{"gene":"SLC30A6","run_date":"2026-06-10T07:46:33","timeline":{"discoveries":[{"year":2002,"finding":"ZnT6 (SLC30A6) localizes to the trans-Golgi network and vesicular compartments (overlapping with TGN38 and transferrin receptor) in normal rat kidney cells, and its intracellular distribution is regulated by zinc levels. Overexpression in wild-type yeast causes growth inhibition, consistent with a zinc transport function that moves cytoplasmic zinc into the Golgi/vesicular compartment.","method":"Overexpression in yeast growth assays, immunofluorescence co-localization with TGN38 and transferrin receptor in NRK cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with functional consequence (yeast growth inhibition), single lab, two orthogonal methods","pmids":["11997387"],"is_preprint":false},{"year":2005,"finding":"ZnT5 and ZnT6 form hetero-oligomers (but not homo-oligomers with each other) that constitute one of two distinct zinc transport complexes in the secretory pathway required for activation of alkaline phosphatases; ZnT7 operates independently as homo-oligomers. The Ser-rich loop of ZnT6 is dispensable for the zinc-supplying function of the ZnT5/ZnT6 hetero-oligomer, suggesting the His-rich loop of ZnT5 provides zinc-binding activity, while ZnT6's loop may serve a structural role in hetero-oligomer formation.","method":"Gene targeting in chicken DT40 cells, co-immunoprecipitation, alkaline phosphatase activity assays, transgene re-expression rescue experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, genetic epistasis via DT40 knockout/rescue, ALP functional assay; replicated across multiple labs","pmids":["15994300"],"is_preprint":false},{"year":2005,"finding":"ZnT5 and ZnT6, mammalian homologues of yeast Msc2p and Zrg17p respectively, functionally interact and form a heteromeric zinc transport complex in the secretory pathway, paralleling the Msc2p/Zrg17p ER zinc transport complex in Saccharomyces cerevisiae.","method":"Co-immunoprecipitation, yeast genetic complementation, functional interaction assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and functional interaction data, single lab, cross-species validation","pmids":["15961382"],"is_preprint":false},{"year":2006,"finding":"ZnT5/ZnT6 hetero-oligomeric complexes in the secretory pathway are required for zinc loading of alkaline phosphatase; in ZnT5−/ZnT7−/− cells, inactive alkaline phosphatase is degraded via proteasome-mediated degradation without trafficking to the plasma membrane, revealing that zinc loading prevents proteasomal degradation of the enzyme.","method":"DT40 gene-targeting knockouts, ALP activity assays, proteasome inhibitor experiments, unfolded protein response assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with defined cellular phenotype (ALP degradation, UPR), multiple orthogonal assays, replicated in same system","pmids":["16636052"],"is_preprint":false},{"year":2009,"finding":"ZnT5 and ZnT6 form heterodimers (not larger complexes) in the early secretory pathway. Mutagenesis showed that the conserved hydrophilic residues in transmembrane domains II and V of ZnT6 are not involved in zinc binding (unlike in homo-oligomeric CDF members). The cytosolic C-terminal tail of ZnT5 determines ZnT6 as its heterodimerization partner. The long N-terminal half of ZnT5 is dispensable for functional interaction with ZnT6.","method":"Co-immunoprecipitation, mutagenesis, chimera studies in DT40 cells deficient in ZnT5/ZnT6/ZnT7","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with Co-IP and functional rescue, multiple orthogonal methods in single rigorous study","pmids":["19759014"],"is_preprint":false},{"year":2011,"finding":"TNAP is activated via a two-step mechanism: first, ZnT5/ZnT6 heterodimers stabilize TNAP as an apo-form (protein stabilization step independent of zinc transport); second, ZNT complexes load zinc to convert apo-TNAP to holo-TNAP. Expression of ZnT5/ZnT6 heterodimers reconstituted with a zinc transport-incompetent ZnT5 mutant stabilized TNAP protein as an apo-form but failed to restore TNAP activity, demonstrating that protein stabilization and zinc loading are separable functions.","method":"Gene disruption/re-expression in DT40 cells, zinc transport-incompetent ZnT5 mutants, ALP activity assays, zinc supplementation experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis separating two mechanistic steps, genetic rescue experiments, multiple orthogonal assays; replicated across labs","pmids":["21402707"],"is_preprint":false},{"year":2014,"finding":"ZnT5 and ZnT6 form heterodimers in situ in live cells, as directly visualized by bimolecular fluorescence complementation (BiFC). The BiFC signal from ZnT5-YC and ZnT6-YN co-transfection confirmed heterodimerization with subcellular compartment-appropriate localization, and the dimerized complex was functionally active as assessed by Zinquin fluorescent zinc probe.","method":"Bimolecular fluorescence complementation (BiFC) in live cells, Zinquin zinc probe functional assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct visualization of protein-protein interaction in live cells with functional validation, single lab","pmids":["24451381"],"is_preprint":false},{"year":2016,"finding":"ZnT5/ZnT6 heterodimers and ZnT7 homodimers activate cancer-promoting zinc-requiring ectoenzymes—autotaxin (ATX), matrix metalloproteinase 9 (MMP9), and carbonic anhydrase IX (CAIX)—via zinc metalation in the early secretory pathway. MMP9 required both ZnT complexes for secretion as well as activation; CAIX was additionally activated by ZnT4 homodimers. ATX followed a similar two-step activation mechanism as TNAP but with different protein stability regulation.","method":"DT40 gene-disruption mutants, activity assays for ATX, MMP9, CAIX; secretion assays; transgene re-expression","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with multiple functional readouts across three ectoenzymes, genetic rescue, multiple orthogonal assays","pmids":["28028180"],"is_preprint":false},{"year":2016,"finding":"The di-proline (PP) motif in luminal loop 2 of ZnT5 is important for TNAP activation by ZnT5/ZnT6 heterodimers. PP-to-AA mutation in ZnT5 reduced TNAP activation by ~90% without significantly impairing zinc transport activity of ZnT7, indicating the PP-motif is involved in the TNAP maturation/stabilization process rather than zinc transport per se.","method":"Site-directed mutagenesis of ZnT5 PP motif, DT40 TKO cell rescue assays, ALP activity assays, apo-to-holo conversion assays","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis dissecting function from transport activity, genetic rescue in defined mutant cells, multiple functional assays","pmids":["27303047"],"is_preprint":false},{"year":2020,"finding":"ZnT5 recruits ZnT6 to the Golgi apparatus to form the heterodimeric complex (ZnT5 recruits ZnT6), revealing a previously unrecognized spatial regulation of ZnT5/ZnT6 heterodimer formation. In human HAP1 cells lacking both ZnT5 and ZnT7, TNAP activation is impaired, confirming conservation of the two-complex activation mechanism in human cells.","method":"Genetic disruption of ZnT5 and ZnT7 in human HAP1 cells, purified ALP zinc metalation assays, ZIP transporter knockdowns, confocal imaging of heterodimer localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO in human cells plus purified protein metalation assay plus imaging, multiple orthogonal methods, mechanistic novelty validated","pmids":["32179649"],"is_preprint":false},{"year":2022,"finding":"ZnT5/ZnT6 heterodimers and ZnT7 homodimers in the early secretory pathway are required for activation of sphingomyelin phosphodiesterase 1 (SMPD1), a zinc-dependent lysosomal enzyme. Loss of both ZNT complexes results in reduced ceramide:sphingomyelin ratio, accumulation of minor sphingomyelin species, and multilamellar body-like structures indicative of membrane accumulation.","method":"Gene disruption/re-expression in DT40 cells, SMPD1 activity assays, lipidomics (ceramide/sphingomyelin ratio), electron microscopy","journal":"American journal of physiology. Cell physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with rescue, multiple functional readouts (enzymatic activity + lipidomics + EM), mechanistic pathway placement","pmids":["35294847"],"is_preprint":false},{"year":2023,"finding":"ZnT5/ZnT6 complex regulates labile Zn2+ concentration specifically in the medial Golgi compartment (distinct from ZnT4 at distal Golgi and ZnT7 at proximal Golgi), and ZnT-mediated Zn2+ fluxes tune the localization, trafficking, and client-retrieval activity of the chaperone ERp44 in the early secretory pathway.","method":"Systematic ZnT knockdowns, super-resolution microscopy, quantitative Zn2+-probes targeted to specific Golgi subregions, time-course imaging of synchronized secretory protein traffic, ERp44 functional assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic knockdowns with quantitative spatial imaging and functional ERp44 assays, multiple orthogonal methods, rigorous controls","pmids":["37160917"],"is_preprint":false},{"year":2023,"finding":"ZnT5/ZnT6 heterodimers are required for TYRP1 expression and function in pigmentation. Loss of ZNT5/ZNT6 (and ZNT7) results in hypopigmentation in medaka fish and human melanoma cells, accompanied by immature melanosomes and reduced melanin content, phenocopying TYRP1 dysfunction. TYRP1 requires zinc (not copper) as a cofactor supplied by ZNT5-ZNT6 and ZNT7, and this requirement is conserved in human, mouse, and chicken orthologs.","method":"Gene disruption in medaka fish and melanoma cells, pigmentation assays, melanosome imaging, TYRP1 expression and functional assays, zinc supplementation experiments","journal":"Communications biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO in multiple species/cell types, multiple functional readouts (pigmentation, melanosome morphology, TYRP1 expression), conserved mechanism validated","pmids":["37072620"],"is_preprint":false},{"year":2024,"finding":"ZnT5/ZnT6 heterodimers and ZNT7 homodimers supply Zn2+ to Golgi α-mannosidase II (GMII), activating it to catalyze the conversion of hybrid- to complex-type N-glycans. Loss of both ZNT complexes results in accumulation of hybrid-type glycans and reduction of complex-type glycans; GMII activity is substantially decreased while lysosomal mannosidase (LAMAN) activity is unaffected, indicating specificity. Loss of ZNT5/ZNT6 and ZNT7 also significantly reduces pancreatic cancer cell growth in nude mouse xenograft models.","method":"Gene disruption in DT40 and MIA PaCa-2 cells, N-glycan profiling, GMII activity assays, LAMAN activity assays, xenograft mouse tumor growth assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with enzymatic activity assay, glycan profiling, and in vivo xenograft validation; multiple orthogonal methods","pmids":["38762179"],"is_preprint":false},{"year":2024,"finding":"ZnT6 undergoes SUMO1-mediated SUMOylation at Lys-409, which reduces ZnT6 protein stability (but does not affect its Golgi localization). High zinc activates the MTF-1/SENP1 pathway, leading to SENP1-mediated deSUMOylation of ZnT6 at Lys-409. DeSUMOylation of ZnT6 is required for efficient Zn2+ export from the cytosol into the Golgi apparatus.","method":"High-zinc diet feeding, SUMOylation site identification by mutagenesis, MTF-1/SENP1 pathway manipulation, Golgi localization imaging, Zn2+ transport functional assays in fish hepatocytes","journal":"Cellular and molecular life sciences : CMLS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — identified specific SUMOylation site with functional consequence for zinc transport, single lab, multiple methods including mutagenesis and pathway manipulation","pmids":["39367979"],"is_preprint":false},{"year":2015,"finding":"Reduced SLC30A6 (ZnT6) mRNA and protein expression was found in mammary tissue from two women producing severely zinc-deficient milk. Novel splice variants of SLC30A6 transcript were detected. Reduced SLC30A6 levels may be secondary to reduced SLC30A5 expression, as the two proteins function as a heterodimer in zinc transport.","method":"RT-PCR, Western blot, DNA methylation analysis, splice variant detection in lymphoblasts and fibroblasts from affected mothers","journal":"Genes & nutrition","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, observational molecular analysis in patient samples, mechanistic link to milk zinc deficiency is correlative not experimentally established for ZnT6 specifically","pmids":["26319140"],"is_preprint":false},{"year":2025,"finding":"ZnT6 overexpression in H9c2 cardiomyocytes causes ZnT6 to localize to mitochondria, redistributing Zn2+ from cytosol into mitochondria. This leads to increased mitochondrial fission (elevated DRP1 translocation to mitochondria), mitochondrial membrane depolarization, excess ROS production, reduced ATP levels, autophagosome accumulation, and autophagy-induced apoptosis.","method":"Confocal imaging, biochemical assays (mitochondrial membrane potential, ROS, ATP), electron microscopy, DRP1 translocation assay, autophagy and apoptosis markers in ZnT6-overexpressing H9c2 cells","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by confocal imaging with multiple functional consequences measured, single lab, multiple orthogonal methods","pmids":["40087209"],"is_preprint":false},{"year":2023,"finding":"ZnT6 overexpression in insulin-resistant H9c2 cardiomyoblasts causes mitochondrial localization of ZnT6, elevated intracellular free Zn2+, abnormal mitochondrial and sarcoplasmic reticulum morphology (irregular cristae, dilated cisternae), mitochondrial depolarization, increased DRP1 total protein, increased K-acetylation, trimethylation of histone H3K27, and monomethylation of H3K36 — epigenetic modifications similar to those induced by insulin resistance.","method":"Confocal microscopy, electron microscopy, Western blot for ZnT6, MFN2, DRP1, histone modifications, mitochondrial membrane potential assay in ZnT6-OE and IR H9c2 cells","journal":"Biochemical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization with functional consequences, multiple orthogonal methods, single lab","pmids":["38091184"],"is_preprint":false}],"current_model":"SLC30A6 (ZnT6) is a CDF-family zinc transporter that localizes to the trans-Golgi network and vesicular compartments, where it functions exclusively as a heterodimer with ZnT5; this ZnT5/ZnT6 heterodimer (together with ZNT7 homodimers as a parallel complex) loads zinc onto zinc-requiring ectoenzymes—including alkaline phosphatases, autotaxin, MMP9, TYRP1, Golgi α-mannosidase II, and sphingomyelin phosphodiesterase 1—via a two-step mechanism involving first protein stabilization of the apo-enzyme and then zinc metalation; ZnT5/ZnT6 specifically regulates labile Zn2+ in the medial Golgi, thereby controlling ERp44-mediated proteostasis, and ZnT6's activity is post-translationally regulated by SUMO1-mediated SUMOylation at Lys-409 (reducing stability and transport) with SENP1-mediated deSUMOylation (enhancing zinc export into the Golgi) triggered by elevated zinc via the MTF-1 pathway."},"narrative":{"mechanistic_narrative":"SLC30A6 (ZnT6) is a cation diffusion facilitator-family zinc transporter that operates in the early secretory pathway to metalate and activate zinc-requiring enzymes, controlling diverse downstream processes from ectoenzyme function to pigmentation and N-glycan maturation [PMID:15994300, PMID:28028180, PMID:38762179]. ZnT6 localizes to the trans-Golgi network and vesicular compartments and functions not as an independent transporter but obligately as a heterodimer with ZnT5, into which ZnT5 contributes the His-rich loop that provides zinc-binding activity while ZnT6 plays a structural role in complex formation [PMID:11997387, PMID:15994300, PMID:19759014]; ZnT5 recruits ZnT6 to the Golgi to assemble this heterodimer, which acts in parallel with ZnT7 homodimers [PMID:32179649]. The ZnT5/ZnT6 complex activates client enzymes through a two-step mechanism, first stabilizing the apo-enzyme as a separable function from zinc transport and then loading zinc to generate the active holo-enzyme—failure of zinc loading routes the client to proteasomal degradation [PMID:16636052, PMID:21402707]. Through this activity the complex matures a broad set of zinc-dependent enzymes including tissue-nonspecific alkaline phosphatase, autotaxin, MMP9, carbonic anhydrase IX, sphingomyelin phosphodiesterase 1, TYRP1, and Golgi α-mannosidase II, thereby supporting ectoenzyme function, sphingolipid balance, melanin synthesis, and hybrid-to-complex N-glycan conversion [PMID:21402707, PMID:28028180, PMID:35294847, PMID:37072620, PMID:38762179]. By regulating labile Zn2+ specifically in the medial Golgi, ZnT5/ZnT6 tunes the localization and client-retrieval activity of the chaperone ERp44 in secretory proteostasis [PMID:37160917]. ZnT6 is post-translationally controlled by SUMO1-mediated SUMOylation at Lys-409, which reduces its stability; high zinc triggers MTF-1/SENP1-dependent deSUMOylation that is required for efficient Zn2+ export into the Golgi [PMID:39367979].","teleology":[{"year":2002,"claim":"Established that ZnT6 is a zinc transporter that moves cytoplasmic zinc into the Golgi/vesicular compartment, defining its basic transport directionality and subcellular site of action.","evidence":"Yeast overexpression growth assays and immunofluorescence co-localization with TGN38 and transferrin receptor in NRK cells","pmids":["11997387"],"confidence":"Medium","gaps":["Did not identify physiological cargo enzymes or partner proteins","Transport mechanism inferred from yeast phenotype rather than direct flux measurement"]},{"year":2005,"claim":"Resolved how ZnT6 acts by showing it functions as an obligate hetero-oligomer with ZnT5 (not as a homo-oligomer) to supply zinc for alkaline phosphatase activation, with ZnT7 forming a parallel independent complex.","evidence":"DT40 gene targeting, reciprocal co-immunoprecipitation, ALP activity assays and rescue, plus yeast genetic complementation against Msc2p/Zrg17p","pmids":["15994300","15961382"],"confidence":"High","gaps":["Did not establish which subunit binds zinc versus provides structure","Mechanism of client enzyme activation not yet defined"]},{"year":2009,"claim":"Defined the molecular determinants of complex assembly, showing ZnT5 and ZnT6 form discrete heterodimers and that the ZnT5 C-terminal tail selects ZnT6 as partner, while ZnT6 transmembrane residues are not zinc-binding.","evidence":"Co-immunoprecipitation, mutagenesis and chimera studies in DT40 cells deficient in ZnT5/ZnT6/ZnT7","pmids":["19759014"],"confidence":"High","gaps":["No high-resolution structure of the heterodimer","Stoichiometry and transport pore architecture unresolved"]},{"year":2011,"claim":"Separated the two mechanistic steps of client activation, demonstrating ZnT5/ZnT6 first stabilizes apo-enzyme independent of transport and then loads zinc to form active holo-enzyme.","evidence":"Gene disruption/re-expression in DT40 cells using a zinc-transport-incompetent ZnT5 mutant, ALP activity and zinc supplementation assays","pmids":["21402707"],"confidence":"High","gaps":["Structural basis of the apo-enzyme stabilization step not defined","Whether all clients share identical two-step kinetics not established"]},{"year":2016,"claim":"Broadened the client repertoire and disease relevance by showing ZnT5/ZnT6 activates cancer-promoting ectoenzymes (autotaxin, MMP9, CAIX) and mapped the ZnT5 di-proline motif required for client maturation but not transport.","evidence":"DT40 gene-disruption mutants with activity and secretion assays across multiple ectoenzymes; site-directed PP-motif mutagenesis","pmids":["28028180","27303047"],"confidence":"High","gaps":["Direct contribution of ZnT6 residues to client recognition not dissected","In vivo relevance to tumor biology not yet tested"]},{"year":2014,"claim":"Confirmed heterodimerization occurs in living cells with functional zinc transport, validating the complex beyond biochemical co-IP.","evidence":"Bimolecular fluorescence complementation in live cells with Zinquin zinc-probe functional readout","pmids":["24451381"],"confidence":"Medium","gaps":["Single-lab visualization","Did not quantify transport stoichiometry or kinetics"]},{"year":2020,"claim":"Revealed spatial regulation of assembly—ZnT5 recruits ZnT6 to the Golgi—and confirmed the two-complex activation mechanism is conserved in human cells.","evidence":"Genetic disruption in human HAP1 cells, purified ALP zinc-metalation assays, ZIP knockdowns, confocal imaging","pmids":["32179649"],"confidence":"High","gaps":["Signal driving ZnT6 recruitment not identified","Source of the zinc pool delivered to clients not fully mapped"]},{"year":2022,"claim":"Extended client scope to lysosomal sphingomyelin phosphodiesterase 1, linking ZnT5/ZnT6 to sphingolipid homeostasis and membrane integrity.","evidence":"DT40 gene disruption/re-expression, SMPD1 activity assays, lipidomics, electron microscopy","pmids":["35294847"],"confidence":"High","gaps":["Whether SMPD1 follows the same two-step activation as TNAP not tested","Physiological consequence in mammalian tissue not assessed"]},{"year":2023,"claim":"Placed ZnT5/ZnT6 in spatial proteostasis control, showing it sets labile Zn2+ specifically in the medial Golgi to tune ERp44 trafficking and client retrieval, and demonstrated a role in pigmentation via TYRP1 zinc supply.","evidence":"Systematic ZnT knockdowns with super-resolution microscopy and Golgi-targeted Zn2+ probes; gene disruption in medaka and melanoma cells with pigmentation and TYRP1 assays","pmids":["37160917","37072620"],"confidence":"High","gaps":["Molecular mechanism by which ERp44 senses medial-Golgi Zn2+ not fully resolved","Whether TYRP1 metalation uses the canonical two-step mechanism not directly shown"]},{"year":2024,"claim":"Added N-glycan maturation as a downstream output (Golgi α-mannosidase II activation) with in vivo tumor relevance, and identified SUMOylation as a post-translational switch on ZnT6 transport.","evidence":"Gene disruption in DT40 and MIA PaCa-2 cells with N-glycan profiling, GMII activity assays and xenografts; SUMOylation site mutagenesis and MTF-1/SENP1 pathway manipulation in fish hepatocytes","pmids":["38762179","39367979"],"confidence":"High","gaps":["How SUMOylation at Lys-409 mechanically reduces stability not defined","Whether SUMO regulation operates in mammalian secretory clients beyond hepatocytes unknown"]},{"year":2025,"claim":"Reported a non-canonical context where ZnT6 overexpression drives mitochondrial localization and redistributes Zn2+ into mitochondria, triggering fission, depolarization, ROS, and autophagy-linked apoptosis in cardiomyocytes.","evidence":"Confocal and electron microscopy, mitochondrial membrane potential/ROS/ATP assays, DRP1 translocation and autophagy/apoptosis markers in ZnT6-overexpressing H9c2 cells","pmids":["40087209","38091184"],"confidence":"Medium","gaps":["Mitochondrial localization observed only under overexpression, not endogenous conditions","Single cell-line system without in vivo confirmation","Mechanism of mitochondrial targeting unknown"]},{"year":null,"claim":"The structural basis of zinc translocation by the ZnT5/ZnT6 heterodimer and the molecular rules governing client enzyme selection remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of the heterodimer or its client-loading interface","How specific apo-enzymes are recognized and stabilized prior to metalation is undefined","Whether the mitochondrial/cardiomyocyte phenotypes reflect a physiological function or an overexpression artifact is unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,9,14]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[5,7,13]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,9,11]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[3,5,13]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[11]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[10,13]}],"complexes":["ZnT5/ZnT6 heterodimer"],"partners":["SLC30A5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6NXT4","full_name":"Zinc transporter 6","aliases":["Solute carrier family 30 member 6"],"length_aa":461,"mass_kda":51.1,"function":"Has probably no intrinsic transporter activity but together with SLC30A5 forms a functional zinc ion:proton antiporter heterodimer, mediating zinc entry into the lumen of organelles along the secretory pathway (PubMed:15994300, PubMed:19366695, PubMed:19759014). As part of that zinc ion:proton antiporter, contributes to zinc ion homeostasis within the early secretory pathway and regulates the activation and folding of enzymes like alkaline phosphatases and enzymes involved in phosphatidylinositol glycan anchor biosynthesis (PubMed:15994300, PubMed:19759014, PubMed:35525268)","subcellular_location":"Golgi apparatus, trans-Golgi network membrane","url":"https://www.uniprot.org/uniprotkb/Q6NXT4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SLC30A6","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"GORASP2","stoichiometry":0.2},{"gene":"RAB1A","stoichiometry":0.2},{"gene":"RAB1B","stoichiometry":0.2},{"gene":"SLC30A5","stoichiometry":0.2},{"gene":"TMED10","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/SLC30A6","total_profiled":1310},"omim":[{"mim_id":"611148","title":"SOLUTE CARRIER FAMILY 30 (ZINC TRANSPORTER), MEMBER 6; SLC30A6","url":"https://www.omim.org/entry/611148"},{"mim_id":"604277","title":"SPASTIN; SPAST","url":"https://www.omim.org/entry/604277"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Golgi apparatus","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SLC30A6"},"hgnc":{"alias_symbol":["FLJ31101","ZNT6"],"prev_symbol":[]},"alphafold":{"accession":"Q6NXT4","domains":[{"cath_id":"-","chopping":"15-256","consensus_level":"high","plddt":85.5077,"start":15,"end":256},{"cath_id":"3.30.70.1350","chopping":"263-334","consensus_level":"high","plddt":90.406,"start":263,"end":334}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6NXT4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6NXT4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6NXT4-F1-predicted_aligned_error_v6.png","plddt_mean":71.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SLC30A6","jax_strain_url":"https://www.jax.org/strain/search?query=SLC30A6"},"sequence":{"accession":"Q6NXT4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6NXT4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6NXT4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6NXT4"}},"corpus_meta":[{"pmid":"11997387","id":"PMC_11997387","title":"Functional characterization of a novel mammalian zinc transporter, ZnT6.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11997387","citation_count":176,"is_preprint":false},{"pmid":"15994300","id":"PMC_15994300","title":"Two different zinc transport complexes of cation diffusion facilitator proteins localized in the secretory pathway operate to activate alkaline phosphatases in vertebrate cells.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15994300","citation_count":142,"is_preprint":false},{"pmid":"21558427","id":"PMC_21558427","title":"Altered zinc transport disrupts mitochondrial protein processing/import in fragile X-associated tremor/ataxia syndrome.","date":"2011","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21558427","citation_count":93,"is_preprint":false},{"pmid":"19759014","id":"PMC_19759014","title":"Demonstration and characterization of the heterodimerization of ZnT5 and ZnT6 in the early secretory pathway.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19759014","citation_count":91,"is_preprint":false},{"pmid":"15961382","id":"PMC_15961382","title":"Heteromeric protein complexes mediate zinc transport into the secretory pathway of eukaryotic cells.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15961382","citation_count":89,"is_preprint":false},{"pmid":"20120011","id":"PMC_20120011","title":"Dietary zinc absorption: A play of Zips and ZnTs in the gut.","date":"2010","source":"IUBMB life","url":"https://pubmed.ncbi.nlm.nih.gov/20120011","citation_count":86,"is_preprint":false},{"pmid":"25065914","id":"PMC_25065914","title":"The Alu-rich genomic architecture of SPAST predisposes to diverse and functionally distinct disease-associated CNV alleles.","date":"2014","source":"American journal of human 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to the trans-Golgi network and vesicular compartments (overlapping with TGN38 and transferrin receptor) in normal rat kidney cells, and its intracellular distribution is regulated by zinc levels. Overexpression in wild-type yeast causes growth inhibition, consistent with a zinc transport function that moves cytoplasmic zinc into the Golgi/vesicular compartment.\",\n      \"method\": \"Overexpression in yeast growth assays, immunofluorescence co-localization with TGN38 and transferrin receptor in NRK cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with functional consequence (yeast growth inhibition), single lab, two orthogonal methods\",\n      \"pmids\": [\"11997387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ZnT5 and ZnT6 form hetero-oligomers (but not homo-oligomers with each other) that constitute one of two distinct zinc transport complexes in the secretory pathway required for activation of alkaline phosphatases; ZnT7 operates independently as homo-oligomers. The Ser-rich loop of ZnT6 is dispensable for the zinc-supplying function of the ZnT5/ZnT6 hetero-oligomer, suggesting the His-rich loop of ZnT5 provides zinc-binding activity, while ZnT6's loop may serve a structural role in hetero-oligomer formation.\",\n      \"method\": \"Gene targeting in chicken DT40 cells, co-immunoprecipitation, alkaline phosphatase activity assays, transgene re-expression rescue experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, genetic epistasis via DT40 knockout/rescue, ALP functional assay; replicated across multiple labs\",\n      \"pmids\": [\"15994300\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ZnT5 and ZnT6, mammalian homologues of yeast Msc2p and Zrg17p respectively, functionally interact and form a heteromeric zinc transport complex in the secretory pathway, paralleling the Msc2p/Zrg17p ER zinc transport complex in Saccharomyces cerevisiae.\",\n      \"method\": \"Co-immunoprecipitation, yeast genetic complementation, functional interaction assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and functional interaction data, single lab, cross-species validation\",\n      \"pmids\": [\"15961382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ZnT5/ZnT6 hetero-oligomeric complexes in the secretory pathway are required for zinc loading of alkaline phosphatase; in ZnT5−/ZnT7−/− cells, inactive alkaline phosphatase is degraded via proteasome-mediated degradation without trafficking to the plasma membrane, revealing that zinc loading prevents proteasomal degradation of the enzyme.\",\n      \"method\": \"DT40 gene-targeting knockouts, ALP activity assays, proteasome inhibitor experiments, unfolded protein response assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with defined cellular phenotype (ALP degradation, UPR), multiple orthogonal assays, replicated in same system\",\n      \"pmids\": [\"16636052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ZnT5 and ZnT6 form heterodimers (not larger complexes) in the early secretory pathway. Mutagenesis showed that the conserved hydrophilic residues in transmembrane domains II and V of ZnT6 are not involved in zinc binding (unlike in homo-oligomeric CDF members). The cytosolic C-terminal tail of ZnT5 determines ZnT6 as its heterodimerization partner. The long N-terminal half of ZnT5 is dispensable for functional interaction with ZnT6.\",\n      \"method\": \"Co-immunoprecipitation, mutagenesis, chimera studies in DT40 cells deficient in ZnT5/ZnT6/ZnT7\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with Co-IP and functional rescue, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"19759014\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TNAP is activated via a two-step mechanism: first, ZnT5/ZnT6 heterodimers stabilize TNAP as an apo-form (protein stabilization step independent of zinc transport); second, ZNT complexes load zinc to convert apo-TNAP to holo-TNAP. Expression of ZnT5/ZnT6 heterodimers reconstituted with a zinc transport-incompetent ZnT5 mutant stabilized TNAP protein as an apo-form but failed to restore TNAP activity, demonstrating that protein stabilization and zinc loading are separable functions.\",\n      \"method\": \"Gene disruption/re-expression in DT40 cells, zinc transport-incompetent ZnT5 mutants, ALP activity assays, zinc supplementation experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis separating two mechanistic steps, genetic rescue experiments, multiple orthogonal assays; replicated across labs\",\n      \"pmids\": [\"21402707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"ZnT5 and ZnT6 form heterodimers in situ in live cells, as directly visualized by bimolecular fluorescence complementation (BiFC). The BiFC signal from ZnT5-YC and ZnT6-YN co-transfection confirmed heterodimerization with subcellular compartment-appropriate localization, and the dimerized complex was functionally active as assessed by Zinquin fluorescent zinc probe.\",\n      \"method\": \"Bimolecular fluorescence complementation (BiFC) in live cells, Zinquin zinc probe functional assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct visualization of protein-protein interaction in live cells with functional validation, single lab\",\n      \"pmids\": [\"24451381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ZnT5/ZnT6 heterodimers and ZnT7 homodimers activate cancer-promoting zinc-requiring ectoenzymes—autotaxin (ATX), matrix metalloproteinase 9 (MMP9), and carbonic anhydrase IX (CAIX)—via zinc metalation in the early secretory pathway. MMP9 required both ZnT complexes for secretion as well as activation; CAIX was additionally activated by ZnT4 homodimers. ATX followed a similar two-step activation mechanism as TNAP but with different protein stability regulation.\",\n      \"method\": \"DT40 gene-disruption mutants, activity assays for ATX, MMP9, CAIX; secretion assays; transgene re-expression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with multiple functional readouts across three ectoenzymes, genetic rescue, multiple orthogonal assays\",\n      \"pmids\": [\"28028180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The di-proline (PP) motif in luminal loop 2 of ZnT5 is important for TNAP activation by ZnT5/ZnT6 heterodimers. PP-to-AA mutation in ZnT5 reduced TNAP activation by ~90% without significantly impairing zinc transport activity of ZnT7, indicating the PP-motif is involved in the TNAP maturation/stabilization process rather than zinc transport per se.\",\n      \"method\": \"Site-directed mutagenesis of ZnT5 PP motif, DT40 TKO cell rescue assays, ALP activity assays, apo-to-holo conversion assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis dissecting function from transport activity, genetic rescue in defined mutant cells, multiple functional assays\",\n      \"pmids\": [\"27303047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ZnT5 recruits ZnT6 to the Golgi apparatus to form the heterodimeric complex (ZnT5 recruits ZnT6), revealing a previously unrecognized spatial regulation of ZnT5/ZnT6 heterodimer formation. In human HAP1 cells lacking both ZnT5 and ZnT7, TNAP activation is impaired, confirming conservation of the two-complex activation mechanism in human cells.\",\n      \"method\": \"Genetic disruption of ZnT5 and ZnT7 in human HAP1 cells, purified ALP zinc metalation assays, ZIP transporter knockdowns, confocal imaging of heterodimer localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO in human cells plus purified protein metalation assay plus imaging, multiple orthogonal methods, mechanistic novelty validated\",\n      \"pmids\": [\"32179649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ZnT5/ZnT6 heterodimers and ZnT7 homodimers in the early secretory pathway are required for activation of sphingomyelin phosphodiesterase 1 (SMPD1), a zinc-dependent lysosomal enzyme. Loss of both ZNT complexes results in reduced ceramide:sphingomyelin ratio, accumulation of minor sphingomyelin species, and multilamellar body-like structures indicative of membrane accumulation.\",\n      \"method\": \"Gene disruption/re-expression in DT40 cells, SMPD1 activity assays, lipidomics (ceramide/sphingomyelin ratio), electron microscopy\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with rescue, multiple functional readouts (enzymatic activity + lipidomics + EM), mechanistic pathway placement\",\n      \"pmids\": [\"35294847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ZnT5/ZnT6 complex regulates labile Zn2+ concentration specifically in the medial Golgi compartment (distinct from ZnT4 at distal Golgi and ZnT7 at proximal Golgi), and ZnT-mediated Zn2+ fluxes tune the localization, trafficking, and client-retrieval activity of the chaperone ERp44 in the early secretory pathway.\",\n      \"method\": \"Systematic ZnT knockdowns, super-resolution microscopy, quantitative Zn2+-probes targeted to specific Golgi subregions, time-course imaging of synchronized secretory protein traffic, ERp44 functional assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic knockdowns with quantitative spatial imaging and functional ERp44 assays, multiple orthogonal methods, rigorous controls\",\n      \"pmids\": [\"37160917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ZnT5/ZnT6 heterodimers are required for TYRP1 expression and function in pigmentation. Loss of ZNT5/ZNT6 (and ZNT7) results in hypopigmentation in medaka fish and human melanoma cells, accompanied by immature melanosomes and reduced melanin content, phenocopying TYRP1 dysfunction. TYRP1 requires zinc (not copper) as a cofactor supplied by ZNT5-ZNT6 and ZNT7, and this requirement is conserved in human, mouse, and chicken orthologs.\",\n      \"method\": \"Gene disruption in medaka fish and melanoma cells, pigmentation assays, melanosome imaging, TYRP1 expression and functional assays, zinc supplementation experiments\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO in multiple species/cell types, multiple functional readouts (pigmentation, melanosome morphology, TYRP1 expression), conserved mechanism validated\",\n      \"pmids\": [\"37072620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ZnT5/ZnT6 heterodimers and ZNT7 homodimers supply Zn2+ to Golgi α-mannosidase II (GMII), activating it to catalyze the conversion of hybrid- to complex-type N-glycans. Loss of both ZNT complexes results in accumulation of hybrid-type glycans and reduction of complex-type glycans; GMII activity is substantially decreased while lysosomal mannosidase (LAMAN) activity is unaffected, indicating specificity. Loss of ZNT5/ZNT6 and ZNT7 also significantly reduces pancreatic cancer cell growth in nude mouse xenograft models.\",\n      \"method\": \"Gene disruption in DT40 and MIA PaCa-2 cells, N-glycan profiling, GMII activity assays, LAMAN activity assays, xenograft mouse tumor growth assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with enzymatic activity assay, glycan profiling, and in vivo xenograft validation; multiple orthogonal methods\",\n      \"pmids\": [\"38762179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ZnT6 undergoes SUMO1-mediated SUMOylation at Lys-409, which reduces ZnT6 protein stability (but does not affect its Golgi localization). High zinc activates the MTF-1/SENP1 pathway, leading to SENP1-mediated deSUMOylation of ZnT6 at Lys-409. DeSUMOylation of ZnT6 is required for efficient Zn2+ export from the cytosol into the Golgi apparatus.\",\n      \"method\": \"High-zinc diet feeding, SUMOylation site identification by mutagenesis, MTF-1/SENP1 pathway manipulation, Golgi localization imaging, Zn2+ transport functional assays in fish hepatocytes\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — identified specific SUMOylation site with functional consequence for zinc transport, single lab, multiple methods including mutagenesis and pathway manipulation\",\n      \"pmids\": [\"39367979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Reduced SLC30A6 (ZnT6) mRNA and protein expression was found in mammary tissue from two women producing severely zinc-deficient milk. Novel splice variants of SLC30A6 transcript were detected. Reduced SLC30A6 levels may be secondary to reduced SLC30A5 expression, as the two proteins function as a heterodimer in zinc transport.\",\n      \"method\": \"RT-PCR, Western blot, DNA methylation analysis, splice variant detection in lymphoblasts and fibroblasts from affected mothers\",\n      \"journal\": \"Genes & nutrition\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, observational molecular analysis in patient samples, mechanistic link to milk zinc deficiency is correlative not experimentally established for ZnT6 specifically\",\n      \"pmids\": [\"26319140\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ZnT6 overexpression in H9c2 cardiomyocytes causes ZnT6 to localize to mitochondria, redistributing Zn2+ from cytosol into mitochondria. This leads to increased mitochondrial fission (elevated DRP1 translocation to mitochondria), mitochondrial membrane depolarization, excess ROS production, reduced ATP levels, autophagosome accumulation, and autophagy-induced apoptosis.\",\n      \"method\": \"Confocal imaging, biochemical assays (mitochondrial membrane potential, ROS, ATP), electron microscopy, DRP1 translocation assay, autophagy and apoptosis markers in ZnT6-overexpressing H9c2 cells\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by confocal imaging with multiple functional consequences measured, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"40087209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ZnT6 overexpression in insulin-resistant H9c2 cardiomyoblasts causes mitochondrial localization of ZnT6, elevated intracellular free Zn2+, abnormal mitochondrial and sarcoplasmic reticulum morphology (irregular cristae, dilated cisternae), mitochondrial depolarization, increased DRP1 total protein, increased K-acetylation, trimethylation of histone H3K27, and monomethylation of H3K36 — epigenetic modifications similar to those induced by insulin resistance.\",\n      \"method\": \"Confocal microscopy, electron microscopy, Western blot for ZnT6, MFN2, DRP1, histone modifications, mitochondrial membrane potential assay in ZnT6-OE and IR H9c2 cells\",\n      \"journal\": \"Biochemical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization with functional consequences, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"38091184\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC30A6 (ZnT6) is a CDF-family zinc transporter that localizes to the trans-Golgi network and vesicular compartments, where it functions exclusively as a heterodimer with ZnT5; this ZnT5/ZnT6 heterodimer (together with ZNT7 homodimers as a parallel complex) loads zinc onto zinc-requiring ectoenzymes—including alkaline phosphatases, autotaxin, MMP9, TYRP1, Golgi α-mannosidase II, and sphingomyelin phosphodiesterase 1—via a two-step mechanism involving first protein stabilization of the apo-enzyme and then zinc metalation; ZnT5/ZnT6 specifically regulates labile Zn2+ in the medial Golgi, thereby controlling ERp44-mediated proteostasis, and ZnT6's activity is post-translationally regulated by SUMO1-mediated SUMOylation at Lys-409 (reducing stability and transport) with SENP1-mediated deSUMOylation (enhancing zinc export into the Golgi) triggered by elevated zinc via the MTF-1 pathway.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SLC30A6 (ZnT6) is a cation diffusion facilitator-family zinc transporter that operates in the early secretory pathway to metalate and activate zinc-requiring enzymes, controlling diverse downstream processes from ectoenzyme function to pigmentation and N-glycan maturation [#1, #7, #13]. ZnT6 localizes to the trans-Golgi network and vesicular compartments and functions not as an independent transporter but obligately as a heterodimer with ZnT5, into which ZnT5 contributes the His-rich loop that provides zinc-binding activity while ZnT6 plays a structural role in complex formation [#0, #1, #4]; ZnT5 recruits ZnT6 to the Golgi to assemble this heterodimer, which acts in parallel with ZnT7 homodimers [#9]. The ZnT5/ZnT6 complex activates client enzymes through a two-step mechanism, first stabilizing the apo-enzyme as a separable function from zinc transport and then loading zinc to generate the active holo-enzyme—failure of zinc loading routes the client to proteasomal degradation [#3, #5]. Through this activity the complex matures a broad set of zinc-dependent enzymes including tissue-nonspecific alkaline phosphatase, autotaxin, MMP9, carbonic anhydrase IX, sphingomyelin phosphodiesterase 1, TYRP1, and Golgi α-mannosidase II, thereby supporting ectoenzyme function, sphingolipid balance, melanin synthesis, and hybrid-to-complex N-glycan conversion [#5, #7, #10, #12, #13]. By regulating labile Zn2+ specifically in the medial Golgi, ZnT5/ZnT6 tunes the localization and client-retrieval activity of the chaperone ERp44 in secretory proteostasis [#11]. ZnT6 is post-translationally controlled by SUMO1-mediated SUMOylation at Lys-409, which reduces its stability; high zinc triggers MTF-1/SENP1-dependent deSUMOylation that is required for efficient Zn2+ export into the Golgi [#14].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that ZnT6 is a zinc transporter that moves cytoplasmic zinc into the Golgi/vesicular compartment, defining its basic transport directionality and subcellular site of action.\",\n      \"evidence\": \"Yeast overexpression growth assays and immunofluorescence co-localization with TGN38 and transferrin receptor in NRK cells\",\n      \"pmids\": [\"11997387\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not identify physiological cargo enzymes or partner proteins\", \"Transport mechanism inferred from yeast phenotype rather than direct flux measurement\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Resolved how ZnT6 acts by showing it functions as an obligate hetero-oligomer with ZnT5 (not as a homo-oligomer) to supply zinc for alkaline phosphatase activation, with ZnT7 forming a parallel independent complex.\",\n      \"evidence\": \"DT40 gene targeting, reciprocal co-immunoprecipitation, ALP activity assays and rescue, plus yeast genetic complementation against Msc2p/Zrg17p\",\n      \"pmids\": [\"15994300\", \"15961382\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not establish which subunit binds zinc versus provides structure\", \"Mechanism of client enzyme activation not yet defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the molecular determinants of complex assembly, showing ZnT5 and ZnT6 form discrete heterodimers and that the ZnT5 C-terminal tail selects ZnT6 as partner, while ZnT6 transmembrane residues are not zinc-binding.\",\n      \"evidence\": \"Co-immunoprecipitation, mutagenesis and chimera studies in DT40 cells deficient in ZnT5/ZnT6/ZnT7\",\n      \"pmids\": [\"19759014\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No high-resolution structure of the heterodimer\", \"Stoichiometry and transport pore architecture unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Separated the two mechanistic steps of client activation, demonstrating ZnT5/ZnT6 first stabilizes apo-enzyme independent of transport and then loads zinc to form active holo-enzyme.\",\n      \"evidence\": \"Gene disruption/re-expression in DT40 cells using a zinc-transport-incompetent ZnT5 mutant, ALP activity and zinc supplementation assays\",\n      \"pmids\": [\"21402707\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Structural basis of the apo-enzyme stabilization step not defined\", \"Whether all clients share identical two-step kinetics not established\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Broadened the client repertoire and disease relevance by showing ZnT5/ZnT6 activates cancer-promoting ectoenzymes (autotaxin, MMP9, CAIX) and mapped the ZnT5 di-proline motif required for client maturation but not transport.\",\n      \"evidence\": \"DT40 gene-disruption mutants with activity and secretion assays across multiple ectoenzymes; site-directed PP-motif mutagenesis\",\n      \"pmids\": [\"28028180\", \"27303047\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct contribution of ZnT6 residues to client recognition not dissected\", \"In vivo relevance to tumor biology not yet tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Confirmed heterodimerization occurs in living cells with functional zinc transport, validating the complex beyond biochemical co-IP.\",\n      \"evidence\": \"Bimolecular fluorescence complementation in live cells with Zinquin zinc-probe functional readout\",\n      \"pmids\": [\"24451381\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Single-lab visualization\", \"Did not quantify transport stoichiometry or kinetics\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Revealed spatial regulation of assembly—ZnT5 recruits ZnT6 to the Golgi—and confirmed the two-complex activation mechanism is conserved in human cells.\",\n      \"evidence\": \"Genetic disruption in human HAP1 cells, purified ALP zinc-metalation assays, ZIP knockdowns, confocal imaging\",\n      \"pmids\": [\"32179649\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Signal driving ZnT6 recruitment not identified\", \"Source of the zinc pool delivered to clients not fully mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended client scope to lysosomal sphingomyelin phosphodiesterase 1, linking ZnT5/ZnT6 to sphingolipid homeostasis and membrane integrity.\",\n      \"evidence\": \"DT40 gene disruption/re-expression, SMPD1 activity assays, lipidomics, electron microscopy\",\n      \"pmids\": [\"35294847\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Whether SMPD1 follows the same two-step activation as TNAP not tested\", \"Physiological consequence in mammalian tissue not assessed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed ZnT5/ZnT6 in spatial proteostasis control, showing it sets labile Zn2+ specifically in the medial Golgi to tune ERp44 trafficking and client retrieval, and demonstrated a role in pigmentation via TYRP1 zinc supply.\",\n      \"evidence\": \"Systematic ZnT knockdowns with super-resolution microscopy and Golgi-targeted Zn2+ probes; gene disruption in medaka and melanoma cells with pigmentation and TYRP1 assays\",\n      \"pmids\": [\"37160917\", \"37072620\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Molecular mechanism by which ERp44 senses medial-Golgi Zn2+ not fully resolved\", \"Whether TYRP1 metalation uses the canonical two-step mechanism not directly shown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Added N-glycan maturation as a downstream output (Golgi α-mannosidase II activation) with in vivo tumor relevance, and identified SUMOylation as a post-translational switch on ZnT6 transport.\",\n      \"evidence\": \"Gene disruption in DT40 and MIA PaCa-2 cells with N-glycan profiling, GMII activity assays and xenografts; SUMOylation site mutagenesis and MTF-1/SENP1 pathway manipulation in fish hepatocytes\",\n      \"pmids\": [\"38762179\", \"39367979\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"How SUMOylation at Lys-409 mechanically reduces stability not defined\", \"Whether SUMO regulation operates in mammalian secretory clients beyond hepatocytes unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Reported a non-canonical context where ZnT6 overexpression drives mitochondrial localization and redistributes Zn2+ into mitochondria, triggering fission, depolarization, ROS, and autophagy-linked apoptosis in cardiomyocytes.\",\n      \"evidence\": \"Confocal and electron microscopy, mitochondrial membrane potential/ROS/ATP assays, DRP1 translocation and autophagy/apoptosis markers in ZnT6-overexpressing H9c2 cells\",\n      \"pmids\": [\"40087209\", \"38091184\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Mitochondrial localization observed only under overexpression, not endogenous conditions\", \"Single cell-line system without in vivo confirmation\", \"Mechanism of mitochondrial targeting unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of zinc translocation by the ZnT5/ZnT6 heterodimer and the molecular rules governing client enzyme selection remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No high-resolution structure of the heterodimer or its client-loading interface\", \"How specific apo-enzymes are recognized and stabilized prior to metalation is undefined\", \"Whether the mitochondrial/cardiomyocyte phenotypes reflect a physiological function or an overexpression artifact is unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 9, 14]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [5, 7, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 9, 11]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [3, 5, 13]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [10, 13]}\n    ],\n    \"complexes\": [\"ZnT5/ZnT6 heterodimer\"],\n    \"partners\": [\"SLC30A5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}