{"gene":"CHST1","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":1995,"finding":"Chick chondrocyte chondroitin 6-sulfotransferase (C6ST, ortholog of CHST1) was cloned and shown to catalyze transfer of sulfate from PAPS to position 6 of N-acetylgalactosamine residues of chondroitin; it also exhibits keratan sulfate sulfotransferase activity. The protein has Type II transmembrane topology and is an N-linked glycoprotein.","method":"cDNA cloning, COS-7 cell transfection/overexpression, enzymatic activity assay, antibody cross-reactivity, N-glycosylation analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted enzymatic activity in heterologous cells, protein sequence confirmed against purified enzyme, multiple orthogonal methods","pmids":["7629189"],"is_preprint":false},{"year":1996,"finding":"C6ST (CHST1 ortholog) transfers sulfate specifically to position 6 of galactose residues in keratan sulfate chains, including Gal linked to GlcNAc-6-sulfate and to unsulfated GlcNAc residues; a single protein catalyzes both chondroitin and keratan sulfate 6-O-sulfation.","method":"In vitro sulfotransferase assay with purified C6ST, product characterization by hydrazinolysis, HNO2 deamination, NaBH4 reduction, SAX-HPLC and paper chromatography; recombinant C6ST transfection in COS-7 cells","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic assay with structural product identification, confirmed with recombinant enzyme","pmids":["8991509"],"is_preprint":false},{"year":1997,"finding":"C6ST (CHST1 ortholog) sulfates sialyl lactosamine oligosaccharides at position 6 of galactose in NeuAcα2-3Galβ1-4GlcNAc (SLN) and related structures, but not sialyl Lewis x (fucosylated); a single enzyme thus sulfates chondroitin, keratan sulfate, and sialyl lactosamine oligosaccharides, suggesting a role in biosynthesis of sulfated sialyl Lewis x L-selectin ligands.","method":"In vitro sulfotransferase assay with purified and recombinant C6ST, product degradation with neuraminidase, hydrazinolysis, HNO2 deamination, NaBH4 reduction, SAX-HPLC","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic assay with chemical product identification using multiple degradative methods","pmids":["9147050"],"is_preprint":false},{"year":1997,"finding":"Human KSGal6ST (CHST1) was cloned from a human fetal brain library; when expressed in COS-7 cells it produced keratan sulfate sulfotransferase activity (sulfating Gal residues of KS) but not chondroitin 6-sulfotransferase activity, distinguishing it functionally from chick C6ST. Structural analysis confirmed 6-O-sulfation of galactose in KS. Gene maps to chromosome 11p11.1-11.2.","method":"cDNA cloning by cross-hybridization, COS-7 cell transfection, enzymatic activity assay, structural analysis of 35S-labeled GAG products, Northern blot, FISH chromosomal mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — heterologous expression with enzymatic activity and product structural analysis; substrate specificity defined","pmids":["9405439"],"is_preprint":false},{"year":1998,"finding":"Human C6ST (CHST1) cDNA was cloned and encodes a protein with 74% identity to chick C6ST. Expression of a soluble recombinant form demonstrated active sulfotransferase transferring sulfate to position 6 of GalNAc in GlcAbeta1-3GalNAc sequences in polymer chondroitin, various CS isoforms, and tetrasaccharides, but not in IdoAα1-3GalNAc or GlcAbeta1-3GalNAc(4-O-sulfate) sequences. The gene spans >20 kb with 3 exons; protein-coding domain split into 2 exons.","method":"cDNA cloning, COS-1 cell expression, enzymatic activity assay with defined acceptor substrates, product identification, gene structure analysis","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — direct enzymatic assay defining substrate specificity with structural product identification","pmids":["9883891"],"is_preprint":false},{"year":1998,"finding":"Human C6ST (CHST1) expressed in CHO-K1 cells produced marked increases in both C6ST and keratan sulfate sulfotransferase (KSST) enzymatic activities. The protein is predicted as a Type II transmembrane protein of 411 amino acids with N-terminal hydrophobic domain, four N-glycosylation sites, and maps to chromosome 11 by radiation hybrid mapping.","method":"Stable CHO-K1 transfection, enzymatic activity assay in cell homogenates, cDNA cloning/5'-RACE, radiation hybrid panel chromosomal mapping","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 — heterologous expression with direct enzymatic activity confirmation","pmids":["9639683"],"is_preprint":false},{"year":1998,"finding":"Human C6ST (CHST1) cDNA was isolated; ubiquitous 7.8-kb message in human adult tissues; the human enzyme contains a unique hydrophilic domain not present in chick C6ST.","method":"cDNA cloning by cross-hybridization with chick C6ST, Northern blot","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 — cloning with expression confirmation, but limited functional characterization beyond identification","pmids":["9714738"],"is_preprint":false},{"year":1999,"finding":"CHST1 (identical to human C6ST) and CHST2 were identified from human vascular endothelial cell cDNA libraries as sulfotransferases homologous to chicken C6ST; CHST1 is expressed by endothelial cells and may contribute to generation of L-selectin ligands.","method":"cDNA library screening, Northern blot, chromosomal mapping","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 — cloning and expression characterization in endothelial cells; functional role inferred from context","pmids":["10049591"],"is_preprint":false},{"year":1999,"finding":"Sulfation of GlyCAM-1 by related sulfotransferases including KSGal6ST (CHST1) generating Gal-6-sulfate, together with fucosylation, enhanced rolling ligand activity for L-selectin, increasing tethered/rolling lymphocyte numbers, reducing rolling velocity with more frequent pausing, and enhancing resistance to detachment by shear in flow chamber assays.","method":"Flow chamber rolling assay with sulfated/fucosylated GlyCAM-1, peripheral blood lymphocytes and Jurkat cells","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1-2 — functional reconstitution in flow chamber assay demonstrating that Gal-6-sulfate generated by CHST1-related enzyme directly modulates L-selectin ligand rolling behavior","pmids":["10510083"],"is_preprint":false},{"year":2001,"finding":"CHST1 and CHST2 expressed by vascular endothelial cells contribute to generation of shear-resistant leukocyte rolling via L-selectin. Human umbilical vein endothelial cells predominantly express CHST1 and CHST2; overexpression of CHST1 in a cell line with low L-selectin ligand activity increased rolling leukocyte numbers, reduced rolling velocities, and enhanced rolling under higher shear stresses in flow chamber assays.","method":"RT-PCR expression profiling, stable transfection/overexpression in endothelial cell lines, in vitro flow chamber leukocyte rolling assay","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 1-2 — direct gain-of-function experiment with defined cellular phenotype (rolling behavior) in flow chamber","pmids":["11310842"],"is_preprint":false},{"year":2006,"finding":"N-linked oligosaccharides on C6ST-1 (CHST1) are required for production of active enzyme, Golgi localization, and keratan sulfate sulfotransferase (KSST) activity. Specifically: deletion of the 4th N-glycosylation site abolished Golgi localization (enzyme retained in ER with calnexin colocalization) and abolished activity; deletion of the 5th site markedly reduced KSST activity but not C6ST activity; removal of N-glycans by PNGase F increased C6ST activity but decreased KSST activity.","method":"Tunicamycin treatment, site-directed mutagenesis of N-glycosylation sites, PNGase F treatment, immunofluorescence colocalization, WGA lectin affinity, EndoH sensitivity, enzymatic activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis of specific N-glycosylation sites combined with subcellular localization and enzymatic activity assays; multiple orthogonal methods","pmids":["16720579"],"is_preprint":false},{"year":2008,"finding":"Recombinant human C6ST-1 (CHST1) catalyzes sulfation of C6 on both galactose residues in the glycosaminoglycan-protein linkage region (GlcUA-Gal-Gal-Xyl-Ser), including before the first N-acetylhexosamine is attached. Intact xylose is required for sulfation of the second galactose from the reducing end; pre-4-O-sulfation of Gal blocks the reaction.","method":"Recombinant CHST1 expressed as protein A chimera in COS-1 cells, purified by IgG-Sepharose, in vitro sulfotransferase assay with defined linkage region saccharide substrates, product identification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — purified recombinant enzyme with defined substrates and structural product analysis; identifies novel substrates and substrate requirements","pmids":["18697746"],"is_preprint":false},{"year":2011,"finding":"CHST1 (C6ST-1) drives sialoglycan binding of multiple Siglecs (Siglec-3/7/8/15) at the cell surface; CHST1 generates the 6'-sulfated sialyl LacNAc epitope (Neu5Acα2-3(6-O-sulfo)Galβ1-4GlcNAc, 6'-Su-SLacNAc) recognized by Siglec-3 (CD33). Sulfation on both the Gal (by CHST1) and GlcNAc positions creates a disulfated ligand with ≥28-fold enhanced affinity for CD33.","method":"Cell-based glycan array using isogenic HEK293 cells with combinatorial loss/gain of sulfotransferase genes, Siglec-Fc fusion protein binding assay, mass-spectrometry-based binding assay with homogeneous Siglec-3 fragment, synthetic glycan inhibition","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — isogenic cell-based glycan array combined with MS-based affinity measurement and synthetic glycan validation; multiple orthogonal methods in one study","pmids":["33893239"],"is_preprint":false},{"year":2021,"finding":"Overexpression of CHST1 in multiple cell lines significantly enhances binding of numerous Siglecs; joint overexpression of CHST1 with CHST2 greatly enhanced binding of CD33 and several other Siglecs. MS-based assay confirmed ≥8-fold enhanced affinity of CD33 for Neu5Acα2-3(6-O-sulfo)Galβ1-4GlcNAc over unsulfated counterpart, and ≥28-fold for disulfated ligand.","method":"Sulfotransferase overexpression in five cell lines, Siglec-Fc binding assay, pharmacological N/O-glycan blockade, MS-based binding assay with homogeneous Siglec-3 fragment, sodium chlorate treatment","journal":"ACS chemical biology","confidence":"High","confidence_rationale":"Tier 1-2 — cell-type-dependent overexpression combined with MS affinity assay; replicated findings across multiple Siglecs and cell lines","pmids":["34661385"],"is_preprint":false},{"year":2021,"finding":"CHST1 sulfates Gal residues on O-glycans on PSGL-1/mIgG2b, including both C-3/core-1/core-2 and C-6-branch of core-2 structures, as defined by transfection into CHO cells expressing PSGL-1/mIgG2b and subsequent O-glycan characterization.","method":"Transfection of CHST1 expression plasmid in CHO cells co-expressing PSGL-1/mIgG2b and core 2 transferase (GCNT1), O-glycan characterization by LC-MSn","journal":"Molecular & cellular proteomics","confidence":"Medium","confidence_rationale":"Tier 2 — direct expression with glycan product characterization, single lab","pmids":["34555499"],"is_preprint":false},{"year":2022,"finding":"CHST1 (KSGal6ST) is required for biosynthesis of the CD33/Siglec-8 sialoglycoprotein ligand RPTPζS3L (sialylated keratan sulfate on RPTPζ/phosphacan) in mouse brain; brains from CHST1 knockout mice lacked Siglec-F/CD33/Siglec-8 binding activity.","method":"CHST1 knockout mice, Siglec-Fc binding assay on brain extracts, comparison with St3gal4 and RPTPζ knockout mice, biochemical ligand identification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — clean genetic KO with specific biochemical phenotype (loss of Siglec ligand), triangulated with two other KO mouse models","pmids":["35452678"],"is_preprint":false},{"year":2023,"finding":"In Xenopus embryos, chst1 (CHST1 ortholog) is expressed specifically in otic vesicles; loss-of-function of chst1 led to loss of highly sulfated keratan sulfate (HSKS) in otic vesicles and reduction in their size, establishing that CHST1 is required for HSKS biosynthesis and for maintaining otic vesicle structure during organogenesis.","method":"In situ hybridization for expression mapping, morpholino loss-of-function, immunostaining for HSKS, measurement of otic vesicle size","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 — morpholino knockdown in Xenopus with specific structural phenotype, single lab","pmids":["36998246"],"is_preprint":false},{"year":2018,"finding":"CHST1 knockout mice showed that CHST1 does not contribute substantially to synthesis of glycan ligands for Siglec-F in airways; however, its absence results in exaggerated accumulation of airway macrophages and lymphocytes after OVA sensitization and challenge, indicating a role in controlling airway immune cell composition.","method":"CHST1-/- knockout mice, OVA sensitization/challenge model, Siglec-F-Fc binding assay on lung tissue, differential cell counts in BAL, O-glycan characterization by mass spectrometry, Western blotting","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype (macrophage/lymphocyte accumulation), but mechanism for immune phenotype not fully resolved","pmids":["29659839"],"is_preprint":false},{"year":2025,"finding":"CHST1 exhibits significantly higher sulfotransferase activity toward branched O-Man glycans than toward linear counterparts in enzymatic assays; this establishes that GnT-IX-mediated O-Man branching promotes KS biosynthesis by providing a preferred scaffold for CHST1 activity in the brain.","method":"In vitro enzymatic assay comparing CHST1 activity on branched vs. linear O-Man glycan substrates; GnT-IX knockout mouse brain analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic assay defining substrate preference, corroborated by KO mouse data","pmids":["41513091"],"is_preprint":false},{"year":2025,"finding":"The glycan classes presenting CHST1-dependent sulfated Siglec ligands include both N-glycans and mucin-type O-glycans for Siglec-3 and Siglec-8 binding; O-mannose glycans in CHST1-expressing cells also contribute modestly to Siglec-3 and Siglec-8 binding. For Siglec-3, N-glycans are the major sulfated trans ligands, while mucin-type O-glycans have the largest impact on Siglec-3 cis masking.","method":"Genetic disruption of glycan classes (N-glycan, mucin O-glycan, O-Man glycan) in CHST1-expressing cells, pharmacological inhibition, enzymatic treatment, Siglec-Fc binding assay","journal":"ACS chemical biology","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic/pharmacological/enzymatic strategies to dissect glycan class contributions; convergent findings","pmids":["39836965"],"is_preprint":false},{"year":2024,"finding":"CHST1 (KSGal6ST) sulfates galactose residues in keratan sulfate but cannot act on galactosides blocked by α1,3-fucosides or α2,6-sialosides; exploiting this mutual exclusivity allows regioselective enzymatic installation of Gal-6-sulfate on poly-LacNAc chains to build defined KS oligosaccharides.","method":"Enzymatic synthesis using recombinant CHST1 on defined oligosaccharide substrates with and without blocking glycan modifications; product characterization","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic reconstitution with defined substrates demonstrating substrate selectivity rules","pmids":["38494637"],"is_preprint":false}],"current_model":"CHST1 (KSGal6ST/C6ST-1) is a Golgi-resident Type II transmembrane sulfotransferase that transfers sulfate from PAPS to the C-6 position of galactose residues in keratan sulfate chains, sialyl N-acetyllactosamine oligosaccharides, and galactose residues in the glycosaminoglycan-protein linkage region; its N-glycosylation is required for proper Golgi localization and enzymatic activity; on cell surfaces it generates 6'-sulfated sialyl LacNAc epitopes that serve as high-affinity ligands for immunomodulatory Siglec receptors (including CD33/Siglec-3 and Siglec-8), and it contributes to generation of L-selectin ligands on vascular endothelial cells and promotes shear-resistant lymphocyte rolling."},"narrative":{"teleology":[{"year":1995,"claim":"Cloning of chick C6ST (CHST1 ortholog) established that a single Type II transmembrane sulfotransferase catalyzes 6-O-sulfation of both chondroitin and keratan sulfate, resolving whether these activities reside in separate or the same enzyme.","evidence":"cDNA cloning and COS-7 expression with enzymatic activity assays and N-glycosylation analysis","pmids":["7629189"],"confidence":"High","gaps":["Substrate specificity for non-GAG glycans unknown","Human ortholog not yet cloned","Subcellular targeting determinants undefined"]},{"year":1997,"claim":"Substrate specificity was expanded beyond GAGs when C6ST was shown to sulfate sialyl lactosamine oligosaccharides at Gal C-6, and human KSGal6ST (CHST1) was cloned and shown to have keratan sulfate but not chondroitin 6-sulfotransferase activity, distinguishing it from the chick enzyme and revealing species-specific substrate preferences.","evidence":"In vitro sulfotransferase assays with defined oligosaccharide substrates and structural product identification; COS-7 expression of human CHST1","pmids":["9147050","9405439"],"confidence":"High","gaps":["Basis for species difference in CS activity unclear","Crystal structure unavailable to explain selectivity"]},{"year":1998,"claim":"Full cloning and characterization of human CHST1 defined its gene structure, chromosomal locus, dual C6ST/KSST enzymatic activities, and Type II transmembrane topology with four N-glycosylation sites.","evidence":"cDNA cloning, COS-1/CHO-K1 expression with enzymatic activity assays on defined substrates, gene structure and radiation hybrid mapping","pmids":["9883891","9639683"],"confidence":"High","gaps":["Endogenous regulation of expression not addressed","Functional significance of N-glycosylation sites unknown"]},{"year":2001,"claim":"A direct role for CHST1 in vascular biology was established when overexpression in endothelial cells enhanced L-selectin-dependent leukocyte rolling under shear, demonstrating that CHST1-generated Gal-6-sulfate on endothelial glycans is a functional component of L-selectin ligands.","evidence":"Stable transfection/overexpression in endothelial cell lines, in vitro flow chamber leukocyte rolling assay","pmids":["10510083","11310842"],"confidence":"High","gaps":["In vivo contribution to lymphocyte homing not tested genetically","Relative contribution vs. CHST2 unresolved"]},{"year":2006,"claim":"Specific N-glycosylation sites on CHST1 were shown to differentially control Golgi localization and substrate-specific enzymatic activities, resolving how post-translational modification regulates this enzyme's function and trafficking.","evidence":"Site-directed mutagenesis of individual N-glycosylation sites, immunofluorescence colocalization with Golgi/ER markers, enzymatic activity assays","pmids":["16720579"],"confidence":"High","gaps":["Structural basis for how N-glycans regulate activity unknown","Whether other post-translational modifications regulate CHST1 untested"]},{"year":2008,"claim":"CHST1's substrate repertoire was further broadened to include galactose residues in the common GAG-protein linkage region tetrasaccharide, revealing that CHST1 can act at early steps of GAG chain initiation before the first hexosamine is added.","evidence":"Purified recombinant CHST1 in vitro assay with defined linkage-region saccharide substrates","pmids":["18697746"],"confidence":"High","gaps":["In vivo significance of linkage-region sulfation for GAG assembly unknown","Whether this occurs in specific cell types not examined"]},{"year":2018,"claim":"CHST1 knockout mice revealed an in vivo immunoregulatory role: loss of CHST1 led to exaggerated airway macrophage and lymphocyte accumulation after allergen challenge, even though CHST1 did not substantially contribute to airway Siglec-F ligand synthesis.","evidence":"CHST1−/− knockout mice, OVA sensitization/challenge, BAL cell counts, Siglec-F-Fc binding, O-glycan MS","pmids":["29659839"],"confidence":"Medium","gaps":["Mechanism by which CHST1 loss exaggerates immune cell accumulation unresolved","Relevant glycoprotein substrates in airway not identified","Single challenge model tested"]},{"year":2021,"claim":"CHST1 was identified as the key sulfotransferase generating 6'-sulfated sialyl LacNAc, a high-affinity ligand for CD33/Siglec-3 and multiple other Siglecs, with disulfation (together with CHST2) enhancing CD33 affinity ≥28-fold, establishing CHST1 as a central regulator of Siglec-mediated immunomodulation.","evidence":"Isogenic cell-based glycan arrays, Siglec-Fc binding, MS-based affinity measurements, overexpression across five cell lines","pmids":["33893239","34661385"],"confidence":"High","gaps":["In vivo consequences of CHST1-dependent Siglec engagement for immune regulation not fully defined","Whether tumor cells exploit CHST1 to engage inhibitory Siglecs untested in this context"]},{"year":2022,"claim":"Genetic ablation of CHST1 in mice abolished Siglec-F/CD33/Siglec-8 ligand activity in brain, identifying RPTPζ/phosphacan-associated sialylated keratan sulfate as the endogenous CHST1-dependent Siglec ligand in brain tissue.","evidence":"CHST1 knockout mice brain extracts, Siglec-Fc binding, triangulation with St3gal4 and RPTPζ KO mice","pmids":["35452678"],"confidence":"High","gaps":["Functional consequence of losing brain Siglec ligands for neuroinflammation or microglia regulation not examined","Whether other brain glycoproteins carry CHST1-dependent ligands unknown"]},{"year":2023,"claim":"Developmental relevance was demonstrated in Xenopus, where CHST1 is required for highly sulfated keratan sulfate biosynthesis in otic vesicles and for maintaining otic vesicle size, linking CHST1 to organogenesis.","evidence":"Morpholino knockdown in Xenopus embryos, HSKS immunostaining, otic vesicle morphometry","pmids":["36998246"],"confidence":"Medium","gaps":["Morpholino approach requires genetic confirmation (CRISPR)","Whether mammalian ear development similarly requires CHST1 untested","Mechanism linking HSKS loss to reduced vesicle size unknown"]},{"year":2025,"claim":"CHST1's substrate preferences were refined: it preferentially sulfates GnT-IX-generated branched O-Man glycans over linear ones, and its sulfated Siglec ligands are presented on N-glycans, mucin O-glycans, and O-Man glycans with glycan-class-specific roles in trans versus cis Siglec engagement.","evidence":"In vitro enzymatic assays on branched vs. linear O-Man substrates; genetic/pharmacological/enzymatic dissection of glycan classes in CHST1-expressing cells with Siglec-Fc binding","pmids":["41513091","39836965"],"confidence":"High","gaps":["Structural basis for preference for branched O-Man substrates not resolved","In vivo significance of O-Man-borne Siglec ligands in brain not tested functionally"]},{"year":null,"claim":"No crystal or cryo-EM structure of CHST1 exists, and the structural determinants of its broad but selective substrate specificity — excluding α1,3-fucosylated and α2,6-sialylated galactosides while accepting diverse glycan backbones — remain mechanistically unexplained.","evidence":"","pmids":[],"confidence":"High","gaps":["No atomic structure available","Catalytic mechanism details at the active site unresolved","In vivo functional consequences of CHST1 loss for Siglec-mediated immunoregulation incompletely defined across tissues"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,2,3,4,5,11,18,20]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[10]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[8,9,12,13,15,17]}],"complexes":[],"partners":["CHST2","PTPRZ1","SELPLG"],"other_free_text":[]},"mechanistic_narrative":"CHST1 (C6ST-1/KSGal6ST) is a Golgi-resident Type II transmembrane sulfotransferase that transfers sulfate from PAPS to the C-6 hydroxyl of galactose residues across multiple glycan classes, including keratan sulfate, chondroitin sulfate, sialyl N-acetyllactosamine oligosaccharides, the glycosaminoglycan-protein linkage region, O-mannose glycans, and mucin-type O-glycans [PMID:7629189, PMID:8991509, PMID:18697746, PMID:34555499, PMID:41513091]. N-glycosylation of CHST1 is essential for its Golgi retention and catalytic activity, with specific N-glycosylation sites differentially required for keratan sulfate versus chondroitin sulfate sulfotransferase functions [PMID:16720579]. By generating 6'-sulfated sialyl LacNAc epitopes, CHST1 creates high-affinity ligands for immunomodulatory Siglec receptors including CD33/Siglec-3 and Siglec-8 on both N-glycans and O-glycans, and is required in mouse brain for biosynthesis of the sialylated keratan sulfate Siglec ligand on RPTPζ/phosphacan [PMID:33893239, PMID:35452678, PMID:39836965]. On vascular endothelial cells, CHST1-mediated Gal-6-sulfation contributes to L-selectin ligand generation, promoting shear-resistant lymphocyte rolling, and CHST1 knockout mice display exaggerated airway macrophage and lymphocyte accumulation after allergen challenge [PMID:11310842, PMID:29659839]."},"prefetch_data":{"uniprot":{"accession":"O43916","full_name":"Carbohydrate sulfotransferase 1","aliases":["Galactose/N-acetylglucosamine/N-acetylglucosamine 6-O-sulfotransferase 1","GST-1","Keratan sulfate Gal-6 sulfotransferase","KS6ST","KSGal6ST","KSST"],"length_aa":411,"mass_kda":46.7,"function":"Sulfotransferase that utilizes 3'-phospho-5'-adenylyl sulfate (PAPS) as sulfonate donor to catalyze the transfer of sulfate to position 6 of internal galactose (Gal) residues of keratan. Cooperates with B4GALT4 and B3GNT7 glycosyltransferases and CHST6 sulfotransferase to construct and elongate disulfated disaccharide unit [->3(6-sulfoGalbeta)1->4(6-sulfoGlcNAcbeta)1->] within keratan sulfate polymer (PubMed:10642612, PubMed:17690104, PubMed:9405439). Has a preference for sulfating keratan sulfate, but it also transfers sulfate to the unsulfated polymer (PubMed:9405439). Involved in biosynthesis of phosphacan, a major keratan sulfate proteoglycan in the developing brain (By similarity). Involved in biosynthesis of 6-sulfoGalbeta-containing O-linked glycans in high endothelial venules of lymph nodes. May act in a synergistic manner with CHST4 to generate sialyl 6',6-disulfo Lewis X motif, a recognition determinant for immune cell receptors implicated in leukocyte trafficking (PubMed:10330415). Catalyzes sulfation of N-acetyllactosamine (LacNAc) oligosaccharides with highest efficiency for sialylated LacNAc structures (PubMed:10642612)","subcellular_location":"Golgi apparatus membrane","url":"https://www.uniprot.org/uniprotkb/O43916/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CHST1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CHST1","total_profiled":1310},"omim":[{"mim_id":"604817","title":"CARBOHYDRATE SULFOTRANSFERASE 5; CHST5","url":"https://www.omim.org/entry/604817"},{"mim_id":"603799","title":"CARBOHYDRATE SULFOTRANSFERASE 3; CHST3","url":"https://www.omim.org/entry/603799"},{"mim_id":"603798","title":"CARBOHYDRATE SULFOTRANSFERASE 2; CHST2","url":"https://www.omim.org/entry/603798"},{"mim_id":"603797","title":"CARBOHYDRATE SULFOTRANSFERASE 1; 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The protein has Type II transmembrane topology and is an N-linked glycoprotein.\",\n      \"method\": \"cDNA cloning, COS-7 cell transfection/overexpression, enzymatic activity assay, antibody cross-reactivity, N-glycosylation analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted enzymatic activity in heterologous cells, protein sequence confirmed against purified enzyme, multiple orthogonal methods\",\n      \"pmids\": [\"7629189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"C6ST (CHST1 ortholog) transfers sulfate specifically to position 6 of galactose residues in keratan sulfate chains, including Gal linked to GlcNAc-6-sulfate and to unsulfated GlcNAc residues; a single protein catalyzes both chondroitin and keratan sulfate 6-O-sulfation.\",\n      \"method\": \"In vitro sulfotransferase assay with purified C6ST, product characterization by hydrazinolysis, HNO2 deamination, NaBH4 reduction, SAX-HPLC and paper chromatography; recombinant C6ST transfection in COS-7 cells\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic assay with structural product identification, confirmed with recombinant enzyme\",\n      \"pmids\": [\"8991509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"C6ST (CHST1 ortholog) sulfates sialyl lactosamine oligosaccharides at position 6 of galactose in NeuAcα2-3Galβ1-4GlcNAc (SLN) and related structures, but not sialyl Lewis x (fucosylated); a single enzyme thus sulfates chondroitin, keratan sulfate, and sialyl lactosamine oligosaccharides, suggesting a role in biosynthesis of sulfated sialyl Lewis x L-selectin ligands.\",\n      \"method\": \"In vitro sulfotransferase assay with purified and recombinant C6ST, product degradation with neuraminidase, hydrazinolysis, HNO2 deamination, NaBH4 reduction, SAX-HPLC\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic assay with chemical product identification using multiple degradative methods\",\n      \"pmids\": [\"9147050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Human KSGal6ST (CHST1) was cloned from a human fetal brain library; when expressed in COS-7 cells it produced keratan sulfate sulfotransferase activity (sulfating Gal residues of KS) but not chondroitin 6-sulfotransferase activity, distinguishing it functionally from chick C6ST. Structural analysis confirmed 6-O-sulfation of galactose in KS. Gene maps to chromosome 11p11.1-11.2.\",\n      \"method\": \"cDNA cloning by cross-hybridization, COS-7 cell transfection, enzymatic activity assay, structural analysis of 35S-labeled GAG products, Northern blot, FISH chromosomal mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — heterologous expression with enzymatic activity and product structural analysis; substrate specificity defined\",\n      \"pmids\": [\"9405439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human C6ST (CHST1) cDNA was cloned and encodes a protein with 74% identity to chick C6ST. Expression of a soluble recombinant form demonstrated active sulfotransferase transferring sulfate to position 6 of GalNAc in GlcAbeta1-3GalNAc sequences in polymer chondroitin, various CS isoforms, and tetrasaccharides, but not in IdoAα1-3GalNAc or GlcAbeta1-3GalNAc(4-O-sulfate) sequences. The gene spans >20 kb with 3 exons; protein-coding domain split into 2 exons.\",\n      \"method\": \"cDNA cloning, COS-1 cell expression, enzymatic activity assay with defined acceptor substrates, product identification, gene structure analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct enzymatic assay defining substrate specificity with structural product identification\",\n      \"pmids\": [\"9883891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human C6ST (CHST1) expressed in CHO-K1 cells produced marked increases in both C6ST and keratan sulfate sulfotransferase (KSST) enzymatic activities. The protein is predicted as a Type II transmembrane protein of 411 amino acids with N-terminal hydrophobic domain, four N-glycosylation sites, and maps to chromosome 11 by radiation hybrid mapping.\",\n      \"method\": \"Stable CHO-K1 transfection, enzymatic activity assay in cell homogenates, cDNA cloning/5'-RACE, radiation hybrid panel chromosomal mapping\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — heterologous expression with direct enzymatic activity confirmation\",\n      \"pmids\": [\"9639683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human C6ST (CHST1) cDNA was isolated; ubiquitous 7.8-kb message in human adult tissues; the human enzyme contains a unique hydrophilic domain not present in chick C6ST.\",\n      \"method\": \"cDNA cloning by cross-hybridization with chick C6ST, Northern blot\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cloning with expression confirmation, but limited functional characterization beyond identification\",\n      \"pmids\": [\"9714738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CHST1 (identical to human C6ST) and CHST2 were identified from human vascular endothelial cell cDNA libraries as sulfotransferases homologous to chicken C6ST; CHST1 is expressed by endothelial cells and may contribute to generation of L-selectin ligands.\",\n      \"method\": \"cDNA library screening, Northern blot, chromosomal mapping\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cloning and expression characterization in endothelial cells; functional role inferred from context\",\n      \"pmids\": [\"10049591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Sulfation of GlyCAM-1 by related sulfotransferases including KSGal6ST (CHST1) generating Gal-6-sulfate, together with fucosylation, enhanced rolling ligand activity for L-selectin, increasing tethered/rolling lymphocyte numbers, reducing rolling velocity with more frequent pausing, and enhancing resistance to detachment by shear in flow chamber assays.\",\n      \"method\": \"Flow chamber rolling assay with sulfated/fucosylated GlyCAM-1, peripheral blood lymphocytes and Jurkat cells\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — functional reconstitution in flow chamber assay demonstrating that Gal-6-sulfate generated by CHST1-related enzyme directly modulates L-selectin ligand rolling behavior\",\n      \"pmids\": [\"10510083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CHST1 and CHST2 expressed by vascular endothelial cells contribute to generation of shear-resistant leukocyte rolling via L-selectin. Human umbilical vein endothelial cells predominantly express CHST1 and CHST2; overexpression of CHST1 in a cell line with low L-selectin ligand activity increased rolling leukocyte numbers, reduced rolling velocities, and enhanced rolling under higher shear stresses in flow chamber assays.\",\n      \"method\": \"RT-PCR expression profiling, stable transfection/overexpression in endothelial cell lines, in vitro flow chamber leukocyte rolling assay\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct gain-of-function experiment with defined cellular phenotype (rolling behavior) in flow chamber\",\n      \"pmids\": [\"11310842\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"N-linked oligosaccharides on C6ST-1 (CHST1) are required for production of active enzyme, Golgi localization, and keratan sulfate sulfotransferase (KSST) activity. Specifically: deletion of the 4th N-glycosylation site abolished Golgi localization (enzyme retained in ER with calnexin colocalization) and abolished activity; deletion of the 5th site markedly reduced KSST activity but not C6ST activity; removal of N-glycans by PNGase F increased C6ST activity but decreased KSST activity.\",\n      \"method\": \"Tunicamycin treatment, site-directed mutagenesis of N-glycosylation sites, PNGase F treatment, immunofluorescence colocalization, WGA lectin affinity, EndoH sensitivity, enzymatic activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis of specific N-glycosylation sites combined with subcellular localization and enzymatic activity assays; multiple orthogonal methods\",\n      \"pmids\": [\"16720579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Recombinant human C6ST-1 (CHST1) catalyzes sulfation of C6 on both galactose residues in the glycosaminoglycan-protein linkage region (GlcUA-Gal-Gal-Xyl-Ser), including before the first N-acetylhexosamine is attached. Intact xylose is required for sulfation of the second galactose from the reducing end; pre-4-O-sulfation of Gal blocks the reaction.\",\n      \"method\": \"Recombinant CHST1 expressed as protein A chimera in COS-1 cells, purified by IgG-Sepharose, in vitro sulfotransferase assay with defined linkage region saccharide substrates, product identification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified recombinant enzyme with defined substrates and structural product analysis; identifies novel substrates and substrate requirements\",\n      \"pmids\": [\"18697746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CHST1 (C6ST-1) drives sialoglycan binding of multiple Siglecs (Siglec-3/7/8/15) at the cell surface; CHST1 generates the 6'-sulfated sialyl LacNAc epitope (Neu5Acα2-3(6-O-sulfo)Galβ1-4GlcNAc, 6'-Su-SLacNAc) recognized by Siglec-3 (CD33). Sulfation on both the Gal (by CHST1) and GlcNAc positions creates a disulfated ligand with ≥28-fold enhanced affinity for CD33.\",\n      \"method\": \"Cell-based glycan array using isogenic HEK293 cells with combinatorial loss/gain of sulfotransferase genes, Siglec-Fc fusion protein binding assay, mass-spectrometry-based binding assay with homogeneous Siglec-3 fragment, synthetic glycan inhibition\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — isogenic cell-based glycan array combined with MS-based affinity measurement and synthetic glycan validation; multiple orthogonal methods in one study\",\n      \"pmids\": [\"33893239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Overexpression of CHST1 in multiple cell lines significantly enhances binding of numerous Siglecs; joint overexpression of CHST1 with CHST2 greatly enhanced binding of CD33 and several other Siglecs. MS-based assay confirmed ≥8-fold enhanced affinity of CD33 for Neu5Acα2-3(6-O-sulfo)Galβ1-4GlcNAc over unsulfated counterpart, and ≥28-fold for disulfated ligand.\",\n      \"method\": \"Sulfotransferase overexpression in five cell lines, Siglec-Fc binding assay, pharmacological N/O-glycan blockade, MS-based binding assay with homogeneous Siglec-3 fragment, sodium chlorate treatment\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — cell-type-dependent overexpression combined with MS affinity assay; replicated findings across multiple Siglecs and cell lines\",\n      \"pmids\": [\"34661385\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CHST1 sulfates Gal residues on O-glycans on PSGL-1/mIgG2b, including both C-3/core-1/core-2 and C-6-branch of core-2 structures, as defined by transfection into CHO cells expressing PSGL-1/mIgG2b and subsequent O-glycan characterization.\",\n      \"method\": \"Transfection of CHST1 expression plasmid in CHO cells co-expressing PSGL-1/mIgG2b and core 2 transferase (GCNT1), O-glycan characterization by LC-MSn\",\n      \"journal\": \"Molecular & cellular proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct expression with glycan product characterization, single lab\",\n      \"pmids\": [\"34555499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CHST1 (KSGal6ST) is required for biosynthesis of the CD33/Siglec-8 sialoglycoprotein ligand RPTPζS3L (sialylated keratan sulfate on RPTPζ/phosphacan) in mouse brain; brains from CHST1 knockout mice lacked Siglec-F/CD33/Siglec-8 binding activity.\",\n      \"method\": \"CHST1 knockout mice, Siglec-Fc binding assay on brain extracts, comparison with St3gal4 and RPTPζ knockout mice, biochemical ligand identification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic KO with specific biochemical phenotype (loss of Siglec ligand), triangulated with two other KO mouse models\",\n      \"pmids\": [\"35452678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In Xenopus embryos, chst1 (CHST1 ortholog) is expressed specifically in otic vesicles; loss-of-function of chst1 led to loss of highly sulfated keratan sulfate (HSKS) in otic vesicles and reduction in their size, establishing that CHST1 is required for HSKS biosynthesis and for maintaining otic vesicle structure during organogenesis.\",\n      \"method\": \"In situ hybridization for expression mapping, morpholino loss-of-function, immunostaining for HSKS, measurement of otic vesicle size\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — morpholino knockdown in Xenopus with specific structural phenotype, single lab\",\n      \"pmids\": [\"36998246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CHST1 knockout mice showed that CHST1 does not contribute substantially to synthesis of glycan ligands for Siglec-F in airways; however, its absence results in exaggerated accumulation of airway macrophages and lymphocytes after OVA sensitization and challenge, indicating a role in controlling airway immune cell composition.\",\n      \"method\": \"CHST1-/- knockout mice, OVA sensitization/challenge model, Siglec-F-Fc binding assay on lung tissue, differential cell counts in BAL, O-glycan characterization by mass spectrometry, Western blotting\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype (macrophage/lymphocyte accumulation), but mechanism for immune phenotype not fully resolved\",\n      \"pmids\": [\"29659839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CHST1 exhibits significantly higher sulfotransferase activity toward branched O-Man glycans than toward linear counterparts in enzymatic assays; this establishes that GnT-IX-mediated O-Man branching promotes KS biosynthesis by providing a preferred scaffold for CHST1 activity in the brain.\",\n      \"method\": \"In vitro enzymatic assay comparing CHST1 activity on branched vs. linear O-Man glycan substrates; GnT-IX knockout mouse brain analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic assay defining substrate preference, corroborated by KO mouse data\",\n      \"pmids\": [\"41513091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The glycan classes presenting CHST1-dependent sulfated Siglec ligands include both N-glycans and mucin-type O-glycans for Siglec-3 and Siglec-8 binding; O-mannose glycans in CHST1-expressing cells also contribute modestly to Siglec-3 and Siglec-8 binding. For Siglec-3, N-glycans are the major sulfated trans ligands, while mucin-type O-glycans have the largest impact on Siglec-3 cis masking.\",\n      \"method\": \"Genetic disruption of glycan classes (N-glycan, mucin O-glycan, O-Man glycan) in CHST1-expressing cells, pharmacological inhibition, enzymatic treatment, Siglec-Fc binding assay\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic/pharmacological/enzymatic strategies to dissect glycan class contributions; convergent findings\",\n      \"pmids\": [\"39836965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CHST1 (KSGal6ST) sulfates galactose residues in keratan sulfate but cannot act on galactosides blocked by α1,3-fucosides or α2,6-sialosides; exploiting this mutual exclusivity allows regioselective enzymatic installation of Gal-6-sulfate on poly-LacNAc chains to build defined KS oligosaccharides.\",\n      \"method\": \"Enzymatic synthesis using recombinant CHST1 on defined oligosaccharide substrates with and without blocking glycan modifications; product characterization\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic reconstitution with defined substrates demonstrating substrate selectivity rules\",\n      \"pmids\": [\"38494637\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CHST1 (KSGal6ST/C6ST-1) is a Golgi-resident Type II transmembrane sulfotransferase that transfers sulfate from PAPS to the C-6 position of galactose residues in keratan sulfate chains, sialyl N-acetyllactosamine oligosaccharides, and galactose residues in the glycosaminoglycan-protein linkage region; its N-glycosylation is required for proper Golgi localization and enzymatic activity; on cell surfaces it generates 6'-sulfated sialyl LacNAc epitopes that serve as high-affinity ligands for immunomodulatory Siglec receptors (including CD33/Siglec-3 and Siglec-8), and it contributes to generation of L-selectin ligands on vascular endothelial cells and promotes shear-resistant lymphocyte rolling.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CHST1 (C6ST-1/KSGal6ST) is a Golgi-resident Type II transmembrane sulfotransferase that transfers sulfate from PAPS to the C-6 hydroxyl of galactose residues across multiple glycan classes, including keratan sulfate, chondroitin sulfate, sialyl N-acetyllactosamine oligosaccharides, the glycosaminoglycan-protein linkage region, O-mannose glycans, and mucin-type O-glycans [PMID:7629189, PMID:8991509, PMID:18697746, PMID:34555499, PMID:41513091]. N-glycosylation of CHST1 is essential for its Golgi retention and catalytic activity, with specific N-glycosylation sites differentially required for keratan sulfate versus chondroitin sulfate sulfotransferase functions [PMID:16720579]. By generating 6'-sulfated sialyl LacNAc epitopes, CHST1 creates high-affinity ligands for immunomodulatory Siglec receptors including CD33/Siglec-3 and Siglec-8 on both N-glycans and O-glycans, and is required in mouse brain for biosynthesis of the sialylated keratan sulfate Siglec ligand on RPTPζ/phosphacan [PMID:33893239, PMID:35452678, PMID:39836965]. On vascular endothelial cells, CHST1-mediated Gal-6-sulfation contributes to L-selectin ligand generation, promoting shear-resistant lymphocyte rolling, and CHST1 knockout mice display exaggerated airway macrophage and lymphocyte accumulation after allergen challenge [PMID:11310842, PMID:29659839].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Cloning of chick C6ST (CHST1 ortholog) established that a single Type II transmembrane sulfotransferase catalyzes 6-O-sulfation of both chondroitin and keratan sulfate, resolving whether these activities reside in separate or the same enzyme.\",\n      \"evidence\": \"cDNA cloning and COS-7 expression with enzymatic activity assays and N-glycosylation analysis\",\n      \"pmids\": [\"7629189\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate specificity for non-GAG glycans unknown\", \"Human ortholog not yet cloned\", \"Subcellular targeting determinants undefined\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Substrate specificity was expanded beyond GAGs when C6ST was shown to sulfate sialyl lactosamine oligosaccharides at Gal C-6, and human KSGal6ST (CHST1) was cloned and shown to have keratan sulfate but not chondroitin 6-sulfotransferase activity, distinguishing it from the chick enzyme and revealing species-specific substrate preferences.\",\n      \"evidence\": \"In vitro sulfotransferase assays with defined oligosaccharide substrates and structural product identification; COS-7 expression of human CHST1\",\n      \"pmids\": [\"9147050\", \"9405439\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Basis for species difference in CS activity unclear\", \"Crystal structure unavailable to explain selectivity\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Full cloning and characterization of human CHST1 defined its gene structure, chromosomal locus, dual C6ST/KSST enzymatic activities, and Type II transmembrane topology with four N-glycosylation sites.\",\n      \"evidence\": \"cDNA cloning, COS-1/CHO-K1 expression with enzymatic activity assays on defined substrates, gene structure and radiation hybrid mapping\",\n      \"pmids\": [\"9883891\", \"9639683\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous regulation of expression not addressed\", \"Functional significance of N-glycosylation sites unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"A direct role for CHST1 in vascular biology was established when overexpression in endothelial cells enhanced L-selectin-dependent leukocyte rolling under shear, demonstrating that CHST1-generated Gal-6-sulfate on endothelial glycans is a functional component of L-selectin ligands.\",\n      \"evidence\": \"Stable transfection/overexpression in endothelial cell lines, in vitro flow chamber leukocyte rolling assay\",\n      \"pmids\": [\"10510083\", \"11310842\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution to lymphocyte homing not tested genetically\", \"Relative contribution vs. CHST2 unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Specific N-glycosylation sites on CHST1 were shown to differentially control Golgi localization and substrate-specific enzymatic activities, resolving how post-translational modification regulates this enzyme's function and trafficking.\",\n      \"evidence\": \"Site-directed mutagenesis of individual N-glycosylation sites, immunofluorescence colocalization with Golgi/ER markers, enzymatic activity assays\",\n      \"pmids\": [\"16720579\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how N-glycans regulate activity unknown\", \"Whether other post-translational modifications regulate CHST1 untested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"CHST1's substrate repertoire was further broadened to include galactose residues in the common GAG-protein linkage region tetrasaccharide, revealing that CHST1 can act at early steps of GAG chain initiation before the first hexosamine is added.\",\n      \"evidence\": \"Purified recombinant CHST1 in vitro assay with defined linkage-region saccharide substrates\",\n      \"pmids\": [\"18697746\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo significance of linkage-region sulfation for GAG assembly unknown\", \"Whether this occurs in specific cell types not examined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"CHST1 knockout mice revealed an in vivo immunoregulatory role: loss of CHST1 led to exaggerated airway macrophage and lymphocyte accumulation after allergen challenge, even though CHST1 did not substantially contribute to airway Siglec-F ligand synthesis.\",\n      \"evidence\": \"CHST1−/− knockout mice, OVA sensitization/challenge, BAL cell counts, Siglec-F-Fc binding, O-glycan MS\",\n      \"pmids\": [\"29659839\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which CHST1 loss exaggerates immune cell accumulation unresolved\", \"Relevant glycoprotein substrates in airway not identified\", \"Single challenge model tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CHST1 was identified as the key sulfotransferase generating 6'-sulfated sialyl LacNAc, a high-affinity ligand for CD33/Siglec-3 and multiple other Siglecs, with disulfation (together with CHST2) enhancing CD33 affinity ≥28-fold, establishing CHST1 as a central regulator of Siglec-mediated immunomodulation.\",\n      \"evidence\": \"Isogenic cell-based glycan arrays, Siglec-Fc binding, MS-based affinity measurements, overexpression across five cell lines\",\n      \"pmids\": [\"33893239\", \"34661385\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo consequences of CHST1-dependent Siglec engagement for immune regulation not fully defined\", \"Whether tumor cells exploit CHST1 to engage inhibitory Siglecs untested in this context\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Genetic ablation of CHST1 in mice abolished Siglec-F/CD33/Siglec-8 ligand activity in brain, identifying RPTPζ/phosphacan-associated sialylated keratan sulfate as the endogenous CHST1-dependent Siglec ligand in brain tissue.\",\n      \"evidence\": \"CHST1 knockout mice brain extracts, Siglec-Fc binding, triangulation with St3gal4 and RPTPζ KO mice\",\n      \"pmids\": [\"35452678\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of losing brain Siglec ligands for neuroinflammation or microglia regulation not examined\", \"Whether other brain glycoproteins carry CHST1-dependent ligands unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Developmental relevance was demonstrated in Xenopus, where CHST1 is required for highly sulfated keratan sulfate biosynthesis in otic vesicles and for maintaining otic vesicle size, linking CHST1 to organogenesis.\",\n      \"evidence\": \"Morpholino knockdown in Xenopus embryos, HSKS immunostaining, otic vesicle morphometry\",\n      \"pmids\": [\"36998246\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Morpholino approach requires genetic confirmation (CRISPR)\", \"Whether mammalian ear development similarly requires CHST1 untested\", \"Mechanism linking HSKS loss to reduced vesicle size unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"CHST1's substrate preferences were refined: it preferentially sulfates GnT-IX-generated branched O-Man glycans over linear ones, and its sulfated Siglec ligands are presented on N-glycans, mucin O-glycans, and O-Man glycans with glycan-class-specific roles in trans versus cis Siglec engagement.\",\n      \"evidence\": \"In vitro enzymatic assays on branched vs. linear O-Man substrates; genetic/pharmacological/enzymatic dissection of glycan classes in CHST1-expressing cells with Siglec-Fc binding\",\n      \"pmids\": [\"41513091\", \"39836965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for preference for branched O-Man substrates not resolved\", \"In vivo significance of O-Man-borne Siglec ligands in brain not tested functionally\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No crystal or cryo-EM structure of CHST1 exists, and the structural determinants of its broad but selective substrate specificity — excluding α1,3-fucosylated and α2,6-sialylated galactosides while accepting diverse glycan backbones — remain mechanistically unexplained.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic structure available\", \"Catalytic mechanism details at the active site unresolved\", \"In vivo functional consequences of CHST1 loss for Siglec-mediated immunoregulation incompletely defined across tissues\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 11, 18, 20]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:1430728\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 11, 18, 20]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [8, 9, 12, 13, 15, 17]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CHST2\",\n      \"PTPRZ1\",\n      \"SELPLG\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}