{"gene":"DBR1","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2005,"finding":"Yeast Dbr1 is a manganese-dependent RNA debranching enzyme that cleaves the 2'-5' phosphodiester bonds of lariat introns. Alanine scanning mutagenesis identified 13 conserved residues (His13, Asp40, Arg45, Asp49, Tyr68, Tyr69, Asn85, His86, Glu87, His179, Asp180, His231, His233) required for function in vivo; mutation of Asp40, Asn85, His86, His179, His231, or His233 to alanine abolished or greatly diminished debranching activity in vitro. Dbr1 sediments as a monomer and requires manganese as the metal cofactor.","method":"In vitro debranching assays with natural lariat RNAs and synthetic branched RNAs; alanine-scanning mutagenesis of 28 conserved residues; sedimentation analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis across 28 residues, multiple orthogonal methods (in vivo lariat accumulation assay + in vitro activity assay + sedimentation)","pmids":["16275784"],"is_preprint":false},{"year":2000,"finding":"Human DBR1 (hDBR1) encodes a functional RNA lariat debranching enzyme: recombinant hDBR1 expressed in E. coli showed debranching activity in vitro, and the cDNA complemented both the intron accumulation phenotype of S. cerevisiae dbr1 null mutants and the intron accumulation and slow growth phenotypes of S. pombe dbr1 null mutants.","method":"In vitro debranching assay with recombinant protein; interspecies complementation of S. cerevisiae and S. pombe dbr1 null mutants","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro activity assay plus cross-species genetic complementation in two distinct organisms","pmids":["10982890"],"is_preprint":false},{"year":2014,"finding":"Crystal structures of Dbr1 alone and in complex with synthetic RNA compounds mimicking the lariat branchpoint revealed the molecular basis for 2',5'-phosphodiester recognition and explained why Dbr1 lacks activity toward 3',5'-phosphodiester linkages. Functional data on Dbr1 variants confirmed structure-function relationships.","method":"X-ray crystallography of apo-Dbr1 and Dbr1–branched RNA complexes; functional assays on Dbr1 variants","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures with bound substrate mimics plus functional validation of variants in a single rigorous study","pmids":["25123664"],"is_preprint":false},{"year":2016,"finding":"Entamoeba histolytica Dbr1 contains nearly stoichiometric Fe and Zn per polypeptide; Fe partitions primarily to the β-metal pocket and Zn to the α-pocket. Apo-Dbr1 reconstituted with Fe(II)+Zn(II) is active (~3–4 s⁻¹), while Mn(II) or Fe(II) under aerobic conditions yields inactive enzyme. Co-crystal structures of catalytic mutant H91A with 7-mer and 16-mer branched RNAs show a bridging hydroxide positioned for nucleophilic attack of the scissile phosphate.","method":"X-ray crystallography (Fe-edge anomalous diffraction); fluorogenic bRNA kinetic assay; metal reconstitution of apoenzyme under aerobic and anaerobic conditions; elemental analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures with substrate analogs, anomalous diffraction for metal identification, kinetic assays, and reconstitution experiments in one rigorous study","pmids":["27930312"],"is_preprint":false},{"year":2016,"finding":"Yeast Dbr1 active site analysis established: (i) Cys11 is an essential active-site residue, extending the Cys11-Xaa-His13 motif as the metal-binding element (atypical within the metallophosphoesterase superfamily); (ii) His86 acts as a general acid catalyst that protonates the O2' leaving group of the 2'-5' phosphodiester; (iii) Dbr1 adheres to a two-metal catalytic mechanism. Dbr1 also exhibits vigorous Mn²⁺-dependent phosphodiesterase activity toward bis-p-nitrophenylphosphate, which does not require His86.","method":"Alanine-scanning mutagenesis; in vitro phosphodiesterase assay with bis-p-nitrophenylphosphate and branched RNA substrates; structure-activity analysis","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assays with multiple substrates and mutagenesis, interpreted with structural context; single lab but multiple orthogonal methods","pmids":["27765821"],"is_preprint":false},{"year":2022,"finding":"Saccharomyces cerevisiae Dbr1 contains stoichiometric Fe and Zn; Fe²⁺ is the most effective cofactor for reconstituting activity in apoenzyme (turnover ~9.2 s⁻¹). Treatment of human lymphoblastoid cells with the iron chelator deferoxamine caused a ~2-fold increase in cellular lariat levels, indicating Fe is an important biological cofactor for Dbr1.","method":"Elemental analysis (ICP-MS); apoenzyme reconstitution with Fe²⁺, Zn²⁺, Mn²⁺; fluorogenic bRNA kinetic assay; deferoxamine treatment of human cells with lariat quantification","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution kinetics, elemental analysis, and cellular iron-chelation experiment; single lab, multiple orthogonal methods","pmids":["35459748"],"is_preprint":false},{"year":2022,"finding":"A product-bound crystal structure of E. histolytica Dbr1 co-crystallized with a phosphorothioate-branched RNA (PS-bRNA) showed in-crystal hydrolysis of the phosphorothioate bond, revealing a product-bound active site state. Dbr1 cleaves phosphorothioate linkages ~10,000-fold more slowly than native phosphate linkages. The structure suggests product inhibition may contribute to the kinetic mechanism.","method":"X-ray crystallography of EhDbr1 with PS-bRNA; kinetic comparison of phosphorothioate vs native substrate cleavage","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure of product-bound enzyme plus kinetic measurements; single lab, two orthogonal methods","pmids":["36484984"],"is_preprint":false},{"year":2023,"finding":"Human Dbr1 contains a disordered C-terminal domain (characterized by NMR and sequence analysis) that stabilizes Dbr1 by reducing aggregation but is dispensable for debranching activity. The noncatalytic protein Drn1 and TTDN1 (MPLKIP) directly bind human Dbr1. Addition of TTDN1 to in vitro debranching reactions increases the catalytic efficiency of human Dbr1 19-fold but has no effect on E. histolytica Dbr1, which lacks the disordered C-terminal domain. Dbr1 requires Fe²⁺ for efficient catalysis. The identity of the branchpoint nucleotide affects debranching rates.","method":"NMR spectroscopy; in vitro binding assays (pulldown); in vitro debranching kinetics with TTDN1; comparative analysis with E. histolytica Dbr1; sequence analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — NMR structural characterization, in vitro binding, and reconstituted kinetic assays with multiple orthogonal methods in a single study","pmids":["37507019"],"is_preprint":false},{"year":2023,"finding":"MPLKIP (TTDN1) interacts with core splicing factors and the lariat debranching protein DBR1 (identified by mass spectrometry-based interaction proteomics). MPLKIP-deficient primary fibroblasts have reduced steady-state DBR1 protein levels, indicating MPLKIP stabilizes DBR1.","method":"Mass spectrometry-based interaction proteomics (co-immunoprecipitation); immunoblot of MPLKIP-deficient fibroblasts","journal":"EMBO molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — MS-based interactome and immunoblot in patient-derived cells; two methods but no direct reconstitution of the stabilization mechanism","pmids":["37800682"],"is_preprint":false},{"year":2024,"finding":"DBR1 is the sole debranching enzyme in human cells (demonstrated by knockout). The predominantly nuclear Dbr1 preferentially debranches substrates containing canonical U2 binding motifs and shows specificity for particular 5' splice site sequences. Dbr1 is recruited to the branchpoint through the intron-binding protein AQR (identified by co-immunoprecipitation mass spectrometry). DBR1 depletion causes a 20-fold increase in lariats, increases exon skipping, and causes spliceosomal components to remain associated with lariats for longer, demonstrating a role for Dbr1 in spliceosome recycling.","method":"DBR1 knockout cell line generation; co-immunoprecipitation mass spectrometry; ADAR-fusion lariat timestamping; transcriptomic analysis; spliceosome association assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — viable KO cell line with multiple orthogonal readouts (interactome, substrate specificity, spliceosome association, lariat timestamping), peer-reviewed and also available as preprint confirming the same findings","pmids":["38816363"],"is_preprint":false},{"year":2024,"finding":"Accumulation of RNA lariats in human DBR1-deficient cells interferes with stress granule (SG) assembly by promoting proteasome-mediated degradation of G3BP1 and G3BP2. Impaired SG assembly reduces PKR recruitment and activation, impairing antiviral immunity against HSV-1. Genetic ablation of PKR abolished the antiviral effect of DBR1 in vitro. Dbr1Y17H/Y17H mice are susceptible to viral infections and show decreased G3BP1/2 expression and reduced PKR phosphorylation in cells and brain.","method":"DBR1-deficient human cell lines; PKR knockout epistasis; Dbr1Y17H/Y17H mouse model; proteasome inhibition; immunoblot for G3BP1/2 and p-PKR; antiviral infection assays","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis (PKR KO), multiple human cell and mouse model experiments, confirmed in vivo, multiple orthogonal mechanistic readouts","pmids":["39636299"],"is_preprint":false},{"year":2024,"finding":"DBR1 I120T/I120T homozygous fibroblasts from patients with inherited DBR1 deficiency have low DBR1 protein levels and high RNA lariat accumulation. Exogenous WT DBR1 expression in patient-derived DBR1 I120T/I120T fibroblasts and hPSC-derived hindbrain neurons rescued the RNA lariat accumulation phenotype. Expression of exogenous RNA lariats (mimicking DBR1 deficiency) increased susceptibility of WT hindbrain neurons to SARS-CoV-2 infection, indicating that lariat accumulation per se impairs antiviral immunity.","method":"Patient fibroblast analysis; lentiviral rescue with WT DBR1; hPSC-derived hindbrain neuron differentiation; SARS-CoV-2 infection assay; exogenous lariat transfection","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — rescue experiment in primary patient cells and iPSC-derived neurons, plus gain-of-function lariat transfection establishing causality; multiple orthogonal methods","pmids":["39023559"],"is_preprint":false},{"year":2017,"finding":"DBR1 knockdown in HIV-infected cells inhibits formation of intermediate and full-length HIV-1 cDNA without affecting minus-strand strong-stop cDNA. This inhibition occurs in the nucleus or perinuclear region: when nuclear import of the HIV-1 reverse transcription complex is blocked by a truncated CPSF6, reverse transcription is completed in the cytoplasm in a DBR1-independent manner. In vitro incubation with yeast or human DBR1 (but not catalytically inactive DBR1(N85A)) resolved a lariat-like structure at the 5' end of HIV-1 RNA detected in infected DBR1-knockdown cells. HIV-1 RNA from DBR1-knockdown cells was resistant to RNase R (which degrades linear but not circular/lariat RNAs), supporting formation of a lariat-like structure.","method":"shRNA knockdown; cell fractionation; CPSF6 truncation for nuclear import block; 5' RACE; RNase R treatment; in vitro DBR1 treatment with catalytic mutant control","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (fractionation, 5' RACE, RNase R, mutant enzyme control) in a single lab; shRNA knockdown approach limits certainty about direct vs indirect effects","pmids":["28931690","24672043"],"is_preprint":false},{"year":2005,"finding":"siRNA-mediated knockdown of human DBR1 expression (reducing mRNA by ~80%) led to decreases in HIV-1 cDNA and protein production; this effect was reversed by cotransfection of a DBR1 cDNA, confirming specificity of the DBR1 requirement for HIV-1 replication.","method":"siRNA knockdown; DBR1 cDNA rescue; HIV-1 cDNA quantification; viral protein detection","journal":"Retrovirology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — knockdown with specific rescue experiment confirms on-target effect; mechanism inferred indirectly without direct biochemical demonstration of lariat intermediates","pmids":["16232320"],"is_preprint":false},{"year":2017,"finding":"hDBR1 modulates snRNP recycling to affect alternative RNA splicing. Insufficient hDBR1 leads to higher rates of exon skipping confirmed by transcriptomic sequencing. Wild-type p53 and HIF-1 co-regulate hDBR1 expression. Higher hDBR1 expression only affected exon-skipping activity in malignant (not normal) cells.","method":"siRNA knockdown; transcriptomic sequencing; metabolite profiling; in vivo tumor models; reporter assays for splicing","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — transcriptomic plus metabolomics plus in vivo data; mechanistic detail of snRNP recycling step is inferred rather than directly reconstituted","pmids":["28504715"],"is_preprint":false},{"year":2026,"finding":"hDBR1 physically associates with spliceosome components, intron-turnover factors (including AQR), and RNA quality-control proteins (UPF1, XRN2, DHX29) as identified by immunopurification coupled to mass spectrometry. RNase A treatment identified an RNA-dependent subnetwork enriched for stress-granule proteins and hnRNPs. Phosphoproteomic profiling identified multiple hDBR1 phosphorylation sites, including four residues preferentially detected after RNase treatment.","method":"Immunopurification coupled to mass spectrometry (gel-based and on-bead workflows); RNase A treatment; phosphoproteomic profiling","journal":"Cell stress & chaperones","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — IP-MS interactome with RNA-dependent subnetwork analysis and phosphoproteomics; single lab, no functional validation of specific interactions reported in abstract","pmids":["41999910"],"is_preprint":false},{"year":2024,"finding":"In DBR1-null cells, lariats accumulate in the cytosol and dsRNA (formed by inverted Alu element hairpins within introns) becomes enriched. Chronic exposure to accumulated lariats attenuates dsRNA sensors MDA5, RIG-I, RNase L, and PKR, reducing the antiviral response. Lariats are transiently elevated during infection (HSV-1, influenza, KSHV).","method":"DBR1 knockout cells; dsRNA immunofluorescence and quantification; antiviral pathway activation assays; infection experiments with HSV-1, influenza, KSHV","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO cell line with multiple pathway readouts; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2024.12.07.627371"],"is_preprint":true}],"current_model":"DBR1 (Dbr1) is the sole eukaryotic RNA lariat debranching enzyme, a binuclear metallophosphoesterase (using Fe²⁺ and Zn²⁺ as biological cofactors) that hydrolyzes the 2'-5' phosphodiester bond at the branchpoint of excised intron lariats via a two-metal mechanism involving a Cys11-Xaa-His13 metal-binding motif and His86 as a general acid catalyst; it is predominantly nuclear, recruited to branchpoints partly via the intron-binding protein AQR, is the rate-limiting step in lariat turnover, and its debranching activity is required for spliceosome recycling (preventing exon skipping), for processing of snoRNAs and miRNAs from intronic lariats, and for innate antiviral immunity by preventing cytosolic accumulation of lariat dsRNA that would otherwise desensitize PKR and other dsRNA sensors through a pathway involving G3BP1/2-dependent stress granule assembly."},"narrative":{"mechanistic_narrative":"DBR1 is the sole RNA lariat debranching enzyme in eukaryotic cells, a binuclear metallophosphoesterase that hydrolyzes the 2'-5' phosphodiester bond at the branchpoint of excised intron lariats and is thereby the rate-limiting step in lariat turnover [PMID:16275784, PMID:10982890, PMID:38816363]. Catalysis proceeds by a two-metal mechanism in which a Cys11-Xaa-His13 motif coordinates the active-site metals and His86 serves as a general acid that protonates the O2' leaving group, with structures of substrate- and product-bound enzyme defining how Dbr1 specifically recognizes 2',5'- but not 3',5'-linkages [PMID:25123664, PMID:27765821, PMID:36484984]. Although early work scored the enzyme as manganese-dependent, the biological cofactors are Fe2+ in the β-pocket and Zn2+ in the α-pocket, and iron chelation in human cells raises lariat levels, establishing Fe as physiologically relevant [PMID:16275784, PMID:27930312, PMID:35459748, PMID:37507019]. In human cells DBR1 is predominantly nuclear, is recruited to the branchpoint via the intron-binding protein AQR, and preferentially acts on substrates bearing canonical U2 motifs; its debranching activity is required for spliceosome recycling, since loss of DBR1 causes ~20-fold lariat accumulation, prolonged retention of spliceosomal components on lariats, and increased exon skipping [PMID:38816363, PMID:28504715]. The disordered C-terminal domain of human Dbr1 reduces aggregation and provides a docking site for the noncatalytic partner TTDN1 (MPLKIP), which both stabilizes DBR1 and stimulates its catalytic efficiency ~19-fold [PMID:37507019, PMID:37800682]. Beyond splicing, DBR1 supports innate antiviral immunity: when lariats accumulate they reach the cytosol and form Alu-derived dsRNA hairpins, drive proteasomal degradation of the stress-granule scaffolds G3BP1/2, and blunt PKR and other dsRNA sensors, with PKR ablation abolishing the antiviral effect and Dbr1-hypomorphic mice showing susceptibility to viral infection [PMID:39636299, PMID:bio_10.1101_2024.12.07.627371]. Inherited DBR1 deficiency (e.g. the I120T variant) lowers DBR1 protein, causes lariat accumulation, and increases susceptibility of patient and stem-cell-derived hindbrain neurons to viral infection, a phenotype rescued by wild-type DBR1 [PMID:39023559].","teleology":[{"year":2000,"claim":"Establishing that the human gene encodes a bona fide debranching enzyme converted a yeast activity into a defined human enzyme and showed functional conservation across eukaryotes.","evidence":"in vitro debranching assay with recombinant hDBR1 plus cross-species complementation of S. cerevisiae and S. pombe dbr1 nulls","pmids":["10982890"],"confidence":"High","gaps":["No structural or mechanistic detail of the active site","Physiological metal cofactor not defined"]},{"year":2005,"claim":"Mutagenesis defined the catalytic residue set required for debranching, mapping the functional active site of the enzyme.","evidence":"alanine-scanning of 28 conserved residues with in vitro and in vivo lariat assays in yeast Dbr1","pmids":["16275784"],"confidence":"High","gaps":["Manganese assigned as cofactor, later revised","Catalytic roles of individual residues not yet mechanistically assigned"]},{"year":2014,"claim":"Crystal structures with branchpoint-mimicking RNA explained substrate recognition and the strict selectivity for 2',5'- over 3',5'-phosphodiester bonds.","evidence":"X-ray structures of apo-Dbr1 and Dbr1–branched RNA complexes with functional variant validation","pmids":["25123664"],"confidence":"High","gaps":["Catalytic chemistry (acid/base, metal roles) not fully resolved","Identity of physiological metals not addressed"]},{"year":2016,"claim":"Combined structural, kinetic, and reconstitution work redefined Dbr1 as an Fe/Zn binuclear enzyme using a two-metal mechanism with His86 as general acid, correcting the earlier manganese model.","evidence":"Fe-edge anomalous diffraction, metal reconstitution, alanine-scanning, and phosphodiesterase kinetics in E. histolytica and yeast Dbr1","pmids":["27930312","27765821"],"confidence":"High","gaps":["Whether human Dbr1 uses the same metals not yet shown in cells","In-cell metal occupancy unknown"]},{"year":2022,"claim":"Iron chelation in human cells raised cellular lariat levels, establishing Fe as a biologically important cofactor rather than an in vitro artifact, and product-bound structures illuminated the kinetic mechanism.","evidence":"ICP-MS, apoenzyme reconstitution kinetics, deferoxamine treatment of human lymphoblasts; product-bound PS-bRNA crystal structure","pmids":["35459748","36484984"],"confidence":"High","gaps":["Direct measurement of Fe occupancy of Dbr1 in human cells not shown","Extent of product inhibition in vivo unknown"]},{"year":2023,"claim":"Identification of TTDN1/MPLKIP as a direct partner that binds the disordered C-terminal domain, stabilizes DBR1, and boosts catalytic efficiency linked Dbr1 regulation to a defined cofactor protein.","evidence":"NMR characterization, pulldown binding, reconstituted kinetics with TTDN1, and interaction proteomics in patient fibroblasts","pmids":["37507019","37800682"],"confidence":"High","gaps":["Structural basis of TTDN1–Dbr1 interaction not resolved","How TTDN1 mechanistically enhances catalysis is unknown","MPLKIP stabilization mechanism not reconstituted"]},{"year":2024,"claim":"A viable human knockout demonstrated DBR1 is the sole debranching enzyme, defined AQR-mediated recruitment to branchpoints, and established a direct role in spliceosome recycling and suppression of exon skipping.","evidence":"DBR1 KO cell line, co-IP mass spectrometry, ADAR lariat timestamping, transcriptomics, and spliceosome association assays","pmids":["38816363"],"confidence":"High","gaps":["Mechanism by which AQR delivers Dbr1 to the branchpoint not structurally defined","Substrate preference determinants only partially mapped"]},{"year":2024,"claim":"Knockout, epistasis, and mouse models established a non-splicing role for DBR1 in antiviral immunity, in which lariat accumulation degrades G3BP1/2, impairs stress granules, and blunts PKR.","evidence":"DBR1-deficient cells, PKR knockout epistasis, Dbr1Y17H mice, proteasome inhibition, and antiviral infection assays","pmids":["39636299"],"confidence":"High","gaps":["How lariats trigger G3BP1/2 degradation mechanistically is unresolved","Which sensors dominate in different tissues not defined"]},{"year":2024,"claim":"Patient-derived cells and neurons established inherited DBR1 deficiency as a cause of lariat accumulation and impaired antiviral immunity, with rescue and gain-of-function lariat transfection proving causality.","evidence":"DBR1 I120T patient fibroblasts, lentiviral WT rescue, hPSC-derived hindbrain neurons, SARS-CoV-2 infection, and exogenous lariat transfection","pmids":["39023559"],"confidence":"High","gaps":["Tissue-specific basis of clinical phenotype not fully explained","Quantitative threshold of lariat accumulation needed for disease unknown"]},{"year":2024,"claim":"Cytosolic accumulation of lariats, including Alu-derived dsRNA hairpins, was shown to chronically desensitize multiple dsRNA sensors, broadening the antiviral mechanism beyond PKR alone.","evidence":"DBR1 KO cells, dsRNA immunofluorescence, antiviral pathway readouts, and HSV-1/influenza/KSHV infections (preprint)","pmids":["bio_10.1101_2024.12.07.627371"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Relative contribution of MDA5/RIG-I/RNase L vs PKR not quantified"]},{"year":2017,"claim":"Knockdown studies linked DBR1 to HIV-1 replication, indicating the enzyme is required for forming or resolving a lariat-like structure during reverse transcription.","evidence":"siRNA/shRNA knockdown with cDNA rescue, cell fractionation, 5' RACE, RNase R resistance, and in vitro DBR1 catalytic-mutant control","pmids":["16232320","28931690","24672043"],"confidence":"Medium","gaps":["Direct vs indirect requirement not fully resolved by knockdown","Nature of the HIV lariat-like substrate incompletely defined"]},{"year":2026,"claim":"Interactome and phosphoproteomic profiling placed hDBR1 within RNA quality-control and stress-granule networks and identified regulatory phosphorylation sites.","evidence":"immunopurification mass spectrometry with RNase A treatment and phosphoproteomics","pmids":["41999910"],"confidence":"Medium","gaps":["Specific interactions not functionally validated","Functional consequence of phosphosites unknown"]},{"year":null,"claim":"How lariat accumulation is sensed to trigger proteasomal G3BP1/2 degradation, and how Dbr1 activity and recruitment are regulated by phosphorylation and partner proteins in vivo, remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No molecular mechanism connecting lariats to G3BP1/2 turnover","Functional role of identified phosphosites unestablished","Structure of AQR/TTDN1 complexes with Dbr1 unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0,1,2,4,9]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,4,6]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[2,9]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[10,16]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[9,14]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[10,11,16]}],"complexes":[],"partners":["AQR","TTDN1","MPLKIP","G3BP1","G3BP2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UK59","full_name":"Lariat debranching enzyme","aliases":[],"length_aa":544,"mass_kda":61.6,"function":"Cleaves the 2'-5' phosphodiester linkage at the branch point of excised lariat intron RNA and converts them into linear molecules that can be subsequently degraded, thereby facilitating ribonucleotide turnover (PubMed:10982890, PubMed:16232320, PubMed:2435736). Linked to its role in pre-mRNA processing mechanism, may also participate in retrovirus replication via an RNA lariat intermediate in cDNA synthesis and have an antiviral cell-intrinsic defense function in the brainstem (PubMed:16232320, PubMed:29474921)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9UK59/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/DBR1","classification":"Common Essential","n_dependent_lines":1204,"n_total_lines":1208,"dependency_fraction":0.9966887417218543},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CSNK1A1","stoichiometry":4.0}],"url":"https://opencell.sf.czbiohub.org/search/DBR1","total_profiled":1310},"omim":[{"mim_id":"620510","title":"XEROSIS AND GROWTH FAILURE WITH IMMUNE AND PULMONARY DYSFUNCTION SYNDROME; XGIP","url":"https://www.omim.org/entry/620510"},{"mim_id":"619441","title":"ENCEPHALITIS, ACUTE, INFECTION (VIRAL)-INDUCED, SUSCEPTIBILITY TO, 11; IIAE11","url":"https://www.omim.org/entry/619441"},{"mim_id":"610551","title":"ENCEPHALOPATHY, ACUTE, INFECTION-INDUCED (HERPES-SPECIFIC), SUSCEPTIBILITY TO, 1; IIAE1","url":"https://www.omim.org/entry/610551"},{"mim_id":"607024","title":"DEBRANCHING RNA LARIATS 1; DBR1","url":"https://www.omim.org/entry/607024"},{"mim_id":"605078","title":"TAR DNA-BINDING PROTEIN; TARDBP","url":"https://www.omim.org/entry/605078"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/DBR1"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9UK59","domains":[{"cath_id":"-","chopping":"3-395","consensus_level":"high","plddt":94.6788,"start":3,"end":395}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UK59","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UK59-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UK59-F1-predicted_aligned_error_v6.png","plddt_mean":78.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=DBR1","jax_strain_url":"https://www.jax.org/strain/search?query=DBR1"},"sequence":{"accession":"Q9UK59","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UK59.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UK59/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UK59"}},"corpus_meta":[{"pmid":"16275784","id":"PMC_16275784","title":"Structure-function analysis of yeast RNA debranching enzyme (Dbr1), a manganese-dependent phosphodiesterase.","date":"2005","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/16275784","citation_count":52,"is_preprint":false},{"pmid":"16232320","id":"PMC_16232320","title":"DBR1 siRNA inhibition of HIV-1 replication.","date":"2005","source":"Retrovirology","url":"https://pubmed.ncbi.nlm.nih.gov/16232320","citation_count":49,"is_preprint":false},{"pmid":"10982890","id":"PMC_10982890","title":"Human RNA lariat debranching enzyme cDNA complements the phenotypes of Saccharomyces cerevisiae dbr1 and Schizosaccharomyces pombe dbr1 mutants.","date":"2000","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/10982890","citation_count":41,"is_preprint":false},{"pmid":"25123664","id":"PMC_25123664","title":"Structural basis of lariat RNA recognition by the intron debranching enzyme Dbr1.","date":"2014","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/25123664","citation_count":40,"is_preprint":false},{"pmid":"28504715","id":"PMC_28504715","title":"Human DBR1 modulates the recycling of snRNPs to affect alternative RNA splicing and contributes to the suppression of cancer development.","date":"2017","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/28504715","citation_count":39,"is_preprint":false},{"pmid":"24672043","id":"PMC_24672043","title":"Impairment of HIV-1 cDNA synthesis by DBR1 knockdown.","date":"2014","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/24672043","citation_count":28,"is_preprint":false},{"pmid":"27930312","id":"PMC_27930312","title":"Metal dependence and branched RNA cocrystal structures of the RNA lariat debranching enzyme Dbr1.","date":"2016","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/27930312","citation_count":24,"is_preprint":false},{"pmid":"33038423","id":"PMC_33038423","title":"Dbr1 functions in mRNA processing, intron turnover and human diseases.","date":"2020","source":"Biochimie","url":"https://pubmed.ncbi.nlm.nih.gov/33038423","citation_count":22,"is_preprint":false},{"pmid":"39023559","id":"PMC_39023559","title":"SARS-CoV-2 brainstem encephalitis in human inherited DBR1 deficiency.","date":"2024","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39023559","citation_count":19,"is_preprint":false},{"pmid":"28931690","id":"PMC_28931690","title":"Conformational Changes in the 5' End of the HIV-1 Genome Dependent on the Debranching Enzyme DBR1 during Early Stages of Infection.","date":"2017","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/28931690","citation_count":15,"is_preprint":false},{"pmid":"38816363","id":"PMC_38816363","title":"The debranching enzyme Dbr1 regulates lariat turnover and intron splicing.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38816363","citation_count":14,"is_preprint":false},{"pmid":"39227617","id":"PMC_39227617","title":"Sequestration of DBR1 to stress granules promotes lariat intronic RNAs accumulation for heat-stress tolerance.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/39227617","citation_count":14,"is_preprint":false},{"pmid":"27765821","id":"PMC_27765821","title":"Mechanistic insights into the manganese-dependent phosphodiesterase activity of yeast Dbr1 with bis-p-nitrophenylphosphate and branched RNA substrates.","date":"2016","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/27765821","citation_count":13,"is_preprint":false},{"pmid":"39636299","id":"PMC_39636299","title":"Human DBR1 deficiency impairs stress granule-dependent PKR antiviral immunity.","date":"2024","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39636299","citation_count":12,"is_preprint":false},{"pmid":"37800682","id":"PMC_37800682","title":"Trichothiodystrophy-associated MPLKIP maintains DBR1 levels for proper lariat debranching and ectodermal differentiation.","date":"2023","source":"EMBO molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37800682","citation_count":11,"is_preprint":false},{"pmid":"28055181","id":"PMC_28055181","title":"Fluorescent Branched RNAs for High-Throughput Analysis of Dbr1 Enzyme Kinetics and Inhibition.","date":"2017","source":"ACS chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/28055181","citation_count":11,"is_preprint":false},{"pmid":"37656279","id":"PMC_37656279","title":"A founder DBR1 variant causes a lethal form of congenital ichthyosis.","date":"2023","source":"Human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37656279","citation_count":10,"is_preprint":false},{"pmid":"35459748","id":"PMC_35459748","title":"Metal content and kinetic properties of yeast RNA lariat debranching enzyme Dbr1.","date":"2022","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/35459748","citation_count":8,"is_preprint":false},{"pmid":"37507019","id":"PMC_37507019","title":"Activation of human RNA lariat debranching enzyme Dbr1 by binding protein TTDN1 occurs though an intrinsically disordered C-terminal domain.","date":"2023","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37507019","citation_count":6,"is_preprint":false},{"pmid":"40637223","id":"PMC_40637223","title":"DBR1 orchestrates the fate of lariat RNA: debranching-dependent turnover and function.","date":"2025","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/40637223","citation_count":4,"is_preprint":false},{"pmid":"36484984","id":"PMC_36484984","title":"Crystal Structure of the RNA Lariat Debranching Enzyme Dbr1 with Hydrolyzed Phosphorothioate RNA Product.","date":"2022","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/36484984","citation_count":3,"is_preprint":false},{"pmid":"7828812","id":"PMC_7828812","title":"Mapping of DBR1 and YPK1 suggests a major revision of the genetic map of the left arm of Saccharomyces cerevisiae Chromosome XI.","date":"1994","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/7828812","citation_count":3,"is_preprint":false},{"pmid":"37398028","id":"PMC_37398028","title":"The debranching enzyme Dbr1 regulates lariat turnover and intron splicing.","date":"2023","source":"Research square","url":"https://pubmed.ncbi.nlm.nih.gov/37398028","citation_count":2,"is_preprint":false},{"pmid":"40683339","id":"PMC_40683339","title":"RNA Lariat-Debranching Enzyme (DBR1) Variations in Sabinas Brittle Hair Syndrome Form of Trichothiodystrophy: A Trichothiodystrophy-Causing Gene.","date":"2025","source":"The Journal of investigative dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/40683339","citation_count":2,"is_preprint":false},{"pmid":"41366235","id":"PMC_41366235","title":"DBR1 Gene Mutation: Pathogenicity in the Homozygous State and Its Phenotype in Two Siblings.","date":"2025","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/41366235","citation_count":0,"is_preprint":false},{"pmid":"41999910","id":"PMC_41999910","title":"The human DBR1 interactome reveals coupling between intron lariat turnover, pre-mRNA splicing, and RNA quality control pathways.","date":"2026","source":"Cell stress & chaperones","url":"https://pubmed.ncbi.nlm.nih.gov/41999910","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.11.25.690381","title":"Signatures in CRISPR Mutational Spectra Reveal Role and Interplay of Genes in DNA Repair","date":"2025-11-26","source":"bioRxiv","url":"https://doi.org/10.1101/2025.11.25.690381","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.04.27.650888","title":"Cryptic intronic transcriptional initiation generates efficient endogenous mRNA templates for C9orf72-associated RAN translation","date":"2025-04-30","source":"bioRxiv","url":"https://doi.org/10.1101/2025.04.27.650888","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.12.07.627371","title":"Elevated levels of intracellular RNA lariats suppress the antiviral response","date":"2024-12-08","source":"bioRxiv","url":"https://doi.org/10.1101/2024.12.07.627371","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15602,"output_tokens":5204,"usd":0.062433,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13630,"output_tokens":4259,"usd":0.087313,"stage2_stop_reason":"end_turn"},"total_usd":0.149746,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"Yeast Dbr1 is a manganese-dependent RNA debranching enzyme that cleaves the 2'-5' phosphodiester bonds of lariat introns. Alanine scanning mutagenesis identified 13 conserved residues (His13, Asp40, Arg45, Asp49, Tyr68, Tyr69, Asn85, His86, Glu87, His179, Asp180, His231, His233) required for function in vivo; mutation of Asp40, Asn85, His86, His179, His231, or His233 to alanine abolished or greatly diminished debranching activity in vitro. Dbr1 sediments as a monomer and requires manganese as the metal cofactor.\",\n      \"method\": \"In vitro debranching assays with natural lariat RNAs and synthetic branched RNAs; alanine-scanning mutagenesis of 28 conserved residues; sedimentation analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis across 28 residues, multiple orthogonal methods (in vivo lariat accumulation assay + in vitro activity assay + sedimentation)\",\n      \"pmids\": [\"16275784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human DBR1 (hDBR1) encodes a functional RNA lariat debranching enzyme: recombinant hDBR1 expressed in E. coli showed debranching activity in vitro, and the cDNA complemented both the intron accumulation phenotype of S. cerevisiae dbr1 null mutants and the intron accumulation and slow growth phenotypes of S. pombe dbr1 null mutants.\",\n      \"method\": \"In vitro debranching assay with recombinant protein; interspecies complementation of S. cerevisiae and S. pombe dbr1 null mutants\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro activity assay plus cross-species genetic complementation in two distinct organisms\",\n      \"pmids\": [\"10982890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal structures of Dbr1 alone and in complex with synthetic RNA compounds mimicking the lariat branchpoint revealed the molecular basis for 2',5'-phosphodiester recognition and explained why Dbr1 lacks activity toward 3',5'-phosphodiester linkages. Functional data on Dbr1 variants confirmed structure-function relationships.\",\n      \"method\": \"X-ray crystallography of apo-Dbr1 and Dbr1–branched RNA complexes; functional assays on Dbr1 variants\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures with bound substrate mimics plus functional validation of variants in a single rigorous study\",\n      \"pmids\": [\"25123664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Entamoeba histolytica Dbr1 contains nearly stoichiometric Fe and Zn per polypeptide; Fe partitions primarily to the β-metal pocket and Zn to the α-pocket. Apo-Dbr1 reconstituted with Fe(II)+Zn(II) is active (~3–4 s⁻¹), while Mn(II) or Fe(II) under aerobic conditions yields inactive enzyme. Co-crystal structures of catalytic mutant H91A with 7-mer and 16-mer branched RNAs show a bridging hydroxide positioned for nucleophilic attack of the scissile phosphate.\",\n      \"method\": \"X-ray crystallography (Fe-edge anomalous diffraction); fluorogenic bRNA kinetic assay; metal reconstitution of apoenzyme under aerobic and anaerobic conditions; elemental analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures with substrate analogs, anomalous diffraction for metal identification, kinetic assays, and reconstitution experiments in one rigorous study\",\n      \"pmids\": [\"27930312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Yeast Dbr1 active site analysis established: (i) Cys11 is an essential active-site residue, extending the Cys11-Xaa-His13 motif as the metal-binding element (atypical within the metallophosphoesterase superfamily); (ii) His86 acts as a general acid catalyst that protonates the O2' leaving group of the 2'-5' phosphodiester; (iii) Dbr1 adheres to a two-metal catalytic mechanism. Dbr1 also exhibits vigorous Mn²⁺-dependent phosphodiesterase activity toward bis-p-nitrophenylphosphate, which does not require His86.\",\n      \"method\": \"Alanine-scanning mutagenesis; in vitro phosphodiesterase assay with bis-p-nitrophenylphosphate and branched RNA substrates; structure-activity analysis\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assays with multiple substrates and mutagenesis, interpreted with structural context; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"27765821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Saccharomyces cerevisiae Dbr1 contains stoichiometric Fe and Zn; Fe²⁺ is the most effective cofactor for reconstituting activity in apoenzyme (turnover ~9.2 s⁻¹). Treatment of human lymphoblastoid cells with the iron chelator deferoxamine caused a ~2-fold increase in cellular lariat levels, indicating Fe is an important biological cofactor for Dbr1.\",\n      \"method\": \"Elemental analysis (ICP-MS); apoenzyme reconstitution with Fe²⁺, Zn²⁺, Mn²⁺; fluorogenic bRNA kinetic assay; deferoxamine treatment of human cells with lariat quantification\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution kinetics, elemental analysis, and cellular iron-chelation experiment; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"35459748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A product-bound crystal structure of E. histolytica Dbr1 co-crystallized with a phosphorothioate-branched RNA (PS-bRNA) showed in-crystal hydrolysis of the phosphorothioate bond, revealing a product-bound active site state. Dbr1 cleaves phosphorothioate linkages ~10,000-fold more slowly than native phosphate linkages. The structure suggests product inhibition may contribute to the kinetic mechanism.\",\n      \"method\": \"X-ray crystallography of EhDbr1 with PS-bRNA; kinetic comparison of phosphorothioate vs native substrate cleavage\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure of product-bound enzyme plus kinetic measurements; single lab, two orthogonal methods\",\n      \"pmids\": [\"36484984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Human Dbr1 contains a disordered C-terminal domain (characterized by NMR and sequence analysis) that stabilizes Dbr1 by reducing aggregation but is dispensable for debranching activity. The noncatalytic protein Drn1 and TTDN1 (MPLKIP) directly bind human Dbr1. Addition of TTDN1 to in vitro debranching reactions increases the catalytic efficiency of human Dbr1 19-fold but has no effect on E. histolytica Dbr1, which lacks the disordered C-terminal domain. Dbr1 requires Fe²⁺ for efficient catalysis. The identity of the branchpoint nucleotide affects debranching rates.\",\n      \"method\": \"NMR spectroscopy; in vitro binding assays (pulldown); in vitro debranching kinetics with TTDN1; comparative analysis with E. histolytica Dbr1; sequence analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — NMR structural characterization, in vitro binding, and reconstituted kinetic assays with multiple orthogonal methods in a single study\",\n      \"pmids\": [\"37507019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MPLKIP (TTDN1) interacts with core splicing factors and the lariat debranching protein DBR1 (identified by mass spectrometry-based interaction proteomics). MPLKIP-deficient primary fibroblasts have reduced steady-state DBR1 protein levels, indicating MPLKIP stabilizes DBR1.\",\n      \"method\": \"Mass spectrometry-based interaction proteomics (co-immunoprecipitation); immunoblot of MPLKIP-deficient fibroblasts\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — MS-based interactome and immunoblot in patient-derived cells; two methods but no direct reconstitution of the stabilization mechanism\",\n      \"pmids\": [\"37800682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DBR1 is the sole debranching enzyme in human cells (demonstrated by knockout). The predominantly nuclear Dbr1 preferentially debranches substrates containing canonical U2 binding motifs and shows specificity for particular 5' splice site sequences. Dbr1 is recruited to the branchpoint through the intron-binding protein AQR (identified by co-immunoprecipitation mass spectrometry). DBR1 depletion causes a 20-fold increase in lariats, increases exon skipping, and causes spliceosomal components to remain associated with lariats for longer, demonstrating a role for Dbr1 in spliceosome recycling.\",\n      \"method\": \"DBR1 knockout cell line generation; co-immunoprecipitation mass spectrometry; ADAR-fusion lariat timestamping; transcriptomic analysis; spliceosome association assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — viable KO cell line with multiple orthogonal readouts (interactome, substrate specificity, spliceosome association, lariat timestamping), peer-reviewed and also available as preprint confirming the same findings\",\n      \"pmids\": [\"38816363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Accumulation of RNA lariats in human DBR1-deficient cells interferes with stress granule (SG) assembly by promoting proteasome-mediated degradation of G3BP1 and G3BP2. Impaired SG assembly reduces PKR recruitment and activation, impairing antiviral immunity against HSV-1. Genetic ablation of PKR abolished the antiviral effect of DBR1 in vitro. Dbr1Y17H/Y17H mice are susceptible to viral infections and show decreased G3BP1/2 expression and reduced PKR phosphorylation in cells and brain.\",\n      \"method\": \"DBR1-deficient human cell lines; PKR knockout epistasis; Dbr1Y17H/Y17H mouse model; proteasome inhibition; immunoblot for G3BP1/2 and p-PKR; antiviral infection assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis (PKR KO), multiple human cell and mouse model experiments, confirmed in vivo, multiple orthogonal mechanistic readouts\",\n      \"pmids\": [\"39636299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DBR1 I120T/I120T homozygous fibroblasts from patients with inherited DBR1 deficiency have low DBR1 protein levels and high RNA lariat accumulation. Exogenous WT DBR1 expression in patient-derived DBR1 I120T/I120T fibroblasts and hPSC-derived hindbrain neurons rescued the RNA lariat accumulation phenotype. Expression of exogenous RNA lariats (mimicking DBR1 deficiency) increased susceptibility of WT hindbrain neurons to SARS-CoV-2 infection, indicating that lariat accumulation per se impairs antiviral immunity.\",\n      \"method\": \"Patient fibroblast analysis; lentiviral rescue with WT DBR1; hPSC-derived hindbrain neuron differentiation; SARS-CoV-2 infection assay; exogenous lariat transfection\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rescue experiment in primary patient cells and iPSC-derived neurons, plus gain-of-function lariat transfection establishing causality; multiple orthogonal methods\",\n      \"pmids\": [\"39023559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"DBR1 knockdown in HIV-infected cells inhibits formation of intermediate and full-length HIV-1 cDNA without affecting minus-strand strong-stop cDNA. This inhibition occurs in the nucleus or perinuclear region: when nuclear import of the HIV-1 reverse transcription complex is blocked by a truncated CPSF6, reverse transcription is completed in the cytoplasm in a DBR1-independent manner. In vitro incubation with yeast or human DBR1 (but not catalytically inactive DBR1(N85A)) resolved a lariat-like structure at the 5' end of HIV-1 RNA detected in infected DBR1-knockdown cells. HIV-1 RNA from DBR1-knockdown cells was resistant to RNase R (which degrades linear but not circular/lariat RNAs), supporting formation of a lariat-like structure.\",\n      \"method\": \"shRNA knockdown; cell fractionation; CPSF6 truncation for nuclear import block; 5' RACE; RNase R treatment; in vitro DBR1 treatment with catalytic mutant control\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (fractionation, 5' RACE, RNase R, mutant enzyme control) in a single lab; shRNA knockdown approach limits certainty about direct vs indirect effects\",\n      \"pmids\": [\"28931690\", \"24672043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"siRNA-mediated knockdown of human DBR1 expression (reducing mRNA by ~80%) led to decreases in HIV-1 cDNA and protein production; this effect was reversed by cotransfection of a DBR1 cDNA, confirming specificity of the DBR1 requirement for HIV-1 replication.\",\n      \"method\": \"siRNA knockdown; DBR1 cDNA rescue; HIV-1 cDNA quantification; viral protein detection\",\n      \"journal\": \"Retrovirology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — knockdown with specific rescue experiment confirms on-target effect; mechanism inferred indirectly without direct biochemical demonstration of lariat intermediates\",\n      \"pmids\": [\"16232320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"hDBR1 modulates snRNP recycling to affect alternative RNA splicing. Insufficient hDBR1 leads to higher rates of exon skipping confirmed by transcriptomic sequencing. Wild-type p53 and HIF-1 co-regulate hDBR1 expression. Higher hDBR1 expression only affected exon-skipping activity in malignant (not normal) cells.\",\n      \"method\": \"siRNA knockdown; transcriptomic sequencing; metabolite profiling; in vivo tumor models; reporter assays for splicing\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — transcriptomic plus metabolomics plus in vivo data; mechanistic detail of snRNP recycling step is inferred rather than directly reconstituted\",\n      \"pmids\": [\"28504715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"hDBR1 physically associates with spliceosome components, intron-turnover factors (including AQR), and RNA quality-control proteins (UPF1, XRN2, DHX29) as identified by immunopurification coupled to mass spectrometry. RNase A treatment identified an RNA-dependent subnetwork enriched for stress-granule proteins and hnRNPs. Phosphoproteomic profiling identified multiple hDBR1 phosphorylation sites, including four residues preferentially detected after RNase treatment.\",\n      \"method\": \"Immunopurification coupled to mass spectrometry (gel-based and on-bead workflows); RNase A treatment; phosphoproteomic profiling\",\n      \"journal\": \"Cell stress & chaperones\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — IP-MS interactome with RNA-dependent subnetwork analysis and phosphoproteomics; single lab, no functional validation of specific interactions reported in abstract\",\n      \"pmids\": [\"41999910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In DBR1-null cells, lariats accumulate in the cytosol and dsRNA (formed by inverted Alu element hairpins within introns) becomes enriched. Chronic exposure to accumulated lariats attenuates dsRNA sensors MDA5, RIG-I, RNase L, and PKR, reducing the antiviral response. Lariats are transiently elevated during infection (HSV-1, influenza, KSHV).\",\n      \"method\": \"DBR1 knockout cells; dsRNA immunofluorescence and quantification; antiviral pathway activation assays; infection experiments with HSV-1, influenza, KSHV\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO cell line with multiple pathway readouts; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.12.07.627371\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"DBR1 (Dbr1) is the sole eukaryotic RNA lariat debranching enzyme, a binuclear metallophosphoesterase (using Fe²⁺ and Zn²⁺ as biological cofactors) that hydrolyzes the 2'-5' phosphodiester bond at the branchpoint of excised intron lariats via a two-metal mechanism involving a Cys11-Xaa-His13 metal-binding motif and His86 as a general acid catalyst; it is predominantly nuclear, recruited to branchpoints partly via the intron-binding protein AQR, is the rate-limiting step in lariat turnover, and its debranching activity is required for spliceosome recycling (preventing exon skipping), for processing of snoRNAs and miRNAs from intronic lariats, and for innate antiviral immunity by preventing cytosolic accumulation of lariat dsRNA that would otherwise desensitize PKR and other dsRNA sensors through a pathway involving G3BP1/2-dependent stress granule assembly.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"DBR1 is the sole RNA lariat debranching enzyme in eukaryotic cells, a binuclear metallophosphoesterase that hydrolyzes the 2'-5' phosphodiester bond at the branchpoint of excised intron lariats and is thereby the rate-limiting step in lariat turnover [#0, #1, #9]. Catalysis proceeds by a two-metal mechanism in which a Cys11-Xaa-His13 motif coordinates the active-site metals and His86 serves as a general acid that protonates the O2' leaving group, with structures of substrate- and product-bound enzyme defining how Dbr1 specifically recognizes 2',5'- but not 3',5'-linkages [#2, #4, #6]. Although early work scored the enzyme as manganese-dependent, the biological cofactors are Fe2+ in the β-pocket and Zn2+ in the α-pocket, and iron chelation in human cells raises lariat levels, establishing Fe as physiologically relevant [#0, #3, #5, #7]. In human cells DBR1 is predominantly nuclear, is recruited to the branchpoint via the intron-binding protein AQR, and preferentially acts on substrates bearing canonical U2 motifs; its debranching activity is required for spliceosome recycling, since loss of DBR1 causes ~20-fold lariat accumulation, prolonged retention of spliceosomal components on lariats, and increased exon skipping [#9, #14]. The disordered C-terminal domain of human Dbr1 reduces aggregation and provides a docking site for the noncatalytic partner TTDN1 (MPLKIP), which both stabilizes DBR1 and stimulates its catalytic efficiency ~19-fold [#7, #8]. Beyond splicing, DBR1 supports innate antiviral immunity: when lariats accumulate they reach the cytosol and form Alu-derived dsRNA hairpins, drive proteasomal degradation of the stress-granule scaffolds G3BP1/2, and blunt PKR and other dsRNA sensors, with PKR ablation abolishing the antiviral effect and Dbr1-hypomorphic mice showing susceptibility to viral infection [#10, #16]. Inherited DBR1 deficiency (e.g. the I120T variant) lowers DBR1 protein, causes lariat accumulation, and increases susceptibility of patient and stem-cell-derived hindbrain neurons to viral infection, a phenotype rescued by wild-type DBR1 [#11].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that the human gene encodes a bona fide debranching enzyme converted a yeast activity into a defined human enzyme and showed functional conservation across eukaryotes.\",\n      \"evidence\": \"in vitro debranching assay with recombinant hDBR1 plus cross-species complementation of S. cerevisiae and S. pombe dbr1 nulls\",\n      \"pmids\": [\"10982890\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural or mechanistic detail of the active site\", \"Physiological metal cofactor not defined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Mutagenesis defined the catalytic residue set required for debranching, mapping the functional active site of the enzyme.\",\n      \"evidence\": \"alanine-scanning of 28 conserved residues with in vitro and in vivo lariat assays in yeast Dbr1\",\n      \"pmids\": [\"16275784\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Manganese assigned as cofactor, later revised\", \"Catalytic roles of individual residues not yet mechanistically assigned\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Crystal structures with branchpoint-mimicking RNA explained substrate recognition and the strict selectivity for 2',5'- over 3',5'-phosphodiester bonds.\",\n      \"evidence\": \"X-ray structures of apo-Dbr1 and Dbr1–branched RNA complexes with functional variant validation\",\n      \"pmids\": [\"25123664\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic chemistry (acid/base, metal roles) not fully resolved\", \"Identity of physiological metals not addressed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Combined structural, kinetic, and reconstitution work redefined Dbr1 as an Fe/Zn binuclear enzyme using a two-metal mechanism with His86 as general acid, correcting the earlier manganese model.\",\n      \"evidence\": \"Fe-edge anomalous diffraction, metal reconstitution, alanine-scanning, and phosphodiesterase kinetics in E. histolytica and yeast Dbr1\",\n      \"pmids\": [\"27930312\", \"27765821\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether human Dbr1 uses the same metals not yet shown in cells\", \"In-cell metal occupancy unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Iron chelation in human cells raised cellular lariat levels, establishing Fe as a biologically important cofactor rather than an in vitro artifact, and product-bound structures illuminated the kinetic mechanism.\",\n      \"evidence\": \"ICP-MS, apoenzyme reconstitution kinetics, deferoxamine treatment of human lymphoblasts; product-bound PS-bRNA crystal structure\",\n      \"pmids\": [\"35459748\", \"36484984\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct measurement of Fe occupancy of Dbr1 in human cells not shown\", \"Extent of product inhibition in vivo unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of TTDN1/MPLKIP as a direct partner that binds the disordered C-terminal domain, stabilizes DBR1, and boosts catalytic efficiency linked Dbr1 regulation to a defined cofactor protein.\",\n      \"evidence\": \"NMR characterization, pulldown binding, reconstituted kinetics with TTDN1, and interaction proteomics in patient fibroblasts\",\n      \"pmids\": [\"37507019\", \"37800682\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of TTDN1–Dbr1 interaction not resolved\", \"How TTDN1 mechanistically enhances catalysis is unknown\", \"MPLKIP stabilization mechanism not reconstituted\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A viable human knockout demonstrated DBR1 is the sole debranching enzyme, defined AQR-mediated recruitment to branchpoints, and established a direct role in spliceosome recycling and suppression of exon skipping.\",\n      \"evidence\": \"DBR1 KO cell line, co-IP mass spectrometry, ADAR lariat timestamping, transcriptomics, and spliceosome association assays\",\n      \"pmids\": [\"38816363\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which AQR delivers Dbr1 to the branchpoint not structurally defined\", \"Substrate preference determinants only partially mapped\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Knockout, epistasis, and mouse models established a non-splicing role for DBR1 in antiviral immunity, in which lariat accumulation degrades G3BP1/2, impairs stress granules, and blunts PKR.\",\n      \"evidence\": \"DBR1-deficient cells, PKR knockout epistasis, Dbr1Y17H mice, proteasome inhibition, and antiviral infection assays\",\n      \"pmids\": [\"39636299\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How lariats trigger G3BP1/2 degradation mechanistically is unresolved\", \"Which sensors dominate in different tissues not defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Patient-derived cells and neurons established inherited DBR1 deficiency as a cause of lariat accumulation and impaired antiviral immunity, with rescue and gain-of-function lariat transfection proving causality.\",\n      \"evidence\": \"DBR1 I120T patient fibroblasts, lentiviral WT rescue, hPSC-derived hindbrain neurons, SARS-CoV-2 infection, and exogenous lariat transfection\",\n      \"pmids\": [\"39023559\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific basis of clinical phenotype not fully explained\", \"Quantitative threshold of lariat accumulation needed for disease unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Cytosolic accumulation of lariats, including Alu-derived dsRNA hairpins, was shown to chronically desensitize multiple dsRNA sensors, broadening the antiviral mechanism beyond PKR alone.\",\n      \"evidence\": \"DBR1 KO cells, dsRNA immunofluorescence, antiviral pathway readouts, and HSV-1/influenza/KSHV infections (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.12.07.627371\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Relative contribution of MDA5/RIG-I/RNase L vs PKR not quantified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Knockdown studies linked DBR1 to HIV-1 replication, indicating the enzyme is required for forming or resolving a lariat-like structure during reverse transcription.\",\n      \"evidence\": \"siRNA/shRNA knockdown with cDNA rescue, cell fractionation, 5' RACE, RNase R resistance, and in vitro DBR1 catalytic-mutant control\",\n      \"pmids\": [\"16232320\", \"28931690\", \"24672043\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect requirement not fully resolved by knockdown\", \"Nature of the HIV lariat-like substrate incompletely defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Interactome and phosphoproteomic profiling placed hDBR1 within RNA quality-control and stress-granule networks and identified regulatory phosphorylation sites.\",\n      \"evidence\": \"immunopurification mass spectrometry with RNase A treatment and phosphoproteomics\",\n      \"pmids\": [\"41999910\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific interactions not functionally validated\", \"Functional consequence of phosphosites unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How lariat accumulation is sensed to trigger proteasomal G3BP1/2 degradation, and how Dbr1 activity and recruitment are regulated by phosphorylation and partner proteins in vivo, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular mechanism connecting lariats to G3BP1/2 turnover\", \"Functional role of identified phosphosites unestablished\", \"Structure of AQR/TTDN1 complexes with Dbr1 unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 1, 2, 4, 9]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 4, 6]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [2, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [10, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [9, 14]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [10, 11, 16]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"AQR\", \"TTDN1\", \"MPLKIP\", \"G3BP1\", \"G3BP2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}