abstract, co-IP and knockdown only\",\n      \"pmids\": [\"37434364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ATG4B host cysteine protease can hydrolyze the substrate of EV71 3C protease with comparable activity, and genetic disruption of ATG4B reduces EV71 viral proliferation in vivo, identifying ATG4B as indispensable for EV71 replication.\",\n      \"method\": \"Activity-based protein profiling (ABP); in vitro substrate cleavage assays; ATG4B genetic disruption; viral titer assays\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — activity-based profiling plus in vitro enzymatic assay plus genetic disruption in vivo, single lab\",\n      \"pmids\": [\"31554687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIRT3 deacetylates ATG4B, and DHM (dihydromyricetin) increases SIRT3 expression leading to SIRT3-mediated ATG4B deacetylation, upregulating ATG4B protein levels and inducing autophagy to attenuate palmitic acid-induced oxidative stress in hepatocytes; the protective effect is abolished in SIRT3-inhibited or ATG4B heterozygous knockout cells.\",\n      \"method\": \"Western blot for ATG4B acetylation; SIRT3 inhibitor treatment; ATG4B+/− heterozygous knockout cells; ROS and mitochondrial function assays\",\n      \"journal\": \"Nutrition & metabolism\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — indirect evidence for deacetylation (no direct deacetylation assay described in abstract), single lab\",\n      \"pmids\": [\"34503544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ATG4B accumulates in pancreatic acinar cells after ethanol treatment, directly inhibits autophagosome formation by reducing LC3-II levels through enhanced ATG4B enzymatic activity and strengthened interaction with LC3-II; adenoviral ATG4B overexpression inhibits autophagy and aggravates trypsinogen activation and necrosis; shRNA ATG4B knockdown enhances autophagosome formation and alleviates ethanol-induced acinar cell damage.\",\n      \"method\": \"Mouse model of alcoholic pancreatitis; adenoviral overexpression; shRNA knockdown; ATG4B activity assays; LC3-II quantification; trypsinogen activation assays\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo model plus gain- and loss-of-function with enzymatic activity measurement, single lab\",\n      \"pmids\": [\"37431575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HSF1 transcription factor upregulates ATG4B expression by directly binding to the ATG4B gene promoter at position −1429 to −1417, thereby enhancing epirubicin-induced protective autophagy and reducing HCC cell sensitivity to chemotherapy.\",\n      \"method\": \"Luciferase reporter assay; chromatin immunoprecipitation (ChIP); HSF1/ATG4B knockdown; xenograft mouse models\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and reporter assay demonstrating direct promoter binding with functional consequence, single lab\",\n      \"pmids\": [\"28889000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Pro-LC3B accumulated aberrantly at the centrosome upon ATG4B knockout, with concomitant increases in centrosomal proteins PCM1 and CEP131; this was rescued by exogenous ATG4B, revealing a role for ATG4B in processing LC3B at the centrosome to permit normal cell cycle progression; ATG4B and ATG4A double knockout causes delays in both G1-S phase transition and mitosis.\",\n      \"method\": \"CRISPR/Cas9 ATG4B/ATG4A single and double knockout; immunofluorescence; rescue experiments; cell cycle analysis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR knockout with rescue experiments and centrosomal localization phenotype, single lab\",\n      \"pmids\": [\"37701987\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATG4B is a cysteine protease (catalytic triad Cys74-His280-Asp278) that acts as the sole processing and deconjugating enzyme for all mammalian ATG8 homologues (LC3, GABARAP, GATE-16, Apg8L/ATG8L); substrate recognition involves LC3 Phe119 lifting a regulatory loop and engagement of the ATG4B C-terminal tail in a bipartite interaction; its activity is tightly regulated by multiple post-translational modifications including stimulatory phosphorylation at Ser383/392 by MST4 and AKT, inhibitory phosphorylation at Ser316 by ULK1 (reversed by PP2A-PP2R3B), inhibitory K33-ubiquitination at Lys119 by UBE3C, inhibitory acetylation at Lys39 by EP300 (reversed by SIRT2 deacetylation), inhibitory S-nitrosation at Cys189/Cys292, redox-dependent inhibition by ROS via the REDD1/TXNIP complex, and stability control through RNF5-mediated ubiquitination of the membrane-associated pool; transcriptional regulation by C/EBPβ, Egr-1, and HSF1 links ATG4B expression to adipogenesis, radiation stress, and chemoresistance; ATG4B additionally mediates melanosome trafficking by delipidating LC3B from melanosomal membranes, interacts with Rab7b on vesicles to modulate autophagic flux, participates in centrosomal LC3 processing for cell cycle progression, and promotes selective autophagic degradation of TBK1 to antagonize innate immune signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ATG4B is the cysteine protease that processes and deconjugates all four mammalian ATG8 homologues (LC3, GABARAP, GATE-16, Apg8L/ATG8L), positioning it as a central enzymatic node in the autophagy machinery [#2, #15]. It is a papain-superfamily cysteine protease with a Cys74-His280-Asp278 catalytic triad whose active-site entrance is masked by a regulatory loop; substrate engagement is driven by LC3 Phe119 lifting this loop to admit the LC3 tail, while the N-terminal tail detaches to expose a flat surface compatible with access to membrane-bound LC3-PE [#0, #1]. Recognition is bipartite and exquisitely sequence-specific: the LC3 ubiquitin-like core binds full-length ATG4B with low-nanomolar affinity and the ATG4B C-terminal tail contributes a ≥1000-fold affinity gain, while a 'molecular ruler' mechanism reading the LC3 C-terminal motif (Gln116/Phe119/Gly120) confers cleavage-site fidelity [#25, #26]. ATG4B performs both pro-LC3 priming and LC3-PE delipidation, and its catalytic level must be balanced—dominant-negative ATG4B(C74A) sequesters LC3 and blocks autophagosome closure, whereas its delipidation activity controls LC3 membrane binding/dissociation dynamics and the efficiency of autophagosome formation at early autophagic membranes [#17, #21]. ATG4B activity is governed by a dense layer of post-translational control: stimulatory phosphorylation at Ser383/Ser392 by MST4 and at Ser34 by PFKP enhances protease activity and flux, ULK1 phosphorylation at Ser316 inhibits it (reversed by PP2A-PP2R3B), and additional inhibitory inputs include UBE3C-mediated K33 ubiquitination at Lys119, EP300 acetylation at Lys39 (antagonized by SIRT2 deacetylation), S-nitrosation at Cys189/Cys292, and ROS/REDD1-TXNIP redox suppression; RNF5 ubiquitination controls the stability of the membrane-associated pool [#3, #10, #4, #11, #12, #6, #7, #8]. At the transcriptional level, C/EBPβ, Egr-1, and HSF1 link ATG4B expression to adipogenesis and to radiation- and chemotherapy-induced protective autophagy [#18, #19, #31]. Beyond bulk autophagy, ATG4B delipidates LC3B from melanosomal membranes during melanosome trafficking, processes centrosomal LC3B to permit normal cell cycle progression, and promotes GABARAP-directed selective degradation of TBK1 to dampen type-I interferon signaling [#20, #32, #27].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Establishing which enzyme processes the mammalian ATG8 family was prerequisite to understanding LC3 lipidation; activity-based profiling identified ATG4B as the single protease handling all four homologues.\",\n      \"evidence\": \"Activity-based protein profiling with electrophilic ubiquitin-like probes in cell lysates\",\n      \"pmids\": [\"14530254\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve substrate-specific kinetic differences among the four ATG8 homologues\", \"No structural basis for recognition yet\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defining the catalytic machinery showed ATG4B is a papain-like cysteine protease, identifying the residues required for both precursor processing and deconjugation.\",\n      \"evidence\": \"X-ray crystallography at 2.0 Å plus active-site mutagenesis (Cys74, His280, Asp278; R229, W142)\",\n      \"pmids\": [\"16325851\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Function of the auxiliary domain unresolved\", \"No substrate-bound structure to explain selectivity\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Genetic and reconstitution work confirmed ATG4B as the dominant LC3-processing enzyme and added Atg8L as a bona fide substrate, completing the substrate roster.\",\n      \"evidence\": \"In vitro cleavage and E1/E2 conjugation reconstitution; RNAi in PC12 cells; tissue expression profiling\",\n      \"pmids\": [\"16704426\", \"16874114\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of ATG4A/C versus ATG4B in vivo not delineated\", \"Physiological meaning of high brain/testis expression untested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Substrate-bound structures and dominant-negative cell biology revealed how LC3 binding remodels the active site and why catalytic balance matters for autophagosome closure.\",\n      \"evidence\": \"Crystallography of inert ATG4B–LC3 complexes; overexpression of catalytically dead ATG4B(C74A) with autophagic-structure imaging\",\n      \"pmids\": [\"19322194\", \"19104152\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the exposed flat surface engages membrane-bound LC3-PE not directly shown\", \"Mechanism coupling delipidation to autophagosome sealing incomplete\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defining ATG4B turnover, RNF5 was shown to ubiquitinate the membrane-associated pool, establishing stability control as a regulatory layer over basal autophagy.\",\n      \"evidence\": \"Reciprocal co-IP, ubiquitination assays, RNF5−/− MEFs, domain-mapping mutants, bacterial infection model\",\n      \"pmids\": [\"23093945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ubiquitin chain linkage and degradation route not fully defined\", \"Selectivity for the membranal fraction mechanistically unexplained\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"A phospho-switch and redox sensing emerged as activity controls: Ser383/392 phosphorylation enhances delipidation activity while a REDD1/TXNIP-driven ROS pathway suppresses the redox-sensitive catalytic cysteine.\",\n      \"evidence\": \"In vitro hydrolase assays, atg4b−/− reconstitution, co-IP; ATG4B activity assays in REDD1/TXNIP knockout cells/mice\",\n      \"pmids\": [\"26378241\", \"25916556\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the kinase for Ser383/392 not established in these studies\", \"Which cysteine(s) sense ROS not pinpointed here\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Multiple opposing signaling inputs were resolved—MST4 (Ser383) and AKT (Ser34) stimulatory phosphorylation, ULK1 (Ser316) inhibitory phosphorylation reversed by PP2A, S-nitrosation, and Rab7b vesicular regulation—mapping ATG4B as a hub integrating stress and metabolic cues.\",\n      \"evidence\": \"In vitro kinase assays, phospho-mutants, phosphatase identification, S-nitrosation proteomics, co-IP/co-localization, xenograft and metabolic models\",\n      \"pmids\": [\"29232556\", \"28821708\", \"29165041\", \"28633005\", \"28835545\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Hierarchy and crosstalk among these modifications unresolved\", \"AKT-Ser34 effect on metabolism separated from autophagy raises unexplained mitochondrial role\", \"Rab7b regulation mechanism (direct vs membrane recruitment) unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Transcriptional control of ATG4B was tied to physiology and disease via C/EBPβ (adipogenesis), Egr-1 (radioresistance), and HSF1 (chemoresistance) directly binding the promoter.\",\n      \"evidence\": \"ChIP, promoter reporter assays, knockdown/overexpression, xenograft and 3T3-L1 models (2013–2017)\",\n      \"pmids\": [\"23754749\", \"28134935\", \"28889000\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether these factors act combinatorially is untested\", \"Quantitative contribution of transcription vs PTM to ATG4B activity unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Quantitative biochemistry defined the bipartite recognition logic—a low-nanomolar ubiquitin-like core interaction plus a ≥1000-fold C-terminal-tail contribution and a molecular-ruler readout of the LC3 cleavage motif—explaining ATG4B fidelity distinct from pathogen mimics.\",\n      \"evidence\": \"Semisynthetic LC3-PE substrates, ATG4B truncation mutants, KD/IC50 measurements, molecular docking\",\n      \"pmids\": [\"32686895\", \"36264309\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural model of the C-terminal tail engagement not crystallographically resolved\", \"How modifications alter these binding parameters not measured\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Newer post-translational and contextual regulators expanded the network: UBE3C K33-ubiquitination, EP300/SIRT2 acetylation switching, copper-induced oxidative inhibition, and roles in melanosome trafficking, centrosomal LC3 processing for cell cycle, and selective TBK1 degradation broadened ATG4B function beyond bulk autophagy.\",\n      \"evidence\": \"MS interactome and chain typing, deacetylation/acetylation assays with sirt2−/− mice, in vitro copper inhibition, live imaging, CRISPR knockout, IFN reporter assays (2017–2024)\",\n      \"pmids\": [\"38146933\", \"36056541\", \"35349929\", \"28598240\", \"37701987\", \"37434364\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"TBK1-degradation finding rests on knockdown/co-IP only\", \"Mechanistic link between centrosomal LC3 processing and cell-cycle machinery undefined\", \"Whether copper oligomerization is physiologically relevant beyond Wilson disease unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many competing post-translational modifications are temporally ordered and spatially partitioned to set ATG4B activity at distinct membranes (phagophore vs melanosome vs centrosome) remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated model of PTM hierarchy and crosstalk\", \"No structural account of how modifications remodel substrate binding\", \"Spatial control of ATG4B targeting to non-canonical membranes uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 15, 16, 25, 26]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [1, 2, 5, 16]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [20]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [21]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [14, 21]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [32]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [2, 5, 17, 21]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 15]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [32]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [27]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"LC3B\", \"GABARAP\", \"RNF5\", \"ULK1\", \"UBE3C\", \"Rab7b\", \"TMED10\", \"MST4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}