hs6st3b encodes a type II transmembrane heparan-sulfate 6-O-sulfotransferase (an HS6ST3 paralog) that acts in the Golgi during heparan sulfate proteoglycan biosynthesis. It transfers sulfate from the universal donor PAPS (3'-phosphoadenosine 5'-phosphosulfate) to position 6 of the N-sulfoglucosamine (GlcNS) residue of heparan sulfate, generating 6-O-sulfated HS motifs that shape the binding of extracellular ligands (growth factors, morphogens, chemokines). The catalytic domain has been crystallized (zebrafish 6-OST; PDB 5T03/5T05/5T0A) showing in-line sulfo transfer to the acceptor 6-hydroxyl, with His158 as the catalytic base and Trp210 orienting the acceptor. hs6st3b is one of several zebrafish 6-OST paralogs (hs6st1a, hs6st1b, hs6st2, hs6st3a, hs6st3b) with distinct spatiotemporal expression; paralog-specific biochemical parameters for hs6st3b remain incompletely defined, so substrate-preference and pathway claims are partly family-based inference.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0015012 heparan sulfate proteoglycan biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: heparan sulfate proteoglycan biosynthetic process (GO:0015012): hs6st3b performs the 6-O-sulfation step of heparan sulfate maturation, one of the ordered Golgi modifications that build the sulfation pattern of HS chains. Reason: The enzyme directly executes a chemical step of HSPG biosynthesis (6-O-sulfation of GlcNS), so it is a participant, not merely required. The crystallized zebrafish enzyme is a bona fide 6-OST and HS chain modification occurs in the Golgi/ER biosynthetic pathway [PMID:28103688]. Supporting Evidence: file:DANRE/hs6st3b/hs6st3b-uniprot.txt 6-O-sulfation enzyme which catalyzes the transfer of sulfate PMID:28103688 HS biosynthesis occurs in the Golgi and endoplasm reticulum |
| GO:0017095 heparan sulfate 6-sulfotransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: heparan sulfate 6-sulfotransferase activity (GO:0017095): hs6st3b transfers sulfate from PAPS to C6 of the N-sulfoglucosamine (GlcNS) residue of heparan sulfate. This is the core molecular function. Reason: Directly demonstrated: the zebrafish 6-OST catalytic domain (the enzyme UniProt assigns to hs6st3b) was crystallized in ternary complexes with PAP and HS oligosaccharides and its 6-O-sulfotransferase activity measured by mutagenesis [PMID:28103688]. UniProt records the same reaction. Supporting Evidence: file:DANRE/hs6st3b/hs6st3b-uniprot.txt 6-O-sulfation enzyme which catalyzes the transfer of sulfate PMID:28103688 transfer a sulfo group from 3′-phosphoadenosine 5′-phosphosulfate (PAPS) to the 6-OH of GlcN PMID:28103688 The zf6-OST shares 71%, 72% and 81% sequence identities with the human 6-OST isoforms 1, 2 and 3 |
| GO:0016020 membrane | IEA GO_REF:0000120 | ACCEPT | Summary: membrane (GO:0016020): hs6st3b is a single-pass type II membrane protein, the topology shared by all Golgi-resident HS sulfotransferases. Reason: UniProt records Membrane / single-pass type II membrane topology; correct but non-specific (the compartment is refined to Golgi membrane in the GO:0000139 entry). Supporting Evidence: file:DANRE/hs6st3b/hs6st3b-uniprot.txt SUBCELLULAR LOCATION: Membrane file:DANRE/hs6st3b/hs6st3b-uniprot.txt Single-pass type II |
| GO:0017095 heparan sulfate 6-sulfotransferase activity | EXP PMID:28103688 Structure Based Substrate Specificity Analysis of Heparan Su... | ACCEPT | Summary: heparan sulfate 6-sulfotransferase activity (GO:0017095), experimentally determined: this is the enzyme characterized by X-ray crystallography and activity assays in Xu et al. 2017, which UniProt links to hs6st3b (EC 2.8.2.-, PubMed:28103688). Reason: The zebrafish 6-OST studied shares 81% identity with human HS6ST3, and the paper measured sulfo-transfer activity of wild-type and active-site mutants on defined HS oligosaccharides; this is the strongest, direct support for the core function. Supporting Evidence: PMID:28103688 transfer a sulfo group from 3′-phosphoadenosine 5′-phosphosulfate (PAPS) to the 6-OH of GlcN PMID:28103688 in ternary complexes with the cofactor product PAP and three oligosaccharides PMID:28103688 The zf6-OST shares 71%, 72% and 81% sequence identities with the human 6-OST isoforms 1, 2 and 3 |
| GO:0008146 sulfotransferase activity | IDA PMID:28103688 Structure Based Substrate Specificity Analysis of Heparan Su... | MODIFY | Summary: sulfotransferase activity (GO:0008146): a correct but overly broad parent of the demonstrated heparan sulfate 6-O-sulfotransferase activity. Reason: The experimentally supported activity is specifically heparan sulfate 6-O-sulfotransferase (GO:0017095); the generic sulfotransferase term should be replaced by that child. Proposed replacements: heparan sulfate 6-sulfotransferase activity Supporting Evidence: file:DANRE/hs6st3b/hs6st3b-uniprot.txt 6-O-sulfation enzyme which catalyzes the transfer of sulfate PMID:28103688 transfer a sulfo group from 3′-phosphoadenosine 5′-phosphosulfate (PAPS) to the 6-OH of GlcN |
| GO:0050656 3'-phosphoadenosine 5'-phosphosulfate binding | IDA PMID:28103688 Structure Based Substrate Specificity Analysis of Heparan Su... | KEEP AS NON CORE | Summary: 3'-phosphoadenosine 5'-phosphosulfate binding (GO:0050656): hs6st3b binds the universal sulfate donor PAPS in its active site, as seen in the ternary crystal complexes (bound as the product PAP). Reason: PAPS binding is a mechanistic component of the sulfotransferase reaction rather than a separate biological function; directly evidenced by the co-crystal structure [PMID:28103688]. Supporting Evidence: PMID:28103688 in ternary complexes with the cofactor product PAP and three oligosaccharides PMID:28103688 binding and proper positioning of the cofactor |
| GO:0070492 oligosaccharide binding | IDA PMID:28103688 Structure Based Substrate Specificity Analysis of Heparan Su... | KEEP AS NON CORE | Summary: oligosaccharide binding (GO:0070492): hs6st3b binds heparan sulfate oligosaccharide acceptors, positioning the nonreducing-end GlcNS in the active site as shown in three co-crystal structures. Reason: Substrate (acceptor) binding is intrinsic to the catalytic mechanism and is directly evidenced by the ternary structures; kept as non-core because it is part of the core catalytic activity rather than a distinct function. Supporting Evidence: PMID:28103688 all three substrates bind in a similar orientation, with the nonreducing end GlcNS residue PMID:28103688 each zf6-OST domain binding simultaneously to PAP and an oli |
| GO:0000139 Golgi membrane | IBA GO_REF:0000033 | NEW | Summary: Golgi membrane (GO:0000139): hs6st3b is proposed to reside in the Golgi membrane, the compartment where heparan sulfate is sulfated during biosynthesis. Reason: Refines the generic membrane annotation. HS biosynthesis (including 6-O-sulfation) occurs in the Golgi [PMID:28103688 "HS biosynthesis occurs in the Golgi and endoplasm reticulum"], hs6st3b is a single-pass type II membrane protein (the canonical Golgi-enzyme topology), and human HS6ST1/HS6ST2 orthologs are annotated to Golgi membrane (comparator check, QuickGO TAS). No direct zebrafish imaging exists yet, so this is a family/pathway-grounded proposal. Supporting Evidence: PMID:28103688 HS biosynthesis occurs in the Golgi and endoplasm reticulum file:DANRE/hs6st3b/hs6st3b-uniprot.txt Single-pass type II |
| GO:0008146 sulfotransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: sulfotransferase activity (GO:0008146): a correct but overly broad parent of the demonstrated heparan sulfate 6-O-sulfotransferase activity. Reason: The experimentally supported activity is specifically heparan sulfate 6-O-sulfotransferase (GO:0017095); the generic sulfotransferase term should be replaced by that child. Proposed replacements: heparan sulfate 6-sulfotransferase activity Supporting Evidence: file:DANRE/hs6st3b/hs6st3b-uniprot.txt 6-O-sulfation enzyme which catalyzes the transfer of sulfate PMID:28103688 transfer a sulfo group from 3′-phosphoadenosine 5′-phosphosulfate (PAPS) to the 6-OH of GlcN |
| GO:0017095 heparan sulfate 6-sulfotransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: heparan sulfate 6-sulfotransferase activity (GO:0017095): hs6st3b transfers sulfate from PAPS to C6 of the N-sulfoglucosamine (GlcNS) residue of heparan sulfate. This is the core molecular function. Reason: Directly demonstrated: the zebrafish 6-OST catalytic domain (the enzyme UniProt assigns to hs6st3b) was crystallized in ternary complexes with PAP and HS oligosaccharides and its 6-O-sulfotransferase activity measured by mutagenesis [PMID:28103688]. UniProt records the same reaction. Supporting Evidence: file:DANRE/hs6st3b/hs6st3b-uniprot.txt 6-O-sulfation enzyme which catalyzes the transfer of sulfate PMID:28103688 transfer a sulfo group from 3′-phosphoadenosine 5′-phosphosulfate (PAPS) to the 6-OH of GlcN PMID:28103688 The zf6-OST shares 71%, 72% and 81% sequence identities with the human 6-OST isoforms 1, 2 and 3 |
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Download this section (compressed HTML)Q: Does zebrafish hs6st3b have a distinct HS acceptor-context preference (e.g., 2-O-sulfated or IdoA-GlcNS contexts) relative to the other zebrafish 6-OST paralogs, and does this differ from hs6st3a?
Q: What is the loss-of-function phenotype of a zebrafish hs6st3b-specific mutant (as opposed to pan-hs6st morpholino knockdown), and which morphogen pathways (Wnt, Shh, FGF) are affected?
Experiment: Generate a zebrafish hs6st3b-specific loss-of-function allele (CRISPR) and quantify HS 6-O-sulfation by disaccharide mapping (heparinase digestion + HPLC) to determine the paralog-specific contribution of hs6st3b to the 6-O-sulfation pattern in vivo.
Experiment: Determine the subcellular localization of tagged hs6st3b in zebrafish (or a cell system) by co-staining with Golgi markers to directly test the family-based inference of Golgi membrane localization.
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