{"gene":"CNNM2","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2005,"finding":"Mouse CNNM2 (ACDP2) expressed in Xenopus laevis oocytes mediates saturable, rheogenic, voltage-dependent Mg2+ uptake (Km ~0.56 mM) and transports a range of divalent cations (Mg2+, Co2+, Mn2+, Sr2+, Ba2+, Cu2+, Fe2+), with Zn2+ acting as an inhibitor; transport is not coupled to Na+ or Cl-.","method":"Two-electrode voltage-clamp electrophysiology in Xenopus oocytes expressing mouse CNNM2","journal":"Physiological genomics","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro functional assay with kinetic characterization in heterologous expression system","pmids":["15899945"],"is_preprint":false},{"year":2011,"finding":"CNNM2 localizes to the basolateral membrane of distal tubular segments in the kidney, and electrophysiological analysis showed it mediates Mg2+-sensitive Na+ currents that are significantly diminished by patient mutations and blocked by increased extracellular Mg2+.","method":"Immunolocalization in kidney tissue and epithelial cell lines; two-electrode voltage-clamp electrophysiology; site-directed mutagenesis of disease-causing variants","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1–2 — direct localization with functional consequence, electrophysiology with mutant comparison, replicated across cell lines and tissue","pmids":["21397062"],"is_preprint":false},{"year":2012,"finding":"CNNM2 has an extracellular N-terminus and intracellular C-terminus (one transmembrane region may be re-entrant); it is glycosylated at Asn-112 by signal peptidase-cleaved signal peptide processing in the ER, which stabilizes CNNM2 at the plasma membrane; CNNM2a forms heterodimers with the smaller isoform CNNM2b.","method":"Membrane topology studies using intramolecular epitopes and immunocytochemistry; mutagenesis screening; co-immunoprecipitation; homology modeling of CBS domains","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods (topology assay, mutagenesis, Co-IP, modeling) in a single study","pmids":["22399287"],"is_preprint":false},{"year":2014,"finding":"CNNM2 increases cellular Mg2+ uptake in HEK293 cells via regulation of the Mg2+-permeable cation channel TRPM7; disease-causing mutant CNNM2 proteins failed to increase Mg2+ uptake; knockdown of cnnm2 in zebrafish reduced body Mg content and caused neurodevelopmental defects rescuable by wild-type mammalian Cnnm2 cRNA.","method":"Stable Mg2+ isotope uptake assays in HEK293 cells; zebrafish morpholino knockdown with rescue by mammalian cRNA injection; behavioral assays","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (isotope uptake, genetic rescue in zebrafish), functional epistasis with TRPM7","pmids":["24699222"],"is_preprint":false},{"year":2014,"finding":"The intracellular Bateman (CBS) module of CNNM2 binds nucleotides (AMP, ADP, ATP) at one of its two cavities; Mg2+ facilitates ATP binding by alleviating charge repulsion; nucleotide binding triggers a conformational change from a twisted to a flat disc-like CBS dimer structure affecting elements connecting the Bateman module to the transmembrane region; the pathogenic mutation T568I mimics the nucleotide-bound flat conformation, locking the CBS module.","method":"X-ray crystallography of CNNM2 CBS domain fragment; structural comparison with/without nucleotides; analysis of T568I pathogenic mutant crystal structure","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with and without ligands, mutation structural analysis, mechanistic model validated by structural data","pmids":["25184538"],"is_preprint":false},{"year":2016,"finding":"PRL-1 phosphatase interacts with the intracellular Bateman module (CBS domains) of CNNM2, forming a heterotetrameric complex (disc-like homodimer of CNNM2-CBS bound to two PRL-1 molecules); Asp-558 at the extended loop of CNNM2 CBS2 is critical for this interaction; PRL-1 binding occurs via its catalytic domain.","method":"X-ray crystal structure of PRL-1 in complex with CNNM2 Bateman module; structure-based mutagenesis analysis of key interface residues","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure of protein complex with identified key interface residue","pmids":["27899452"],"is_preprint":false},{"year":2016,"finding":"CNNM2 isoforms 1 and 2 do not transport Mg2+ in electrogenic or electroneutral mode in HEK293 cells, are not exclusively plasma membrane-localized, and both form higher-order protein complexes; isoform 1 has a much smaller spectrum of potential interactors than isoform 2, suggesting distinct functions.","method":"Patch-clamp and fluorescence-based Mg2+ transport assays in transgenic HEK293 cells; subcellular fractionation; co-immunoprecipitation/mass spectrometry interactome","journal":"Pflugers Archiv : European journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays, but contradicts other studies; single lab","pmids":["27068403"],"is_preprint":false},{"year":2010,"finding":"Human CNNM2 splice variant 1 (isomorph 1), but not isomorph 2, complements the Mg2+-deficient growth of Salmonella MM281 (mgtA/mgtB/corA triple mutant) and mediates measurable Mg2+ influx, demonstrating that isoform 1 is a functional Mg2+-transporting entity.","method":"Genetic complementation assay in Salmonella MM281; Mg2+ influx measurement in bacteria","journal":"Magnesium research","confidence":"Medium","confidence_rationale":"Tier 2 — functional complementation with transport measurement, but in bacterial heterologous system","pmids":["20519162"],"is_preprint":false},{"year":2021,"finding":"CNNM2 knockout mice exhibit mild hypomagnesemia and increased fecal Mg2+ and Ca2+ excretion, indicating a role for CNNM2 in intestinal Mg2+ absorption in addition to its renal function; homozygous knockout is largely lethal, with only rare live-born pups showing significantly lower serum Mg2+.","method":"CRISPR/Cas9 knockout mouse model; serum and fecal mineral analysis; dietary Mg2+ challenge","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined physiological phenotype and dietary intervention","pmids":["33859252"],"is_preprint":false},{"year":2022,"finding":"The CNNM2 R480L mutation in the CBS domain impairs ATP-Mg2+ binding to CNNM2 and diminishes Mg2+ efflux, as shown by increased intracellular Mg2+ in cells expressing the mutant compared to wild-type.","method":"Mg2+ efflux assay in murine DCT cells; molecular simulation modeling of mutant CBS domain-ATP-Mg2+ interaction","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 2–3 — functional efflux assay supported by structural simulation, single lab","pmids":["35846113"],"is_preprint":false},{"year":2021,"finding":"Pathogenic mutations in CNNM2 result in decreased plasma membrane expression of the protein, suggesting that loss of proper membrane trafficking underlies loss of Mg2+ transport function.","method":"25Mg2+ uptake assays in HEK293 cells expressing mutant CNNM2; assessment of plasma membrane expression levels","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 — functional uptake assay plus localization data, moderate evidence","pmids":["33600043"],"is_preprint":false},{"year":2023,"finding":"Reduced Cnnm2 expression in mouse medial prefrontal cortex impairs cognition and sensorimotor gating; knockdown in primary cortical neurons alters dendritic spine morphogenesis; proteomics shows changed expression of proteins associated with neuronal structure and function.","method":"Viral-mediated Cnnm2 knockdown in mouse mPFC; behavioral assays; primary neuronal culture knockdown with proteomics","journal":"Neuropsychopharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — KD with defined cellular and behavioral phenotype, single lab","pmids":["37715107"],"is_preprint":false},{"year":2025,"finding":"Two novel CNNM2 variants (p.E298del and p.P360R) increase CNNM2 transcription and protein levels but impair proper localization to the cell membrane, causing cytoplasmic accumulation and reduced protein stability, resulting in elevated intracellular Mg2+ and disrupted Mg2+ efflux.","method":"qPCR, Western blotting, immunofluorescence, flow cytometry-based intracellular Mg2+ measurement in cells expressing mutant CNNM2","journal":"Frontiers in genetics","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple functional assays in a single study, single lab","pmids":["40612795"],"is_preprint":false}],"current_model":"CNNM2 is a basolateral membrane protein in renal distal tubular cells (and potentially intestinal epithelium) that mediates Mg2+ efflux/transport through a mechanism involving its intracellular CBS/Bateman domain, which binds nucleotides (AMP/ADP/ATP) in a Mg2+-facilitated manner and undergoes conformational changes that regulate transporter activity; it forms homodimers and interacts with the PRL-1 phosphatase via its CBS2 domain, and with the Mg2+-permeable channel TRPM7, to regulate intracellular Mg2+ homeostasis, with disease-causing mutations impairing ATP binding, membrane targeting, or Mg2+ efflux capacity, and brain-specific roles in dendritic spine morphogenesis and neurodevelopment."},"narrative":{"teleology":[{"year":2005,"claim":"Establishing that CNNM2 is a functional divalent cation transporter resolved the basic molecular activity of the protein, showing it mediates saturable, voltage-dependent Mg²⁺ uptake with broad divalent cation selectivity.","evidence":"Two-electrode voltage-clamp electrophysiology of mouse CNNM2 in Xenopus oocytes with kinetic characterization","pmids":["15899945"],"confidence":"High","gaps":["Transport mechanism (channel vs. carrier) not defined","Physiological transport direction in native tissues not established","Molecular determinants of ion selectivity unknown"]},{"year":2010,"claim":"Demonstrating isoform-specific Mg²⁺ transport function revealed that CNNM2 splice variant 1, but not variant 2, is a functional Mg²⁺-transporting entity, indicating functional divergence among isoforms.","evidence":"Genetic complementation of Salmonella Mg²⁺-transport-deficient mutant MM281 with human CNNM2 isoforms","pmids":["20519162"],"confidence":"Medium","gaps":["Bacterial heterologous system may not recapitulate mammalian transport properties","Mechanism underlying isoform difference not identified"]},{"year":2011,"claim":"Localizing CNNM2 to the basolateral membrane of renal distal tubules and showing that patient mutations diminish Mg²⁺-sensitive currents established the protein's physiological site of action and linked it to human hypomagnesemia.","evidence":"Immunolocalization in human kidney tissue; two-electrode voltage-clamp with disease-causing mutants","pmids":["21397062"],"confidence":"High","gaps":["Whether CNNM2 mediates Mg²⁺ influx or efflux at the basolateral membrane was unresolved","Identity of transported ion species in native tissue not confirmed"]},{"year":2012,"claim":"Determining the membrane topology of CNNM2—extracellular N-terminus, intracellular C-terminus with CBS domains, N-glycosylation at Asn-112 stabilizing surface expression, and heterodimerization of isoforms—defined the structural framework for understanding regulatory and transport mechanisms.","evidence":"Intramolecular epitope topology mapping, mutagenesis, co-immunoprecipitation in mammalian cells","pmids":["22399287"],"confidence":"High","gaps":["Full-length high-resolution structure unavailable","Functional significance of heterodimerization not tested"]},{"year":2014,"claim":"Solving the crystal structure of the CBS/Bateman domain revealed that nucleotide binding (ATP/ADP/AMP) triggers a twisted-to-flat conformational switch that is facilitated by Mg²⁺ and transmitted toward the transmembrane region, providing the first structural mechanism for regulation of CNNM2 activity; the pathogenic T568I mutation mimics the nucleotide-bound conformation, explaining its loss of function.","evidence":"X-ray crystallography of CNNM2 CBS domain ± nucleotides and T568I mutant","pmids":["25184538"],"confidence":"High","gaps":["How conformational change couples to ion translocation through the transmembrane domain is unknown","No full-length transporter structure"]},{"year":2014,"claim":"Showing that CNNM2 regulates Mg²⁺ uptake through the TRPM7 channel and that zebrafish cnnm2 knockdown causes Mg²⁺ depletion and neurodevelopmental defects established CNNM2 as an in vivo Mg²⁺ homeostasis regulator with roles beyond the kidney.","evidence":"²⁵Mg²⁺ uptake assays in HEK293 cells; zebrafish morpholino knockdown with mammalian rescue","pmids":["24699222"],"confidence":"High","gaps":["Molecular mechanism of CNNM2–TRPM7 functional interaction not defined","Direction of CNNM2-dependent Mg²⁺ flux in native cells debated"]},{"year":2016,"claim":"Solving the crystal structure of the PRL-1–CNNM2 Bateman module complex revealed a heterotetrameric architecture with Asp-558 as a critical interface residue, identifying a phosphatase-based regulatory input to the transporter.","evidence":"X-ray crystallography of PRL-1 bound to CNNM2 CBS domain; structure-guided mutagenesis","pmids":["27899452"],"confidence":"High","gaps":["Functional consequence of PRL-1 binding on Mg²⁺ transport not directly measured","Whether PRL-1 dephosphorylates CNNM2 or acts allosterically is unknown"]},{"year":2016,"claim":"A challenge to the transport model reported that CNNM2 isoforms 1 and 2 did not mediate electrogenic or electroneutral Mg²⁺ transport in patch-clamp and fluorescence assays in HEK293 cells, suggesting CNNM2 may function as a regulator rather than a direct transporter.","evidence":"Patch-clamp and fluorescence Mg²⁺ assays in HEK293 cells stably expressing CNNM2 isoforms","pmids":["27068403"],"confidence":"Medium","gaps":["Contradicts oocyte electrophysiology data; discrepancy may reflect system-dependent differences","Negative result in one cell type does not exclude transport in native tissue"]},{"year":2021,"claim":"CNNM2 knockout mice confirmed that CNNM2 is required for systemic Mg²⁺ homeostasis in vivo and revealed a role in intestinal Mg²⁺ absorption in addition to renal reabsorption; homozygous knockout is largely lethal.","evidence":"CRISPR/Cas9 CNNM2 knockout mouse with serum and fecal mineral analysis","pmids":["33859252"],"confidence":"High","gaps":["Relative contribution of intestinal vs. renal CNNM2 not deconvoluted","Cause of lethality in homozygous KO not defined"]},{"year":2021,"claim":"Demonstrating that pathogenic mutations reduce CNNM2 plasma membrane expression provided a unifying trafficking-based mechanism for loss of Mg²⁺ transport across multiple disease variants.","evidence":"²⁵Mg²⁺ uptake assay and surface expression quantification in HEK293 cells expressing mutant CNNM2","pmids":["33600043"],"confidence":"Medium","gaps":["Trafficking pathway and quality-control checkpoint that retains mutant CNNM2 not identified","Not all known mutations tested"]},{"year":2022,"claim":"The R480L CBS-domain mutation was shown to impair ATP-Mg²⁺ binding and diminish Mg²⁺ efflux, directly linking the nucleotide-sensing structural mechanism to the transport direction (efflux) in distal convoluted tubule cells.","evidence":"Mg²⁺ efflux assay in murine DCT cells with molecular dynamics simulation of mutant CBS domain","pmids":["35846113"],"confidence":"Medium","gaps":["Single mutation study; generalizability to other CBS mutations not confirmed","Efflux measurement in cultured DCT cells, not in intact epithelium"]},{"year":2023,"claim":"Establishing that CNNM2 knockdown in mouse prefrontal cortex impairs cognition and alters dendritic spine morphogenesis expanded the functional role of CNNM2 beyond epithelial Mg²⁺ transport to neuronal structural plasticity.","evidence":"Viral Cnnm2 knockdown in mouse mPFC with behavioral testing; primary neuronal culture with proteomics","pmids":["37715107"],"confidence":"Medium","gaps":["Whether neuronal phenotype is Mg²⁺-dependent or reflects a distinct CNNM2 function is unknown","Downstream neuronal targets not validated individually"]},{"year":null,"claim":"Key open questions include whether CNNM2 is a direct Mg²⁺ transporter or an indirect regulator of Mg²⁺ channels, the full-length structure and ion translocation pathway, the functional consequence of PRL-1 binding on transport, and the molecular basis of CNNM2's neuronal functions.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length CNNM2 structure or reconstituted transport in proteoliposomes","Transport vs. regulator debate unresolved","PRL-1 functional impact on Mg²⁺ flux not measured"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,7,9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,2,10,12]}],"pathway":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0]}],"complexes":[],"partners":["PRL-1","TRPM7"],"other_free_text":[]},"mechanistic_narrative":"CNNM2 is a transmembrane protein that functions as a critical regulator of Mg²⁺ homeostasis in kidney, intestine, and brain by mediating Mg²⁺ transport across the basolateral membrane of epithelial cells. CNNM2 localizes to the basolateral membrane of renal distal tubular cells, where it mediates Mg²⁺ efflux regulated by nucleotide (ATP/ADP/AMP) binding to its intracellular CBS/Bateman domain; Mg²⁺ facilitates ATP binding, which triggers a conformational switch from a twisted to a flat CBS dimer that controls transporter activity [PMID:25184538, PMID:21397062, PMID:35846113]. The CBS2 domain also serves as a docking site for the PRL-1 phosphatase, forming a heterotetrameric complex, and CNNM2 functionally interacts with the Mg²⁺-permeable channel TRPM7 to regulate intracellular Mg²⁺ [PMID:27899452, PMID:24699222]. Pathogenic CNNM2 mutations cause hypomagnesemia by impairing ATP-Mg²⁺ binding, disrupting plasma membrane targeting, or locking the CBS module in an inactive conformation, and CNNM2 deficiency additionally impairs dendritic spine morphogenesis and cognition, linking it to neurodevelopmental phenotypes [PMID:33600043, PMID:25184538, PMID:37715107, PMID:33859252]."},"prefetch_data":{"uniprot":{"accession":"Q9H8M5","full_name":"Metal transporter CNNM2","aliases":["Ancient conserved domain-containing protein 2","Cyclin-M2"],"length_aa":875,"mass_kda":96.6,"function":"Divalent metal cation transporter. Mediates transport of divalent metal cations in an order of Mg(2+) > Co(2+) > Mn(2+) > Sr(2+) > Ba(2+) > Cu(2+) > Fe(2+) (By similarity)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9H8M5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CNNM2","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":[{"gene":"CANX","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CNNM2","total_profiled":1310},"omim":[{"mim_id":"618314","title":"HYPOMAGNESEMIA, SEIZURES, AND IMPAIRED INTELLECTUAL DEVELOPMENT 2; HOMGSMR2","url":"https://www.omim.org/entry/618314"},{"mim_id":"616418","title":"HYPOMAGNESEMIA, SEIZURES, AND IMPAIRED INTELLECTUAL DEVELOPMENT 1; HOMGSMR1","url":"https://www.omim.org/entry/616418"},{"mim_id":"613882","title":"HYPOMAGNESEMIA 6, RENAL; HOMG6","url":"https://www.omim.org/entry/613882"},{"mim_id":"607803","title":"CYCLIN M2; CNNM2","url":"https://www.omim.org/entry/607803"},{"mim_id":"602014","title":"HYPOMAGNESEMIA 1, INTESTINAL; HOMG1","url":"https://www.omim.org/entry/602014"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"choroid plexus","ntpm":22.2},{"tissue":"parathyroid gland","ntpm":29.6}],"url":"https://www.proteinatlas.org/search/CNNM2"},"hgnc":{"alias_symbol":["SLC70A2"],"prev_symbol":["ACDP2"]},"alphafold":{"accession":"Q9H8M5","domains":[{"cath_id":"2.60.40","chopping":"71-124_148-196_231-248","consensus_level":"medium","plddt":79.7796,"start":71,"end":248},{"cath_id":"-","chopping":"254-408","consensus_level":"high","plddt":86.3047,"start":254,"end":408},{"cath_id":"3.10.580.10","chopping":"443-603","consensus_level":"high","plddt":87.7112,"start":443,"end":603},{"cath_id":"2.60.120.10","chopping":"620-720_789-823","consensus_level":"medium","plddt":89.9157,"start":620,"end":823}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H8M5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H8M5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H8M5-F1-predicted_aligned_error_v6.png","plddt_mean":70.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CNNM2","jax_strain_url":"https://www.jax.org/strain/search?query=CNNM2"},"sequence":{"accession":"Q9H8M5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H8M5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H8M5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H8M5"}},"corpus_meta":[{"pmid":"21397062","id":"PMC_21397062","title":"CNNM2, encoding a basolateral protein required for renal Mg2+ handling, is mutated in dominant hypomagnesemia.","date":"2011","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21397062","citation_count":163,"is_preprint":false},{"pmid":"15899945","id":"PMC_15899945","title":"Functional characterization of ACDP2 (ancient conserved domain protein), a divalent metal transporter.","date":"2005","source":"Physiological genomics","url":"https://pubmed.ncbi.nlm.nih.gov/15899945","citation_count":103,"is_preprint":false},{"pmid":"24699222","id":"PMC_24699222","title":"CNNM2 mutations cause impaired brain development and seizures in patients with hypomagnesemia.","date":"2014","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24699222","citation_count":102,"is_preprint":false},{"pmid":"22399287","id":"PMC_22399287","title":"Membrane topology and intracellular processing of cyclin M2 (CNNM2).","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22399287","citation_count":85,"is_preprint":false},{"pmid":"27899452","id":"PMC_27899452","title":"Structural Basis of the Oncogenic Interaction of Phosphatase PRL-1 with the Magnesium Transporter CNNM2.","date":"2016","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27899452","citation_count":55,"is_preprint":false},{"pmid":"27401531","id":"PMC_27401531","title":"Two-stage replication of previous genome-wide association studies of AS3MT-CNNM2-NT5C2 gene cluster region in a large schizophrenia case-control sample from Han Chinese population.","date":"2016","source":"Schizophrenia research","url":"https://pubmed.ncbi.nlm.nih.gov/27401531","citation_count":45,"is_preprint":false},{"pmid":"25184538","id":"PMC_25184538","title":"Nucleotide binding triggers a conformational change of the CBS module of the magnesium transporter CNNM2 from a twisted towards a flat structure.","date":"2014","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/25184538","citation_count":44,"is_preprint":false},{"pmid":"27068403","id":"PMC_27068403","title":"Human CNNM2 is not a Mg(2+) transporter per se.","date":"2016","source":"Pflugers Archiv : European journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/27068403","citation_count":35,"is_preprint":false},{"pmid":"30026055","id":"PMC_30026055","title":"CNNM2 homozygous mutations cause severe refractory hypomagnesemia, epileptic encephalopathy and brain malformations.","date":"2018","source":"European journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30026055","citation_count":27,"is_preprint":false},{"pmid":"24311551","id":"PMC_24311551","title":"Effects of a novel schizophrenia risk variant rs7914558 at CNNM2 on brain structure and attributional style.","date":"2013","source":"The British journal of psychiatry : the journal of mental science","url":"https://pubmed.ncbi.nlm.nih.gov/24311551","citation_count":26,"is_preprint":false},{"pmid":"33859252","id":"PMC_33859252","title":"Cyclin M2 (CNNM2) knockout mice show mild hypomagnesaemia and developmental defects.","date":"2021","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/33859252","citation_count":25,"is_preprint":false},{"pmid":"20519162","id":"PMC_20519162","title":"Splice-variant 1 of the ancient domain protein 2 (ACDP2) complements the magnesium-deficient growth phenotype of Salmonella enterica sv. typhimurium strain MM281.","date":"2010","source":"Magnesium research","url":"https://pubmed.ncbi.nlm.nih.gov/20519162","citation_count":22,"is_preprint":false},{"pmid":"32984406","id":"PMC_32984406","title":"Studies in Zebrafish Demonstrate That CNNM2 and NT5C2 Are Most Likely the Causal Genes at the Blood Pressure-Associated Locus on Human Chromosome 10q24.32.","date":"2020","source":"Frontiers in cardiovascular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32984406","citation_count":19,"is_preprint":false},{"pmid":"33600043","id":"PMC_33600043","title":"The phenotypic and genetic spectrum of patients with heterozygous mutations in cyclin M2 (CNNM2).","date":"2021","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/33600043","citation_count":18,"is_preprint":false},{"pmid":"32997713","id":"PMC_32997713","title":"Novel variant in the CNNM2 gene associated with dominant hypomagnesemia.","date":"2020","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/32997713","citation_count":15,"is_preprint":false},{"pmid":"23027747","id":"PMC_23027747","title":"Purification, crystallization and preliminary crystallographic analysis of the CBS-domain pair of cyclin M2 (CNNM2).","date":"2012","source":"Acta crystallographica. Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/23027747","citation_count":12,"is_preprint":false},{"pmid":"37715107","id":"PMC_37715107","title":"Decreased CNNM2 expression in prefrontal cortex affects sensorimotor gating function, cognition, dendritic spine morphogenesis and risk of schizophrenia.","date":"2023","source":"Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/37715107","citation_count":11,"is_preprint":false},{"pmid":"35846113","id":"PMC_35846113","title":"Novel CNNM2 Mutation Responsible for Autosomal-Dominant Hypomagnesemia With Seizure.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35846113","citation_count":9,"is_preprint":false},{"pmid":"34021155","id":"PMC_34021155","title":"Downregulation by CNNM2 of ATP5MD expression in the 10q24.32 schizophrenia-associated locus involved in impaired ATP production and neurodevelopment.","date":"2021","source":"NPJ schizophrenia","url":"https://pubmed.ncbi.nlm.nih.gov/34021155","citation_count":7,"is_preprint":false},{"pmid":"34490037","id":"PMC_34490037","title":"Case Report: CNNM2 Mutations Cause Damaged Brain Development and Intractable Epilepsy in a Patient Without Hypomagnesemia.","date":"2021","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34490037","citation_count":7,"is_preprint":false},{"pmid":"30180964","id":"PMC_30180964","title":"Associations between polymorphisms of the CXCL12 and CNNM2 gene and hypertension risk: A case-control study.","date":"2018","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/30180964","citation_count":6,"is_preprint":false},{"pmid":"35170241","id":"PMC_35170241","title":"Rare hypomagnesemia, seizures, and mental retardation in a 4-month-old patient caused by novel CNNM2 mutation Tyr189Cys: Genetic analysis and review.","date":"2022","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/35170241","citation_count":6,"is_preprint":false},{"pmid":"35806288","id":"PMC_35806288","title":"The p.Pro482Ala Variant in the CNNM2 Gene Causes Severe Hypomagnesemia Amenable to Treatment with Spironolactone.","date":"2022","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35806288","citation_count":5,"is_preprint":false},{"pmid":"37532502","id":"PMC_37532502","title":"[Analysis of CNNM2 gene variant in a child with Hypomagnesemia, seizures, and mental retardation syndrome].","date":"2023","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37532502","citation_count":3,"is_preprint":false},{"pmid":"38519529","id":"PMC_38519529","title":"Hypomagnesaemia with varying degrees of extrarenal symptoms as a consequence of heterozygous CNNM2 variants.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/38519529","citation_count":2,"is_preprint":false},{"pmid":"40612795","id":"PMC_40612795","title":"Two novel variants in CNNM2 disrupts magnesium efflux leading to neurodevelopmental disorders.","date":"2025","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40612795","citation_count":0,"is_preprint":false},{"pmid":"41022172","id":"PMC_41022172","title":"Novel CNNM2 variant causing hypomagnesemia and early-onset calcium pyrophosphate deposition disease: A case report.","date":"2025","source":"Joint bone spine","url":"https://pubmed.ncbi.nlm.nih.gov/41022172","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15831,"output_tokens":3114,"usd":0.047101},"stage2":{"model":"claude-opus-4-6","input_tokens":6484,"output_tokens":6015,"usd":0.274193},"total_usd":0.321294,"stage1_batch_id":"msgbatch_011kfMfE81o6CTcyhVUqumuW","stage2_batch_id":"msgbatch_01DTputS6WNkH745x1nVSoBo","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"Mouse CNNM2 (ACDP2) expressed in Xenopus laevis oocytes mediates saturable, rheogenic, voltage-dependent Mg2+ uptake (Km ~0.56 mM) and transports a range of divalent cations (Mg2+, Co2+, Mn2+, Sr2+, Ba2+, Cu2+, Fe2+), with Zn2+ acting as an inhibitor; transport is not coupled to Na+ or Cl-.\",\n      \"method\": \"Two-electrode voltage-clamp electrophysiology in Xenopus oocytes expressing mouse CNNM2\",\n      \"journal\": \"Physiological genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro functional assay with kinetic characterization in heterologous expression system\",\n      \"pmids\": [\"15899945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CNNM2 localizes to the basolateral membrane of distal tubular segments in the kidney, and electrophysiological analysis showed it mediates Mg2+-sensitive Na+ currents that are significantly diminished by patient mutations and blocked by increased extracellular Mg2+.\",\n      \"method\": \"Immunolocalization in kidney tissue and epithelial cell lines; two-electrode voltage-clamp electrophysiology; site-directed mutagenesis of disease-causing variants\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct localization with functional consequence, electrophysiology with mutant comparison, replicated across cell lines and tissue\",\n      \"pmids\": [\"21397062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CNNM2 has an extracellular N-terminus and intracellular C-terminus (one transmembrane region may be re-entrant); it is glycosylated at Asn-112 by signal peptidase-cleaved signal peptide processing in the ER, which stabilizes CNNM2 at the plasma membrane; CNNM2a forms heterodimers with the smaller isoform CNNM2b.\",\n      \"method\": \"Membrane topology studies using intramolecular epitopes and immunocytochemistry; mutagenesis screening; co-immunoprecipitation; homology modeling of CBS domains\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (topology assay, mutagenesis, Co-IP, modeling) in a single study\",\n      \"pmids\": [\"22399287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CNNM2 increases cellular Mg2+ uptake in HEK293 cells via regulation of the Mg2+-permeable cation channel TRPM7; disease-causing mutant CNNM2 proteins failed to increase Mg2+ uptake; knockdown of cnnm2 in zebrafish reduced body Mg content and caused neurodevelopmental defects rescuable by wild-type mammalian Cnnm2 cRNA.\",\n      \"method\": \"Stable Mg2+ isotope uptake assays in HEK293 cells; zebrafish morpholino knockdown with rescue by mammalian cRNA injection; behavioral assays\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (isotope uptake, genetic rescue in zebrafish), functional epistasis with TRPM7\",\n      \"pmids\": [\"24699222\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The intracellular Bateman (CBS) module of CNNM2 binds nucleotides (AMP, ADP, ATP) at one of its two cavities; Mg2+ facilitates ATP binding by alleviating charge repulsion; nucleotide binding triggers a conformational change from a twisted to a flat disc-like CBS dimer structure affecting elements connecting the Bateman module to the transmembrane region; the pathogenic mutation T568I mimics the nucleotide-bound flat conformation, locking the CBS module.\",\n      \"method\": \"X-ray crystallography of CNNM2 CBS domain fragment; structural comparison with/without nucleotides; analysis of T568I pathogenic mutant crystal structure\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with and without ligands, mutation structural analysis, mechanistic model validated by structural data\",\n      \"pmids\": [\"25184538\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PRL-1 phosphatase interacts with the intracellular Bateman module (CBS domains) of CNNM2, forming a heterotetrameric complex (disc-like homodimer of CNNM2-CBS bound to two PRL-1 molecules); Asp-558 at the extended loop of CNNM2 CBS2 is critical for this interaction; PRL-1 binding occurs via its catalytic domain.\",\n      \"method\": \"X-ray crystal structure of PRL-1 in complex with CNNM2 Bateman module; structure-based mutagenesis analysis of key interface residues\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure of protein complex with identified key interface residue\",\n      \"pmids\": [\"27899452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CNNM2 isoforms 1 and 2 do not transport Mg2+ in electrogenic or electroneutral mode in HEK293 cells, are not exclusively plasma membrane-localized, and both form higher-order protein complexes; isoform 1 has a much smaller spectrum of potential interactors than isoform 2, suggesting distinct functions.\",\n      \"method\": \"Patch-clamp and fluorescence-based Mg2+ transport assays in transgenic HEK293 cells; subcellular fractionation; co-immunoprecipitation/mass spectrometry interactome\",\n      \"journal\": \"Pflugers Archiv : European journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays, but contradicts other studies; single lab\",\n      \"pmids\": [\"27068403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Human CNNM2 splice variant 1 (isomorph 1), but not isomorph 2, complements the Mg2+-deficient growth of Salmonella MM281 (mgtA/mgtB/corA triple mutant) and mediates measurable Mg2+ influx, demonstrating that isoform 1 is a functional Mg2+-transporting entity.\",\n      \"method\": \"Genetic complementation assay in Salmonella MM281; Mg2+ influx measurement in bacteria\",\n      \"journal\": \"Magnesium research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional complementation with transport measurement, but in bacterial heterologous system\",\n      \"pmids\": [\"20519162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CNNM2 knockout mice exhibit mild hypomagnesemia and increased fecal Mg2+ and Ca2+ excretion, indicating a role for CNNM2 in intestinal Mg2+ absorption in addition to its renal function; homozygous knockout is largely lethal, with only rare live-born pups showing significantly lower serum Mg2+.\",\n      \"method\": \"CRISPR/Cas9 knockout mouse model; serum and fecal mineral analysis; dietary Mg2+ challenge\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined physiological phenotype and dietary intervention\",\n      \"pmids\": [\"33859252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The CNNM2 R480L mutation in the CBS domain impairs ATP-Mg2+ binding to CNNM2 and diminishes Mg2+ efflux, as shown by increased intracellular Mg2+ in cells expressing the mutant compared to wild-type.\",\n      \"method\": \"Mg2+ efflux assay in murine DCT cells; molecular simulation modeling of mutant CBS domain-ATP-Mg2+ interaction\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — functional efflux assay supported by structural simulation, single lab\",\n      \"pmids\": [\"35846113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Pathogenic mutations in CNNM2 result in decreased plasma membrane expression of the protein, suggesting that loss of proper membrane trafficking underlies loss of Mg2+ transport function.\",\n      \"method\": \"25Mg2+ uptake assays in HEK293 cells expressing mutant CNNM2; assessment of plasma membrane expression levels\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional uptake assay plus localization data, moderate evidence\",\n      \"pmids\": [\"33600043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Reduced Cnnm2 expression in mouse medial prefrontal cortex impairs cognition and sensorimotor gating; knockdown in primary cortical neurons alters dendritic spine morphogenesis; proteomics shows changed expression of proteins associated with neuronal structure and function.\",\n      \"method\": \"Viral-mediated Cnnm2 knockdown in mouse mPFC; behavioral assays; primary neuronal culture knockdown with proteomics\",\n      \"journal\": \"Neuropsychopharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD with defined cellular and behavioral phenotype, single lab\",\n      \"pmids\": [\"37715107\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Two novel CNNM2 variants (p.E298del and p.P360R) increase CNNM2 transcription and protein levels but impair proper localization to the cell membrane, causing cytoplasmic accumulation and reduced protein stability, resulting in elevated intracellular Mg2+ and disrupted Mg2+ efflux.\",\n      \"method\": \"qPCR, Western blotting, immunofluorescence, flow cytometry-based intracellular Mg2+ measurement in cells expressing mutant CNNM2\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple functional assays in a single study, single lab\",\n      \"pmids\": [\"40612795\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CNNM2 is a basolateral membrane protein in renal distal tubular cells (and potentially intestinal epithelium) that mediates Mg2+ efflux/transport through a mechanism involving its intracellular CBS/Bateman domain, which binds nucleotides (AMP/ADP/ATP) in a Mg2+-facilitated manner and undergoes conformational changes that regulate transporter activity; it forms homodimers and interacts with the PRL-1 phosphatase via its CBS2 domain, and with the Mg2+-permeable channel TRPM7, to regulate intracellular Mg2+ homeostasis, with disease-causing mutations impairing ATP binding, membrane targeting, or Mg2+ efflux capacity, and brain-specific roles in dendritic spine morphogenesis and neurodevelopment.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CNNM2 is a transmembrane protein that functions as a critical regulator of Mg²⁺ homeostasis in kidney, intestine, and brain by mediating Mg²⁺ transport across the basolateral membrane of epithelial cells. CNNM2 localizes to the basolateral membrane of renal distal tubular cells, where it mediates Mg²⁺ efflux regulated by nucleotide (ATP/ADP/AMP) binding to its intracellular CBS/Bateman domain; Mg²⁺ facilitates ATP binding, which triggers a conformational switch from a twisted to a flat CBS dimer that controls transporter activity [PMID:25184538, PMID:21397062, PMID:35846113]. The CBS2 domain also serves as a docking site for the PRL-1 phosphatase, forming a heterotetrameric complex, and CNNM2 functionally interacts with the Mg²⁺-permeable channel TRPM7 to regulate intracellular Mg²⁺ [PMID:27899452, PMID:24699222]. Pathogenic CNNM2 mutations cause hypomagnesemia by impairing ATP-Mg²⁺ binding, disrupting plasma membrane targeting, or locking the CBS module in an inactive conformation, and CNNM2 deficiency additionally impairs dendritic spine morphogenesis and cognition, linking it to neurodevelopmental phenotypes [PMID:33600043, PMID:25184538, PMID:37715107, PMID:33859252].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing that CNNM2 is a functional divalent cation transporter resolved the basic molecular activity of the protein, showing it mediates saturable, voltage-dependent Mg²⁺ uptake with broad divalent cation selectivity.\",\n      \"evidence\": \"Two-electrode voltage-clamp electrophysiology of mouse CNNM2 in Xenopus oocytes with kinetic characterization\",\n      \"pmids\": [\"15899945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transport mechanism (channel vs. carrier) not defined\", \"Physiological transport direction in native tissues not established\", \"Molecular determinants of ion selectivity unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating isoform-specific Mg²⁺ transport function revealed that CNNM2 splice variant 1, but not variant 2, is a functional Mg²⁺-transporting entity, indicating functional divergence among isoforms.\",\n      \"evidence\": \"Genetic complementation of Salmonella Mg²⁺-transport-deficient mutant MM281 with human CNNM2 isoforms\",\n      \"pmids\": [\"20519162\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Bacterial heterologous system may not recapitulate mammalian transport properties\", \"Mechanism underlying isoform difference not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Localizing CNNM2 to the basolateral membrane of renal distal tubules and showing that patient mutations diminish Mg²⁺-sensitive currents established the protein's physiological site of action and linked it to human hypomagnesemia.\",\n      \"evidence\": \"Immunolocalization in human kidney tissue; two-electrode voltage-clamp with disease-causing mutants\",\n      \"pmids\": [\"21397062\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CNNM2 mediates Mg²⁺ influx or efflux at the basolateral membrane was unresolved\", \"Identity of transported ion species in native tissue not confirmed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Determining the membrane topology of CNNM2—extracellular N-terminus, intracellular C-terminus with CBS domains, N-glycosylation at Asn-112 stabilizing surface expression, and heterodimerization of isoforms—defined the structural framework for understanding regulatory and transport mechanisms.\",\n      \"evidence\": \"Intramolecular epitope topology mapping, mutagenesis, co-immunoprecipitation in mammalian cells\",\n      \"pmids\": [\"22399287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length high-resolution structure unavailable\", \"Functional significance of heterodimerization not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Solving the crystal structure of the CBS/Bateman domain revealed that nucleotide binding (ATP/ADP/AMP) triggers a twisted-to-flat conformational switch that is facilitated by Mg²⁺ and transmitted toward the transmembrane region, providing the first structural mechanism for regulation of CNNM2 activity; the pathogenic T568I mutation mimics the nucleotide-bound conformation, explaining its loss of function.\",\n      \"evidence\": \"X-ray crystallography of CNNM2 CBS domain ± nucleotides and T568I mutant\",\n      \"pmids\": [\"25184538\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How conformational change couples to ion translocation through the transmembrane domain is unknown\", \"No full-length transporter structure\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showing that CNNM2 regulates Mg²⁺ uptake through the TRPM7 channel and that zebrafish cnnm2 knockdown causes Mg²⁺ depletion and neurodevelopmental defects established CNNM2 as an in vivo Mg²⁺ homeostasis regulator with roles beyond the kidney.\",\n      \"evidence\": \"²⁵Mg²⁺ uptake assays in HEK293 cells; zebrafish morpholino knockdown with mammalian rescue\",\n      \"pmids\": [\"24699222\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of CNNM2–TRPM7 functional interaction not defined\", \"Direction of CNNM2-dependent Mg²⁺ flux in native cells debated\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Solving the crystal structure of the PRL-1–CNNM2 Bateman module complex revealed a heterotetrameric architecture with Asp-558 as a critical interface residue, identifying a phosphatase-based regulatory input to the transporter.\",\n      \"evidence\": \"X-ray crystallography of PRL-1 bound to CNNM2 CBS domain; structure-guided mutagenesis\",\n      \"pmids\": [\"27899452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of PRL-1 binding on Mg²⁺ transport not directly measured\", \"Whether PRL-1 dephosphorylates CNNM2 or acts allosterically is unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"A challenge to the transport model reported that CNNM2 isoforms 1 and 2 did not mediate electrogenic or electroneutral Mg²⁺ transport in patch-clamp and fluorescence assays in HEK293 cells, suggesting CNNM2 may function as a regulator rather than a direct transporter.\",\n      \"evidence\": \"Patch-clamp and fluorescence Mg²⁺ assays in HEK293 cells stably expressing CNNM2 isoforms\",\n      \"pmids\": [\"27068403\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Contradicts oocyte electrophysiology data; discrepancy may reflect system-dependent differences\", \"Negative result in one cell type does not exclude transport in native tissue\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CNNM2 knockout mice confirmed that CNNM2 is required for systemic Mg²⁺ homeostasis in vivo and revealed a role in intestinal Mg²⁺ absorption in addition to renal reabsorption; homozygous knockout is largely lethal.\",\n      \"evidence\": \"CRISPR/Cas9 CNNM2 knockout mouse with serum and fecal mineral analysis\",\n      \"pmids\": [\"33859252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of intestinal vs. renal CNNM2 not deconvoluted\", \"Cause of lethality in homozygous KO not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that pathogenic mutations reduce CNNM2 plasma membrane expression provided a unifying trafficking-based mechanism for loss of Mg²⁺ transport across multiple disease variants.\",\n      \"evidence\": \"²⁵Mg²⁺ uptake assay and surface expression quantification in HEK293 cells expressing mutant CNNM2\",\n      \"pmids\": [\"33600043\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trafficking pathway and quality-control checkpoint that retains mutant CNNM2 not identified\", \"Not all known mutations tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The R480L CBS-domain mutation was shown to impair ATP-Mg²⁺ binding and diminish Mg²⁺ efflux, directly linking the nucleotide-sensing structural mechanism to the transport direction (efflux) in distal convoluted tubule cells.\",\n      \"evidence\": \"Mg²⁺ efflux assay in murine DCT cells with molecular dynamics simulation of mutant CBS domain\",\n      \"pmids\": [\"35846113\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single mutation study; generalizability to other CBS mutations not confirmed\", \"Efflux measurement in cultured DCT cells, not in intact epithelium\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Establishing that CNNM2 knockdown in mouse prefrontal cortex impairs cognition and alters dendritic spine morphogenesis expanded the functional role of CNNM2 beyond epithelial Mg²⁺ transport to neuronal structural plasticity.\",\n      \"evidence\": \"Viral Cnnm2 knockdown in mouse mPFC with behavioral testing; primary neuronal culture with proteomics\",\n      \"pmids\": [\"37715107\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether neuronal phenotype is Mg²⁺-dependent or reflects a distinct CNNM2 function is unknown\", \"Downstream neuronal targets not validated individually\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include whether CNNM2 is a direct Mg²⁺ transporter or an indirect regulator of Mg²⁺ channels, the full-length structure and ion translocation pathway, the functional consequence of PRL-1 binding on transport, and the molecular basis of CNNM2's neuronal functions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length CNNM2 structure or reconstituted transport in proteoliposomes\", \"Transport vs. regulator debate unresolved\", \"PRL-1 functional impact on Mg²⁺ flux not measured\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 7, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 2, 10, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PRL-1\", \"TRPM7\"],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I need to fix the pathway section - I used a GO term instead of Reactome. Let me reconsider.\n\n```json\n{\n  \"mechanistic_narrative\": \"CNNM2 is a transmembrane protein that functions as a critical regulator of Mg²⁺ homeostasis in kidney, intestine, and brain by mediating Mg²⁺ transport across the basolateral membrane of epithelial cells. CNNM2 localizes to the basolateral membrane of renal distal tubular cells, where it mediates Mg²⁺ efflux regulated by nucleotide (ATP/ADP/AMP) binding to its intracellular CBS/Bateman domain; Mg²⁺ facilitates ATP binding, which triggers a conformational switch from a twisted to a flat CBS dimer that controls transporter activity [PMID:25184538, PMID:21397062, PMID:35846113]. The CBS2 domain also serves as a docking site for the PRL-1 phosphatase, forming a heterotetrameric complex, and CNNM2 functionally interacts with the Mg²⁺-permeable channel TRPM7 to regulate intracellular Mg²⁺ [PMID:27899452, PMID:24699222]. Pathogenic CNNM2 mutations cause hypomagnesemia by impairing ATP-Mg²⁺ binding, disrupting plasma membrane targeting, or locking the CBS module in an inactive conformation, and CNNM2 deficiency additionally impairs dendritic spine morphogenesis and cognition, linking it to neurodevelopmental phenotypes [PMID:33600043, PMID:25184538, PMID:37715107, PMID:33859252].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing that CNNM2 is a functional divalent cation transporter resolved the basic molecular activity of the protein, showing it mediates saturable, voltage-dependent Mg²⁺ uptake with broad divalent cation selectivity.\",\n      \"evidence\": \"Two-electrode voltage-clamp electrophysiology of mouse CNNM2 in Xenopus oocytes with kinetic characterization\",\n      \"pmids\": [\"15899945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transport mechanism (channel vs. carrier) not defined\", \"Physiological transport direction in native tissues not established\", \"Molecular determinants of ion selectivity unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating isoform-specific Mg²⁺ transport function revealed that CNNM2 splice variant 1, but not variant 2, is a functional Mg²⁺-transporting entity, indicating functional divergence among isoforms.\",\n      \"evidence\": \"Genetic complementation of Salmonella Mg²⁺-transport-deficient mutant MM281 with human CNNM2 isoforms\",\n      \"pmids\": [\"20519162\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Bacterial heterologous system may not recapitulate mammalian transport properties\", \"Mechanism underlying isoform difference not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Localizing CNNM2 to the basolateral membrane of renal distal tubules and showing that patient mutations diminish Mg²⁺-sensitive currents established the protein's physiological site of action and linked it to human hypomagnesemia.\",\n      \"evidence\": \"Immunolocalization in human kidney tissue; two-electrode voltage-clamp with disease-causing mutants\",\n      \"pmids\": [\"21397062\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CNNM2 mediates Mg²⁺ influx or efflux at the basolateral membrane was unresolved\", \"Identity of transported ion species in native tissue not confirmed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Determining the membrane topology of CNNM2—extracellular N-terminus, intracellular C-terminus with CBS domains, N-glycosylation at Asn-112 stabilizing surface expression, and heterodimerization of isoforms—defined the structural framework for understanding regulatory and transport mechanisms.\",\n      \"evidence\": \"Intramolecular epitope topology mapping, mutagenesis, co-immunoprecipitation in mammalian cells\",\n      \"pmids\": [\"22399287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length high-resolution structure unavailable\", \"Functional significance of heterodimerization not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Solving the crystal structure of the CBS/Bateman domain revealed that nucleotide binding (ATP/ADP/AMP) triggers a twisted-to-flat conformational switch facilitated by Mg²⁺ and transmitted toward the transmembrane region, providing the first structural mechanism for regulation of CNNM2 activity; the pathogenic T568I mutation mimics the nucleotide-bound conformation.\",\n      \"evidence\": \"X-ray crystallography of CNNM2 CBS domain ± nucleotides and T568I mutant\",\n      \"pmids\": [\"25184538\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How conformational change couples to ion translocation through the transmembrane domain is unknown\", \"No full-length transporter structure\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showing that CNNM2 regulates Mg²⁺ uptake through the TRPM7 channel and that zebrafish cnnm2 knockdown causes Mg²⁺ depletion and neurodevelopmental defects established CNNM2 as an in vivo Mg²⁺ homeostasis regulator with roles beyond the kidney.\",\n      \"evidence\": \"²⁵Mg²⁺ uptake assays in HEK293 cells; zebrafish morpholino knockdown with mammalian rescue\",\n      \"pmids\": [\"24699222\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of CNNM2–TRPM7 functional interaction not defined\", \"Direction of CNNM2-dependent Mg²⁺ flux in native cells debated\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Solving the crystal structure of the PRL-1–CNNM2 Bateman module complex revealed a heterotetrameric architecture with Asp-558 as a critical interface residue, identifying a phosphatase-based regulatory input to the transporter.\",\n      \"evidence\": \"X-ray crystallography of PRL-1 bound to CNNM2 CBS domain; structure-guided mutagenesis\",\n      \"pmids\": [\"27899452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of PRL-1 binding on Mg²⁺ transport not directly measured\", \"Whether PRL-1 dephosphorylates CNNM2 or acts allosterically is unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"A challenge to the transport model reported that CNNM2 isoforms did not mediate electrogenic or electroneutral Mg²⁺ transport in patch-clamp and fluorescence assays in HEK293 cells, suggesting CNNM2 may function as a regulator rather than a direct transporter.\",\n      \"evidence\": \"Patch-clamp and fluorescence Mg²⁺ assays in HEK293 cells stably expressing CNNM2 isoforms\",\n      \"pmids\": [\"27068403\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Contradicts oocyte electrophysiology data; discrepancy may reflect system-dependent differences\", \"Negative result in one cell type does not exclude transport in native tissue\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CNNM2 knockout mice confirmed that CNNM2 is required for systemic Mg²⁺ homeostasis in vivo and revealed a role in intestinal Mg²⁺ absorption in addition to renal reabsorption; homozygous knockout is largely lethal.\",\n      \"evidence\": \"CRISPR/Cas9 CNNM2 knockout mouse with serum and fecal mineral analysis\",\n      \"pmids\": [\"33859252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of intestinal vs. renal CNNM2 not deconvoluted\", \"Cause of lethality in homozygous KO not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that pathogenic mutations reduce CNNM2 plasma membrane expression provided a unifying trafficking-based mechanism for loss of Mg²⁺ transport across multiple disease variants.\",\n      \"evidence\": \"²⁵Mg²⁺ uptake assay and surface expression quantification in HEK293 cells expressing mutant CNNM2\",\n      \"pmids\": [\"33600043\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trafficking pathway and quality-control checkpoint that retains mutant CNNM2 not identified\", \"Not all known mutations tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The R480L CBS-domain mutation was shown to impair ATP-Mg²⁺ binding and diminish Mg²⁺ efflux, directly linking the nucleotide-sensing structural mechanism to the transport direction (efflux) in distal convoluted tubule cells.\",\n      \"evidence\": \"Mg²⁺ efflux assay in murine DCT cells with molecular dynamics simulation of mutant CBS domain\",\n      \"pmids\": [\"35846113\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single mutation study; generalizability to other CBS mutations not confirmed\", \"Efflux measurement in cultured DCT cells, not in intact epithelium\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Establishing that CNNM2 knockdown in mouse prefrontal cortex impairs cognition and alters dendritic spine morphogenesis expanded the functional role of CNNM2 beyond epithelial Mg²⁺ transport to neuronal structural plasticity.\",\n      \"evidence\": \"Viral Cnnm2 knockdown in mouse mPFC with behavioral testing; primary neuronal culture with proteomics\",\n      \"pmids\": [\"37715107\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether neuronal phenotype is Mg²⁺-dependent or reflects a distinct CNNM2 function is unknown\", \"Downstream neuronal targets not validated individually\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include whether CNNM2 is a direct Mg²⁺ transporter or an indirect regulator of Mg²⁺ channels, the full-length structure and ion translocation pathway, the functional consequence of PRL-1 binding on transport, and the molecular basis of CNNM2's neuronal functions.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length CNNM2 structure or reconstituted transport in proteoliposomes\", \"Transport vs. regulator debate unresolved\", \"PRL-1 functional impact on Mg²⁺ flux not measured\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 7, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 2, 10, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1, 3, 8, 9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PRL-1\", \"TRPM7\"],\n    \"other_free_text\": []\n  }\n}\n```"}