GO:0008118 N-acetyllactosaminide alpha-2,3-sialyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0008118 describes the enzymatic activity that transfers sialic acid from CMP-NeuAc to the 3-position of galactose on N-acetyllactosamine (Galβ1-4GlcNAc) acceptors, forming α2,3-linked sialylated glycans.
• This activity is carried out by ST3GAL family enzymes, including ST3GAL3 and ST3GAL4, which were cloned and characterized in the 1990s.
• The reaction is essential for the biosynthesis of sialyl Lewis x and related selectin ligands that mediate cell-cell adhesion and immune cell trafficking.
• Altered α2,3-sialyltransferase activity is associated with cancer progression, metastasis, and altered cell death responses in glioma and colorectal tumor models.
• Small-molecule inhibitors such as lithocholic acid analogues can modulate α2,3-sialyltransferase activity, offering chemical biology tools for functional studies.
• CRISPR-based knockout, point mutation, knock-in, and overexpression models enable precise dissection of GO:0008118 in health and disease.
Description
N-acetyllactosaminide alpha-2,3-sialyltransferase activity (GO:0008118) is a molecular function that catalyzes the transfer of sialic acid from CMP-N-acetylneuraminate to the 3-hydroxyl group of galactose in β-D-galactosyl-(1→4)-N-acetyl-β-D-glucosaminyl (N-acetyllactosamine) derivatives, generating α2,3-sialylated glycoconjugates. This activity was first detected in fetal calf liver and other tissues, establishing its broad tissue distribution. The enzyme belongs to the sialyltransferase family and is responsible for adding terminal sialic acid residues to N-acetyllactosamine units on glycoproteins and glycolipids, a modification that influences glycan recognition by lectins and antibodies. Researchers study GO:0008118 because α2,3-sialylation is critical for the biosynthesis of sialyl Lewis x (sLex) and related selectin ligands, which mediate leukocyte rolling and extravasation during inflammation. In cancer, increased α2,3-sialyltransferase activity correlates with metastatic potential and altered cell survival signaling. The availability of cloned ST3GAL genes and specific inhibitors has enabled functional studies linking this activity to cell adhesion, immune recognition, and tumor progression. Understanding GO:0008118 at the molecular level provides a foundation for developing therapeutic strategies that target sialylation in inflammatory diseases and cancer. This article integrates authoritative QuickGO annotation data with verified PubMed literature to summarize the mechanism, key genes, disease relevance, and experimental models for studying this enzymatic activity.
N-acetyllactosaminide alpha-2,3-sialyltransferase activity At A Glance
| GO ID | GO:0008118 |
|---|---|
| GO term | N-acetyllactosaminide alpha-2,3-sialyltransferase activity |
| Ontology | molecular_function |
| Synonym | alpha2->3 sialyltransferase activity; cytidine monophosphoacetylneuraminate-beta-galactosyl(1->4)acetylglucosaminide alpha2->3-sialyltransferase activity; N-acetyllactosaminide alpha-2,3-sialyltransferase; neolactotetraosylceramide alpha-2,3-sialyltransferase activity |
| Major function | Transfer of sialic acid from CMP-NeuAc to the 3-position of galactose on N-acetyllactosamine acceptors, forming α2,3-sialylated glycans. |
| Reaction direction | Forward: CMP-NeuAc + Galβ1-4GlcNAc-R → α2,3-sialyl-Galβ1-4GlcNAc-R + CMP + H+. |
| Subcellular location | Golgi apparatus (as inferred from sialyltransferase family localization). |
| Cofactor | CMP-N-acetylneuraminate as the sialic acid donor. |
| Representative genes | ST3GAL3, ST3GAL4 (formerly SIAT4C, SIAT6). |
What Is GO:0008118?
GO:0008118, N-acetyllactosaminide alpha-2,3-sialyltransferase activity, is defined as the catalysis of the reaction: a beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP-N-acetyl-beta-neuraminate = an N-acetyl-alpha-neuraminyl-(2->3)-beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP + H+. In simpler terms, this activity attaches a sialic acid molecule to a specific galactose sugar on glycans, forming an α2,3 linkage. This modification is a terminal step in glycan biosynthesis and is mediated by enzymes of the ST3GAL family.
Why Is N-acetyllactosaminide alpha-2,3-sialyltransferase activity Important in Cell Biology?
GO:0008118 is important because α2,3-sialylation of N-acetyllactosamine structures is a key determinant of glycan recognition in cell adhesion, immune surveillance, and cancer progression. This activity generates ligands for selectins and siglecs, thereby modulating leukocyte trafficking and immune cell activation. In cancer, elevated α2,3-sialyltransferase activity is linked to metastatic spread and resistance to cell death, making it a potential biomarker and therapeutic target. Moreover, specific inhibitors of α2,3-sialyltransferases provide chemical tools to probe these functions in vitro and in vivo.
• Generates sialyl Lewis x and related selectin ligands that mediate leukocyte rolling and extravasation.
• Modulates cell-cell and cell-matrix adhesion through sialylated glycan epitopes.
• Associated with enhanced metastatic potential in colorectal and other cancers.
• Influences cell death pathways in glioma cells, as shown by transfection of sialyltransferase genes.
• Provides a target for small-molecule inhibitors such as lithocholic acid analogues.
• Plays a role in nervous system development, as indicated by expression in mouse brain.
• Contributes to the diversity of cell surface glycoconjugates recognized by lectins and antibodies.
• Enables functional studies using lectin resistance selection and expression cloning.
• Serves as a model for understanding Golgi glycosyltransferase specificity and regulation.
• Has potential implications for inflammatory diseases and cancer immunotherapy.
Molecular Mechanism of N-acetyllactosaminide alpha-2,3-sialyltransferase activity
Substrate Recognition and Binding
In simple terms: The enzyme grabs a sugar chain and a sialic acid donor molecule.
The enzyme recognizes terminal N-acetyllactosamine (Galβ1-4GlcNAc) units on glycoproteins or glycolipids and binds the donor substrate CMP-N-acetylneuraminate. The acceptor specificity is determined by the galactose residue, and the enzyme forms a Michaelis complex with both substrates. Expression cloning using lectin resistance selection identified a Galβ1-3/1-4GlcNAc α2,3-sialyltransferase that preferentially uses type 1 and type 2 chains.
Catalytic Transfer of Sialic Acid
In simple terms: The enzyme snips off sialic acid from CMP and attaches it to the sugar chain.
The catalytic mechanism involves nucleophilic attack by the 3-hydroxyl group of galactose on the anomeric carbon of sialic acid in CMP-NeuAc, resulting in the formation of an α2,3-glycosidic bond and release of CMP and H+. This reaction is characteristic of retaining glycosyltransferases, although the exact stereochemical course for α2,3-sialyltransferases has been studied through kinetic and structural approaches.
Cofactors and Metal Ion Requirements
In simple terms: No special metal helpers are needed; the enzyme uses CMP-NeuAc directly.
Unlike many glycosyltransferases, α2,3-sialyltransferases do not require divalent metal ions for activity. The donor substrate CMP-NeuAc serves as both the sialic acid donor and the energy source for the transfer reaction. The enzyme's activity is dependent on the availability of CMP-NeuAc in the Golgi lumen, which is supplied by specific transporters.
Regulation by Small Molecules and Inhibitors
In simple terms: Certain chemicals can block the enzyme's ability to add sialic acid.
Lithocholic acid analogues have been identified as potent inhibitors of α2,3-sialyltransferase activity, providing chemical tools to modulate sialylation in cells. These inhibitors can be used to probe the biological consequences of reduced α2,3-sialylation, such as altered cell adhesion or signaling. Additionally, the enzyme's activity can be regulated at the transcriptional level, as shown by changes in sialyltransferase gene expression during tumor progression.
Subcellular Localization and Topology
In simple terms: The enzyme works inside the Golgi apparatus, a cellular compartment for modifying proteins and lipids.
α2,3-sialyltransferases are type II membrane proteins localized to the Golgi apparatus, where they catalyze the terminal step of glycan biosynthesis. Their catalytic domain faces the lumen of the Golgi, allowing access to both donor and acceptor substrates. The Golgi localization is mediated by N-terminal cytoplasmic and transmembrane domains, which are conserved across the sialyltransferase family.
Key Genes Involved in GO:0008118 N-acetyllactosaminide alpha-2,3-sialyltransferase activity
The following genes encode enzymes with N-acetyllactosaminide alpha-2,3-sialyltransferase activity or are directly involved in its regulation and function.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ST3GAL3 | Encodes a Galβ1-3/1-4GlcNAc α2,3-sialyltransferase that synthesizes sialyl Lewis x and related structures. | Used in expression cloning and lectin resistance studies; implicated in brain development. |
| ST3GAL4 | Encodes a Galβ1-3(4)GlcNAc α2,3-sialyltransferase with broad acceptor specificity. | First sialyltransferase cloned by mass spectrometry; model for enzyme structure-function studies. |
| ST3GAL1 | Encodes a Galβ1-3GalNAc α2,3-sialyltransferase (also known as SIAT4A). | Studied in mouse brain; involved in ganglioside biosynthesis. |
| ST3GAL2 | Encodes a Galβ1-3GalNAc α2,3-sialyltransferase with specificity for O-glycans. | Relevant for mucin-type O-glycan sialylation. |
| ST3GAL5 | Encodes a GM3 synthase (α2,3-sialyltransferase) that acts on lactosylceramide. | Involved in ganglioside biosynthesis; potential role in cancer and neurodevelopment. |
| ST3GAL6 | Encodes an α2,3-sialyltransferase that modifies N-glycans and glycolipids. | Associated with selectin ligand synthesis and cancer metastasis. |
| ST6GAL1 | Encodes a β-galactoside α2,6-sialyltransferase, a related enzyme with distinct linkage specificity. | Often studied in parallel to contrast α2,3 versus α2,6 sialylation in cancer. |
| FUT4 | Encodes fucosyltransferase 4, which acts downstream of α2,3-sialylation to form sialyl Lewis x. | Cooperates with ST3GAL genes in selectin ligand biosynthesis. |
| FUT7 | Encodes fucosyltransferase 7, involved in sialyl Lewis x synthesis on leukocytes. | Relevant for immune cell trafficking studies. |
| B4GALT1 | Encodes β1,4-galactosyltransferase 1, which generates the N-acetyllactosamine acceptor for α2,3-sialylation. | Upstream enzyme in the pathway; knockout models affect sialylation. |
| B3GNT2 | Encodes β1,3-N-acetylglucosaminyltransferase 2, which extends poly-N-acetyllactosamine chains. | Modulates acceptor availability for α2,3-sialyltransferases. |
| GNE | Encodes UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase, regulating sialic acid biosynthesis. | Affects global sialylation including α2,3-linked structures. |
| SLC35A1 | Encodes a CMP-sialic acid transporter that supplies CMP-NeuAc to the Golgi. | Loss-of-function reduces all sialylation, including α2,3-linked glycans. |
| NEU1 | Encodes sialidase 1 (lysosomal), which can remove sialic acid from glycoconjugates. | Counteracts sialyltransferase activity; relevant in lysosomal storage disorders. |
| NEU3 | Encodes a plasma membrane sialidase that specifically hydrolyzes α2,3-linked sialic acids. | Modulates cell surface sialylation and signaling. |
| SELPLG | Encodes P-selectin glycoprotein ligand-1, a major carrier of sialyl Lewis x. | Functional readout for α2,3-sialyltransferase activity in leukocytes. |
| CD44 | Cell surface glycoprotein that carries sialylated glycans and modulates adhesion. | Used as a model substrate to study sialylation changes in cancer. |
| EGFR | Receptor tyrosine kinase whose sialylation affects signaling and dimerization. | Studied in glioma cells with altered sialyltransferase expression. |
How Is N-acetyllactosaminide alpha-2,3-sialyltransferase activity Regulated?
The activity of N-acetyllactosaminide alpha-2,3-sialyltransferase is regulated at multiple levels. Transcriptionally, expression of ST3GAL genes can be induced during tumor progression, as shown by enhanced sialyltransferase activity in metastasizing colorectal tumor tissue and xenografts. Post-translationally, the enzyme's Golgi localization and stability are controlled by its transmembrane domain and interactions with other Golgi proteins. Substrate availability, particularly the concentration of CMP-NeuAc in the Golgi lumen, is a key determinant of activity, and the CMP-sialic acid transporter SLC35A1 regulates this pool. Additionally, small-molecule inhibitors such as lithocholic acid analogues can acutely modulate enzyme activity, providing a means for chemical regulation. Sialidases like NEU3 can remove α2,3-linked sialic acids, creating a dynamic balance between sialylation and desialylation.
N-acetyllactosaminide alpha-2,3-sialyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ST3GAL3 | Neurodevelopmental disorders; brain ganglioside synthesis | Knockout mouse or human iPSC-derived neurons |
| ST3GAL4 | Cancer metastasis; selectin ligand synthesis | Xenograft models with overexpression or knockout |
| ST6GAL1 | Colorectal cancer; altered sialylation | Colon cancer cell lines with CRISPR knockout |
| NEU3 | Cancer; sialidase-mediated desialylation | Overexpression in glioma cell lines |
| SLC35A1 | Congenital disorder of glycosylation; global sialylation defect | Patient-derived fibroblasts with complementation |
Cancer Progression and Metastasis
Enhanced α2,3-sialyltransferase activity is associated with metastatic spread in colorectal cancer, where increased sialylation of tumor cell surface glycans promotes adhesion and invasion. In glioma cells, transfection of α2,3-sialyltransferase genes alters glycoconjugate expression and enhances cell death, suggesting a complex role in tumor cell survival. These findings indicate that GO:0008118 contributes to cancer biology and may be a therapeutic target.
Inflammatory and Immune Disorders
α2,3-Sialylation is required for the biosynthesis of sialyl Lewis x, a selectin ligand that mediates leukocyte rolling and extravasation during inflammation. Dysregulated expression of ST3GAL genes can alter immune cell trafficking and contribute to chronic inflammatory diseases. Targeting this activity with inhibitors may modulate inflammatory responses.
Neurological Development and Disease
ST3GAL3 and ST3GAL1 are expressed in the brain, where they participate in ganglioside biosynthesis. Altered sialylation has been implicated in neurodevelopmental disorders and neurodegeneration, although the precise mechanisms remain under investigation. Model systems with modified sialyltransferase activity are valuable for studying these processes.
From N-acetyllactosaminide alpha-2,3-sialyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of ST3GAL4 reduce sialyl Lewis x and metastasis? | ST3GAL4 knockout cancer cell line in xenograft assay |
| What is the effect of a point mutation in the catalytic domain of ST3GAL3? | CRISPR point-mutation knock-in in HEK293 or CHO cells |
| Can a tagged ST3GAL4 be used to track Golgi localization? | Knock-in of fluorescent tag at the endogenous locus |
| Does overexpression of ST3GAL3 enhance cell death in glioma? | Stable overexpression in U-373 MG cells |
| What is the impact of ST3GAL6 knockout on selectin binding? | Knockout in HL-60 or other leukocyte cell lines |
| Can small-molecule inhibitors phenocopy genetic loss of α2,3-sialyltransferase? | Chemical inhibition in wild-type cells followed by lectin staining |
How to Study the N-acetyllactosaminide alpha-2,3-sialyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Lectin blotting | Presence of α2,3-linked sialic acids on glycoproteins | Validation of sialyltransferase knockout or overexpression |
| Flow cytometry with lectins | Cell surface α2,3-sialylation | Immune cell phenotyping and cancer cell analysis |
| Radioactive enzyme assay | Sialyltransferase activity in lysates | Kinetic studies and inhibitor screening |
| Mass spectrometry glycomics | Detailed glycan structures including α2,3 linkages | Global profiling of sialylation changes |
| Expression cloning | Isolation of cDNAs conferring lectin resistance | Discovery of novel sialyltransferases |
| CRISPR knockout screening | Genes required for α2,3-sialylation | Functional genomics of glycosylation |
| Immunofluorescence | Subcellular localization of sialyltransferases | Golgi localization studies |
| qRT-PCR | mRNA levels of ST3GAL genes | Transcriptional regulation in cancer |
Lectin-Based Detection of α2,3-Sialylation
Lectin blotting or flow cytometry with α2,3-sialic acid-specific lectins (e.g., Maackia amurensis lectin) allows direct measurement of α2,3-sialylated glycans on cell surfaces or in cell lysates. This method is widely used to validate changes in sialyltransferase activity after genetic manipulation.
Enzymatic Activity Assays
In vitro sialyltransferase assays using radiolabeled CMP-[3H]NeuAc and defined acceptor substrates (e.g., N-acetyllactosamine) quantify enzyme activity in cell lysates or Golgi fractions. Such assays were instrumental in the initial detection of α2,3-sialyltransferase activity in fetal calf liver.
Expression Cloning and Lectin Resistance Selection
Expression cloning using lectin resistance selection identified the first Galβ1-3/1-4GlcNAc α2,3-sialyltransferase by transfecting cDNA libraries into cells and selecting for resistance to cytotoxic lectins. This approach remains useful for isolating novel sialyltransferases or mutant variants.
CRISPR Screening and Glycan Profiling
Genome-wide CRISPR knockout screens coupled with lectin staining or mass spectrometry-based glycomics can identify genes that regulate α2,3-sialylation. Such screens have revealed networks of glycosyltransferases and transporters that control sialyl Lewis x expression.
How CRISPR Can Be Used to Study GO:0008118 N-acetyllactosaminide alpha-2,3-sialyltransferase activity
Knockout
CRISPR knockout of ST3GAL genes (e.g., ST3GAL3, ST3GAL4) eliminates α2,3-sialyltransferase activity, leading to loss of sialyl Lewis x and altered cell adhesion. These models are used to study the role of GO:0008118 in cancer metastasis and immune cell trafficking.
Point Mutation
Introducing point mutations in the catalytic domain of ST3GAL enzymes via CRISPR base editing or homology-directed repair allows dissection of substrate specificity and catalytic mechanism. Such mutants can be expressed in cells to assess loss-of-function or gain-of-function phenotypes.
Knock-in
Knock-in of epitope tags (e.g., FLAG, HA) or fluorescent proteins at the endogenous ST3GAL locus enables real-time tracking of enzyme localization and interaction partners in the Golgi. This approach preserves endogenous regulatory elements and expression levels.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression of ST3GAL genes increases α2,3-sialyltransferase activity, allowing gain-of-function studies. Overexpression in glioma cells enhanced cell death, demonstrating the utility of this approach for studying disease mechanisms.
How EDITGENE Supports N-acetyllactosaminide alpha-2,3-sialyltransferase activity Research
Researchers studying N-acetyllactosaminide alpha-2,3-sialyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in glycan biosynthesis, cell adhesion, or disease progression. EDITGENE provides a comprehensive suite of CRISPR-based services to generate precisely engineered cell models for functional validation of GO:0008118 and its associated genes.
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Frequently Asked Questions About N-acetyllactosaminide alpha-2,3-sialyltransferase activity
What is N-acetyllactosaminide alpha-2,3-sialyltransferase activity?
It is the enzymatic activity (GO:0008118) that transfers sialic acid from CMP-NeuAc to the 3-position of galactose on N-acetyllactosamine acceptors, forming α2,3-linked sialylated glycans.
What genes are involved in N-acetyllactosaminide alpha-2,3-sialyltransferase activity?
The main genes are ST3GAL3 and ST3GAL4, which encode α2,3-sialyltransferases, along with other ST3GAL family members such as ST3GAL1, ST3GAL2, ST3GAL5, and ST3GAL6.
What is the reaction catalyzed by GO:0008118?
The reaction is: a beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP-N-acetyl-beta-neuraminate = an N-acetyl-alpha-neuraminyl-(2->3)-beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP + H+.
How is α2,3-sialyltransferase activity measured?
It is measured using in vitro enzyme assays with radiolabeled CMP-NeuAc and defined acceptors, or by lectin blotting/flow cytometry with α2,3-sialic acid-specific lectins.
What diseases are associated with altered α2,3-sialyltransferase activity?
Altered activity is linked to cancer metastasis, inflammatory disorders, and neurological conditions, as shown in colorectal cancer and glioma models.
Can CRISPR be used to study GO:0008118?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models allow precise manipulation of ST3GAL genes to study the function of α2,3-sialyltransferase activity.
What are the inhibitors of α2,3-sialyltransferase?
Lithocholic acid analogues have been identified as potent inhibitors of α2,3-sialyltransferase activity, useful for chemical biology studies.
Where is α2,3-sialyltransferase located in the cell?
It is a Golgi-resident enzyme, with its catalytic domain facing the Golgi lumen where it modifies glycoproteins and glycolipids.
What is the difference between α2,3- and α2,6-sialyltransferase?
α2,3-Sialyltransferases add sialic acid to the 3-position of galactose, while α2,6-sialyltransferases add it to the 6-position; they have distinct acceptor specificities and biological roles.
How does α2,3-sialylation affect immune cell function?
It generates sialyl Lewis x, a selectin ligand that mediates leukocyte rolling and extravasation during inflammation.
Conclusion
N-acetyllactosaminide alpha-2,3-sialyltransferase activity (GO:0008118) is a fundamental enzymatic function that shapes cell surface glycans and influences diverse biological processes, from immune cell trafficking to cancer progression. The cloning and characterization of ST3GAL genes have provided critical tools to dissect this activity, while small-molecule inhibitors and CRISPR models enable precise functional studies. Continued research into GO:0008118 will likely uncover new therapeutic opportunities for inflammatory diseases and cancer.
References
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- 5. Dall'Olio F et al.. 1992. Enhanced CMP-NeuAc:Gal beta 1,4GlcNAc-R alpha 2,6 sialyltransferase activity of human colon cancer xenografts in athymic nude mice and of xenograft-derived cell lines.. Int J Cancer 50(2):325-30 PMID: 1730528
- 6. Lee YC et al.. 1993. Molecular cloning and expression of Gal beta 1,3GalNAc alpha 2,3-sialyltransferase from mouse brain.. Eur J Biochem 216(2):377-85 PMID: 8375377
- 7. Wen DX et al.. 1992. Primary structure of Gal beta 1,3(4)GlcNAc alpha 2,3-sialyltransferase determined by mass spectrometry sequence analysis and molecular cloning. Evidence for a protein motif in the sialyltransferase gene family.. J Biol Chem 267(29):21011-9 PMID: 1400416
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