CHSY1 is a type-II Golgi membrane glycosyltransferase that elongates the chondroitin backbone of proteoglycans. Its luminal catalytic region alternately adds glucuronic acid through a beta1,3 linkage and N-acetylgalactosamine through a beta1,4 linkage, using UDP-sugar donors. CHSY1 forms functional polymerase complexes with CHPF or CHPF2, which support complex assembly and activity, while CHSY1 supplies both sugar-transfer reactions. The resulting chains can subsequently be modified by sulfotransferases. CHSY1-dependent chondroitin production contributes to extracellular-matrix organization and skeletal development. A soluble CHSY1 pool has also been detected in primary human fibroblast conditioned medium; its processing and the relationship between chondroitin synthesis and altered NOTCH signaling remain incompletely resolved.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-1971487 | ACCEPT | Summary: Retain the Golgi membrane site of chondroitin-chain synthesis. Reason: The live source chain reaches CHSY1/Q86X52 via catalyst 1971459, complex 9941504, synthase set 9955243 and protein 1971431. Its compartment is explicitly Golgi membrane. The catalytic domains of the type-II membrane protein operate on luminal glycan acceptors; no plasma-membrane polymerization is inferred. Supporting Evidence: Reactome:R-HSA-1971487 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-1971491 | ACCEPT | Summary: Retain the Golgi membrane site of chondroitin-chain synthesis. Reason: The live source chain reaches CHSY1/Q86X52 via catalyst 1971466, complex 9941504, synthase set 9955243 and protein 1971431. Its compartment is explicitly Golgi membrane. The catalytic domains of the type-II membrane protein operate on luminal glycan acceptors; no plasma-membrane polymerization is inferred. Supporting Evidence: Reactome:R-HSA-1971491 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-3595176 | ACCEPT | Summary: Retain Golgi membrane localization while distinguishing the disease reaction. Reason: This source models a CHSY1 mutant set (3636795) at the Golgi membrane and links the defective reaction to its normal counterpart. The set contains E33Sfs*2, G19_L28del, P539R and Q69* entities sharing reference 223471/Q86X52. This is not experimental proof that every truncated mutant retains Golgi targeting. The unscoped gene-level location is corroborated by the normal CHSY1 event chain and established type-II Golgi enzyme biology; source identity and qualifier are preserved. Supporting Evidence: Reactome:R-HSA-3595176 Reactome:R-HSA-1971487 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-3595178 | ACCEPT | Summary: Retain Golgi membrane localization while distinguishing the disease reaction. Reason: This source models a CHSY1 mutant set (3636795) at the Golgi membrane and links the defective reaction to its normal counterpart. The set contains E33Sfs*2, G19_L28del, P539R and Q69* entities sharing reference 223471/Q86X52. This is not experimental proof that every truncated mutant retains Golgi targeting. The unscoped gene-level location is corroborated by the normal CHSY1 event chain and established type-II Golgi enzyme biology; source identity and qualifier are preserved. Supporting Evidence: Reactome:R-HSA-3595178 Reactome:R-HSA-1971487 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0005576 extracellular region | IDA PMID:21129727 Loss of CHSY1, a secreted FRINGE enzyme, causes syndromic br... | KEEP AS NON CORE | Summary: Retain the observed extracellular CHSY1 pool. Reason: PMID 21129727 detects CHSY1 by immunoblot in conditioned medium from unaffected primary human dermal fibroblasts, with loss in the affected frameshift-mutant cells. This supports the extracellular location independently of its principal Golgi biosynthetic role. Proposed N-terminal shedding and disulfide-linked processing remain interpretations, not mapped cleavage or a verified secreted isoform. Extracellular detection does not establish that the full polymerization reaction occurs there. Supporting Evidence: |
| GO:0005576 extracellular region | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Retain the extracellular-location mapping at the experimentally observed scope. Reason: The UniProt subcellular-location mapping agrees with the positive primary human fibroblast conditioned-medium result in PMID 21129727. This soluble pool is peripheral to the Golgi polymerase mechanism; neither a specific secretion pathway nor direct extracellular NOTCH glycosylation was demonstrated. |
| GO:0005794 Golgi apparatus | IBA GO_REF:0000033 | ACCEPT | Summary: Retain inherited Golgi activity. Reason: The curated PAINT assertion is consistent with the target enzyme acting on glycan chains within the Golgi. The broader apparatus term represents the same core compartment as the more specific membrane assertions. Current donor records provide context, not a reconstruction of the historical ancestral node. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN008994615 SUPPORTS TRANSFER The actual PAINT source places Golgi activity at PTN008994615. Current human B4GALNT3/CHPF2 and mouse Chsy1 records supply compartment context, while the authenticated CHSY1 Reactome target chain independently supports Golgi localization. This is qualified support for the curated transfer, not a reconstructed historical tree, alignment or IBD placement. Supporting Evidence: GO_REF:0000033 Reactome:R-HSA-1971487 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0005794 Golgi apparatus | IEA GO_REF:0000120 | ACCEPT | Summary: Retain Golgi activity inferred from the authenticated ortholog and rule sources. Reason: Q6ZQ11 is mouse Chsy1, and its current Golgi annotation and the target Reactome entity agree with human CHSY1 biosynthetic organization. The broad apparatus term is biologically appropriate; the original ARBA/Ensembl source fields are not rewritten or treated as direct microscopy. Supporting Evidence: GO_REF:0000120 Reactome:R-HSA-1971487 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0016020 membrane | HDA PMID:19946888 Defining the membrane proteome of NK cells. | UNDECIDED | Summary: Leave the source-specific membrane proteomics assertion unresolved. Reason: The authentic PMID 19946888 abstract describes membrane-enriched YTS human NK-like cells, peripheral-protein removal, TFE extraction and mass spectrometry. The original target-level supporting XLS could not be read after bounded publisher retrieval attempts, so the exact CHSY1 identification, peptide evidence and fraction remain unverified. Independent Golgi/type-II topology supports membrane association in general, but does not substitute for this source-specific proteomics check. There is no wrong-gene or negative-localization claim. Supporting Evidence: |
| GO:0016757 glycosyltransferase activity | IEA GO_REF:0000107 | MODIFY | Summary: Specify both demonstrated sugar-transfer reactions. Reason: The generic enzyme-class transfer from mouse Chsy1 is sound but unnecessarily broad. Human recombinant CHSY1 performs beta1,4 GalNAc transfer and beta1,3 GlcA transfer on chondroitin-chain acceptors. The two replacement terms distinguish these coupled, experimentally separable catalytic activities; neither denotes sulfate transfer or glycosylation of NOTCH. Proposed replacements: glucuronosyl-N-acetylgalactosaminyl-proteoglycan 4-beta-N-acetylgalactosaminyltransferase activity N-acetylgalactosaminyl-proteoglycan 3-beta-glucuronosyltransferase activity Supporting Evidence: GO_REF:0000107 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0030279 negative regulation of ossification | IMP PMID:21129727 Loss of CHSY1, a secreted FRINGE enzyme, causes syndromic br... | KEEP AS NON CORE | Summary: Retain the context-dependent negative effect on osteoblast differentiation. Reason: In PMID 21129727, CHSY1 knockdown in human fetal osteoblast cells increases osteogenic markers and reported alkaline-phosphatase activity. This supports the existing negative-regulation direction as a downstream developmental consequence. The experiment does not identify a separate bone-inhibition molecular activity, and the NOTCH rescue experiments do not prove a direct receptor glycosylation substrate. Supporting Evidence: |
| GO:0031667 response to nutrient levels | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Retain nutrient-response expression at ortholog scope. Reason: The exact rat donor D3ZRM3 is Chsy1; its current RGD annotation is IEP/PMID 14975935. The authentic abstract and indexed original Fig 3 Results report increased skin chondroitin-synthase1 mRNA after dietary NaCl loading. This fits the term definition, which includes altered gene expression, and supports a peripheral ortholog response rather than sodium transport, nutrient sensing or an intrinsic regulatory activity. The complete original body and linked erratum were not recovered; no human salt-challenge experiment is claimed. |
| GO:0032580 Golgi cisterna membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Retain the cisternal membrane assignment for the Golgi glycosyltransferase. Reason: The InterPro/UniProt location mapping is consistent with the type-II membrane enzyme and its luminal chondroitin-chain synthesis. This is a compartment inference, not direct resolution of a particular cis-, medial- or trans-Golgi cisterna. It remains compatible with the broader experimentally and pathway-supported Golgi location. |
| GO:0047238 glucuronosyl-N-acetylgalactosaminyl-proteoglycan 4-beta-N-acetylgalactosaminyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Retain the GalNAc elongation activity. Reason: Curated PAINT inference is corroborated by direct target enzymology; the target appearing among descendant sources is not circular. CHSY1 adds GalNAc from UDP-GalNAc to a GlcA-terminated glycan acceptor. Recent human CHSY1βCHPF assays distinguish this GT7 reaction from GlcA transfer. The activity is chain elongation, not a sulfate-transfer reaction. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000961850 SUPPORTS TRANSFER The actual PAINT source places this GalNAc-transfer capability at PTN000961850. Human CHSY1 radiolabeled product analysis and modern domain-selective assays independently establish the target reaction. Q86X52 is legitimately among the descendant evidence sources; that is not circularity. Historical node placement and the family alignment were not reconstructed. Supporting Evidence: GO_REF:0000033 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0047238 glucuronosyl-N-acetylgalactosaminyl-proteoglycan 4-beta-N-acetylgalactosaminyltransferase activity | IDA PMID:11514575 Molecular cloning and expression of a human chondroitin synt... | ACCEPT | Summary: Retain the GalNAc elongation activity. Reason: The original study uses human KIAA0990/AB023207 with residues 1β46 replaced by a signal/protein-A fusion, expressed in COS-1 and isolated on IgG-Sepharose. Product characterization supports the beta1,4 linkage. CHSY1 adds GalNAc from UDP-GalNAc to a GlcA-terminated glycan acceptor. Recent human CHSY1βCHPF assays distinguish this GT7 reaction from GlcA transfer. The activity is chain elongation, not a sulfate-transfer reaction. |
| GO:0047238 glucuronosyl-N-acetylgalactosaminyl-proteoglycan 4-beta-N-acetylgalactosaminyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Retain the GalNAc elongation activity. Reason: The combined rule, mouse Chsy1 and EC 2.4.1.175 mapping agree with direct human enzyme evidence. CHSY1 adds GalNAc from UDP-GalNAc to a GlcA-terminated glycan acceptor. Recent human CHSY1βCHPF assays distinguish this GT7 reaction from GlcA transfer. The activity is chain elongation, not a sulfate-transfer reaction. Supporting Evidence: GO_REF:0000120 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0047238 glucuronosyl-N-acetylgalactosaminyl-proteoglycan 4-beta-N-acetylgalactosaminyltransferase activity | TAS Reactome:R-HSA-3595176 | ACCEPT | Summary: Retain the normal GalNAc-transfer function represented by the disease pathway. Reason: The source is a defective-mutant reaction, not a positive assay of its truncated or missense entities. Its summation explicitly states the normal CHSY1 activity and its normalReaction link reaches 1971487. Independent direct human CHSY1 biochemistry establishes the gene-level MF, so the unscoped assertion is retained without claiming that every disease mutant catalyzes the reaction. Supporting Evidence: Reactome:R-HSA-3595176 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0050510 N-acetylgalactosaminyl-proteoglycan 3-beta-glucuronosyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Retain the glucuronic-acid elongation activity. Reason: The curated ancestral assertion has independent target biochemical grounding. Historical placement was not reconstructed, and target self-inclusion is legitimate. CHSY1 transfers GlcA to a GalNAc-terminated acceptor. Human CHSY1 catalytic-domain mutants in the recent reconstituted complexes separate this GT31 activity from GalNAc transfer; CHPF supports the complex rather than supplying this catalytic reaction. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000271262 SUPPORTS TRANSFER The actual PAINT source places this GlcA-transfer capability at PTN000271262. Human CHSY1 product analysis and selective GT31 disruption independently support the target reaction. Target Q86X52 and related CHSY3 are present in the current source context, without implying a new pairwise transfer or independent reconstruction of the ancestral node. Supporting Evidence: GO_REF:0000033 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0050510 N-acetylgalactosaminyl-proteoglycan 3-beta-glucuronosyltransferase activity | IDA PMID:11514575 Molecular cloning and expression of a human chondroitin synt... | ACCEPT | Summary: Retain the glucuronic-acid elongation activity. Reason: The original human protein-A fusion assay measures transfer from radiolabeled UDP-GlcA and identifies the beta1,3-linked product. CHSY1 transfers GlcA to a GalNAc-terminated acceptor. Human CHSY1 catalytic-domain mutants in the recent reconstituted complexes separate this GT31 activity from GalNAc transfer; CHPF supports the complex rather than supplying this catalytic reaction. |
| GO:0050510 N-acetylgalactosaminyl-proteoglycan 3-beta-glucuronosyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Retain the glucuronic-acid elongation activity. Reason: The combined rule, mouse Chsy1 and EC 2.4.1.226 mapping agree with direct human enzymology. CHSY1 transfers GlcA to a GalNAc-terminated acceptor. Human CHSY1 catalytic-domain mutants in the recent reconstituted complexes separate this GT31 activity from GalNAc transfer; CHPF supports the complex rather than supplying this catalytic reaction. Supporting Evidence: GO_REF:0000120 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0050510 N-acetylgalactosaminyl-proteoglycan 3-beta-glucuronosyltransferase activity | TAS Reactome:R-HSA-3595178 | ACCEPT | Summary: Retain the normal GlcA-transfer function represented by the disease pathway. Reason: The source models loss of activity in the CHSY1 mutant set and links normalReaction 1971491; it is not a WT turnover experiment. Its positive gene-level function is independently established by human biochemical assays. Preserve the TAS source while separating normal molecular capability from the modeled failure of individual variants. Supporting Evidence: Reactome:R-HSA-3595178 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0050650 chondroitin sulfate proteoglycan biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: Retain inherited participation in chondroitin sulfate proteoglycan biosynthesis. Reason: CHSY1 itself performs the two glycosyl-transfer steps that extend the chondroitin backbone, rather than merely serving as a substrate or being necessary for an unrelated outcome. Human reconstitution and cellular complementation corroborate the PAINT assertion. This does not assign sulfation chemistry, initiation of the common proteoglycan linkage region, or an autonomous CHPF catalytic activity to CHSY1. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000961850 SUPPORTS TRANSFER The actual PAINT source assigns chondroitin sulfate proteoglycan biosynthesis through PTN000961850. CHSY1 itself performs backbone elongation in human biochemical and cellular assays, supporting participation rather than a substrate-only or necessity inference. Current descendant records, including the target, contextualize this curated judgment; the historical tree and IBD placement remain uninspected. Supporting Evidence: GO_REF:0000033 file:human/CHSY1/CHSY1-source-evidence.json |
| GO:0050650 chondroitin sulfate proteoglycan biosynthetic process | IDA PMID:11514575 Molecular cloning and expression of a human chondroitin synt... | ACCEPT | Summary: Retain the original biosynthesis assertion and its source relation. Reason: The original human enzyme directly extends chondroitin acceptors through two transfer reactions. This supports biosynthesis while the original acts_upstream_of_or_within qualifier is preserved exactly. The 2001 construct did not by itself establish sustained copolymerization; later CHPF coexpression and reconstitution supply that additional evidence. |
| GO:0050650 chondroitin sulfate proteoglycan biosynthetic process | IDA PMID:12716890 Molecular cloning of a chondroitin polymerizing factor that ... | ACCEPT | Summary: Retain directly demonstrated cooperative chain polymerization. Reason: The actual original Methods coexpress human CHSY1 and soluble CHPF in COS-1, recover the protein-A-tagged material on IgG-Sepharose and test both nucleotide-sugar donors. Product chromatography and glycosidase analysis demonstrate polymer formation on alpha-thrombomodulin linkage-region acceptors; simple mixing of separately expressed proteins does not reproduce coexpression. This is a performed biosynthetic step. |
| GO:0050650 chondroitin sulfate proteoglycan biosynthetic process | IEA GO_REF:0000117 | ACCEPT | Summary: Retain biosynthesis inferred by the automated rule. Reason: The ARBA assertion is independently confirmed by human CHSY1 catalytic reactions and CHSY1βCHPF chain elongation. Its scope is backbone synthesis within proteoglycan biosynthesis; CHSY1 does not perform the sulfate-transfer reactions represented by other enzymes in this pathway. Supporting Evidence: GO_REF:0000117 file:human/CHSY1/CHSY1-source-evidence.json |
Loading supporting contentβ¦
Download this section (compressed HTML)Q: How is the soluble CHSY1 pool generated in human fibroblasts, and is it catalytically active with a CHPF partner outside the Golgi?
Q: Do the NOTCH readouts after CHSY1 loss reflect altered chondroitin-dependent signaling or direct modification of a receptor or ligand, and what is the experimentally established glycan substrate?
Q: How do CHPF versus CHPF2 partnerships alter CHSY1 stability, acceptor selection and chain-length control in native tissues?
Q: Can the original PMID 19946888 target peptide/table record and the PMID 14975935 erratum be recovered to complete the source-specific localization and nutrient-response checks?
Experiment: Reconstitute matched human CHSY1βCHPF and CHSY1βCHPF2 complexes on defined proteoglycan acceptors, normalizing enzyme abundance and integrity while measuring each transfer step and product chain length separately.
Experiment: Map the N- and C-termini and partner composition of endogenous extracellular CHSY1, then compare its activity with Golgi-associated material using both UDP-sugars and verified glycan acceptors.
Experiment: Measure NOTCH glycopeptides alongside chondroitin products after CHSY1 perturbation and rescue with matched catalytic mutants, distinguishing direct receptor modification from an indirect matrix-dependent signaling effect.
Loading supporting contentβ¦
Download this section (compressed HTML)Loading supporting contentβ¦
Download this section (compressed HTML)