{"gene":"MMGT1","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2007,"finding":"MMgT1 (MMGT1) is a small integral membrane protein of 131 amino acids with two predicted transmembrane domains that mediates saturable Mg2+ transport when expressed in Xenopus laevis oocytes, with a Michaelis constant of 1.47 ± 0.17 mM. Its mRNA is upregulated approximately threefold in kidney epithelial cells and kidney cortex under low-magnesium conditions.","method":"Two-electrode voltage-clamp analysis and fluorescence measurements in Xenopus oocytes; real-time RT-PCR; Michaelis-Menten kinetic analysis","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution in oocyte system with quantitative kinetics and multiple orthogonal methods","pmids":["18057121"],"is_preprint":false},{"year":2007,"finding":"MMgT1 protein localizes to the Golgi complex and post-Golgi vesicles, including early endosomes, in COS-7 cells expressing HA-tagged MMgT1. MMgT1 and MMgT2 are found in separate populations of post-Golgi vesicles, suggesting distinct vesicular trafficking pathways for each transporter.","method":"Immunohistochemistry with HA-tagged fusion protein in transfected COS-7 cells; subcellular fractionation","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 3 — direct localization by immunofluorescence in transfected cells, single lab, single method","pmids":["18057121"],"is_preprint":false},{"year":2023,"finding":"MMGT1 loss-of-function in macrophages promotes a switch of Mycobacterium tuberculosis from active replication to a persistence state. MMGT1-deficient macrophages upregulate lipid metabolism genes and accumulate lipid droplets during Mtb infection; targeting triacylglycerol synthesis reduces both lipid droplet formation and Mtb persistence. The orphan G protein-coupled receptor GPR156 is identified as a key inducer of lipid droplet accumulation downstream of MMGT1 loss.","method":"Genome-wide CRISPR screen; MMGT1-knockout macrophages; multi-fluorescent Mtb reporter strain; siRNA knockdown; triacylglycerol synthesis inhibition; host transcriptome analysis of infected macrophages","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 — genome-wide CRISPR screen with targeted mechanistic validation, multiple orthogonal functional readouts in a single rigorous study","pmids":["37269834"],"is_preprint":false}],"current_model":"MMGT1 encodes a small two-transmembrane-domain Mg2+ transporter that resides in the Golgi and post-Golgi vesicles, mediates saturable Mg2+ uptake, and in macrophages suppresses lipid droplet accumulation via a GPR156-dependent pathway; loss of MMGT1 promotes Mycobacterium tuberculosis persistence by upregulating lipid metabolism and triacylglycerol-dependent lipid droplet formation."},"narrative":{"teleology":[{"year":2007,"claim":"Identification of MMGT1 as a bona fide Mg²⁺ transporter resolved the molecular identity of an intracellular magnesium uptake pathway and established its kinetic parameters and transcriptional regulation by magnesium availability.","evidence":"Two-electrode voltage clamp and fluorescence-based Mg²⁺ uptake in Xenopus oocytes; RT-PCR of kidney epithelial cells under low-Mg conditions","pmids":["18057121"],"confidence":"High","gaps":["No crystal or cryo-EM structure to define the ion permeation pathway","Physiological role of MMGT1-mediated Mg²⁺ transport in native tissues not established by knockout or knockdown","Selectivity for Mg²⁺ over other divalent cations not fully characterized"]},{"year":2007,"claim":"Localization of MMGT1 to the Golgi and post-Golgi vesicles (including early endosomes) established that this transporter operates in endomembrane compartments rather than at the plasma membrane, distinguishing it from classical surface Mg²⁺ channels.","evidence":"Immunofluorescence of HA-tagged MMGT1 in transfected COS-7 cells with organelle markers","pmids":["18057121"],"confidence":"Medium","gaps":["Localization based on overexpressed tagged protein in a single cell line; endogenous localization not confirmed","Functional significance of Golgi/vesicular Mg²⁺ transport not tested","Whether MMGT1 also traffics to the ER (consistent with its EMC5 designation) was not examined"]},{"year":2023,"claim":"A genome-wide CRISPR screen in macrophages revealed that MMGT1 loss promotes Mycobacterium tuberculosis persistence by upregulating lipid metabolism and lipid droplet formation through a GPR156-dependent pathway, linking MMGT1 function to host innate immune control of intracellular pathogens.","evidence":"CRISPR screen in macrophages with multi-fluorescent Mtb reporter; MMGT1-KO macrophages; siRNA knockdown of GPR156; triacylglycerol synthesis inhibition; host transcriptomics","pmids":["37269834"],"confidence":"High","gaps":["Whether the lipid-droplet phenotype is a direct consequence of impaired Mg²⁺ transport or an independent function of MMGT1 is unknown","Mechanism connecting MMGT1 to GPR156 signaling not defined","In vivo relevance of MMGT1-dependent Mtb persistence not tested in animal models"]},{"year":null,"claim":"The relationship between MMGT1's Mg²⁺ transport activity, its reported EMC5 identity as a subunit of the ER membrane protein complex, and its role in lipid metabolism/pathogen persistence remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No study has tested whether MMGT1 functions as part of the EMC in the context of membrane protein insertion","Structural basis of MMGT1 ion transport and potential dual functionality is entirely unknown","Whether Mg²⁺ homeostasis mechanistically links to the lipid-droplet accumulation phenotype has not been examined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[1]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2]}],"complexes":[],"partners":["GPR156"],"other_free_text":[]},"mechanistic_narrative":"MMGT1 (also designated ER membrane protein complex subunit 5) is a small, two-transmembrane-domain integral membrane protein that mediates saturable Mg²⁺ transport with a Km of ~1.5 mM, as demonstrated by reconstitution in Xenopus oocytes, and its transcript is upregulated under low-magnesium conditions in kidney epithelial cells [PMID:18057121]. The protein localizes to the Golgi complex and post-Golgi vesicles, including early endosomes, where it occupies vesicular compartments distinct from its paralog MMgT2 [PMID:18057121]. In macrophages, MMGT1 loss-of-function upregulates lipid metabolism genes and drives triacylglycerol-dependent lipid droplet accumulation via the orphan receptor GPR156, creating a metabolic environment that shifts Mycobacterium tuberculosis from active replication to a persistence state [PMID:37269834]."},"prefetch_data":{"uniprot":{"accession":"Q8N4V1","full_name":"ER membrane protein complex subunit 5","aliases":["Membrane magnesium transporter 1","Transmembrane protein 32"],"length_aa":131,"mass_kda":14.7,"function":"Part of the endoplasmic reticulum membrane protein complex (EMC) that enables the energy-independent insertion into endoplasmic reticulum membranes of newly synthesized membrane proteins (PubMed:29242231, PubMed:29809151, PubMed:30415835, PubMed:32439656, PubMed:32459176). Preferentially accommodates proteins with transmembrane domains that are weakly hydrophobic or contain destabilizing features such as charged and aromatic residues (PubMed:29242231, PubMed:29809151, PubMed:30415835). Involved in the cotranslational insertion of multi-pass membrane proteins in which stop-transfer membrane-anchor sequences become ER membrane spanning helices (PubMed:29809151, PubMed:30415835). It is also required for the post-translational insertion of tail-anchored/TA proteins in endoplasmic reticulum membranes (PubMed:29242231, PubMed:29809151). By mediating the proper cotranslational insertion of N-terminal transmembrane domains in an N-exo topology, with translocated N-terminus in the lumen of the ER, controls the topology of multi-pass membrane proteins like the G protein-coupled receptors (PubMed:30415835). By regulating the insertion of various proteins in membranes, it is indirectly involved in many cellular processes (By similarity). May be involved in Mg(2+) transport (By similarity)","subcellular_location":"Endoplasmic reticulum membrane; Golgi apparatus membrane; Early endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q8N4V1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MMGT1","classification":"Not Classified","n_dependent_lines":500,"n_total_lines":1208,"dependency_fraction":0.4139072847682119},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000169446","cell_line_id":"CID001519","localizations":[{"compartment":"er","grade":3}],"interactors":[{"gene":"EMC2","stoichiometry":0.2},{"gene":"EMC4","stoichiometry":0.2},{"gene":"EMC7","stoichiometry":0.2},{"gene":"EMC1","stoichiometry":0.2},{"gene":"LBR","stoichiometry":0.2},{"gene":"EMC3","stoichiometry":0.2},{"gene":"CCDC47","stoichiometry":0.2},{"gene":"NDUFA3","stoichiometry":0.2},{"gene":"TMEM33","stoichiometry":0.2},{"gene":"GCSH","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001519","total_profiled":1310},"omim":[{"mim_id":"620273","title":"ENDOPLASMIC RETICULUM MEMBRANE PROTEIN COMPLEX, SUBUNIT 3; EMC3","url":"https://www.omim.org/entry/620273"},{"mim_id":"620261","title":"ENDOPLASMIC RETICULUM MEMBRANE PROTEIN COMPLEX, SUBUNIT 6; EMC6","url":"https://www.omim.org/entry/620261"},{"mim_id":"301098","title":"MEMBRANE MAGNESIUM TRANSPORTER 1; MMGT1","url":"https://www.omim.org/entry/301098"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MMGT1"},"hgnc":{"alias_symbol":["EMC5"],"prev_symbol":["TMEM32"]},"alphafold":{"accession":"Q8N4V1","domains":[{"cath_id":"1.10.287","chopping":"2-67","consensus_level":"medium","plddt":91.6438,"start":2,"end":67}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N4V1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N4V1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N4V1-F1-predicted_aligned_error_v6.png","plddt_mean":79.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MMGT1","jax_strain_url":"https://www.jax.org/strain/search?query=MMGT1"},"sequence":{"accession":"Q8N4V1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8N4V1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8N4V1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N4V1"}},"corpus_meta":[{"pmid":"32494008","id":"PMC_32494008","title":"Structure of the ER membrane complex, a transmembrane-domain insertase.","date":"2020","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/32494008","citation_count":108,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"18057121","id":"PMC_18057121","title":"Identification and characterization of a novel family of membrane magnesium transporters, MMgT1 and MMgT2.","date":"2007","source":"American journal of physiology. 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Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct functional transport assay with electrophysiology and fluorescence in heterologous expression system\",\n      \"pmids\": [\"18057121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"MMgT1 protein localizes to the Golgi complex and post-Golgi vesicles, including early endosomes, in COS-7 cells expressing MMgT1-HA fusion protein; its expression in these compartments increases upon low-Mg2+ conditions.\",\n      \"method\": \"Immunohistochemistry with HA-tagged fusion protein in COS-7 cells; RT-PCR for mRNA quantification\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment with tagged construct, with functional correlation to Mg2+ availability\",\n      \"pmids\": [\"18057121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"MMgT1 mRNA and protein are upregulated approximately threefold in kidney epithelial cells cultured in low-magnesium media and in kidney cortex of mice on low-magnesium diets, indicating transcriptional regulation by extracellular Mg2+ levels.\",\n      \"method\": \"Microarray analysis, real-time RT-PCR, immunohistochemistry in kidney epithelial cells and mouse kidney cortex\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods (microarray, RT-PCR, IHC) in both in vitro and in vivo models\",\n      \"pmids\": [\"18057121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MMGT1 deficiency in macrophages promotes a switch of Mycobacterium tuberculosis to a persistence state, accompanied by upregulation of lipid metabolism genes and accumulation of lipid droplets; the orphan GPCR GPR156 is identified as a key downstream inducer of lipid droplet accumulation in MMGT1-deficient cells, and targeting triacylglycerol synthesis reduces both droplet formation and Mtb persistence.\",\n      \"method\": \"Genome-wide CRISPR screen, MMGT1-knockout macrophages, multi-fluorescent Mtb reporter strain, lipid droplet quantification, siRNA/pharmacological inhibition of triacylglycerol synthesis\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR KO with defined cellular phenotype, mechanistic validation via GPR156 and triacylglycerol synthesis targeting, multiple orthogonal approaches\",\n      \"pmids\": [\"37269834\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MMGT1 is a two-transmembrane-domain magnesium transporter that localizes to the Golgi and post-Golgi vesicles and mediates saturable Mg2+ uptake; its expression is upregulated by low extracellular Mg2+, and in macrophages it suppresses a GPR156-driven lipid droplet accumulation pathway that otherwise promotes Mycobacterium tuberculosis persistence.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries from KEEP papers.\n\n**Classification:**\n\n- [Corpus paper 1] PMID:32494008 — EMC structure (yeast/cryo-EM). EMC subunits include Emc5 (MMGT1 ortholog in yeast). KEEP as ortholog context, but need to verify if Emc5 = MMGT1. Emc5 is the yeast ortholog of human EMC5, not MMGT1. MMGT1 encodes the membrane Mg2+ transporter 1, not an EMC subunit. EXCLUDE — symbol/function collision.\n\n- [Corpus paper 2] PMID:18057121 — Directly characterizes MMgT1 and MMgT2 as membrane Mg2+ transporters. KEEP.\n\n- [Corpus paper 3] PMID:33356397 — Mentions Mmgt1 mRNA upregulation in pulmonary hypertension context, but no direct mechanistic experiment on MMGT1 protein itself. Expression correlation only. EXCLUDE.\n\n- [Corpus paper 4] PMID:8034755 — \"MMGT1\" here is a murine microglial cell line name, not the gene MMGT1. ALIAS COLLISION — EXCLUDE.\n\n- [Corpus paper 5] PMID:31263175 — About EMC3/5/6 in Drosophila/mice for rhodopsin biosynthesis. Not about MMGT1. EXCLUDE.\n\n- [Corpus paper 6] PMID:37269834 — Directly investigates MMGT1 gene in macrophages, Mtb persistence, lipid droplets, GPR156. KEEP.\n\n- All gene2pubmed additional papers: Large interactome/proteome datasets (BioPlex, BioID, HuRI, etc.) — these may contain MMGT1 as a protein in a network but describe no specific mechanistic findings about MMGT1. EXCLUDE or no extractable MMGT1-specific mechanism. The EMC-related papers (PMIDs 29242231, 30415835, 29809151, 32439656) are about EMC complex subunits, not MMGT1. EXCLUDE.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"MMgT1 (MMGT1) is a small integral membrane protein of 131 amino acids with two predicted transmembrane domains that mediates saturable Mg2+ transport when expressed in Xenopus laevis oocytes, with a Michaelis constant of 1.47 ± 0.17 mM. Its mRNA is upregulated approximately threefold in kidney epithelial cells and kidney cortex under low-magnesium conditions.\",\n      \"method\": \"Two-electrode voltage-clamp analysis and fluorescence measurements in Xenopus oocytes; real-time RT-PCR; Michaelis-Menten kinetic analysis\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution in oocyte system with quantitative kinetics and multiple orthogonal methods\",\n      \"pmids\": [\"18057121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"MMgT1 protein localizes to the Golgi complex and post-Golgi vesicles, including early endosomes, in COS-7 cells expressing HA-tagged MMgT1. MMgT1 and MMgT2 are found in separate populations of post-Golgi vesicles, suggesting distinct vesicular trafficking pathways for each transporter.\",\n      \"method\": \"Immunohistochemistry with HA-tagged fusion protein in transfected COS-7 cells; subcellular fractionation\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — direct localization by immunofluorescence in transfected cells, single lab, single method\",\n      \"pmids\": [\"18057121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MMGT1 loss-of-function in macrophages promotes a switch of Mycobacterium tuberculosis from active replication to a persistence state. MMGT1-deficient macrophages upregulate lipid metabolism genes and accumulate lipid droplets during Mtb infection; targeting triacylglycerol synthesis reduces both lipid droplet formation and Mtb persistence. The orphan G protein-coupled receptor GPR156 is identified as a key inducer of lipid droplet accumulation downstream of MMGT1 loss.\",\n      \"method\": \"Genome-wide CRISPR screen; MMGT1-knockout macrophages; multi-fluorescent Mtb reporter strain; siRNA knockdown; triacylglycerol synthesis inhibition; host transcriptome analysis of infected macrophages\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide CRISPR screen with targeted mechanistic validation, multiple orthogonal functional readouts in a single rigorous study\",\n      \"pmids\": [\"37269834\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MMGT1 encodes a small two-transmembrane-domain Mg2+ transporter that resides in the Golgi and post-Golgi vesicles, mediates saturable Mg2+ uptake, and in macrophages suppresses lipid droplet accumulation via a GPR156-dependent pathway; loss of MMGT1 promotes Mycobacterium tuberculosis persistence by upregulating lipid metabolism and triacylglycerol-dependent lipid droplet formation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MMGT1 is a membrane magnesium transporter that mediates saturable Mg²⁺ uptake (Km ~1.5 mM), localizes to the Golgi complex and post-Golgi vesicles including early endosomes, and is transcriptionally upregulated under low-magnesium conditions in both kidney epithelial cells and mouse kidney cortex [PMID:18057121]. In macrophages, MMGT1 deficiency drives lipid droplet accumulation through upregulation of the orphan GPCR GPR156, creating a metabolic environment that promotes Mycobacterium tuberculosis persistence; inhibition of triacylglycerol synthesis reverses both lipid droplet formation and bacterial persistence [PMID:37269834].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"The molecular identity of MMGT1 as a functional magnesium transporter was established, resolving whether this previously uncharacterized membrane protein contributes to Mg²⁺ homeostasis.\",\n      \"evidence\": \"Two-electrode voltage-clamp and fluorescence Mg²⁺ measurements in Xenopus oocytes expressing MMGT1 demonstrated saturable Mg²⁺ uptake with Km of ~1.5 mM\",\n      \"pmids\": [\"18057121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Transport mechanism (channel vs. carrier) not determined\",\n        \"No structure available to explain selectivity or gating\",\n        \"Endogenous transport contribution not isolated from other Mg²⁺ transporters\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"MMGT1 was placed in the Golgi/post-Golgi vesicle compartment and shown to be transcriptionally responsive to magnesium deprivation, linking its expression to systemic Mg²⁺ sensing in kidney.\",\n      \"evidence\": \"HA-tagged MMGT1 localized to Golgi and early endosomes in COS-7 cells; mRNA/protein upregulated ~3-fold in low-Mg²⁺ cultured kidney cells and mouse kidney cortex by microarray, RT-PCR, and immunohistochemistry\",\n      \"pmids\": [\"18057121\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Localization relied on overexpressed tagged construct; endogenous localization not confirmed\",\n        \"Transcriptional regulatory elements mediating Mg²⁺-responsive expression not identified\",\n        \"Functional consequence of Golgi Mg²⁺ transport for organelle biology unknown\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A genome-wide CRISPR screen in macrophages revealed that MMGT1 loss promotes Mycobacterium tuberculosis persistence by inducing GPR156-dependent lipid droplet accumulation, establishing an unexpected connection between intracellular Mg²⁺ transport and host lipid metabolism during infection.\",\n      \"evidence\": \"CRISPR knockout of MMGT1 in macrophages combined with multi-fluorescent Mtb reporter, lipid droplet quantification, and pharmacological/siRNA inhibition of triacylglycerol synthesis\",\n      \"pmids\": [\"37269834\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How Mg²⁺ transport deficiency activates GPR156 expression is unknown\",\n        \"Whether the lipid droplet phenotype is cell-type specific or generalizable beyond macrophages is untested\",\n        \"Direct physical or signaling link between MMGT1 and GPR156 not established\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The transport mechanism (channel vs. carrier), structural basis of Mg²⁺ selectivity, and the signaling pathway connecting intracellular Mg²⁺ homeostasis to GPR156-driven lipid metabolism remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural model of MMGT1\",\n        \"No reconstitution in proteoliposomes to confirm direct transport\",\n        \"Mechanism linking Mg²⁺ depletion to GPR156 transcriptional upregulation uncharacterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0382551\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"GPR156\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait, I need to fix the pathway entry. \"GO:0382551\" is not valid — the correct ID is \"R-HSA-382551\". Let me correct:\n\n```json\n{\n  \"mechanistic_narrative\": \"MMGT1 is a membrane magnesium transporter that mediates saturable Mg²⁺ uptake (Km ~1.5 mM), localizes to the Golgi complex and post-Golgi vesicles including early endosomes, and is transcriptionally upregulated under low-magnesium conditions in both kidney epithelial cells and mouse kidney cortex [PMID:18057121]. In macrophages, MMGT1 deficiency drives lipid droplet accumulation through upregulation of the orphan GPCR GPR156, creating a metabolic environment that promotes Mycobacterium tuberculosis persistence; inhibition of triacylglycerol synthesis reverses both lipid droplet formation and bacterial persistence [PMID:37269834].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"The molecular identity of MMGT1 as a functional magnesium transporter was established, resolving whether this previously uncharacterized membrane protein contributes to Mg²⁺ homeostasis.\",\n      \"evidence\": \"Two-electrode voltage-clamp and fluorescence Mg²⁺ measurements in Xenopus oocytes expressing MMGT1 demonstrated saturable Mg²⁺ uptake with Km of ~1.5 mM\",\n      \"pmids\": [\"18057121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Transport mechanism (channel vs. carrier) not determined\",\n        \"No structure available to explain selectivity or gating\",\n        \"Endogenous transport contribution not isolated from other Mg²⁺ transporters\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"MMGT1 was placed in the Golgi/post-Golgi vesicle compartment and shown to be transcriptionally responsive to magnesium deprivation, linking its expression to systemic Mg²⁺ sensing in kidney.\",\n      \"evidence\": \"HA-tagged MMGT1 localized to Golgi and early endosomes in COS-7 cells; mRNA/protein upregulated ~3-fold in low-Mg²⁺ cultured kidney cells and mouse kidney cortex by microarray, RT-PCR, and immunohistochemistry\",\n      \"pmids\": [\"18057121\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Localization relied on overexpressed tagged construct; endogenous localization not confirmed\",\n        \"Transcriptional regulatory elements mediating Mg²⁺-responsive expression not identified\",\n        \"Functional consequence of Golgi Mg²⁺ transport for organelle biology unknown\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A genome-wide CRISPR screen in macrophages revealed that MMGT1 loss promotes Mycobacterium tuberculosis persistence by inducing GPR156-dependent lipid droplet accumulation, establishing an unexpected connection between intracellular Mg²⁺ transport and host lipid metabolism during infection.\",\n      \"evidence\": \"CRISPR knockout of MMGT1 in macrophages combined with multi-fluorescent Mtb reporter, lipid droplet quantification, and pharmacological/siRNA inhibition of triacylglycerol synthesis\",\n      \"pmids\": [\"37269834\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How Mg²⁺ transport deficiency activates GPR156 expression is unknown\",\n        \"Whether the lipid droplet phenotype is cell-type specific or generalizable beyond macrophages is untested\",\n        \"Direct physical or signaling link between MMGT1 and GPR156 not established\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The transport mechanism (channel vs. carrier), structural basis of Mg²⁺ selectivity, and the signaling pathway connecting intracellular Mg²⁺ homeostasis to GPR156-driven lipid metabolism remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural model of MMGT1\",\n        \"No reconstitution in proteoliposomes to confirm direct transport\",\n        \"Mechanism linking Mg²⁺ depletion to GPR156 transcriptional upregulation uncharacterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"GPR156\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"MMGT1 (also designated ER membrane protein complex subunit 5) is a small, two-transmembrane-domain integral membrane protein that mediates saturable Mg²⁺ transport with a Km of ~1.5 mM, as demonstrated by reconstitution in Xenopus oocytes, and its transcript is upregulated under low-magnesium conditions in kidney epithelial cells [PMID:18057121]. The protein localizes to the Golgi complex and post-Golgi vesicles, including early endosomes, where it occupies vesicular compartments distinct from its paralog MMgT2 [PMID:18057121]. In macrophages, MMGT1 loss-of-function upregulates lipid metabolism genes and drives triacylglycerol-dependent lipid droplet accumulation via the orphan receptor GPR156, creating a metabolic environment that shifts Mycobacterium tuberculosis from active replication to a persistence state [PMID:37269834].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Identification of MMGT1 as a bona fide Mg²⁺ transporter resolved the molecular identity of an intracellular magnesium uptake pathway and established its kinetic parameters and transcriptional regulation by magnesium availability.\",\n      \"evidence\": \"Two-electrode voltage clamp and fluorescence-based Mg²⁺ uptake in Xenopus oocytes; RT-PCR of kidney epithelial cells under low-Mg conditions\",\n      \"pmids\": [\"18057121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No crystal or cryo-EM structure to define the ion permeation pathway\",\n        \"Physiological role of MMGT1-mediated Mg²⁺ transport in native tissues not established by knockout or knockdown\",\n        \"Selectivity for Mg²⁺ over other divalent cations not fully characterized\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Localization of MMGT1 to the Golgi and post-Golgi vesicles (including early endosomes) established that this transporter operates in endomembrane compartments rather than at the plasma membrane, distinguishing it from classical surface Mg²⁺ channels.\",\n      \"evidence\": \"Immunofluorescence of HA-tagged MMGT1 in transfected COS-7 cells with organelle markers\",\n      \"pmids\": [\"18057121\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Localization based on overexpressed tagged protein in a single cell line; endogenous localization not confirmed\",\n        \"Functional significance of Golgi/vesicular Mg²⁺ transport not tested\",\n        \"Whether MMGT1 also traffics to the ER (consistent with its EMC5 designation) was not examined\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A genome-wide CRISPR screen in macrophages revealed that MMGT1 loss promotes Mycobacterium tuberculosis persistence by upregulating lipid metabolism and lipid droplet formation through a GPR156-dependent pathway, linking MMGT1 function to host innate immune control of intracellular pathogens.\",\n      \"evidence\": \"CRISPR screen in macrophages with multi-fluorescent Mtb reporter; MMGT1-KO macrophages; siRNA knockdown of GPR156; triacylglycerol synthesis inhibition; host transcriptomics\",\n      \"pmids\": [\"37269834\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the lipid-droplet phenotype is a direct consequence of impaired Mg²⁺ transport or an independent function of MMGT1 is unknown\",\n        \"Mechanism connecting MMGT1 to GPR156 signaling not defined\",\n        \"In vivo relevance of MMGT1-dependent Mtb persistence not tested in animal models\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The relationship between MMGT1's Mg²⁺ transport activity, its reported EMC5 identity as a subunit of the ER membrane protein complex, and its role in lipid metabolism/pathogen persistence remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No study has tested whether MMGT1 functions as part of the EMC in the context of membrane protein insertion\",\n        \"Structural basis of MMGT1 ion transport and potential dual functionality is entirely unknown\",\n        \"Whether Mg²⁺ homeostasis mechanistically links to the lipid-droplet accumulation phenotype has not been examined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"GPR156\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}