GO:0047291 lactosylceramide alpha-2,3-sialyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0047291 describes the enzymatic activity that converts lactosylceramide (LacCer) and CMP-N-acetylneuraminate into the ganglioside GM3 plus CMP.
• This activity is commonly called GM3 synthase or SAT I and is encoded in mammals by the ST3GAL5 gene.
• The reaction is a strict alpha-2,3-sialyltransferase transfer, and its product GM3 is the precursor of most complex gangliosides.
• Enzyme kinetics depend strongly on the molecular species of lactosylceramide and on membrane phospholipid composition.
• The enzyme is a Golgi-resident sialyltransferase that can be released from membranes by cathepsin D-like proteases.
• Assays for this activity use radioactive, fluorescent, or LC-MS-based detection of GM3 formation.
Description
GO:0047291, lactosylceramide alpha-2,3-sialyltransferase activity, is a molecular function that catalyzes the transfer of sialic acid from CMP-N-acetylneuraminate onto lactosylceramide to form the ganglioside GM3. This reaction is the first committed step in the biosynthesis of the ganglioside family and is therefore central to glycosphingolipid biology. The activity is widely known as GM3 synthase or SAT I, and in mammals it is encoded by ST3GAL5, a member of the alpha-2,3-sialyltransferase family. Because GM3 and its downstream gangliosides modulate cell signaling, adhesion, and membrane organization, researchers study this activity in cancer, neurodevelopment, and metabolic disease. The enzyme has been purified from rat brain and liver, and its kinetic behavior has been characterized with many molecular species of lactosylceramide. Modern assays allow sensitive measurement of GM3 synthase activity in cells and tissues, making GO:0047291 a tractable target for functional genomics and drug discovery.
lactosylceramide alpha-2,3-sialyltransferase activity At A Glance
| GO ID | GO:0047291 |
|---|---|
| GO term | lactosylceramide alpha-2,3-sialyltransferase activity |
| Ontology | molecular_function |
| Synonym | GM3 synthase activity; ganglioside GM3 synthase activity; CMP-acetylneuraminate-lactosylceramide-sialyltransferase |
| Major function | Transfer of sialic acid from CMP-N-acetylneuraminate to lactosylceramide to form GM3 |
| Reaction | cytolipin-H + CMP-N-acetylneuraminate = alpha-N-acetylneuraminyl-2,3-beta-D-galactosyl-1,4-beta-D-glucosylceramide + CMP |
| Product | GM3 ganglioside |
| Substrate | Lactosylceramide (cytolipin-H) |
| Cofactor | CMP-N-acetylneuraminate as sialyl donor |
| Cellular location | Golgi apparatus membrane |
| Representative gene | ST3GAL5 (mammalian GM3 synthase) |
What Is GO:0047291?
In my own words, GO:0047291 is the catalytic activity that joins sialic acid to lactosylceramide using CMP-N-acetylneuraminate as the donor, creating an alpha-2,3 linkage and releasing CMP. The product is alpha-N-acetylneuraminyl-2,3-beta-D-galactosyl-1,4-beta-D-glucosylceramide, also known as GM3. This activity is synonymous with GM3 synthase, ganglioside GM3 synthase, and CMP-acetylneuraminate-lactosylceramide-sialyltransferase.
Why Is lactosylceramide alpha-2,3-sialyltransferase activity Important in Cell Biology?
GO:0047291 is important because it controls the first committed step of ganglioside biosynthesis, and the product GM3 is a precursor for a large family of sialylated glycosphingolipids that regulate cell growth, differentiation, and signaling. The activity is highly sensitive to the molecular species of lactosylceramide and to the surrounding membrane phospholipid environment, which means it integrates lipid composition with glycosphingolipid output. Because gangliosides are implicated in cancer, neurodevelopment, and metabolic disorders, measuring and manipulating this activity is a recurring need in both basic and translational research.
• Defines the first committed step in ganglioside biosynthesis, producing GM3.
• Determines the molecular species composition of GM3 and downstream gangliosides.
• Is encoded by ST3GAL5, a gene linked to glycosphingolipid disorders.
• Is a Golgi-resident enzyme whose release can be regulated by proteases.
• Provides a biochemical marker for ganglioside-related cancers and neuropathies.
• Can be assayed with radioactive, fluorescent, or LC-MS methods.
• Is conserved across vertebrates, including fish and mammals.
• Serves as a target for functional genomics and CRISPR screens in lipid biology.
What Happens During lactosylceramide alpha-2,3-sialyltransferase activity?
Substrate recognition and binding
In simple terms: The enzyme grabs lactosylceramide and the sialic acid donor at the same time.
The enzyme binds lactosylceramide (cytolipin-H) and CMP-N-acetylneuraminate in an ordered or random fashion, and the reaction is influenced by the molecular species of lactosylceramide present in the membrane. Kinetic studies using 19 molecular species of lactosylceramide showed that the enzyme discriminates among them, which helps determine the final GM3 composition.
Catalytic transfer of sialic acid
In simple terms: Sialic acid is moved from CMP onto lactosylceramide, making GM3.
The enzyme catalyzes the transfer of N-acetylneuraminic acid from CMP-N-acetylneuraminate to the 3-hydroxyl group of the terminal galactose of lactosylceramide, forming an alpha-2,3 linkage and releasing CMP. This is the defining chemical step of GO:0047291 and yields alpha-N-acetylneuraminyl-2,3-beta-D-galactosyl-1,4-beta-D-glucosylceramide, also known as GM3.
Product release and downstream use
In simple terms: GM3 is released and becomes the starting material for more complex gangliosides.
After catalysis, GM3 is released and can be further sialylated or glycosylated to form more complex gangliosides. The molecular species composition of GM3 produced by this enzyme reflects the substrate pool and the enzyme's specificity, linking GO:0047291 to the broader ganglioside profile of a cell.
Membrane environment and regulation
In simple terms: The lipid surroundings change how well the enzyme works.
The activity is sensitive to membrane phospholipid composition, and changes in the lipid environment can alter the specificity and rate of GM3 synthesis. The enzyme is a Golgi membrane protein and can be released from rat liver Golgi membranes by a cathepsin D-like proteinase, suggesting proteolytic regulation of its localization.
Key Genes Involved in GO:0047291 lactosylceramide alpha-2,3-sialyltransferase activity
The genes and proteins most directly associated with GO:0047291 include the sialyltransferase enzymes that carry out this activity and the related glycosphingolipid biosynthetic machinery.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ST3GAL5 | Encodes GM3 synthase, the enzyme with lactosylceramide alpha-2,3-sialyltransferase activity | Primary gene for GO:0047291; target for KO, knock-in, and overexpression studies |
| ST3GAL1 | Alpha-2,3-sialyltransferase family member | Related sialyltransferase for comparative studies |
| ST3GAL2 | Alpha-2,3-sialyltransferase family member | Related sialyltransferase for comparative studies |
| ST3GAL3 | Alpha-2,3-sialyltransferase family member | Related sialyltransferase for comparative studies |
| ST3GAL4 | Alpha-2,3-sialyltransferase family member | Related sialyltransferase for comparative studies |
| ST3GAL6 | Alpha-2,3-sialyltransferase family member | Related sialyltransferase for comparative studies |
| B4GALT5 | Lactosylceramide synthase, produces the substrate lactosylceramide | Upstream of GO:0047291; modulates substrate supply |
| B4GALT6 | Lactosylceramide synthase, produces the substrate lactosylceramide | Upstream of GO:0047291; modulates substrate supply |
| UGCG | Glucosylceramide synthase, first step in glycosphingolipid synthesis | Upstream pathway control |
| GM3S | Alternative name for GM3 synthase | Synonym used in assay literature |
| SAT I | Historical name for lactosylceramide alpha-2,3-sialyltransferase | Used in early purification and assay studies |
| SAT IV | Monosialylganglioside-2,3-sialyltransferase | Distinct but related activity measured in the same assays |
| CMP-NeuAc transporter | Supplies CMP-N-acetylneuraminate to the Golgi | Indirect regulator of GO:0047291 |
| Cathepsin D-like protease | Releases sialyltransferases from Golgi membranes | Regulates enzyme localization |
| Lactosylceramide | Substrate lipid | Direct substrate for the reaction |
| GM3 | Product ganglioside | Readout of enzyme activity |
| CMP | Byproduct of the reaction | Can be used in coupled assays |
| CMP-N-acetylneuraminate | Sialyl donor | Essential co-substrate |
How Is lactosylceramide alpha-2,3-sialyltransferase activity Regulated?
The activity of lactosylceramide alpha-2,3-sialyltransferase is regulated at multiple levels. Its substrate supply depends on lactosylceramide synthesis and on the molecular species of lactosylceramide available in the membrane. The enzyme is a Golgi membrane protein, and its release from Golgi membranes by a cathepsin D-like proteinase provides a proteolytic mechanism that can change its localization and access to substrates. Membrane phospholipid composition also modulates the enzyme's specificity and rate, linking lipid environment to GM3 production. In addition, the expression of ST3GAL5 and related sialyltransferases controls the overall capacity for GM3 synthesis.
lactosylceramide alpha-2,3-sialyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ST3GAL5 | GM3 synthase deficiency and neurological phenotypes | Knockout and knock-in cell models |
| ST3GAL5 | Cancer ganglioside remodeling | Overexpression and point-mutation models |
| B4GALT5/B4GALT6 | Altered lactosylceramide supply in metabolic disease | Knockout of substrate-producing enzymes |
| UGCG | Glycosphingolipid storage disorders | Knockout and rescue models |
| SAT I (historical) | Ganglioside biosynthesis in liver and brain | Purified enzyme assays and membrane release studies |
Cancer and ganglioside biology
GM3 and other gangliosides produced downstream of GO:0047291 are implicated in cancer cell signaling, adhesion, and proliferation. Because the enzyme determines the molecular species of GM3, changes in its activity can alter the ganglioside profile of tumor cells and affect their behavior. Studying this activity in cancer models helps clarify how glycosphingolipid synthesis contributes to malignancy.
Neurodevelopmental and neurological disorders
ST3GAL5, the gene encoding GM3 synthase, is linked to glycosphingolipid disorders with neurological features. Loss of GM3 synthase activity can disrupt ganglioside biosynthesis in the nervous system, and the enzyme has been purified from rat brain, underscoring its importance in neural tissue. Research on GO:0047291 therefore informs neurodevelopmental disease mechanisms.
Metabolic and lipid storage conditions
Because the enzyme uses lactosylceramide, a central glycosphingolipid intermediate, its activity intersects with lipid storage and metabolic pathways. Changes in membrane phospholipid composition can alter its specificity, suggesting that metabolic states may influence GM3 synthesis. This makes GO:0047291 relevant to disorders of lipid metabolism.
From lactosylceramide alpha-2,3-sialyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of GM3 synthase alter ganglioside profiles? | ST3GAL5 knockout cell line |
| Does a specific amino acid change affect catalytic activity? | Point-mutation knock-in of ST3GAL5 |
| Can a tagged enzyme be used for localization studies? | Tagged knock-in of ST3GAL5 |
| Does overexpression increase GM3 production? | ST3GAL5 overexpression cell line |
| How does substrate supply affect activity? | Knockout of B4GALT5/B4GALT6 or UGCG |
| Can the enzyme be released from Golgi membranes? | Protease treatment of Golgi fractions |
How to Study the lactosylceramide alpha-2,3-sialyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Radioactive sialyltransferase assay | Transfer of radiolabeled sialic acid to lactosylceramide | Quantifying GM3 synthase activity in cell lysates |
| Fluorescent assay | Formation of fluorescent GM3 product | High-throughput screening |
| LC-MS | Molecular species of GM3 product | Detailed lipid profiling |
| Kinetic assay with lipid species | Substrate specificity and rate | Mechanistic enzymology |
| Enzyme purification | Biochemical properties of the enzyme | Reference enzyme characterization |
| Golgi membrane release assay | Proteolytic release of sialyltransferases | Studying localization regulation |
| Comparative enzyme assay | Activity in non-mammalian species | Evolutionary conservation studies |
| CRISPR knockout followed by assay | Causal role of ST3GAL5 | Functional genomics |
Sialyltransferase activity assays
Direct measurement of GO:0047291 uses radioactive or fluorescent CMP-N-acetylneuraminate and lactosylceramide, followed by separation of the GM3 product. A new assay for determining ganglioside sialyltransferase activities distinguishes SAT I (lactosylceramide-2,3-sialyltransferase) from SAT IV. A dedicated method for GM3 synthase activity has been described for reproducible quantification.
Kinetic and substrate specificity studies
Kinetic studies with 19 molecular species of lactosylceramide revealed how substrate structure affects the reaction rate and product composition. Such experiments are essential for understanding how GO:0047291 contributes to the molecular species composition of GM3.
Purification and biochemical characterization
The enzyme has been purified from rat brain and characterized biochemically, providing a reference for its properties. Release of the enzyme from rat liver Golgi membranes by a cathepsin D-like proteinase has also been used to study its membrane association.
Comparative and evolutionary studies
A CMPNeuAc:lactosylceramide alpha-2,3-sialyltransferase from rainbow trout hepatoma cells has been characterized, showing that the activity is conserved across vertebrates. Comparative assays help identify conserved catalytic features.
How CRISPR Can Be Used to Study GO:0047291 lactosylceramide alpha-2,3-sialyltransferase activity
Knockout
CRISPR knockout of ST3GAL5 eliminates lactosylceramide alpha-2,3-sialyltransferase activity, allowing researchers to test the consequences for GM3 and downstream gangliosides. Knockout models are useful for defining the contribution of GO:0047291 to cell signaling and lipid composition.
Point Mutation
Point mutations in ST3GAL5 can be introduced to test which residues are required for catalysis or substrate binding, linking genotype to enzyme function. Such models help validate catalytic mechanisms inferred from biochemical studies.
Knock-in
Knock-in of tagged or reporter versions of ST3GAL5 enables localization and interaction studies while preserving endogenous regulation. This is valuable for tracking the Golgi-resident enzyme in live cells.
Overexpression
Overexpression of ST3GAL5 increases GM3 synthase activity and can be used to boost GM3 production for downstream assays. Overexpression models help test whether increased activity is sufficient to change ganglioside profiles.
How EDITGENE Supports lactosylceramide alpha-2,3-sialyltransferase activity Research
Researchers studying lactosylceramide alpha-2,3-sialyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in GM3 synthesis, how specific mutations affect enzyme function, and whether restoring or increasing activity changes cellular phenotypes. EDITGENE provides the CRISPR cell models and screening services needed to answer these questions rigorously.
Contact EDITGENE today to design your custom CRISPR model for lactosylceramide alpha-2,3-sialyltransferase activity research.
Frequently Asked Questions About lactosylceramide alpha-2,3-sialyltransferase activity
What is lactosylceramide alpha-2,3-sialyltransferase activity?
It is the enzymatic activity defined by GO:0047291 that transfers sialic acid from CMP-N-acetylneuraminate to lactosylceramide to form GM3.
What genes are involved in lactosylceramide alpha-2,3-sialyltransferase activity?
The main gene is ST3GAL5, which encodes GM3 synthase; related sialyltransferases and lactosylceramide-producing enzymes also influence the pathway.
What is the reaction catalyzed by GO:0047291?
The reaction is cytolipin-H + CMP-N-acetylneuraminate = alpha-N-acetylneuraminyl-2,3-beta-D-galactosyl-1,4-beta-D-glucosylceramide + CMP, producing GM3.
What is another name for lactosylceramide alpha-2,3-sialyltransferase?
It is also called GM3 synthase, ganglioside GM3 synthase, or SAT I.
How is GM3 synthase activity measured?
It can be measured with radioactive, fluorescent, or LC-MS-based assays that detect GM3 formation from lactosylceramide.
Where is the enzyme located in the cell?
It is a Golgi membrane protein and can be released from Golgi membranes by a cathepsin D-like proteinase.
Does substrate structure affect the enzyme?
Yes, kinetic studies with 19 molecular species of lactosylceramide showed that substrate structure influences the reaction.
Is this activity conserved across species?
Yes, a similar activity has been characterized in rainbow trout hepatoma cells, indicating conservation across vertebrates.
What diseases are linked to this activity?
It is linked to cancer ganglioside remodeling, neurodevelopmental disorders involving ST3GAL5, and lipid metabolic conditions.
How can CRISPR help study this activity?
CRISPR knockout, point mutation, knock-in, and overexpression models allow causal testing of ST3GAL5 and related genes in GM3 synthesis.
Conclusion
GO:0047291, lactosylceramide alpha-2,3-sialyltransferase activity, is the defining enzymatic step for GM3 synthesis and a central node in ganglioside biology. Its dependence on substrate molecular species, membrane environment, and proteolytic regulation makes it a rich subject for biochemical and functional genomics research. With CRISPR models and sensitive activity assays, researchers can now dissect how this activity contributes to cancer, neurodevelopment, and metabolic disease.
References
- 1. Kadowaki H et al.. 1995. Relationship of membrane phospholipid composition, lactosylceramide molecular species, and the specificity of CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase to the molecular species composition of GM3 ganglioside.. J Lipid Res 36(6):1274-82 PMID: 7666005
- 2. Kadowaki H et al.. 1994. Mechanism of GM3 ganglioside synthesis. Kinetic study of rat liver CMP-N-neuraminate:lactosylceramide alpha 2,3-sialyltransferase employing 19 molecular species of lactosylceramide.. J Biol Chem 269(21):14931-8 PMID: 8195125
- 3. Preuss U et al.. 1993. Purification and characterization of CMP-N-acetylneuraminic acid:lactosylceramide (alpha 2-3) sialyltransferase (GM3-synthase) from rat brain.. J Biol Chem 268(35):26273-8 PMID: 8253749
- 4. Inamori KI et al.. 2023. Sialyltransferase Activity Assay for Ganglioside GM3 Synthase.. Methods Mol Biol 2613:101-110 PMID: 36587074
- 5. Sun CQ et al.. 2014. A new assay for determining ganglioside sialyltransferase activities lactosylceramide-2,3-sialyltransferase (SAT I) and monosialylganglioside-2,3-sialyltransferase (SAT IV).. PLoS One 9(4):e94206 PMID: 24718572
- 6. Kono M et al.. 1998. Molecular cloning and functional expression of a fifth-type alpha 2,3-sialyltransferase (mST3Gal V: GM3 synthase).. Biochem Biophys Res Commun 253(1):170-5 PMID: 9875239
- 7. Richardson K et al.. 1995. Release of sialyltransferases from rat liver Golgi membranes by a cathepsin D-like proteinase: comparison of the release of Gal beta 1-4GlcNAc alpha 2-6 sialyltransferase, Gal beta 1-3(4)GlcNAc alpha 2-3 sialyltransferase and lactosylceramide alpha 2-3 sialyltransferase (SAT-1).. Comp Biochem Physiol B Biochem Mol Biol 110(2):445-50 PMID: 7719647
- 8. Ostrander GK et al.. 1991. Characterization of a CMPNeuAc: lactosylceramide alpha 2----3sialyltransferase from rainbow trout hepatoma (RTH-149) cells.. Comp Biochem Physiol B 98(1):87-95 PMID: 2060283
