Existing Annotations Review

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) is supported as the direct pathway context. Glce performs the C5-epimerization step of the HS modification cascade, acting after N-sulfation to generate IdoA residues that are subsequently O-sulfated. In zebrafish, this activity is developmentally regulated and required for HS fine structure that controls morphogen signaling. Reason: Glce is a heparan sulfate biosynthetic enzyme. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt PATHWAY: Glycan metabolism; heparan sulfate biosynthesis. PMID:25568314 D-glucuronyl C5-epimerase (Glce) is a crucial enzyme in HS synthesis file:DANRE/glceb/glceb-deep-research-falcon.md Glce participates in the canonical HS modification sequence in which N-sulfation creates substrate contexts for subsequent modifications; GLCE-mediated epimerization creates IdoA residues that can subsequently be O-sulfated and incorporated into high-affinity binding sites
GO:0047464 heparosan-N-sulfate-glucuronate 5-epimerase activity	IBA GO_REF:0000033	ACCEPT	Summary: heparosan-N-sulfate-glucuronate 5-epimerase activity (GO:0047464) is the direct supported molecular function. Reason: The enzyme converts D-glucuronic acid to L-iduronic acid in heparan sulfate/heparin chains. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt Converts D-glucuronic acid residues adjacent to N-sulfate PMID:25568314 converting D-glucuronic acid to L-iduronic file:DANRE/glceb/glceb-deep-research-falcon.md converts D-glucuronic acid (GlcA) residues to L-iduronic acid (IdoA) within the polymer
GO:0005794 Golgi apparatus	IBA GO_REF:0000033	ACCEPT	Summary: Golgi apparatus (GO:0005794) is supported for glceb. Reason: Golgi localization is coherent with the more specific Golgi membrane annotation. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt SUBCELLULAR LOCATION: Golgi apparatus membrane
GO:0000139 Golgi membrane	IEA GO_REF:0000044	ACCEPT	Summary: Golgi membrane (GO:0000139) is supported for glceb. GLCE is a type II transmembrane Golgi-resident glycan modification enzyme; its HS-modified products subsequently act at the cell surface and extracellular matrix. Reason: UniProt places Glceb at the Golgi apparatus membrane. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt SUBCELLULAR LOCATION: Golgi apparatus membrane file:DANRE/glceb/glceb-deep-research-falcon.md GLCE/Glce is generally described as a type II transmembrane protein in the HS biosynthetic machinery, which is consistent with function as a Golgi-resident glycan modification enzyme
GO:0015012 heparan sulfate proteoglycan biosynthetic process	IEA GO_REF:0000120	ACCEPT	Summary: heparan sulfate proteoglycan biosynthetic process (GO:0015012) is supported as the direct pathway context. Reason: Glce is a heparan sulfate biosynthetic enzyme. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt PATHWAY: Glycan metabolism; heparan sulfate biosynthesis. PMID:25568314 D-glucuronyl C5-epimerase (Glce) is a crucial enzyme in HS synthesis
GO:0047464 heparosan-N-sulfate-glucuronate 5-epimerase activity	IEA GO_REF:0000120	ACCEPT	Summary: heparosan-N-sulfate-glucuronate 5-epimerase activity (GO:0047464) is the direct supported molecular function. Reason: The enzyme converts D-glucuronic acid to L-iduronic acid in heparan sulfate/heparin chains. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt Converts D-glucuronic acid residues adjacent to N-sulfate PMID:25568314 converting D-glucuronic acid to L-iduronic
GO:0030210 heparin proteoglycan biosynthetic process	IEA GO_REF:0000041	KEEP AS NON CORE	Summary: heparin proteoglycan biosynthetic process (GO:0030210) is supported by pathway context but is not the main zebrafish core annotation. Reason: UniProt includes heparin biosynthesis, but the central conserved role in this review is heparan sulfate chain epimerization. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt PATHWAY: Glycan metabolism; heparin biosynthesis.
GO:0042802 identical protein binding	IPI PMID:25568314 Structural and functional study of D-glucuronyl C5-epimerase...	KEEP AS NON CORE	Summary: identical protein binding (GO:0042802) is supported as homodimerization but is not a core function. The zebrafish Glce crystal structure shows a stable dimer with two catalytic sites per dimer; dimerization is thus the functional quaternary state that builds the active sites, but it remains structural context rather than the GO molecular function of the enzyme. Reason: Dimerization is structural context for the enzyme rather than its GO molecular function. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt SUBUNIT: Homodimer. PMID:25568314 zebrafish Glce has a dimeric structure file:DANRE/glceb/glceb-deep-research-falcon.md Glce forms a stable dimer in which each dimer contains two catalytic sites located in C-terminal helical domains
GO:0000139 Golgi membrane	ISS GO_REF:0000024	ACCEPT	Summary: Golgi membrane (GO:0000139) is supported for glceb. Reason: UniProt places Glceb at the Golgi apparatus membrane. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt SUBCELLULAR LOCATION: Golgi apparatus membrane
GO:0047464 heparosan-N-sulfate-glucuronate 5-epimerase activity	IDA PMID:25568314 Structural and functional study of D-glucuronyl C5-epimerase...	ACCEPT	Summary: heparosan-N-sulfate-glucuronate 5-epimerase activity (GO:0047464) is the direct supported molecular function, experimentally demonstrated for zebrafish Glce. The enzyme epimerizes C5 of D-glucuronic acid to L-iduronic acid within heparan sulfate/heparin chains, and substrate recognition requires N-sulfated glucosamine adjacent to the epimerization site. Structure-guided mutagenesis identified active-site tyrosines (Tyr468, Tyr528, Tyr546) essential for catalysis, confirming F1QR43 is a functional GLCE-family epimerase. Reason: The enzyme converts D-glucuronic acid to L-iduronic acid in heparan sulfate/heparin chains. Supporting Evidence: file:DANRE/glceb/glceb-uniprot.txt Converts D-glucuronic acid residues adjacent to N-sulfate PMID:25568314 converting D-glucuronic acid to L-iduronic file:DANRE/glceb/glceb-deep-research-falcon.md GLCE preferentially recognizes HS regions where adjacent glucosamine residues are N-sulfated (GlcNS) file:DANRE/glceb/glceb-deep-research-falcon.md Tyr468, Tyr528, and Tyr546 were identified as essential for enzymatic activity

Core Functions

glceb enables Golgi membrane heparosan-N-sulfate-glucuronate 5-epimerase activity, converting D-glucuronic acid to L-iduronic acid during heparan sulfate proteoglycan biosynthesis.

Molecular Function:

heparosan-N-sulfate-glucuronate 5-epimerase activity

Directly Involved In:

heparan sulfate proteoglycan biosynthetic process

Cellular Locations:

Golgi membrane

Supporting Evidence:

file:DANRE/glceb/glceb-uniprot.txt
Converts D-glucuronic acid residues adjacent to N-sulfate
PMID:25568314
converting D-glucuronic acid to L-iduronic
file:DANRE/glceb/glceb-uniprot.txt
SUBCELLULAR LOCATION: Golgi apparatus membrane
file:DANRE/glceb/glceb-deep-research-falcon.md
converts **D-glucuronic acid (GlcA)** residues to **L-iduronic acid (IdoA)** within the polymer

References

GO_REF:0000024

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000041

Gene Ontology annotation based on UniPathway vocabulary mapping.

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:25568314

Structural and functional study of D-glucuronyl C5-epimerase.

Zebrafish Glce catalyzes the C5 epimerization step in heparan sulfate synthesis.

"converting D-glucuronic acid to L-iduronic"
The paper supports dimeric Glce structure.

"zebrafish Glce has a dimeric structure"

file:DANRE/glceb/glceb-uniprot.txt

UniProtKB entry F1QR43 for Danio rerio glceb

UniProt describes Glceb as a Golgi membrane C5 epimerase in heparan sulfate and heparin biosynthesis.

"Converts D-glucuronic acid residues adjacent to N-sulfate"

file:DANRE/glceb/glceb-deep-research-falcon.md

Falcon deep research report for Danio rerio glceb (D-glucuronyl C5-epimerase B, F1QR43)

Glce catalyzes C5 epimerization converting D-glucuronic acid (GlcA) to L-iduronic acid (IdoA) within the heparan sulfate/heparin polymer, increasing chain conformational flexibility important for HS-protein interactions.

"converts **D-glucuronic acid (GlcA)** residues to **L-iduronic acid (IdoA)** within the polymer"
Substrate recognition requires N-sulfation context: GLCE preferentially recognizes HS regions where adjacent glucosamine residues are N-sulfated, coupling epimerization to the modification phase of HS biosynthesis.

"GLCE preferentially recognizes HS regions where adjacent glucosamine residues are **N-sulfated** (GlcNS)"
The zebrafish Glce crystal structure shows a stable dimer with two catalytic sites per dimer in C-terminal helical domains; active-site tyrosines Tyr468, Tyr528 and Tyr546 are essential for activity.

"Glce forms a **stable dimer** in which each dimer contains **two catalytic sites** located in C-terminal helical domains"
Active-site tyrosines Tyr468, Tyr528 and Tyr546 were shown by structure-guided mutagenesis to be essential for zebrafish Glce enzymatic activity.

"Tyr468, Tyr528, and Tyr546 were identified as essential for enzymatic activity"
GLCE is a type II transmembrane Golgi-resident glycan modification enzyme; its HS-modified products act at the cell surface and ECM after proteoglycan trafficking.

"GLCE/Glce is generally described as a **type II transmembrane protein** in the HS biosynthetic machinery, which is consistent with function as a Golgi-resident glycan modification enzyme"
Zebrafish has two Glce paralogs (Glce-A, Glce-B) arising as duplicated orthologs of the single human GLCE gene, with ~67% and ~73% homology to human GLCE respectively.

"zebrafish were shown to have **two Glce-like paralogs**, **Glce-A and Glce-B**, arising as duplicated orthologs of the **single human GLCE gene**"
glce-A and glce-B transcripts are maternally supplied, broadly expressed during gastrulation, and become restricted by 24 hpf with enrichment in the developing hindbrain.

"both **glce-A and glce-B transcripts are maternally supplied**"
Overexpression of glce-A or glce-B causes dose-dependent ventralization in zebrafish embryos (smaller head, expanded blood islands, abnormal somites).

"Overexpression** of glce-A or glce-B causes **dose-dependent ventralization**"
Morpholino knockdown of glce causes dorsalization (reduced ventral tail fin, kinked/coiled tail, enlarged heart cavity), resembling reduced BMP signaling.

"Morpholino knockdown** causes **dorsalization**"
glce activity modulates BMP signaling: overexpression enhances the ventralizing activity of Bmp2b and knockdown impairs it, linking HS fine structure to BMP-mediated dorsoventral patterning.

"overexpression enhances the ventralizing activity of **Bmp2b**, and knockdown impairs Bmp2b activity"
Zebrafish Glce was reported to interact with 2-O- and 6-O-sulfotransferases, consistent with a coordinated 'GAGosome' coupling of epimerization with downstream O-sulfation.

"Glce was reported to interact with **2-O- and 6-O-sulfotransferases**"

Suggested Experiments

Experiment: Generate glceb loss-of-function mutants (CRISPR) and assay HS disaccharide composition (IdoA content) together with dorsoventral patterning markers to define the in vivo requirement for glceb specifically versus glcea.

Deep Research

Falcon

(glceb-deep-research-falcon.md)

Functional annotation research report: **Danio rerio glceb (UniProt F1QR43)** — D-glucuronyl C5-epimerase B (EC 5.1.3.17) Falcon Edison Scientific Literature 9 citations 2 artifacts 2026-05-30T11:57:34.682186

Edison artifact artifact-00 (text/markdown)

## Context ID: pqac-00000008 The requested information on zebrafish D-glucuronyl C5-epimerase (Glce) is provided in the following figures: 1. **Dimer Structure* (image/png)

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Functional annotation research report: Danio rerio glceb (UniProt F1QR43) — D-glucuronyl C5-epimerase B (EC 5.1.3.17)

0. Target verification and disambiguation (MANDATORY)

The UniProt target F1QR43 is annotated as D-glucuronyl C5-epimerase B and the gene name as glceb in zebrafish (Danio rerio). In the foundational zebrafish study of this activity, zebrafish were shown to have two Glce-like paralogs, Glce-A and Glce-B, arising as duplicated orthologs of the single human GLCE gene (with reported ~67% and ~73% homology to human GLCE, respectively). The same study explicitly describes these proteins as D-glucuronyl C5-epimerases acting on heparan sulfate (HS), aligning with UniProt’s description and domain-family expectations for a GLCE-family HS epimerase. Therefore, the literature in this report is focused on the intended zebrafish paralog Glce-B / glce-b (glceb) and not another gene with a similar symbol. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5)

1. Key concepts and definitions (current understanding)

1.1. What GLCE/Glce does in glycosaminoglycan biosynthesis

Heparan sulfate (HS) is a sulfated glycosaminoglycan found on the cell surface and in the extracellular matrix (ECM) as part of heparan sulfate proteoglycans; it binds many proteins (e.g., morphogens and growth factors) and modulates signaling by shaping ligand diffusion, receptor interactions, and extracellular retention. (qin2015structuralandfunctional pages 1-2)

Glucuronyl C5-epimerase (GLCE; Glce in zebrafish) is a key HS chain-modifying enzyme in the HS/heparin biosynthetic pathway that converts D-glucuronic acid (GlcA) residues to L-iduronic acid (IdoA) within the polymer. This C5 epimerization increases HS chain conformational flexibility, a feature important for many HS–protein interactions. (qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)

1.2. Enzymatic function: reaction and substrate context

Reaction (EC 5.1.3.17): C5 epimerization on polymeric HS/heparin: GlcA → IdoA (and, in principle, the reverse). (qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)

Substrate specificity (current model): GLCE acts at the polymer level and requires specific precursor contexts; in particular, GLCE preferentially recognizes HS regions where adjacent glucosamine residues are N-sulfated (GlcNS), i.e., GLCE “only recognizes” polysaccharide regions that are N-sulfated at GlcN units. This couples C5 epimerization to the canonical “modification” phase of HS biosynthesis that follows N-deacetylation/N-sulfation. (li2010glucuronylc5epimerasean pages 1-3)

1.3. Reversibility and apparent directionality in vivo

Biochemically, C5 epimerization can be reversible in vitro, but the pathway behaves as effectively irreversible in vivo, consistent with structural/biochemical observations that downstream O-sulfation patterns and product features constrain reversal and can create product inhibition. (qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)

2. Molecular mechanism (structural and catalytic understanding)

2.1. Overall architecture and active site organization

A key advance for mechanistic annotation is the determination of zebrafish Glce structures showing that Glce forms a stable dimer in which each dimer contains two catalytic sites located in C-terminal helical domains that bind negatively charged oligosaccharides. (qin2015structuralandfunctional pages 1-2, qin2015structuralandfunctional media a4e3a39f)

Active-site tyrosines are critical for catalysis; in zebrafish Glce, Tyr468, Tyr528, and Tyr546 were identified as essential for enzymatic activity by structure-guided analysis. (qin2015structuralandfunctional pages 1-2, qin2015structuralandfunctional media a4e3a39f)

2.2. Product inhibition and quantitative inhibition data

Structural and biochemical experiments using zebrafish Glce report that sulfated heparin-like products inhibit Glce activity. Reported inhibition values include IC50 ≈ 225 µg/mL for heparin and IC50 ≈ 10 µg/mL for N-sulfated heparin, supporting strong inhibition by highly N-sulfated (and/or otherwise product-like) GAGs and providing a quantitative handle for interpreting pathway directionality and regulation. (qin2015structuralandfunctional pages 8-9, qin2015structuralandfunctional media 7f409ad0)

3. Cellular and subcellular localization

GLCE/Glce is generally described as a type II transmembrane protein in the HS biosynthetic machinery, which is consistent with function as a Golgi-resident glycan modification enzyme. A zebrafish study of glce paralogs reports a conserved hydrophobic N-terminal segment consistent with type II membrane topology and predicted Golgi localization for Glce-A/Glce-B. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, li2010glucuronylc5epimerasean pages 1-3)

Interpretation for functional annotation: Glceb (F1QR43) is most parsimoniously annotated as acting in the Golgi lumen during HS chain maturation, with its HS-modified products functioning at the cell surface/ECM after proteoglycan trafficking and secretion. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)

4. Zebrafish-specific biology of glce-B / glceb: expression and developmental roles

4.1. Expression dynamics during embryogenesis

In zebrafish embryos, both glce-A and glce-B transcripts are maternally supplied (detected in fertilized embryos prior to zygotic transcription). Expression is broad during gastrulation and becomes more restricted by 24 hours post-fertilization, with enrichment in the developing brain/hindbrain region (including localization around the fourth ventricle perimeter in reported in situ patterns). The study reports no major differences between glce-A and glce-B patterns in those assays. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5)

4.2. Enzymatic activity during development (quantitative)

In zebrafish embryos, epimerase activity increases during early development: activity at 10 hpf is ~2× that at the 64-cell stage. Perturbation experiments link gene dosage to enzyme activity: overexpression increased activity at 10 hpf by ~73%, while antisense morpholino knockdown reduced activity to ~34% of control. These data support that the measured enzymatic activity in embryos is Glce-dependent and developmentally regulated. (ghiselli2005dglucuronylc5epimeraseacts pages 2-5, ghiselli2005dglucuronylc5epimeraseacts pages 5-7)

4.3. Developmental phenotypes and pathway linkage (BMP-dependent dorsoventral patterning)

Functional perturbations demonstrate a direct developmental role in dorsoventral patterning:

Overexpression of glce-A or glce-B causes dose-dependent ventralization, including smaller head size, expanded blood islands, and abnormal somite/tail phenotypes. Co-injection of both mRNAs produces more severe defects in which many embryos fail to form an anterior axis. (ghiselli2005dglucuronylc5epimeraseacts pages 2-5, ghiselli2005dglucuronylc5epimeraseacts pages 5-7)
Morpholino knockdown causes dorsalization, including reduced ventral tail fin and additional morphological defects (e.g., kinked/coiled tail, enlarged heart cavity), resembling reduced BMP signaling phenotypes. (ghiselli2005dglucuronylc5epimeraseacts pages 5-7)

Mechanistically, glce activity modulates BMP signaling: overexpression enhances the ventralizing activity of Bmp2b, and knockdown impairs Bmp2b activity, providing a concrete pathway connection between HS fine structure (IdoA content) and BMP-mediated cell specification during gastrulation. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5)

5. Pathways and biochemical network context

5.1. Placement in HS/heparin biosynthesis

GLCE/Glce participates in the canonical HS modification sequence in which N-sulfation creates substrate contexts for subsequent modifications; GLCE-mediated epimerization creates IdoA residues that can subsequently be O-sulfated and incorporated into high-affinity binding sites. This step is central to controlling HS flexibility and ligand-binding properties. (li2010glucuronylc5epimerasean pages 1-3)

5.2. “GAGosome” and coordinated modification hypothesis

Structural/biochemical work on zebrafish Glce supports the concept that HS biosynthetic enzymes may physically associate: Glce was reported to interact with 2-O- and 6-O-sulfotransferases, consistent with coordinated coupling of epimerization and downstream O-sulfations (a potential mechanism for generating specific IdoA/O-sulfation patterns). (qin2015structuralandfunctional pages 8-9)

6. Current applications and real-world implementations

6.1. Chemoenzymatic synthesis and glycoengineering

Because GLCE dictates where IdoA is introduced into HS/heparin chains, mechanistic/structural frameworks for GLCE function are used to support chemoenzymatic synthesis or engineering of HS/heparin analogs with tailored binding properties. Structural studies explicitly present GLCE as a framework for understanding (and manipulating) the key epimerization step in HS biosynthesis, including product inhibition features relevant to in vitro engineering workflows. (qin2015structuralandfunctional pages 8-9, qin2015structuralandfunctional pages 1-2)

6.2. Developmental model utility (zebrafish)

Zebrafish glce-A/glce-B perturbation provides an in vivo model connecting HS fine structure to morphogen signaling and patterning, particularly in the context of BMP-dependent dorsoventral axis formation. This supports practical use of zebrafish for functional testing of HS-biosynthetic enzymes and for interpreting how HS structure encodes developmental information. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5, ghiselli2005dglucuronylc5epimeraseacts pages 5-7)

7. Expert analysis and interpretation

7.1. Primary function of glceb (F1QR43)

The most defensible primary functional annotation for zebrafish glceb (F1QR43) is:

Molecular function: D-glucuronyl C5-epimerase (EC 5.1.3.17) catalyzing C5 epimerization of uronic acids in HS (GlcA → IdoA), acting on polymeric HS precursors and requiring N-sulfation context. (qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)
Subcellular site of action: Golgi/secretory pathway as a type II membrane HS-modifying enzyme. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, li2010glucuronylc5epimerasean pages 1-3)
Physiological role in zebrafish: regulation of HS structure required for correct morphogen signaling, with direct evidence for modulating Bmp2b-driven ventralization during gastrulation and thus dorsoventral axis formation. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5)

7.2. Mechanistic plausibility connecting HS structure to BMP outcomes

The zebrafish genetic results are consistent with a mechanistic chain: altered Glce activity changes the abundance/distribution of IdoA in HS, which changes HS–protein binding behavior and thereby alters morphogen distribution or receptor engagement. This is strongly supported by the established biochemical role of IdoA in increasing GAG flexibility and ligand recognition and by the direct BMP pathway modulation observed in embryos. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)

8. Evidence map (summary table)

The following table consolidates the main findings supporting functional annotation, including quantitative parameters.

Aspect	Key finding	Species/system	Evidence type	Source (author year journal)	URL	Citation context id
Identity	The target corresponds to zebrafish Glce-B / glce-b (glceb), one of two zebrafish paralogs of the single human GLCE gene; zebrafish Glce-A and Glce-B encode 585-aa proteins with ~67% and ~73% homology to human GLCE, respectively, and both map as orthologous counterparts of human GLCE.	Danio rerio embryos/genome comparison	Gene cloning, sequence comparison, chromosomal mapping	Ghiselli & Farber 2005, BMC Developmental Biology	https://doi.org/10.1186/1471-213x-5-19	(ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5)
Enzymatic reaction	Glce/GLCE is a D-glucuronyl C5-epimerase (EC 5.1.3.17) that catalyzes conversion of D-glucuronic acid (GlcA) to L-iduronic acid (IdoA) in heparan sulfate/heparin chains, increasing chain flexibility and ligand-binding capacity.	Zebrafish Glce; vertebrate HS biosynthesis	Biochemical assay, structural biology, review synthesis	Qin et al. 2015, J Biol Chem; Li 2010, Prog Mol Biol Transl Sci	https://doi.org/10.1074/jbc.m114.602201 ; https://doi.org/10.1016/S1877-1173(10)93004-4	(qin2015structuralandfunctional pages 8-9, qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)
Substrate specificity	Substrate recognition requires N-sulfated glucosamine adjacent to the epimerization site; Glce recognizes motifs such as (GlcA-GlcNS)n and binds/inverts uronic acid within HS precursor chains. O-sulfated heparin-like products behave as inhibitors rather than optimal substrates.	Human/zebrafish GLCE systems; HS/heparin oligosaccharides	Structural biology, biochemical mechanism, review synthesis	Debarnot et al. 2019, PNAS; Qin et al. 2015, J Biol Chem; Li 2010, Prog Mol Biol Transl Sci	https://doi.org/10.1073/pnas.1818333116 ; https://doi.org/10.1074/jbc.m114.602201 ; https://doi.org/10.1016/S1877-1173(10)93004-4	(qin2015structuralandfunctional pages 8-9, li2010glucuronylc5epimerasean pages 1-3)
Reversibility / in vivo directionality	The catalytic step is reversible in vitro (GlcA ↔ IdoA), but HS biosynthesis appears effectively irreversible in vivo, because subsequent O-sulfation/product formation disfavors reversal and helps lock in IdoA-containing products.	Vertebrate GLCE/HS biosynthesis	Structural biology, biochemical review	Qin et al. 2015, J Biol Chem; Li 2010, Prog Mol Biol Transl Sci	https://doi.org/10.1074/jbc.m114.602201 ; https://doi.org/10.1016/S1877-1173(10)93004-4	(qin2015structuralandfunctional pages 8-9, qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)
Localization	GLCE is a type II transmembrane Golgi enzyme in the HS biosynthetic machinery; zebrafish Glce proteins are predicted to contain an N-terminal hydrophobic segment consistent with Golgi localization. HS products act at the cell surface and extracellular matrix after biosynthesis.	Zebrafish and vertebrate cells	Sequence-based inference, cell biology review, pathway context	Ghiselli & Farber 2005, BMC Developmental Biology; Li 2010, Prog Mol Biol Transl Sci	https://doi.org/10.1186/1471-213x-5-19 ; https://doi.org/10.1016/S1877-1173(10)93004-4	(ghiselli2005dglucuronylc5epimeraseacts pages 1-2, li2010glucuronylc5epimerasean pages 1-3)
Expression pattern	glce-A and glce-B transcripts are maternally supplied, broadly expressed during gastrulation, and become more restricted by 24 hpf, with enrichment in the hindbrain/around the fourth ventricle; no major expression difference between the two paralogs was detected in the original zebrafish study.	Danio rerio embryos	RT-PCR, whole-mount in situ hybridization	Ghiselli & Farber 2005, BMC Developmental Biology	https://doi.org/10.1186/1471-213x-5-19	(ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5)
Developmental phenotype	Overexpression of zebrafish Glce causes dose-dependent ventralization (smaller head, expanded blood islands, abnormal somites), while morpholino knockdown causes dorsalization (reduced ventral tail fin, kinked/coiled tail, enlarged heart cavity), establishing an essential role in dorso-ventral axis formation.	Danio rerio embryos	Gain-of-function and loss-of-function embryology	Ghiselli & Farber 2005, BMC Developmental Biology	https://doi.org/10.1186/1471-213x-5-19	(ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5, ghiselli2005dglucuronylc5epimeraseacts pages 5-7)
Pathway links	Glce functions in the heparan sulfate biosynthesis pathway, after N-sulfation and before/with O-sulfation steps; it modulates HS-dependent morphogen systems including BMP, and is discussed in the context of Wnt, FGF, and Hedgehog signaling. Zebrafish experiments directly showed that Glce enhances Bmp2b ventralizing activity, while knockdown impairs it.	Zebrafish embryos; vertebrate HS pathway	Developmental genetics, pathway review, protein interaction/structure	Ghiselli & Farber 2005, BMC Developmental Biology; Li 2010, Prog Mol Biol Transl Sci; Qin et al. 2015, J Biol Chem	https://doi.org/10.1186/1471-213x-5-19 ; https://doi.org/10.1016/S1877-1173(10)93004-4 ; https://doi.org/10.1074/jbc.m114.602201	(ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5, ghiselli2005dglucuronylc5epimeraseacts pages 5-7, qin2015structuralandfunctional pages 8-9, li2010glucuronylc5epimerasean pages 1-3)
Quantitative data	Zebrafish embryonic epimerase activity at 10 hpf was ~2× that at the 64-cell stage; overexpression increased activity at 10 hpf by ~73%; morpholino knockdown reduced activity to ~34% of control.	Danio rerio embryos	Enzyme assay during development and perturbation	Ghiselli & Farber 2005, BMC Developmental Biology	https://doi.org/10.1186/1471-213x-5-19	(ghiselli2005dglucuronylc5epimeraseacts pages 2-5, ghiselli2005dglucuronylc5epimeraseacts pages 5-7)
Quantitative data	Product/inhibitor analysis in structural-biochemical work showed heparin IC50 ≈ 225 µg/mL and N-sulfated heparin IC50 ≈ 10 µg/mL, supporting strong inhibition by highly sulfated products/analogs and explaining how downstream sulfation can constrain reversal.	Zebrafish Glce with heparin/HS analogs	In vitro inhibition assay, structural interpretation	Qin et al. 2015, J Biol Chem	https://doi.org/10.1074/jbc.m114.602201	(qin2015structuralandfunctional pages 8-9, qin2015structuralandfunctional media a4e3a39f, qin2015structuralandfunctional media 2669519a, qin2015structuralandfunctional media 7f409ad0)
Quantitative data	Zebrafish and human GLCE proteins form stable dimers with two catalytic sites per dimer; active-site tyrosines Tyr468, Tyr528, Tyr546 are required for activity, providing mechanistic support for annotation of F1QR43 as a functional Glce-family epimerase.	Zebrafish structural construct; conserved vertebrate GLCE	X-ray crystallography, mutagenesis	Qin et al. 2015, J Biol Chem	https://doi.org/10.1074/jbc.m114.602201	(qin2015structuralandfunctional pages 8-9, qin2015structuralandfunctional pages 1-2, qin2015structuralandfunctional media a4e3a39f)

Table: This table summarizes the key functional annotation evidence for zebrafish glceb/Glce-B (UniProt F1QR43), including enzyme function, localization, developmental roles, pathway context, and quantitative measurements. It is useful as a compact evidence map linking the zebrafish gene to the broader GLCE/heparan sulfate biosynthesis literature.

9. Limitations and gaps (with respect to 2023–2024 prioritization)

This report prioritizes direct experimental evidence available in the retrieved full texts. In this run, the most relevant zebrafish-specific functional evidence is from 2005 (expression/phenotype) and 2015 (zebrafish structure/mechanism), complemented by an authoritative 2010 review on GLCE biology. (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, qin2015structuralandfunctional pages 1-2, li2010glucuronylc5epimerasean pages 1-3)

Recent (2023–2024) developments in HS biology exist broadly, but corresponding full-text evidence was not successfully incorporated into the citable context for this tool run; therefore, this report does not make uncited claims about 2023–2024-specific advances for glceb beyond the mechanistic and developmental conclusions supported by the cited sources.

Key sources (publication dates and URLs)

Ghiselli G, Farber SA. 2005-09. BMC Developmental Biology. “D-glucuronyl C5-epimerase acts in dorso-ventral axis formation in zebrafish.” https://doi.org/10.1186/1471-213x-5-19 (ghiselli2005dglucuronylc5epimeraseacts pages 1-2, ghiselli2005dglucuronylc5epimeraseacts pages 2-5, ghiselli2005dglucuronylc5epimeraseacts pages 5-7)
Qin Y, et al. 2015-02. Journal of Biological Chemistry. “Structural and Functional Study of d-Glucuronyl C5-epimerase.” https://doi.org/10.1074/jbc.m114.602201 (qin2015structuralandfunctional pages 8-9, qin2015structuralandfunctional pages 1-2, qin2015structuralandfunctional media a4e3a39f, qin2015structuralandfunctional media 7f409ad0)
Li J-P. 2010-01. Progress in Molecular Biology and Translational Science. “Glucuronyl C5-epimerase… in heparan sulfate/heparin biosynthesis.” https://doi.org/10.1016/S1877-1173(10)93004-4 (li2010glucuronylc5epimerasean pages 1-3)

References

(ghiselli2005dglucuronylc5epimeraseacts pages 1-2): Giancarlo Ghiselli and Steven A. Farber. D-glucuronyl c5-epimerase acts in dorso-ventral axis formation in zebrafish. BMC Developmental Biology, 5:19-19, Sep 2005. URL: https://doi.org/10.1186/1471-213x-5-19, doi:10.1186/1471-213x-5-19. This article has 127 citations and is from a peer-reviewed journal.
(ghiselli2005dglucuronylc5epimeraseacts pages 2-5): Giancarlo Ghiselli and Steven A. Farber. D-glucuronyl c5-epimerase acts in dorso-ventral axis formation in zebrafish. BMC Developmental Biology, 5:19-19, Sep 2005. URL: https://doi.org/10.1186/1471-213x-5-19, doi:10.1186/1471-213x-5-19. This article has 127 citations and is from a peer-reviewed journal.
(qin2015structuralandfunctional pages 1-2): Yi Qin, Jiyuan Ke, Xin Gu, Jianping Fang, Wucheng Wang, Qifei Cong, Jie Li, Jinzhi Tan, Joseph S. Brunzelle, Chenghai Zhang, Yi Jiang, Karsten Melcher, Jin-ping Li, H.Eric Xu, and Kan Ding. Structural and functional study of d-glucuronyl c5-epimerase. Feb 2015. URL: https://doi.org/10.1074/jbc.m114.602201, doi:10.1074/jbc.m114.602201. This article has 70 citations and is from a domain leading peer-reviewed journal.
(li2010glucuronylc5epimerasean pages 1-3): Jin-ping Li. Glucuronyl c5-epimerase an enzyme converting glucuronic acid to iduronic acid in heparan sulfate/heparin biosynthesis. Progress in molecular biology and translational science, 93:59-78, Jan 2010. URL: https://doi.org/10.1016/s1877-1173(10)93004-4, doi:10.1016/s1877-1173(10)93004-4. This article has 59 citations and is from a peer-reviewed journal.
(qin2015structuralandfunctional media a4e3a39f): Yi Qin, Jiyuan Ke, Xin Gu, Jianping Fang, Wucheng Wang, Qifei Cong, Jie Li, Jinzhi Tan, Joseph S. Brunzelle, Chenghai Zhang, Yi Jiang, Karsten Melcher, Jin-ping Li, H.Eric Xu, and Kan Ding. Structural and functional study of d-glucuronyl c5-epimerase. Feb 2015. URL: https://doi.org/10.1074/jbc.m114.602201, doi:10.1074/jbc.m114.602201. This article has 70 citations and is from a domain leading peer-reviewed journal.
(qin2015structuralandfunctional pages 8-9): Yi Qin, Jiyuan Ke, Xin Gu, Jianping Fang, Wucheng Wang, Qifei Cong, Jie Li, Jinzhi Tan, Joseph S. Brunzelle, Chenghai Zhang, Yi Jiang, Karsten Melcher, Jin-ping Li, H.Eric Xu, and Kan Ding. Structural and functional study of d-glucuronyl c5-epimerase. Feb 2015. URL: https://doi.org/10.1074/jbc.m114.602201, doi:10.1074/jbc.m114.602201. This article has 70 citations and is from a domain leading peer-reviewed journal.
(qin2015structuralandfunctional media 7f409ad0): Yi Qin, Jiyuan Ke, Xin Gu, Jianping Fang, Wucheng Wang, Qifei Cong, Jie Li, Jinzhi Tan, Joseph S. Brunzelle, Chenghai Zhang, Yi Jiang, Karsten Melcher, Jin-ping Li, H.Eric Xu, and Kan Ding. Structural and functional study of d-glucuronyl c5-epimerase. Feb 2015. URL: https://doi.org/10.1074/jbc.m114.602201, doi:10.1074/jbc.m114.602201. This article has 70 citations and is from a domain leading peer-reviewed journal.
(ghiselli2005dglucuronylc5epimeraseacts pages 5-7): Giancarlo Ghiselli and Steven A. Farber. D-glucuronyl c5-epimerase acts in dorso-ventral axis formation in zebrafish. BMC Developmental Biology, 5:19-19, Sep 2005. URL: https://doi.org/10.1186/1471-213x-5-19, doi:10.1186/1471-213x-5-19. This article has 127 citations and is from a peer-reviewed journal.
(qin2015structuralandfunctional media 2669519a): Yi Qin, Jiyuan Ke, Xin Gu, Jianping Fang, Wucheng Wang, Qifei Cong, Jie Li, Jinzhi Tan, Joseph S. Brunzelle, Chenghai Zhang, Yi Jiang, Karsten Melcher, Jin-ping Li, H.Eric Xu, and Kan Ding. Structural and functional study of d-glucuronyl c5-epimerase. Feb 2015. URL: https://doi.org/10.1074/jbc.m114.602201, doi:10.1074/jbc.m114.602201. This article has 70 citations and is from a domain leading peer-reviewed journal.

Artifacts

Edison artifact artifact-00

Citations

qin2015structuralandfunctional pages 1-2
qin2015structuralandfunctional pages 8-9
https://doi.org/10.1186/1471-213x-5-19
https://doi.org/10.1074/jbc.m114.602201
https://doi.org/10.1016/S1877-1173(10
https://doi.org/10.1073/pnas.1818333116
https://doi.org/10.1186/1471-213x-5-19,
https://doi.org/10.1074/jbc.m114.602201,
https://doi.org/10.1016/s1877-1173(10

📚 Additional Documentation

Notes

(glceb-notes.md)

Notes for DANRE glceb

2026-05-09 review notes

Core function is Golgi membrane D-glucuronyl C5 epimerase activity in heparan sulfate biosynthesis [file:DANRE/glceb/glceb-uniprot.txt "Converts D-glucuronic acid residues adjacent to N-sulfate"].
Heparin biosynthesis is kept as non-core because UniProt lists it as a pathway, but the central review emphasis is heparan sulfate chain epimerization [file:DANRE/glceb/glceb-uniprot.txt "PATHWAY: Glycan metabolism; heparin biosynthesis."].
Identical protein binding reflects homodimerization, not the core catalytic function PMID:25568314.

📄 View Raw YAML

id: F1QR43
gene_symbol: glceb
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:7955
  label: Danio rerio
description: |-
  glceb encodes zebrafish D-glucuronyl C5-epimerase B, a Golgi membrane (type II transmembrane) enzyme that converts
  D-glucuronic acid residues adjacent to N-sulfated sugars into L-iduronic acid during heparan sulfate and heparin chain
  biosynthesis. The core function is heparosan-N-sulfate-glucuronate 5-epimerase activity (EC 5.1.3.17) in heparan
  sulfate proteoglycan biosynthesis, performed as a homodimer with two catalytic sites per dimer and active-site
  tyrosines (Tyr468/Tyr528/Tyr546) required for catalysis. glceb is one of two zebrafish paralogs (glce-A/glce-B) of
  the single human GLCE gene. Functionally, glce activity tunes HS fine structure (IdoA content) that controls morphogen
  signaling; in zebrafish embryos overexpression causes BMP-like ventralization and morpholino knockdown causes
  dorsalization, placing glce in BMP-dependent dorsoventral axis formation. Homodimerization/protein-binding evidence is
  retained as non-core structural information.
existing_annotations:
- term:
    id: GO:0015012
    label: heparan sulfate proteoglycan biosynthetic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      heparan sulfate proteoglycan biosynthetic process (GO:0015012) is supported as the direct pathway context.
      Glce performs the C5-epimerization step of the HS modification cascade, acting after N-sulfation to generate
      IdoA residues that are subsequently O-sulfated. In zebrafish, this activity is developmentally regulated and
      required for HS fine structure that controls morphogen signaling.
    action: ACCEPT
    reason: Glce is a heparan sulfate biosynthetic enzyme.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: 'PATHWAY: Glycan metabolism; heparan sulfate biosynthesis.'
    - reference_id: PMID:25568314
      supporting_text: D-glucuronyl C5-epimerase (Glce) is a crucial enzyme in HS synthesis
    - reference_id: file:DANRE/glceb/glceb-deep-research-falcon.md
      supporting_text: |-
        Glce participates in the canonical HS modification sequence in which N-sulfation creates substrate contexts
        for subsequent modifications; GLCE-mediated epimerization creates IdoA residues that can subsequently be
        O-sulfated and incorporated into high-affinity binding sites
      reference_section_type: DISCUSSION
- term:
    id: GO:0047464
    label: heparosan-N-sulfate-glucuronate 5-epimerase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: heparosan-N-sulfate-glucuronate 5-epimerase activity (GO:0047464) is the direct supported molecular function.
    action: ACCEPT
    reason: The enzyme converts D-glucuronic acid to L-iduronic acid in heparan sulfate/heparin chains.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: Converts D-glucuronic acid residues adjacent to N-sulfate
    - reference_id: PMID:25568314
      supporting_text: converting D-glucuronic acid to L-iduronic
    - reference_id: file:DANRE/glceb/glceb-deep-research-falcon.md
      supporting_text: |-
        converts **D-glucuronic acid (GlcA)** residues to **L-iduronic acid (IdoA)** within the polymer
      reference_section_type: RESULTS
- term:
    id: GO:0005794
    label: Golgi apparatus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: Golgi apparatus (GO:0005794) is supported for glceb.
    action: ACCEPT
    reason: Golgi localization is coherent with the more specific Golgi membrane annotation.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Golgi apparatus membrane'
- term:
    id: GO:0000139
    label: Golgi membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: |-
      Golgi membrane (GO:0000139) is supported for glceb. GLCE is a type II transmembrane Golgi-resident glycan
      modification enzyme; its HS-modified products subsequently act at the cell surface and extracellular matrix.
    action: ACCEPT
    reason: UniProt places Glceb at the Golgi apparatus membrane.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Golgi apparatus membrane'
    - reference_id: file:DANRE/glceb/glceb-deep-research-falcon.md
      supporting_text: |-
        GLCE/Glce is generally described as a **type II transmembrane protein** in the HS biosynthetic machinery,
        which is consistent with function as a Golgi-resident glycan modification enzyme
      reference_section_type: DISCUSSION
- term:
    id: GO:0015012
    label: heparan sulfate proteoglycan biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: heparan sulfate proteoglycan biosynthetic process (GO:0015012) is supported as the direct pathway context.
    action: ACCEPT
    reason: Glce is a heparan sulfate biosynthetic enzyme.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: 'PATHWAY: Glycan metabolism; heparan sulfate biosynthesis.'
    - reference_id: PMID:25568314
      supporting_text: D-glucuronyl C5-epimerase (Glce) is a crucial enzyme in HS synthesis
- term:
    id: GO:0047464
    label: heparosan-N-sulfate-glucuronate 5-epimerase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: heparosan-N-sulfate-glucuronate 5-epimerase activity (GO:0047464) is the direct supported molecular function.
    action: ACCEPT
    reason: The enzyme converts D-glucuronic acid to L-iduronic acid in heparan sulfate/heparin chains.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: Converts D-glucuronic acid residues adjacent to N-sulfate
    - reference_id: PMID:25568314
      supporting_text: converting D-glucuronic acid to L-iduronic
- term:
    id: GO:0030210
    label: heparin proteoglycan biosynthetic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000041
  review:
    summary: heparin proteoglycan biosynthetic process (GO:0030210) is supported by pathway context but is not the main zebrafish
      core annotation.
    action: KEEP_AS_NON_CORE
    reason: UniProt includes heparin biosynthesis, but the central conserved role in this review is heparan sulfate chain
      epimerization.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: 'PATHWAY: Glycan metabolism; heparin biosynthesis.'
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:25568314
  review:
    summary: |-
      identical protein binding (GO:0042802) is supported as homodimerization but is not a core function. The
      zebrafish Glce crystal structure shows a stable dimer with two catalytic sites per dimer; dimerization is
      thus the functional quaternary state that builds the active sites, but it remains structural context rather
      than the GO molecular function of the enzyme.
    action: KEEP_AS_NON_CORE
    reason: Dimerization is structural context for the enzyme rather than its GO molecular function.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: 'SUBUNIT: Homodimer.'
    - reference_id: PMID:25568314
      supporting_text: zebrafish Glce has a dimeric structure
    - reference_id: file:DANRE/glceb/glceb-deep-research-falcon.md
      supporting_text: |-
        Glce forms a **stable dimer** in which each dimer contains **two catalytic sites** located in C-terminal
        helical domains
      reference_section_type: RESULTS
- term:
    id: GO:0000139
    label: Golgi membrane
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: Golgi membrane (GO:0000139) is supported for glceb.
    action: ACCEPT
    reason: UniProt places Glceb at the Golgi apparatus membrane.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Golgi apparatus membrane'
- term:
    id: GO:0047464
    label: heparosan-N-sulfate-glucuronate 5-epimerase activity
  evidence_type: IDA
  original_reference_id: PMID:25568314
  review:
    summary: |-
      heparosan-N-sulfate-glucuronate 5-epimerase activity (GO:0047464) is the direct supported molecular function,
      experimentally demonstrated for zebrafish Glce. The enzyme epimerizes C5 of D-glucuronic acid to L-iduronic
      acid within heparan sulfate/heparin chains, and substrate recognition requires N-sulfated glucosamine adjacent
      to the epimerization site. Structure-guided mutagenesis identified active-site tyrosines (Tyr468, Tyr528,
      Tyr546) essential for catalysis, confirming F1QR43 is a functional GLCE-family epimerase.
    action: ACCEPT
    reason: The enzyme converts D-glucuronic acid to L-iduronic acid in heparan sulfate/heparin chains.
    supported_by:
    - reference_id: file:DANRE/glceb/glceb-uniprot.txt
      supporting_text: Converts D-glucuronic acid residues adjacent to N-sulfate
    - reference_id: PMID:25568314
      supporting_text: converting D-glucuronic acid to L-iduronic
    - reference_id: file:DANRE/glceb/glceb-deep-research-falcon.md
      supporting_text: |-
        GLCE preferentially recognizes HS regions where adjacent glucosamine residues are **N-sulfated** (GlcNS)
      reference_section_type: RESULTS
    - reference_id: file:DANRE/glceb/glceb-deep-research-falcon.md
      supporting_text: |-
        Tyr468, Tyr528, and Tyr546 were identified as essential for enzymatic activity
      reference_section_type: RESULTS
references:
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence
    similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000041
  title: Gene Ontology annotation based on UniPathway vocabulary mapping.
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative
    changes to GO terms applied by UniProt
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:25568314
  title: Structural and functional study of D-glucuronyl C5-epimerase.
  findings:
  - statement: Zebrafish Glce catalyzes the C5 epimerization step in heparan sulfate synthesis.
    supporting_text: converting D-glucuronic acid to L-iduronic
  - statement: The paper supports dimeric Glce structure.
    supporting_text: zebrafish Glce has a dimeric structure
- id: file:DANRE/glceb/glceb-uniprot.txt
  title: UniProtKB entry F1QR43 for Danio rerio glceb
  findings:
  - statement: UniProt describes Glceb as a Golgi membrane C5 epimerase in heparan sulfate and heparin biosynthesis.
    supporting_text: Converts D-glucuronic acid residues adjacent to N-sulfate
- id: file:DANRE/glceb/glceb-deep-research-falcon.md
  title: Falcon deep research report for Danio rerio glceb (D-glucuronyl C5-epimerase B, F1QR43)
  findings:
  - statement: |-
      Glce catalyzes C5 epimerization converting D-glucuronic acid (GlcA) to L-iduronic acid (IdoA) within the
      heparan sulfate/heparin polymer, increasing chain conformational flexibility important for HS-protein
      interactions.
    supporting_text: |-
      converts **D-glucuronic acid (GlcA)** residues to **L-iduronic acid (IdoA)** within the polymer
    reference_section_type: RESULTS
  - statement: |-
      Substrate recognition requires N-sulfation context: GLCE preferentially recognizes HS regions where adjacent
      glucosamine residues are N-sulfated, coupling epimerization to the modification phase of HS biosynthesis.
    supporting_text: |-
      GLCE preferentially recognizes HS regions where adjacent glucosamine residues are **N-sulfated** (GlcNS)
    reference_section_type: RESULTS
  - statement: |-
      The zebrafish Glce crystal structure shows a stable dimer with two catalytic sites per dimer in C-terminal
      helical domains; active-site tyrosines Tyr468, Tyr528 and Tyr546 are essential for activity.
    supporting_text: |-
      Glce forms a **stable dimer** in which each dimer contains **two catalytic sites** located in C-terminal
      helical domains
    reference_section_type: RESULTS
  - statement: |-
      Active-site tyrosines Tyr468, Tyr528 and Tyr546 were shown by structure-guided mutagenesis to be essential
      for zebrafish Glce enzymatic activity.
    supporting_text: |-
      Tyr468, Tyr528, and Tyr546 were identified as essential for enzymatic activity
    reference_section_type: RESULTS
  - statement: |-
      GLCE is a type II transmembrane Golgi-resident glycan modification enzyme; its HS-modified products act at the
      cell surface and ECM after proteoglycan trafficking.
    supporting_text: |-
      GLCE/Glce is generally described as a **type II transmembrane protein** in the HS biosynthetic machinery,
      which is consistent with function as a Golgi-resident glycan modification enzyme
    reference_section_type: DISCUSSION
  - statement: |-
      Zebrafish has two Glce paralogs (Glce-A, Glce-B) arising as duplicated orthologs of the single human GLCE
      gene, with ~67% and ~73% homology to human GLCE respectively.
    supporting_text: |-
      zebrafish were shown to have **two Glce-like paralogs**, **Glce-A and Glce-B**, arising as duplicated
      orthologs of the **single human GLCE gene**
    reference_section_type: RESULTS
  - statement: |-
      glce-A and glce-B transcripts are maternally supplied, broadly expressed during gastrulation, and become
      restricted by 24 hpf with enrichment in the developing hindbrain.
    supporting_text: |-
      both **glce-A and glce-B transcripts are maternally supplied**
    reference_section_type: RESULTS
  - statement: |-
      Overexpression of glce-A or glce-B causes dose-dependent ventralization in zebrafish embryos (smaller head,
      expanded blood islands, abnormal somites).
    supporting_text: |-
      Overexpression** of glce-A or glce-B causes **dose-dependent ventralization**
    reference_section_type: RESULTS
  - statement: |-
      Morpholino knockdown of glce causes dorsalization (reduced ventral tail fin, kinked/coiled tail, enlarged
      heart cavity), resembling reduced BMP signaling.
    supporting_text: |-
      Morpholino knockdown** causes **dorsalization**
    reference_section_type: RESULTS
  - statement: |-
      glce activity modulates BMP signaling: overexpression enhances the ventralizing activity of Bmp2b and
      knockdown impairs it, linking HS fine structure to BMP-mediated dorsoventral patterning.
    supporting_text: |-
      overexpression enhances the ventralizing activity of **Bmp2b**, and knockdown impairs Bmp2b activity
    reference_section_type: RESULTS
  - statement: |-
      Zebrafish Glce was reported to interact with 2-O- and 6-O-sulfotransferases, consistent with a coordinated
      'GAGosome' coupling of epimerization with downstream O-sulfation.
    supporting_text: |-
      Glce was reported to interact with **2-O- and 6-O-sulfotransferases**
    reference_section_type: DISCUSSION
core_functions:
- description: glceb enables Golgi membrane heparosan-N-sulfate-glucuronate 5-epimerase activity, converting D-glucuronic
    acid to L-iduronic acid during heparan sulfate proteoglycan biosynthesis.
  molecular_function:
    id: GO:0047464
    label: heparosan-N-sulfate-glucuronate 5-epimerase activity
  directly_involved_in:
  - id: GO:0015012
    label: heparan sulfate proteoglycan biosynthetic process
  locations:
  - id: GO:0000139
    label: Golgi membrane
  supported_by:
  - reference_id: file:DANRE/glceb/glceb-uniprot.txt
    supporting_text: Converts D-glucuronic acid residues adjacent to N-sulfate
  - reference_id: PMID:25568314
    supporting_text: converting D-glucuronic acid to L-iduronic
  - reference_id: file:DANRE/glceb/glceb-uniprot.txt
    supporting_text: 'SUBCELLULAR LOCATION: Golgi apparatus membrane'
  - reference_id: file:DANRE/glceb/glceb-deep-research-falcon.md
    supporting_text: |-
      converts **D-glucuronic acid (GlcA)** residues to **L-iduronic acid (IdoA)** within the polymer
    reference_section_type: RESULTS
suggested_questions:
- question: |-
    Do zebrafish glceb (glce-B) and glcea (glce-A) have distinct or redundant roles in HS fine structure and
    morphogen signaling, given their overlapping expression and similar overexpression/knockdown phenotypes?
- question: |-
    Does the reported physical association of Glce with 2-O- and 6-O-sulfotransferases (the proposed 'GAGosome')
    operate in zebrafish, and is it required for proper IdoA/O-sulfation patterning in vivo?
suggested_experiments:
- description: |-
    Generate glceb loss-of-function mutants (CRISPR) and assay HS disaccharide composition (IdoA content) together
    with dorsoventral patterning markers to define the in vivo requirement for glceb specifically versus glcea.

glceb

Gene Description

Existing Annotations Review

Core Functions

glceb enables Golgi membrane heparosan-N-sulfate-glucuronate 5-epimerase activity, converting D-glucuronic acid to L-iduronic acid during heparan sulfate proteoglycan biosynthesis.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Functional annotation research report: Danio rerio glceb (UniProt F1QR43) — D-glucuronyl C5-epimerase B (EC 5.1.3.17)

0. Target verification and disambiguation (MANDATORY)

1. Key concepts and definitions (current understanding)

1.1. What GLCE/Glce does in glycosaminoglycan biosynthesis

1.2. Enzymatic function: reaction and substrate context

1.3. Reversibility and apparent directionality in vivo

2. Molecular mechanism (structural and catalytic understanding)

2.1. Overall architecture and active site organization

2.2. Product inhibition and quantitative inhibition data

3. Cellular and subcellular localization

4. Zebrafish-specific biology of glce-B / glceb: expression and developmental roles

4.1. Expression dynamics during embryogenesis

4.2. Enzymatic activity during development (quantitative)

4.3. Developmental phenotypes and pathway linkage (BMP-dependent dorsoventral patterning)

5. Pathways and biochemical network context

5.1. Placement in HS/heparin biosynthesis

5.2. “GAGosome” and coordinated modification hypothesis

6. Current applications and real-world implementations

6.1. Chemoenzymatic synthesis and glycoengineering

6.2. Developmental model utility (zebrafish)

7. Expert analysis and interpretation

7.1. Primary function of glceb (F1QR43)

7.2. Mechanistic plausibility connecting HS structure to BMP outcomes

8. Evidence map (summary table)

9. Limitations and gaps (with respect to 2023–2024 prioritization)

Key sources (publication dates and URLs)

Artifacts

Citations

📚 Additional Documentation

Notes

Notes for DANRE glceb

2026-05-09 review notes

📄 View Raw YAML