GO:0047276 N-acetyllactosaminide 3-alpha-galactosyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0047276 describes the enzymatic activity that transfers galactose from UDP-galactose to N-acetyllactosamine, forming the Galα1-3Galβ1-4GlcNAc (α-Gal) epitope.
• The enzyme responsible is α1,3-galactosyltransferase (α1,3GT), encoded by the GGTA1 gene in mammals.
• This activity is absent in humans and Old World primates due to inactivation of the GGTA1 gene, leading to natural anti-Gal antibodies.
• The α-Gal epitope is a major barrier in xenotransplantation and a target for cancer immunotherapy.
• Bacterial homologs of α1,3-galactosyltransferase exist in the human gut microbiome, potentially influencing immune responses.
• Studying GO:0047276 requires glycosylation assays, CRISPR knockout models, and glycan analysis techniques.
Description
N-acetyllactosaminide 3-alpha-galactosyltransferase activity (GO:0047276) is a molecular function that catalyzes the transfer of galactose from UDP-galactose to the N-acetyllactosamine core of glycoproteins and glycolipids, creating the Galα1-3Galβ1-4GlcNAc (α-Gal) epitope. This enzymatic activity is critical for the synthesis of terminal α-galactose-containing glycans, which are widely expressed in non-primate mammals but absent in humans and Old World primates. The α-Gal epitope is a key antigen in xenotransplantation and has been implicated in immune responses and cancer biology. Understanding GO:0047276 is therefore essential for researchers in glycobiology, transplantation, and immunotherapy.
N-acetyllactosaminide 3-alpha-galactosyltransferase activity At A Glance
| GO ID | GO:0047276 |
|---|---|
| GO term | N-acetyllactosaminide 3-alpha-galactosyltransferase activity |
| Ontology | molecular_function |
| Synonym | alpha-galactosyltransferase activity; UDP-Gal:N-acetyllactosaminide alpha-1,3-D-galactosyltransferase activity |
| Major function | Transfer of galactose to N-acetyllactosamine to form the α-Gal epitope |
| Reaction | UDP-galactose + N-acetyllactosaminide → α-1,3-galactosyl-N-acetyllactosaminide + UDP |
| Substrates | UDP-galactose (donor), N-acetyllactosamine (acceptor) |
| Localization | Golgi apparatus (as a type II membrane protein) |
| Enzyme | α1,3-galactosyltransferase (α1,3GT), encoded by GGTA1 |
What Is GO:0047276?
GO:0047276 is defined as the catalysis of the reaction: beta-D-galactosyl-(1,4)-beta-N-acetyl-D-glucosaminyl-R + UDP-galactose = alpha-D-galactosyl-(1,3)-beta-D-galactosyl-(1,4)-beta-N-acetyl-D-glucosaminyl-R + UDP. In simpler terms, it is the enzyme activity that adds a galactose molecule in an alpha-1,3 linkage to an N-acetyllactosamine acceptor, using UDP-galactose as the donor substrate.
Why Is N-acetyllactosaminide 3-alpha-galactosyltransferase activity Important in Cell Biology?
GO:0047276 is important because it governs the synthesis of the α-Gal epitope, a carbohydrate structure that plays a central role in xenotransplantation rejection and is a target for cancer immunotherapy. The absence of this activity in humans leads to the production of natural anti-Gal antibodies, which constitute a major immunological barrier. Moreover, bacterial enzymes with this activity are present in the human gut microbiome, suggesting a role in host-microbe interactions. Thus, understanding this activity has broad implications for transplantation, cancer, and microbiome research.
• The α-Gal epitope is the primary antigen responsible for hyperacute rejection in pig-to-human xenotransplantation.
• Humans and Old World primates lack α1,3GT activity and produce anti-Gal antibodies, which can be exploited for cancer immunotherapy.
• The enzyme is a target for genetic engineering to create α-Gal-free donor organs.
• Bacterial α1,3-galactosyltransferase genes in the gut microbiome may influence immune responses and disease.
• The activity is involved in the synthesis of glycolipids and glycoproteins that modulate cell signaling and adhesion.
• Studying this activity aids in understanding glycan biosynthesis and its role in development and disease.
• It serves as a model for studying enzyme evolution and gene inactivation in primates.
• Inhibitors or modulators of this activity could have therapeutic potential in transplantation and cancer.
What Happens During N-acetyllactosaminide 3-alpha-galactosyltransferase activity?
Substrate Recognition and Binding
In simple terms: The enzyme grabs UDP-galactose and the acceptor sugar.
The enzyme α1,3-galactosyltransferase binds to its donor substrate UDP-galactose and an acceptor substrate, typically N-acetyllactosamine (Galβ1-4GlcNAc-R) present on glycoproteins or glycolipids. The binding is mediated by specific amino acid residues in the catalytic domain, which ensure high specificity for the acceptor.
Catalytic Transfer of Galactose
In simple terms: The enzyme moves galactose from UDP to the acceptor, forming a new linkage.
The catalytic mechanism involves the transfer of galactose from UDP-galactose to the 3-hydroxyl group of the terminal galactose of N-acetyllactosamine, forming an α-1,3 linkage. This reaction proceeds via a glycosyltransferase mechanism, likely involving a metal ion-independent process, and results in the release of UDP.
Product Formation and Elongation
In simple terms: The new sugar structure can be further modified or displayed on the cell surface.
The product, Galα1-3Galβ1-4GlcNAc-R, is a terminal α-Gal epitope that can be further elongated by other glycosyltransferases or remain as a terminal structure. This epitope is prominently expressed on the surface of cells from non-primate mammals and is recognized by anti-Gal antibodies.
Biological Context and Regulation
In simple terms: The activity is controlled by gene expression and cellular location.
The enzyme is a type II membrane protein localized to the Golgi apparatus, where it acts in the secretory pathway. Its expression is regulated at the transcriptional level, and in humans, the gene is inactivated, leading to loss of activity. In other species, the activity can be modulated by cytokines and growth factors, although specific regulators are not fully defined.
Key Genes Involved in GO:0047276 N-acetyllactosaminide 3-alpha-galactosyltransferase activity
The following genes are directly or indirectly associated with N-acetyllactosaminide 3-alpha-galactosyltransferase activity, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| GGTA1 | Encodes α1,3-galactosyltransferase, the enzyme responsible for GO:0047276 | Knockout in pigs for xenotransplantation; target for cancer immunotherapy |
| B3GNT2 | Encodes a β1,3-N-acetylglucosaminyltransferase that can modify N-acetyllactosamine acceptors | May influence substrate availability for α1,3GT |
| B4GALT1 | Encodes β1,4-galactosyltransferase, involved in N-acetyllactosamine synthesis | Provides acceptor substrate for α1,3GT |
| B4GALT2 | β1,4-galactosyltransferase family member | Potential role in acceptor synthesis |
| B3GALT1 | β1,3-galactosyltransferase | May compete or cooperate in glycan elongation |
| B3GALT2 | β1,3-galactosyltransferase | Similar to B3GALT1 |
| B3GALT4 | β1,3-galactosyltransferase | Similar to B3GALT1 |
| B3GALT5 | β1,3-galactosyltransferase | Similar to B3GALT1 |
| B3GNT3 | β1,3-N-acetylglucosaminyltransferase | Modifies N-acetyllactosamine |
| B3GNT4 | β1,3-N-acetylglucosaminyltransferase | Modifies N-acetyllactosamine |
| B3GNT5 | β1,3-N-acetylglucosaminyltransferase | Modifies N-acetyllactosamine |
| B3GNT6 | β1,3-N-acetylglucosaminyltransferase | Modifies N-acetyllactosamine |
| B3GNT7 | β1,3-N-acetylglucosaminyltransferase | Modifies N-acetyllactosamine |
| B3GNT8 | β1,3-N-acetylglucosaminyltransferase | Modifies N-acetyllactosamine |
| FUT1 | α1,2-fucosyltransferase, competes for N-acetyllactosamine | May regulate α-Gal epitope expression |
| FUT2 | α1,2-fucosyltransferase, similar to FUT1 | May regulate α-Gal epitope expression |
| ST3GAL1 | α2,3-sialyltransferase, competes for N-acetyllactosamine | May regulate α-Gal epitope expression |
| ST6GAL1 | α2,6-sialyltransferase, competes for N-acetyllactosamine | May regulate α-Gal epitope expression |
How Is N-acetyllactosaminide 3-alpha-galactosyltransferase activity Regulated?
The expression of GGTA1, the gene encoding α1,3-galactosyltransferase, is regulated at the transcriptional level. In humans, the gene is inactivated due to mutations, leading to loss of enzyme activity. In other species, the promoter region contains binding sites for transcription factors such as Sp1 and NF-κB, although specific regulatory mechanisms are not fully elucidated. Additionally, the activity can be influenced by the availability of substrate UDP-galactose and acceptor N-acetyllactosamine, which are regulated by other glycosyltransferases.
N-acetyllactosaminide 3-alpha-galactosyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| GGTA1 | Xenotransplantation rejection | GGTA1 knockout pig cells or mice |
| GGTA1 | Cancer immunotherapy | Tumor cells overexpressing GGTA1 |
| GGTA1 | Immune response to α-Gal | Human serum antibody binding assays |
| Bacterial α1,3GT | Gut microbiome interactions | Gnotobiotic mice colonized with α1,3GT-expressing bacteria |
| GGTA1 | Evolutionary loss in primates | Comparative genomics and gene inactivation studies |
Xenotransplantation Rejection
The α-Gal epitope produced by GO:0047276 is the major xenoantigen responsible for hyperacute rejection of pig organs transplanted into humans. Humans have pre-existing anti-Gal antibodies that bind to the α-Gal epitope on pig endothelial cells, triggering complement activation and rapid graft destruction. Knocking out GGTA1 in pigs eliminates this epitope and is a key strategy to overcome rejection.
Cancer Immunotherapy
The α-Gal epitope can be exploited for cancer immunotherapy. Tumor cells engineered to express α1,3GT and thus the α-Gal epitope are recognized by anti-Gal antibodies, leading to complement-mediated lysis and enhanced antigen presentation. This approach has been tested in clinical trials for various cancers.
Microbiome and Immune Interactions
Bacterial α1,3-galactosyltransferase genes are present in the human gut microbiome, and their expression may lead to α-Gal epitope production on bacterial surfaces. This could influence host immune responses and has been linked to autoimmune and inflammatory conditions, although the exact role remains under investigation.
From N-acetyllactosaminide 3-alpha-galactosyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of GGTA1 in xenotransplantation? | GGTA1 knockout pig (CRISPR/Cas9) |
| How does α-Gal epitope affect cancer immunotherapy? | Mouse tumor models with GGTA1 overexpression |
| What is the catalytic mechanism of α1,3GT? | Point mutations in GGTA1 in cell lines |
| How does α-Gal epitope influence immune responses? | Knock-in mice expressing GGTA1 |
| What is the impact of gut bacterial α1,3GT? | Gnotobiotic mice with bacterial α1,3GT |
| How is GGTA1 regulated? | Reporter assays with GGTA1 promoter |
How to Study the N-acetyllactosaminide 3-alpha-galactosyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Radioactive glycosyltransferase assay | Enzyme activity using 14C-UDP-Gal | Kinetic studies and inhibitor screening |
| LC-MS/MS glycomics | Structure and abundance of α-Gal epitopes | Characterization of glycoproteins |
| Flow cytometry with IB4 lectin | Cell surface α-Gal expression | Phenotyping of knockout cells |
| CRISPR/Cas9 knockout | Loss of GGTA1 function | Xenotransplantation research |
| Western blot | Protein expression of α1,3GT | Validation of knockout or overexpression |
| qRT-PCR | mRNA levels of GGTA1 | Transcriptional regulation studies |
| Immunohistochemistry | Tissue distribution of α-Gal | Xenograft analysis |
| ELISA with anti-Gal antibodies | Antibody binding to α-Gal | Serum antibody titers |
Glycosyltransferase Activity Assays
Enzymatic activity of α1,3-galactosyltransferase can be measured using radioactive or fluorescently labeled UDP-galactose and acceptor substrates, followed by product separation by chromatography. These assays are essential for kinetic characterization and inhibitor screening.
Glycan Analysis by Mass Spectrometry
Mass spectrometry (e.g., MALDI-TOF, LC-MS/MS) is used to detect and quantify the α-Gal epitope on glycoproteins and glycolipids. This method provides structural confirmation and relative abundance of the product.
CRISPR/Cas9 Genome Editing
CRISPR/Cas9 is used to knock out GGTA1 in cells and animals to study the loss of α-Gal epitope and its consequences. This approach is particularly valuable for creating xenotransplantation models.
Antibody-Based Detection
Anti-Gal antibodies or lectins (e.g., Griffonia simplicifolia IB4) can be used in flow cytometry, immunofluorescence, or ELISA to detect α-Gal epitopes on cell surfaces.
How CRISPR Can Be Used to Study GO:0047276 N-acetyllactosaminide 3-alpha-galactosyltransferase activity
Knockout
CRISPR/Cas9-mediated knockout of GGTA1 eliminates α1,3-galactosyltransferase activity, resulting in loss of the α-Gal epitope. This is widely used to generate α-Gal-free pig cells and organs for xenotransplantation research.
Point Mutation
Introducing point mutations in the catalytic domain of GGTA1 can help identify critical residues for substrate binding and catalysis. Such mutants are valuable for mechanistic studies and for engineering enzymes with altered specificity.
Knock-in
Knock-in of GGTA1 into human cells or mice can restore α-Gal epitope expression, enabling studies on immune recognition and cancer immunotherapy. This approach is also used to create humanized models for α-Gal-related diseases.
Overexpression
Overexpression of GGTA1 in cell lines or tumor cells increases α-Gal epitope density, which can enhance immunogenicity and is explored in cancer vaccine strategies.
How EDITGENE Supports N-acetyllactosaminide 3-alpha-galactosyltransferase activity Research
Researchers studying N-acetyllactosaminide 3-alpha-galactosyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in α-Gal epitope synthesis, immune recognition, or disease. EDITGENE provides comprehensive CRISPR-based services to accelerate this research.
Contact EDITGENE today to design your custom CRISPR model for N-acetyllactosaminide 3-alpha-galactosyltransferase activity research.
Frequently Asked Questions About N-acetyllactosaminide 3-alpha-galactosyltransferase activity
What is N-acetyllactosaminide 3-alpha-galactosyltransferase activity?
It is the enzyme activity that transfers galactose from UDP-galactose to N-acetyllactosamine, forming the α-Gal epitope (Galα1-3Galβ1-4GlcNAc).
What gene encodes N-acetyllactosaminide 3-alpha-galactosyltransferase?
The GGTA1 gene encodes α1,3-galactosyltransferase, the enzyme responsible for this activity in mammals.
Why is this enzyme absent in humans?
The GGTA1 gene was inactivated in humans and Old World primates after divergence from monkeys, leading to loss of α-Gal epitope expression.
What diseases are associated with α-Gal epitope?
The α-Gal epitope is a major barrier in xenotransplantation and is exploited in cancer immunotherapy; it may also play a role in gut microbiome interactions.
How can I study N-acetyllactosaminide 3-alpha-galactosyltransferase activity?
You can use enzymatic assays, glycan mass spectrometry, CRISPR knockout models, and antibody-based detection methods.
What is the α-Gal epitope?
It is a carbohydrate structure Galα1-3Galβ1-4GlcNAc-R produced by α1,3-galactosyltransferase and recognized by anti-Gal antibodies.
What are the substrates of this enzyme?
The donor substrate is UDP-galactose, and the acceptor is N-acetyllactosamine (Galβ1-4GlcNAc-R).
Is this enzyme found in bacteria?
Yes, bacterial homologs of α1,3-galactosyltransferase are present in the human gut microbiome.
What is the role of α1,3-galactosyltransferase in xenotransplantation?
It produces the α-Gal epitope that triggers hyperacute rejection; knocking out GGTA1 in pigs prevents this rejection.
How is α1,3-galactosyltransferase regulated?
Its expression is primarily regulated at the transcriptional level, and in humans, the gene is inactivated.
Conclusion
N-acetyllactosaminide 3-alpha-galactosyltransferase activity (GO:0047276) is a key enzymatic function in glycobiology, responsible for the synthesis of the α-Gal epitope. Its absence in humans has profound implications for xenotransplantation and cancer immunotherapy, while its presence in other mammals and bacteria offers diverse research opportunities. Understanding this activity through CRISPR models and biochemical assays can unlock new therapeutic strategies.
References
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- 2. Blanken WM et al.. 1985. Biosynthesis of terminal Gal alpha 1----3Gal beta 1----4GlcNAc-R oligosaccharide sequences on glycoconjugates. Purification and acceptor specificity of a UDP-Gal:N-acetyllactosaminide alpha 1----3-galactosyltransferase from calf thymus.. J Biol Chem 260(24):12927-34 PMID: 3932335
- 3. Gupta S et al.. 2023. Engineering protein glycosylation in CHO cells to be highly similar to murine host cells.. Front Bioeng Biotechnol 11:1113994 PMID: 36873370
- 4. Zeyland J et al.. 2015. The current state of xenotransplantation.. J Appl Genet 56(2):211-8 PMID: 25487710
- 5. Huai G et al.. 2016. Characteristics of α-Gal epitope, anti-Gal antibody, α1,3 galactosyltransferase and its clinical exploitation (Review).. Int J Mol Med 37(1):11-20 PMID: 26531137
- 6. Montassier E et al.. 2019. Distribution of Bacterial α1,3-Galactosyltransferase Genes in the Human Gut Microbiome.. Front Immunol 10:3000 PMID: 31998300
- 7. Galili U et al.. 1991. Gene sequences suggest inactivation of alpha-1,3-galactosyltransferase in catarrhines after the divergence of apes from monkeys.. Proc Natl Acad Sci U S A 88(16):7401-4 PMID: 1908095
- 8. van den Eijnden DH et al.. 1983. Novikoff ascites tumor cells contain N-acetyllactosaminide beta 1 leads to 3 and beta 1 leads to 6 N-acetylglucosaminyltransferase activity.. J Biol Chem 258(6):3435-7 PMID: 6219989
