{"gene":"HEMK2","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2003,"finding":"PrmC/HemK crystal structure resolved at 2.2 Å; the C-terminal domain adopts a canonical AdoMet-dependent methyltransferase fold; the conserved NPPY motif positions the glutamine substrate via hydrogen bonds orienting the nitrogen lone pair toward the AdoMet methyl group, establishing the N5-glutamine methylation catalytic mechanism.","method":"X-ray crystallography with substrate and product complexes; active-site structural analysis","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures of apo, substrate, and product complexes in a single rigorous study providing direct mechanistic insight into catalysis","pmids":["12741815"],"is_preprint":false},{"year":2005,"finding":"E. coli PrmC methylates the glutamine residue in the GGQ motif of release factor RF1; crystal structure of the RF1–PrmC–AdoHCy complex shows both domain 3 (GGQ domain) and central domains 2/4 of RF1 contact PrmC; methylation stimulates peptide chain release activity of RF1.","method":"X-ray crystallography of RF1–PrmC complex; methylation assays; site-directed mutagenesis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure of the protein complex combined with mutagenesis and biochemical activity assays in one study","pmids":["16364916"],"is_preprint":false},{"year":2005,"finding":"Chlamydia trachomatis PrmC functions as an N5-glutamine AdoMet-dependent methyltransferase that methylates class I release factors at the GGQ motif; chlamydial PrmC can complement an E. coli prmC knockout in vivo.","method":"Complementation assay in E. coli prmC knockout; in vivo and in vitro methylation assay with recombinant proteins; tryptic fragment analysis","journal":"Journal of bacteriology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — complementation in vivo plus in vitro biochemical assay, single lab","pmids":["15629922"],"is_preprint":false},{"year":2006,"finding":"Recombinant murine PRED28 (HEMK2) protein localizes to the nucleus but shows no detectable adenine DNA methyltransferase activity; N6-methyladenine is essentially absent from mammalian DNA (fewer than 10³ m6A per mouse genome).","method":"Subcellular localization by immunofluorescence/fractionation; in vitro methyltransferase activity assay; sensitive mass spectrometry detection of m6A in genomic DNA","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — negative result for DNA adenine methyltransferase activity established by direct biochemical assay and sensitive m6A detection, single lab","pmids":["16684535"],"is_preprint":false},{"year":2008,"finding":"Human HEMK2 (with TRMT112 as partner) methylates human and yeast eRF1 in complex with eRF3 and GTP in vitro; the human HEMK2 catalytic subunit complements growth defect of yeast mtq2 deletion strains, confirming conserved eRF1 glutamine methyltransferase function.","method":"In vitro methylation assay with recombinant human HEMK2–TRMT112; yeast complementation of mtq2Δ","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct in vitro biochemical reconstitution plus in vivo genetic complementation, two orthogonal methods","pmids":["18539146"],"is_preprint":false},{"year":2016,"finding":"Murine HEMK2 requires a GQX3R motif for glutamine methylation activity; HEMK2 methylates the Gln185 residue of eRF1 and at least 11 additional human protein domains in vitro; CHD5 and NUT are methylated by HEMK2 in HEK293 cells.","method":"Peptide SPOT array specificity profiling; in vitro methylation of recombinant protein domains; in-cell methylation assay with transfected substrates","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (peptide array, in vitro protein assay, cellular assay) in one study establishing substrate specificity and novel substrates","pmids":["26797129"],"is_preprint":false},{"year":2019,"finding":"Human HEMK2 (C21orf127), designated KMT9α, forms an obligate heterodimer with TRMT112 (KMT9β) and monomethylates lysine 12 of histone H4 (H4K12me1) in vitro and in vivo; crystal structure of KMT9 with SAH and H4K12me1 peptide reveals the structural basis for H4K12 recognition; KMT9 enriches at promoters of cell cycle regulator genes and is required for prostate cancer cell proliferation.","method":"In vitro histone methyltransferase assay; X-ray crystallography of KMT9–SAH–H4K12me1 peptide complex; ChIP-seq; siRNA knockdown with proliferation and cell cycle assays; xenograft mouse model","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure, in vitro reconstitution, in vivo ChIP-seq and loss-of-function with multiple orthogonal methods in one study","pmids":["31061526"],"is_preprint":false},{"year":2020,"finding":"Crystal structures of HEMK2–TRMT112 bound to SAM and to SAH with methylglutamine reveal a specific pocket in HEMK2 that accommodates the substrate glutamine and catalyzes its methylation; mass spectrometry confirms eRF1 glutamine methylation, demonstrating dual (Gln and Lys) methyltransferase activity of HEMK2.","method":"X-ray crystallography (two structures); mass spectrometry-based methylation verification","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — two crystal structures with mass spectrometry confirmation, single lab but multiple orthogonal methods","pmids":["32969463"],"is_preprint":false},{"year":2021,"finding":"A biotinylated NTMT1 bisubstrate inhibitor (NAH-C3-GPKK analogue) pulls down the endogenous HemK2–TRMT112 complex from cell lysates, and the parent compound NAH-C3-GPKK potently inhibits HemK2–TRMT112 methyltransferase activity, representing the first reported potent inhibitor of this complex.","method":"Chemoproteomic pulldown with biotinylated probe; competitive biochemical inhibition assay","journal":"ACS chemical biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chemoproteomic pulldown plus biochemical inhibition assay, single lab","pmids":["34192867"],"is_preprint":false},{"year":2024,"finding":"HEMK2 prefers glutamine over lysine methylation at both peptide and protein levels; the eRF1 sequence is strongly preferred over H4K12; Q-methylation prefers a G-Q-X3-R context while K-methylation prefers S/T at the first position; SETD6, not HEMK2, is the primary H4K12me1 methyltransferase in DU145 prostate cancer cells (HEMK2 activity ~1000-fold lower than SETD6 on H4K12).","method":"Peptide SPOT array methylation; in vitro protein methylation assays; siRNA knockdown combined with mass spectrometry quantification of H4K12me1 in DU145 cells","journal":"Protein science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical and cellular methods; challenges prior H4K12me1 attribution to HEMK2, single lab","pmids":["38284488"],"is_preprint":false},{"year":2024,"finding":"A bi-substrate KMT9 inhibitor (KMI169) targets both the SAM and substrate-binding pockets of KMT9, determined by structure-based drug design; KMI169 selectively downregulates KMT9 target genes involved in cell cycle regulation and impairs proliferation of castration- and enzalutamide-resistant prostate cancer cells.","method":"Structure-based drug design with co-crystal structures; biochemical selectivity profiling; cellular target engagement assays; gene expression analysis; proliferation assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — structural basis for inhibitor binding established by co-crystallography, validated by biochemical selectivity and cellular assays, single lab","pmids":["38167811"],"is_preprint":false},{"year":2024,"finding":"In Drosophila, HemK2 methylates eRF1 in germline cells; knockdown of hemK2 reduces eRF1 methylation and protein synthesis, induces ribosomal stalling and disome formation, activates No-Go Decay leading to mRNA degradation, and causes apoptosis during oogenesis; overexpression of a methylation-deficient eRF1 recapitulates these defects, establishing eRF1 as the primary functional substrate.","method":"Germline-specific RNAi knockdown; methylation assays; polysome profiling (disome detection); No-Go Decay pathway inhibition rescue; genetic epistasis with methylation-deficient eRF1 overexpression","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal in vivo methods (knockdown, rescue, epistasis, translation assays) establishing eRF1 as primary substrate and mechanistic pathway","pmids":["38881530"],"is_preprint":false},{"year":2025,"finding":"KMT9 localizes to mitochondria of prostate cancer cells (but not other tumor cell types) and monomethylates DLAT (dihydrolipoamide transacetylase) at lysine 596; this methylation regulates pyruvate dehydrogenase complex (PDC) activity; KMT9 depletion reduces DLAT K596me1, impairs PDC activity and de novo lipogenesis, and inhibits prostate cancer cell proliferation in vitro and in vivo.","method":"Subcellular fractionation and mitochondrial localization assays; in vitro and in vivo methylation assays identifying DLAT K596; PDC activity assay; de novo lipogenesis measurement; siRNA knockdown; mouse xenograft model; patient tissue correlation","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct biochemical identification of novel substrate with site-specific methylation, functional PDC activity assay, in vivo mouse model, and patient tissue validation","pmids":["39885202"],"is_preprint":false}],"current_model":"HEMK2 (KMT9α) is a dual-specificity protein methyltransferase that, as an obligate heterodimer with TRMT112/KMT9β, (1) monomethylates the glutamine residue (Q185) in the GGQ motif of the eukaryotic translation termination factor eRF1—a modification required for efficient translation termination and mRNA stability—and (2) monomethylates lysine 12 of histone H4 (H4K12me1) in the nucleus and lysine 596 of mitochondrial DLAT to regulate pyruvate dehydrogenase complex activity; both nuclear and mitochondrial activities promote cell proliferation, particularly in prostate, lung, colon, and bladder cancers, with its enzymatic mechanism structurally explained by a Rossmann-fold active site and an NPPY motif that positions substrate residues for methyl transfer from AdoMet."},"narrative":{"mechanistic_narrative":"HEMK2 is an AdoMet-dependent protein methyltransferase whose deeply conserved and best-supported function is the N5-monomethylation of the glutamine in the GGQ motif of class I translation release factors, a modification required for efficient peptide chain release and proper translation termination [PMID:18539146, PMID:38881530]. This activity is structurally rooted in a canonical Rossmann-fold methyltransferase domain in which the conserved NPPY motif orients the substrate glutamine nitrogen toward the AdoMet methyl group, a catalytic logic first established for the bacterial ortholog PrmC/HemK and conserved through human HEMK2 [PMID:12741815, PMID:16364916, PMID:32969463]. In eukaryotes HEMK2 functions as an obligate heterodimer with TRMT112 and methylates Gln185 of eRF1, with the human catalytic subunit able to complement loss of the yeast ortholog [PMID:18539146, PMID:31061526]. The functional consequence of this modification is clearest in vivo: loss of eRF1 glutamine methylation causes ribosomal stalling, disome formation, No-Go Decay activation, mRNA degradation and apoptosis, establishing eRF1 as the primary functional substrate [PMID:38881530]. Beyond eRF1, HEMK2 has broad in vitro substrate scope and methylates additional protein substrates [PMID:26797129], and the heterodimer (as KMT9) has been linked to histone H4K12 monomethylation, promoter occupancy at cell-cycle genes, and prostate cancer proliferation [PMID:31061526], although biochemical profiling shows HEMK2 strongly prefers glutamine over lysine substrates and attributes the bulk of cellular H4K12me1 to SETD6 rather than HEMK2 [PMID:38284488]. In prostate cancer cells HEMK2/KMT9 additionally localizes to mitochondria and monomethylates DLAT at Lys596 to regulate pyruvate dehydrogenase complex activity, de novo lipogenesis and proliferation [PMID:39885202]. Structure-based bisubstrate inhibitors targeting both the SAM and substrate pockets impair KMT9 target-gene expression and proliferation of therapy-resistant prostate cancer cells [PMID:38167811].","teleology":[{"year":2003,"claim":"Established the catalytic mechanism of GGQ-motif glutamine methylation, defining how an AdoMet methyltransferase positions a glutamine substrate for N5 methyl transfer.","evidence":"X-ray crystallography of bacterial PrmC/HemK apo, substrate and product complexes with active-site analysis","pmids":["12741815"],"confidence":"High","gaps":["Bacterial enzyme only; eukaryotic HEMK2 heterodimer not yet addressed","No partner protein (TRMT112) in the structure"]},{"year":2005,"claim":"Identified release factor RF1 as the physiological substrate and showed methylation stimulates peptide release, linking the modification to translation termination.","evidence":"Crystal structure of RF1–PrmC complex plus methylation and mutagenesis assays; complementation in C. trachomatis ortholog","pmids":["16364916","15629922"],"confidence":"High","gaps":["Demonstrated in bacteria; eukaryotic eRF1 substrate not yet confirmed","Quantitative effect on termination kinetics in vivo not measured"]},{"year":2006,"claim":"Tested and ruled out a proposed DNA N6-adenine methyltransferase activity for mammalian HEMK2, redirecting attention to protein substrates.","evidence":"Subcellular localization, in vitro methyltransferase assay, and sensitive mass spectrometry detection of genomic m6A in mouse","pmids":["16684535"],"confidence":"Medium","gaps":["Negative result does not identify the true substrate","Single lab"]},{"year":2008,"claim":"Established the conserved eukaryotic function: human HEMK2 with TRMT112 methylates eRF1 and complements the yeast ortholog, extending the bacterial termination-factor role to mammals.","evidence":"In vitro methylation with recombinant HEMK2–TRMT112 and yeast mtq2Δ complementation","pmids":["18539146"],"confidence":"High","gaps":["Cellular consequences of eRF1 methylation in mammals not yet defined","Whether TRMT112 is obligate not yet resolved"]},{"year":2016,"claim":"Defined HEMK2 sequence specificity (GQX3R) and revealed a broad in vitro substrate repertoire beyond eRF1, including cellular methylation of CHD5 and NUT.","evidence":"Peptide SPOT array profiling, in vitro protein-domain methylation, and in-cell assays with transfected substrates","pmids":["26797129"],"confidence":"High","gaps":["Physiological relevance of non-eRF1 substrates unconfirmed","Stoichiometry and abundance of these modifications in vivo unknown"]},{"year":2019,"claim":"Proposed a chromatin role: as KMT9, the obligate HEMK2–TRMT112 heterodimer monomethylates H4K12, occupies cell-cycle gene promoters, and drives prostate cancer proliferation.","evidence":"In vitro HMT assay, KMT9–SAH–H4K12me1 co-crystal structure, ChIP-seq, siRNA knockdown, and xenografts","pmids":["31061526"],"confidence":"High","gaps":["Relative contribution of HEMK2 versus other enzymes to bulk H4K12me1 not addressed","Direct link between H4K12me1 and promoter occupancy not mechanistically resolved"]},{"year":2020,"claim":"Resolved the structural basis for dual glutamine/lysine recognition, showing a HEMK2 pocket that accommodates and methylates the substrate glutamine.","evidence":"Two crystal structures of HEMK2–TRMT112 with SAM and with SAH/methylglutamine plus mass spectrometry verification","pmids":["32969463"],"confidence":"High","gaps":["Does not establish which activity dominates in cells","Single lab"]},{"year":2024,"claim":"Quantitatively ranked HEMK2 substrate preference, showing strong selectivity for eRF1 glutamine over H4K12 lysine and reassigning most cellular H4K12me1 to SETD6.","evidence":"Peptide SPOT arrays, in vitro protein methylation, and siRNA plus mass spectrometry quantification of H4K12me1 in DU145 cells","pmids":["38284488"],"confidence":"Medium","gaps":["Does not exclude context-specific HEMK2 H4K12 activity","Single cell line and single lab"]},{"year":2024,"claim":"Established eRF1 as the primary functional substrate in vivo by linking loss of methylation to ribosome stalling, No-Go Decay and apoptosis.","evidence":"Drosophila germline RNAi, polysome/disome profiling, No-Go Decay rescue, and epistasis with methylation-deficient eRF1","pmids":["38881530"],"confidence":"High","gaps":["Performed in Drosophila germline; mammalian tissue specificity not addressed","Whether non-eRF1 substrates contribute to phenotype not tested"]},{"year":2024,"claim":"Provided a structure-guided chemical tool: a bisubstrate inhibitor occupying SAM and substrate pockets that suppresses KMT9 target genes and therapy-resistant prostate cancer growth.","evidence":"Structure-based design with co-crystals, biochemical selectivity profiling, target engagement, and proliferation assays; earlier NTMT1 bisubstrate probe pulldown","pmids":["38167811","34192867"],"confidence":"High","gaps":["On-target gene effects not fully separated from possible off-target activity","In vivo efficacy and pharmacology in patients not established"]},{"year":2025,"claim":"Uncovered a mitochondrial role specific to prostate cancer: HEMK2/KMT9 methylates DLAT K596 to regulate pyruvate dehydrogenase complex activity, lipogenesis and proliferation.","evidence":"Subcellular fractionation, in vitro/in vivo methylation mapping DLAT K596, PDC activity and lipogenesis assays, siRNA, xenografts, and patient tissue correlation","pmids":["39885202"],"confidence":"High","gaps":["Mechanism of mitochondrial targeting of the heterodimer unknown","Generality beyond prostate cancer not established"]},{"year":null,"claim":"It remains unresolved how HEMK2 partitions among its glutamine, lysine and mitochondrial substrates across normal tissues and which activities dominate in physiological versus oncogenic settings.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No quantitative substrate flux measured in normal mammalian tissues","Determinants of nuclear versus mitochondrial localization unknown","Relative physiological weight of eRF1, H4K12 and DLAT methylation undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,4,6,7]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4,5,6,12]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,6]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[12]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,11]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[11]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[12]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[6]}],"complexes":["HEMK2–TRMT112 (KMT9) heterodimer"],"partners":["TRMT112","ERF1","ERF3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y5N5","full_name":"Methyltransferase HEMK2","aliases":["HemK methyltransferase family member 2","M.HsaHemK2P","Lysine N-methyltransferase 9","Methylarsonite methyltransferase N6AMT1","Methyltransferase N6AMT1","Protein N(5)-glutamine methyltransferase"],"length_aa":214,"mass_kda":23.0,"function":"Methyltransferase that can methylate proteins and, to a lower extent, arsenic (PubMed:18539146, PubMed:21193388, PubMed:30017583, PubMed:31061526, PubMed:31636962). Catalytic subunit of a heterodimer with TRMT112, which monomethylates 'Lys-12' of histone H4 (H4K12me1), a modification present at the promoters of numerous genes encoding cell cycle regulators (PubMed:31061526). Catalytic subunit of a heterodimer with TRMT112, which catalyzes N5-methylation of Glu residue of proteins with a Gly-Gln-Xaa-Xaa-Xaa-Arg motif (PubMed:18539146, PubMed:31632689, PubMed:31636962). Methylates ETF1 on 'Gln-185'; ETF1 needs to be complexed to ERF3 in its GTP-bound form to be efficiently methylated (PubMed:18539146, PubMed:20606008, PubMed:31061526, PubMed:31636962). May also play a role in the modulation of arsenic-induced toxicity by mediating the conversion of monomethylarsonous acid (3+) into the less toxic dimethylarsonic acid (PubMed:21193388, PubMed:25997655). It however only plays a limited role in arsenic metabolism compared with AS3MT (PubMed:25997655)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9Y5N5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HEMK2","classification":"Not Classified","n_dependent_lines":674,"n_total_lines":1208,"dependency_fraction":0.5579470198675497},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HEMK2","total_profiled":1310},"omim":[],"hpa":{"profiled":true,"resolved_as":"N6AMT1","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Centrosome","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/N6AMT1"},"hgnc":{"alias_symbol":["PRED28","N6AMT","MTQ2","KMT9","PrmC"],"prev_symbol":["N6AMT1","C21orf127"]},"alphafold":{"accession":"Q9Y5N5","domains":[{"cath_id":"3.40.50.150","chopping":"20-214","consensus_level":"high","plddt":95.7915,"start":20,"end":214}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5N5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5N5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5N5-F1-predicted_aligned_error_v6.png","plddt_mean":94.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HEMK2","jax_strain_url":"https://www.jax.org/strain/search?query=HEMK2"},"sequence":{"accession":"Q9Y5N5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y5N5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y5N5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5N5"}},"corpus_meta":[{"pmid":"16364916","id":"PMC_16364916","title":"Molecular 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letters","url":"https://pubmed.ncbi.nlm.nih.gov/16684535","citation_count":63,"is_preprint":false},{"pmid":"12741815","id":"PMC_12741815","title":"Structures along the catalytic pathway of PrmC/HemK, an N5-glutamine AdoMet-dependent methyltransferase.","date":"2003","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12741815","citation_count":52,"is_preprint":false},{"pmid":"32095117","id":"PMC_32095117","title":"Depletion of histone methyltransferase KMT9 inhibits lung cancer cell proliferation by inducing non-apoptotic cell death.","date":"2020","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/32095117","citation_count":33,"is_preprint":false},{"pmid":"26797129","id":"PMC_26797129","title":"Substrate Specificity of the HEMK2 Protein Glutamine Methyltransferase and Identification of Novel Substrates.","date":"2016","source":"The Journal of biological 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biosensors","date":"2024-06-29","source":"bioRxiv","url":"https://doi.org/10.1101/2024.06.29.601303","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11559,"output_tokens":3434,"usd":0.043093,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10962,"output_tokens":3920,"usd":0.076405,"stage2_stop_reason":"end_turn"},"total_usd":0.119498,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"PrmC/HemK crystal structure resolved at 2.2 Å; the C-terminal domain adopts a canonical AdoMet-dependent methyltransferase fold; the conserved NPPY motif positions the glutamine substrate via hydrogen bonds orienting the nitrogen lone pair toward the AdoMet methyl group, establishing the N5-glutamine methylation catalytic mechanism.\",\n      \"method\": \"X-ray crystallography with substrate and product complexes; active-site structural analysis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures of apo, substrate, and product complexes in a single rigorous study providing direct mechanistic insight into catalysis\",\n      \"pmids\": [\"12741815\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"E. coli PrmC methylates the glutamine residue in the GGQ motif of release factor RF1; crystal structure of the RF1–PrmC–AdoHCy complex shows both domain 3 (GGQ domain) and central domains 2/4 of RF1 contact PrmC; methylation stimulates peptide chain release activity of RF1.\",\n      \"method\": \"X-ray crystallography of RF1–PrmC complex; methylation assays; site-directed mutagenesis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure of the protein complex combined with mutagenesis and biochemical activity assays in one study\",\n      \"pmids\": [\"16364916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Chlamydia trachomatis PrmC functions as an N5-glutamine AdoMet-dependent methyltransferase that methylates class I release factors at the GGQ motif; chlamydial PrmC can complement an E. coli prmC knockout in vivo.\",\n      \"method\": \"Complementation assay in E. coli prmC knockout; in vivo and in vitro methylation assay with recombinant proteins; tryptic fragment analysis\",\n      \"journal\": \"Journal of bacteriology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — complementation in vivo plus in vitro biochemical assay, single lab\",\n      \"pmids\": [\"15629922\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Recombinant murine PRED28 (HEMK2) protein localizes to the nucleus but shows no detectable adenine DNA methyltransferase activity; N6-methyladenine is essentially absent from mammalian DNA (fewer than 10³ m6A per mouse genome).\",\n      \"method\": \"Subcellular localization by immunofluorescence/fractionation; in vitro methyltransferase activity assay; sensitive mass spectrometry detection of m6A in genomic DNA\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — negative result for DNA adenine methyltransferase activity established by direct biochemical assay and sensitive m6A detection, single lab\",\n      \"pmids\": [\"16684535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human HEMK2 (with TRMT112 as partner) methylates human and yeast eRF1 in complex with eRF3 and GTP in vitro; the human HEMK2 catalytic subunit complements growth defect of yeast mtq2 deletion strains, confirming conserved eRF1 glutamine methyltransferase function.\",\n      \"method\": \"In vitro methylation assay with recombinant human HEMK2–TRMT112; yeast complementation of mtq2Δ\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct in vitro biochemical reconstitution plus in vivo genetic complementation, two orthogonal methods\",\n      \"pmids\": [\"18539146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Murine HEMK2 requires a GQX3R motif for glutamine methylation activity; HEMK2 methylates the Gln185 residue of eRF1 and at least 11 additional human protein domains in vitro; CHD5 and NUT are methylated by HEMK2 in HEK293 cells.\",\n      \"method\": \"Peptide SPOT array specificity profiling; in vitro methylation of recombinant protein domains; in-cell methylation assay with transfected substrates\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (peptide array, in vitro protein assay, cellular assay) in one study establishing substrate specificity and novel substrates\",\n      \"pmids\": [\"26797129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Human HEMK2 (C21orf127), designated KMT9α, forms an obligate heterodimer with TRMT112 (KMT9β) and monomethylates lysine 12 of histone H4 (H4K12me1) in vitro and in vivo; crystal structure of KMT9 with SAH and H4K12me1 peptide reveals the structural basis for H4K12 recognition; KMT9 enriches at promoters of cell cycle regulator genes and is required for prostate cancer cell proliferation.\",\n      \"method\": \"In vitro histone methyltransferase assay; X-ray crystallography of KMT9–SAH–H4K12me1 peptide complex; ChIP-seq; siRNA knockdown with proliferation and cell cycle assays; xenograft mouse model\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure, in vitro reconstitution, in vivo ChIP-seq and loss-of-function with multiple orthogonal methods in one study\",\n      \"pmids\": [\"31061526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal structures of HEMK2–TRMT112 bound to SAM and to SAH with methylglutamine reveal a specific pocket in HEMK2 that accommodates the substrate glutamine and catalyzes its methylation; mass spectrometry confirms eRF1 glutamine methylation, demonstrating dual (Gln and Lys) methyltransferase activity of HEMK2.\",\n      \"method\": \"X-ray crystallography (two structures); mass spectrometry-based methylation verification\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — two crystal structures with mass spectrometry confirmation, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"32969463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A biotinylated NTMT1 bisubstrate inhibitor (NAH-C3-GPKK analogue) pulls down the endogenous HemK2–TRMT112 complex from cell lysates, and the parent compound NAH-C3-GPKK potently inhibits HemK2–TRMT112 methyltransferase activity, representing the first reported potent inhibitor of this complex.\",\n      \"method\": \"Chemoproteomic pulldown with biotinylated probe; competitive biochemical inhibition assay\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chemoproteomic pulldown plus biochemical inhibition assay, single lab\",\n      \"pmids\": [\"34192867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HEMK2 prefers glutamine over lysine methylation at both peptide and protein levels; the eRF1 sequence is strongly preferred over H4K12; Q-methylation prefers a G-Q-X3-R context while K-methylation prefers S/T at the first position; SETD6, not HEMK2, is the primary H4K12me1 methyltransferase in DU145 prostate cancer cells (HEMK2 activity ~1000-fold lower than SETD6 on H4K12).\",\n      \"method\": \"Peptide SPOT array methylation; in vitro protein methylation assays; siRNA knockdown combined with mass spectrometry quantification of H4K12me1 in DU145 cells\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical and cellular methods; challenges prior H4K12me1 attribution to HEMK2, single lab\",\n      \"pmids\": [\"38284488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A bi-substrate KMT9 inhibitor (KMI169) targets both the SAM and substrate-binding pockets of KMT9, determined by structure-based drug design; KMI169 selectively downregulates KMT9 target genes involved in cell cycle regulation and impairs proliferation of castration- and enzalutamide-resistant prostate cancer cells.\",\n      \"method\": \"Structure-based drug design with co-crystal structures; biochemical selectivity profiling; cellular target engagement assays; gene expression analysis; proliferation assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — structural basis for inhibitor binding established by co-crystallography, validated by biochemical selectivity and cellular assays, single lab\",\n      \"pmids\": [\"38167811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In Drosophila, HemK2 methylates eRF1 in germline cells; knockdown of hemK2 reduces eRF1 methylation and protein synthesis, induces ribosomal stalling and disome formation, activates No-Go Decay leading to mRNA degradation, and causes apoptosis during oogenesis; overexpression of a methylation-deficient eRF1 recapitulates these defects, establishing eRF1 as the primary functional substrate.\",\n      \"method\": \"Germline-specific RNAi knockdown; methylation assays; polysome profiling (disome detection); No-Go Decay pathway inhibition rescue; genetic epistasis with methylation-deficient eRF1 overexpression\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal in vivo methods (knockdown, rescue, epistasis, translation assays) establishing eRF1 as primary substrate and mechanistic pathway\",\n      \"pmids\": [\"38881530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"KMT9 localizes to mitochondria of prostate cancer cells (but not other tumor cell types) and monomethylates DLAT (dihydrolipoamide transacetylase) at lysine 596; this methylation regulates pyruvate dehydrogenase complex (PDC) activity; KMT9 depletion reduces DLAT K596me1, impairs PDC activity and de novo lipogenesis, and inhibits prostate cancer cell proliferation in vitro and in vivo.\",\n      \"method\": \"Subcellular fractionation and mitochondrial localization assays; in vitro and in vivo methylation assays identifying DLAT K596; PDC activity assay; de novo lipogenesis measurement; siRNA knockdown; mouse xenograft model; patient tissue correlation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct biochemical identification of novel substrate with site-specific methylation, functional PDC activity assay, in vivo mouse model, and patient tissue validation\",\n      \"pmids\": [\"39885202\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HEMK2 (KMT9α) is a dual-specificity protein methyltransferase that, as an obligate heterodimer with TRMT112/KMT9β, (1) monomethylates the glutamine residue (Q185) in the GGQ motif of the eukaryotic translation termination factor eRF1—a modification required for efficient translation termination and mRNA stability—and (2) monomethylates lysine 12 of histone H4 (H4K12me1) in the nucleus and lysine 596 of mitochondrial DLAT to regulate pyruvate dehydrogenase complex activity; both nuclear and mitochondrial activities promote cell proliferation, particularly in prostate, lung, colon, and bladder cancers, with its enzymatic mechanism structurally explained by a Rossmann-fold active site and an NPPY motif that positions substrate residues for methyl transfer from AdoMet.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HEMK2 is an AdoMet-dependent protein methyltransferase whose deeply conserved and best-supported function is the N5-monomethylation of the glutamine in the GGQ motif of class I translation release factors, a modification required for efficient peptide chain release and proper translation termination [#4, #11]. This activity is structurally rooted in a canonical Rossmann-fold methyltransferase domain in which the conserved NPPY motif orients the substrate glutamine nitrogen toward the AdoMet methyl group, a catalytic logic first established for the bacterial ortholog PrmC/HemK and conserved through human HEMK2 [#0, #1, #7]. In eukaryotes HEMK2 functions as an obligate heterodimer with TRMT112 and methylates Gln185 of eRF1, with the human catalytic subunit able to complement loss of the yeast ortholog [#4, #6]. The functional consequence of this modification is clearest in vivo: loss of eRF1 glutamine methylation causes ribosomal stalling, disome formation, No-Go Decay activation, mRNA degradation and apoptosis, establishing eRF1 as the primary functional substrate [#11]. Beyond eRF1, HEMK2 has broad in vitro substrate scope and methylates additional protein substrates [#5], and the heterodimer (as KMT9) has been linked to histone H4K12 monomethylation, promoter occupancy at cell-cycle genes, and prostate cancer proliferation [#6], although biochemical profiling shows HEMK2 strongly prefers glutamine over lysine substrates and attributes the bulk of cellular H4K12me1 to SETD6 rather than HEMK2 [#9]. In prostate cancer cells HEMK2/KMT9 additionally localizes to mitochondria and monomethylates DLAT at Lys596 to regulate pyruvate dehydrogenase complex activity, de novo lipogenesis and proliferation [#12]. Structure-based bisubstrate inhibitors targeting both the SAM and substrate pockets impair KMT9 target-gene expression and proliferation of therapy-resistant prostate cancer cells [#10].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established the catalytic mechanism of GGQ-motif glutamine methylation, defining how an AdoMet methyltransferase positions a glutamine substrate for N5 methyl transfer.\",\n      \"evidence\": \"X-ray crystallography of bacterial PrmC/HemK apo, substrate and product complexes with active-site analysis\",\n      \"pmids\": [\"12741815\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Bacterial enzyme only; eukaryotic HEMK2 heterodimer not yet addressed\", \"No partner protein (TRMT112) in the structure\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified release factor RF1 as the physiological substrate and showed methylation stimulates peptide release, linking the modification to translation termination.\",\n      \"evidence\": \"Crystal structure of RF1\\u2013PrmC complex plus methylation and mutagenesis assays; complementation in C. trachomatis ortholog\",\n      \"pmids\": [\"16364916\", \"15629922\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Demonstrated in bacteria; eukaryotic eRF1 substrate not yet confirmed\", \"Quantitative effect on termination kinetics in vivo not measured\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Tested and ruled out a proposed DNA N6-adenine methyltransferase activity for mammalian HEMK2, redirecting attention to protein substrates.\",\n      \"evidence\": \"Subcellular localization, in vitro methyltransferase assay, and sensitive mass spectrometry detection of genomic m6A in mouse\",\n      \"pmids\": [\"16684535\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative result does not identify the true substrate\", \"Single lab\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established the conserved eukaryotic function: human HEMK2 with TRMT112 methylates eRF1 and complements the yeast ortholog, extending the bacterial termination-factor role to mammals.\",\n      \"evidence\": \"In vitro methylation with recombinant HEMK2\\u2013TRMT112 and yeast mtq2\\u0394 complementation\",\n      \"pmids\": [\"18539146\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular consequences of eRF1 methylation in mammals not yet defined\", \"Whether TRMT112 is obligate not yet resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defined HEMK2 sequence specificity (GQX3R) and revealed a broad in vitro substrate repertoire beyond eRF1, including cellular methylation of CHD5 and NUT.\",\n      \"evidence\": \"Peptide SPOT array profiling, in vitro protein-domain methylation, and in-cell assays with transfected substrates\",\n      \"pmids\": [\"26797129\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of non-eRF1 substrates unconfirmed\", \"Stoichiometry and abundance of these modifications in vivo unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Proposed a chromatin role: as KMT9, the obligate HEMK2\\u2013TRMT112 heterodimer monomethylates H4K12, occupies cell-cycle gene promoters, and drives prostate cancer proliferation.\",\n      \"evidence\": \"In vitro HMT assay, KMT9\\u2013SAH\\u2013H4K12me1 co-crystal structure, ChIP-seq, siRNA knockdown, and xenografts\",\n      \"pmids\": [\"31061526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of HEMK2 versus other enzymes to bulk H4K12me1 not addressed\", \"Direct link between H4K12me1 and promoter occupancy not mechanistically resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the structural basis for dual glutamine/lysine recognition, showing a HEMK2 pocket that accommodates and methylates the substrate glutamine.\",\n      \"evidence\": \"Two crystal structures of HEMK2\\u2013TRMT112 with SAM and with SAH/methylglutamine plus mass spectrometry verification\",\n      \"pmids\": [\"32969463\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not establish which activity dominates in cells\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Quantitatively ranked HEMK2 substrate preference, showing strong selectivity for eRF1 glutamine over H4K12 lysine and reassigning most cellular H4K12me1 to SETD6.\",\n      \"evidence\": \"Peptide SPOT arrays, in vitro protein methylation, and siRNA plus mass spectrometry quantification of H4K12me1 in DU145 cells\",\n      \"pmids\": [\"38284488\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not exclude context-specific HEMK2 H4K12 activity\", \"Single cell line and single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established eRF1 as the primary functional substrate in vivo by linking loss of methylation to ribosome stalling, No-Go Decay and apoptosis.\",\n      \"evidence\": \"Drosophila germline RNAi, polysome/disome profiling, No-Go Decay rescue, and epistasis with methylation-deficient eRF1\",\n      \"pmids\": [\"38881530\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Performed in Drosophila germline; mammalian tissue specificity not addressed\", \"Whether non-eRF1 substrates contribute to phenotype not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided a structure-guided chemical tool: a bisubstrate inhibitor occupying SAM and substrate pockets that suppresses KMT9 target genes and therapy-resistant prostate cancer growth.\",\n      \"evidence\": \"Structure-based design with co-crystals, biochemical selectivity profiling, target engagement, and proliferation assays; earlier NTMT1 bisubstrate probe pulldown\",\n      \"pmids\": [\"38167811\", \"34192867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"On-target gene effects not fully separated from possible off-target activity\", \"In vivo efficacy and pharmacology in patients not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Uncovered a mitochondrial role specific to prostate cancer: HEMK2/KMT9 methylates DLAT K596 to regulate pyruvate dehydrogenase complex activity, lipogenesis and proliferation.\",\n      \"evidence\": \"Subcellular fractionation, in vitro/in vivo methylation mapping DLAT K596, PDC activity and lipogenesis assays, siRNA, xenografts, and patient tissue correlation\",\n      \"pmids\": [\"39885202\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of mitochondrial targeting of the heterodimer unknown\", \"Generality beyond prostate cancer not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how HEMK2 partitions among its glutamine, lysine and mitochondrial substrates across normal tissues and which activities dominate in physiological versus oncogenic settings.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No quantitative substrate flux measured in normal mammalian tissues\", \"Determinants of nuclear versus mitochondrial localization unknown\", \"Relative physiological weight of eRF1, H4K12 and DLAT methylation undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 4, 6, 7]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 5, 6, 12]},\n      {\"term_id\": \"GO:0008168\", \"supporting_discovery_ids\": [0, 4, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 6]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 11]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [\n      \"HEMK2\\u2013TRMT112 (KMT9) heterodimer\"\n    ],\n    \"partners\": [\n      \"TRMT112\",\n      \"eRF1\",\n      \"eRF3\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}