{"gene":"TOMM5","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":1998,"finding":"Tom5 is a component of the general import pore (GIP) complex of the TOM translocase, where it participates in preprotein transfer from surface receptors (Tom20, Tom70) to the channel protein Tom40. The GIP complex (~400 kDa) contains Tom40, Tom22, Tom5, Tom6, and Tom7.","method":"Biochemical fractionation, native PAGE, immunoprecipitation, yeast genetics","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP and native PAGE across multiple labs, replicated in multiple organisms","pmids":["9774667","9603986"],"is_preprint":false},{"year":2001,"finding":"Tom5 associates with the precursor of Tom40 during the first assembly intermediate (~250 kDa) at the sorting and assembly machinery (SAM complex), forming a step prior to the 100 kDa and 400 kDa mature TOM complex. Tom5 is required for progression of Tom40 assembly from the SAM complex to the mature TOM complex.","method":"Pulse-chase assembly assays, native PAGE, yeast mutant analysis","journal":"Nature structural biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in organello assembly assay with defined intermediates, replicated in subsequent studies","pmids":["11276259"],"is_preprint":false},{"year":2001,"finding":"The Tom40-Tom22 core is the stable unit retaining preproteins in the GIP complex; Tom5 (along with Tom6 and Tom7) is released under stringent detergent conditions while preprotein remains bound, indicating Tom5 is a peripheral/modulatory component rather than part of the core translocation unit.","method":"Urea/detergent dissociation assays, native PAGE, channel activity reconstitution","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical methods, replicated across labs","pmids":["11259583"],"is_preprint":false},{"year":2001,"finding":"Tom5 is required for the import and assembly of porin (VDAC) into the mitochondrial outer membrane, as shown by reduced import in tom5 mutant mitochondria. Porin biogenesis requires Tom5 in addition to Tom20, Tom22, Tom40, and Tom7.","method":"In vitro import assay with yeast tom5 mutant mitochondria","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in organello import assay in mutant mitochondria, single lab","pmids":["11266446"],"is_preprint":false},{"year":1999,"finding":"Tom5 of the GIP complex is crucial for the import of small Tim proteins of the intermembrane space, representing a third novel import pathway in which surface receptors (Tom20, Tom70) are dispensable but Tom5 is essential.","method":"In vitro import assays using yeast strains lacking individual TOM components","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in organello import assay in multiple tom mutant strains, single lab","pmids":["10397776"],"is_preprint":false},{"year":2002,"finding":"Tom5 is required for import of bacterial PorB (a VDAC-like beta-barrel protein) into the mitochondrial outer membrane in vitro; insertion is dependent on Tom5, Tom20, and Tom40 but independent of Tom70.","method":"In vitro import assay into isolated mitochondria with antibody inhibition of specific TOM subunits","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro import assay with antibody blockade, single lab","pmids":["11953311"],"is_preprint":false},{"year":2002,"finding":"The transmembrane segment (TMS) length, proline residue position in the TMS, and positive charges in the C-terminal segment (C-segment) together constitute the mitochondrial targeting signal of Tom5 as a C-tail-anchored protein. Reduction of net positive charge in the C-segment causes mislocalization to intracellular membranes; elongation of the TMS or separation of TMS and C-segment impairs targeting.","method":"Systematic deletion/mutation analysis of Tom5 TMS and flanking regions with GFP reporter, confocal microscopy, cell fractionation in COS-7 cells","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — systematic mutagenesis with multiple orthogonal readouts (imaging + fractionation), single lab","pmids":["12006657"],"is_preprint":false},{"year":2003,"finding":"Correct targeting and assembly of Tom5 into the TOM complex requires an appropriate TMS length (not merely hydrophobicity), a proline residue at the correct position in the TMS with specific flanking residues, but unlike other C-tail-anchored outer membrane proteins, does not require positive charges in the C-terminal segment. A minimal targeting signal (Ser-Pro-Met in Leu-Ala repeat context) is sufficient for mitochondrial targeting and functional complementation.","method":"In vivo GFP reporter assays, blue native PAGE, complementation of temperature-sensitive deltaTOM5 yeast cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — systematic mutagenesis with functional complementation assay, in vivo localization, and native complex assembly, single lab","pmids":["12896971"],"is_preprint":false},{"year":2000,"finding":"The cytosolic domain of Tom5 forms a stable helical core between residues E11 and R15, with a less structurally rigid helix extending to the C-terminus, as determined by CD and NMR spectroscopy.","method":"Circular dichroism (CD) and NMR (NOESY) spectroscopy","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — NMR structure determination, single lab, no functional mutagenesis validation","pmids":["10683449"],"is_preprint":false},{"year":2005,"finding":"Tom5 is required for maintaining the structural integrity of the TOM complex in yeast; deletion of TOM5 destabilizes the TOM complex and reduces protein import efficiency. In Neurospora crassa, Tom5 deletion does not affect TOM stability or import efficiency, indicating a species-specific structural role. Tom5 crosses the outer membrane with its C-terminus facing the IMS.","method":"Identification of Neurospora Tom5 by sequence homology; TOM complex stability assessed by native PAGE; import assays in deltaTOM5 yeast and N. crassa; complementation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — cross-species genetic complementation, native PAGE, import assays, replicated in two organisms","pmids":["15701639"],"is_preprint":false},{"year":2005,"finding":"Transport of Tafazzin (Taz1) into mitochondria depends on the receptor Tom5 of the TOM complex and the small Tim proteins of the IMS, but is independent of the SAM complex. This establishes Tom5 as required for import of this outer membrane IMS-exposed protein.","method":"In vitro import assays into yeast mitochondria lacking individual TOM/SAM/Tim components","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in organello import assays in multiple mutant backgrounds, single lab","pmids":["16135531"],"is_preprint":false},{"year":2009,"finding":"A Tom5-Tom40 subcomplex associates with the SAM core complex to form a large SAM-Tom5/Tom40 assembly that binds the alpha-helical precursor of Tom6 after its Mim1-dependent membrane insertion, functioning in the biogenesis of alpha-helical TOM subunits.","method":"Native PAGE, co-immunoprecipitation, pulse-chase assembly assays in yeast mutants","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — native complex isolation with co-IP and assembly kinetics, replicated in follow-up study","pmids":["20026336"],"is_preprint":false},{"year":2010,"finding":"Tom5 plays a stimulatory role in TOM complex biogenesis at an early stage of Tom40 assembly at the SAM complex; Tom5 promotes progression of Tom40 from the first SAM stage to the second SAM stage, and Tom5 assembly with Tom40 at the SAM complex is the direct initiation step of newly imported Tom40 assembly. This function is antagonized by Tom7.","method":"Pulse-chase assembly assays, native PAGE, yeast genetic analysis of deletion strains","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistatic analysis with multiple deletion strains, assembly intermediate characterization, two independent studies","pmids":["21059357","20668160"],"is_preprint":false},{"year":2010,"finding":"Tom5 is required for the second stage of Tom40 interaction with the SAM complex during TOM biogenesis. Mim1-deficient mitochondria accumulate Tom40 at the first SAM stage similarly to Tom5-deficient mitochondria, and Tom5 overexpression suppresses the Tom40 assembly defect in mim1Δ cells, placing Mim1 function upstream of Tom5 in Tom40 biogenesis.","method":"Pulse-chase assembly assay, native PAGE, genetic epistasis in yeast deletion strains","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with assembly kinetics, multiple orthogonal methods, single lab with functional suppression","pmids":["20668160"],"is_preprint":false},{"year":2017,"finding":"Cryo-EM structure of the Neurospora crassa TOM core complex reveals Tom5 transmembrane segment surrounds the Tom40 β-barrel pore within a symmetrical dimeric complex (148 kDa), together with Tom6, Tom7, and Tom22.","method":"Cryo-electron microscopy (cryo-EM) structure determination","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structure with defined subunit assignments, major structural study","pmids":["28802041"],"is_preprint":false},{"year":2020,"finding":"Cryo-EM structure of the human TOM core complex at near-atomic resolution shows Tom5 surrounds the Tom40 channel as part of the dimeric complex; the N-terminal segment of Tom40 spans the channel to interact with Tom5 at the periphery of the dimer, and this region serves as an exit/recruitment site for presequence-lacking preproteins.","method":"Single-particle cryo-EM structure determination","journal":"Cell discovery","confidence":"High","confidence_rationale":"Tier 1 / Strong — atomic resolution cryo-EM structure with functional interpretation, human protein","pmids":["33083003"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM structure of PINK1 at the TOM-VDAC array shows Tom5 facilitates the symmetric arrangement of two TOM core complexes around a central VDAC2 dimer, and Tom5 directly binds the C-lobe of PINK1 kinase domain, stabilizing PINK1 at the mitochondrial surface. Tom5 (as part of TOM) is required for PINK1 retention on the mitochondrial surface.","method":"Cryo-EM structure determination (3.1 Å resolution), genetic ablation of TOMM5 in cell-based PINK1 retention assays","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structure plus functional genetic validation, human protein","pmids":["40080546"],"is_preprint":false},{"year":2025,"finding":"TOM (including subunit TOMM5) is required for PINK1 retention on the mitochondrial surface. Loss of MMP stalls PINK1 during transfer from TOM to TIM23, causing accumulation at TOM; ablation of TOMM5 abrogates PINK1 retention.","method":"Genome-wide screen with Parkin reporter, siRNA knockdown of TOMM5, cell-based PINK1 localization assays","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic screen plus targeted knockdown, single lab, functional readout","pmids":["41266657"],"is_preprint":false},{"year":2014,"finding":"All EMC (ER membrane protein complex) proteins interact with the mitochondrial TOM complex protein Tom5, and this interaction is important for phosphatidylserine (PS) transfer from ER to mitochondria and for cell growth. The EMC-TOM5 interaction supports ER-mitochondria tethering, required for phospholipid synthesis.","method":"Yeast genetic screen for lipid exchange mutants, co-immunoprecipitation of EMC with Tom5, PS transfer assay, growth assays in EMC/ERMES double mutants","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, lipid transfer assay, genetic epistasis with rescue by artificial tether, multiple orthogonal methods","pmids":["25313861"],"is_preprint":false},{"year":2002,"finding":"Bcl-2alpha insertion into the mitochondrial outer membrane does not require Tom5 or Tom40, indicating Bcl-2alpha bypasses the general import pore and follows a distinct pathway from Tom20 into the outer membrane.","method":"In vitro import assay into yeast mitochondria lacking individual TOM subunits (negative result for Tom5 requirement)","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in organello import in deletion mutants; this is a negative result establishing specificity of Tom5 requirement","pmids":["12419260"],"is_preprint":false},{"year":2003,"finding":"Tom5 is not required for cytochrome c import into the mitochondrial IMS; neither Tom5, Tom6, nor Tom7 are needed for cytochrome c import, establishing that cytochrome c uses a Tom5-independent pathway.","method":"In organello import assay in yeast mutants lacking individual Tom proteins","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in organello import assay with multiple deletion mutants; negative result informative for pathway specificity","pmids":["12628251"],"is_preprint":false},{"year":2012,"finding":"Tomm5 knockout mice develop a lung-specific phenotype of cryptogenic organizing pneumonia (COP/BOOP), characterized by intra-alveolar fibrosis with fibroblasts/myofibroblasts, macrophage and eosinophil infiltration, while performing normally in other broad phenotyping assays.","method":"Tomm5(-/-) knockout mouse generation; histopathological analysis of lung tissue","journal":"Veterinary pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — in vivo knockout with specific organ phenotype, single lab, no defined molecular mechanism for lung specificity","pmids":["22688586"],"is_preprint":false},{"year":2024,"finding":"TOM5 regulates mitochondrial membrane potential in alveolar epithelial cells; TOM5 reduces early apoptosis and promotes cell proliferation in vitro. TOM5 expression is increased in lung tissue of organizing pneumonia patients and correlates with collagen deposition.","method":"In vitro knockdown/overexpression in alveolar epithelial cells with mitochondrial membrane potential assay; bleomycin-induced murine OP model","journal":"Redox report","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, cell-based assay with phenotypic readout, mechanism not fully defined","pmids":["38794801"],"is_preprint":false},{"year":2011,"finding":"A fusion protein of wild-type p53 with the mitochondrial transmembrane domain of Tom5 (p53-Tom5) localizes exclusively to mitochondria in ARF-null A549 lung cancer cells, induces mitochondrial dysfunction and cytochrome c release, and suppresses cell proliferation, whereas wild-type p53 alone does not. This demonstrates Tom5's TMS is sufficient to direct a cytosolic protein to mitochondria and cause direct mitochondrial dysfunction.","method":"Plasmid transfection, confocal microscopy for localization, cell proliferation assay, cytochrome c release assay, mitochondrial function assay","journal":"Biological & pharmaceutical bulletin","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, uses Tom5 TMS as a targeting tool, limited mechanistic detail about TOMM5 itself","pmids":["21467644"],"is_preprint":false},{"year":2025,"finding":"HSP90-CDC37 chaperone complex covers the C-terminal extension (CTE) of PINK1, which overlaps with interaction sites for TOM5 and TOM20. This structural finding indicates that HSP90 and TOM5 binding to PINK1 are mutually exclusive, providing mechanistic insight into how PINK1 transitions from cytosolic chaperone to TOM complex engagement.","method":"Cryo-EM structure of PINK1-HSP90-CDC37 complex","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 1 / Weak — cryo-EM structure (preprint), TOM5 interaction site inferred from structural overlap but not directly validated by mutagenesis of TOM5","pmids":["bio_10.1101_2025.10.17.682828"],"is_preprint":true}],"current_model":"TOMM5 (Tom5) is a small C-tail-anchored subunit of the translocase of the outer mitochondrial membrane (TOM complex) that plays multiple mechanistic roles: it is required for structural integrity of the TOM complex, acts as an early assembly factor promoting Tom40 integration at the SAM complex, facilitates import of specific substrate classes (small Tims, VDAC/porin, Tafazzin) through the GIP, physically links the ER membrane protein complex (EMC) to TOM to enable ER-mitochondria tethering and phospholipid transfer, directly binds PINK1 kinase C-lobe to stabilize PINK1 at the mitochondrial surface (required for PINK1-Parkin mitophagy signaling), and its targeting to the outer membrane is specified by a defined signal involving TMS length, a proline residue in the TMS, and proximity of TMS to the C-terminal segment—all established by structural (cryo-EM at up to 3.1 Å), biochemical, genetic epistasis, and mutagenesis experiments."},"narrative":{"mechanistic_narrative":"TOMM5 (Tom5) is a small C-tail-anchored subunit of the translocase of the outer mitochondrial membrane (TOM complex), where it surrounds the Tom40 β-barrel channel within the dimeric general import pore alongside Tom6, Tom7, and Tom22 [PMID:9774667, PMID:9603986, PMID:28802041, PMID:33083003]. Within the assembled complex it behaves as a peripheral, modulatory element: it can be released from the stable Tom40-Tom22 core under stringent detergent conditions while preprotein remains bound, yet its deletion destabilizes the TOM complex and reduces import efficiency in yeast in a species-specific manner [PMID:11259583, PMID:15701639]. Beyond steady-state structure, Tom5 acts as an early biogenesis factor that initiates and promotes integration of newly imported Tom40 at the SAM complex, advancing Tom40 from the first to the second SAM-associated assembly stage downstream of Mim1 and antagonized by Tom7 [PMID:11276259, PMID:20026336, PMID:21059357, PMID:20668160]. Tom5 confers substrate specificity at the import pore, being required for biogenesis of porin/VDAC and VDAC-like β-barrels, the small Tim intermembrane-space proteins, and Tafazzin, while being dispensable for pathways used by Bcl-2α and cytochrome c [PMID:11266446, PMID:10397776, PMID:16135531, PMID:12419260, PMID:12628251]. Its outer-membrane targeting is encoded by a defined C-tail-anchor signal in which transmembrane-segment length, a correctly positioned proline residue, and the relationship of the TMS to the C-terminal segment are the critical determinants [PMID:12006657, PMID:12896971]. Tom5 also serves as a physical hub linking mitochondria to other membranes and to quality-control signaling: it binds all ER membrane protein complex (EMC) subunits to support ER–mitochondria tethering and phosphatidylserine transfer [PMID:25313861], and it directly binds the C-lobe of the PINK1 kinase domain, organizing a symmetric TOM–VDAC array that retains and stabilizes PINK1 at the mitochondrial surface for PINK1-Parkin mitophagy signaling [PMID:40080546, PMID:41266657]. A Tomm5 knockout mouse develops an organ-restricted lung phenotype of cryptogenic organizing pneumonia [PMID:22688586].","teleology":[{"year":1998,"claim":"Established that Tom5 is a bona fide constituent of the TOM general import pore that bridges surface receptors and the Tom40 channel, defining its place in the import machinery.","evidence":"Biochemical fractionation, native PAGE and immunoprecipitation of the ~400 kDa GIP complex in yeast","pmids":["9774667","9603986"],"confidence":"High","gaps":["Did not resolve whether Tom5 is core or peripheral","No structural placement relative to Tom40"]},{"year":1999,"claim":"Showed that Tom5 confers substrate selectivity by being essential for a receptor-independent small Tim import pathway, indicating the pore subunits define distinct import routes.","evidence":"In vitro import assays in yeast strains lacking individual TOM components","pmids":["10397776"],"confidence":"Medium","gaps":["Single lab","Molecular basis of Tom5 selectivity for small Tims not defined"]},{"year":2000,"claim":"Provided the first structural description of the Tom5 cytosolic domain, establishing a defined helical core.","evidence":"CD and NMR (NOESY) spectroscopy of the cytosolic domain","pmids":["10683449"],"confidence":"Medium","gaps":["No functional mutagenesis link to the helical structure","Isolated domain, not in complex"]},{"year":2001,"claim":"Distinguished Tom5 as a peripheral/modulatory subunit while assigning it an active role in Tom40 assembly, showing the protein contributes to biogenesis rather than the core translocation unit.","evidence":"Urea/detergent dissociation, channel reconstitution, and pulse-chase assembly assays with native PAGE in yeast","pmids":["11259583","11276259"],"confidence":"High","gaps":["Mechanism by which Tom5 promotes Tom40 progression unresolved at this stage","Order relative to other assembly factors unknown"]},{"year":2001,"claim":"Extended Tom5's substrate role to β-barrel biogenesis by showing porin/VDAC import requires Tom5.","evidence":"In vitro import assay using yeast tom5 mutant mitochondria","pmids":["11266446"],"confidence":"Medium","gaps":["Single lab","Does not separate import defect from TOM destabilization"]},{"year":2002,"claim":"Defined the C-tail-anchor targeting determinants of Tom5 in a mammalian system, identifying TMS length, a TMS proline, and C-segment charge as the targeting code.","evidence":"Systematic TMS/flanking mutagenesis with GFP reporter, microscopy and fractionation in COS-7 cells","pmids":["12006657"],"confidence":"High","gaps":["Single lab","Receptor/insertase machinery for Tom5 targeting not identified"]},{"year":2002,"claim":"Sharpened pathway specificity by showing some outer-membrane proteins (Bcl-2α) bypass Tom5 and Tom40, demonstrating Tom5 dependence is substrate-class specific.","evidence":"In vitro import into yeast mitochondria lacking individual TOM subunits (negative result for Bcl-2α); PorB import dependent on Tom5","pmids":["11953311","12419260"],"confidence":"Medium","gaps":["Single lab","Alternative insertion route for Bcl-2α not molecularly mapped"]},{"year":2003,"claim":"Refined the targeting signal with functional complementation, showing TMS length and a positioned proline, but not C-segment positive charge, are required for Tom5 assembly into TOM.","evidence":"GFP reporter localization, blue native PAGE and complementation of ts deltaTOM5 yeast","pmids":["12896971"],"confidence":"High","gaps":["Discrepancy with COS-7 charge requirement not reconciled","Single lab"]},{"year":2003,"claim":"Further delineated substrate specificity by showing cytochrome c import is Tom5-independent.","evidence":"In organello import assay in yeast lacking individual Tom proteins (negative result)","pmids":["12628251"],"confidence":"Medium","gaps":["Single lab","Negative result; pathway used by cytochrome c not defined here"]},{"year":2005,"claim":"Established Tom5's role in TOM structural integrity and added Tafazzin to its substrate repertoire, while revealing species-specific dependence on Tom5 for complex stability.","evidence":"Cross-species complementation, native PAGE and import assays in yeast and N. crassa; Taz1 import assays in mutant backgrounds","pmids":["15701639","16135531"],"confidence":"High","gaps":["Basis for yeast vs Neurospora difference unexplained","Taz1 import single lab"]},{"year":2010,"claim":"Resolved the mechanistic order of TOM assembly, placing Tom5 as the initiating step of Tom40 integration at SAM, downstream of Mim1 and antagonized by Tom7.","evidence":"Pulse-chase assembly assays, native PAGE and genetic epistasis/suppression in yeast deletion strains","pmids":["21059357","20668160","20026336"],"confidence":"High","gaps":["Structural basis of Tom5-Tom40 SAM intermediate unknown","How Tom7 antagonizes Tom5 not defined"]},{"year":2014,"claim":"Revealed an inter-organelle function by showing Tom5 physically links the ER EMC to mitochondria to enable lipid transfer, expanding its role beyond import.","evidence":"Yeast genetic screen, reciprocal Co-IP of EMC with Tom5, PS transfer assay and rescue by artificial tether","pmids":["25313861"],"confidence":"High","gaps":["Which EMC subunit contacts Tom5 directly not mapped","Structural detail of the tether absent"]},{"year":2017,"claim":"Placed Tom5 structurally around the Tom40 pore in the dimeric TOM core complex.","evidence":"Cryo-EM structure of the N. crassa TOM core complex","pmids":["28802041"],"confidence":"High","gaps":["No bound substrate captured","Human complex not resolved here"]},{"year":2020,"claim":"Resolved the human TOM core complex and linked Tom5 to the Tom40 N-terminal segment that serves as an exit/recruitment site for presequence-lacking preproteins.","evidence":"Single-particle cryo-EM of the human TOM core complex","pmids":["33083003"],"confidence":"High","gaps":["No trapped substrate at the Tom5 site","Functional test of the recruitment role not in this study"]},{"year":2025,"claim":"Connected Tom5 to mitophagy quality control by showing it directly binds the PINK1 kinase C-lobe and organizes the TOM-VDAC array to retain PINK1 at the mitochondrial surface.","evidence":"Cryo-EM at 3.1 Å of PINK1 at the TOM-VDAC array plus TOMM5 genetic ablation/knockdown in PINK1 retention assays; HSP90-CDC37 overlap shown by preprint cryo-EM","pmids":["40080546","41266657","bio_10.1101_2025.10.17.682828"],"confidence":"High","gaps":["TOM5-PINK1 interface not validated by TOM5 mutagenesis (HSP90 overlap is preprint)","How Tom5 import role and PINK1-binding role are coordinated unclear"]},{"year":2012,"claim":"Showed an organism-level consequence of TOMM5 loss with an organ-restricted lung phenotype.","evidence":"Tomm5(-/-) knockout mice with lung histopathology (cryptogenic organizing pneumonia)","pmids":["22688586"],"confidence":"Medium","gaps":["No molecular mechanism for lung specificity","Link to import or PINK1 functions not established"]},{"year":null,"claim":"How Tom5's distinct roles—pore subunit, Tom40 assembly initiator, substrate-selectivity factor, EMC tether, and PINK1 retention platform—are mechanistically coordinated, and how loss of these activities produces the tissue-specific in vivo phenotype, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No integrated model linking import and signaling roles","Mechanism of lung-restricted phenotype unknown","TOM5-PINK1 interface not validated by direct mutagenesis"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2,9,14]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[18,16]}],"localization":[],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,1,3,4]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[16,17]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,12]}],"complexes":["TOM complex","SAM-Tom5/Tom40 assembly intermediate","TOM-VDAC array"],"partners":["TOMM40","TOMM22","TOMM6","TOMM7","PINK1","VDAC2","EMC"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8N4H5","full_name":"Mitochondrial import receptor subunit TOM5 homolog","aliases":[],"length_aa":51,"mass_kda":6.0,"function":"Component of the translocase of the outer membrane of mitochondria (TOM) complex essential for the recognition and translocation of cytosolically synthesized mitochondrial preproteins (PubMed:40080546). The TOM complex associates with the ion channel VDAC2 and PINK1 kinase at depolarized mitochondria, this interaction stabilizes PINK1 at the outer mitochondrial membrane and triggers downstream mitophagy by the recruitment of the E3 ubiquitin ligase PRKN (PubMed:40080546)","subcellular_location":"Mitochondrion outer membrane","url":"https://www.uniprot.org/uniprotkb/Q8N4H5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TOMM5","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"FKBP8","stoichiometry":0.2},{"gene":"RAB1A","stoichiometry":0.2},{"gene":"RAB2A","stoichiometry":0.2},{"gene":"TOMM20A","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/TOMM5","total_profiled":1310},"omim":[{"mim_id":"616169","title":"TRANSLOCASE OF OUTER MITOCHONDRIAL MEMBRANE 5; TOMM5","url":"https://www.omim.org/entry/616169"},{"mim_id":"616168","title":"TRANSLOCASE OF OUTER MITOCHONDRIAL MEMBRANE 6; TOMM6","url":"https://www.omim.org/entry/616168"},{"mim_id":"607980","title":"TRANSLOCASE OF OUTER MITOCHONDRIAL MEMBRANE 7; TOMM7","url":"https://www.omim.org/entry/607980"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Mitochondria","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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The GIP complex (~400 kDa) contains Tom40, Tom22, Tom5, Tom6, and Tom7.\",\n      \"method\": \"Biochemical fractionation, native PAGE, immunoprecipitation, yeast genetics\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP and native PAGE across multiple labs, replicated in multiple organisms\",\n      \"pmids\": [\"9774667\", \"9603986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Tom5 associates with the precursor of Tom40 during the first assembly intermediate (~250 kDa) at the sorting and assembly machinery (SAM complex), forming a step prior to the 100 kDa and 400 kDa mature TOM complex. Tom5 is required for progression of Tom40 assembly from the SAM complex to the mature TOM complex.\",\n      \"method\": \"Pulse-chase assembly assays, native PAGE, yeast mutant analysis\",\n      \"journal\": \"Nature structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in organello assembly assay with defined intermediates, replicated in subsequent studies\",\n      \"pmids\": [\"11276259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The Tom40-Tom22 core is the stable unit retaining preproteins in the GIP complex; Tom5 (along with Tom6 and Tom7) is released under stringent detergent conditions while preprotein remains bound, indicating Tom5 is a peripheral/modulatory component rather than part of the core translocation unit.\",\n      \"method\": \"Urea/detergent dissociation assays, native PAGE, channel activity reconstitution\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical methods, replicated across labs\",\n      \"pmids\": [\"11259583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Tom5 is required for the import and assembly of porin (VDAC) into the mitochondrial outer membrane, as shown by reduced import in tom5 mutant mitochondria. Porin biogenesis requires Tom5 in addition to Tom20, Tom22, Tom40, and Tom7.\",\n      \"method\": \"In vitro import assay with yeast tom5 mutant mitochondria\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in organello import assay in mutant mitochondria, single lab\",\n      \"pmids\": [\"11266446\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Tom5 of the GIP complex is crucial for the import of small Tim proteins of the intermembrane space, representing a third novel import pathway in which surface receptors (Tom20, Tom70) are dispensable but Tom5 is essential.\",\n      \"method\": \"In vitro import assays using yeast strains lacking individual TOM components\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in organello import assay in multiple tom mutant strains, single lab\",\n      \"pmids\": [\"10397776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Tom5 is required for import of bacterial PorB (a VDAC-like beta-barrel protein) into the mitochondrial outer membrane in vitro; insertion is dependent on Tom5, Tom20, and Tom40 but independent of Tom70.\",\n      \"method\": \"In vitro import assay into isolated mitochondria with antibody inhibition of specific TOM subunits\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro import assay with antibody blockade, single lab\",\n      \"pmids\": [\"11953311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The transmembrane segment (TMS) length, proline residue position in the TMS, and positive charges in the C-terminal segment (C-segment) together constitute the mitochondrial targeting signal of Tom5 as a C-tail-anchored protein. Reduction of net positive charge in the C-segment causes mislocalization to intracellular membranes; elongation of the TMS or separation of TMS and C-segment impairs targeting.\",\n      \"method\": \"Systematic deletion/mutation analysis of Tom5 TMS and flanking regions with GFP reporter, confocal microscopy, cell fractionation in COS-7 cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic mutagenesis with multiple orthogonal readouts (imaging + fractionation), single lab\",\n      \"pmids\": [\"12006657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Correct targeting and assembly of Tom5 into the TOM complex requires an appropriate TMS length (not merely hydrophobicity), a proline residue at the correct position in the TMS with specific flanking residues, but unlike other C-tail-anchored outer membrane proteins, does not require positive charges in the C-terminal segment. A minimal targeting signal (Ser-Pro-Met in Leu-Ala repeat context) is sufficient for mitochondrial targeting and functional complementation.\",\n      \"method\": \"In vivo GFP reporter assays, blue native PAGE, complementation of temperature-sensitive deltaTOM5 yeast cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic mutagenesis with functional complementation assay, in vivo localization, and native complex assembly, single lab\",\n      \"pmids\": [\"12896971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The cytosolic domain of Tom5 forms a stable helical core between residues E11 and R15, with a less structurally rigid helix extending to the C-terminus, as determined by CD and NMR spectroscopy.\",\n      \"method\": \"Circular dichroism (CD) and NMR (NOESY) spectroscopy\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — NMR structure determination, single lab, no functional mutagenesis validation\",\n      \"pmids\": [\"10683449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Tom5 is required for maintaining the structural integrity of the TOM complex in yeast; deletion of TOM5 destabilizes the TOM complex and reduces protein import efficiency. In Neurospora crassa, Tom5 deletion does not affect TOM stability or import efficiency, indicating a species-specific structural role. Tom5 crosses the outer membrane with its C-terminus facing the IMS.\",\n      \"method\": \"Identification of Neurospora Tom5 by sequence homology; TOM complex stability assessed by native PAGE; import assays in deltaTOM5 yeast and N. crassa; complementation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cross-species genetic complementation, native PAGE, import assays, replicated in two organisms\",\n      \"pmids\": [\"15701639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Transport of Tafazzin (Taz1) into mitochondria depends on the receptor Tom5 of the TOM complex and the small Tim proteins of the IMS, but is independent of the SAM complex. This establishes Tom5 as required for import of this outer membrane IMS-exposed protein.\",\n      \"method\": \"In vitro import assays into yeast mitochondria lacking individual TOM/SAM/Tim components\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in organello import assays in multiple mutant backgrounds, single lab\",\n      \"pmids\": [\"16135531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A Tom5-Tom40 subcomplex associates with the SAM core complex to form a large SAM-Tom5/Tom40 assembly that binds the alpha-helical precursor of Tom6 after its Mim1-dependent membrane insertion, functioning in the biogenesis of alpha-helical TOM subunits.\",\n      \"method\": \"Native PAGE, co-immunoprecipitation, pulse-chase assembly assays in yeast mutants\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — native complex isolation with co-IP and assembly kinetics, replicated in follow-up study\",\n      \"pmids\": [\"20026336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Tom5 plays a stimulatory role in TOM complex biogenesis at an early stage of Tom40 assembly at the SAM complex; Tom5 promotes progression of Tom40 from the first SAM stage to the second SAM stage, and Tom5 assembly with Tom40 at the SAM complex is the direct initiation step of newly imported Tom40 assembly. This function is antagonized by Tom7.\",\n      \"method\": \"Pulse-chase assembly assays, native PAGE, yeast genetic analysis of deletion strains\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistatic analysis with multiple deletion strains, assembly intermediate characterization, two independent studies\",\n      \"pmids\": [\"21059357\", \"20668160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Tom5 is required for the second stage of Tom40 interaction with the SAM complex during TOM biogenesis. Mim1-deficient mitochondria accumulate Tom40 at the first SAM stage similarly to Tom5-deficient mitochondria, and Tom5 overexpression suppresses the Tom40 assembly defect in mim1Δ cells, placing Mim1 function upstream of Tom5 in Tom40 biogenesis.\",\n      \"method\": \"Pulse-chase assembly assay, native PAGE, genetic epistasis in yeast deletion strains\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with assembly kinetics, multiple orthogonal methods, single lab with functional suppression\",\n      \"pmids\": [\"20668160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Cryo-EM structure of the Neurospora crassa TOM core complex reveals Tom5 transmembrane segment surrounds the Tom40 β-barrel pore within a symmetrical dimeric complex (148 kDa), together with Tom6, Tom7, and Tom22.\",\n      \"method\": \"Cryo-electron microscopy (cryo-EM) structure determination\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structure with defined subunit assignments, major structural study\",\n      \"pmids\": [\"28802041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cryo-EM structure of the human TOM core complex at near-atomic resolution shows Tom5 surrounds the Tom40 channel as part of the dimeric complex; the N-terminal segment of Tom40 spans the channel to interact with Tom5 at the periphery of the dimer, and this region serves as an exit/recruitment site for presequence-lacking preproteins.\",\n      \"method\": \"Single-particle cryo-EM structure determination\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — atomic resolution cryo-EM structure with functional interpretation, human protein\",\n      \"pmids\": [\"33083003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structure of PINK1 at the TOM-VDAC array shows Tom5 facilitates the symmetric arrangement of two TOM core complexes around a central VDAC2 dimer, and Tom5 directly binds the C-lobe of PINK1 kinase domain, stabilizing PINK1 at the mitochondrial surface. Tom5 (as part of TOM) is required for PINK1 retention on the mitochondrial surface.\",\n      \"method\": \"Cryo-EM structure determination (3.1 Å resolution), genetic ablation of TOMM5 in cell-based PINK1 retention assays\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structure plus functional genetic validation, human protein\",\n      \"pmids\": [\"40080546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TOM (including subunit TOMM5) is required for PINK1 retention on the mitochondrial surface. Loss of MMP stalls PINK1 during transfer from TOM to TIM23, causing accumulation at TOM; ablation of TOMM5 abrogates PINK1 retention.\",\n      \"method\": \"Genome-wide screen with Parkin reporter, siRNA knockdown of TOMM5, cell-based PINK1 localization assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic screen plus targeted knockdown, single lab, functional readout\",\n      \"pmids\": [\"41266657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"All EMC (ER membrane protein complex) proteins interact with the mitochondrial TOM complex protein Tom5, and this interaction is important for phosphatidylserine (PS) transfer from ER to mitochondria and for cell growth. The EMC-TOM5 interaction supports ER-mitochondria tethering, required for phospholipid synthesis.\",\n      \"method\": \"Yeast genetic screen for lipid exchange mutants, co-immunoprecipitation of EMC with Tom5, PS transfer assay, growth assays in EMC/ERMES double mutants\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, lipid transfer assay, genetic epistasis with rescue by artificial tether, multiple orthogonal methods\",\n      \"pmids\": [\"25313861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Bcl-2alpha insertion into the mitochondrial outer membrane does not require Tom5 or Tom40, indicating Bcl-2alpha bypasses the general import pore and follows a distinct pathway from Tom20 into the outer membrane.\",\n      \"method\": \"In vitro import assay into yeast mitochondria lacking individual TOM subunits (negative result for Tom5 requirement)\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in organello import in deletion mutants; this is a negative result establishing specificity of Tom5 requirement\",\n      \"pmids\": [\"12419260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Tom5 is not required for cytochrome c import into the mitochondrial IMS; neither Tom5, Tom6, nor Tom7 are needed for cytochrome c import, establishing that cytochrome c uses a Tom5-independent pathway.\",\n      \"method\": \"In organello import assay in yeast mutants lacking individual Tom proteins\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in organello import assay with multiple deletion mutants; negative result informative for pathway specificity\",\n      \"pmids\": [\"12628251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Tomm5 knockout mice develop a lung-specific phenotype of cryptogenic organizing pneumonia (COP/BOOP), characterized by intra-alveolar fibrosis with fibroblasts/myofibroblasts, macrophage and eosinophil infiltration, while performing normally in other broad phenotyping assays.\",\n      \"method\": \"Tomm5(-/-) knockout mouse generation; histopathological analysis of lung tissue\",\n      \"journal\": \"Veterinary pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — in vivo knockout with specific organ phenotype, single lab, no defined molecular mechanism for lung specificity\",\n      \"pmids\": [\"22688586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TOM5 regulates mitochondrial membrane potential in alveolar epithelial cells; TOM5 reduces early apoptosis and promotes cell proliferation in vitro. TOM5 expression is increased in lung tissue of organizing pneumonia patients and correlates with collagen deposition.\",\n      \"method\": \"In vitro knockdown/overexpression in alveolar epithelial cells with mitochondrial membrane potential assay; bleomycin-induced murine OP model\",\n      \"journal\": \"Redox report\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, cell-based assay with phenotypic readout, mechanism not fully defined\",\n      \"pmids\": [\"38794801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A fusion protein of wild-type p53 with the mitochondrial transmembrane domain of Tom5 (p53-Tom5) localizes exclusively to mitochondria in ARF-null A549 lung cancer cells, induces mitochondrial dysfunction and cytochrome c release, and suppresses cell proliferation, whereas wild-type p53 alone does not. This demonstrates Tom5's TMS is sufficient to direct a cytosolic protein to mitochondria and cause direct mitochondrial dysfunction.\",\n      \"method\": \"Plasmid transfection, confocal microscopy for localization, cell proliferation assay, cytochrome c release assay, mitochondrial function assay\",\n      \"journal\": \"Biological & pharmaceutical bulletin\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, uses Tom5 TMS as a targeting tool, limited mechanistic detail about TOMM5 itself\",\n      \"pmids\": [\"21467644\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HSP90-CDC37 chaperone complex covers the C-terminal extension (CTE) of PINK1, which overlaps with interaction sites for TOM5 and TOM20. This structural finding indicates that HSP90 and TOM5 binding to PINK1 are mutually exclusive, providing mechanistic insight into how PINK1 transitions from cytosolic chaperone to TOM complex engagement.\",\n      \"method\": \"Cryo-EM structure of PINK1-HSP90-CDC37 complex\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — cryo-EM structure (preprint), TOM5 interaction site inferred from structural overlap but not directly validated by mutagenesis of TOM5\",\n      \"pmids\": [\"bio_10.1101_2025.10.17.682828\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"TOMM5 (Tom5) is a small C-tail-anchored subunit of the translocase of the outer mitochondrial membrane (TOM complex) that plays multiple mechanistic roles: it is required for structural integrity of the TOM complex, acts as an early assembly factor promoting Tom40 integration at the SAM complex, facilitates import of specific substrate classes (small Tims, VDAC/porin, Tafazzin) through the GIP, physically links the ER membrane protein complex (EMC) to TOM to enable ER-mitochondria tethering and phospholipid transfer, directly binds PINK1 kinase C-lobe to stabilize PINK1 at the mitochondrial surface (required for PINK1-Parkin mitophagy signaling), and its targeting to the outer membrane is specified by a defined signal involving TMS length, a proline residue in the TMS, and proximity of TMS to the C-terminal segment—all established by structural (cryo-EM at up to 3.1 Å), biochemical, genetic epistasis, and mutagenesis experiments.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TOMM5 (Tom5) is a small C-tail-anchored subunit of the translocase of the outer mitochondrial membrane (TOM complex), where it surrounds the Tom40 β-barrel channel within the dimeric general import pore alongside Tom6, Tom7, and Tom22 [#0, #14, #15]. Within the assembled complex it behaves as a peripheral, modulatory element: it can be released from the stable Tom40-Tom22 core under stringent detergent conditions while preprotein remains bound, yet its deletion destabilizes the TOM complex and reduces import efficiency in yeast in a species-specific manner [#2, #9]. Beyond steady-state structure, Tom5 acts as an early biogenesis factor that initiates and promotes integration of newly imported Tom40 at the SAM complex, advancing Tom40 from the first to the second SAM-associated assembly stage downstream of Mim1 and antagonized by Tom7 [#1, #11, #12, #13]. Tom5 confers substrate specificity at the import pore, being required for biogenesis of porin/VDAC and VDAC-like β-barrels, the small Tim intermembrane-space proteins, and Tafazzin, while being dispensable for pathways used by Bcl-2α and cytochrome c [#3, #4, #10, #19, #20]. Its outer-membrane targeting is encoded by a defined C-tail-anchor signal in which transmembrane-segment length, a correctly positioned proline residue, and the relationship of the TMS to the C-terminal segment are the critical determinants [#6, #7]. Tom5 also serves as a physical hub linking mitochondria to other membranes and to quality-control signaling: it binds all ER membrane protein complex (EMC) subunits to support ER–mitochondria tethering and phosphatidylserine transfer [#18], and it directly binds the C-lobe of the PINK1 kinase domain, organizing a symmetric TOM–VDAC array that retains and stabilizes PINK1 at the mitochondrial surface for PINK1-Parkin mitophagy signaling [#16, #17]. A Tomm5 knockout mouse develops an organ-restricted lung phenotype of cryptogenic organizing pneumonia [#21].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established that Tom5 is a bona fide constituent of the TOM general import pore that bridges surface receptors and the Tom40 channel, defining its place in the import machinery.\",\n      \"evidence\": \"Biochemical fractionation, native PAGE and immunoprecipitation of the ~400 kDa GIP complex in yeast\",\n      \"pmids\": [\"9774667\", \"9603986\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether Tom5 is core or peripheral\", \"No structural placement relative to Tom40\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed that Tom5 confers substrate selectivity by being essential for a receptor-independent small Tim import pathway, indicating the pore subunits define distinct import routes.\",\n      \"evidence\": \"In vitro import assays in yeast strains lacking individual TOM components\",\n      \"pmids\": [\"10397776\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Molecular basis of Tom5 selectivity for small Tims not defined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Provided the first structural description of the Tom5 cytosolic domain, establishing a defined helical core.\",\n      \"evidence\": \"CD and NMR (NOESY) spectroscopy of the cytosolic domain\",\n      \"pmids\": [\"10683449\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional mutagenesis link to the helical structure\", \"Isolated domain, not in complex\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Distinguished Tom5 as a peripheral/modulatory subunit while assigning it an active role in Tom40 assembly, showing the protein contributes to biogenesis rather than the core translocation unit.\",\n      \"evidence\": \"Urea/detergent dissociation, channel reconstitution, and pulse-chase assembly assays with native PAGE in yeast\",\n      \"pmids\": [\"11259583\", \"11276259\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which Tom5 promotes Tom40 progression unresolved at this stage\", \"Order relative to other assembly factors unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Extended Tom5's substrate role to β-barrel biogenesis by showing porin/VDAC import requires Tom5.\",\n      \"evidence\": \"In vitro import assay using yeast tom5 mutant mitochondria\",\n      \"pmids\": [\"11266446\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Does not separate import defect from TOM destabilization\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined the C-tail-anchor targeting determinants of Tom5 in a mammalian system, identifying TMS length, a TMS proline, and C-segment charge as the targeting code.\",\n      \"evidence\": \"Systematic TMS/flanking mutagenesis with GFP reporter, microscopy and fractionation in COS-7 cells\",\n      \"pmids\": [\"12006657\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Single lab\", \"Receptor/insertase machinery for Tom5 targeting not identified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Sharpened pathway specificity by showing some outer-membrane proteins (Bcl-2α) bypass Tom5 and Tom40, demonstrating Tom5 dependence is substrate-class specific.\",\n      \"evidence\": \"In vitro import into yeast mitochondria lacking individual TOM subunits (negative result for Bcl-2α); PorB import dependent on Tom5\",\n      \"pmids\": [\"11953311\", \"12419260\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Alternative insertion route for Bcl-2α not molecularly mapped\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Refined the targeting signal with functional complementation, showing TMS length and a positioned proline, but not C-segment positive charge, are required for Tom5 assembly into TOM.\",\n      \"evidence\": \"GFP reporter localization, blue native PAGE and complementation of ts deltaTOM5 yeast\",\n      \"pmids\": [\"12896971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Discrepancy with COS-7 charge requirement not reconciled\", \"Single lab\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Further delineated substrate specificity by showing cytochrome c import is Tom5-independent.\",\n      \"evidence\": \"In organello import assay in yeast lacking individual Tom proteins (negative result)\",\n      \"pmids\": [\"12628251\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Negative result; pathway used by cytochrome c not defined here\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Established Tom5's role in TOM structural integrity and added Tafazzin to its substrate repertoire, while revealing species-specific dependence on Tom5 for complex stability.\",\n      \"evidence\": \"Cross-species complementation, native PAGE and import assays in yeast and N. crassa; Taz1 import assays in mutant backgrounds\",\n      \"pmids\": [\"15701639\", \"16135531\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Basis for yeast vs Neurospora difference unexplained\", \"Taz1 import single lab\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Resolved the mechanistic order of TOM assembly, placing Tom5 as the initiating step of Tom40 integration at SAM, downstream of Mim1 and antagonized by Tom7.\",\n      \"evidence\": \"Pulse-chase assembly assays, native PAGE and genetic epistasis/suppression in yeast deletion strains\",\n      \"pmids\": [\"21059357\", \"20668160\", \"20026336\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of Tom5-Tom40 SAM intermediate unknown\", \"How Tom7 antagonizes Tom5 not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Revealed an inter-organelle function by showing Tom5 physically links the ER EMC to mitochondria to enable lipid transfer, expanding its role beyond import.\",\n      \"evidence\": \"Yeast genetic screen, reciprocal Co-IP of EMC with Tom5, PS transfer assay and rescue by artificial tether\",\n      \"pmids\": [\"25313861\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which EMC subunit contacts Tom5 directly not mapped\", \"Structural detail of the tether absent\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Placed Tom5 structurally around the Tom40 pore in the dimeric TOM core complex.\",\n      \"evidence\": \"Cryo-EM structure of the N. crassa TOM core complex\",\n      \"pmids\": [\"28802041\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No bound substrate captured\", \"Human complex not resolved here\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the human TOM core complex and linked Tom5 to the Tom40 N-terminal segment that serves as an exit/recruitment site for presequence-lacking preproteins.\",\n      \"evidence\": \"Single-particle cryo-EM of the human TOM core complex\",\n      \"pmids\": [\"33083003\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No trapped substrate at the Tom5 site\", \"Functional test of the recruitment role not in this study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected Tom5 to mitophagy quality control by showing it directly binds the PINK1 kinase C-lobe and organizes the TOM-VDAC array to retain PINK1 at the mitochondrial surface.\",\n      \"evidence\": \"Cryo-EM at 3.1 Å of PINK1 at the TOM-VDAC array plus TOMM5 genetic ablation/knockdown in PINK1 retention assays; HSP90-CDC37 overlap shown by preprint cryo-EM\",\n      \"pmids\": [\"40080546\", \"41266657\", \"bio_10.1101_2025.10.17.682828\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"TOM5-PINK1 interface not validated by TOM5 mutagenesis (HSP90 overlap is preprint)\", \"How Tom5 import role and PINK1-binding role are coordinated unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed an organism-level consequence of TOMM5 loss with an organ-restricted lung phenotype.\",\n      \"evidence\": \"Tomm5(-/-) knockout mice with lung histopathology (cryptogenic organizing pneumonia)\",\n      \"pmids\": [\"22688586\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular mechanism for lung specificity\", \"Link to import or PINK1 functions not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How Tom5's distinct roles—pore subunit, Tom40 assembly initiator, substrate-selectivity factor, EMC tether, and PINK1 retention platform—are mechanistically coordinated, and how loss of these activities produces the tissue-specific in vivo phenotype, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No integrated model linking import and signaling roles\", \"Mechanism of lung-restricted phenotype unknown\", \"TOM5-PINK1 interface not validated by direct mutagenesis\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008565\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 9, 14]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [18, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005741\", \"supporting_discovery_ids\": [0, 6, 14, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 1, 3, 4]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [16, 17]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 12]}\n    ],\n    \"complexes\": [\n      \"TOM complex\",\n      \"SAM-Tom5/Tom40 assembly intermediate\",\n      \"TOM-VDAC array\"\n    ],\n    \"partners\": [\n      \"TOMM40\",\n      \"TOMM22\",\n      \"TOMM6\",\n      \"TOMM7\",\n      \"PINK1\",\n      \"VDAC2\",\n      \"EMC\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}