{"gene":"AK9","run_date":"2026-06-09T22:02:43","timeline":{"discoveries":[{"year":2013,"finding":"AK9 (adenylate kinase 9) was cloned, expressed in E. coli, and shown by in vitro enzymatic assay to catalyze phosphorylation of AMP, dAMP, CMP, and dCMP using ATP as phosphate donor, and AMP and CMP using GTP as phosphate donor. Additionally, AK9 possesses nucleoside diphosphate kinase (NDPK) activity, producing triphosphates (ATP, CTP, GTP, UTP, dATP, dCTP, dGTP, TTP) from corresponding diphosphate substrates.","method":"Recombinant protein expression in E. coli, in vitro enzymatic assay, kinetic parameter determination","journal":"The international journal of biochemistry & cell biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro reconstitution with recombinant protein, substrate specificity and kinetic parameters determined, multiple substrates tested","pmids":["23416111"],"is_preprint":false},{"year":2014,"finding":"AK9 is one of nine human adenylate kinase isoenzymes that catalyze interconversion of adenine nucleotides; review confirms AK9 possesses nucleoside mono- and diphosphate kinase activity, with preferred substrates AMP and ATP as phosphate donor, and a role in activation of deoxyadenosine and deoxycytidine nucleoside analogues.","method":"Review of biochemical characterization data including in vitro enzymatic assays","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — review consolidating prior in vitro data, no new independent replication reported in this paper","pmids":["24495878"],"is_preprint":false},{"year":2023,"finding":"Bi-allelic loss-of-function mutations in AK9 in human patients and Ak9-knockout mice cause asthenozoospermia with decreased sperm nucleotide homeostasis and inhibited glycolysis in sperm, establishing AK9 as required for maintaining nucleotide/energy metabolism in spermatozoa.","method":"Whole-exome sequencing of patients, CRISPR-Cas9 Ak9-knockout mice, Papanicolaou/H&E staining, scanning and transmission electron microscopy, liquid chromatography-mass spectrometry for adenosine detection, targeted sperm metabolomics","journal":"EBioMedicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — human genetics plus knockout mouse model with multiple orthogonal readouts (morphology, metabolomics, nucleotide quantification)","pmids":["37713809"],"is_preprint":false},{"year":2023,"finding":"A critical splicing mutation in bovine AK9 causes a premature termination codon and severely truncated protein; Ak9-knockout mice produce immotile sperm with low ATP concentration, abnormal flagella ultrastructure, and are infertile, establishing AK9 as essential for sperm ATP metabolism, motility, hyperactivation, and zona pellucida penetration.","method":"Whole-genome sequencing of bull, RNA sequencing of testis, Ak9-knockout mouse generation, sperm motility assay, ATP concentration measurement, sperm ultrastructural analysis by electron microscopy, IVF/AI fertility assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent species (bovine mutation + mouse KO), multiple orthogonal functional assays, mechanistic link to ATP and axoneme established","pmids":["37812723"],"is_preprint":false},{"year":2024,"finding":"AK8 and AK9 interact with the radial spoke (RS) of the sperm flagellar axoneme, as shown by immunoprecipitation combined with mass spectrometry. The head of radial spoke 3 (RSP3) acts as an adapter for AK9 in the flagellar axoneme. AK8 and AK9 cooperatively regulate ATP transfer in the axoneme and are concentrated at sites of energy consumption in the flagellum, defining an adenylate kinase phosphate energy shuttle.","method":"Immunoprecipitation combined with mass spectrometry, ATP probe assay, metabolomic analysis, knockout mouse models","journal":"Science China. Life sciences","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP/MS identifying specific binding partner (RSP3), supported by ATP probe and metabolomics in KO models","pmids":["38761355"],"is_preprint":false},{"year":2023,"finding":"Damaging heterozygous mutations in AK9 were detected in 9.6% of idiopathic normal pressure hydrocephalus (iNPH) patients. Mice homozygous for an iNPH-associated AK9 mutation showed normal cilia structure and number but decreased cilia motility and beat frequency, communicating hydrocephalus, and balance impairment. AK9+/- mice developed communicating hydrocephalus in early adulthood, establishing AK9 as required for ependymal cilia motility.","method":"Patient sequencing, knock-in mouse model (homozygous iNPH-associated mutation), cilia motility/beat frequency measurement, behavioral testing, brain imaging","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo mouse model with direct cilia motility measurement and hydrocephalus phenotype, corroborated by human genetics","pmids":["38100419"],"is_preprint":false},{"year":2016,"finding":"A start-gain mutation in intron 5 of AK9 introduces a cryptic 5'-UTR signal causing defective splicing. AK9 was identified as a disease modifier for RAPSN-associated limb-girdle congenital myasthenic syndrome, with the proposed mechanism that AK9-associated nucleotide deficiency impairs N-glycosylation of neuromuscular junction proteins.","method":"Homozygosity mapping, whole-exome sequencing, Sanger sequencing, splicing analysis","journal":"European journal of human genetics : EJHG","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — human genetics with splicing analysis, but the N-glycosylation mechanism is proposed rather than directly demonstrated experimentally","pmids":["27966543"],"is_preprint":false},{"year":2023,"finding":"AK9 expression is downregulated in lung cancer tissues, and in vitro assays verified a tumor-suppressing role for AK9 in lung cancer cells. An m6A-SNP (rs1321328) near AK9 reduces m6A modification level of AK9 mRNA (C allele vs G allele by MeRIP-qPCR) and significantly reduces AK9 expression.","method":"MeRIP-qPCR for m6A modification, in vitro functional assays in lung cancer cell lines, bioinformatics/TCGA expression analysis","journal":"Molecular carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2–3 / Weak — direct m6A modification assay and in vitro tumor suppressor validation, single lab, limited mechanistic detail in abstract","pmids":["38051288"],"is_preprint":false}],"current_model":"AK9 (adenylate kinase 9) is a nucleoside mono- and diphosphate kinase that phosphorylates AMP, dAMP, CMP, and dCMP using ATP or GTP as phosphate donors and also exhibits NDPK activity; in sperm flagella it localizes to the axoneme via an interaction with radial spoke head 3 (RSP3) and cooperates with AK8 to maintain local ATP homeostasis required for motility and hyperactivation, while in ependymal cells it supports cilia beat frequency necessary to prevent hydrocephalus."},"narrative":{"mechanistic_narrative":"AK9 is an adenylate kinase that maintains local nucleotide and energy homeostasis in motile ciliated and flagellated cells [PMID:23416111, PMID:37812723]. Biochemically, recombinant AK9 phosphorylates AMP, dAMP, CMP, and dCMP using ATP or GTP as phosphate donor and additionally exhibits nucleoside diphosphate kinase activity, generating tri-phosphates from the corresponding diphosphates [PMID:23416111]. In sperm, bi-allelic loss-of-function in humans and Ak9 knockout in mice cause asthenozoospermia, immotile sperm, depleted ATP, abnormal flagellar ultrastructure, and infertility, establishing AK9 as essential for sperm nucleotide metabolism, motility, hyperactivation, and zona pellucida penetration [PMID:37713809, PMID:37812723]. Mechanistically, AK9 localizes to the flagellar axoneme via the head of radial spoke 3 (RSP3) and cooperates with AK8 as an adenylate kinase phosphate energy shuttle that transfers ATP to sites of high energy consumption [PMID:38761355]. The same activity supports ependymal cilia: an AK9 mutation reduces ciliary beat frequency without altering cilia structure and produces communicating hydrocephalus, with damaging heterozygous variants enriched in idiopathic normal pressure hydrocephalus patients [PMID:38100419].","teleology":[{"year":2013,"claim":"Established the core enzymatic identity of AK9 by defining which nucleotide substrates and phosphate donors it uses, answering what biochemical reaction this previously uncharacterized kinase catalyzes.","evidence":"Recombinant expression in E. coli with in vitro enzymatic assays and kinetic parameter determination","pmids":["23416111"],"confidence":"High","gaps":["No cellular or tissue context for the activity","Physiological substrate preference in vivo not addressed","No structural model of the active site"]},{"year":2014,"claim":"Placed AK9 within the broader adenylate kinase isoenzyme family and noted its potential to activate nucleoside analogue prodrugs, framing its biochemistry in a pharmacological context.","evidence":"Review consolidating prior in vitro biochemical characterization","pmids":["24495878"],"confidence":"Medium","gaps":["No new experimental data","Nucleoside analogue activation not demonstrated in cells","Tissue-specific role unresolved"]},{"year":2016,"claim":"First in vivo disease link, identifying an AK9 splicing mutation as a modifier of congenital myasthenic syndrome and proposing nucleotide deficiency impairs N-glycosylation.","evidence":"Homozygosity mapping, whole-exome and Sanger sequencing, splicing analysis in patients","pmids":["27966543"],"confidence":"Medium","gaps":["N-glycosylation mechanism is proposed but not experimentally demonstrated","No functional assay of mutant AK9 enzyme activity","Modifier effect not modeled in animals"]},{"year":2023,"claim":"Connected AK9 enzymatic activity to a physiological requirement by showing loss-of-function depletes sperm nucleotide pools and impairs glycolysis, causing asthenozoospermia.","evidence":"Patient whole-exome sequencing, CRISPR Ak9-knockout mice, electron microscopy, LC-MS adenosine detection, targeted sperm metabolomics","pmids":["37713809"],"confidence":"High","gaps":["Subcellular localization within sperm not resolved here","Direct link between AK9 activity and glycolytic enzymes not defined","Binding partners unidentified"]},{"year":2023,"claim":"Independently confirmed AK9 essentiality for sperm motility across species and tied the phenotype to ATP levels and axonemal ultrastructure, establishing a flagellar energy role.","evidence":"Bovine whole-genome and testis RNA sequencing, Ak9-knockout mice, sperm motility and ATP assays, electron microscopy, IVF/AI fertility tests","pmids":["37812723"],"confidence":"High","gaps":["Molecular tethering of AK9 to the axoneme not yet shown","Distinction between hyperactivation and basal motility defects unresolved","No structural basis for axonemal localization"]},{"year":2023,"claim":"Extended AK9 function to ependymal cilia, showing its activity sets ciliary beat frequency and that mutations cause communicating hydrocephalus, linking the energy-shuttle role to brain fluid dynamics.","evidence":"Patient sequencing, knock-in and heterozygous mouse models, cilia beat frequency measurement, behavioral testing, brain imaging","pmids":["38100419"],"confidence":"High","gaps":["Cilia structure unaffected, so the precise step requiring AK9 within beating is undefined","Mechanism connecting nucleotide shuttle to motor activity not detailed","Dose dependence of heterozygous phenotype incomplete"]},{"year":2023,"claim":"Implicated AK9 as a tumor suppressor in lung cancer regulated by m6A modification, broadening its role beyond ciliary biology.","evidence":"MeRIP-qPCR for m6A, in vitro functional assays in lung cancer cell lines, TCGA expression analysis","pmids":["38051288"],"confidence":"Medium","gaps":["Single-lab in vitro evidence without in vivo tumor model","Mechanism connecting AK9 enzymatic activity to growth suppression not defined","m6A reader/writer mediating the effect unidentified"]},{"year":2024,"claim":"Resolved how AK9 is positioned to act in the flagellum, identifying RSP3 as the axonemal adapter and demonstrating cooperative ATP transfer with AK8 as a phosphate energy shuttle.","evidence":"Reciprocal immunoprecipitation-mass spectrometry, ATP probe assay, metabolomics in knockout mouse models","pmids":["38761355"],"confidence":"High","gaps":["Stoichiometry and structure of the AK8/AK9/RSP3 assembly unknown","Whether RSP3 adapter mechanism applies in ependymal cilia untested","Directionality and regulation of the shuttle not fully characterized"]},{"year":null,"claim":"How AK9's enzymatic activity is mechanistically coupled to dynein motor function and beat frequency, and whether its tumor-suppressor and ciliary roles share a common nucleotide-homeostasis basis, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structural model of AK9 or its axonemal complex","Mechanism linking nucleotide shuttle to motor force generation undefined","Unified mechanism across reproductive, ciliary, and oncogenic contexts not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[4,5]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2,3]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[2,3]}],"complexes":["radial spoke (sperm flagellar axoneme)"],"partners":["AK8","RSP3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5TCS8","full_name":"Adenylate kinase 9","aliases":["Adenylate kinase domain-containing protein 1","Adenylate kinase domain-containing protein 2"],"length_aa":1911,"mass_kda":221.4,"function":"Broad-specificity nucleoside phosphate kinase involved in cellular nucleotide homeostasis by catalyzing nucleoside-phosphate interconversions. Similar to other adenylate kinases, preferentially catalyzes the phosphorylation of the nucleoside monophosphate AMP with ATP as phosphate donor to produce ADP. In vitro, can also catalyze the phosphorylation of CMP, dAMP and dCMP and use GTP as an alternate phosphate donor. Moreover, exhibits a diphosphate kinase activity, producing ATP, CTP, GTP, UTP, TTP, dATP, dCTP and dGTP from the corresponding diphosphate substrates with either ATP or GTP as phosphate donors. For this activity shows the following substrate preference CDP > UDP > ADP > TDP","subcellular_location":"Cytoplasm; Nucleus; Cell projection, cilium, flagellum","url":"https://www.uniprot.org/uniprotkb/Q5TCS8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/AK9","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/AK9","total_profiled":1310},"omim":[{"mim_id":"620705","title":"SPERMATOGENIC FAILURE 89; SPGF89","url":"https://www.omim.org/entry/620705"},{"mim_id":"615358","title":"ADENYLATE KINASE 9; AK9","url":"https://www.omim.org/entry/615358"},{"mim_id":"258150","title":"SPERMATOGENIC FAILURE 1; SPGF1","url":"https://www.omim.org/entry/258150"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Nuclear membrane","reliability":"Enhanced"},{"location":"Cytosol","reliability":"Additional"},{"location":"Calyx","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/AK9"},"hgnc":{"alias_symbol":["FLJ42177","FLJ25791","dJ70A9.1","MGC26954"],"prev_symbol":["C6orf224","AKD2","C6orf199","AKD1"]},"alphafold":{"accession":"Q5TCS8","domains":[{"cath_id":"3.40.50.300","chopping":"28-150_249-287","consensus_level":"high","plddt":85.153,"start":28,"end":287},{"cath_id":"-","chopping":"294-389","consensus_level":"medium","plddt":81.0831,"start":294,"end":389},{"cath_id":"-","chopping":"397-415_637-712_823-871","consensus_level":"medium","plddt":76.1574,"start":397,"end":871},{"cath_id":"3.40.50.300","chopping":"994-1064_1086-1165_1275-1315","consensus_level":"high","plddt":81.6339,"start":994,"end":1315},{"cath_id":"-","chopping":"1342-1407","consensus_level":"medium","plddt":83.5577,"start":1342,"end":1407},{"cath_id":"3.40.50.300","chopping":"1413-1538_1550-1617","consensus_level":"high","plddt":85.7272,"start":1413,"end":1617},{"cath_id":"-","chopping":"1703-1786","consensus_level":"medium","plddt":82.6845,"start":1703,"end":1786},{"cath_id":"-","chopping":"1802-1904","consensus_level":"high","plddt":83.3947,"start":1802,"end":1904}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5TCS8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5TCS8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5TCS8-F1-predicted_aligned_error_v6.png","plddt_mean":73.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=AK9","jax_strain_url":"https://www.jax.org/strain/search?query=AK9"},"sequence":{"accession":"Q5TCS8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5TCS8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5TCS8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5TCS8"}},"corpus_meta":[{"pmid":"24495878","id":"PMC_24495878","title":"The 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Additionally, AK9 possesses nucleoside diphosphate kinase (NDPK) activity, producing triphosphates (ATP, CTP, GTP, UTP, dATP, dCTP, dGTP, TTP) from corresponding diphosphate substrates.\",\n      \"method\": \"Recombinant protein expression in E. coli, in vitro enzymatic assay, kinetic parameter determination\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro reconstitution with recombinant protein, substrate specificity and kinetic parameters determined, multiple substrates tested\",\n      \"pmids\": [\"23416111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"AK9 is one of nine human adenylate kinase isoenzymes that catalyze interconversion of adenine nucleotides; review confirms AK9 possesses nucleoside mono- and diphosphate kinase activity, with preferred substrates AMP and ATP as phosphate donor, and a role in activation of deoxyadenosine and deoxycytidine nucleoside analogues.\",\n      \"method\": \"Review of biochemical characterization data including in vitro enzymatic assays\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — review consolidating prior in vitro data, no new independent replication reported in this paper\",\n      \"pmids\": [\"24495878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Bi-allelic loss-of-function mutations in AK9 in human patients and Ak9-knockout mice cause asthenozoospermia with decreased sperm nucleotide homeostasis and inhibited glycolysis in sperm, establishing AK9 as required for maintaining nucleotide/energy metabolism in spermatozoa.\",\n      \"method\": \"Whole-exome sequencing of patients, CRISPR-Cas9 Ak9-knockout mice, Papanicolaou/H&E staining, scanning and transmission electron microscopy, liquid chromatography-mass spectrometry for adenosine detection, targeted sperm metabolomics\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — human genetics plus knockout mouse model with multiple orthogonal readouts (morphology, metabolomics, nucleotide quantification)\",\n      \"pmids\": [\"37713809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A critical splicing mutation in bovine AK9 causes a premature termination codon and severely truncated protein; Ak9-knockout mice produce immotile sperm with low ATP concentration, abnormal flagella ultrastructure, and are infertile, establishing AK9 as essential for sperm ATP metabolism, motility, hyperactivation, and zona pellucida penetration.\",\n      \"method\": \"Whole-genome sequencing of bull, RNA sequencing of testis, Ak9-knockout mouse generation, sperm motility assay, ATP concentration measurement, sperm ultrastructural analysis by electron microscopy, IVF/AI fertility assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent species (bovine mutation + mouse KO), multiple orthogonal functional assays, mechanistic link to ATP and axoneme established\",\n      \"pmids\": [\"37812723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"AK8 and AK9 interact with the radial spoke (RS) of the sperm flagellar axoneme, as shown by immunoprecipitation combined with mass spectrometry. The head of radial spoke 3 (RSP3) acts as an adapter for AK9 in the flagellar axoneme. AK8 and AK9 cooperatively regulate ATP transfer in the axoneme and are concentrated at sites of energy consumption in the flagellum, defining an adenylate kinase phosphate energy shuttle.\",\n      \"method\": \"Immunoprecipitation combined with mass spectrometry, ATP probe assay, metabolomic analysis, knockout mouse models\",\n      \"journal\": \"Science China. Life sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP/MS identifying specific binding partner (RSP3), supported by ATP probe and metabolomics in KO models\",\n      \"pmids\": [\"38761355\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Damaging heterozygous mutations in AK9 were detected in 9.6% of idiopathic normal pressure hydrocephalus (iNPH) patients. Mice homozygous for an iNPH-associated AK9 mutation showed normal cilia structure and number but decreased cilia motility and beat frequency, communicating hydrocephalus, and balance impairment. AK9+/- mice developed communicating hydrocephalus in early adulthood, establishing AK9 as required for ependymal cilia motility.\",\n      \"method\": \"Patient sequencing, knock-in mouse model (homozygous iNPH-associated mutation), cilia motility/beat frequency measurement, behavioral testing, brain imaging\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo mouse model with direct cilia motility measurement and hydrocephalus phenotype, corroborated by human genetics\",\n      \"pmids\": [\"38100419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A start-gain mutation in intron 5 of AK9 introduces a cryptic 5'-UTR signal causing defective splicing. AK9 was identified as a disease modifier for RAPSN-associated limb-girdle congenital myasthenic syndrome, with the proposed mechanism that AK9-associated nucleotide deficiency impairs N-glycosylation of neuromuscular junction proteins.\",\n      \"method\": \"Homozygosity mapping, whole-exome sequencing, Sanger sequencing, splicing analysis\",\n      \"journal\": \"European journal of human genetics : EJHG\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — human genetics with splicing analysis, but the N-glycosylation mechanism is proposed rather than directly demonstrated experimentally\",\n      \"pmids\": [\"27966543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"AK9 expression is downregulated in lung cancer tissues, and in vitro assays verified a tumor-suppressing role for AK9 in lung cancer cells. An m6A-SNP (rs1321328) near AK9 reduces m6A modification level of AK9 mRNA (C allele vs G allele by MeRIP-qPCR) and significantly reduces AK9 expression.\",\n      \"method\": \"MeRIP-qPCR for m6A modification, in vitro functional assays in lung cancer cell lines, bioinformatics/TCGA expression analysis\",\n      \"journal\": \"Molecular carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Weak — direct m6A modification assay and in vitro tumor suppressor validation, single lab, limited mechanistic detail in abstract\",\n      \"pmids\": [\"38051288\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"AK9 (adenylate kinase 9) is a nucleoside mono- and diphosphate kinase that phosphorylates AMP, dAMP, CMP, and dCMP using ATP or GTP as phosphate donors and also exhibits NDPK activity; in sperm flagella it localizes to the axoneme via an interaction with radial spoke head 3 (RSP3) and cooperates with AK8 to maintain local ATP homeostasis required for motility and hyperactivation, while in ependymal cells it supports cilia beat frequency necessary to prevent hydrocephalus.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"AK9 is an adenylate kinase that maintains local nucleotide and energy homeostasis in motile ciliated and flagellated cells [#0, #3]. Biochemically, recombinant AK9 phosphorylates AMP, dAMP, CMP, and dCMP using ATP or GTP as phosphate donor and additionally exhibits nucleoside diphosphate kinase activity, generating tri-phosphates from the corresponding diphosphates [#0]. In sperm, bi-allelic loss-of-function in humans and Ak9 knockout in mice cause asthenozoospermia, immotile sperm, depleted ATP, abnormal flagellar ultrastructure, and infertility, establishing AK9 as essential for sperm nucleotide metabolism, motility, hyperactivation, and zona pellucida penetration [#2, #3]. Mechanistically, AK9 localizes to the flagellar axoneme via the head of radial spoke 3 (RSP3) and cooperates with AK8 as an adenylate kinase phosphate energy shuttle that transfers ATP to sites of high energy consumption [#4]. The same activity supports ependymal cilia: an AK9 mutation reduces ciliary beat frequency without altering cilia structure and produces communicating hydrocephalus, with damaging heterozygous variants enriched in idiopathic normal pressure hydrocephalus patients [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Established the core enzymatic identity of AK9 by defining which nucleotide substrates and phosphate donors it uses, answering what biochemical reaction this previously uncharacterized kinase catalyzes.\",\n      \"evidence\": \"Recombinant expression in E. coli with in vitro enzymatic assays and kinetic parameter determination\",\n      \"pmids\": [\"23416111\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cellular or tissue context for the activity\", \"Physiological substrate preference in vivo not addressed\", \"No structural model of the active site\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed AK9 within the broader adenylate kinase isoenzyme family and noted its potential to activate nucleoside analogue prodrugs, framing its biochemistry in a pharmacological context.\",\n      \"evidence\": \"Review consolidating prior in vitro biochemical characterization\",\n      \"pmids\": [\"24495878\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No new experimental data\", \"Nucleoside analogue activation not demonstrated in cells\", \"Tissue-specific role unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"First in vivo disease link, identifying an AK9 splicing mutation as a modifier of congenital myasthenic syndrome and proposing nucleotide deficiency impairs N-glycosylation.\",\n      \"evidence\": \"Homozygosity mapping, whole-exome and Sanger sequencing, splicing analysis in patients\",\n      \"pmids\": [\"27966543\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"N-glycosylation mechanism is proposed but not experimentally demonstrated\", \"No functional assay of mutant AK9 enzyme activity\", \"Modifier effect not modeled in animals\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Connected AK9 enzymatic activity to a physiological requirement by showing loss-of-function depletes sperm nucleotide pools and impairs glycolysis, causing asthenozoospermia.\",\n      \"evidence\": \"Patient whole-exome sequencing, CRISPR Ak9-knockout mice, electron microscopy, LC-MS adenosine detection, targeted sperm metabolomics\",\n      \"pmids\": [\"37713809\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subcellular localization within sperm not resolved here\", \"Direct link between AK9 activity and glycolytic enzymes not defined\", \"Binding partners unidentified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Independently confirmed AK9 essentiality for sperm motility across species and tied the phenotype to ATP levels and axonemal ultrastructure, establishing a flagellar energy role.\",\n      \"evidence\": \"Bovine whole-genome and testis RNA sequencing, Ak9-knockout mice, sperm motility and ATP assays, electron microscopy, IVF/AI fertility tests\",\n      \"pmids\": [\"37812723\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular tethering of AK9 to the axoneme not yet shown\", \"Distinction between hyperactivation and basal motility defects unresolved\", \"No structural basis for axonemal localization\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended AK9 function to ependymal cilia, showing its activity sets ciliary beat frequency and that mutations cause communicating hydrocephalus, linking the energy-shuttle role to brain fluid dynamics.\",\n      \"evidence\": \"Patient sequencing, knock-in and heterozygous mouse models, cilia beat frequency measurement, behavioral testing, brain imaging\",\n      \"pmids\": [\"38100419\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cilia structure unaffected, so the precise step requiring AK9 within beating is undefined\", \"Mechanism connecting nucleotide shuttle to motor activity not detailed\", \"Dose dependence of heterozygous phenotype incomplete\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Implicated AK9 as a tumor suppressor in lung cancer regulated by m6A modification, broadening its role beyond ciliary biology.\",\n      \"evidence\": \"MeRIP-qPCR for m6A, in vitro functional assays in lung cancer cell lines, TCGA expression analysis\",\n      \"pmids\": [\"38051288\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab in vitro evidence without in vivo tumor model\", \"Mechanism connecting AK9 enzymatic activity to growth suppression not defined\", \"m6A reader/writer mediating the effect unidentified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved how AK9 is positioned to act in the flagellum, identifying RSP3 as the axonemal adapter and demonstrating cooperative ATP transfer with AK8 as a phosphate energy shuttle.\",\n      \"evidence\": \"Reciprocal immunoprecipitation-mass spectrometry, ATP probe assay, metabolomics in knockout mouse models\",\n      \"pmids\": [\"38761355\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and structure of the AK8/AK9/RSP3 assembly unknown\", \"Whether RSP3 adapter mechanism applies in ependymal cilia untested\", \"Directionality and regulation of the shuttle not fully characterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How AK9's enzymatic activity is mechanistically coupled to dynein motor function and beat frequency, and whether its tumor-suppressor and ciliary roles share a common nucleotide-homeostasis basis, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of AK9 or its axonemal complex\", \"Mechanism linking nucleotide shuttle to motor force generation undefined\", \"Unified mechanism across reproductive, ciliary, and oncogenic contexts not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0016301\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"complexes\": [\"radial spoke (sperm flagellar axoneme)\"],\n    \"partners\": [\"AK8\", \"RSP3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}