Tout-velu (Ttv, DEXT1) is the Drosophila ortholog of vertebrate exostosin-1 (EXT1), a 760-residue single-pass type II membrane glycosyltransferase of the GT47/GT64 exostosin family that resides in the endoplasmic reticulum and Golgi apparatus. With its paralog Sister of tout-velu (Sotv, the EXT2 ortholog) it forms a heteromeric heparan sulfate co-polymerase. Ttv itself transfers both beta-1,4-linked glucuronic acid (GlcAT-II) and alpha-1,4-linked N-acetylglucosamine (GlcNAcT-II) from UDP-sugars onto the growing chain, and co-expression with Sotv strongly increases both activities. Unlike human EXT1, the Ttv-Sotv complex has no chain-initiating GlcNAcT-I activity; initiation on the linkage tetrasaccharide is performed by Brother of tout-velu (Botv, the EXTL3 ortholog). Loss of ttv abolishes detectable heparan sulfate without affecting chondroitin sulfate, so glypicans such as Dally and Dally-like lack their HS chains. Through this role in heparan sulfate proteoglycan synthesis, Ttv is required for the extracellular movement and gradient formation of the Hedgehog, Decapentaplegic and Wingless morphogens; its Golgi residence is regulated by the GOLPH3 homolog Rotini.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000139 Golgi membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping to Golgi membrane, consistent with the single-pass type II topology and experimental Golgi localization. Reason: Ttv is a type II membrane glycosyltransferase whose lumenal catalytic domain polymerizes heparan sulfate in the Golgi. Golgi localization is directly observed (PMID:10549295, PMID:14998928) and its intra-Golgi retrograde trafficking is controlled by Rotini/GOLPH3 (PMID:23720043). Golgi membrane is the most precise supported location and the site of the core activity. Supporting Evidence: file:DROME/ttv__Q9V730/ttv__Q9V730-uniprot.txt Golgi apparatus membrane; Single-pass type II PMID:23720043 Here, we show that Rotini (Rti), the Drosophila GOLPH3, regulates the retrograde trafficking of EXTs. |
| GO:0005515 protein binding | IPI PMID:14998928 Distinct and collaborative roles of Drosophila EXT family pr... | REMOVE | Summary: Ttv binds Sotv (Q9Y169), its EXT2-like co-polymerase partner. Reason: The Ttv-Sotv interaction is real and functionally important, but bare protein binding carries no functional information. The interaction is captured informatively by the EXT1-EXT2 complex (GO:0120504) annotation from the same paper and by the co-polymerase activities. Removal does not dispute the interaction. Supporting Evidence: PMID:14998928 We demonstrate further that Ttv and Sotv form a complex and are co-localized in vivo. |
| GO:0005515 protein binding | IPI PMID:16303756 Heparan sulfate polymerization in Drosophila. | REMOVE | Summary: Ttv-Sotv association supporting the enhanced co-polymerase activity of the complex. Reason: As for the PMID:14998928 row, bare protein binding is uninformative; the functional content (a Ttv-Sotv heteromeric co-polymerase with augmented GlcNAcT-II and GlcAT-II activity) is captured by GO:0120504 and the specific MF terms. The interaction itself is not in doubt. Supporting Evidence: PMID:16303756 the coexpression of TTV with SOTV markedly augmented both glycosyltransferase activities when compared with the expression of TTV or SOTV alone |
| GO:0005783 endoplasmic reticulum | IDA PMID:10549295 Hedgehog movement is regulated through tout velu-dependent s... | KEEP AS NON CORE | Summary: Ttv protein detected in the ER in Drosophila tissue. Reason: Direct experimental localization (abstract-only cache; curator read the full text). ER residence is consistent with the UniProt ER-membrane assignment and with EXT complex assembly before Golgi delivery, but heparan sulfate polymerization itself is a Golgi activity, so the ER is retained as a genuine but non-core location. Supporting Evidence: file:DROME/ttv__Q9V730/ttv__Q9V730-uniprot.txt Endoplasmic reticulum membrane; Single-pass type |
| GO:0005783 endoplasmic reticulum | IDA PMID:14998928 Distinct and collaborative roles of Drosophila EXT family pr... | KEEP AS NON CORE | Summary: Ttv observed in ER, co-localizing with Sotv. Reason: Same claim as the PMID:10549295 ER row; consistent action. Experimental co-localization with Sotv is reported; ER is a genuine but non-core location relative to the Golgi site of chain polymerization. Supporting Evidence: PMID:14998928 We demonstrate further that Ttv and Sotv form a complex and are co-localized in vivo. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: UniProt subcellular-location mapping to ER membrane. Reason: Correct and precise (type II membrane protein, experimentally seen in the ER), but peripheral to the Golgi-resident co-polymerase function. Supporting Evidence: file:DROME/ttv__Q9V730/ttv__Q9V730-uniprot.txt Endoplasmic reticulum membrane; Single-pass type |
| GO:0005794 Golgi apparatus | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT propagation of Golgi localization from an EXT-family ancestral node (PTN000115158) whose donors include Ttv itself, Sotv, Botv, EXT1, EXT2 and EXTL3. Reason: Ttv lies inside the EXT clade under this node, and its own Golgi IDA is one of the descendant evidences (its presence among the donors is expected, not circular). Golgi is where Ttv acts. Golgi membrane (GO:0000139, accepted above) is the more specific term, but Golgi apparatus with is_active_in is an appropriate phylogenetic statement and is retained. Supporting Evidence: GO_REF:0000033 PMID:23720043 Here, we show that Rotini (Rti), the Drosophila GOLPH3, regulates the retrograde trafficking of EXTs. |
| GO:0005794 Golgi apparatus | IDA PMID:10549295 Hedgehog movement is regulated through tout velu-dependent s... | ACCEPT | Summary: Ttv protein detected in the Golgi apparatus. Reason: Direct experimental localization (abstract-only cache; curator read the full text), consistent with the UniProt Golgi-membrane assignment and with Golgi-based heparan sulfate polymerization. Supporting Evidence: PMID:10549295 we present in vivo evidence that ttv is involved in heparan sulfate proteoglycan (HSPG) biosynthesis |
| GO:0005794 Golgi apparatus | IDA PMID:14998928 Distinct and collaborative roles of Drosophila EXT family pr... | ACCEPT | Summary: Ttv co-localizes with Sotv in the Golgi in vivo. Reason: Same claim as the other Golgi rows; experimental co-localization of the two co-polymerase subunits. Supporting Evidence: PMID:14998928 We demonstrate further that Ttv and Sotv form a complex and are co-localized in vivo. |
| GO:0006024 glycosaminoglycan biosynthetic process | IMP PMID:10644674 Structural analysis of glycosaminoglycans in Drosophila and ... | ACCEPT | Summary: ttv mutant larvae have markedly reduced heparan sulfate but normal chondroitin sulfate. Reason: Ttv polymerizes the heparan sulfate glycosaminoglycan chain itself, so it does the work of glycosaminoglycan biosynthesis. GO has no heparan sulfate chain biosynthesis term below GO:0006024 (its children are peptidoglycan and hyaluronan biosynthesis), and the proteoglycan-level term GO:0015012 is not a descendant, so GO:0006024 is the most precise chain-level term and is accepted alongside GO:0015012. Supporting Evidence: PMID:10644674 Analysis of total glycosaminoglycans from tout-velu mutant larvae show marked reductions in heparan sulfate but not chondroitin sulfate, consistent with its proposed function as a heparan sulfate co-polymerase. |
| GO:0006024 glycosaminoglycan biosynthetic process | IMP PMID:10806213 Structural analysis of glycosaminoglycans in animals bearing... | ACCEPT | Summary: A ttv mutation reduces all heparan sulfate species below detection without affecting chondroitin sulfate. Reason: Same claim as the PMID:10644674 row; HS-specific loss in the mutant matches the in vitro co-polymerase activity (PMID:16303756). Supporting Evidence: PMID:10806213 likewise does not affect chondroitin sulfate synthesis but reduces all forms of heparan sulfate to below the limit of detection |
| GO:0008354 primordial germ cell migration | IMP PMID:17409068 toutvelu, a regulator of heparan sulfate proteoglycan biosyn... | REMOVE | Summary: Deshpande et al. reported mild germ cell migration defects in zygotic and maternal ttv loss-of-function embryos and defects on ttv overexpression. Reason: Full text of both papers read. Even taken at face value, the effect is indirect; the authors themselves attribute it to somatic, extracellular HSPG-dependent distribution of Hedgehog, not to Ttv doing any step of germ cell migration. The result was also directly contested by Renault et al. (PMID:19389345), who used the verified null allele ttv l(2)00681 and found wild-type migration in maternal-only and zygotic-only mutant embryos. An organismal consequence of a biosynthetic enzyme's loss is not process participation. Supporting Evidence: PMID:17409068 it seems likely that ttv activity is required in the soma, not the germline PMID:19389345 Taken together our results suggest that ttv loss of function has no effect on germ cell migration. |
| GO:0008354 primordial germ cell migration | IMP NOT PMID:19389345 Hedgehog does not guide migrating Drosophila germ cells. | KEEP AS NON CORE | Summary: NOT annotation; ttv null maternal or zygotic mutant embryos show normal germ cell migration. Reason: Full text read. The negative result uses a verified null allele and germline clones, and no ttv alleles were recovered in a dedicated germ cell migration screen of the chromosome arm. The NOT statement is well supported and consistent with Ttv being a biosynthetic enzyme with no direct role in germ cell guidance; it is peripheral to the core function. Supporting Evidence: PMID:19389345 Taken together our results suggest that ttv loss of function has no effect on germ cell migration. |
| GO:0008375 acetylglucosaminyltransferase activity | IBA GO_REF:0000033 | MODIFY | Summary: PAINT propagation from node PTN000869020 (EXT1-like clade; donors Ttv, mouse Ext1, human EXT1, EXTL1). Reason: Correct but general. Ttv's specific GlcNAc-transferase activity is directly assayed as GlcNAcT-II, the alpha-1,4-GlcNAc transfer onto the growing heparan sulfate chain (GO:0050508, a child of GO:0008375, already carried by IDA). The chain-initiating GlcNAcT-I activity is explicitly absent from Ttv-Sotv, so the refinement must be to GO:0050508 only. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000869020 SUPPORTS TRANSFER EXT1-clade node; Ttv is inside it and is itself a donor. Transfer is sound, but the parent term is broader than Ttv's assayed GlcNAcT-II activity. Proposed replacements: glucuronosyl-N-acetylglucosaminyl-proteoglycan 4-alpha-N-acetylglucosaminyltransferase activity Supporting Evidence: PMID:16303756 Here we demonstrated that TTV/DEXT1 and SOTV/DEXT2 had GlcNAcT-II and GlcAT-II activities required for the biosynthesis of repeating disaccharide units of the HS backbone PMID:16303756 In contrast to human, TTV-SOTV exhibited no GlcNAcT-I activity |
| GO:0009101 glycoprotein biosynthetic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the exostosin domain. Reason: True but general. Ttv's glycoprotein-related process is specifically heparan sulfate proteoglycan biosynthesis (GO:0015012), which is a descendant of GO:0009101 via proteoglycan biosynthetic process and is already annotated here by IDA and multiple IMPs. Proposed replacements: heparan sulfate proteoglycan biosynthetic process Supporting Evidence: PMID:10549295 we present in vivo evidence that ttv is involved in heparan sulfate proteoglycan (HSPG) biosynthesis |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IDA PMID:16303756 Heparan sulfate polymerization in Drosophila. | ACCEPT | Summary: In vitro, Ttv-Sotv (with Botv for initiation) polymerizes HS on a linkage region analogue. Reason: Core process. Ttv catalyzes the chain-elongation steps of heparan sulfate synthesis (direct participation, not mere requirement). Supporting Evidence: PMID:16303756 Here we demonstrated that TTV/DEXT1 and SOTV/DEXT2 had GlcNAcT-II and GlcAT-II activities required for the biosynthesis of repeating disaccharide units of the HS backbone |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: Combined electronic annotation (UniPathway heparan sulfate biosynthesis). Reason: Same claim as the experimental rows; consistent action. The electronic prediction agrees with the direct biochemical and genetic evidence. Supporting Evidence: PMID:16303756 Thus, all three EXT members in Drosophila, TTV, SOTV, and BOTV, are required for the biosynthesis of full-length HS in Drosophila. |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IMP PMID:10549295 Hedgehog movement is regulated through tout velu-dependent s... | ACCEPT | Summary: In vivo evidence that ttv is required for HSPG biosynthesis. Reason: Core process, consistent with the enzymology. Supporting Evidence: PMID:10549295 we present in vivo evidence that ttv is involved in heparan sulfate proteoglycan (HSPG) biosynthesis |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IMP PMID:11832488 Demonstration of a novel gene DEXT3 of Drosophila melanogast... | ACCEPT | Summary: Paper characterizing DEXT3/Botv GlcNAc-transferase activity; the cached abstract does not describe a ttv experiment. Reason: The cached abstract is about DEXT3/botv and is abstract-only, so the specific ttv evidence the curator used cannot be verified here; per project policy an experimental annotation is not overruled from an abstract that foregrounds a paralog. The claim (Ttv participates in HSPG biosynthesis) is independently and strongly established, so the row is accepted, deferring to the curator. Supporting Evidence: PMID:11832488 Hereditary multiple exostoses gene (EXT) family members encode glycosyltransferases required for heparan sulfate (HS) biosynthesis in humans as well as in Drosophila. |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IMP PMID:14645127 Three Drosophila EXT genes shape morphogen gradients through... | ACCEPT | Summary: New ttv alleles impair HSPG biosynthesis in vivo, non-redundantly with sotv and botv. Reason: Core process; genetic evidence consistent with the biochemistry. Supporting Evidence: PMID:14645127 Mutation in any of these genes impaired biosynthesis of HSPGs in vivo, indicating that, despite their structural similarity, they are not redundant in the HSPG biosynthesis. |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IMP PMID:14998928 Distinct and collaborative roles of Drosophila EXT family pr... | ACCEPT | Summary: ttv mutant clones are defective in HSPG biosynthesis in the wing disc. Reason: Core process; genetic evidence. Supporting Evidence: PMID:14998928 all three Drosophila EXT proteins are required for the biosynthesis of HSPGs |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IMP PMID:15056609 Abrogation of heparan sulfate synthesis in Drosophila disrup... | ACCEPT | Summary: HS levels are dramatically reduced in ttv (and sotv) mutants. Reason: Core process; biochemical analysis of mutant tissue. Supporting Evidence: PMID:15056609 HS levels are dramatically reduced in the absence of Sotv or its partner co-polymerase Tout velu (Ttv), suggesting that both copolymerases are essential for GAG synthesis |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IMP PMID:16303756 Heparan sulfate polymerization in Drosophila. | ACCEPT | Summary: Same paper as the IDA row; genetic/biochemical support for Ttv in HS polymerization. Reason: Core process; consistent with the IDA row from the same paper. Supporting Evidence: PMID:16303756 Thus, all three EXT members in Drosophila, TTV, SOTV, and BOTV, are required for the biosynthesis of full-length HS in Drosophila. |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IMP PMID:19571145 Cell type-specific requirements for heparan sulfate biosynth... | ACCEPT | Summary: Mutations blocking HS synthesis (including ttv) used to dissect HSPG function at the neuromuscular junction. Reason: The paper uses HS-synthesis mutants (abstract-only cache; curator read the full text) and reports transgene rescue; it reaffirms the core process. The downstream synaptic, trafficking and mitochondrial phenotypes are consequences of HSPG loss and are not proposed as Ttv processes. Supporting Evidence: PMID:19571145 using mutations that block heparan sulfate synthesis or sulfation to compromise HSPG function |
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | ISS GO_REF:0000024 | ACCEPT | Summary: Sequence-similarity transfer from a vertebrate EXT1 ortholog. Reason: Same claim as the experimental rows; Ttv is the fly EXT1 ortholog (EXT1 subfamily in PANTHER; PAINT node PTN000869020 groups Ttv with EXT1). Redundant with direct Drosophila evidence but correct. Supporting Evidence: PMID:15056609 EXT1 and EXT2, the human orthologs of ttv and sotv |
| GO:0015020 glucuronosyltransferase activity | IBA GO_REF:0000033 | MODIFY | Summary: PAINT propagation from node PTN000869020 (donors Ttv, mouse Ext1, human EXT1). Reason: Correct but general. Ttv's glucuronosyltransferase activity is specifically GlcAT-II, beta-1,4-GlcA transfer onto the GlcNAc-terminated heparan sulfate chain (GO:0050509, a child of GO:0015020), directly assayed for Ttv and already carried by IDA. The IBA node placement is sound (Ttv is inside the EXT1 clade and is itself a donor); only the specificity is refined. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000869020 SUPPORTS TRANSFER EXT1-clade node; Ttv is inside it and is itself a donor. Transfer is sound, but the parent term is broader than Ttv's assayed GlcAT-II activity. Proposed replacements: N-acetylglucosaminyl-proteoglycan 4-beta-glucuronosyltransferase activity Supporting Evidence: PMID:16303756 Here we demonstrated that TTV/DEXT1 and SOTV/DEXT2 had GlcNAcT-II and GlcAT-II activities required for the biosynthesis of repeating disaccharide units of the HS backbone |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping to membrane. Reason: True but general. Ttv is a single-pass type II membrane protein of the Golgi and ER membranes; both specific terms are already annotated (GO:0000139, GO:0005789). Proposed replacements: Golgi membrane endoplasmic reticulum membrane Supporting Evidence: file:DROME/ttv__Q9V730/ttv__Q9V730-uniprot.txt Golgi apparatus membrane; Single-pass type II |
| GO:0016020 membrane | NAS PMID:9665133 Tout-velu is a Drosophila homologue of the putative tumour s... | MODIFY | Summary: Original cloning paper describing Ttv as an integral membrane protein. Reason: Same claim as the IEA membrane row; refined to the specific Golgi and ER membranes supported by later localization work. Proposed replacements: Golgi membrane endoplasmic reticulum membrane Supporting Evidence: PMID:9665133 it encodes an integral membrane protein that belongs to the EXT gene family |
| GO:0016757 glycosyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the exostosin GT47 and GT64 domains. Reason: True but general; Ttv's two directly assayed glycosyltransferase activities are GlcNAcT-II (GO:0050508) and GlcAT-II (GO:0050509), both already annotated by IDA. Both are listed since both are supported. Proposed replacements: glucuronosyl-N-acetylglucosaminyl-proteoglycan 4-alpha-N-acetylglucosaminyltransferase activity N-acetylglucosaminyl-proteoglycan 4-beta-glucuronosyltransferase activity Supporting Evidence: PMID:16303756 Here we demonstrated that TTV/DEXT1 and SOTV/DEXT2 had GlcNAcT-II and GlcAT-II activities required for the biosynthesis of repeating disaccharide units of the HS backbone |
| GO:0030210 heparin proteoglycan biosynthetic process | IEA GO_REF:0000041 | MARK AS OVER ANNOTATED | Summary: UniPathway mapping to heparin biosynthesis. Reason: The EXT co-polymerase backbone is shared by heparan sulfate and heparin, so the mapping is mechanistically understandable, but heparin proteoglycan (the highly sulfated serglycin-borne form made by vertebrate mast cells) has not been described in Drosophila. Glycosaminoglycan analyses of fly tissues and ttv mutants report heparan sulfate and chondroitin sulfate only. The experimentally supported process is heparan sulfate proteoglycan biosynthesis (GO:0015012). Supporting Evidence: PMID:10806213 likewise does not affect chondroitin sulfate synthesis but reduces all forms of heparan sulfate to below the limit of detection |
| GO:0050508 glucuronosyl-N-acetylglucosaminyl-proteoglycan 4-alpha-N-acetylglucosaminyltransferase activity | IDA PMID:16303756 Heparan sulfate polymerization in Drosophila. | ACCEPT | Summary: GlcNAcT-II activity of Ttv demonstrated in vitro. Reason: Core activity, directly assayed for Ttv; enhanced in complex with Sotv. Supporting Evidence: PMID:16303756 Here we demonstrated that TTV/DEXT1 and SOTV/DEXT2 had GlcNAcT-II and GlcAT-II activities required for the biosynthesis of repeating disaccharide units of the HS backbone |
| GO:0050508 glucuronosyl-N-acetylglucosaminyl-proteoglycan 4-alpha-N-acetylglucosaminyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic mapping from the UniProt catalytic-activity (RHEA:16213, EC 2.4.1.224) annotation, itself based on PMID:16303756. Reason: Same claim as the IDA row; consistent action. Supporting Evidence: PMID:16303756 Here we demonstrated that TTV/DEXT1 and SOTV/DEXT2 had GlcNAcT-II and GlcAT-II activities required for the biosynthesis of repeating disaccharide units of the HS backbone |
| GO:0050509 N-acetylglucosaminyl-proteoglycan 4-beta-glucuronosyltransferase activity | IDA PMID:16303756 Heparan sulfate polymerization in Drosophila. | ACCEPT | Summary: GlcAT-II activity of Ttv demonstrated in vitro. Reason: Core activity, directly assayed for Ttv; enhanced in complex with Sotv. Supporting Evidence: PMID:16303756 Here we demonstrated that TTV/DEXT1 and SOTV/DEXT2 had GlcNAcT-II and GlcAT-II activities required for the biosynthesis of repeating disaccharide units of the HS backbone |
| GO:0050509 N-acetylglucosaminyl-proteoglycan 4-beta-glucuronosyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic mapping from the UniProt catalytic-activity (RHEA:20908, EC 2.4.1.225) annotation, itself based on PMID:16303756. Reason: Same claim as the IDA row; consistent action. Supporting Evidence: PMID:16303756 Here we demonstrated that TTV/DEXT1 and SOTV/DEXT2 had GlcNAcT-II and GlcAT-II activities required for the biosynthesis of repeating disaccharide units of the HS backbone |
| GO:0120504 EXT1-EXT2 complex | IDA PMID:14998928 Distinct and collaborative roles of Drosophila EXT family pr... | ACCEPT | Summary: Ttv and Sotv form a complex in vivo. Reason: The GO:0120504 definition explicitly names Ttv and Sotv as the Drosophila complex. The complex is the functional co-polymerase unit, as co-expression of the two subunits markedly augments both transferase activities (PMID:16303756). Supporting Evidence: PMID:14998928 We demonstrate further that Ttv and Sotv form a complex and are co-localized in vivo. PMID:16303756 the coexpression of TTV with SOTV markedly augmented both glycosyltransferase activities when compared with the expression of TTV or SOTV alone |
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Download this section (compressed HTML)Q: Human EXT1-EXT2 is reported to have GlcNAcT-I (chain initiation) activity whereas Drosophila Ttv-Sotv does not (PMID:16303756). Should transfer of EXT1-clade functions to insect orthologs exclude GlcNAcT-I, and is the loss lineage-specific?
Q: The cached PANTHER 19.0 HMM classification places ttv in PTHR11062:SF129 with C. elegans rib-1, separate from vertebrate EXT1 (PTHR11062:SF97), while UniProt lists PTHR48261:SF3. Which subfamily placement is current, and do both share the PAINT node PTN000869020?
Q: Should the UniPathway-based heparin proteoglycan biosynthesis mapping be restricted to taxa that make heparin, given that no heparin has been described in Drosophila?
Experiment: Assay purified Ttv-Sotv versus Ttv alone on defined acceptors to measure each subunit's contribution to GlcAT-II and GlcNAcT-II activity, and test catalytic-site mutants of each subunit in vivo for rescue of HS synthesis.
Experiment: Germline-clone and zygotic analysis of an independent ttv null allele with quantitative germ cell counts, to resolve the conflicting germ cell migration reports (PMID:17409068 versus PMID:19389345).
tout-velu (ttv) encodes a glycosyltransferase that forms a complex with sotv to catalyze the alternating transfer of glucuronic acid (GlcA) and N-acetylglucosamine (GlcNAc) to their respective acceptors, GlcNAc and GlcA, during the elongation of the heparan sulfate glycosaminoglycan chain.
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