{"gene":"GHITM","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2022,"finding":"TMBIM5 (GHITM) is the mitochondrial Ca2+/H+ antiporter (calcium/proton exchanger). Cell-based and cell-free biochemical assays demonstrated absence or greatly reduced Na+-independent mitochondrial Ca2+ release in TMBIM5 knockout cells or pH-sensing site mutants, and pH-dependent Ca2+ transport by recombinant TMBIM5. TMBIM5 physically interacts with LETM1 (identified via LETM1 mitochondrial interactome), but it is TMBIM5, not LETM1, that carries the CHE activity.","method":"CRISPR-Cas9 knockout, cell-free reconstitution of recombinant TMBIM5, pH-sensing site mutagenesis, Co-IP/mitochondrial interactome of LETM1, mitochondrial Ca2+ release assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 / Strong — cell-free reconstitution of recombinant protein, mutagenesis of pH-sensing site, knockout cells, multiple orthogonal methods in one rigorous study","pmids":["36321428"],"is_preprint":false},{"year":2022,"finding":"Loss of TMBIM5 results in increased potassium and reduced proton levels in the mitochondrial matrix due to attenuated exchange of these ions. Overexpressed TMBIM5 can mediate mitochondrial calcium uptake. Mice carrying a mutation in the channel pore of TMBIM5 display increased embryonic/perinatal lethality, skeletal myopathy, disrupted cristae architecture, early opening of the mitochondrial permeability transition pore, reduced calcium uptake, and mitochondrial swelling.","method":"TMBIM5 channel pore mutant knock-in mice, TMBIM5 overexpression in cells, mitochondrial ion measurements (K+, H+, Ca2+), mitochondrial permeability transition pore assays, electron microscopy of cristae","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knock-in mouse model with channel pore mutation, multiple orthogonal phenotypic readouts, supported by cell-based Ca2+ transport assays","pmids":["35715207"],"is_preprint":false},{"year":2020,"finding":"TMBIM5 knockout (CRISPR-Cas9) cells show fragmented mitochondria with vacuolar cristae structure, reduced mitochondrial membrane potential, attenuated respiration, reduced mitochondrial ATP generation, and increased sensitivity to apoptosis induced by staurosporine and BH3 mimetics. Unbiased proteomics revealed dramatic downregulation of mitochondrial protein synthesis machinery components in TMBIM5-KO cells. TMBIM5 does not associate with MICOS components Mic10 or Mic60, nor does its KO affect their expression.","method":"CRISPR-Cas9 knockout, mitochondrial membrane potential measurement, oxygen consumption assays, ATP measurement, apoptosis assays, Co-IP (negative for Mic10/Mic60), quantitative proteomics","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean CRISPR KO with multiple orthogonal cellular phenotype readouts plus proteomics, single lab","pmids":["32977469"],"is_preprint":false},{"year":2025,"finding":"TMBIM5 functionally interacts with MICU1 (a component of the mitochondrial calcium uniporter complex). In human cells, MICU1 rescues morphological defects in TMBIM5-KO mitochondria, while TMBIM5 overexpression exacerbates size reduction in MICU1-KO mitochondria. Both proteins show opposing effects on submitochondrial localization and co-exist in the same macromolecular complex (Co-IP). In Drosophila, partial MICU1 depletion ameliorates Tmbim5-deficiency phenotype (disrupted cristae, premature mPTP opening, reduced Ca2+ uptake, mitochondrial swelling, impaired mobility, shortened lifespan).","method":"Co-immunoprecipitation, TMBIM5-KO and MICU1-KO human cells, genetic epistasis in Drosophila (double knockouts), mitochondrial morphology imaging, Ca2+ uptake assays","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal genetic and biochemical interaction evidence (Co-IP + genetic epistasis in two model systems), single lab","pmids":["40973741"],"is_preprint":false},{"year":2026,"finding":"In zebrafish, tmbim5/mcu double knockouts show no additive effects on the tmbim5-KO phenotype, arguing against TMBIM5 functioning as an independent Ca2+ uptake pathway. tmbim5/slc8b1 (NCLX) double knockouts show altered mitochondrial Ca2+ handling with reduced uptake and efflux, suggesting TMBIM5 functions as an auxiliary Ca2+ efflux pathway cooperating with NCLX in a tissue-specific manner. Brain phenotypes were rescued and muscle dysfunction was exacerbated in double mutants, corresponding to restored mitochondrial membrane potential in brain and decreased Ca2+ levels in muscle.","method":"Zebrafish tmbim5, slc8b1, tmbim5/mcu, and tmbim5/slc8b1 double knockouts; mitochondrial Ca2+ uptake/efflux measurements; mitochondrial membrane potential measurements; phenotypic assessment (growth, muscle, brain cell death)","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple double-KO zebrafish lines and multiple orthogonal functional readouts, single lab","pmids":["41501441"],"is_preprint":false},{"year":2006,"finding":"GHITM requires cleavage of its N-terminal portion for proper expression; Western blot analyses demonstrated that this cleavage regulates the expression level of the protein. GHITM is ubiquitously expressed in mammalian cells and mouse tissues, and requires an N-terminal signal sequence for expression.","method":"Western blot, expression pattern analysis in mouse embryo and adult tissues, signal sequence analysis","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, Western blot only, no functional follow-up of the cleavage event","pmids":["16412389"],"is_preprint":false},{"year":2007,"finding":"GHITM contains the UPF0005/TMBIM domain and was identified as a member of the BI-1 (Bax inhibitory protein-like) family based on phylogenetic and domain analysis. It is the only mitochondrially-localized member of the TMBIM family.","method":"Phylogenetic analysis, domain analysis, expression profiling in cancer cell lines","journal":"International journal of biological sciences","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational/bioinformatic classification, no direct functional experiment","pmids":["18071587"],"is_preprint":false},{"year":2024,"finding":"GHITM overexpression in renal clear cell carcinoma cells inhibits cell proliferation, migration, and invasion in vitro and in vivo, and induces downregulation of Notch1. Overexpression of Notch1 rescues the inhibitory effects of GHITM upregulation. YY1 transcription factor decreases GHITM levels by binding to its promoter. GHITM also regulates PD-L1 protein abundance.","method":"GHITM overexpression in KIRC cell lines, rescue by Notch1 overexpression, ChIP/promoter binding assay for YY1, in vivo xenograft, PD-L1 protein quantification","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic rescue epistasis (Notch1 overexpression), promoter binding assay, multiple orthogonal methods, single lab","pmids":["38588015"],"is_preprint":false}],"current_model":"TMBIM5/GHITM is the mitochondrial Ca2+/H+ antiporter localized to the inner mitochondrial membrane; it mediates Na+-independent Ca2+ release coupled to H+ exchange (established by reconstitution of recombinant protein and pH-sensing site mutagenesis), regulates mitochondrial matrix K+/H+ balance, maintains cristae architecture and mitochondrial membrane potential, supports mitochondrial protein synthesis machinery, interacts physically with LETM1 and functionally with MICU1 to govern mitochondrial Ca2+ homeostasis, and its loss causes skeletal myopathy, early mPTP opening, and increased apoptotic sensitivity."},"narrative":{"mechanistic_narrative":"GHITM (TMBIM5) is the mitochondrial inner-membrane Ca2+/H+ antiporter that governs matrix ion balance and organelle integrity [PMID:36321428]. Cell-free reconstitution of recombinant protein, knockout cells, and mutagenesis of its pH-sensing site established that GHITM carries Na+-independent, pH-coupled Ca2+ transport activity; it physically associates with LETM1, but the channel activity resides in GHITM itself [PMID:36321428]. Loss of GHITM shifts matrix ion levels toward elevated K+ and reduced H+, reflecting impaired ion exchange, and a channel-pore mutant in mice produces skeletal myopathy, disrupted cristae, early opening of the mitochondrial permeability transition pore, reduced Ca2+ uptake, and mitochondrial swelling [PMID:35715207]. At the cellular level GHITM is required to maintain cristae architecture, mitochondrial membrane potential, respiration and ATP output, and its loss downregulates the mitochondrial protein synthesis machinery and heightens apoptotic sensitivity, independent of the MICOS components Mic10/Mic60 [PMID:32977469]. GHITM acts within the broader mitochondrial Ca2+ network: it co-exists in a macromolecular complex with MICU1 and shows reciprocal, opposing morphological effects with it [PMID:40973741], and genetic epistasis in zebrafish places GHITM as an auxiliary, tissue-specific Ca2+ efflux pathway cooperating with NCLX (slc8b1) rather than as an independent uptake route paralleling MCU [PMID:41501441]. In renal clear cell carcinoma, GHITM overexpression suppresses proliferation, migration and invasion through downregulation of Notch1 and modulates PD-L1 abundance, with the transcription factor YY1 repressing GHITM by promoter binding [PMID:38588015].","teleology":[{"year":2006,"claim":"Established the basic protein biology of GHITM by showing that N-terminal signal sequence cleavage controls its expression level, framing it as a processed, ubiquitously expressed membrane protein before any transport function was known.","evidence":"Western blot and expression profiling across mouse embryo/adult tissues with signal sequence analysis","pmids":["16412389"],"confidence":"Low","gaps":["Single-lab Western blot only with no functional follow-up of the cleavage event","No localization to a specific submitochondrial compartment demonstrated","Protease responsible for cleavage not identified"]},{"year":2007,"claim":"Placed GHITM phylogenetically as the only mitochondrial member of the TMBIM/BI-1 family, predicting a connection to apoptosis-regulatory ion handling.","evidence":"Phylogenetic and domain analysis plus expression profiling in cancer cell lines","pmids":["18071587"],"confidence":"Low","gaps":["Computational classification with no direct functional experiment","Did not test any transport or apoptotic activity","Domain architecture not linked to a measured biochemical function"]},{"year":2020,"claim":"Connected GHITM to mitochondrial integrity by showing its loss fragments mitochondria, collapses membrane potential and respiration, suppresses the mitochondrial translation machinery, and sensitizes cells to apoptosis.","evidence":"CRISPR-Cas9 knockout with membrane potential, oxygen consumption, ATP, apoptosis assays and quantitative proteomics, plus negative Co-IP against Mic10/Mic60","pmids":["32977469"],"confidence":"Medium","gaps":["Did not identify the molecular activity underlying these phenotypes","Mechanism linking GHITM loss to translation machinery downregulation unresolved","Single-lab cell-line phenotyping without in vivo confirmation"]},{"year":2022,"claim":"Defined the molecular activity by demonstrating GHITM is itself the Na+-independent mitochondrial Ca2+/H+ antiporter, distinguishing its catalytic role from its physical partner LETM1.","evidence":"Cell-free reconstitution of recombinant protein, pH-sensing site mutagenesis, knockout cells, mitochondrial Ca2+ release assays, and LETM1 interactome Co-IP","pmids":["36321428"],"confidence":"High","gaps":["Structural basis of the antiporter and its pH-sensing site not solved","Stoichiometry and directionality of Ca2+/H+ coupling not fully defined","Functional consequence of the LETM1 interaction not resolved"]},{"year":2022,"claim":"Linked transport activity to physiology in vivo by showing a channel-pore mutation alters matrix K+/H+ balance and Ca2+ uptake and causes myopathy, cristae disruption, and early mPTP opening.","evidence":"Channel-pore mutant knock-in mice, overexpression Ca2+ uptake assays, matrix ion measurements, mPTP assays, and electron microscopy","pmids":["35715207"],"confidence":"High","gaps":["Causal chain from ion imbalance to cristae remodeling not delineated","Tissue specificity of the myopathy phenotype not mechanistically explained","Whether matrix K+/H+ effects are direct or secondary remains open"]},{"year":2025,"claim":"Embedded GHITM in the mitochondrial Ca2+ regulatory network by demonstrating reciprocal, opposing functional and physical interactions with MICU1 across human cells and Drosophila.","evidence":"Co-IP, reciprocal KO rescue/exacerbation of mitochondrial morphology in human cells, and genetic epistasis in Drosophila double knockouts","pmids":["40973741"],"confidence":"Medium","gaps":["Whether MICU1 directly modulates GHITM transport activity not established","Architecture of the shared macromolecular complex undefined","Single-lab interaction data without orthogonal structural validation"]},{"year":2026,"claim":"Resolved GHITM's position relative to canonical Ca2+ transporters, showing it is not an independent MCU-like uptake route but an auxiliary, tissue-specific efflux pathway cooperating with NCLX.","evidence":"Zebrafish tmbim5/mcu and tmbim5/slc8b1 double knockouts with Ca2+ uptake/efflux, membrane potential, and tissue-specific phenotyping","pmids":["41501441"],"confidence":"Medium","gaps":["Molecular basis of cooperation with NCLX unknown","Mechanism of tissue-specific opposing brain vs muscle outcomes unresolved","Single-lab genetic epistasis in zebrafish only"]},{"year":2024,"claim":"Extended GHITM function to tumor suppression in renal clear cell carcinoma, where it restrains proliferation and invasion via Notch1 downregulation and is itself transcriptionally repressed by YY1.","evidence":"GHITM overexpression with Notch1 rescue, YY1 promoter-binding assay, xenografts, and PD-L1 protein quantification","pmids":["38588015"],"confidence":"Medium","gaps":["Link between mitochondrial transport activity and Notch1/PD-L1 regulation not mechanistically connected","How GHITM controls PD-L1 abundance unresolved","Single-lab cancer-context study without in vivo Ca2+-handling correlation"]},{"year":null,"claim":"How GHITM's Ca2+/H+ antiport activity mechanistically drives cristae maintenance, mitochondrial translation, and its tissue-specific cancer-suppressive signaling remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the antiporter or its regulatory complexes","Causal link between ion transport and downstream organelle/signaling phenotypes undefined","Mechanism connecting mitochondrial function to Notch1/PD-L1 regulation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1,2,6]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[2]}],"complexes":[],"partners":["LETM1","MICU1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H3K2","full_name":"Growth hormone-inducible transmembrane protein","aliases":["Dermal papilla-derived protein 2","Mitochondrial morphology and cristae structure 1","MICS1","Transmembrane BAX inhibitor motif-containing protein 5"],"length_aa":345,"mass_kda":37.2,"function":"Plays an important role in maintenance of mitochondrial morphology and in mediating either calcium or potassium/proton antiport (PubMed:18417609, PubMed:32977469, PubMed:35912435, PubMed:36321428). Mediates proton-dependent calcium efflux from mitochondrion (PubMed:35912435, PubMed:36321428). Also functions as an electroneutral mitochondrial proton/potassium exchanger (PubMed:36321428). Required for the mitochondrial tubular network and cristae organization (PubMed:18417609, PubMed:32977469, PubMed:36321428). Involved in apoptotic release of cytochrome c (PubMed:18417609). Inhibits the proteolytic activity of AFG3L2, stimulating respiration and stabilizing respiratory enzymes in actively respiring mitochondria (PubMed:36321428). However, when mitochondria become hyperpolarized, GHITM loses its inhibitory activity toward AFG3L2 and the now the active AFG3L2 turns first on GHITM and, if hyperpolarization persists, on other proteins of the mitochondria, leading to a broad remodeling of the mitochondrial proteome (PubMed:36321428)","subcellular_location":"Mitochondrion inner membrane","url":"https://www.uniprot.org/uniprotkb/Q9H3K2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GHITM","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GHITM","total_profiled":1310},"omim":[{"mim_id":"619205","title":"GROWTH HORMONE-INDUCIBLE TRANSMEMBRANE PROTEIN; GHITM","url":"https://www.omim.org/entry/619205"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Mitochondria","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/GHITM"},"hgnc":{"alias_symbol":["HSPC282","PTD010","DERP2","My021","TMBIM5","MICS1"],"prev_symbol":[]},"alphafold":{"accession":"Q9H3K2","domains":[{"cath_id":"-","chopping":"72-341","consensus_level":"high","plddt":87.3838,"start":72,"end":341}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H3K2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H3K2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H3K2-F1-predicted_aligned_error_v6.png","plddt_mean":77.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GHITM","jax_strain_url":"https://www.jax.org/strain/search?query=GHITM"},"sequence":{"accession":"Q9H3K2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H3K2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H3K2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H3K2"}},"corpus_meta":[{"pmid":"36321428","id":"PMC_36321428","title":"TMBIM5 is the Ca2+ /H+ antiporter of mammalian mitochondria.","date":"2022","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/36321428","citation_count":56,"is_preprint":false},{"pmid":"35715207","id":"PMC_35715207","title":"TMBIM5 loss of function alters mitochondrial matrix ion homeostasis and causes a skeletal myopathy.","date":"2022","source":"Life science alliance","url":"https://pubmed.ncbi.nlm.nih.gov/35715207","citation_count":28,"is_preprint":false},{"pmid":"21909400","id":"PMC_21909400","title":"Mite allergen Der-p2 triggers human B lymphocyte activation and Toll-like receptor-4 induction.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21909400","citation_count":26,"is_preprint":false},{"pmid":"32977469","id":"PMC_32977469","title":"Transmembrane BAX Inhibitor-1 Motif Containing Protein 5 (TMBIM5) Sustains Mitochondrial Structure, Shape, and Function by Impacting the Mitochondrial Protein Synthesis Machinery.","date":"2020","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/32977469","citation_count":19,"is_preprint":false},{"pmid":"20388233","id":"PMC_20388233","title":"Der-p2 ( Dermatophagoides pteronyssinus) allergen-like protein from the hard tick Ixodes ricinus - a novel member of ML (MD-2-related lipid-recognition) domain protein family.","date":"2010","source":"Parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/20388233","citation_count":16,"is_preprint":false},{"pmid":"30661317","id":"PMC_30661317","title":"A Fusion Protein of Derp2 Allergen and Flagellin Suppresses Experimental Allergic Asthma.","date":"2019","source":"Allergy, asthma & immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/30661317","citation_count":15,"is_preprint":false},{"pmid":"18071587","id":"PMC_18071587","title":"The growth-hormone inducible transmembrane protein (Ghitm) belongs to the Bax inhibitory protein-like family.","date":"2007","source":"International journal of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/18071587","citation_count":15,"is_preprint":false},{"pmid":"27896542","id":"PMC_27896542","title":"Immunomodulatory Effects of Adjuvants CPG, MPLA, and BCG on the Derp2-Induced Acute Asthma at Early Life in an Animal Model of BALB/c Mice.","date":"2017","source":"Inflammation","url":"https://pubmed.ncbi.nlm.nih.gov/27896542","citation_count":12,"is_preprint":false},{"pmid":"31906861","id":"PMC_31906861","title":"Preliminary investigation demonstrating the GHITM gene probably involved in apoptosis and growth of the golden apple snail (Pomacea canaliculata).","date":"2020","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/31906861","citation_count":10,"is_preprint":false},{"pmid":"21337914","id":"PMC_21337914","title":"Derp2-mutant gene vaccine inhibits airway inflammation and up-regulates Toll-like receptor 9 in an allergic asthmatic mouse model.","date":"2010","source":"Asian Pacific journal of allergy and immunology","url":"https://pubmed.ncbi.nlm.nih.gov/21337914","citation_count":9,"is_preprint":false},{"pmid":"16412389","id":"PMC_16412389","title":"Ghitm is an ortholog of the Bombyx mori prothoracic gland-derived receptor (Pgdr) that is ubiquitously expressed in mammalian cells and requires an N-terminal signal sequence for expression.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/16412389","citation_count":8,"is_preprint":false},{"pmid":"29270127","id":"PMC_29270127","title":"miR-1338-5p Modulates Growth Hormone Secretion and Glucose Utilization by Regulating ghitm in Genetically Improved Farmed Tilapia (GIFT, Oreochromis niloticus).","date":"2017","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/29270127","citation_count":8,"is_preprint":false},{"pmid":"38588015","id":"PMC_38588015","title":"GHITM regulates malignant phenotype and sensitivity to PD-1 blockade of renal cancer cells via Notch signalling.","date":"2024","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38588015","citation_count":7,"is_preprint":false},{"pmid":"24589117","id":"PMC_24589117","title":"Whole antigenic lysates of Ixodes ricinus, but not Der-p2 allergen-like protein, are potent inducers of basophil activation in previously tick-exposed human hosts.","date":"2013","source":"Transboundary and emerging diseases","url":"https://pubmed.ncbi.nlm.nih.gov/24589117","citation_count":4,"is_preprint":false},{"pmid":"35912455","id":"PMC_35912455","title":"The mystery of mitochondrial plasticity: TMBIM5 integrates metabolic state and proteostasis.","date":"2022","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/35912455","citation_count":2,"is_preprint":false},{"pmid":"40973741","id":"PMC_40973741","title":"Interaction of the mitochondrial calcium/proton exchanger TMBIM5 with MICU1.","date":"2025","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/40973741","citation_count":1,"is_preprint":false},{"pmid":"41501441","id":"PMC_41501441","title":"Tmbim5 and Slc8b1 cooperate in tissue-specific mitochondrial calcium regulation in zebrafish.","date":"2026","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/41501441","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10044,"output_tokens":2451,"usd":0.033448,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9660,"output_tokens":3333,"usd":0.065812,"stage2_stop_reason":"end_turn"},"total_usd":0.09926,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2022,\n      \"finding\": \"TMBIM5 (GHITM) is the mitochondrial Ca2+/H+ antiporter (calcium/proton exchanger). Cell-based and cell-free biochemical assays demonstrated absence or greatly reduced Na+-independent mitochondrial Ca2+ release in TMBIM5 knockout cells or pH-sensing site mutants, and pH-dependent Ca2+ transport by recombinant TMBIM5. TMBIM5 physically interacts with LETM1 (identified via LETM1 mitochondrial interactome), but it is TMBIM5, not LETM1, that carries the CHE activity.\",\n      \"method\": \"CRISPR-Cas9 knockout, cell-free reconstitution of recombinant TMBIM5, pH-sensing site mutagenesis, Co-IP/mitochondrial interactome of LETM1, mitochondrial Ca2+ release assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cell-free reconstitution of recombinant protein, mutagenesis of pH-sensing site, knockout cells, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"36321428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Loss of TMBIM5 results in increased potassium and reduced proton levels in the mitochondrial matrix due to attenuated exchange of these ions. Overexpressed TMBIM5 can mediate mitochondrial calcium uptake. Mice carrying a mutation in the channel pore of TMBIM5 display increased embryonic/perinatal lethality, skeletal myopathy, disrupted cristae architecture, early opening of the mitochondrial permeability transition pore, reduced calcium uptake, and mitochondrial swelling.\",\n      \"method\": \"TMBIM5 channel pore mutant knock-in mice, TMBIM5 overexpression in cells, mitochondrial ion measurements (K+, H+, Ca2+), mitochondrial permeability transition pore assays, electron microscopy of cristae\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knock-in mouse model with channel pore mutation, multiple orthogonal phenotypic readouts, supported by cell-based Ca2+ transport assays\",\n      \"pmids\": [\"35715207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TMBIM5 knockout (CRISPR-Cas9) cells show fragmented mitochondria with vacuolar cristae structure, reduced mitochondrial membrane potential, attenuated respiration, reduced mitochondrial ATP generation, and increased sensitivity to apoptosis induced by staurosporine and BH3 mimetics. Unbiased proteomics revealed dramatic downregulation of mitochondrial protein synthesis machinery components in TMBIM5-KO cells. TMBIM5 does not associate with MICOS components Mic10 or Mic60, nor does its KO affect their expression.\",\n      \"method\": \"CRISPR-Cas9 knockout, mitochondrial membrane potential measurement, oxygen consumption assays, ATP measurement, apoptosis assays, Co-IP (negative for Mic10/Mic60), quantitative proteomics\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean CRISPR KO with multiple orthogonal cellular phenotype readouts plus proteomics, single lab\",\n      \"pmids\": [\"32977469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TMBIM5 functionally interacts with MICU1 (a component of the mitochondrial calcium uniporter complex). In human cells, MICU1 rescues morphological defects in TMBIM5-KO mitochondria, while TMBIM5 overexpression exacerbates size reduction in MICU1-KO mitochondria. Both proteins show opposing effects on submitochondrial localization and co-exist in the same macromolecular complex (Co-IP). In Drosophila, partial MICU1 depletion ameliorates Tmbim5-deficiency phenotype (disrupted cristae, premature mPTP opening, reduced Ca2+ uptake, mitochondrial swelling, impaired mobility, shortened lifespan).\",\n      \"method\": \"Co-immunoprecipitation, TMBIM5-KO and MICU1-KO human cells, genetic epistasis in Drosophila (double knockouts), mitochondrial morphology imaging, Ca2+ uptake assays\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal genetic and biochemical interaction evidence (Co-IP + genetic epistasis in two model systems), single lab\",\n      \"pmids\": [\"40973741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"In zebrafish, tmbim5/mcu double knockouts show no additive effects on the tmbim5-KO phenotype, arguing against TMBIM5 functioning as an independent Ca2+ uptake pathway. tmbim5/slc8b1 (NCLX) double knockouts show altered mitochondrial Ca2+ handling with reduced uptake and efflux, suggesting TMBIM5 functions as an auxiliary Ca2+ efflux pathway cooperating with NCLX in a tissue-specific manner. Brain phenotypes were rescued and muscle dysfunction was exacerbated in double mutants, corresponding to restored mitochondrial membrane potential in brain and decreased Ca2+ levels in muscle.\",\n      \"method\": \"Zebrafish tmbim5, slc8b1, tmbim5/mcu, and tmbim5/slc8b1 double knockouts; mitochondrial Ca2+ uptake/efflux measurements; mitochondrial membrane potential measurements; phenotypic assessment (growth, muscle, brain cell death)\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple double-KO zebrafish lines and multiple orthogonal functional readouts, single lab\",\n      \"pmids\": [\"41501441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GHITM requires cleavage of its N-terminal portion for proper expression; Western blot analyses demonstrated that this cleavage regulates the expression level of the protein. GHITM is ubiquitously expressed in mammalian cells and mouse tissues, and requires an N-terminal signal sequence for expression.\",\n      \"method\": \"Western blot, expression pattern analysis in mouse embryo and adult tissues, signal sequence analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, Western blot only, no functional follow-up of the cleavage event\",\n      \"pmids\": [\"16412389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GHITM contains the UPF0005/TMBIM domain and was identified as a member of the BI-1 (Bax inhibitory protein-like) family based on phylogenetic and domain analysis. It is the only mitochondrially-localized member of the TMBIM family.\",\n      \"method\": \"Phylogenetic analysis, domain analysis, expression profiling in cancer cell lines\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational/bioinformatic classification, no direct functional experiment\",\n      \"pmids\": [\"18071587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GHITM overexpression in renal clear cell carcinoma cells inhibits cell proliferation, migration, and invasion in vitro and in vivo, and induces downregulation of Notch1. Overexpression of Notch1 rescues the inhibitory effects of GHITM upregulation. YY1 transcription factor decreases GHITM levels by binding to its promoter. GHITM also regulates PD-L1 protein abundance.\",\n      \"method\": \"GHITM overexpression in KIRC cell lines, rescue by Notch1 overexpression, ChIP/promoter binding assay for YY1, in vivo xenograft, PD-L1 protein quantification\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic rescue epistasis (Notch1 overexpression), promoter binding assay, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"38588015\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TMBIM5/GHITM is the mitochondrial Ca2+/H+ antiporter localized to the inner mitochondrial membrane; it mediates Na+-independent Ca2+ release coupled to H+ exchange (established by reconstitution of recombinant protein and pH-sensing site mutagenesis), regulates mitochondrial matrix K+/H+ balance, maintains cristae architecture and mitochondrial membrane potential, supports mitochondrial protein synthesis machinery, interacts physically with LETM1 and functionally with MICU1 to govern mitochondrial Ca2+ homeostasis, and its loss causes skeletal myopathy, early mPTP opening, and increased apoptotic sensitivity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GHITM (TMBIM5) is the mitochondrial inner-membrane Ca2+/H+ antiporter that governs matrix ion balance and organelle integrity [#0]. Cell-free reconstitution of recombinant protein, knockout cells, and mutagenesis of its pH-sensing site established that GHITM carries Na+-independent, pH-coupled Ca2+ transport activity; it physically associates with LETM1, but the channel activity resides in GHITM itself [#0]. Loss of GHITM shifts matrix ion levels toward elevated K+ and reduced H+, reflecting impaired ion exchange, and a channel-pore mutant in mice produces skeletal myopathy, disrupted cristae, early opening of the mitochondrial permeability transition pore, reduced Ca2+ uptake, and mitochondrial swelling [#1]. At the cellular level GHITM is required to maintain cristae architecture, mitochondrial membrane potential, respiration and ATP output, and its loss downregulates the mitochondrial protein synthesis machinery and heightens apoptotic sensitivity, independent of the MICOS components Mic10/Mic60 [#2]. GHITM acts within the broader mitochondrial Ca2+ network: it co-exists in a macromolecular complex with MICU1 and shows reciprocal, opposing morphological effects with it [#3], and genetic epistasis in zebrafish places GHITM as an auxiliary, tissue-specific Ca2+ efflux pathway cooperating with NCLX (slc8b1) rather than as an independent uptake route paralleling MCU [#4]. In renal clear cell carcinoma, GHITM overexpression suppresses proliferation, migration and invasion through downregulation of Notch1 and modulates PD-L1 abundance, with the transcription factor YY1 repressing GHITM by promoter binding [#7].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established the basic protein biology of GHITM by showing that N-terminal signal sequence cleavage controls its expression level, framing it as a processed, ubiquitously expressed membrane protein before any transport function was known.\",\n      \"evidence\": \"Western blot and expression profiling across mouse embryo/adult tissues with signal sequence analysis\",\n      \"pmids\": [\"16412389\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Single-lab Western blot only with no functional follow-up of the cleavage event\",\n        \"No localization to a specific submitochondrial compartment demonstrated\",\n        \"Protease responsible for cleavage not identified\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Placed GHITM phylogenetically as the only mitochondrial member of the TMBIM/BI-1 family, predicting a connection to apoptosis-regulatory ion handling.\",\n      \"evidence\": \"Phylogenetic and domain analysis plus expression profiling in cancer cell lines\",\n      \"pmids\": [\"18071587\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Computational classification with no direct functional experiment\",\n        \"Did not test any transport or apoptotic activity\",\n        \"Domain architecture not linked to a measured biochemical function\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected GHITM to mitochondrial integrity by showing its loss fragments mitochondria, collapses membrane potential and respiration, suppresses the mitochondrial translation machinery, and sensitizes cells to apoptosis.\",\n      \"evidence\": \"CRISPR-Cas9 knockout with membrane potential, oxygen consumption, ATP, apoptosis assays and quantitative proteomics, plus negative Co-IP against Mic10/Mic60\",\n      \"pmids\": [\"32977469\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Did not identify the molecular activity underlying these phenotypes\",\n        \"Mechanism linking GHITM loss to translation machinery downregulation unresolved\",\n        \"Single-lab cell-line phenotyping without in vivo confirmation\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined the molecular activity by demonstrating GHITM is itself the Na+-independent mitochondrial Ca2+/H+ antiporter, distinguishing its catalytic role from its physical partner LETM1.\",\n      \"evidence\": \"Cell-free reconstitution of recombinant protein, pH-sensing site mutagenesis, knockout cells, mitochondrial Ca2+ release assays, and LETM1 interactome Co-IP\",\n      \"pmids\": [\"36321428\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the antiporter and its pH-sensing site not solved\",\n        \"Stoichiometry and directionality of Ca2+/H+ coupling not fully defined\",\n        \"Functional consequence of the LETM1 interaction not resolved\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Linked transport activity to physiology in vivo by showing a channel-pore mutation alters matrix K+/H+ balance and Ca2+ uptake and causes myopathy, cristae disruption, and early mPTP opening.\",\n      \"evidence\": \"Channel-pore mutant knock-in mice, overexpression Ca2+ uptake assays, matrix ion measurements, mPTP assays, and electron microscopy\",\n      \"pmids\": [\"35715207\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Causal chain from ion imbalance to cristae remodeling not delineated\",\n        \"Tissue specificity of the myopathy phenotype not mechanistically explained\",\n        \"Whether matrix K+/H+ effects are direct or secondary remains open\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Embedded GHITM in the mitochondrial Ca2+ regulatory network by demonstrating reciprocal, opposing functional and physical interactions with MICU1 across human cells and Drosophila.\",\n      \"evidence\": \"Co-IP, reciprocal KO rescue/exacerbation of mitochondrial morphology in human cells, and genetic epistasis in Drosophila double knockouts\",\n      \"pmids\": [\"40973741\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether MICU1 directly modulates GHITM transport activity not established\",\n        \"Architecture of the shared macromolecular complex undefined\",\n        \"Single-lab interaction data without orthogonal structural validation\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Resolved GHITM's position relative to canonical Ca2+ transporters, showing it is not an independent MCU-like uptake route but an auxiliary, tissue-specific efflux pathway cooperating with NCLX.\",\n      \"evidence\": \"Zebrafish tmbim5/mcu and tmbim5/slc8b1 double knockouts with Ca2+ uptake/efflux, membrane potential, and tissue-specific phenotyping\",\n      \"pmids\": [\"41501441\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular basis of cooperation with NCLX unknown\",\n        \"Mechanism of tissue-specific opposing brain vs muscle outcomes unresolved\",\n        \"Single-lab genetic epistasis in zebrafish only\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended GHITM function to tumor suppression in renal clear cell carcinoma, where it restrains proliferation and invasion via Notch1 downregulation and is itself transcriptionally repressed by YY1.\",\n      \"evidence\": \"GHITM overexpression with Notch1 rescue, YY1 promoter-binding assay, xenografts, and PD-L1 protein quantification\",\n      \"pmids\": [\"38588015\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Link between mitochondrial transport activity and Notch1/PD-L1 regulation not mechanistically connected\",\n        \"How GHITM controls PD-L1 abundance unresolved\",\n        \"Single-lab cancer-context study without in vivo Ca2+-handling correlation\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GHITM's Ca2+/H+ antiport activity mechanistically drives cristae maintenance, mitochondrial translation, and its tissue-specific cancer-suppressive signaling remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No structure of the antiporter or its regulatory complexes\",\n        \"Causal link between ion transport and downstream organelle/signaling phenotypes undefined\",\n        \"Mechanism connecting mitochondrial function to Notch1/PD-L1 regulation unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 2, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"LETM1\", \"MICU1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}