B4GALT5 is beta-1,4-galactosyltransferase 5, a Golgi membrane-resident, Mn2+-dependent glycosyltransferase (family GT7) that acts as the major lactosylceramide (LacCer) synthase in human cells. Its principal reaction is the transfer of galactose from UDP-galactose to glucosylceramide (GlcCer) on the lumenal face of the Golgi, producing lactosylceramide (Galbeta1-4Glc-ceramide; EC 2.4.1.274). Lactosylceramide is the common branch-point precursor from which the ganglio-, globo-, isoglobo- and (neo)lacto-series glycosphingolipids are built, so B4GALT5 sits at a central node of glycosphingolipid biosynthesis. As a beta-1,4-galactosyltransferase, B4GALT5 can also transfer galactose to terminal N-acetylglucosamine on glycoprotein N-glycans (forming N-acetyllactosamine), contributing to glycoprotein galactosylation. B4GALT5 is a single-pass type II membrane protein localized to the trans cisternae of the Golgi stack and is broadly expressed. Through its downstream glycosphingolipid products it is implicated in nervous-system processes (neuronal maturation, axonogenesis, CNS myelination) and in embryonic development; loss of the mouse ortholog is embryonic lethal.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0009101 glycoprotein biosynthetic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic (IBA) propagation of a role in glycoprotein biosynthesis, based on the broader beta-1,4-galactosyltransferase family, which galactosylates terminal GlcNAc on glycoprotein glycans. B4GALT5 does have this secondary activity, but its dominant, experimentally established role is lactosylceramide synthesis; keep as a non-core function. Reason: Plausible family-level activity (Gal transfer to glycoprotein N-glycans), but not the core function of B4GALT5; the core role is glycosphingolipid (LacCer) synthesis. |
| GO:0005794 Golgi apparatus | IBA GO_REF:0000033 | ACCEPT | Summary: IBA localization to the Golgi apparatus, consistent with UniProt subcellular location (Golgi stack membrane, trans cisternae) and with the enzyme acting on lumenal Golgi substrates. Correct but general; the more specific Golgi membrane / trans-Golgi network terms capture the location better. |
| GO:0008489 UDP-galactose:glucosylceramide beta-1,4-galactosyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA assignment of the lactosylceramide synthase activity (GlcCer + UDP-Gal -> LacCer). This is the core molecular function of B4GALT5 and is independently supported experimentally (IMP, PMID:24498430) and by the UniProt catalytic-activity annotation (EC 2.4.1.274, RHEA:31495). |
| GO:0000139 Golgi membrane | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA electronic annotation to Golgi membrane, consistent with UniProt subcellular location (Golgi stack membrane). Accurate localization for this single-pass type II Golgi membrane enzyme. |
| GO:0005794 Golgi apparatus | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell mapping to Golgi apparatus. Correct but general; redundant with the more specific Golgi membrane / trans-Golgi network annotations. |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro2GO (IPR003859, galactosyltransferase) mapping to the very general carbohydrate metabolic process. Not wrong, but far too general to be informative given the specific LacCer-synthase / glycosphingolipid role. Reason: Over-general parent term; the specific glycosphingolipid/LacCer biosynthetic process terms convey the actual biology. |
| GO:0008489 UDP-galactose:glucosylceramide beta-1,4-galactosyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined-IEA (ARBA + Ensembl ortholog + Rhea/EC 2.4.1.274) assignment of the lactosylceramide synthase activity. Correct core molecular function, corroborating the IBA and IMP annotations to the same term. |
| GO:0016757 glycosyltransferase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro2GO mapping to the general glycosyltransferase activity. Correct at the family level but subsumed by the specific GO:0008489 (LacCer synthase) and GO:0003831 (beta-1,4-galactosyltransferase) terms. Reason: Over-general MF parent; more specific galactosyltransferase terms are available and better supported. |
| GO:0032580 Golgi cisterna membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell mapping to Golgi cisterna membrane, matching the UniProt note that the enzyme resides in the trans cisternae of the Golgi stack. Accurate localization. |
| GO:1901137 carbohydrate derivative biosynthetic process | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: ARBA mapping to the very general carbohydrate-derivative biosynthetic process. True (glycosphingolipids and glycoproteins are carbohydrate derivatives) but uninformative relative to the specific pathway terms. Reason: Over-general parent; specific glycosphingolipid/LacCer biosynthesis terms capture the biology. |
| GO:0005515 protein binding | IPI PMID:28514442 Architecture of the human interactome defines protein commun... | MARK AS OVER ANNOTATED | Summary: Bare "protein binding" from a proteome-scale AP-MS interactome screen (BioPlex, Huttlin et al. 2017); the recorded partner is HSPA13 (P48723), matching the UniProt INTERACTION line. Uninformative about molecular function and not evidence of a specific biological interaction; retained but flagged as over-annotated per policy (do not remove an IPI). Reason: Uninformative bare protein-binding from a high-throughput interactome screen; no specific functional interaction established. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MARK AS OVER ANNOTATED | Summary: Second bare "protein binding" IPI, from the BioPlex 3.0 interactome (Huttlin et al. 2021), again to HSPA13 (P48723). Same high-throughput AP-MS source; uninformative about molecular function. Retained but flagged as over-annotated (IPI not removed per policy). Reason: Uninformative bare protein-binding from a high-throughput interactome screen. |
| GO:0001574 ganglioside biosynthetic process | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl ortholog (mouse Q9JMK0) transfer of a role in ganglioside biosynthesis. Biologically sound: LacCer produced by B4GALT5 is the obligatory precursor of gangliosides. This is a downstream/pathway-level process rather than the direct enzymatic step; keep as non-core. Reason: Downstream consequence of LacCer synthesis (LacCer is the ganglioside precursor); pathway-level rather than the direct catalytic function. |
| GO:0009101 glycoprotein biosynthetic process | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl ortholog transfer of a role in glycoprotein biosynthesis, reflecting the family-level galactosyltransferase activity on glycoprotein N-glycans. Secondary to the core LacCer-synthase role; keep as non-core. Reason: Secondary/broader galactosyltransferase activity on glycoproteins, not the core glycosphingolipid function. |
| GO:0021955 central nervous system neuron axonogenesis | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl ortholog transfer (from mouse Q9JMK0) of a CNS axonogenesis role, reflecting the importance of gangliosides/glycosphingolipids in neuronal development. Indirect, tissue-level process downstream of the enzymatic function and not demonstrated in human; keep as non-core. Reason: Indirect developmental role transferred from mouse ortholog; downstream of glycosphingolipid synthesis, not a direct molecular function. |
| GO:0022010 central nervous system myelination | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl ortholog transfer of a CNS myelination role. Plausible via glycosphingolipid (myelin galactolipid/ganglioside) metabolism, but indirect and mouse-derived; keep as non-core. Reason: Indirect, tissue-level developmental process transferred from mouse ortholog. |
| GO:0031647 regulation of protein stability | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl ortholog transfer reflecting the mouse-derived observation that B4GALT5 glycosylates BMPR1A and regulates its stability. Highly indirect and specific to one substrate; not a core function and not demonstrated in human. Keep as non-core. Reason: Indirect, substrate-specific role (BMPR1A glycosylation) inferred from mouse ortholog; not the core enzymatic function. |
| GO:0040019 positive regulation of embryonic development | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl ortholog transfer reflecting the essential role of mouse B4galt5 in (extra)embryonic development; knockout is embryonic lethal. Organism-level phenotype downstream of the enzymatic function; keep as non-core. Reason: Organism-level developmental phenotype from mouse ortholog, downstream of glycosphingolipid biosynthesis. |
| GO:0042551 neuron maturation | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl ortholog transfer of a neuron-maturation role, again reflecting the role of glycosphingolipids in neural development. Indirect and mouse-derived; keep as non-core. Reason: Indirect developmental process transferred from mouse ortholog. |
| GO:0016266 protein O-linked glycosylation via N-acetylgalactosamine | TAS Reactome:R-HSA-913709 | KEEP AS NON CORE | Summary: Reactome pathway annotation ("O-linked glycosylation of mucins"). B4GALT5 can add galactose within elongating O-glycan cores, hence its inclusion in this pathway, but O-GalNAc mucin glycosylation is a peripheral, pathway-membership activity rather than a core function of this enzyme. Keep as non-core. Reason: Peripheral pathway membership (Gal addition within O-glycan cores); not the core glycosphingolipid function. |
| GO:0005794 Golgi apparatus | ISS GO_REF:0000024 | ACCEPT | Summary: ISS localization to the Golgi apparatus (by similarity to ortholog A0A1S6M251). Consistent with UniProt and with the IBA/IEA Golgi annotations. Correct but general. |
| GO:0005802 trans-Golgi network | IDA PMID:23913272 Vesicular and non-vesicular transport feed distinct glycosyl... | ACCEPT | Summary: Experimental (IDA) localization to the trans-Golgi network from D'Angelo et al. 2013, a study of intra-Golgi GlcCer transport and glycosphingolipid glycosylation tracks. Consistent with the UniProt note that B4GALT5 resides in the trans cisternae of the Golgi stack. This is the most specific and best-supported localization; accepted (cached record is abstract-only, so the specific figure is deferred to the curator). |
| GO:0008378 galactosyltransferase activity | TAS Reactome:R-HSA-1964501 | MARK AS OVER ANNOTATED | Summary: Reactome TAS to the general galactosyltransferase activity (via the "Addition of galactose to Core 6 glycoprotein" reaction). Correct at the family level but subsumed by the specific LacCer-synthase (GO:0008489) and beta-1,4-galactosyltransferase (GO:0003831) terms. Reason: Over-general MF; specific galactosyltransferase activities are better supported. |
| GO:0001574 ganglioside biosynthetic process | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS (from mouse Q9JMK0) role in ganglioside biosynthesis. Same downstream, pathway-level process as the Ensembl-derived duplicate above; LacCer is the ganglioside precursor. Keep as non-core. Reason: Downstream pathway-level process; duplicate of the IEA ganglioside annotation. |
| GO:0008489 UDP-galactose:glucosylceramide beta-1,4-galactosyltransferase activity | IMP PMID:24498430 Establishment of HeLa cell mutants deficient in sphingolipid... | ACCEPT | Summary: Direct experimental support (IMP): TALEN-mediated disruption of B4GALT5 in HeLa cells caused loss of Shiga-toxin binding and reduced Gb3 and GM3 (downstream LacCer metabolites), demonstrating that B4GALT5 is the major lactosylceramide synthase. This is the strongest evidence for the core molecular function and anchors the whole review. |
| GO:0009101 glycoprotein biosynthetic process | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS (from mouse Q9JMK0) role in glycoprotein biosynthesis, reflecting the family-level galactosyltransferase activity on glycoprotein glycans. Secondary to the LacCer-synthase core function; keep as non-core. Reason: Secondary/broader activity on glycoproteins; duplicate of the IBA/IEA glycoprotein annotations. |
| GO:0021955 central nervous system neuron axonogenesis | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS (from mouse Q9JMK0) CNS axonogenesis role; duplicate of the Ensembl IEA annotation. Indirect developmental process downstream of glycosphingolipid synthesis. Keep as non-core. Reason: Indirect developmental role from mouse ortholog; downstream of the core function. |
| GO:0022010 central nervous system myelination | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS (from mouse Q9JMK0) CNS myelination role; duplicate of the Ensembl IEA annotation. Indirect, mouse-derived. Keep as non-core. Reason: Indirect developmental role from mouse ortholog. |
| GO:0031647 regulation of protein stability | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS (from mouse Q9JMK0) role in protein-stability regulation (BMPR1A glycosylation); duplicate of the Ensembl IEA annotation. Highly indirect and substrate-specific. Keep as non-core. Reason: Indirect, substrate-specific role inferred from mouse ortholog. |
| GO:0040019 positive regulation of embryonic development | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS (from mouse Q9JMK0) role in embryonic development; duplicate of the Ensembl IEA annotation. Organism-level phenotype downstream of the enzymatic function. Keep as non-core. Reason: Organism-level developmental phenotype from mouse ortholog. |
| GO:0042551 neuron maturation | ISS GO_REF:0000024 | KEEP AS NON CORE | Summary: ISS (from mouse Q9JMK0) neuron-maturation role; duplicate of the Ensembl IEA annotation. Indirect, mouse-derived. Keep as non-core. Reason: Indirect developmental role from mouse ortholog. |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-1964501 | ACCEPT | Summary: Reactome TAS localization to Golgi membrane. Accurate and consistent with UniProt; redundant with the ARBA IEA Golgi-membrane annotation. |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-2025723 | ACCEPT | Summary: Reactome TAS Golgi-membrane localization from a distinct N-glycan reaction; redundant duplicate of the same correct location. Localization accepted. |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-2046265 | ACCEPT | Summary: Reactome TAS Golgi-membrane localization (keratan sulfate reaction); redundant duplicate of the same correct location. Localization accepted. |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-2046298 | ACCEPT | Summary: Reactome TAS Golgi-membrane localization (keratan branch reaction); redundant duplicate of the same correct location. Localization accepted. |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-975919 | ACCEPT | Summary: Reactome TAS Golgi-membrane localization (Gal addition by beta-4-GalTs); redundant duplicate of the same correct location. Localization accepted. |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-9851347 | ACCEPT | Summary: Reactome TAS Golgi-membrane localization from the reaction "B4GALT5/6 transfer Gal to GlcCer" (LacCer synthesis) - the most directly relevant Reactome reaction for this enzyme. Localization is correct and consistent with UniProt; accepted. |
| GO:0008378 galactosyltransferase activity | TAS PMID:9597550 The expanding beta 4-galactosyltransferase gene family: mess... | MARK AS OVER ANNOTATED | Summary: TAS to general galactosyltransferase activity from Lo et al. 1998, the family-defining paper that identified beta-4GalT-V (B4GALT5). Correct at the family level but subsumed by the specific LacCer-synthase and beta-1,4-galactosyltransferase terms; the abstract does not itself assay the LacCer reaction. Marked over-annotated (superseded by specific MF terms). Reason: Over-general MF; specific galactosyltransferase activities are better supported. |
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