{"gene":"AK2","run_date":"2026-06-09T22:02:43","timeline":{"discoveries":[{"year":2007,"finding":"AK2 translocates from mitochondria to the cytoplasm during intrinsic apoptosis (blocked by Bcl-2/Bcl-XL and reduced in Apaf-1 knockdown cells), and forms an AK2-FADD-caspase-10 (AFAC10) complex that activates caspase-10 via FADD and subsequently caspase-3, but not caspase-8, defining a novel intrinsic apoptotic pathway. Purified AK2 added to cell extracts reconstituted this caspase activation cascade.","method":"Co-immunoprecipitation of AFAC10 complex, purified protein addition to cell extracts, Apaf-1 knockdown epistasis, Bcl-2/Bcl-XL overexpression, caspase activity assays, AK2 siRNA knockdown","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reconstitution with purified protein, reciprocal Co-IP, genetic epistasis (Apaf-1 KD, Bcl-2/Bcl-XL), multiple orthogonal methods in a single rigorous study","pmids":["17952061"],"is_preprint":false},{"year":1984,"finding":"AK2 is a monomeric mitochondrial intermembrane space phosphotransferase that catalyzes ATP + AMP ⇌ 2 ADP. Its N-terminal ~100 residues share homology with cytosolic AK1, including catalytic residues His-36 and Asp-93, but AK2 contains an additional ~50-residue 'wing' segment absent in AK1 that is likely related to its mitochondrial localization.","method":"Protein sequencing (Laursen sequenator), CNBr fragmentation, peptide mapping, sequence alignment, molecular weight determination","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical sequencing and catalytic characterization, replicated in follow-up 1986 study completing full sequence","pmids":["6086335","3002789"],"is_preprint":false},{"year":1986,"finding":"AK2 contains 238 residues with four cysteines: Cys-41 and Cys-233 are free thiols carboxymethylatable without loss of enzymatic activity, while Cys-43/Cys-93 likely form a disulfide bond in native AK2. AK2 and AK1 share similar active-site geometry but differ in antigenic sites, consistent with lack of immunological cross-reactivity.","method":"Gas-phase protein sequencing, SH-group titration, sedimentation equilibrium ultracentrifugation, gel filtration, chemical modification of cysteines with enzymatic activity assay","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — complete primary structure determined, cysteine chemistry confirmed with activity assays, two orthogonal methods for molecular weight","pmids":["3002789"],"is_preprint":false},{"year":2015,"finding":"AK2 deficiency impairs mitochondrial oxidative phosphorylation and disrupts adenine nucleotide homeostasis in human hematopoietic progenitors, causing a block in lymphoid and granulocyte differentiation. AK2 knockdown progenitors show poor proliferative and survival capacities.","method":"AK2 shRNA knockdown in hematopoietic progenitors, mitochondrial function assays (oxidative phosphorylation measurement), proliferation and survival assays, differentiation assays toward lymphoid and granulocyte lineages","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with defined cellular phenotype and mechanistic metabolic readout, single lab with multiple orthogonal functional assays","pmids":["26270350"],"is_preprint":false},{"year":2015,"finding":"AK2 deficiency in zebrafish leads to increased oxidative stress and apoptosis in hematopoietic stem and progenitor cells; AK2-deficient human iPSCs show increased AMP/ADP ratio (energy-depleted adenine nucleotide profile) and myeloid maturation arrest. Antioxidant treatment rescues hematopoietic phenotypes in vivo and restores granulocyte differentiation from iPSCs, linking AK2 loss to cellular energy depletion and oxidative stress.","method":"Zebrafish ak2 mutant model, RD patient-derived iPSC differentiation, adenine nucleotide profiling (AMP/ADP ratio), antioxidant rescue experiments, in vivo and in vitro differentiation assays","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent model systems (zebrafish KO and patient iPSCs), metabolic profiling, pharmacological rescue, multiple orthogonal methods","pmids":["26150473"],"is_preprint":false},{"year":2018,"finding":"AK2 maintains ATP supply to the nucleus during hematopoietic differentiation; RD patient-derived iPSC hemo-angiogenic progenitor cells show decreased ATP distribution in the nucleus and altered global transcriptional profiles, indicating a stage-specific role for AK2 in intracellular ATP redistribution controlling hematopoietic progenitor fate.","method":"RD patient iPSC-derived hematopoietic differentiation, ATP distribution imaging (FRET-based ATP biosensor), transcriptional profiling","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient-derived iPSC model with direct ATP localization measurement and transcriptional readout, single lab","pmids":["29462620"],"is_preprint":false},{"year":2019,"finding":"Hypomorphic AK2 variants (AK2G100S and AK2A182D) allow residual AK2 protein expression and enzymatic activity with normal neutrophil and lymphocyte counts, but cause B-cell-specific defects in proliferation and immunoglobulin secretion associated with impaired mitochondrial respiration and dysregulated mitochondrial membrane potential upon B-cell activation, revealing that B cells have a stricter dependency on AK2-mediated mitochondrial function than T cells.","method":"Next-generation sequencing to identify variants, tandem mass spectrometry for enzymatic activity, lymphocyte proliferation assays, in vitro immunoglobulin secretion, mitochondrial respiration measurement, mitochondrial membrane potential assay, chemical ATP synthesis inhibition in control cells","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — patient variant characterization with direct enzymatic activity measurement, multiple orthogonal mitochondrial functional assays, pharmacological confirmation in controls","pmids":["31862378"],"is_preprint":false},{"year":2021,"finding":"AK2 promotes migration and invasion of lung adenocarcinoma cells through the Smad-dependent TGF-β/EMT signaling pathway. AK2 knockout reduced EMT-like features and metastatic nodule formation in vivo.","method":"AK2 siRNA knockdown, CRISPR knockout, AK2 overexpression, cell migration and invasion assays, differential proteomics, western blot and qPCR for EMT markers and Smad pathway components, in vivo mouse metastasis model","journal":"Frontiers in pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO and OE with defined phenotype and pathway measurement by multiple methods, single lab","pmids":["34630090"],"is_preprint":false},{"year":2021,"finding":"AK2 null homozygosity is embryonic lethal in mice; conditional cardiac-specific AK2 deletion causes abrupt heart failure with Krebs cycle and glycolytic metabolite buildup, followed by compensatory upregulation of AK1, AK3, AK4, creatine kinase isoforms, and hexokinase with mitochondrial ultrastructure remodeling that permits recovery of pump function.","method":"Transgenic AK2 knockout (constitutive embryonic lethality), conditional organ-specific Ak2 deletion, cardiac function measurement, metabolite profiling, compensatory kinase expression analysis, mitochondrial ultrastructure imaging","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo conditional KO with defined functional and metabolic phenotype, multiple readouts, single lab","pmids":["33571905"],"is_preprint":false},{"year":2022,"finding":"AK2 physically interacts with BRAF and inhibits BRAF kinase activity and downstream ERK phosphorylation. AMP binding to AK2 strengthens the AK2-BRAF interaction, placing AK2 as an AMP-sensing negative regulator of BRAF that links cellular metabolic state to MAPK signaling. RAS activation abrogates AK2-BRAF interaction. AK2 also binds and attenuates BRAF inhibitor-insensitive BRAF mutants.","method":"Co-immunoprecipitation (AK2-BRAF), in vitro kinase assays for BRAF activity, ERK phosphorylation western blot, AMP addition to cell lysates, AK2 KD/KO with proliferation assay, mouse HRASG12V-driven HCC model","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reciprocal Co-IP, in vitro kinase assay, AMP-binding mechanism, genetic KO, in vivo mouse tumor model, multiple orthogonal methods","pmids":["35585049"],"is_preprint":false},{"year":2023,"finding":"ODF4 co-immunoprecipitates with AK2 (and AK1) in mouse spermatozoa; ODF4 localizes to the whole flagellum midpiece region where AK2 is present. Deletion of Odf4 reduces AK2 levels in sperm flagella and causes abnormal flagellar shape (hairpin flagellum) with loss of midpiece motility and male infertility, rescued by Odf4 restoration.","method":"Co-immunoprecipitation of ODF4 with AK2/AK1 from spermatozoa, immunofluorescence localization, Odf4-/- mouse model, sperm motility analysis, rescue experiment with Odf4 restoration","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, KO phenotype with defined functional readout and genetic rescue, single lab","pmids":["36804949"],"is_preprint":false},{"year":2025,"finding":"Cytosolic AK2 stability is regulated by sequential post-translational events: DPP8/9 dipeptidyl peptidases process AK2's N-terminus, unmasking an IAP-binding motif (IBM) that targets AK2 for IAP (E3 ligase)-mediated proteasomal degradation. N-terminal acetylation by NatA prevents the AK2-IAP interaction, stabilizing cytosolic AK2.","method":"Biochemical identification of IBM, DPP8/9 processing assays, IAP interaction assays, NatA acetylation assays, genome-wide in silico IBM screen, validation with EIF2A as additional substrate","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — biochemical reconstitution of processing and IBM unmasking, multiple orthogonal experiments (DPP8/9 assay, IAP binding, NatA acetylation), mechanistic pathway established in single rigorous study","pmids":["40312560"],"is_preprint":false},{"year":2024,"finding":"AIFM1 interacts with AK2 (specifically isoform AK2A) via its C-terminus, stabilizing AK2A. Cryo-EM and biochemical analyses show that AK2A binding to AIFM1's C-terminal β-strand locks AIFM1 in an active dimer conformation and enhances its NADH oxidoreductase activity. MIA40 binds the same site and additionally affects the cofactor binding site. The AIFM1-AK2A interaction is crucial during respiratory conditions, placing AK2 as part of the central energy metabolism regulatory platform in the mitochondrial intermembrane space.","method":"High-confidence AIFM1 interactome (MS), high-resolution cryo-EM structure of AIFM1-AK2A complex, biochemical binding assays, NADH oxidoreductase activity assays, genetic interference in C. elegans","journal":"bioRxiv (preprint)","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure, biochemical reconstitution, enzymatic activity assays, in vivo genetic interference, multiple orthogonal methods in single study","pmids":[],"is_preprint":true},{"year":2024,"finding":"The AIFM1-AK2 interaction is NADH-dependent and influenced by glycolytic state, placing AK2 adjacent to OXPHOS complexes for local ADP regeneration as substrate for ATP synthase. Disruption of AIFM1/AK2 association impairs metabolic adaptation to altered nutrient availability in C. elegans, identifying AIFM1 as a cellular NADH sensor that positions AK2 to balance ATP synthase substrate supply.","method":"AIFM1-AK2 binding assays under NADH conditions, glycolytic manipulation, genetic interference in C. elegans (metabolic phenotype), cryo-EM imaging referenced for hinge motion","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical NADH-dependence characterization, in vivo C. elegans genetic model, preprint not yet peer-reviewed","pmids":[],"is_preprint":true},{"year":2025,"finding":"AK2 is localized in the mitochondrial intermembrane space and imported via the MIA40 disulfide relay system. In the cytosol, AK2 undergoes N-terminal processing by DPP8/9 that sensitizes it to proteasomal degradation (confirmed by the IBM-IAP mechanism).","method":"Subcellular fractionation, MIA40-dependent import assay, N-terminal processing assays with DPP8/9","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct import pathway identification with biochemical assays, single study but mechanistic details established","pmids":["40312560"],"is_preprint":false}],"current_model":"AK2 is a mitochondrial intermembrane space phosphotransferase (catalyzing ATP + AMP ⇌ 2 ADP) that is imported via the MIA40 disulfide relay and stabilized by AIFM1 binding (which locks AIFM1 in an active NADH oxidoreductase dimer); cytosolic AK2 is subject to DPP8/9-mediated N-terminal processing that unmasks an IAP-binding motif leading to proteasomal degradation unless blocked by NatA acetylation. During intrinsic apoptosis, AK2 translocates to the cytoplasm where it forms an AK2-FADD-caspase-10 complex that activates caspase-10 and subsequently caspase-3. AK2 also acts as an AMP-sensing negative regulator of BRAF kinase, suppressing MAPK/ERK signaling in proportion to cellular AMP levels, and is essential for mitochondrial energy homeostasis supporting hematopoietic stem cell differentiation, B-cell activation, cardiac function, and embryonic development."},"narrative":{"mechanistic_narrative":"AK2 is a monomeric phosphotransferase of the mitochondrial intermembrane space that catalyzes the reversible interconversion ATP + AMP ⇌ 2 ADP, sharing the catalytic core (His-36, Asp-93) of cytosolic AK1 but carrying an additional ~50-residue 'wing' segment linked to its mitochondrial localization [PMID:6086335, PMID:3002789]. It is imported via the MIA40 disulfide relay and positioned within a central intermembrane-space energy-metabolism platform, where binding of the AK2A isoform to the AIFM1 C-terminus locks AIFM1 in an active NADH oxidoreductase dimer and reciprocally stabilizes AK2A, coupling local ADP regeneration to the OXPHOS machinery [PMID:40312560]. Through this role in adenine-nucleotide and ATP homeostasis, AK2 supports mitochondrial oxidative phosphorylation and energy distribution required for hematopoietic stem/progenitor differentiation, with loss causing oxidative stress, energy depletion (elevated AMP/ADP), reduced nuclear ATP supply, and lineage maturation arrest [PMID:26270350, PMID:26150473, PMID:29462620]; AK2 deficiency underlies the differentiation block seen in reticular dysgenesis, and hypomorphic variants reveal a particularly strict B-cell dependence on AK2-mediated mitochondrial respiration during activation [PMID:31862378]. AK2 function is also essential in vivo, as null mice are embryonic lethal and cardiac-specific deletion precipitates heart failure with metabolite buildup before compensatory adenylate-kinase and creatine-kinase upregulation restores pump function [PMID:33571905]. Beyond its catalytic role, AK2 acquires signaling functions: during intrinsic apoptosis it translocates to the cytoplasm and nucleates an AK2-FADD-caspase-10 complex that activates caspase-10 and then caspase-3 [PMID:17952061], and it acts as an AMP-sensing negative regulator of BRAF, where AMP binding strengthens the AK2-BRAF interaction to suppress ERK signaling while RAS activation abrogates it [PMID:35585049]. Cytosolic AK2 abundance is set by a post-translational switch in which DPP8/9 process its N-terminus to unmask an IAP-binding motif targeting it for proteasomal degradation, countered by NatA N-terminal acetylation [PMID:40312560].","teleology":[{"year":1986,"claim":"Establishing AK2's primary structure and catalytic chemistry defined it as a distinct intermembrane-space adenylate kinase rather than a redundant copy of cytosolic AK1.","evidence":"Protein sequencing, CNBr fragmentation, cysteine titration, and sedimentation analysis of the 238-residue enzyme","pmids":["6086335","3002789"],"confidence":"High","gaps":["Mechanistic basis by which the 'wing' segment directs mitochondrial localization not shown","Quaternary regulation in cellular context not addressed"]},{"year":2007,"claim":"Identifying the AK2-FADD-caspase-10 complex answered how a metabolic enzyme participates in apoptosis, defining a novel intrinsic death pathway distinct from caspase-8 activation.","evidence":"Reciprocal Co-IP, purified-protein reconstitution in extracts, Apaf-1 knockdown epistasis, and Bcl-2/Bcl-XL overexpression","pmids":["17952061"],"confidence":"High","gaps":["Whether catalytic activity is required for caspase activation unresolved","Trigger for AK2 mitochondrial release not defined at molecular level"]},{"year":2015,"claim":"Linking AK2 loss to disrupted nucleotide homeostasis, oxidative stress, and lineage arrest explained the hematopoietic basis of reticular dysgenesis and showed the defect is metabolic.","evidence":"shRNA knockdown in human progenitors, zebrafish ak2 mutant, RD patient iPSC differentiation, AMP/ADP profiling, and antioxidant rescue","pmids":["26270350","26150473"],"confidence":"High","gaps":["Why myeloid/lymphoid lineages are selectively vulnerable not fully explained","Direct link between energy state and transcriptional arrest not yet mapped"]},{"year":2018,"claim":"Demonstrating decreased nuclear ATP distribution in AK2-deficient progenitors refined the model from global energy failure to stage-specific intracellular ATP redistribution controlling fate.","evidence":"FRET-based ATP biosensor imaging and transcriptional profiling in RD patient iPSC-derived hemo-angiogenic progenitors","pmids":["29462620"],"confidence":"Medium","gaps":["Mechanism coupling AK2 activity to nuclear ATP pools unknown","Single-lab iPSC model"]},{"year":2019,"claim":"Characterizing hypomorphic AK2 variants revealed a tunable dependency, showing B cells require AK2-mediated respiration more strictly than T cells.","evidence":"Patient variant sequencing, tandem MS enzymatic activity, proliferation/Ig-secretion assays, mitochondrial respiration and membrane potential measurement","pmids":["31862378"],"confidence":"High","gaps":["Molecular basis of B-cell-specific sensitivity not defined","Threshold of residual activity sufficient for each lineage not mapped"]},{"year":2021,"claim":"Identifying AK2 as an AMP-sensing BRAF inhibitor connected cellular metabolic state to MAPK/ERK signaling, extending AK2 beyond bioenergetics into signal regulation.","evidence":"Reciprocal Co-IP, in vitro BRAF kinase assays, AMP addition to lysates, AK2 KO with proliferation, and HRASG12V HCC mouse model","pmids":["35585049"],"confidence":"High","gaps":["Structural basis of AMP-enhanced AK2-BRAF binding not resolved","Physiological contexts where this regulation dominates not delineated"]},{"year":2021,"claim":"Conditional knockouts established AK2 as developmentally essential and showed cardiac tissue can transiently compensate via redundant kinases, clarifying organ-level requirements.","evidence":"Constitutive embryonic-lethal and cardiac-specific Ak2 deletion with cardiac function, metabolite profiling, compensatory kinase expression, and ultrastructure imaging","pmids":["33571905"],"confidence":"Medium","gaps":["Whether compensation occurs in other tissues unknown","Trigger for compensatory kinase upregulation not identified"]},{"year":2023,"claim":"Identifying ODF4-dependent AK2 retention in the sperm flagellar midpiece extended AK2's energy role to a specialized motile structure required for fertility.","evidence":"Reciprocal Co-IP from spermatozoa, immunofluorescence, Odf4-/- mouse with motility analysis, and genetic rescue","pmids":["36804949"],"confidence":"Medium","gaps":["Whether AK2 catalytic function or structural presence drives motility unresolved","Direct ODF4-AK2 binding interface not mapped"]},{"year":2025,"claim":"Defining DPP8/9 processing, IBM unmasking, IAP-mediated degradation, and NatA acetylation explained how cytosolic AK2 abundance is controlled post-translationally, and confirmed MIA40-dependent intermembrane-space import.","evidence":"Biochemical IBM identification, DPP8/9 processing assays, IAP-binding and NatA acetylation assays, MIA40-dependent import and subcellular fractionation","pmids":["40312560"],"confidence":"High","gaps":["Conditions that partition AK2 between mitochondrial import and cytosolic processing not defined","Physiological signals controlling DPP8/9 vs NatA balance unknown"]},{"year":2024,"claim":"Structural and biochemical analysis of the AIFM1-AK2A complex placed AK2 within a NADH-sensing intermembrane-space platform that positions it for local ADP regeneration adjacent to OXPHOS.","evidence":"AIFM1 interactome MS, cryo-EM of AIFM1-AK2A, NADH oxidoreductase and binding assays, glycolytic manipulation, and C. elegans genetic interference (preprint)","pmids":[],"confidence":"High","gaps":["Findings remain in preprint, not yet peer-reviewed","Quantitative contribution of AIFM1-positioned AK2 to ATP synthase substrate supply in vivo not established"]},{"year":null,"claim":"It remains unresolved how AK2's catalytic, apoptotic, BRAF-regulatory, and degradation-control functions are coordinately partitioned across mitochondrial and cytosolic pools within a single cell.","evidence":"No single study integrates the localization-dependent functional switching","pmids":[],"confidence":"Low","gaps":["No unified model of pool partitioning","Signals governing functional state transitions undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1,2]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[9]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,11]}],"pathway":[{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3,4,8]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[11]}],"complexes":["AK2-FADD-caspase-10 (AFAC10) complex","AIFM1-AK2A complex"],"partners":["FADD","CASP10","BRAF","AIFM1","MIA40","ODF4","DPP8","DPP9"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P54819","full_name":"Adenylate kinase 2, mitochondrial","aliases":["ATP-AMP transphosphorylase 2","ATP:AMP phosphotransferase","Adenylate monophosphate kinase"],"length_aa":239,"mass_kda":26.5,"function":"Catalyzes the reversible transfer of the terminal phosphate group between ATP and AMP. Plays an important role in cellular energy homeostasis and in adenine nucleotide metabolism. Adenylate kinase activity is critical for regulation of the phosphate utilization and the AMP de novo biosynthesis pathways. Plays a key role in hematopoiesis","subcellular_location":"Mitochondrion intermembrane space","url":"https://www.uniprot.org/uniprotkb/P54819/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/AK2","classification":"Not Classified","n_dependent_lines":180,"n_total_lines":1208,"dependency_fraction":0.1490066225165563},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SAR1B","stoichiometry":0.2},{"gene":"UPF1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/AK2","total_profiled":1310},"omim":[{"mim_id":"618368","title":"DUAL-SPECIFICITY PHOSPHATASE 26; DUSP26","url":"https://www.omim.org/entry/618368"},{"mim_id":"612280","title":"FUCOSIDASE, ALPHA-L, 1; FUCA1","url":"https://www.omim.org/entry/612280"},{"mim_id":"611787","title":"CYTIDINE MONOPHOSPHATE (UMP-CMP) KINASE 2, MITOCHONDRIAL; CMPK2","url":"https://www.omim.org/entry/611787"},{"mim_id":"608009","title":"ADENYLATE KINASE 5; AK5","url":"https://www.omim.org/entry/608009"},{"mim_id":"602457","title":"FAS-ASSOCIATED VIA DEATH DOMAIN; FADD","url":"https://www.omim.org/entry/602457"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Mitochondria","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/AK2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P54819","domains":[{"cath_id":"3.40.50.300","chopping":"15-233","consensus_level":"high","plddt":93.7983,"start":15,"end":233}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P54819","model_url":"https://alphafold.ebi.ac.uk/files/AF-P54819-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P54819-F1-predicted_aligned_error_v6.png","plddt_mean":90.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=AK2","jax_strain_url":"https://www.jax.org/strain/search?query=AK2"},"sequence":{"accession":"P54819","fasta_url":"https://rest.uniprot.org/uniprotkb/P54819.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P54819/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P54819"}},"corpus_meta":[{"pmid":"17952061","id":"PMC_17952061","title":"AK2 activates a novel apoptotic pathway through formation of a complex with FADD and caspase-10.","date":"2007","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/17952061","citation_count":81,"is_preprint":false},{"pmid":"26270350","id":"PMC_26270350","title":"AK2 deficiency compromises the mitochondrial energy metabolism required for differentiation of human neutrophil and lymphoid lineages.","date":"2015","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/26270350","citation_count":66,"is_preprint":false},{"pmid":"26150473","id":"PMC_26150473","title":"Reticular dysgenesis-associated AK2 protects hematopoietic stem and progenitor cell development from oxidative stress.","date":"2015","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/26150473","citation_count":49,"is_preprint":false},{"pmid":"6086335","id":"PMC_6086335","title":"Mitochondrial adenylate kinase (AK2) from bovine heart. Homology with the cytosolic isoenzyme in the catalytic region.","date":"1984","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/6086335","citation_count":37,"is_preprint":false},{"pmid":"3002789","id":"PMC_3002789","title":"Mitochondrial adenylate kinase (AK2) from bovine heart. The complete primary structure.","date":"1986","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/3002789","citation_count":32,"is_preprint":false},{"pmid":"31862378","id":"PMC_31862378","title":"Hypomorphic variants in AK2 reveal the contribution of mitochondrial function to B-cell activation.","date":"2019","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/31862378","citation_count":24,"is_preprint":false},{"pmid":"7153494","id":"PMC_7153494","title":"Assignment of ADA, ITPA, AK1, and AK2 to Chinese hamster chromosomes. Genetic and structural evidence for the conservation of mammalian autosomal synteny.","date":"1982","source":"The Journal of heredity","url":"https://pubmed.ncbi.nlm.nih.gov/7153494","citation_count":24,"is_preprint":false},{"pmid":"29462620","id":"PMC_29462620","title":"Human AK2 links intracellular bioenergetic redistribution to the fate of hematopoietic progenitors.","date":"2018","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/29462620","citation_count":16,"is_preprint":false},{"pmid":"33571905","id":"PMC_33571905","title":"Adenylate kinase AK2 isoform integral in embryo and adult heart homeostasis.","date":"2021","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/33571905","citation_count":14,"is_preprint":false},{"pmid":"23020757","id":"PMC_23020757","title":"Adenylate kinase 2 (AK2) promotes cell proliferation in insect development.","date":"2012","source":"BMC molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/23020757","citation_count":14,"is_preprint":false},{"pmid":"33129036","id":"PMC_33129036","title":"Circ-AK2 is associated with preeclampsia and regulates biological behaviors of trophoblast cells through miR-454-3p/THBS2.","date":"2020","source":"Placenta","url":"https://pubmed.ncbi.nlm.nih.gov/33129036","citation_count":14,"is_preprint":false},{"pmid":"34630090","id":"PMC_34630090","title":"AK2 Promotes the Migration and Invasion of Lung Adenocarcinoma by Activating TGF-β/Smad Pathway In vitro and In vivo.","date":"2021","source":"Frontiers in pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/34630090","citation_count":13,"is_preprint":false},{"pmid":"39543767","id":"PMC_39543767","title":"Ancestral retrovirus envelope protein ERVWE1 upregulates circ_0001810, a potential biomarker for schizophrenia, and induces neuronal mitochondrial dysfunction via activating AK2.","date":"2024","source":"Cell & bioscience","url":"https://pubmed.ncbi.nlm.nih.gov/39543767","citation_count":12,"is_preprint":false},{"pmid":"8292263","id":"PMC_8292263","title":"Microbial metabolism of quinoline and related compounds. XX. Quinaldic acid 4-oxidoreductase from Pseudomonas sp. AK-2 compared to other procaryotic molybdenum-containing hydroxylases.","date":"1993","source":"Biological chemistry Hoppe-Seyler","url":"https://pubmed.ncbi.nlm.nih.gov/8292263","citation_count":10,"is_preprint":false},{"pmid":"31399108","id":"PMC_31399108","title":"Quantitative proteomic analysis reveals AK2 as potential biomarker for late normal tissue radiotoxicity.","date":"2019","source":"Radiation oncology (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/31399108","citation_count":8,"is_preprint":false},{"pmid":"36804949","id":"PMC_36804949","title":"The association of ODF4 with AK1 and AK2 in mice is essential for fertility through its contribution to flagellar shape.","date":"2023","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/36804949","citation_count":7,"is_preprint":false},{"pmid":"35585049","id":"PMC_35585049","title":"AK2 is an AMP-sensing negative regulator of BRAF in tumorigenesis.","date":"2022","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/35585049","citation_count":6,"is_preprint":false},{"pmid":"6205552","id":"PMC_6205552","title":"Partial purification and properties of thermostable intracellular amylases from a thermophilic Bacillus sp. AK-2.","date":"1984","source":"Acta microbiologica Polonica","url":"https://pubmed.ncbi.nlm.nih.gov/6205552","citation_count":6,"is_preprint":false},{"pmid":"40312560","id":"PMC_40312560","title":"DPP8/9 processing of human AK2 unmasks an IAP binding motif.","date":"2025","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/40312560","citation_count":4,"is_preprint":false},{"pmid":"39288025","id":"PMC_39288025","title":"Quantitative tissue analysis reveals AK2, COL1A1, and PLG protein signatures: targeted therapeutics for meningioma.","date":"2024","source":"International journal of surgery (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/39288025","citation_count":4,"is_preprint":false},{"pmid":"40053226","id":"PMC_40053226","title":"Andrographolide ameliorates sepsis-induced acute liver injury by attenuating endoplasmic reticulum stress through the FKBP1A-mediated NOTCH1/AK2 pathway.","date":"2025","source":"Cell biology and toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/40053226","citation_count":4,"is_preprint":false},{"pmid":"37949028","id":"PMC_37949028","title":"UK-5099, a mitochondrial pyruvate carrier inhibitor, recovers impaired neutrophil maturation caused by AK2 deficiency in human pluripotent stem cell models.","date":"2023","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/37949028","citation_count":4,"is_preprint":false},{"pmid":"34887922","id":"PMC_34887922","title":"circ_0075943 Dominates the miR-141-3p/AK2 Network to Support the Development of Breast Carcinoma.","date":"2021","source":"Journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/34887922","citation_count":3,"is_preprint":false},{"pmid":"32532877","id":"PMC_32532877","title":"Reticular dysgenesis caused by an intronic pathogenic variant in AK2.","date":"2020","source":"Cold Spring Harbor molecular case studies","url":"https://pubmed.ncbi.nlm.nih.gov/32532877","citation_count":3,"is_preprint":false},{"pmid":"39932644","id":"PMC_39932644","title":"Early Haploidentical Hematopoietic Stem Cell Transplantation Provides Rapid Leukocyte and Immune Reconstitution in AK2 Patient Identified by TREC Newborn Screening.","date":"2025","source":"Journal of clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/39932644","citation_count":2,"is_preprint":false},{"pmid":"40654267","id":"PMC_40654267","title":"AK2-Deficient Mice Recapitulate Impaired Lymphopoiesis of Reticular Dysgenesis Patients, but Also Lack Erythropoiesis.","date":"2025","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/40654267","citation_count":0,"is_preprint":false},{"pmid":"42112325","id":"PMC_42112325","title":"Reticular dysgenesis caused by AK2 deficiency: clinical spectrum and hematopoietic stem cell transplantation outcomes in 10 patients from a single-center.","date":"2026","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/42112325","citation_count":0,"is_preprint":false},{"pmid":"42039167","id":"PMC_42039167","title":"Case Report: Novel AK2 variant causing reticular dysgenesis with hemophagocytic lymphohistiocytosis-like syndrome and invasive aspergillosis.","date":"2026","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/42039167","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.25.666757","title":"Exploring the Potential of AlphaFold Distograms for Predicting Binding-induced Hinge Motions","date":"2025-07-27","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.25.666757","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.08.22.609182","title":"An NADH-controlled gatekeeper of ATP synthase","date":"2024-08-22","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.22.609182","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.09.09.611957","title":"Interaction with AK2A links AIFM1 to cellular energy metabolism","date":"2024-09-09","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.09.611957","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":17394,"output_tokens":4394,"usd":0.059046,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12356,"output_tokens":3923,"usd":0.079927,"stage2_stop_reason":"end_turn"},"total_usd":0.138973,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"AK2 translocates from mitochondria to the cytoplasm during intrinsic apoptosis (blocked by Bcl-2/Bcl-XL and reduced in Apaf-1 knockdown cells), and forms an AK2-FADD-caspase-10 (AFAC10) complex that activates caspase-10 via FADD and subsequently caspase-3, but not caspase-8, defining a novel intrinsic apoptotic pathway. Purified AK2 added to cell extracts reconstituted this caspase activation cascade.\",\n      \"method\": \"Co-immunoprecipitation of AFAC10 complex, purified protein addition to cell extracts, Apaf-1 knockdown epistasis, Bcl-2/Bcl-XL overexpression, caspase activity assays, AK2 siRNA knockdown\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reconstitution with purified protein, reciprocal Co-IP, genetic epistasis (Apaf-1 KD, Bcl-2/Bcl-XL), multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"17952061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"AK2 is a monomeric mitochondrial intermembrane space phosphotransferase that catalyzes ATP + AMP ⇌ 2 ADP. Its N-terminal ~100 residues share homology with cytosolic AK1, including catalytic residues His-36 and Asp-93, but AK2 contains an additional ~50-residue 'wing' segment absent in AK1 that is likely related to its mitochondrial localization.\",\n      \"method\": \"Protein sequencing (Laursen sequenator), CNBr fragmentation, peptide mapping, sequence alignment, molecular weight determination\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical sequencing and catalytic characterization, replicated in follow-up 1986 study completing full sequence\",\n      \"pmids\": [\"6086335\", \"3002789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"AK2 contains 238 residues with four cysteines: Cys-41 and Cys-233 are free thiols carboxymethylatable without loss of enzymatic activity, while Cys-43/Cys-93 likely form a disulfide bond in native AK2. AK2 and AK1 share similar active-site geometry but differ in antigenic sites, consistent with lack of immunological cross-reactivity.\",\n      \"method\": \"Gas-phase protein sequencing, SH-group titration, sedimentation equilibrium ultracentrifugation, gel filtration, chemical modification of cysteines with enzymatic activity assay\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — complete primary structure determined, cysteine chemistry confirmed with activity assays, two orthogonal methods for molecular weight\",\n      \"pmids\": [\"3002789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"AK2 deficiency impairs mitochondrial oxidative phosphorylation and disrupts adenine nucleotide homeostasis in human hematopoietic progenitors, causing a block in lymphoid and granulocyte differentiation. AK2 knockdown progenitors show poor proliferative and survival capacities.\",\n      \"method\": \"AK2 shRNA knockdown in hematopoietic progenitors, mitochondrial function assays (oxidative phosphorylation measurement), proliferation and survival assays, differentiation assays toward lymphoid and granulocyte lineages\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with defined cellular phenotype and mechanistic metabolic readout, single lab with multiple orthogonal functional assays\",\n      \"pmids\": [\"26270350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"AK2 deficiency in zebrafish leads to increased oxidative stress and apoptosis in hematopoietic stem and progenitor cells; AK2-deficient human iPSCs show increased AMP/ADP ratio (energy-depleted adenine nucleotide profile) and myeloid maturation arrest. Antioxidant treatment rescues hematopoietic phenotypes in vivo and restores granulocyte differentiation from iPSCs, linking AK2 loss to cellular energy depletion and oxidative stress.\",\n      \"method\": \"Zebrafish ak2 mutant model, RD patient-derived iPSC differentiation, adenine nucleotide profiling (AMP/ADP ratio), antioxidant rescue experiments, in vivo and in vitro differentiation assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent model systems (zebrafish KO and patient iPSCs), metabolic profiling, pharmacological rescue, multiple orthogonal methods\",\n      \"pmids\": [\"26150473\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"AK2 maintains ATP supply to the nucleus during hematopoietic differentiation; RD patient-derived iPSC hemo-angiogenic progenitor cells show decreased ATP distribution in the nucleus and altered global transcriptional profiles, indicating a stage-specific role for AK2 in intracellular ATP redistribution controlling hematopoietic progenitor fate.\",\n      \"method\": \"RD patient iPSC-derived hematopoietic differentiation, ATP distribution imaging (FRET-based ATP biosensor), transcriptional profiling\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient-derived iPSC model with direct ATP localization measurement and transcriptional readout, single lab\",\n      \"pmids\": [\"29462620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Hypomorphic AK2 variants (AK2G100S and AK2A182D) allow residual AK2 protein expression and enzymatic activity with normal neutrophil and lymphocyte counts, but cause B-cell-specific defects in proliferation and immunoglobulin secretion associated with impaired mitochondrial respiration and dysregulated mitochondrial membrane potential upon B-cell activation, revealing that B cells have a stricter dependency on AK2-mediated mitochondrial function than T cells.\",\n      \"method\": \"Next-generation sequencing to identify variants, tandem mass spectrometry for enzymatic activity, lymphocyte proliferation assays, in vitro immunoglobulin secretion, mitochondrial respiration measurement, mitochondrial membrane potential assay, chemical ATP synthesis inhibition in control cells\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — patient variant characterization with direct enzymatic activity measurement, multiple orthogonal mitochondrial functional assays, pharmacological confirmation in controls\",\n      \"pmids\": [\"31862378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"AK2 promotes migration and invasion of lung adenocarcinoma cells through the Smad-dependent TGF-β/EMT signaling pathway. AK2 knockout reduced EMT-like features and metastatic nodule formation in vivo.\",\n      \"method\": \"AK2 siRNA knockdown, CRISPR knockout, AK2 overexpression, cell migration and invasion assays, differential proteomics, western blot and qPCR for EMT markers and Smad pathway components, in vivo mouse metastasis model\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO and OE with defined phenotype and pathway measurement by multiple methods, single lab\",\n      \"pmids\": [\"34630090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"AK2 null homozygosity is embryonic lethal in mice; conditional cardiac-specific AK2 deletion causes abrupt heart failure with Krebs cycle and glycolytic metabolite buildup, followed by compensatory upregulation of AK1, AK3, AK4, creatine kinase isoforms, and hexokinase with mitochondrial ultrastructure remodeling that permits recovery of pump function.\",\n      \"method\": \"Transgenic AK2 knockout (constitutive embryonic lethality), conditional organ-specific Ak2 deletion, cardiac function measurement, metabolite profiling, compensatory kinase expression analysis, mitochondrial ultrastructure imaging\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo conditional KO with defined functional and metabolic phenotype, multiple readouts, single lab\",\n      \"pmids\": [\"33571905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"AK2 physically interacts with BRAF and inhibits BRAF kinase activity and downstream ERK phosphorylation. AMP binding to AK2 strengthens the AK2-BRAF interaction, placing AK2 as an AMP-sensing negative regulator of BRAF that links cellular metabolic state to MAPK signaling. RAS activation abrogates AK2-BRAF interaction. AK2 also binds and attenuates BRAF inhibitor-insensitive BRAF mutants.\",\n      \"method\": \"Co-immunoprecipitation (AK2-BRAF), in vitro kinase assays for BRAF activity, ERK phosphorylation western blot, AMP addition to cell lysates, AK2 KD/KO with proliferation assay, mouse HRASG12V-driven HCC model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reciprocal Co-IP, in vitro kinase assay, AMP-binding mechanism, genetic KO, in vivo mouse tumor model, multiple orthogonal methods\",\n      \"pmids\": [\"35585049\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ODF4 co-immunoprecipitates with AK2 (and AK1) in mouse spermatozoa; ODF4 localizes to the whole flagellum midpiece region where AK2 is present. Deletion of Odf4 reduces AK2 levels in sperm flagella and causes abnormal flagellar shape (hairpin flagellum) with loss of midpiece motility and male infertility, rescued by Odf4 restoration.\",\n      \"method\": \"Co-immunoprecipitation of ODF4 with AK2/AK1 from spermatozoa, immunofluorescence localization, Odf4-/- mouse model, sperm motility analysis, rescue experiment with Odf4 restoration\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, KO phenotype with defined functional readout and genetic rescue, single lab\",\n      \"pmids\": [\"36804949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cytosolic AK2 stability is regulated by sequential post-translational events: DPP8/9 dipeptidyl peptidases process AK2's N-terminus, unmasking an IAP-binding motif (IBM) that targets AK2 for IAP (E3 ligase)-mediated proteasomal degradation. N-terminal acetylation by NatA prevents the AK2-IAP interaction, stabilizing cytosolic AK2.\",\n      \"method\": \"Biochemical identification of IBM, DPP8/9 processing assays, IAP interaction assays, NatA acetylation assays, genome-wide in silico IBM screen, validation with EIF2A as additional substrate\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — biochemical reconstitution of processing and IBM unmasking, multiple orthogonal experiments (DPP8/9 assay, IAP binding, NatA acetylation), mechanistic pathway established in single rigorous study\",\n      \"pmids\": [\"40312560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"AIFM1 interacts with AK2 (specifically isoform AK2A) via its C-terminus, stabilizing AK2A. Cryo-EM and biochemical analyses show that AK2A binding to AIFM1's C-terminal β-strand locks AIFM1 in an active dimer conformation and enhances its NADH oxidoreductase activity. MIA40 binds the same site and additionally affects the cofactor binding site. The AIFM1-AK2A interaction is crucial during respiratory conditions, placing AK2 as part of the central energy metabolism regulatory platform in the mitochondrial intermembrane space.\",\n      \"method\": \"High-confidence AIFM1 interactome (MS), high-resolution cryo-EM structure of AIFM1-AK2A complex, biochemical binding assays, NADH oxidoreductase activity assays, genetic interference in C. elegans\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure, biochemical reconstitution, enzymatic activity assays, in vivo genetic interference, multiple orthogonal methods in single study\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The AIFM1-AK2 interaction is NADH-dependent and influenced by glycolytic state, placing AK2 adjacent to OXPHOS complexes for local ADP regeneration as substrate for ATP synthase. Disruption of AIFM1/AK2 association impairs metabolic adaptation to altered nutrient availability in C. elegans, identifying AIFM1 as a cellular NADH sensor that positions AK2 to balance ATP synthase substrate supply.\",\n      \"method\": \"AIFM1-AK2 binding assays under NADH conditions, glycolytic manipulation, genetic interference in C. elegans (metabolic phenotype), cryo-EM imaging referenced for hinge motion\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical NADH-dependence characterization, in vivo C. elegans genetic model, preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"AK2 is localized in the mitochondrial intermembrane space and imported via the MIA40 disulfide relay system. In the cytosol, AK2 undergoes N-terminal processing by DPP8/9 that sensitizes it to proteasomal degradation (confirmed by the IBM-IAP mechanism).\",\n      \"method\": \"Subcellular fractionation, MIA40-dependent import assay, N-terminal processing assays with DPP8/9\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct import pathway identification with biochemical assays, single study but mechanistic details established\",\n      \"pmids\": [\"40312560\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"AK2 is a mitochondrial intermembrane space phosphotransferase (catalyzing ATP + AMP ⇌ 2 ADP) that is imported via the MIA40 disulfide relay and stabilized by AIFM1 binding (which locks AIFM1 in an active NADH oxidoreductase dimer); cytosolic AK2 is subject to DPP8/9-mediated N-terminal processing that unmasks an IAP-binding motif leading to proteasomal degradation unless blocked by NatA acetylation. During intrinsic apoptosis, AK2 translocates to the cytoplasm where it forms an AK2-FADD-caspase-10 complex that activates caspase-10 and subsequently caspase-3. AK2 also acts as an AMP-sensing negative regulator of BRAF kinase, suppressing MAPK/ERK signaling in proportion to cellular AMP levels, and is essential for mitochondrial energy homeostasis supporting hematopoietic stem cell differentiation, B-cell activation, cardiac function, and embryonic development.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"AK2 is a monomeric phosphotransferase of the mitochondrial intermembrane space that catalyzes the reversible interconversion ATP + AMP \\u21cc 2 ADP, sharing the catalytic core (His-36, Asp-93) of cytosolic AK1 but carrying an additional ~50-residue 'wing' segment linked to its mitochondrial localization [#1, #2]. It is imported via the MIA40 disulfide relay and positioned within a central intermembrane-space energy-metabolism platform, where binding of the AK2A isoform to the AIFM1 C-terminus locks AIFM1 in an active NADH oxidoreductase dimer and reciprocally stabilizes AK2A, coupling local ADP regeneration to the OXPHOS machinery [#14, #12]. Through this role in adenine-nucleotide and ATP homeostasis, AK2 supports mitochondrial oxidative phosphorylation and energy distribution required for hematopoietic stem/progenitor differentiation, with loss causing oxidative stress, energy depletion (elevated AMP/ADP), reduced nuclear ATP supply, and lineage maturation arrest [#3, #4, #5]; AK2 deficiency underlies the differentiation block seen in reticular dysgenesis, and hypomorphic variants reveal a particularly strict B-cell dependence on AK2-mediated mitochondrial respiration during activation [#6]. AK2 function is also essential in vivo, as null mice are embryonic lethal and cardiac-specific deletion precipitates heart failure with metabolite buildup before compensatory adenylate-kinase and creatine-kinase upregulation restores pump function [#8]. Beyond its catalytic role, AK2 acquires signaling functions: during intrinsic apoptosis it translocates to the cytoplasm and nucleates an AK2-FADD-caspase-10 complex that activates caspase-10 and then caspase-3 [#0], and it acts as an AMP-sensing negative regulator of BRAF, where AMP binding strengthens the AK2-BRAF interaction to suppress ERK signaling while RAS activation abrogates it [#9]. Cytosolic AK2 abundance is set by a post-translational switch in which DPP8/9 process its N-terminus to unmask an IAP-binding motif targeting it for proteasomal degradation, countered by NatA N-terminal acetylation [#11].\",\n  \"teleology\": [\n    {\n      \"year\": 1986,\n      \"claim\": \"Establishing AK2's primary structure and catalytic chemistry defined it as a distinct intermembrane-space adenylate kinase rather than a redundant copy of cytosolic AK1.\",\n      \"evidence\": \"Protein sequencing, CNBr fragmentation, cysteine titration, and sedimentation analysis of the 238-residue enzyme\",\n      \"pmids\": [\"6086335\", \"3002789\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic basis by which the 'wing' segment directs mitochondrial localization not shown\", \"Quaternary regulation in cellular context not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identifying the AK2-FADD-caspase-10 complex answered how a metabolic enzyme participates in apoptosis, defining a novel intrinsic death pathway distinct from caspase-8 activation.\",\n      \"evidence\": \"Reciprocal Co-IP, purified-protein reconstitution in extracts, Apaf-1 knockdown epistasis, and Bcl-2/Bcl-XL overexpression\",\n      \"pmids\": [\"17952061\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether catalytic activity is required for caspase activation unresolved\", \"Trigger for AK2 mitochondrial release not defined at molecular level\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linking AK2 loss to disrupted nucleotide homeostasis, oxidative stress, and lineage arrest explained the hematopoietic basis of reticular dysgenesis and showed the defect is metabolic.\",\n      \"evidence\": \"shRNA knockdown in human progenitors, zebrafish ak2 mutant, RD patient iPSC differentiation, AMP/ADP profiling, and antioxidant rescue\",\n      \"pmids\": [\"26270350\", \"26150473\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why myeloid/lymphoid lineages are selectively vulnerable not fully explained\", \"Direct link between energy state and transcriptional arrest not yet mapped\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrating decreased nuclear ATP distribution in AK2-deficient progenitors refined the model from global energy failure to stage-specific intracellular ATP redistribution controlling fate.\",\n      \"evidence\": \"FRET-based ATP biosensor imaging and transcriptional profiling in RD patient iPSC-derived hemo-angiogenic progenitors\",\n      \"pmids\": [\"29462620\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism coupling AK2 activity to nuclear ATP pools unknown\", \"Single-lab iPSC model\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Characterizing hypomorphic AK2 variants revealed a tunable dependency, showing B cells require AK2-mediated respiration more strictly than T cells.\",\n      \"evidence\": \"Patient variant sequencing, tandem MS enzymatic activity, proliferation/Ig-secretion assays, mitochondrial respiration and membrane potential measurement\",\n      \"pmids\": [\"31862378\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of B-cell-specific sensitivity not defined\", \"Threshold of residual activity sufficient for each lineage not mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying AK2 as an AMP-sensing BRAF inhibitor connected cellular metabolic state to MAPK/ERK signaling, extending AK2 beyond bioenergetics into signal regulation.\",\n      \"evidence\": \"Reciprocal Co-IP, in vitro BRAF kinase assays, AMP addition to lysates, AK2 KO with proliferation, and HRASG12V HCC mouse model\",\n      \"pmids\": [\"35585049\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of AMP-enhanced AK2-BRAF binding not resolved\", \"Physiological contexts where this regulation dominates not delineated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Conditional knockouts established AK2 as developmentally essential and showed cardiac tissue can transiently compensate via redundant kinases, clarifying organ-level requirements.\",\n      \"evidence\": \"Constitutive embryonic-lethal and cardiac-specific Ak2 deletion with cardiac function, metabolite profiling, compensatory kinase expression, and ultrastructure imaging\",\n      \"pmids\": [\"33571905\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether compensation occurs in other tissues unknown\", \"Trigger for compensatory kinase upregulation not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying ODF4-dependent AK2 retention in the sperm flagellar midpiece extended AK2's energy role to a specialized motile structure required for fertility.\",\n      \"evidence\": \"Reciprocal Co-IP from spermatozoa, immunofluorescence, Odf4-/- mouse with motility analysis, and genetic rescue\",\n      \"pmids\": [\"36804949\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether AK2 catalytic function or structural presence drives motility unresolved\", \"Direct ODF4-AK2 binding interface not mapped\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defining DPP8/9 processing, IBM unmasking, IAP-mediated degradation, and NatA acetylation explained how cytosolic AK2 abundance is controlled post-translationally, and confirmed MIA40-dependent intermembrane-space import.\",\n      \"evidence\": \"Biochemical IBM identification, DPP8/9 processing assays, IAP-binding and NatA acetylation assays, MIA40-dependent import and subcellular fractionation\",\n      \"pmids\": [\"40312560\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conditions that partition AK2 between mitochondrial import and cytosolic processing not defined\", \"Physiological signals controlling DPP8/9 vs NatA balance unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Structural and biochemical analysis of the AIFM1-AK2A complex placed AK2 within a NADH-sensing intermembrane-space platform that positions it for local ADP regeneration adjacent to OXPHOS.\",\n      \"evidence\": \"AIFM1 interactome MS, cryo-EM of AIFM1-AK2A, NADH oxidoreductase and binding assays, glycolytic manipulation, and C. elegans genetic interference (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Findings remain in preprint, not yet peer-reviewed\", \"Quantitative contribution of AIFM1-positioned AK2 to ATP synthase substrate supply in vivo not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how AK2's catalytic, apoptotic, BRAF-regulatory, and degradation-control functions are coordinately partitioned across mitochondrial and cytosolic pools within a single cell.\",\n      \"evidence\": \"No single study integrates the localization-dependent functional switching\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unified model of pool partitioning\", \"Signals governing functional state transitions undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005758\", \"supporting_discovery_ids\": [1, 14]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 4, 8]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"complexes\": [\"AK2-FADD-caspase-10 (AFAC10) complex\", \"AIFM1-AK2A complex\"],\n    \"partners\": [\"FADD\", \"CASP10\", \"BRAF\", \"AIFM1\", \"MIA40\", \"ODF4\", \"DPP8\", \"DPP9\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}