{"gene":"CKB","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":2009,"finding":"CK-B (CKB) transiently accumulates in membrane ruffles of astrocytes and fibroblasts during spreading and migration, and ablation of CKB activity impairs spreading and migration performance. Complementation experiments using forced relocalization of CKB from cytosol to cortical membrane sites confirmed that compartmentalized CKB-generated ATP locally supports actomyosin dynamics and cell motility.","method":"Live-cell imaging, CKB-deficient fibroblast complementation with targeted protein relocalization constructs, migration/spreading assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO fibroblast complementation with spatial relocalization strategy and defined phenotypic readout (migration/spreading), single lab with multiple orthogonal approaches","pmids":["19333390"],"is_preprint":false},{"year":2021,"finding":"CKB interacts directly with AKT and sequesters it from activation by mTOR. The interaction is mediated by an 84-amino acid C-terminal fragment of CKB binding to AKT's PH domain. Ectopic expression of this 84aa fragment inhibits AKT activation, EMT, and cell proliferation in prostate cancer cells. Molecular dynamics simulation on crystal structures independently confirmed this interaction interface.","method":"Co-immunoprecipitation, kinase cDNA screen, domain mapping with truncation mutants, ectopic 84aa fragment overexpression, xenograft tumor models, molecular dynamics simulation","journal":"Neoplasia (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with domain mapping and functional rescue, supported by MD simulation, single lab","pmids":["34706306"],"is_preprint":false},{"year":2022,"finding":"ADRA1A-Gαq signaling (triggered by noradrenaline) induces expression of thermogenic genes of the futile creatine cycle including CKB, and CKB is required as an effector protein for this thermogenic output. Combined Gαq and Gαs signaling in adipocytes promotes whole-body energy expenditure in a CKB-dependent manner.","method":"Adipocyte-selective genetic knockout of CKB in vivo, whole-body energy expenditure measurement, gene expression analysis, adrenergic receptor signaling pathway dissection","journal":"Nature metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — adipocyte-selective KO with defined thermogenic phenotype, in vivo energy expenditure measurement, pathway dissection across multiple adrenergic receptor subtypes, replicated in vivo","pmids":["36344764"],"is_preprint":false},{"year":2024,"finding":"CKB functions in parallel with UCP1 as a non-redundant mediator of cold-triggered adipocyte thermogenesis. Inducible adipocyte-selective co-deletion of both Ucp1 and Ckb exacerbates cold intolerance beyond either single deletion, establishing CKB as an independent effector of UCP1-independent thermogenesis in brown adipocytes.","method":"Inducible adipocyte-selective Ucp1 knockout, inducible co-deletion of Ucp1 and Ckb, cold-tolerance challenge, body temperature measurement","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — inducible adipocyte-selective double KO with rigorous cold-tolerance phenotyping, genetic epistasis establishing non-paralogous redundancy, in vivo","pmids":["38272036"],"is_preprint":false},{"year":2024,"finding":"CKB promotes mitochondrial ATP production by suppressing mitochondrial calcium (mCa2+) levels, thereby preventing mitochondrial permeability transition pore (mPTP) activation. CKB achieves mCa2+ suppression through inhibition of AKT activity. Silencing CKB (but not CKMT1A or CKMT1B) causes loss of sensitivity to F1F0 ATP synthase inhibition, linking CKB specifically to this pathway.","method":"CKB siRNA knockdown, mitochondrial calcium measurement, mPTP activity assay, AKT activity measurement, F1F0 ATP synthase inhibitor sensitivity assay, in vivo mouse tumor model","journal":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD with defined mechanistic readouts (mCa2+, mPTP, AKT), isoform-specific comparisons (CKB vs CKMT1A/B), single lab","pmids":["38896801"],"is_preprint":false},{"year":2012,"finding":"Crystal structure of hASB9-2 (an isoform of the CKB-targeting E3 ubiquitin ligase substrate receptor ASB9) was solved at 2.2-Å resolution. Amino acid substitution analysis based on docking showed His103 and Phe107 in hASB9-2 are essential for binding to CKB. Truncation analysis showed the first six ankyrin repeats plus the N-terminal region of hASB9-2 are required for CKB interaction. ASB9 recognizes CKB via its ankyrin repeat domain and mediates CKB polyubiquitination and proteasomal degradation via its SOCS box domain.","method":"X-ray crystallography (2.2 Å), site-directed mutagenesis, docking, truncation mutant binding assays","journal":"The protein journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — crystal structure with mutagenesis and docking to map CKB interaction interface, single lab, no in-cell ubiquitination reconstitution described in abstract","pmids":["22418839"],"is_preprint":false},{"year":2000,"finding":"His65 in human CK-BB (CKB) contributes to protein stability rather than catalysis: the ΔH65 mutant retains near-normal substrate affinity but shows very low stability. The double mutant ΔH65P66 shows eight-fold decreased affinity for creatine phosphate and inability to dephosphorylate cyclocreatine phosphate, indicating that the flexible loop containing Pro66 accounts for isoenzyme-specific substrate discrimination.","method":"Site-directed mutagenesis of CKB expressed in COS-7 cells, substrate affinity (Km) measurements, cyclocreatine phosphate dephosphorylation assay, stability assay","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay with active-site mutagenesis and substrate kinetics, multiple mutants tested, single lab with clear mechanistic dissection","pmids":["10854850"],"is_preprint":false},{"year":2020,"finding":"GnRH antagonist (GnRH-ant) reduces CKB expression in endometrial epithelial cells, leading to decreased ATP generation, F-actin depolymerization, and impaired cell migration. CKB knockdown phenocopies these effects; CKB overexpression rescues both the GnRH-ant-induced and knockdown-induced defects in actin polymerization and migration.","method":"CKB knockdown and overexpression in Ishikawa cells, ATP measurement, F-actin/G-actin assay, cell migration assay, in vitro GnRH-ant treatment","journal":"Reproduction (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function with rescue, defined readouts (ATP, actin, migration), single lab","pmids":["32213653"],"is_preprint":false},{"year":2021,"finding":"CKB expression is induced downstream of HIF-1 in mammary tumor cells. CKB is necessary for breast cancer cell invasion in vitro and promotes tumor growth and lung metastasis in vivo. Cyclocreatine (a creatine kinase activity inhibitor) represses cell migration, invasion, invadopodia formation, and lung metastasis, indicating that CKB creatine kinase enzymatic activity mediates these pro-metastatic effects.","method":"HIF-1 WT vs knockout mammary tumor cell gene screen, CKB loss/gain-of-function, invasion assays, invadopodia assay, in vivo lung metastasis model, cyclocreatine pharmacological inhibition","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss/gain-of-function plus pharmacological enzyme inhibition with in vivo metastasis readout, single lab","pmids":["35008190"],"is_preprint":false},{"year":2024,"finding":"Creatine supplementation increases CKB-BB activity and expression in brain, and AAV-mediated CKB knockdown (34% reduction) in mouse brain causes deficits in learning/memory, oxidative stress, and hippocampal spine morphology damage, establishing CKB as a required mediator of structural synaptic plasticity and cognitive function in the brain.","method":"AAV-directed CKB knockdown in mouse brain, behavioral cognitive testing, hippocampal spine morphology analysis, CKB activity measurement, creatine dietary supplementation","journal":"Food science & nutrition","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo viral KD with defined structural and cognitive phenotypes, single lab","pmids":["39816485"],"is_preprint":false},{"year":2022,"finding":"Ckb (CKB ortholog in Xenopus laevis) localizes to the axoneme of multi-cilia on embryonic epithelium and interacts with Ribc2 (identified by IP/MS). Morpholino-mediated knockdown of Ckb results in abnormal ciliary beating and reduced cilia-driven fluid flow; Ckb localization at the ciliary axoneme is dependent on Ribc2.","method":"Immunoprecipitation/mass spectrometry (IP/MS), antisense morpholino knockdown in Xenopus, fluorescent bead fluid-flow assay, immunostaining, western blot of flag-tagged proteins","journal":"Genes & genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — IP/MS identification plus morpholino KD with defined ciliary phenotype and localization analysis in Xenopus ortholog, single lab","pmids":["36508087"],"is_preprint":false},{"year":2004,"finding":"In mouse brain, CK-B (CKB) protein is selectively expressed in astrocytes among glial populations and in inhibitory neurons among neuronal populations, as determined by immunohistochemistry. This distribution is complementary to GAMT (expressed in oligodendrocytes/astrocytes) and uCK-Mi (expressed in neurons), suggesting CKB in astrocytes buffers energy for cells highly resistant to hypoxia/hypoglycemia.","method":"Immunohistochemistry in mouse brain tissue sections","journal":"The European journal of neuroscience","confidence":"Low","confidence_rationale":"Tier 3 / Moderate — direct localization by IHC, replicated across multiple brain regions, but no functional consequence directly tested in this paper; functional inference","pmids":["15245487"],"is_preprint":false},{"year":2016,"finding":"Increased CKB promoter methylation is associated with decreased CKB mRNA and protein expression in gastric cancer. In hematologic malignancies, CKB mRNA expression correlates with CKB promoter unmethylated status, indicating DNA methylation as a regulatory mechanism for CKB expression.","method":"Bisulfite sequencing/methylation analysis, RT-PCR for CKB mRNA, western blot for protein, correlation with promoter methylation status","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 / Weak — methylation-expression correlation without direct functional manipulation of the methylation state; single lab, correlative","pmids":["26460485"],"is_preprint":false},{"year":2005,"finding":"CKB mRNA expression in peripheral blood leukemia blasts correlates with serum CK-BB activity, and CKB promoter hypomethylation is associated with higher CKB mRNA expression in cancer cell lines, supporting promoter DNA methylation as a mechanism regulating CKB transcription.","method":"RT-PCR, CK isoenzyme analysis, bisulfite methylation analysis of CKB promoter, correlation analysis","journal":"Clinica chimica acta; international journal of clinical chemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — correlative methylation-expression analysis without functional manipulation, single lab","pmids":["15996648"],"is_preprint":false},{"year":2025,"finding":"Celastrol directly binds CKB protein (confirmed by photoaffinity labeling, click chemistry, and surface plasmon resonance), increasing CKB protein stability and modulating the futile creatine cycle in human brown adipocytes to promote thermogenesis.","method":"Photoaffinity labeling (PAL), click chemistry, surface plasmon resonance (SPR), celastrol-based small molecule probe","journal":"Metabolism open","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct binding established by SPR and chemical biology (PAL + click chemistry), multiple orthogonal methods, single lab","pmids":["40213647"],"is_preprint":false},{"year":2016,"finding":"CKB (CKBB) interacts with Peroxiredoxin II (Prx II) under physiological and heat-stress conditions in A549 and HeLa cells, as demonstrated by co-immunoprecipitation. Heat treatment enhances this association, and Prx II oligomerization under thermal stress may protect CKB enzyme activity from heat-induced inactivation.","method":"Co-immunoprecipitation (Co-IP) of overexpressed HA-Prx II and Flag-CK BB in A549 and HeLa cell lysates, heat stress treatment","journal":"Ukrainian biochemical journal","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP with overexpressed tagged proteins, single lab, no functional enzymatic rescue formally quantified in abstract","pmids":["29227081"],"is_preprint":false},{"year":2025,"finding":"During RANKL-induced osteoclastogenesis, CKB expression is upregulated. ACAT1 inhibitor Avasimibe downregulates CKB expression and consequently inhibits the PI3K-AKT signaling pathway, suppressing osteoclast differentiation. Exogenous phosphocreatine reverses the inhibitory effects of Avasimibe on osteoclast differentiation and PI3K-AKT activation, placing CKB upstream of PI3K-AKT in the osteoclastogenesis pathway.","method":"RNA-seq, western blot, TRAP staining, phosphocreatine rescue experiment, OVX mouse model, CKB knockdown","journal":"International immunopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis by pharmacological rescue with phosphocreatine, in vitro and in vivo corroboration, single lab","pmids":["41352098"],"is_preprint":false},{"year":2024,"finding":"IGF2BP2 (an RNA-binding protein) enhances CKB mRNA stability by directly binding to CKB mRNA (demonstrated by RIP-seq), thereby increasing CKB expression. This mechanism underlies IGF2BP2-mediated suppression of ccRCC metastasis.","method":"RIP-seq, actinomycin D mRNA stability assay, IGF2BP2 knockdown/overexpression, migration/invasion assays in vitro and in vivo","journal":"Translational oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RIP-seq plus actinomycin D decay assay establishing direct mRNA binding and stability mechanism, single lab","pmids":["38341962"],"is_preprint":false},{"year":2022,"finding":"CKB overexpression suppresses IL-1β-induced chondrocyte senescence in vitro by upregulating RAP1 expression, thereby activating the PI3K/AKT signaling pathway; this anti-senescence effect is reversed by pathway inhibition (rescue experiments). CKB overexpression also delays OA progression in a rat knee joint model in vivo.","method":"Lentiviral CKB overexpression, IL-1β senescence model, RAP1/PI3K/AKT pathway analysis by western blot, rescue experiments, rat OA in vivo model","journal":"Cellular signalling","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, gain-of-function with pathway rescue but mechanism connecting CKB enzymatic activity to RAP1 upregulation not biochemically elucidated in abstract","pmids":["42128154"],"is_preprint":false}],"current_model":"CKB (brain-type creatine kinase) catalyzes the reversible transfer of phosphate from phosphocreatine to ADP to regenerate ATP, with isoenzyme-specific substrate discrimination conferred by a flexible loop (His65/Pro66); it localizes to cortical membrane microdomains where locally generated ATP fuels actomyosin dynamics and cell motility, functions as a key effector of UCP1-independent thermogenesis in brown adipocytes (operating in parallel with UCP1 downstream of ADRA1A-Gαq and β3-AR/cAMP signaling via the futile creatine cycle), suppresses AKT activation by sequestering AKT's PH domain away from mTOR, promotes mitochondrial ATP production by suppressing mitochondrial calcium and mPTP opening (also via AKT inhibition), is targeted for proteasomal degradation by the ASB9 E3 ubiquitin ligase through its ankyrin repeat domain, and is required for ciliary axoneme function and brain energy homeostasis."},"narrative":{"mechanistic_narrative":"CKB (brain-type creatine kinase) catalyzes the reversible transfer of phosphate between phosphocreatine and ADP to buffer cellular ATP, and the resulting locally regenerated ATP couples its enzymatic output to diverse energy-demanding processes [PMID:10854850, PMID:19333390]. Within the catalytic core, His65 stabilizes the protein while a flexible loop containing Pro66 confers isoenzyme-specific substrate discrimination, accounting for CKB's distinct kinetic recognition of creatine versus cyclocreatine phosphate [PMID:10854850]. Compartmentalized CKB activity supports actomyosin dynamics and cell motility: CKB accumulates in cortical membrane ruffles and supplies ATP that sustains F-actin polymerization and migration, a function repurposed by cancer cells where HIF-1-induced CKB drives invasion, invadopodia formation, and metastasis through its creatine kinase activity [PMID:19333390, PMID:32213653, PMID:35008190]. In adipose tissue, CKB operates as a non-redundant effector of the futile creatine cycle, acting in parallel with UCP1 downstream of ADRA1A-Gαq and adrenergic signaling to mediate cold-triggered thermogenesis and whole-body energy expenditure [PMID:36344764, PMID:38272036]. CKB additionally restrains PI3K-AKT signaling by binding AKT's PH domain through an 84-amino-acid C-terminal fragment and sequestering it from mTOR-dependent activation, which in turn suppresses mitochondrial calcium accumulation and mPTP opening to favor mitochondrial ATP production [PMID:34706306, PMID:38896801]. CKB protein levels are set by multiple inputs: the ASB9 E3 ubiquitin ligase recognizes CKB via its ankyrin repeat domain and targets it for polyubiquitination and proteasomal degradation, while IGF2BP2 stabilizes CKB mRNA [PMID:22418839, PMID:38341962]. CKB is also required for ciliary axoneme function via interaction with Ribc2 and for brain energy homeostasis underlying synaptic plasticity and cognition [PMID:36508087, PMID:39816485].","teleology":[{"year":2000,"claim":"Resolved how CKB achieves isoenzyme-specific substrate recognition, distinguishing residues governing catalysis from those governing stability.","evidence":"Site-directed mutagenesis of CKB in COS-7 cells with substrate kinetics and stability assays","pmids":["10854850"],"confidence":"High","gaps":["No full-length crystal structure of CKB itself reported here","Physiological consequence of substrate discrimination not tested in cells"]},{"year":2009,"claim":"Established that CKB is not merely cytosolic but acts in a spatially compartmentalized manner at cortical membrane sites to fuel motility.","evidence":"Live-cell imaging and CKB-deficient fibroblast complementation with targeted relocalization constructs","pmids":["19333390"],"confidence":"Medium","gaps":["Molecular anchor recruiting CKB to membrane ruffles not identified","Direct link to specific actomyosin components not defined"]},{"year":2012,"claim":"Defined the structural basis by which CKB protein stability is controlled, mapping the ASB9 substrate-receptor interface that routes CKB to degradation.","evidence":"X-ray crystallography of hASB9-2, docking, and truncation/mutagenesis binding assays","pmids":["22418839"],"confidence":"Medium","gaps":["In-cell ubiquitination reconstitution not described","Conditions triggering CKB degradation in vivo unknown"]},{"year":2020,"claim":"Showed CKB-generated ATP is required for actin remodeling and migration in a hormone-responsive epithelial context, generalizing the cortical-energy model.","evidence":"CKB knockdown/overexpression with rescue in Ishikawa cells, ATP and F-actin assays under GnRH-antagonist treatment","pmids":["32213653"],"confidence":"Medium","gaps":["Mechanistic link between GnRH signaling and CKB transcription not resolved","In vivo relevance not tested"]},{"year":2021,"claim":"Revealed a non-catalytic moonlighting function: CKB binds and sequesters AKT to restrain its activation, connecting CKB to growth signaling beyond ATP buffering.","evidence":"Co-IP, domain mapping, 84aa fragment overexpression, xenografts, and MD simulation in prostate cancer cells","pmids":["34706306"],"confidence":"Medium","gaps":["Whether endogenous full-length CKB stoichiometrically controls AKT in vivo unclear","Relationship to CKB enzymatic activity not separated"]},{"year":2022,"claim":"Identified CKB as an essential downstream effector of adrenergic thermogenic signaling via the futile creatine cycle.","evidence":"Adipocyte-selective CKB knockout in vivo, energy-expenditure measurement, adrenergic pathway dissection","pmids":["36344764"],"confidence":"High","gaps":["Molecular target of CKB-driven ATP turnover in the futile cycle not fully defined","Subcellular site of thermogenic CKB activity not pinpointed"]},{"year":2024,"claim":"Established genetic non-redundancy between CKB and UCP1, defining CKB as an independent arm of brown-fat thermogenesis.","evidence":"Inducible adipocyte-selective Ucp1/Ckb co-deletion and cold-tolerance phenotyping","pmids":["38272036"],"confidence":"High","gaps":["Quantitative contribution of CKB versus UCP1 across temperatures unresolved","Tissue-specific creatine flux not directly measured"]},{"year":2024,"claim":"Connected CKB's AKT inhibition to mitochondrial homeostasis, showing it suppresses mitochondrial calcium and mPTP opening to sustain ATP production.","evidence":"CKB siRNA, mCa2+ and mPTP assays, AKT activity, F1F0 inhibitor sensitivity, isoform comparison vs CKMT1A/B, mouse tumor model","pmids":["38896801"],"confidence":"Medium","gaps":["Direct biochemical chain from AKT to mCa2+ channels not fully defined","Isoform-specificity mechanism not explained"]},{"year":2024,"claim":"Demonstrated CKB is required for structural synaptic plasticity and cognition, linking creatine-kinase activity to brain energy homeostasis.","evidence":"AAV-mediated CKB knockdown in mouse brain with behavioral, oxidative-stress, and spine-morphology readouts","pmids":["39816485"],"confidence":"Medium","gaps":["Cell-type-specific contribution within brain not dissected","Partial (34%) knockdown limits quantitative interpretation"]},{"year":2024,"claim":"Identified a post-transcriptional mechanism setting CKB abundance via IGF2BP2-mediated mRNA stabilization.","evidence":"RIP-seq and actinomycin D decay assays with IGF2BP2 manipulation in ccRCC, in vitro and in vivo","pmids":["38341962"],"confidence":"Medium","gaps":["Whether mRNA stabilization is the dominant route of CKB induction in other tissues unknown","Binding site on CKB transcript not mapped"]},{"year":2022,"claim":"Identified the ciliary axoneme as a distinct CKB compartment, requiring Ribc2 for localization and supporting ciliary motility.","evidence":"IP/MS, morpholino knockdown, and fluid-flow assays in Xenopus laevis ortholog","pmids":["36508087"],"confidence":"Medium","gaps":["Human CKB ciliary role not directly confirmed","Mechanism by which Ribc2 anchors CKB unknown"]},{"year":2025,"claim":"Showed CKB protein stability can be pharmacologically enhanced to boost thermogenesis, validating CKB as a druggable thermogenic node.","evidence":"Photoaffinity labeling, click chemistry, and SPR with celastrol in human brown adipocytes","pmids":["40213647"],"confidence":"Medium","gaps":["Binding site on CKB not mapped","Mechanism of stabilization at structural level undefined"]},{"year":null,"claim":"How CKB's enzymatic ATP-buffering function and its non-catalytic AKT-sequestering function are coordinated and partitioned across subcellular compartments remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure separating catalytic and AKT-binding functions in full-length CKB","Tissue-specific balance between these roles unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[6,8]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,7]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[10]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2,3]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,4]}],"complexes":[],"partners":["AKT1","ASB9","RIBC2","IGF2BP2","PRDX2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P12277","full_name":"Creatine kinase B-type","aliases":["Brain creatine kinase","B-CK","Creatine kinase B chain","Creatine phosphokinase B-type","CPK-B"],"length_aa":381,"mass_kda":42.6,"function":"Reversibly catalyzes the transfer of phosphate between ATP and various phosphogens (e.g. creatine phosphate) (PubMed:8186255). Creatine kinase isoenzymes play a central role in energy transduction in tissues with large, fluctuating energy demands, such as skeletal muscle, heart, brain and spermatozoa (Probable). Acts as a key regulator of adaptive thermogenesis as part of the futile creatine cycle: localizes to the mitochondria of thermogenic fat cells and acts by mediating phosphorylation of creatine to initiate a futile cycle of creatine phosphorylation and dephosphorylation (By similarity). During the futile creatine cycle, creatine and N-phosphocreatine are in a futile cycle, which dissipates the high energy charge of N-phosphocreatine as heat without performing any mechanical or chemical work (By similarity)","subcellular_location":"Cytoplasm, cytosol; Mitochondrion; Cell membrane","url":"https://www.uniprot.org/uniprotkb/P12277/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CKB","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000166165","cell_line_id":"CID001544","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"NCLN","stoichiometry":0.2},{"gene":"CKM","stoichiometry":0.2},{"gene":"LMNA","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001544","total_profiled":1310},"omim":[{"mim_id":"612395","title":"CHOLINE KINASE, BETA; CHKB","url":"https://www.omim.org/entry/612395"},{"mim_id":"604878","title":"SOLUTE CARRIER FAMILY 12 (POTASSIUM/CHLORIDE TRANSPORTER), MEMBER 6; SLC12A6","url":"https://www.omim.org/entry/604878"},{"mim_id":"300036","title":"SOLUTE CARRIER FAMILY 6 (NEUROTRANSMITTER TRANSPORTER, CREATINE), MEMBER 8; SLC6A8","url":"https://www.omim.org/entry/300036"},{"mim_id":"166600","title":"OSTEOPETROSIS, AUTOSOMAL DOMINANT 2; OPTA2","url":"https://www.omim.org/entry/166600"},{"mim_id":"147170","title":"IMMUNOGLOBULIN: HEAVY DELTA CHAIN; IGHD","url":"https://www.omim.org/entry/147170"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":1487.2},{"tissue":"intestine","ntpm":1025.7}],"url":"https://www.proteinatlas.org/search/CKB"},"hgnc":{"alias_symbol":[],"prev_symbol":["CKBB"]},"alphafold":{"accession":"P12277","domains":[{"cath_id":"1.10.135.10","chopping":"14-96","consensus_level":"medium","plddt":96.7076,"start":14,"end":96},{"cath_id":"3.30.590.10","chopping":"111-368","consensus_level":"high","plddt":95.479,"start":111,"end":368}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P12277","model_url":"https://alphafold.ebi.ac.uk/files/AF-P12277-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P12277-F1-predicted_aligned_error_v6.png","plddt_mean":95.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CKB","jax_strain_url":"https://www.jax.org/strain/search?query=CKB"},"sequence":{"accession":"P12277","fasta_url":"https://rest.uniprot.org/uniprotkb/P12277.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P12277/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P12277"}},"corpus_meta":[{"pmid":"15245487","id":"PMC_15245487","title":"Distinct cellular expressions of creatine synthetic enzyme GAMT and creatine kinases uCK-Mi and CK-B suggest a novel neuron-glial relationship for brain energy homeostasis.","date":"2004","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/15245487","citation_count":135,"is_preprint":false},{"pmid":"7234757","id":"PMC_7234757","title":"Several conditions causing elevation of serum CK-MB and CK-BB.","date":"1981","source":"American journal of clinical pathology","url":"https://pubmed.ncbi.nlm.nih.gov/7234757","citation_count":75,"is_preprint":false},{"pmid":"38272036","id":"PMC_38272036","title":"Parallel control of cold-triggered adipocyte thermogenesis by UCP1 and CKB.","date":"2024","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/38272036","citation_count":69,"is_preprint":false},{"pmid":"36344764","id":"PMC_36344764","title":"ADRA1A-Gαq signalling potentiates adipocyte thermogenesis through CKB and TNAP.","date":"2022","source":"Nature metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/36344764","citation_count":52,"is_preprint":false},{"pmid":"19333390","id":"PMC_19333390","title":"Local ATP generation by brain-type creatine kinase (CK-B) facilitates cell motility.","date":"2009","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/19333390","citation_count":48,"is_preprint":false},{"pmid":"8064306","id":"PMC_8064306","title":"Neural tissue-related proteins (NSE, G0 alpha, 28-kDa calbindin-D, S100b and CK-BB) in serum and cerebrospinal fluid after cardiac arrest.","date":"1994","source":"Journal of the neurological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/8064306","citation_count":45,"is_preprint":false},{"pmid":"7143180","id":"PMC_7143180","title":"Assessment of neurologic outcome in asphyxiated term infants by use of serial CK-BB isoenzyme measurement.","date":"1982","source":"The Journal of 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Complementation experiments using forced relocalization of CKB from cytosol to cortical membrane sites confirmed that compartmentalized CKB-generated ATP locally supports actomyosin dynamics and cell motility.\",\n      \"method\": \"Live-cell imaging, CKB-deficient fibroblast complementation with targeted protein relocalization constructs, migration/spreading assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO fibroblast complementation with spatial relocalization strategy and defined phenotypic readout (migration/spreading), single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"19333390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CKB interacts directly with AKT and sequesters it from activation by mTOR. The interaction is mediated by an 84-amino acid C-terminal fragment of CKB binding to AKT's PH domain. Ectopic expression of this 84aa fragment inhibits AKT activation, EMT, and cell proliferation in prostate cancer cells. Molecular dynamics simulation on crystal structures independently confirmed this interaction interface.\",\n      \"method\": \"Co-immunoprecipitation, kinase cDNA screen, domain mapping with truncation mutants, ectopic 84aa fragment overexpression, xenograft tumor models, molecular dynamics simulation\",\n      \"journal\": \"Neoplasia (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with domain mapping and functional rescue, supported by MD simulation, single lab\",\n      \"pmids\": [\"34706306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ADRA1A-Gαq signaling (triggered by noradrenaline) induces expression of thermogenic genes of the futile creatine cycle including CKB, and CKB is required as an effector protein for this thermogenic output. Combined Gαq and Gαs signaling in adipocytes promotes whole-body energy expenditure in a CKB-dependent manner.\",\n      \"method\": \"Adipocyte-selective genetic knockout of CKB in vivo, whole-body energy expenditure measurement, gene expression analysis, adrenergic receptor signaling pathway dissection\",\n      \"journal\": \"Nature metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — adipocyte-selective KO with defined thermogenic phenotype, in vivo energy expenditure measurement, pathway dissection across multiple adrenergic receptor subtypes, replicated in vivo\",\n      \"pmids\": [\"36344764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CKB functions in parallel with UCP1 as a non-redundant mediator of cold-triggered adipocyte thermogenesis. Inducible adipocyte-selective co-deletion of both Ucp1 and Ckb exacerbates cold intolerance beyond either single deletion, establishing CKB as an independent effector of UCP1-independent thermogenesis in brown adipocytes.\",\n      \"method\": \"Inducible adipocyte-selective Ucp1 knockout, inducible co-deletion of Ucp1 and Ckb, cold-tolerance challenge, body temperature measurement\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — inducible adipocyte-selective double KO with rigorous cold-tolerance phenotyping, genetic epistasis establishing non-paralogous redundancy, in vivo\",\n      \"pmids\": [\"38272036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CKB promotes mitochondrial ATP production by suppressing mitochondrial calcium (mCa2+) levels, thereby preventing mitochondrial permeability transition pore (mPTP) activation. CKB achieves mCa2+ suppression through inhibition of AKT activity. Silencing CKB (but not CKMT1A or CKMT1B) causes loss of sensitivity to F1F0 ATP synthase inhibition, linking CKB specifically to this pathway.\",\n      \"method\": \"CKB siRNA knockdown, mitochondrial calcium measurement, mPTP activity assay, AKT activity measurement, F1F0 ATP synthase inhibitor sensitivity assay, in vivo mouse tumor model\",\n      \"journal\": \"Advanced science (Weinheim, Baden-Wurttemberg, Germany)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD with defined mechanistic readouts (mCa2+, mPTP, AKT), isoform-specific comparisons (CKB vs CKMT1A/B), single lab\",\n      \"pmids\": [\"38896801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Crystal structure of hASB9-2 (an isoform of the CKB-targeting E3 ubiquitin ligase substrate receptor ASB9) was solved at 2.2-Å resolution. Amino acid substitution analysis based on docking showed His103 and Phe107 in hASB9-2 are essential for binding to CKB. Truncation analysis showed the first six ankyrin repeats plus the N-terminal region of hASB9-2 are required for CKB interaction. ASB9 recognizes CKB via its ankyrin repeat domain and mediates CKB polyubiquitination and proteasomal degradation via its SOCS box domain.\",\n      \"method\": \"X-ray crystallography (2.2 Å), site-directed mutagenesis, docking, truncation mutant binding assays\",\n      \"journal\": \"The protein journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with mutagenesis and docking to map CKB interaction interface, single lab, no in-cell ubiquitination reconstitution described in abstract\",\n      \"pmids\": [\"22418839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"His65 in human CK-BB (CKB) contributes to protein stability rather than catalysis: the ΔH65 mutant retains near-normal substrate affinity but shows very low stability. The double mutant ΔH65P66 shows eight-fold decreased affinity for creatine phosphate and inability to dephosphorylate cyclocreatine phosphate, indicating that the flexible loop containing Pro66 accounts for isoenzyme-specific substrate discrimination.\",\n      \"method\": \"Site-directed mutagenesis of CKB expressed in COS-7 cells, substrate affinity (Km) measurements, cyclocreatine phosphate dephosphorylation assay, stability assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay with active-site mutagenesis and substrate kinetics, multiple mutants tested, single lab with clear mechanistic dissection\",\n      \"pmids\": [\"10854850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"GnRH antagonist (GnRH-ant) reduces CKB expression in endometrial epithelial cells, leading to decreased ATP generation, F-actin depolymerization, and impaired cell migration. CKB knockdown phenocopies these effects; CKB overexpression rescues both the GnRH-ant-induced and knockdown-induced defects in actin polymerization and migration.\",\n      \"method\": \"CKB knockdown and overexpression in Ishikawa cells, ATP measurement, F-actin/G-actin assay, cell migration assay, in vitro GnRH-ant treatment\",\n      \"journal\": \"Reproduction (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function with rescue, defined readouts (ATP, actin, migration), single lab\",\n      \"pmids\": [\"32213653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CKB expression is induced downstream of HIF-1 in mammary tumor cells. CKB is necessary for breast cancer cell invasion in vitro and promotes tumor growth and lung metastasis in vivo. Cyclocreatine (a creatine kinase activity inhibitor) represses cell migration, invasion, invadopodia formation, and lung metastasis, indicating that CKB creatine kinase enzymatic activity mediates these pro-metastatic effects.\",\n      \"method\": \"HIF-1 WT vs knockout mammary tumor cell gene screen, CKB loss/gain-of-function, invasion assays, invadopodia assay, in vivo lung metastasis model, cyclocreatine pharmacological inhibition\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss/gain-of-function plus pharmacological enzyme inhibition with in vivo metastasis readout, single lab\",\n      \"pmids\": [\"35008190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Creatine supplementation increases CKB-BB activity and expression in brain, and AAV-mediated CKB knockdown (34% reduction) in mouse brain causes deficits in learning/memory, oxidative stress, and hippocampal spine morphology damage, establishing CKB as a required mediator of structural synaptic plasticity and cognitive function in the brain.\",\n      \"method\": \"AAV-directed CKB knockdown in mouse brain, behavioral cognitive testing, hippocampal spine morphology analysis, CKB activity measurement, creatine dietary supplementation\",\n      \"journal\": \"Food science & nutrition\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo viral KD with defined structural and cognitive phenotypes, single lab\",\n      \"pmids\": [\"39816485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Ckb (CKB ortholog in Xenopus laevis) localizes to the axoneme of multi-cilia on embryonic epithelium and interacts with Ribc2 (identified by IP/MS). Morpholino-mediated knockdown of Ckb results in abnormal ciliary beating and reduced cilia-driven fluid flow; Ckb localization at the ciliary axoneme is dependent on Ribc2.\",\n      \"method\": \"Immunoprecipitation/mass spectrometry (IP/MS), antisense morpholino knockdown in Xenopus, fluorescent bead fluid-flow assay, immunostaining, western blot of flag-tagged proteins\",\n      \"journal\": \"Genes & genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — IP/MS identification plus morpholino KD with defined ciliary phenotype and localization analysis in Xenopus ortholog, single lab\",\n      \"pmids\": [\"36508087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In mouse brain, CK-B (CKB) protein is selectively expressed in astrocytes among glial populations and in inhibitory neurons among neuronal populations, as determined by immunohistochemistry. This distribution is complementary to GAMT (expressed in oligodendrocytes/astrocytes) and uCK-Mi (expressed in neurons), suggesting CKB in astrocytes buffers energy for cells highly resistant to hypoxia/hypoglycemia.\",\n      \"method\": \"Immunohistochemistry in mouse brain tissue sections\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization by IHC, replicated across multiple brain regions, but no functional consequence directly tested in this paper; functional inference\",\n      \"pmids\": [\"15245487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Increased CKB promoter methylation is associated with decreased CKB mRNA and protein expression in gastric cancer. In hematologic malignancies, CKB mRNA expression correlates with CKB promoter unmethylated status, indicating DNA methylation as a regulatory mechanism for CKB expression.\",\n      \"method\": \"Bisulfite sequencing/methylation analysis, RT-PCR for CKB mRNA, western blot for protein, correlation with promoter methylation status\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — methylation-expression correlation without direct functional manipulation of the methylation state; single lab, correlative\",\n      \"pmids\": [\"26460485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CKB mRNA expression in peripheral blood leukemia blasts correlates with serum CK-BB activity, and CKB promoter hypomethylation is associated with higher CKB mRNA expression in cancer cell lines, supporting promoter DNA methylation as a mechanism regulating CKB transcription.\",\n      \"method\": \"RT-PCR, CK isoenzyme analysis, bisulfite methylation analysis of CKB promoter, correlation analysis\",\n      \"journal\": \"Clinica chimica acta; international journal of clinical chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — correlative methylation-expression analysis without functional manipulation, single lab\",\n      \"pmids\": [\"15996648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Celastrol directly binds CKB protein (confirmed by photoaffinity labeling, click chemistry, and surface plasmon resonance), increasing CKB protein stability and modulating the futile creatine cycle in human brown adipocytes to promote thermogenesis.\",\n      \"method\": \"Photoaffinity labeling (PAL), click chemistry, surface plasmon resonance (SPR), celastrol-based small molecule probe\",\n      \"journal\": \"Metabolism open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct binding established by SPR and chemical biology (PAL + click chemistry), multiple orthogonal methods, single lab\",\n      \"pmids\": [\"40213647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CKB (CKBB) interacts with Peroxiredoxin II (Prx II) under physiological and heat-stress conditions in A549 and HeLa cells, as demonstrated by co-immunoprecipitation. Heat treatment enhances this association, and Prx II oligomerization under thermal stress may protect CKB enzyme activity from heat-induced inactivation.\",\n      \"method\": \"Co-immunoprecipitation (Co-IP) of overexpressed HA-Prx II and Flag-CK BB in A549 and HeLa cell lysates, heat stress treatment\",\n      \"journal\": \"Ukrainian biochemical journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP with overexpressed tagged proteins, single lab, no functional enzymatic rescue formally quantified in abstract\",\n      \"pmids\": [\"29227081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"During RANKL-induced osteoclastogenesis, CKB expression is upregulated. ACAT1 inhibitor Avasimibe downregulates CKB expression and consequently inhibits the PI3K-AKT signaling pathway, suppressing osteoclast differentiation. Exogenous phosphocreatine reverses the inhibitory effects of Avasimibe on osteoclast differentiation and PI3K-AKT activation, placing CKB upstream of PI3K-AKT in the osteoclastogenesis pathway.\",\n      \"method\": \"RNA-seq, western blot, TRAP staining, phosphocreatine rescue experiment, OVX mouse model, CKB knockdown\",\n      \"journal\": \"International immunopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis by pharmacological rescue with phosphocreatine, in vitro and in vivo corroboration, single lab\",\n      \"pmids\": [\"41352098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"IGF2BP2 (an RNA-binding protein) enhances CKB mRNA stability by directly binding to CKB mRNA (demonstrated by RIP-seq), thereby increasing CKB expression. This mechanism underlies IGF2BP2-mediated suppression of ccRCC metastasis.\",\n      \"method\": \"RIP-seq, actinomycin D mRNA stability assay, IGF2BP2 knockdown/overexpression, migration/invasion assays in vitro and in vivo\",\n      \"journal\": \"Translational oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RIP-seq plus actinomycin D decay assay establishing direct mRNA binding and stability mechanism, single lab\",\n      \"pmids\": [\"38341962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CKB overexpression suppresses IL-1β-induced chondrocyte senescence in vitro by upregulating RAP1 expression, thereby activating the PI3K/AKT signaling pathway; this anti-senescence effect is reversed by pathway inhibition (rescue experiments). CKB overexpression also delays OA progression in a rat knee joint model in vivo.\",\n      \"method\": \"Lentiviral CKB overexpression, IL-1β senescence model, RAP1/PI3K/AKT pathway analysis by western blot, rescue experiments, rat OA in vivo model\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, gain-of-function with pathway rescue but mechanism connecting CKB enzymatic activity to RAP1 upregulation not biochemically elucidated in abstract\",\n      \"pmids\": [\"42128154\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CKB (brain-type creatine kinase) catalyzes the reversible transfer of phosphate from phosphocreatine to ADP to regenerate ATP, with isoenzyme-specific substrate discrimination conferred by a flexible loop (His65/Pro66); it localizes to cortical membrane microdomains where locally generated ATP fuels actomyosin dynamics and cell motility, functions as a key effector of UCP1-independent thermogenesis in brown adipocytes (operating in parallel with UCP1 downstream of ADRA1A-Gαq and β3-AR/cAMP signaling via the futile creatine cycle), suppresses AKT activation by sequestering AKT's PH domain away from mTOR, promotes mitochondrial ATP production by suppressing mitochondrial calcium and mPTP opening (also via AKT inhibition), is targeted for proteasomal degradation by the ASB9 E3 ubiquitin ligase through its ankyrin repeat domain, and is required for ciliary axoneme function and brain energy homeostasis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CKB (brain-type creatine kinase) catalyzes the reversible transfer of phosphate between phosphocreatine and ADP to buffer cellular ATP, and the resulting locally regenerated ATP couples its enzymatic output to diverse energy-demanding processes [#6, #0]. Within the catalytic core, His65 stabilizes the protein while a flexible loop containing Pro66 confers isoenzyme-specific substrate discrimination, accounting for CKB's distinct kinetic recognition of creatine versus cyclocreatine phosphate [#6]. Compartmentalized CKB activity supports actomyosin dynamics and cell motility: CKB accumulates in cortical membrane ruffles and supplies ATP that sustains F-actin polymerization and migration, a function repurposed by cancer cells where HIF-1-induced CKB drives invasion, invadopodia formation, and metastasis through its creatine kinase activity [#0, #7, #8]. In adipose tissue, CKB operates as a non-redundant effector of the futile creatine cycle, acting in parallel with UCP1 downstream of ADRA1A-Gαq and adrenergic signaling to mediate cold-triggered thermogenesis and whole-body energy expenditure [#2, #3]. CKB additionally restrains PI3K-AKT signaling by binding AKT's PH domain through an 84-amino-acid C-terminal fragment and sequestering it from mTOR-dependent activation, which in turn suppresses mitochondrial calcium accumulation and mPTP opening to favor mitochondrial ATP production [#1, #4]. CKB protein levels are set by multiple inputs: the ASB9 E3 ubiquitin ligase recognizes CKB via its ankyrin repeat domain and targets it for polyubiquitination and proteasomal degradation, while IGF2BP2 stabilizes CKB mRNA [#5, #17]. CKB is also required for ciliary axoneme function via interaction with Ribc2 and for brain energy homeostasis underlying synaptic plasticity and cognition [#10, #9].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Resolved how CKB achieves isoenzyme-specific substrate recognition, distinguishing residues governing catalysis from those governing stability.\",\n      \"evidence\": \"Site-directed mutagenesis of CKB in COS-7 cells with substrate kinetics and stability assays\",\n      \"pmids\": [\"10854850\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length crystal structure of CKB itself reported here\", \"Physiological consequence of substrate discrimination not tested in cells\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established that CKB is not merely cytosolic but acts in a spatially compartmentalized manner at cortical membrane sites to fuel motility.\",\n      \"evidence\": \"Live-cell imaging and CKB-deficient fibroblast complementation with targeted relocalization constructs\",\n      \"pmids\": [\"19333390\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular anchor recruiting CKB to membrane ruffles not identified\", \"Direct link to specific actomyosin components not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the structural basis by which CKB protein stability is controlled, mapping the ASB9 substrate-receptor interface that routes CKB to degradation.\",\n      \"evidence\": \"X-ray crystallography of hASB9-2, docking, and truncation/mutagenesis binding assays\",\n      \"pmids\": [\"22418839\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In-cell ubiquitination reconstitution not described\", \"Conditions triggering CKB degradation in vivo unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed CKB-generated ATP is required for actin remodeling and migration in a hormone-responsive epithelial context, generalizing the cortical-energy model.\",\n      \"evidence\": \"CKB knockdown/overexpression with rescue in Ishikawa cells, ATP and F-actin assays under GnRH-antagonist treatment\",\n      \"pmids\": [\"32213653\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between GnRH signaling and CKB transcription not resolved\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed a non-catalytic moonlighting function: CKB binds and sequesters AKT to restrain its activation, connecting CKB to growth signaling beyond ATP buffering.\",\n      \"evidence\": \"Co-IP, domain mapping, 84aa fragment overexpression, xenografts, and MD simulation in prostate cancer cells\",\n      \"pmids\": [\"34706306\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether endogenous full-length CKB stoichiometrically controls AKT in vivo unclear\", \"Relationship to CKB enzymatic activity not separated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified CKB as an essential downstream effector of adrenergic thermogenic signaling via the futile creatine cycle.\",\n      \"evidence\": \"Adipocyte-selective CKB knockout in vivo, energy-expenditure measurement, adrenergic pathway dissection\",\n      \"pmids\": [\"36344764\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular target of CKB-driven ATP turnover in the futile cycle not fully defined\", \"Subcellular site of thermogenic CKB activity not pinpointed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established genetic non-redundancy between CKB and UCP1, defining CKB as an independent arm of brown-fat thermogenesis.\",\n      \"evidence\": \"Inducible adipocyte-selective Ucp1/Ckb co-deletion and cold-tolerance phenotyping\",\n      \"pmids\": [\"38272036\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of CKB versus UCP1 across temperatures unresolved\", \"Tissue-specific creatine flux not directly measured\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected CKB's AKT inhibition to mitochondrial homeostasis, showing it suppresses mitochondrial calcium and mPTP opening to sustain ATP production.\",\n      \"evidence\": \"CKB siRNA, mCa2+ and mPTP assays, AKT activity, F1F0 inhibitor sensitivity, isoform comparison vs CKMT1A/B, mouse tumor model\",\n      \"pmids\": [\"38896801\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biochemical chain from AKT to mCa2+ channels not fully defined\", \"Isoform-specificity mechanism not explained\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated CKB is required for structural synaptic plasticity and cognition, linking creatine-kinase activity to brain energy homeostasis.\",\n      \"evidence\": \"AAV-mediated CKB knockdown in mouse brain with behavioral, oxidative-stress, and spine-morphology readouts\",\n      \"pmids\": [\"39816485\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cell-type-specific contribution within brain not dissected\", \"Partial (34%) knockdown limits quantitative interpretation\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified a post-transcriptional mechanism setting CKB abundance via IGF2BP2-mediated mRNA stabilization.\",\n      \"evidence\": \"RIP-seq and actinomycin D decay assays with IGF2BP2 manipulation in ccRCC, in vitro and in vivo\",\n      \"pmids\": [\"38341962\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether mRNA stabilization is the dominant route of CKB induction in other tissues unknown\", \"Binding site on CKB transcript not mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified the ciliary axoneme as a distinct CKB compartment, requiring Ribc2 for localization and supporting ciliary motility.\",\n      \"evidence\": \"IP/MS, morpholino knockdown, and fluid-flow assays in Xenopus laevis ortholog\",\n      \"pmids\": [\"36508087\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Human CKB ciliary role not directly confirmed\", \"Mechanism by which Ribc2 anchors CKB unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed CKB protein stability can be pharmacologically enhanced to boost thermogenesis, validating CKB as a druggable thermogenic node.\",\n      \"evidence\": \"Photoaffinity labeling, click chemistry, and SPR with celastrol in human brown adipocytes\",\n      \"pmids\": [\"40213647\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding site on CKB not mapped\", \"Mechanism of stabilization at structural level undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CKB's enzymatic ATP-buffering function and its non-catalytic AKT-sequestering function are coordinated and partitioned across subcellular compartments remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure separating catalytic and AKT-binding functions in full-length CKB\", \"Tissue-specific balance between these roles unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [6, 8]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"AKT1\", \"ASB9\", \"RIBC2\", \"IGF2BP2\", \"PRDX2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}