{"gene":"MCOLN3","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2002,"finding":"MCOLN3/TRPML3 is a putative six-transmembrane-domain ion channel protein with sequence and motif similarities to TRP channels; it localizes to cytoplasmic compartments of hair cells and the plasma membrane of stereocilia, and plays an essential role during early hair cell maturation acting cell-autonomously. The Va allele A419P substitution in TM5 causes the varitint-waddler phenotype.","method":"Positional cloning, immunolocalization, mouse genetics (dominant mutant alleles)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — positional cloning plus direct localization, foundational discovery replicated across subsequent studies","pmids":["12403827"],"is_preprint":false},{"year":2006,"finding":"TRPML1, TRPML2, and TRPML3 interact to form homo- and heteromultimers. TRPML3 homomultimers localize to the ER, but TRPML3 is redirected to lysosomes when co-expressed with TRPML1 or TRPML2, demonstrating a hierarchy in which TRPML1 and TRPML2 dictate TRPML3 subcellular localization.","method":"Co-immunoprecipitation, confocal co-localization, dominant-negative lysosomal targeting mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus functional localization rescue, strong evidence from multiple approaches","pmids":["16606612"],"is_preprint":false},{"year":2007,"finding":"The varitint-waddler A419P mutation in TM5 renders TRPML3 constitutively active as a cation channel; a proline substitution scan showed the inner third of TM5 is highly susceptible to proline-based kinks that constitutively open the channel, causing hair cell death and deafness.","method":"Electrophysiology (patch clamp in heterologous cells and native hair cells), proline substitution scan mutagenesis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — direct electrophysiology with systematic mutagenesis, confirmed in native cells","pmids":["18048323"],"is_preprint":false},{"year":2007,"finding":"Wild-type TRPML3 is a strongly inward-rectifying cation channel regulated by extracytosolic Na+; preincubating the extracytosolic face in Na+-free medium is required for channel activation. The A419P mutation locks the channel in an open, unregulated state (gain-of-function), affects channel glycosylation, and causes cell death. The I362T mutation results in an inactive channel but reduces surface expression and current density of the A419P background.","method":"Patch-clamp electrophysiology (excised inside-out patches), mutagenesis, surface biotinylation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro electrophysiology with mutagenesis, multiple orthogonal methods","pmids":["17962195"],"is_preprint":false},{"year":2007,"finding":"Wild-type TRPML3 forms cation channels with ~50–70 pS conductance that are blocked by Gd3+ and rectify outwardly; the A419P (and I362T/A419P) mutations generate a constitutive inwardly rectifying current that depolarizes cells. Cells expressing A419P TRPML3 die and are extruded from the epithelium, mimicking hair cell degeneration.","method":"Patch-clamp electrophysiology (heterologous LLC-PK1-CL4 cells), cell death assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — direct electrophysiology with defined conductance measurements and mutagenesis","pmids":["18162548"],"is_preprint":false},{"year":2008,"finding":"TRPML3 is a Ca2+-permeable channel uniquely regulated by extracytosolic (luminal) H+ through three histidines (H252, H273, H283) in the large extracytosolic loop between TM1 and TM2. H283 is the inhibitory residue; H283A mimics A419P gain-of-function, while H283R inactivates the channel. The A419P mutation eliminates H+-mediated regulation by disrupting communication between the extracytosolic loop and TM5 pore gating.","method":"Patch-clamp electrophysiology, site-directed mutagenesis of histidine residues, pH titration","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis combined with electrophysiology revealing specific regulatory residues","pmids":["18369318"],"is_preprint":false},{"year":2008,"finding":"TRPML3 localizes to the base of stereocilia near the ankle-link position in postnatal hair cells. The Va(J) mutations (I362T/A419P) abolish this stereociliary localization, reduce mechano-electrical transducer (MET) currents, and decrease FM1-43/gentamicin uptake; outer hair cells of Va(J) homozygotes additionally show an inwardly rectifying leak current causing depolarization.","method":"Immunohistochemistry with TRPML3-specific antibody, electrophysiology (MET current recordings), FM1-43 uptake, [3H]gentamicin accumulation","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 — specific antibody localization linked to functional MET current phenotype; multiple orthogonal readouts","pmids":["18801844"],"is_preprint":false},{"year":2009,"finding":"TRPML3 is a regulator of endocytosis, membrane trafficking, and autophagy. It dynamically localizes to the plasma membrane and multiple intracellular compartments; its plasma membrane accumulation increases upon endocytosis inhibition and it is recruited to autophagosomes upon autophagy induction. Overexpression reduces endocytosis and increases autophagy; siRNA knockdown and dominant-negative TRPML3(D458K) reduce both endocytosis and autophagy.","method":"Gradient fractionation, confocal localization, siRNA knockdown, dominant-negative overexpression, autophagy/endocytosis assays","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KD, DN, fractionation) with quantitative functional readouts","pmids":["19522758"],"is_preprint":false},{"year":2009,"finding":"PMCA2 (plasma membrane Ca2+-ATPase 2) rescues the cytosolic Ca2+ overload and apoptosis caused by constitutively active TRPML3(A419P); reducing PMCA2 activity (deaf-waddler allele) exacerbates hair cell loss and vestibular/auditory defects in varitint-waddler mice, providing a molecular basis for delayed hair cell death.","method":"Heterologous co-expression in HEK293 cells, intracellular Ca2+ imaging, apoptosis assays, mouse double-mutant genetics","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in vivo combined with in vitro Ca2+ rescue experiments","pmids":["19299509"],"is_preprint":false},{"year":2010,"finding":"The TRPML3 pore is dynamic during Ca2+ conduction, with conductance and permeability modulated by Ca2+ trapping within the pore; strong depolarization or Na+ conduction restores pore properties. The A419P mutation produces a stably expanded pore with altered permeability that cannot be modulated by Ca2+, a mechanism specific to A419P and not shared by A419G, H283A, or other TM5 proline mutations.","method":"Patch-clamp electrophysiology (inside-out patches), ion substitution experiments, mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct biophysical characterization with systematic mutagenesis","pmids":["20378547"],"is_preprint":false},{"year":2010,"finding":"TRPML3 constitutive activity in low/no extracellular Na+ is sodium-independent intracellularly; Glu-361 in the second extracellular loop is critical for sodium-mediated block of TRPML3. TRPML2 shares similar activation by low extracellular sodium and responds to a subset of TRPML3 activating small molecules, suggesting conserved gating mechanisms.","method":"Mutagenesis of negatively charged extracellular loop residues, patch-clamp electrophysiology, small molecule pharmacology","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with electrophysiology identifying specific regulatory residue","pmids":["22753890"],"is_preprint":false},{"year":2010,"finding":"A high-throughput screen identified 53 small molecule activators of TRPML3 from nine chemical scaffolds. These activators synergize with low extracytosolic Na+ to potentiate TRPML3 activation, revealing distinct and cooperative activation mechanisms. Native hair cell or melanocyte TRPML3 did not respond to activators, suggesting plasma membrane absence or heteromeric channel formation in native cells.","method":"High-throughput electrophysiology screen, cheminformatics, native cell recordings","journal":"Chemistry & biology","confidence":"Medium","confidence_rationale":"Tier 1 for channel pharmacology; native cell data is negative/indirect","pmids":["20189104"],"is_preprint":false},{"year":2013,"finding":"TRPML3 associates with TRPV5 to form a novel heteromeric ion channel with pharmacological similarity to TRPML3 homomers and requiring functional versions of both subunits; single-channel analysis revealed distinct features and potentially different stoichiometric configurations compared to homomers.","method":"Co-immunoprecipitation, patch-clamp electrophysiology (single-channel), mutagenesis of both subunits","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus electrophysiology but single lab study","pmids":["23469151"],"is_preprint":false},{"year":2017,"finding":"Cryo-EM structure of full-length TRPML3 at 2.9 Å resolution reveals a unique cytosolic 'mucolipin domain' linking the voltage sensor-like domain to the pore; this domain is responsible for PtdIns(3,5)P2 binding and acts as a 'gating pulley' for lipid-dependent channel gating. The structure also reveals the molecular basis of ion conduction.","method":"Cryo-electron microscopy (2.9 Å), functional electrophysiology, mutagenesis of PtdIns(3,5)P2 binding residues","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — near-atomic resolution cryo-EM structure with functional validation by mutagenesis and electrophysiology","pmids":["29019979"],"is_preprint":false},{"year":2017,"finding":"Cryo-EM structures of human TRPML3 in closed (4.06 Å), agonist-activated (3.62 Å), and low-pH-inhibited (4.65 Å) states reveal that the agonist ML-SA1 lodges between S5 and S6 to open the S6 gate; S1 extends into a luminal PMD cap as a 'gating rod' connected to a luminal pore loop that changes conformation at low pH; S2 extends intracellularly as a 'gating knob'. These features define pH- and PIP2-dependent TRPML3 gating.","method":"Cryo-EM (three conformational states), electrophysiology (ML-SA1 and pH experiments), mutagenesis","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — multiple cryo-EM states plus functional electrophysiology, rigorous structural-functional correlation","pmids":["29106414"],"is_preprint":false},{"year":2018,"finding":"MCOLN3/TRPML3 undergoes palmitoylation at its C-terminal region; palmitoylation is required for dynamic trafficking of TRPML3 to autophagic structures and for its function as a Ca2+ channel supporting autophagy, but does not affect intrinsic channel properties or localization/function of intracellular TRPML3. Nutrient starvation increases TRPML3 palmitoylation and Ca2+ release; disruption of palmitoylation abolishes starvation-induced TRPML3 activation.","method":"17-ODYA metabolic labeling, 2-bromopalmitate inhibition, hydroxylamine treatment, mass spectrometry, Ca2+ imaging, autophagy flux assays","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1–2 — chemical labeling plus MS identification of palmitoylation sites, combined with functional Ca2+ and autophagy readouts","pmids":["30215288"],"is_preprint":false},{"year":2022,"finding":"TRPML3 localizes in phagophores and is a direct effector of PI3P; PI3P binds TRPML3 and directly activates its current and Ca2+ release from the phagophore to promote autophagosome biogenesis. Inhibition of TRPML3 blocks autophagy even with excess PI3P; TRPML3 also interacts with the ATG8 homolog GATE16.","method":"TRPML3-GCaMP6 targeted Ca2+ reporter, lipid binding assays, patch-clamp electrophysiology, autophagy flux assays, TRPML3 KO/KD","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including targeted Ca2+ reporter, direct lipid activation, and genetic rescue","pmids":["36252030"],"is_preprint":false},{"year":2022,"finding":"FGL2 directly interacts with MCOLN3/mucolipin 3, triggering calcium influx and initiating autophagy that leads to neutrophil extracellular trap (NET) formation and liver injury in fulminant viral hepatitis.","method":"Co-immunoprecipitation (FGL2-MCOLN3 interaction), Ca2+ flux assay, adoptive transfer, mouse model","journal":"Cellular and molecular gastroenterology and hepatology","confidence":"Medium","confidence_rationale":"Tier 3 — single Co-IP with functional Ca2+ and phenotypic readouts but single lab","pmids":["35926777"],"is_preprint":false},{"year":2022,"finding":"TRPML3 senses elevation of lysosomal pH (caused by gefitinib) to trigger lysosomal Ca2+ release, lysosomal trafficking and exocytosis, and exosomal release, promoting drug resistance in NSCLC; TRPML3 deficiency enhances gefitinib-mediated cell death.","method":"TRPML3 KD (siRNA), lysosomal pH measurement, Ca2+ imaging, exosome quantification, drug sensitivity assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — KD with functional readouts but single lab, no reconstitution","pmids":["36037747"],"is_preprint":false},{"year":2025,"finding":"MCOLN1/TRPML1 and MCOLN3/TRPML3 form a heteromer that acts as the Ca2+ provider for autophagosome-lysosome fusion downstream of PtdIns4P. The Ca2+ signal is decoded by Ca2+ sensor SYT5 (synaptotagmin 5), whose binding to both Ca2+ and PtdIns4P is critical for assembling the fusion complex.","method":"Co-immunoprecipitation (TRPML1-TRPML3 heteromer), Ca2+ imaging, PtdIns4P binding assays, autophagy flux assays, KO/KD experiments","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus functional lipid and Ca2+ readouts in single lab study","pmids":["40413756"],"is_preprint":false},{"year":2025,"finding":"TRPML3 specifically interacts with the ATG8 homolog GATE16 (but not LC3B) via single amino acid motifs in both proteins; RAB33B, a Golgi-resident GTPase, also interacts with TRPML3 through an LIR motif that specifically binds GATE16, and is recruited from the Golgi to the phagophore upon autophagy induction to promote autophagosome formation.","method":"Co-immunoprecipitation, mutagenesis of interaction motifs, confocal imaging of RAB33B recruitment, autophagy flux assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP with motif mutagenesis and functional autophagy readouts but single lab","pmids":["40855209"],"is_preprint":false},{"year":2025,"finding":"Somatic gain-of-function mutations in MCOLN3 (p.Y391D, p.F415I, p.N411_V412delinsI), located near the ion pore and selectivity filter, cause cell membrane depolarization and calcium influx in adrenocortical cells, leading to increased aldosterone synthase (CYP11B2) expression and aldosterone production, identifying MCOLN3 as a driver of primary aldosteronism.","method":"Next-generation sequencing of APAs, patch-clamp electrophysiology, fura-2 Ca2+ measurements, gene expression (CYP11B2), steroid quantification in HAC15 cells","journal":"Hypertension (Dallas, Tex. : 1979)","confidence":"High","confidence_rationale":"Tier 1–2 — direct electrophysiology and Ca2+ measurements with gain-of-function mutants and functional aldosterone readout","pmids":["40772318"],"is_preprint":false},{"year":2025,"finding":"Alkaline extracellular pH elevates lysosomal pH and activates the lysosomal Ca2+ channel TRPML3, which in turn activates RNF13 (an E3 ubiquitin ligase) to drive perinuclear lysosomal repositioning via ARL8B degradation.","method":"Lysosomal Ca2+ measurements, TRPML3 pharmacological activation/inhibition, lysosomal positioning imaging, RNF13 activity assays","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 — preprint, pharmacological activation, indirect functional link","pmids":[],"is_preprint":true}],"current_model":"MCOLN3/TRPML3 is an inwardly rectifying, Ca2+-permeable cation channel of the TRP superfamily that resides primarily in endolysosomal membranes (with dynamic trafficking to autophagosomes and the plasma membrane); it is activated by the lysosomal lipid PtdIns(3,5)P2 (via a cytosolic mucolipin domain acting as a gating pulley) and by PI3P on phagophores, inhibited by low luminal pH through histidine residues in its extracytosolic loop, and blocked by extracytosolic Na+; gain-of-function mutations (especially A419P) constitutively open the channel by disrupting TM5 helical structure; it forms homo- and heteromultimers (including with TRPML1 and TRPV5) that dictate its subcellular localization; it is palmitoylated at its C-terminus to regulate trafficking to autophagic structures; and it provides Ca2+ at distinct stages of autophagy—during phagophore/autophagosome formation (as a PI3P effector interacting with GATE16 and RAB33B) and during autophagosome-lysosome fusion (as a TRPML1-TRPML3 heteromer acting via PtdIns4P and the Ca2+ sensor SYT5)—while its constitutive activity in varitint-waddler mice causes hair cell degeneration and deafness through Ca2+ overload countered by PMCA2."},"narrative":{"teleology":[{"year":2002,"claim":"Positional cloning of the varitint-waddler locus established MCOLN3 as a TRP-family channel essential for hair cell maturation and identified the A419P substitution in TM5 as the causative mutation, opening the field to functional characterization.","evidence":"Positional cloning, immunolocalization in hair cells, mouse genetics with dominant Va alleles","pmids":["12403827"],"confidence":"High","gaps":["Channel activity not yet demonstrated electrophysiologically","Mechanism by which A419P causes hair cell death unknown","Subcellular trafficking and endolysosomal function not explored"]},{"year":2006,"claim":"Demonstration that TRPML1–3 form homo- and heteromultimers, with TRPML1/2 redirecting TRPML3 from the ER to lysosomes, established that heteromerization dictates TRPML3 subcellular localization and functional context.","evidence":"Reciprocal co-immunoprecipitation, confocal co-localization, dominant-negative lysosomal targeting","pmids":["16606612"],"confidence":"High","gaps":["Stoichiometry of heteromeric complexes undetermined","Functional consequences of heteromerization on channel conductance unknown"]},{"year":2007,"claim":"Electrophysiological recordings revealed that TRPML3 is a strongly inward-rectifying cation channel regulated by extracytosolic Na⁺, and that the A419P mutation locks it in a constitutively open state — explaining hair cell death as a gain-of-function Ca²⁺ overload mechanism.","evidence":"Patch-clamp electrophysiology in heterologous cells and native hair cells, proline substitution scan mutagenesis, surface biotinylation","pmids":["18048323","17962195","18162548"],"confidence":"High","gaps":["Endogenous regulatory lipids not yet identified","Structural basis of TM5 gating not resolved","Physiological activator in vivo unknown"]},{"year":2008,"claim":"Identification of three extracytosolic histidines (H252, H273, H283) as pH sensors, with H283 serving as the inhibitory switch, established luminal pH as a gating mechanism and showed that A419P bypasses pH regulation — linking TRPML3 activity to the acidic endolysosomal lumen.","evidence":"Systematic histidine mutagenesis combined with patch-clamp pH titration","pmids":["18369318"],"confidence":"High","gaps":["Structural mechanism of pH-induced conformational change unresolved","Relative contributions of pH vs. Na⁺ block in vivo unclear"]},{"year":2008,"claim":"Localization of TRPML3 to the stereocilia ankle-link region and demonstration that Va(J) mutations abolish this localization while reducing mechanotransduction currents provided the first evidence that TRPML3 functions at a specific subcellular site in hair cells.","evidence":"TRPML3-specific immunohistochemistry, MET current recordings, FM1-43 uptake in Va(J) mice","pmids":["18801844"],"confidence":"High","gaps":["Whether TRPML3 is a component of the MET complex or an accessory channel remains unresolved","Mechanism of TRPML3 stereociliary targeting unknown"]},{"year":2009,"claim":"Functional studies showing that TRPML3 dynamically traffics between the plasma membrane and intracellular compartments, is recruited to autophagosomes upon starvation, and is required for both endocytosis and autophagy established its role as a membrane trafficking regulator beyond hair cells.","evidence":"Gradient fractionation, siRNA knockdown, dominant-negative TRPML3(D458K), autophagy/endocytosis flux assays","pmids":["19522758"],"confidence":"High","gaps":["Ca²⁺-dependent mechanism linking TRPML3 to autophagosome formation unknown","Lipid activators of TRPML3 autophagy function not identified"]},{"year":2009,"claim":"Genetic epistasis between varitint-waddler and deaf-waddler (PMCA2) mice, combined with Ca²⁺ imaging rescue experiments, established that PMCA2 counteracts TRPML3-mediated Ca²⁺ overload, providing a quantitative model for delayed hair cell death.","evidence":"Double-mutant mouse genetics, HEK293 co-expression, intracellular Ca²⁺ imaging, apoptosis assays","pmids":["19299509"],"confidence":"High","gaps":["Whether other Ca²⁺ clearance mechanisms contribute in vivo is untested","Downstream Ca²⁺-dependent death pathways not fully mapped"]},{"year":2010,"claim":"Biophysical characterization showed that A419P produces a uniquely expanded pore resistant to Ca²⁺-mediated modulation, and identification of E361 as the critical residue for Na⁺ block refined understanding of extracytosolic gating mechanisms.","evidence":"Inside-out patch clamp with ion substitution, systematic mutagenesis of charged extracellular loop residues","pmids":["20378547","22753890"],"confidence":"High","gaps":["Atomic-resolution pore structure not yet available","Physiological significance of pore plasticity in normal TRPML3 function unclear"]},{"year":2017,"claim":"Cryo-EM structures of TRPML3 at near-atomic resolution in multiple states revealed the mucolipin domain as a PtdIns(3,5)P₂-binding gating pulley, defined the agonist-binding site between S5–S6, and showed how the luminal PMD cap and S1 gating rod transduce pH inhibition — providing the first complete structural framework for TRPML gating.","evidence":"Cryo-EM at 2.9–4.65 Å in closed, ML-SA1-activated, and low-pH-inhibited states; mutagenesis with electrophysiology","pmids":["29019979","29106414"],"confidence":"High","gaps":["No structure of the heteromeric TRPML1–TRPML3 complex","Structural basis of Na⁺ block not captured","Lipid-bound open-state structure lacking"]},{"year":2018,"claim":"Discovery that C-terminal palmitoylation is required for starvation-induced TRPML3 trafficking to autophagic structures and Ca²⁺ release identified a post-translational switch that couples nutrient status to TRPML3 activation.","evidence":"17-ODYA metabolic labeling, mass spectrometry, 2-bromopalmitate inhibition, Ca²⁺ imaging, autophagy flux assays","pmids":["30215288"],"confidence":"High","gaps":["Palmitoyl transferase(s) responsible not identified","Whether depalmitoylation terminates TRPML3 autophagy function untested"]},{"year":2022,"claim":"Identification of PI3P as a direct activator of TRPML3 on phagophores, and of TRPML3 as a PI3P effector required for autophagosome biogenesis, resolved how early autophagy lipid signals are transduced into Ca²⁺ release at the phagophore membrane.","evidence":"TRPML3-GCaMP6 targeted Ca²⁺ reporter, lipid binding assays, patch-clamp electrophysiology, TRPML3 KO/KD with autophagy flux rescue","pmids":["36252030"],"confidence":"High","gaps":["How PI3P and PtdIns(3,5)P₂ activation are distinguished structurally unknown","Downstream Ca²⁺ effectors at the phagophore not fully defined"]},{"year":2022,"claim":"Demonstration that TRPML3 senses lysosomal pH elevation (e.g., gefitinib-induced) to trigger lysosomal exocytosis and exosome release linked TRPML3 pH-sensing to drug resistance, while the FGL2–TRPML3 interaction connected TRPML3-dependent Ca²⁺/autophagy to NET formation in viral hepatitis.","evidence":"siRNA knockdown with lysosomal pH/Ca²⁺ imaging and exosome quantification (gefitinib); Co-IP with Ca²⁺ flux and mouse models (FGL2)","pmids":["36037747","35926777"],"confidence":"Medium","gaps":["FGL2–TRPML3 interaction awaits reciprocal validation and structural characterization","Whether TRPML3-mediated exocytosis occurs in non-cancer contexts untested","Direct binding site of FGL2 on TRPML3 unknown"]},{"year":2025,"claim":"The TRPML1–TRPML3 heteromer was identified as the Ca²⁺ source for PtdIns4P/SYT5-dependent autophagosome–lysosome fusion, establishing that TRPML3 participates in two distinct lipid-gated Ca²⁺ release steps during autophagy (PI3P at the phagophore and PtdIns4P at fusion).","evidence":"Co-immunoprecipitation of TRPML1–TRPML3, Ca²⁺ imaging, PtdIns4P binding assays, KO/KD autophagy flux","pmids":["40413756"],"confidence":"Medium","gaps":["Stoichiometry and structure of the TRPML1–TRPML3 heteromer unknown","Whether SYT5 is the sole Ca²⁺ sensor for this fusion step untested"]},{"year":2025,"claim":"Mapping of GATE16-specific and RAB33B-specific interaction motifs on TRPML3 defined a TRPML3–GATE16–RAB33B axis at the phagophore, resolving how TRPML3 selectively recruits Golgi-derived RAB33B to promote autophagosome formation.","evidence":"Co-immunoprecipitation, LIR/GIM motif mutagenesis, confocal RAB33B recruitment imaging, autophagy flux assays","pmids":["40855209"],"confidence":"Medium","gaps":["Direct structural evidence for ternary complex lacking","Whether GATE16 selectivity over LC3B has functional consequences for autophagy cargo selection unknown"]},{"year":2025,"claim":"Discovery of somatic gain-of-function MCOLN3 mutations (Y391D, F415I, N411_V412delinsI) in aldosterone-producing adenomas established TRPML3 as a driver of primary aldosteronism through constitutive Ca²⁺ influx and CYP11B2 upregulation.","evidence":"Next-generation sequencing of APAs, patch-clamp electrophysiology, fura-2 Ca²⁺ measurements, CYP11B2 expression and aldosterone quantification in HAC15 cells","pmids":["40772318"],"confidence":"High","gaps":["Frequency of MCOLN3 mutations across APA cohorts not established","Mechanism by which Ca²⁺ influx activates CYP11B2 transcription not delineated","Whether these mutants also affect autophagy in adrenocortical cells unknown"]},{"year":null,"claim":"Key unresolved questions include the structure of the TRPML1–TRPML3 heteromeric complex, the identity of palmitoyl transferases regulating TRPML3 autophagy trafficking, the structural basis for PI3P versus PtdIns(3,5)P₂ discrimination, and whether TRPML3's dual role in phagophore biogenesis and autophagosome–lysosome fusion is coordinated by a single regulatory switch.","evidence":"","pmids":[],"confidence":"Low","gaps":["No heteromeric cryo-EM structure","Palmitoyl transferase identity unknown","PI3P vs PtdIns(3,5)P₂ binding site discrimination unresolved structurally"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[2,3,4,5,9,13,14]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[13,16]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[1,7,18,22]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,7]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[7,15,16]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[0,6]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[7,15,16,19,20]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[7,18]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[2,3,5,13,14]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[0,6]}],"complexes":["TRPML1-TRPML3 heteromer","TRPML3-TRPV5 heteromer"],"partners":["MCOLN1","MCOLN2","TRPV5","GABARAPL2","RAB33B","SYT5","ATP2B2","FGL2"],"other_free_text":[]},"mechanistic_narrative":"MCOLN3/TRPML3 is a Ca²⁺-permeable, inwardly rectifying cation channel of the mucolipin/TRPML subfamily that functions in endolysosomal ion homeostasis, autophagy, and sensory cell development. The channel is gated by the endolysosomal lipid PtdIns(3,5)P₂ via a unique cytosolic mucolipin domain that acts as a gating pulley, is inhibited by low luminal pH through extracytosolic histidine residues (notably H283), and is blocked by extracytosolic Na⁺ at residue E361; cryo-EM structures in closed, agonist-bound, and pH-inhibited states define the structural basis of these regulatory mechanisms [PMID:29019979, PMID:29106414, PMID:18369318, PMID:22753890]. TRPML3 provides Ca²⁺ at multiple stages of autophagy: it is activated by PI3P on phagophores to promote autophagosome biogenesis in concert with GATE16 and RAB33B, and forms a heteromer with TRPML1 that supplies Ca²⁺ for PtdIns4P/SYT5-dependent autophagosome–lysosome fusion; palmitoylation at its C-terminus is required for starvation-induced trafficking to autophagic structures [PMID:36252030, PMID:40855209, PMID:40413756, PMID:30215288]. Somatic gain-of-function mutations near the pore (Y391D, F415I, N411_V412delinsI) cause constitutive Ca²⁺ influx in adrenocortical cells and drive aldosterone overproduction, identifying MCOLN3 as a causative gene in primary aldosteronism, while the classical A419P gain-of-function mutation in TM5 causes hair cell degeneration and deafness in varitint-waddler mice through Ca²⁺ overload counteracted by PMCA2 [PMID:40772318, PMID:12403827, PMID:18048323, PMID:19299509]."},"prefetch_data":{"uniprot":{"accession":"Q8TDD5","full_name":"Mucolipin-3","aliases":["Transient receptor potential channel mucolipin 3","TRPML3"],"length_aa":553,"mass_kda":64.2,"function":"Nonselective cation channel probably playing a role in the regulation of membrane trafficking events. Acts as a Ca(2+)-permeable cation channel with inwardly rectifying activity (PubMed:18369318, PubMed:19497048, PubMed:19522758, PubMed:19885840, PubMed:29106414). Mediates release of Ca(2+) from endosomes to the cytoplasm, contributes to endosomal acidification and is involved in the regulation of membrane trafficking and fusion in the endosomal pathway (PubMed:21245134). Also permeable to Mg(2+), Na(+) and K(+) (By similarity). Does not seem to act as mechanosensory transduction channel in inner ear sensory hair cells. Proposed to play a critical role at the cochlear stereocilia ankle-link region during hair-bundle growth (By similarity). Involved in the regulation of autophagy (PubMed:19522758). Through association with GABARAPL2 may be involved in autophagosome formation possibly providing Ca(2+) for the fusion process (By similarity). Through a possible and probably tissue-specific heteromerization with MCOLN1 may be at least in part involved in many lysosome-dependent cellular events (PubMed:19885840). Possible heteromeric ion channel assemblies with TRPV5 show pharmacological similarity with TRPML3 (PubMed:23469151)","subcellular_location":"Cell membrane; Early endosome membrane; Late endosome membrane; Lysosome membrane; Cytoplasmic vesicle, autophagosome membrane","url":"https://www.uniprot.org/uniprotkb/Q8TDD5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MCOLN3","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":[],"url":"https://opencell.sf.czbiohub.org/search/MCOLN3","total_profiled":1310},"omim":[{"mim_id":"607400","title":"MUCOLIPIN 3; MCOLN3","url":"https://www.omim.org/entry/607400"},{"mim_id":"607399","title":"MUCOLIPIN 2; MCOLN2","url":"https://www.omim.org/entry/607399"},{"mim_id":"605248","title":"MUCOLIPIN 1; MCOLN1","url":"https://www.omim.org/entry/605248"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"adrenal gland","ntpm":41.3},{"tissue":"epididymis","ntpm":13.3},{"tissue":"parathyroid gland","ntpm":33.2}],"url":"https://www.proteinatlas.org/search/MCOLN3"},"hgnc":{"alias_symbol":["TRPML3","FLJ11006","TRP-ML3"],"prev_symbol":[]},"alphafold":{"accession":"Q8TDD5","domains":[{"cath_id":"-","chopping":"104-195_205-275","consensus_level":"high","plddt":87.0309,"start":104,"end":275},{"cath_id":"1.20.120","chopping":"53-82_280-395","consensus_level":"high","plddt":90.2226,"start":53,"end":395},{"cath_id":"1.10.287","chopping":"400-528","consensus_level":"high","plddt":92.7819,"start":400,"end":528}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDD5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDD5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8TDD5-F1-predicted_aligned_error_v6.png","plddt_mean":84.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MCOLN3","jax_strain_url":"https://www.jax.org/strain/search?query=MCOLN3"},"sequence":{"accession":"Q8TDD5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8TDD5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8TDD5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8TDD5"}},"corpus_meta":[{"pmid":"12403827","id":"PMC_12403827","title":"Mutations 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The Va allele A419P substitution in TM5 causes the varitint-waddler phenotype.\",\n      \"method\": \"Positional cloning, immunolocalization, mouse genetics (dominant mutant alleles)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — positional cloning plus direct localization, foundational discovery replicated across subsequent studies\",\n      \"pmids\": [\"12403827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"TRPML1, TRPML2, and TRPML3 interact to form homo- and heteromultimers. TRPML3 homomultimers localize to the ER, but TRPML3 is redirected to lysosomes when co-expressed with TRPML1 or TRPML2, demonstrating a hierarchy in which TRPML1 and TRPML2 dictate TRPML3 subcellular localization.\",\n      \"method\": \"Co-immunoprecipitation, confocal co-localization, dominant-negative lysosomal targeting mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus functional localization rescue, strong evidence from multiple approaches\",\n      \"pmids\": [\"16606612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The varitint-waddler A419P mutation in TM5 renders TRPML3 constitutively active as a cation channel; a proline substitution scan showed the inner third of TM5 is highly susceptible to proline-based kinks that constitutively open the channel, causing hair cell death and deafness.\",\n      \"method\": \"Electrophysiology (patch clamp in heterologous cells and native hair cells), proline substitution scan mutagenesis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct electrophysiology with systematic mutagenesis, confirmed in native cells\",\n      \"pmids\": [\"18048323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Wild-type TRPML3 is a strongly inward-rectifying cation channel regulated by extracytosolic Na+; preincubating the extracytosolic face in Na+-free medium is required for channel activation. The A419P mutation locks the channel in an open, unregulated state (gain-of-function), affects channel glycosylation, and causes cell death. The I362T mutation results in an inactive channel but reduces surface expression and current density of the A419P background.\",\n      \"method\": \"Patch-clamp electrophysiology (excised inside-out patches), mutagenesis, surface biotinylation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro electrophysiology with mutagenesis, multiple orthogonal methods\",\n      \"pmids\": [\"17962195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Wild-type TRPML3 forms cation channels with ~50–70 pS conductance that are blocked by Gd3+ and rectify outwardly; the A419P (and I362T/A419P) mutations generate a constitutive inwardly rectifying current that depolarizes cells. Cells expressing A419P TRPML3 die and are extruded from the epithelium, mimicking hair cell degeneration.\",\n      \"method\": \"Patch-clamp electrophysiology (heterologous LLC-PK1-CL4 cells), cell death assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct electrophysiology with defined conductance measurements and mutagenesis\",\n      \"pmids\": [\"18162548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"TRPML3 is a Ca2+-permeable channel uniquely regulated by extracytosolic (luminal) H+ through three histidines (H252, H273, H283) in the large extracytosolic loop between TM1 and TM2. H283 is the inhibitory residue; H283A mimics A419P gain-of-function, while H283R inactivates the channel. The A419P mutation eliminates H+-mediated regulation by disrupting communication between the extracytosolic loop and TM5 pore gating.\",\n      \"method\": \"Patch-clamp electrophysiology, site-directed mutagenesis of histidine residues, pH titration\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis combined with electrophysiology revealing specific regulatory residues\",\n      \"pmids\": [\"18369318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"TRPML3 localizes to the base of stereocilia near the ankle-link position in postnatal hair cells. The Va(J) mutations (I362T/A419P) abolish this stereociliary localization, reduce mechano-electrical transducer (MET) currents, and decrease FM1-43/gentamicin uptake; outer hair cells of Va(J) homozygotes additionally show an inwardly rectifying leak current causing depolarization.\",\n      \"method\": \"Immunohistochemistry with TRPML3-specific antibody, electrophysiology (MET current recordings), FM1-43 uptake, [3H]gentamicin accumulation\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — specific antibody localization linked to functional MET current phenotype; multiple orthogonal readouts\",\n      \"pmids\": [\"18801844\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TRPML3 is a regulator of endocytosis, membrane trafficking, and autophagy. It dynamically localizes to the plasma membrane and multiple intracellular compartments; its plasma membrane accumulation increases upon endocytosis inhibition and it is recruited to autophagosomes upon autophagy induction. Overexpression reduces endocytosis and increases autophagy; siRNA knockdown and dominant-negative TRPML3(D458K) reduce both endocytosis and autophagy.\",\n      \"method\": \"Gradient fractionation, confocal localization, siRNA knockdown, dominant-negative overexpression, autophagy/endocytosis assays\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KD, DN, fractionation) with quantitative functional readouts\",\n      \"pmids\": [\"19522758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PMCA2 (plasma membrane Ca2+-ATPase 2) rescues the cytosolic Ca2+ overload and apoptosis caused by constitutively active TRPML3(A419P); reducing PMCA2 activity (deaf-waddler allele) exacerbates hair cell loss and vestibular/auditory defects in varitint-waddler mice, providing a molecular basis for delayed hair cell death.\",\n      \"method\": \"Heterologous co-expression in HEK293 cells, intracellular Ca2+ imaging, apoptosis assays, mouse double-mutant genetics\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in vivo combined with in vitro Ca2+ rescue experiments\",\n      \"pmids\": [\"19299509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The TRPML3 pore is dynamic during Ca2+ conduction, with conductance and permeability modulated by Ca2+ trapping within the pore; strong depolarization or Na+ conduction restores pore properties. The A419P mutation produces a stably expanded pore with altered permeability that cannot be modulated by Ca2+, a mechanism specific to A419P and not shared by A419G, H283A, or other TM5 proline mutations.\",\n      \"method\": \"Patch-clamp electrophysiology (inside-out patches), ion substitution experiments, mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biophysical characterization with systematic mutagenesis\",\n      \"pmids\": [\"20378547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"TRPML3 constitutive activity in low/no extracellular Na+ is sodium-independent intracellularly; Glu-361 in the second extracellular loop is critical for sodium-mediated block of TRPML3. TRPML2 shares similar activation by low extracellular sodium and responds to a subset of TRPML3 activating small molecules, suggesting conserved gating mechanisms.\",\n      \"method\": \"Mutagenesis of negatively charged extracellular loop residues, patch-clamp electrophysiology, small molecule pharmacology\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with electrophysiology identifying specific regulatory residue\",\n      \"pmids\": [\"22753890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"A high-throughput screen identified 53 small molecule activators of TRPML3 from nine chemical scaffolds. These activators synergize with low extracytosolic Na+ to potentiate TRPML3 activation, revealing distinct and cooperative activation mechanisms. Native hair cell or melanocyte TRPML3 did not respond to activators, suggesting plasma membrane absence or heteromeric channel formation in native cells.\",\n      \"method\": \"High-throughput electrophysiology screen, cheminformatics, native cell recordings\",\n      \"journal\": \"Chemistry & biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 for channel pharmacology; native cell data is negative/indirect\",\n      \"pmids\": [\"20189104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TRPML3 associates with TRPV5 to form a novel heteromeric ion channel with pharmacological similarity to TRPML3 homomers and requiring functional versions of both subunits; single-channel analysis revealed distinct features and potentially different stoichiometric configurations compared to homomers.\",\n      \"method\": \"Co-immunoprecipitation, patch-clamp electrophysiology (single-channel), mutagenesis of both subunits\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus electrophysiology but single lab study\",\n      \"pmids\": [\"23469151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Cryo-EM structure of full-length TRPML3 at 2.9 Å resolution reveals a unique cytosolic 'mucolipin domain' linking the voltage sensor-like domain to the pore; this domain is responsible for PtdIns(3,5)P2 binding and acts as a 'gating pulley' for lipid-dependent channel gating. The structure also reveals the molecular basis of ion conduction.\",\n      \"method\": \"Cryo-electron microscopy (2.9 Å), functional electrophysiology, mutagenesis of PtdIns(3,5)P2 binding residues\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — near-atomic resolution cryo-EM structure with functional validation by mutagenesis and electrophysiology\",\n      \"pmids\": [\"29019979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Cryo-EM structures of human TRPML3 in closed (4.06 Å), agonist-activated (3.62 Å), and low-pH-inhibited (4.65 Å) states reveal that the agonist ML-SA1 lodges between S5 and S6 to open the S6 gate; S1 extends into a luminal PMD cap as a 'gating rod' connected to a luminal pore loop that changes conformation at low pH; S2 extends intracellularly as a 'gating knob'. These features define pH- and PIP2-dependent TRPML3 gating.\",\n      \"method\": \"Cryo-EM (three conformational states), electrophysiology (ML-SA1 and pH experiments), mutagenesis\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple cryo-EM states plus functional electrophysiology, rigorous structural-functional correlation\",\n      \"pmids\": [\"29106414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MCOLN3/TRPML3 undergoes palmitoylation at its C-terminal region; palmitoylation is required for dynamic trafficking of TRPML3 to autophagic structures and for its function as a Ca2+ channel supporting autophagy, but does not affect intrinsic channel properties or localization/function of intracellular TRPML3. Nutrient starvation increases TRPML3 palmitoylation and Ca2+ release; disruption of palmitoylation abolishes starvation-induced TRPML3 activation.\",\n      \"method\": \"17-ODYA metabolic labeling, 2-bromopalmitate inhibition, hydroxylamine treatment, mass spectrometry, Ca2+ imaging, autophagy flux assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — chemical labeling plus MS identification of palmitoylation sites, combined with functional Ca2+ and autophagy readouts\",\n      \"pmids\": [\"30215288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TRPML3 localizes in phagophores and is a direct effector of PI3P; PI3P binds TRPML3 and directly activates its current and Ca2+ release from the phagophore to promote autophagosome biogenesis. Inhibition of TRPML3 blocks autophagy even with excess PI3P; TRPML3 also interacts with the ATG8 homolog GATE16.\",\n      \"method\": \"TRPML3-GCaMP6 targeted Ca2+ reporter, lipid binding assays, patch-clamp electrophysiology, autophagy flux assays, TRPML3 KO/KD\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including targeted Ca2+ reporter, direct lipid activation, and genetic rescue\",\n      \"pmids\": [\"36252030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FGL2 directly interacts with MCOLN3/mucolipin 3, triggering calcium influx and initiating autophagy that leads to neutrophil extracellular trap (NET) formation and liver injury in fulminant viral hepatitis.\",\n      \"method\": \"Co-immunoprecipitation (FGL2-MCOLN3 interaction), Ca2+ flux assay, adoptive transfer, mouse model\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP with functional Ca2+ and phenotypic readouts but single lab\",\n      \"pmids\": [\"35926777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TRPML3 senses elevation of lysosomal pH (caused by gefitinib) to trigger lysosomal Ca2+ release, lysosomal trafficking and exocytosis, and exosomal release, promoting drug resistance in NSCLC; TRPML3 deficiency enhances gefitinib-mediated cell death.\",\n      \"method\": \"TRPML3 KD (siRNA), lysosomal pH measurement, Ca2+ imaging, exosome quantification, drug sensitivity assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — KD with functional readouts but single lab, no reconstitution\",\n      \"pmids\": [\"36037747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MCOLN1/TRPML1 and MCOLN3/TRPML3 form a heteromer that acts as the Ca2+ provider for autophagosome-lysosome fusion downstream of PtdIns4P. The Ca2+ signal is decoded by Ca2+ sensor SYT5 (synaptotagmin 5), whose binding to both Ca2+ and PtdIns4P is critical for assembling the fusion complex.\",\n      \"method\": \"Co-immunoprecipitation (TRPML1-TRPML3 heteromer), Ca2+ imaging, PtdIns4P binding assays, autophagy flux assays, KO/KD experiments\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus functional lipid and Ca2+ readouts in single lab study\",\n      \"pmids\": [\"40413756\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TRPML3 specifically interacts with the ATG8 homolog GATE16 (but not LC3B) via single amino acid motifs in both proteins; RAB33B, a Golgi-resident GTPase, also interacts with TRPML3 through an LIR motif that specifically binds GATE16, and is recruited from the Golgi to the phagophore upon autophagy induction to promote autophagosome formation.\",\n      \"method\": \"Co-immunoprecipitation, mutagenesis of interaction motifs, confocal imaging of RAB33B recruitment, autophagy flux assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP with motif mutagenesis and functional autophagy readouts but single lab\",\n      \"pmids\": [\"40855209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Somatic gain-of-function mutations in MCOLN3 (p.Y391D, p.F415I, p.N411_V412delinsI), located near the ion pore and selectivity filter, cause cell membrane depolarization and calcium influx in adrenocortical cells, leading to increased aldosterone synthase (CYP11B2) expression and aldosterone production, identifying MCOLN3 as a driver of primary aldosteronism.\",\n      \"method\": \"Next-generation sequencing of APAs, patch-clamp electrophysiology, fura-2 Ca2+ measurements, gene expression (CYP11B2), steroid quantification in HAC15 cells\",\n      \"journal\": \"Hypertension (Dallas, Tex. : 1979)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct electrophysiology and Ca2+ measurements with gain-of-function mutants and functional aldosterone readout\",\n      \"pmids\": [\"40772318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Alkaline extracellular pH elevates lysosomal pH and activates the lysosomal Ca2+ channel TRPML3, which in turn activates RNF13 (an E3 ubiquitin ligase) to drive perinuclear lysosomal repositioning via ARL8B degradation.\",\n      \"method\": \"Lysosomal Ca2+ measurements, TRPML3 pharmacological activation/inhibition, lysosomal positioning imaging, RNF13 activity assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — preprint, pharmacological activation, indirect functional link\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"MCOLN3/TRPML3 is an inwardly rectifying, Ca2+-permeable cation channel of the TRP superfamily that resides primarily in endolysosomal membranes (with dynamic trafficking to autophagosomes and the plasma membrane); it is activated by the lysosomal lipid PtdIns(3,5)P2 (via a cytosolic mucolipin domain acting as a gating pulley) and by PI3P on phagophores, inhibited by low luminal pH through histidine residues in its extracytosolic loop, and blocked by extracytosolic Na+; gain-of-function mutations (especially A419P) constitutively open the channel by disrupting TM5 helical structure; it forms homo- and heteromultimers (including with TRPML1 and TRPV5) that dictate its subcellular localization; it is palmitoylated at its C-terminus to regulate trafficking to autophagic structures; and it provides Ca2+ at distinct stages of autophagy—during phagophore/autophagosome formation (as a PI3P effector interacting with GATE16 and RAB33B) and during autophagosome-lysosome fusion (as a TRPML1-TRPML3 heteromer acting via PtdIns4P and the Ca2+ sensor SYT5)—while its constitutive activity in varitint-waddler mice causes hair cell degeneration and deafness through Ca2+ overload countered by PMCA2.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MCOLN3/TRPML3 is a Ca²⁺-permeable, inwardly rectifying cation channel of the mucolipin/TRPML subfamily that functions in endolysosomal ion homeostasis, autophagy, and sensory cell development. The channel is gated by the endolysosomal lipid PtdIns(3,5)P₂ via a unique cytosolic mucolipin domain that acts as a gating pulley, is inhibited by low luminal pH through extracytosolic histidine residues (notably H283), and is blocked by extracytosolic Na⁺ at residue E361; cryo-EM structures in closed, agonist-bound, and pH-inhibited states define the structural basis of these regulatory mechanisms [PMID:29019979, PMID:29106414, PMID:18369318, PMID:22753890]. TRPML3 provides Ca²⁺ at multiple stages of autophagy: it is activated by PI3P on phagophores to promote autophagosome biogenesis in concert with GATE16 and RAB33B, and forms a heteromer with TRPML1 that supplies Ca²⁺ for PtdIns4P/SYT5-dependent autophagosome–lysosome fusion; palmitoylation at its C-terminus is required for starvation-induced trafficking to autophagic structures [PMID:36252030, PMID:40855209, PMID:40413756, PMID:30215288]. Somatic gain-of-function mutations near the pore (Y391D, F415I, N411_V412delinsI) cause constitutive Ca²⁺ influx in adrenocortical cells and drive aldosterone overproduction, identifying MCOLN3 as a causative gene in primary aldosteronism, while the classical A419P gain-of-function mutation in TM5 causes hair cell degeneration and deafness in varitint-waddler mice through Ca²⁺ overload counteracted by PMCA2 [PMID:40772318, PMID:12403827, PMID:18048323, PMID:19299509].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Positional cloning of the varitint-waddler locus established MCOLN3 as a TRP-family channel essential for hair cell maturation and identified the A419P substitution in TM5 as the causative mutation, opening the field to functional characterization.\",\n      \"evidence\": \"Positional cloning, immunolocalization in hair cells, mouse genetics with dominant Va alleles\",\n      \"pmids\": [\"12403827\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Channel activity not yet demonstrated electrophysiologically\", \"Mechanism by which A419P causes hair cell death unknown\", \"Subcellular trafficking and endolysosomal function not explored\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstration that TRPML1–3 form homo- and heteromultimers, with TRPML1/2 redirecting TRPML3 from the ER to lysosomes, established that heteromerization dictates TRPML3 subcellular localization and functional context.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, confocal co-localization, dominant-negative lysosomal targeting\",\n      \"pmids\": [\"16606612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of heteromeric complexes undetermined\", \"Functional consequences of heteromerization on channel conductance unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Electrophysiological recordings revealed that TRPML3 is a strongly inward-rectifying cation channel regulated by extracytosolic Na⁺, and that the A419P mutation locks it in a constitutively open state — explaining hair cell death as a gain-of-function Ca²⁺ overload mechanism.\",\n      \"evidence\": \"Patch-clamp electrophysiology in heterologous cells and native hair cells, proline substitution scan mutagenesis, surface biotinylation\",\n      \"pmids\": [\"18048323\", \"17962195\", \"18162548\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous regulatory lipids not yet identified\", \"Structural basis of TM5 gating not resolved\", \"Physiological activator in vivo unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of three extracytosolic histidines (H252, H273, H283) as pH sensors, with H283 serving as the inhibitory switch, established luminal pH as a gating mechanism and showed that A419P bypasses pH regulation — linking TRPML3 activity to the acidic endolysosomal lumen.\",\n      \"evidence\": \"Systematic histidine mutagenesis combined with patch-clamp pH titration\",\n      \"pmids\": [\"18369318\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism of pH-induced conformational change unresolved\", \"Relative contributions of pH vs. Na⁺ block in vivo unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Localization of TRPML3 to the stereocilia ankle-link region and demonstration that Va(J) mutations abolish this localization while reducing mechanotransduction currents provided the first evidence that TRPML3 functions at a specific subcellular site in hair cells.\",\n      \"evidence\": \"TRPML3-specific immunohistochemistry, MET current recordings, FM1-43 uptake in Va(J) mice\",\n      \"pmids\": [\"18801844\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TRPML3 is a component of the MET complex or an accessory channel remains unresolved\", \"Mechanism of TRPML3 stereociliary targeting unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Functional studies showing that TRPML3 dynamically traffics between the plasma membrane and intracellular compartments, is recruited to autophagosomes upon starvation, and is required for both endocytosis and autophagy established its role as a membrane trafficking regulator beyond hair cells.\",\n      \"evidence\": \"Gradient fractionation, siRNA knockdown, dominant-negative TRPML3(D458K), autophagy/endocytosis flux assays\",\n      \"pmids\": [\"19522758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ca²⁺-dependent mechanism linking TRPML3 to autophagosome formation unknown\", \"Lipid activators of TRPML3 autophagy function not identified\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Genetic epistasis between varitint-waddler and deaf-waddler (PMCA2) mice, combined with Ca²⁺ imaging rescue experiments, established that PMCA2 counteracts TRPML3-mediated Ca²⁺ overload, providing a quantitative model for delayed hair cell death.\",\n      \"evidence\": \"Double-mutant mouse genetics, HEK293 co-expression, intracellular Ca²⁺ imaging, apoptosis assays\",\n      \"pmids\": [\"19299509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other Ca²⁺ clearance mechanisms contribute in vivo is untested\", \"Downstream Ca²⁺-dependent death pathways not fully mapped\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biophysical characterization showed that A419P produces a uniquely expanded pore resistant to Ca²⁺-mediated modulation, and identification of E361 as the critical residue for Na⁺ block refined understanding of extracytosolic gating mechanisms.\",\n      \"evidence\": \"Inside-out patch clamp with ion substitution, systematic mutagenesis of charged extracellular loop residues\",\n      \"pmids\": [\"20378547\", \"22753890\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution pore structure not yet available\", \"Physiological significance of pore plasticity in normal TRPML3 function unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Cryo-EM structures of TRPML3 at near-atomic resolution in multiple states revealed the mucolipin domain as a PtdIns(3,5)P₂-binding gating pulley, defined the agonist-binding site between S5–S6, and showed how the luminal PMD cap and S1 gating rod transduce pH inhibition — providing the first complete structural framework for TRPML gating.\",\n      \"evidence\": \"Cryo-EM at 2.9–4.65 Å in closed, ML-SA1-activated, and low-pH-inhibited states; mutagenesis with electrophysiology\",\n      \"pmids\": [\"29019979\", \"29106414\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of the heteromeric TRPML1–TRPML3 complex\", \"Structural basis of Na⁺ block not captured\", \"Lipid-bound open-state structure lacking\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery that C-terminal palmitoylation is required for starvation-induced TRPML3 trafficking to autophagic structures and Ca²⁺ release identified a post-translational switch that couples nutrient status to TRPML3 activation.\",\n      \"evidence\": \"17-ODYA metabolic labeling, mass spectrometry, 2-bromopalmitate inhibition, Ca²⁺ imaging, autophagy flux assays\",\n      \"pmids\": [\"30215288\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Palmitoyl transferase(s) responsible not identified\", \"Whether depalmitoylation terminates TRPML3 autophagy function untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of PI3P as a direct activator of TRPML3 on phagophores, and of TRPML3 as a PI3P effector required for autophagosome biogenesis, resolved how early autophagy lipid signals are transduced into Ca²⁺ release at the phagophore membrane.\",\n      \"evidence\": \"TRPML3-GCaMP6 targeted Ca²⁺ reporter, lipid binding assays, patch-clamp electrophysiology, TRPML3 KO/KD with autophagy flux rescue\",\n      \"pmids\": [\"36252030\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PI3P and PtdIns(3,5)P₂ activation are distinguished structurally unknown\", \"Downstream Ca²⁺ effectors at the phagophore not fully defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstration that TRPML3 senses lysosomal pH elevation (e.g., gefitinib-induced) to trigger lysosomal exocytosis and exosome release linked TRPML3 pH-sensing to drug resistance, while the FGL2–TRPML3 interaction connected TRPML3-dependent Ca²⁺/autophagy to NET formation in viral hepatitis.\",\n      \"evidence\": \"siRNA knockdown with lysosomal pH/Ca²⁺ imaging and exosome quantification (gefitinib); Co-IP with Ca²⁺ flux and mouse models (FGL2)\",\n      \"pmids\": [\"36037747\", \"35926777\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"FGL2–TRPML3 interaction awaits reciprocal validation and structural characterization\", \"Whether TRPML3-mediated exocytosis occurs in non-cancer contexts untested\", \"Direct binding site of FGL2 on TRPML3 unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The TRPML1–TRPML3 heteromer was identified as the Ca²⁺ source for PtdIns4P/SYT5-dependent autophagosome–lysosome fusion, establishing that TRPML3 participates in two distinct lipid-gated Ca²⁺ release steps during autophagy (PI3P at the phagophore and PtdIns4P at fusion).\",\n      \"evidence\": \"Co-immunoprecipitation of TRPML1–TRPML3, Ca²⁺ imaging, PtdIns4P binding assays, KO/KD autophagy flux\",\n      \"pmids\": [\"40413756\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and structure of the TRPML1–TRPML3 heteromer unknown\", \"Whether SYT5 is the sole Ca²⁺ sensor for this fusion step untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mapping of GATE16-specific and RAB33B-specific interaction motifs on TRPML3 defined a TRPML3–GATE16–RAB33B axis at the phagophore, resolving how TRPML3 selectively recruits Golgi-derived RAB33B to promote autophagosome formation.\",\n      \"evidence\": \"Co-immunoprecipitation, LIR/GIM motif mutagenesis, confocal RAB33B recruitment imaging, autophagy flux assays\",\n      \"pmids\": [\"40855209\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct structural evidence for ternary complex lacking\", \"Whether GATE16 selectivity over LC3B has functional consequences for autophagy cargo selection unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery of somatic gain-of-function MCOLN3 mutations (Y391D, F415I, N411_V412delinsI) in aldosterone-producing adenomas established TRPML3 as a driver of primary aldosteronism through constitutive Ca²⁺ influx and CYP11B2 upregulation.\",\n      \"evidence\": \"Next-generation sequencing of APAs, patch-clamp electrophysiology, fura-2 Ca²⁺ measurements, CYP11B2 expression and aldosterone quantification in HAC15 cells\",\n      \"pmids\": [\"40772318\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Frequency of MCOLN3 mutations across APA cohorts not established\", \"Mechanism by which Ca²⁺ influx activates CYP11B2 transcription not delineated\", \"Whether these mutants also affect autophagy in adrenocortical cells unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structure of the TRPML1–TRPML3 heteromeric complex, the identity of palmitoyl transferases regulating TRPML3 autophagy trafficking, the structural basis for PI3P versus PtdIns(3,5)P₂ discrimination, and whether TRPML3's dual role in phagophore biogenesis and autophagosome–lysosome fusion is coordinated by a single regulatory switch.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No heteromeric cryo-EM structure\", \"Palmitoyl transferase identity unknown\", \"PI3P vs PtdIns(3,5)P₂ binding site discrimination unresolved structurally\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [2, 3, 4, 5, 9, 13, 14]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [13, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [1, 7, 18, 22]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [7, 15, 16]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [7, 15, 16, 19, 20]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [7, 18]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [2, 3, 5, 13, 14]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"complexes\": [\n      \"TRPML1-TRPML3 heteromer\",\n      \"TRPML3-TRPV5 heteromer\"\n    ],\n    \"partners\": [\n      \"MCOLN1\",\n      \"MCOLN2\",\n      \"TRPV5\",\n      \"GABARAPL2\",\n      \"RAB33B\",\n      \"SYT5\",\n      \"ATP2B2\",\n      \"FGL2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}