Tango5, also called Vmp1, is the Drosophila member of the VMP1 subfamily of DedA/VTT-domain multipass membrane proteins and is orthologous to human VMP1 (PANTHER PTHR10281:SF1). Q9W2S1 is the 530-residue product. It has a disordered N-terminal region of about 130 residues followed by a conserved membrane core with four predicted transmembrane helices and the VMP1 C-terminal helical domain. A shorter product (Q7KVQ7) begins at the internal Met103. Endogenously GFP-tagged Vmp1 resides in the endoplasmic reticulum, and the gene is essential for viability. Experiments in flies show that Vmp1 is required for autophagosome formation and autophagic flux in the larval intestine. It also acts genetically upstream of Vps13D and Marf/Mfn2 in clearing mitochondria and limiting mitochondria-ER contact. An RNAi screen in S2 cells found that its depletion impairs constitutive secretion and causes Golgi membranes to fuse with the ER. Reconstituted human VMP1 is an ATP- and calcium-independent phospholipid scramblase. On that basis and by phylogenetic inference, Tango5 is thought to equilibrate phospholipids between the leaflets of the ER membrane, for example during phagophore expansion. Its own biochemical activity has not been measured.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000045 autophagosome assembly | IBA GO_REF:0000033 | ACCEPT | Summary: Autophagosome assembly, propagated from the VMP1 node PTN000031591. Fly experiments independently show that Vmp1 is required for autophagosome formation. Reason: A PAINT curator placed autophagosome assembly at PTN000031591, using human VMP1 and Dictyostelium Vmp1 as donors. The fly gene lies inside this clade (PTHR10281:SF1), and there is no evidence that it has lost the function. Fly data agree with the node placement. Without vmp1, larval intestine cells fail to accumulate mCherry-Atg8a puncta and they accumulate the cargo receptor Ref2p. Requirement alone would not show participation. The family mechanism supplies that. VMP1 is an ER scramblase that re-equilibrates the ER donor leaflet while ATG2 transfers lipid to the growing phagophore, so it does part of the work of autophagosome assembly. Fly Tango5 has not been tested biochemically, so the mechanistic part of this claim is inferred. Supporting Evidence: PMID:34019822 did not accumulate mCherryAtg8a autophagy reporter puncta PMID:34019822 accumulated the autophagic cargo receptor Ref2p PMID:33850023 In vitro assays reveal TMEM41B, VMP1, and ATG9 as scramblases. |
| GO:0003674 molecular_function | ND GO_REF:0000015 | ACCEPT | Summary: Root molecular function ND annotation: when it was made, no molecular function had been curated for this gene product from literature. Reason: ACCEPT under the ND acceptance rule (projects/NO_DATA.md). The evidence this review cites for the molecular function is inferred (from orthologs, family membership or sequence features) or comes from other species; none of it is literature on this gene product in this species. This was judged from the review's own content during the NO_DATA re-action pass, not from a new literature search. Earlier action: MODIFY. Re-checked 2026-10-31: the scramblase assays cited in core_functions are on human VMP1 (PMID:33929485); the Drosophila study (PMID:34019822) is genetic and does not assay the activity. The gene's own literature-search record finds no study of this gene product in this species that identifies a molecular function. Supporting Evidence: file:DROME/Tango5__Q9W2S1/Tango5__Q9W2S1-notes.md The fly protein has not been assayed. |
| GO:0005774 vacuolar membrane | IEA GO_REF:0000044 | MARK AS OVER ANNOTATED | Summary: The vacuolar-membrane location comes from the historical family name, not from any localization data for the fly protein. Reason: The UniProt subcellular-location line behind this row is an ARBA rule prediction. It traces back to the name "vacuole membrane protein 1", which was given to the rodent protein because it is induced during pancreatitis-associated vacuolization. Endogenously GFP-tagged fly Vmp1 co-localizes with the ER markers Sec61beta and SERCA, and no fly data place it on vacuoles or lysosomes. A minor endolysosomal pool cannot be ruled out, but this term overstates what is known. Supporting Evidence: PMID:34019822 GFP-Vmp1 co-localizes with the ER markers Sec61Ξ² and SERCA in intestine cells |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | MODIFY | Summary: The ER location is correct and was placed at the eukaryotic VMP1 node. The more precise supported term is ER membrane. Reason: PTN000031590 carries the ER location, seeded by the plant KMS1/KMS2 proteins, human VMP1, Dictyostelium Vmp1 and fly Tango5 itself. The fly gene's presence among the donors marks its own experimental grounding, which is correct and not circular. The protein is an integral multipass protein (four predicted TM helices on Q9W2S1), and endogenous GFP-Vmp1 co-localizes with ER-membrane markers. The specific supported location is therefore the endoplasmic reticulum membrane, where the inferred scramblase acts. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000031590 SUPPORTS TRANSFER The eukaryotic VMP1-clade node, seeded by plant, human, Dictyostelium and fly members. The ER placement is sound and Q9W2S1 lies inside the clade. The only issue is that ER membrane is the more precise supported term. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:34019822 GFP-Vmp1 co-localizes with the ER markers Sec61Ξ² and SERCA in intestine cells file:DROME/Tango5__Q9W2S1/Tango5__Q9W2S1-uniprot.txt FT TRANSMEM 171..188 |
| GO:0005783 endoplasmic reticulum | IDA PMID:16452979 Functional genomics reveals genes involved in protein secret... | MODIFY | Summary: Tango5 is in the ER, as Bard et al. reported. More precisely, it is an integral ER membrane protein. Reason: The direct-assay ER localization from the Bard et al. secretion screen is correct. Only the abstract is cached, so I defer to the FlyBase curator on the assay itself. The localization is confirmed independently by endogenous GFP-Vmp1 co-localizing with Sec61beta and SERCA in fly intestine. Because the protein is a multipass membrane protein, the specific supported location is ER membrane. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:34019822 GFP-Vmp1 co-localizes with the ER markers Sec61Ξ² and SERCA in intestine cells file:genes/DROME/Tango5/Tango5-flybase.txt located_in endoplasmic reticulum inferred from direct assay |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000044 | MODIFY | Summary: The ER location is correct, and the more precise supported term is ER membrane. Reason: This electronic row makes the same claim as the IBA and IDA rows and gets the same action. The ER localization has been confirmed experimentally in fly, and the protein is an integral multipass protein, so the specific term is endoplasmic reticulum membrane. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:34019822 GFP-Vmp1 co-localizes with the ER markers Sec61Ξ² and SERCA in intestine cells |
| GO:0007030 Golgi organization | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Golgi organization was propagated at PTN000031591 from the fly and Dictyostelium experimental annotations. The phenotype is genuine but probably secondary to the protein's ER membrane role. Reason: The PAINT curator judged Golgi organization to be an ancestral feature of the VMP1 clade, seeded by the fly S2-cell phenotype (Golgi membranes fusing with the ER) and by Dictyostelium Vmp1. The node placement is reasonable, and the fly gene is correctly among the donors. The protein resides in the ER and is inferred to scramble lipids there, not in the Golgi. Its effect on Golgi integrity is therefore best read as a consequence of ER membrane homeostasis and ER export, not as a core activity. The term is kept, but as non-core. Supporting Evidence: PMID:16452979 Here we show that depletion of class A genes redistributes Golgi membranes into the endoplasmic reticulum file:genes/DROME/Tango5/Tango5-flybase.txt results in fusion of Golgi membranes with the endoplasmic reticulum in more than 50% of the treated cells |
| GO:0007030 Golgi organization | IMP PMID:16452979 Functional genomics reveals genes involved in protein secret... | KEEP AS NON CORE | Summary: In S2 cells, Tango5 depletion causes Golgi membranes to fuse with the ER. The experimental phenotype is genuine but is probably secondary. Reason: Bard et al. placed Tango5 among the screen genes whose depletion redistributes Golgi membranes into the ER. According to FlyBase curation of the full text, this happened in more than 50% of treated cells. Only the abstract is cached, so I defer to the curator on the phenotype. The action matches the IBA row for the same term. The phenotype is real, but given the protein's ER location and inferred lipid-scrambling activity it is unlikely to be the protein's direct function. Supporting Evidence: PMID:16452979 Here we show that depletion of class A genes redistributes Golgi membranes into the endoplasmic reticulum file:genes/DROME/Tango5/Tango5-flybase.txt results in fusion of Golgi membranes with the endoplasmic reticulum in more than 50% of the treated cells |
| GO:0009306 protein secretion | IMP PMID:16452979 Functional genomics reveals genes involved in protein secret... | KEEP AS NON CORE | Summary: Tango5 is required for constitutive secretion in S2 cells. This screen-level phenotype is probably an indirect effect. Reason: The genome-wide RNAi screen identified Tango5 as necessary for constitutive secretion, and the experimental annotation stands. The evidence, however, is necessity in a screen. The PAINT curator propagated the gene's Golgi-organization annotation to PTN000031591 but did not propagate protein secretion, and I treat that omission as deliberate. The likely mechanism is indirect, through ER membrane lipid homeostasis and Golgi integrity. Mammalian VMP1 supports lipoprotein secretion, which is consistent with this but not a direct secretory-machinery function. The row is kept as non-core. Supporting Evidence: PMID:16452979 We performed a genome-wide RNA-mediated interference screen in a Drosophila cell line to identify genes required for constitutive protein secretion. file:genes/DROME/Tango5/Tango5-flybase.txt dsRNA directed against Tango5 inhibits protein secretion in S2 cells |
| GO:0010256 endomembrane system organization | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Endomembrane system organization was placed at the eukaryotic VMP1 node. It is a broad process consistent with the fly Golgi-ER phenotype and the inferred ER-membrane role. Reason: PTN000031590 carries this broad process, seeded by the plant KMS proteins, Dictyostelium Vmp1 and fly Tango5. In fly, the supporting observation is that Golgi membranes fuse with the ER after Tango5 depletion. The term is accurate at the level of membrane-compartment maintenance. The specific mechanistic contribution, ER-leaflet scrambling, is captured by the molecular function and by autophagosome assembly, so this broader organizational process is kept as non-core. Supporting Evidence: file:genes/DROME/Tango5/Tango5-flybase.txt results in fusion of Golgi membranes with the endoplasmic reticulum in more than 50% of the treated cells |
| GO:0012505 endomembrane system | IBA GO_REF:0000033 | TOO GENERAL | Summary: The endomembrane system is a correct but uninformative location. It is entailed by the supported ER membrane location. Reason: This term was placed at the PTHR10281 root node PTN000031541. That node spans both the VMP1 subfamilies and the unrelated cytochrome-b5-domain MAPR proteins (for example PGRMC2, O15173), so it can only carry a very broad location. The term is true of Tango5, but ER membrane (proposed in the ER rows of this review) already entails it. Supporting Evidence: file:interpro/panther/panther.obo name: MEMBRANE-ASSOCIATED PROGESTERONE RECEPTOR COMPONENT-RELATED PMID:34019822 GFP-Vmp1 co-localizes with the ER markers Sec61Ξ² and SERCA in intestine cells |
| GO:0016020 membrane | IBA GO_REF:0000033 | TOO GENERAL | Summary: Membrane is correct for a multipass protein but uninformative beside ER membrane. Reason: This is another root-node (PTN000031541) location covering the whole heterogeneous PTHR10281 family. Q9W2S1 has four predicted transmembrane helices, so membrane is true, but ER membrane, proposed in this review, entails it. Supporting Evidence: file:DROME/Tango5__Q9W2S1/Tango5__Q9W2S1-uniprot.txt FT TRANSMEM 470..491 |
| GO:0017121 plasma membrane phospholipid scrambling | IEA GO_REF:0000108 | MODIFY | Summary: Inferring the process from the scramblase function puts the scrambling in the wrong membrane. Tango5 is an ER protein, not a plasma-membrane protein. Reason: This row was generated by an inter-ontology rule from the phospholipid scramblase activity IBA. The resulting process term is specific to the plasma membrane and describes loss of plasma-membrane lipid asymmetry with surface exposure of phosphatidylserine, as mediated by TMEM16 and XKR scramblases. Fly Vmp1 co-localizes with ER markers, and VMP1-family scrambling is understood to act on the ER bilayer. What is sound here is transbilayer phospholipid movement, so the location-neutral process phospholipid translocation is proposed instead. The ER-specific scrambling itself is inferred, not measured in fly. Proposed replacements: phospholipid translocation Supporting Evidence: PMID:34019822 GFP-Vmp1 co-localizes with the ER markers Sec61Ξ² and SERCA in intestine cells PMID:33929485 Together, these data indicate that both TMEM41B and VMP1 are scramblases. |
| GO:0017128 phospholipid scramblase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phospholipid scramblase activity was inferred phylogenetically at the eukaryotic VMP1 node from reconstituted human VMP1. It is the core molecular function, but it has not been measured for the fly protein. Reason: Reconstituted human VMP1 scrambles phospholipids without needing ATP or calcium. A PAINT curator placed this activity at PTN000031590, the eukaryotic VMP1 clade. Q9W2S1 falls inside that clade and is in the same PANTHER subfamily as VMP1 (PTHR10281:SF1, about 55% identity). It keeps the whole conserved membrane core, including the VMP1 C-terminal helical domain, and has no known lineage-specific loss. The single human donor is enough for the node placement, because the claim concerns where in the tree the function arose. This is a phylogenetic inference only. Purified Drosophila Tango5 has not been assayed. Supporting Evidence: PMID:33929485 The scramblase activity of TMEM41B/VMP1 did not depend on ATP and was not affected by calcium PMID:33850023 In vitro assays reveal TMEM41B, VMP1, and ATG9 as scramblases. file:DROME/Tango5/Tango5-bioinformatics/RESULTS.md PANTHER: Q7KVQ7, Q9W2S1 and human VMP1 (Q96GC9) are all placed in PTHR10281:SF1 VACUOLE MEMBRANE PROTEIN 1. file:DROME/Tango5__Q9W2S1/Tango5__Q9W2S1-uniprot.txt Vacuole membrane protein 1 C-terminal helical |
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Download this section (compressed HTML)Q: Does purified Drosophila Tango5, in either the long (Q9W2S1) or the short (Q7KVQ7) form, scramble phospholipids in proteoliposomes? Does the disordered N-terminal 102 residues of Q9W2S1 have any function?
Q: Should the inter-ontology inference from phospholipid scramblase activity to plasma membrane phospholipid scrambling (GO_REF:0000108) be restricted, so that ER scramblases such as VMP1 and TMEM41B do not receive a plasma-membrane process term?
Q: Are the S2-cell secretion and Golgi-ER fusion phenotypes direct consequences of losing ER lipid scrambling, or secondary to impaired autophagy or ER stress?
Experiment: Reconstitute purified Tango5 isoforms in NBD-lipid proteoliposomes to measure scramblase activity. Test whether scramblase-dead point mutants in the conserved VTT core rescue vmp1(delta) lethality, autophagy and Golgi integrity.
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