GO:0004573 Glc3Man9GlcNAc2 oligosaccharide glucosidase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004573 describes the enzymatic activity that removes the terminal glucose from the Glc3Man9GlcNAc2 oligosaccharide, the first step in N-linked glycoprotein processing.
• This activity is catalyzed by glucosidase I, encoded by CWH41 in yeast and homologous genes in higher organisms.
• The reaction occurs in the endoplasmic reticulum and is essential for glycoprotein folding and quality control.
• Defects in glucosidase I can lead to congenital disorders of glycosylation and other pathologies.
• Studying this activity helps understand viral glycoprotein processing and potential antiviral targets.
• CRISPR-based models (knockout, point mutation, knock-in, overexpression) enable precise functional dissection of glucosidase I in health and disease.
Description
Glc3Man9GlcNAc2 oligosaccharide glucosidase activity (GO:0004573) is a molecular function that catalyzes the exohydrolysis of the non-reducing terminal glucose residue from the mannosyl-oligosaccharide Glc3Man9GlcNAc2. This activity is the first committed step in the processing of N-linked glycans, a pathway that is highly conserved from yeast to humans. The enzyme responsible, glucosidase I, trims the terminal glucose to generate Glc2Man9GlcNAc2, which is further processed by glucosidase II and other glycosidases. This trimming is critical for the interaction of glycoproteins with lectin chaperones calnexin and calreticulin, thereby influencing protein folding, quality control, and degradation. Researchers study this activity to understand fundamental glycobiology, viral pathogenesis, and inherited disorders of glycosylation.
Glc3Man9GlcNAc2 oligosaccharide glucosidase activity At A Glance
| GO ID | GO:0004573 |
|---|---|
| GO term | Glc3Man9GlcNAc2 oligosaccharide glucosidase activity |
| Ontology | molecular_function |
| Synonym | mannosyl-oligosaccharide glucohydrolase activity; mannosyl-oligosaccharide glucosidase activity; processing A-glucosidase I activity; trimming glucosidase I |
| Major function | Removes the terminal glucose from Glc3Man9GlcNAc2 during N-linked glycan processing |
| Substrate | Glc3Man9GlcNAc2 oligosaccharide |
| Product | Glc2Man9GlcNAc2 oligosaccharide and free glucose |
| Cellular location | Endoplasmic reticulum membrane |
| Representative enzyme | Glucosidase I (CWH41 in yeast, MOGS in humans) |
What Is GO:0004573?
GO:0004573 is defined as the catalysis of the exohydrolysis of the non-reducing terminal glucose residue in the mannosyl-oligosaccharide Glc3Man9GlcNAc2. In simpler terms, it is the enzymatic removal of the outermost glucose from a specific three-glucose-capped N-linked glycan precursor, a key trimming reaction in the endoplasmic reticulum.
Why Is Glc3Man9GlcNAc2 oligosaccharide glucosidase activity Important in Cell Biology?
Glc3Man9GlcNAc2 oligosaccharide glucosidase activity is essential for the early steps of N-linked glycosylation, a process that affects the folding, stability, and function of a vast array of secreted and membrane proteins. By removing the terminal glucose, it generates the monoglucosylated glycan that serves as a ligand for the lectin chaperones calnexin and calreticulin, thereby coupling glycan processing to protein folding and quality control. This activity is also exploited by enveloped viruses, such as HIV and influenza, which rely on host glycosylation machinery for the proper folding of their envelope glycoproteins. Consequently, inhibitors of glucosidase I have been explored as antiviral and anticancer agents. Moreover, mutations in the human glucosidase I gene (MOGS) cause a congenital disorder of glycosylation (CDG-IIb), highlighting its clinical relevance.
• Initiates the trimming of N-linked glycans, a prerequisite for glycoprotein maturation.
• Generates monoglucosylated glycans that interact with calnexin/calreticulin to promote proper folding.
• Plays a role in ER-associated degradation (ERAD) of misfolded glycoproteins.
• Is a target for antiviral drugs because many enveloped viruses depend on host glycosylation.
• Defects cause congenital disorders of glycosylation, such as CDG-IIb.
• Inhibitors like pseudo-aminosugars can block glucosidase I and alter glycan processing.
• The activity is conserved across eukaryotes, from yeast to plants and mammals.
• Its study informs biotechnological production of therapeutic glycoproteins with defined glycan structures.
What Happens During Glc3Man9GlcNAc2 oligosaccharide glucosidase activity?
Substrate recognition and binding
In simple terms: The enzyme grabs the sugar chain and positions the terminal glucose for removal.
Glucosidase I specifically recognizes the Glc3Man9GlcNAc2 oligosaccharide, which is transferred en bloc to nascent polypeptides in the ER. The enzyme binds the substrate through interactions with the three terminal glucose residues, with the terminal alpha-1,2-linked glucose being the first to be cleaved. This specificity ensures that only properly assembled lipid-linked oligosaccharides are processed.
Catalytic hydrolysis of the terminal glucose
In simple terms: The enzyme cuts off the outermost glucose molecule using water.
The catalytic mechanism involves exohydrolysis, where a water molecule attacks the glycosidic bond between the terminal glucose and the underlying mannose, releasing free glucose and leaving Glc2Man9GlcNAc2. This reaction is stereospecific and requires no metal cofactors, as shown for the purified yeast and plant enzymes.
Product release and downstream processing
In simple terms: After the glucose is removed, the trimmed glycan is handed off to the next enzyme.
Following the removal of the first glucose, the resulting Glc2Man9GlcNAc2 is further trimmed by glucosidase II, which removes the remaining two glucose residues. This sequential processing is essential for the glycoprotein to enter the calnexin/calreticulin cycle and achieve its native conformation.
Role in glycoprotein folding and quality control
In simple terms: The trimmed sugar acts like a tag that helps proteins fold correctly.
The monoglucosylated glycan generated by glucosidase I (and later by glucosidase II) is recognized by the lectin chaperones calnexin and calreticulin, which retain the glycoprotein in the ER until it folds properly. If folding fails, the protein is targeted for degradation via the ERAD pathway. Thus, glucosidase I activity is a key determinant of glycoprotein fate.
Key Genes Involved in GO:0004573 Glc3Man9GlcNAc2 oligosaccharide glucosidase activity
The following genes and proteins are directly or indirectly involved in Glc3Man9GlcNAc2 oligosaccharide glucosidase activity and its associated pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CWH41 (yeast) | Encodes glucosidase I, the enzyme that removes the terminal glucose from Glc3Man9GlcNAc2 | Model for studying glucosidase I function and N-glycan processing in yeast |
| MOGS (human) | Encodes human glucosidase I; mutations cause CDG-IIb | Disease modeling, drug target for antiviral and anticancer therapies |
| GANAB (human) | Encodes glucosidase II alpha subunit; removes remaining glucose residues | Downstream processing, ER quality control |
| PRKCSH (human) | Encodes glucosidase II beta subunit; regulates glucosidase II activity | Polycystic liver disease, glycoprotein folding |
| CANX (human) | Calnexin, a lectin chaperone that binds monoglucosylated glycans | Protein folding, ER quality control |
| CALR (human) | Calreticulin, a soluble lectin chaperone | Protein folding, calcium homeostasis |
| UGGT1 (human) | UDP-glucose:glycoprotein glucosyltransferase, re-glucosylates misfolded glycoproteins | ER quality control, glycoprotein folding sensor |
| EDEM1 (human) | ER degradation-enhancing alpha-mannosidase-like protein 1, targets misfolded glycoproteins for ERAD | ER-associated degradation |
| SEC61A1 (human) | Core component of the ER translocon; facilitates entry of nascent polypeptides | Co-translational translocation, glycoprotein biogenesis |
| OST (oligosaccharyltransferase complex) | Transfers Glc3Man9GlcNAc2 from dolichol to asparagine residues | N-linked glycosylation initiation |
| DOLK (human) | Dolichol kinase, required for dolichol-linked oligosaccharide synthesis | Congenital disorders of glycosylation |
| ALG5 (human) | Dolichyl-phosphate beta-glucosyltransferase, adds glucose to lipid-linked oligosaccharide | Biosynthesis of the Glc3Man9GlcNAc2 precursor |
| ALG6 (human) | Alpha-1,3-glucosyltransferase, adds first glucose to Man9GlcNAc2 | CDG-Ic, glycan precursor assembly |
| ALG8 (human) | Alpha-1,3-glucosyltransferase, adds second glucose | CDG-Ih, glycan precursor assembly |
| ALG10 (human) | Alpha-1,2-glucosyltransferase, adds third glucose | CDG-Ip, glycan precursor assembly |
| MOGS (mouse) | Mouse ortholog of glucosidase I; knockout causes glycosylation defects | Animal model for CDG-IIb and viral pathogenesis |
| GCS1 (yeast) | Glucosidase I gene in S. cerevisiae, ortholog of CWH41 | Yeast genetics, N-glycan processing |
| ROT2 (yeast) | Glucosidase II gene in yeast | Downstream processing, ER quality control |
How Is Glc3Man9GlcNAc2 oligosaccharide glucosidase activity Regulated?
The activity of glucosidase I is primarily regulated at the level of gene expression and by the availability of its substrate. In yeast, CWH41 expression is induced under conditions of ER stress, suggesting a role for the unfolded protein response (UPR) in modulating glucosidase I levels. In mammalian cells, the UPR also upregulates genes involved in ER quality control, including MOGS, to cope with increased folding demand. Additionally, the activity can be inhibited by specific inhibitors such as castanospermine and pseudo-aminosugars, which mimic the terminal glucose and block the enzyme's active site. These inhibitors are valuable tools for studying the role of glucosidase I in glycoprotein processing and viral replication.
Glc3Man9GlcNAc2 oligosaccharide glucosidase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MOGS | CDG-IIb (congenital disorder of glycosylation type IIb) | Patient fibroblasts, MOGS knockout HEK293 cells, mouse model |
| MOGS | Viral infection (HIV, HCV, influenza) | MOGS knockout cell lines, viral replication assays |
| MOGS | Cancer progression and metastasis | MOGS knockdown in cancer cell lines, xenograft models |
| CWH41 (yeast) | N-glycan processing defects | Yeast deletion strains, growth assays |
| GANAB | Polycystic liver disease, CDG-II | GANAB knockout cell lines, zebrafish models |
Congenital Disorders of Glycosylation (CDG)
Mutations in the human MOGS gene, which encodes glucosidase I, cause CDG-IIb, a severe multisystem disorder characterized by developmental delay, seizures, and dysmorphic features. This highlights the critical role of Glc3Man9GlcNAc2 oligosaccharide glucosidase activity in normal development. Studies using patient-derived fibroblasts and animal models have shown that loss of glucosidase I leads to accumulation of Glc3Man9GlcNAc2 on glycoproteins and impaired folding of secretory proteins.
Viral infections
Many enveloped viruses, including HIV, hepatitis C, and influenza, depend on host N-linked glycosylation for the proper folding of their envelope glycoproteins. Glucosidase I inhibitors, such as castanospermine, have been shown to impair viral replication by preventing the trimming of viral glycans, thereby blocking interaction with calnexin and reducing infectivity. This makes glucosidase I a potential broad-spectrum antiviral target.
Cancer
Altered glycosylation is a hallmark of cancer, and glucosidase I activity can influence tumor progression by modulating cell surface glycoproteins involved in adhesion, signaling, and immune recognition. Inhibitors of glucosidase I have been investigated for their ability to reduce metastasis and enhance the efficacy of immunotherapies, although further research is needed to establish clinical utility.
From Glc3Man9GlcNAc2 oligosaccharide glucosidase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the effect of glucosidase I loss on glycoprotein folding? | MOGS knockout HEK293 or HeLa cells; pulse-chase labeling with [35S]methionine |
| How does a specific point mutation in MOGS affect enzyme activity? | Point-mutation knock-in cell lines (e.g., MOGS catalytic mutant) generated by CRISPR |
| Can glucosidase I be tagged for live-cell imaging? | Knock-in of fluorescent tags (e.g., GFP) at the endogenous MOGS locus |
| What is the impact of glucosidase I overexpression on viral replication? | Overexpression of MOGS in permissive cells followed by viral infection |
| Which genes interact with glucosidase I in the ER? | Proximity-dependent biotinylation (BioID) with knock-in MOGS-BirA |
| Does loss of glucosidase I alter the cell surface glycome? | MOGS knockout cells analyzed by lectin microarrays or mass spectrometry |
How to Study the Glc3Man9GlcNAc2 oligosaccharide glucosidase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Fluorogenic glucosidase assay | Enzymatic activity of glucosidase I | Screening for inhibitors or characterizing mutants |
| Mass spectrometry of N-glycans | Glycan structures and glucose trimming | CDG diagnosis, glycoengineering |
| CRISPR knockout screens | Genes affecting glucosidase I function or viral replication | Identifying host factors in viral infection |
| Pulse-chase metabolic labeling | Folding and degradation kinetics of glycoproteins | ER quality control studies |
| Co-immunoprecipitation | Interaction of glycoproteins with calnexin/calreticulin | Chaperone cycle analysis |
| Lectin microarray | Cell surface glycan profile | Cancer glycomics, biomarker discovery |
| Site-directed mutagenesis | Structure-function relationships of glucosidase I | Mapping catalytic residues |
| X-ray crystallography | Three-dimensional structure of glucosidase I | Rational drug design |
Enzymatic assays for glucosidase I activity
Glucosidase I activity can be measured using fluorogenic or radiolabeled substrates, such as 4-methylumbelliferyl-alpha-D-glucopyranoside or [3H]glucose-labeled Glc3Man9GlcNAc2. These assays are typically performed with microsomal fractions or purified enzyme and can be used to assess the impact of mutations or inhibitors.
Glycan analysis by mass spectrometry
Mass spectrometry (e.g., MALDI-TOF or LC-ESI-MS) of released N-glycans is a powerful method to determine the extent of glucose trimming in cells or tissues. This approach can reveal accumulation of Glc3Man9GlcNAc2 in glucosidase I-deficient samples and is widely used for CDG diagnostics.
CRISPR-based genetic screens
Genome-wide CRISPR knockout screens can identify genes that modulate glucosidase I activity or its downstream effects. For example, a screen for resistance to glucosidase I inhibitors or for altered viral replication can uncover novel regulators. Such screens often use lentiviral sgRNA libraries and deep sequencing to quantify sgRNA enrichment.
Protein folding and ER quality control assays
The role of glucosidase I in glycoprotein folding can be studied using pulse-chase metabolic labeling, co-immunoprecipitation with calnexin/calreticulin, and ERAD assays. These methods track the fate of newly synthesized glycoproteins and assess the impact of glucosidase I loss on folding kinetics and degradation.
How CRISPR Can Be Used to Study GO:0004573 Glc3Man9GlcNAc2 oligosaccharide glucosidase activity
Knockout
CRISPR-Cas9 knockout of MOGS or CWH41 generates cell lines completely lacking glucosidase I activity. These models are invaluable for studying the consequences of blocked glycan trimming, including accumulation of Glc3Man9GlcNAc2, ER stress, and altered viral susceptibility. Knockout cells can be validated by western blotting and enzymatic assays.
Point Mutation
Introducing specific point mutations (e.g., in the catalytic domain of MOGS) via CRISPR prime editing or homology-directed repair allows precise dissection of enzyme mechanism and substrate specificity. Such models can mimic patient mutations found in CDG-IIb and help determine genotype-phenotype correlations.
Knock-in
Knock-in of epitope tags (e.g., FLAG, HA) or fluorescent proteins (e.g., GFP) at the endogenous MOGS locus enables live-cell imaging, immunoprecipitation, and proteomic studies of glucosidase I in its native context. This approach avoids artifacts from overexpression and provides physiological expression levels.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression of MOGS can be used to study the effects of increased glucosidase I activity on glycoprotein processing, viral replication, and cell viability. Overexpression models are particularly useful for testing whether enhanced trimming protects against ER stress or alters the glycome.
How EDITGENE Supports Glc3Man9GlcNAc2 oligosaccharide glucosidase activity Research
Researchers studying Glc3Man9GlcNAc2 oligosaccharide glucosidase activity-related genes often need to determine whether a candidate gene is causally involved in glycan processing, protein folding, or disease. EDITGENE provides a comprehensive suite of CRISPR services to generate precisely engineered cell models, enabling rigorous functional studies.
Contact EDITGENE today to design your custom CRISPR model for Glc3Man9GlcNAc2 oligosaccharide glucosidase activity research.
Frequently Asked Questions About Glc3Man9GlcNAc2 oligosaccharide glucosidase activity
What is Glc3Man9GlcNAc2 oligosaccharide glucosidase activity?
It is the enzymatic activity (GO:0004573) that removes the terminal glucose from the Glc3Man9GlcNAc2 oligosaccharide, the first step in N-linked glycan processing.
What genes are involved in Glc3Man9GlcNAc2 oligosaccharide glucosidase activity?
The main gene is MOGS in humans (CWH41 in yeast), which encodes glucosidase I. Other genes like GANAB and PRKCSH are involved in downstream processing.
Where does this activity occur in the cell?
It occurs in the endoplasmic reticulum membrane, where newly synthesized glycoproteins are processed.
What diseases are associated with defects in this activity?
Mutations in MOGS cause congenital disorder of glycosylation type IIb (CDG-IIb), and the activity is also implicated in viral infections and cancer.
How can I study glucosidase I activity in the lab?
Common methods include fluorogenic enzyme assays, mass spectrometry of N-glycans, and CRISPR knockout cell models.
What are the inhibitors of glucosidase I?
Inhibitors include castanospermine and pseudo-aminosugars, which block the enzyme and are used as antiviral and research tools.
Is glucosidase I conserved across species?
Yes, glucosidase I is conserved from yeast to humans, with orthologs in plants and other eukaryotes.
What is the role of glucosidase I in protein folding?
It generates monoglucosylated glycans that interact with calnexin and calreticulin, promoting proper folding and quality control.
Can CRISPR be used to create models for glucosidase I research?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are widely used to study glucosidase I function and disease.
What is the difference between glucosidase I and glucosidase II?
Glucosidase I removes the terminal glucose from Glc3Man9GlcNAc2, while glucosidase II removes the remaining two glucose residues in subsequent steps.
Conclusion
Glc3Man9GlcNAc2 oligosaccharide glucosidase activity (GO:0004573) is a fundamental enzymatic function in the N-linked glycosylation pathway, catalyzed by glucosidase I. Its role in glycoprotein folding, viral pathogenesis, and congenital disorders makes it a compelling target for basic and translational research. Advances in CRISPR genome editing now allow precise manipulation of the responsible genes, enabling detailed mechanistic studies and the development of novel therapeutic strategies. EDITGENE's comprehensive CRISPR services support researchers in creating tailored cell models to explore this critical activity.
References
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- 2. Herscovics A. 1999. Processing glycosidases of Saccharomyces cerevisiae.. Biochim Biophys Acta 1426(2):275-85 PMID: 9878780
- 3. Rush JS et al.. 1998. Topological studies on the enzymes catalyzing the biosynthesis of Glc-P-dolichol and the triglucosyl cap of Glc3Man9GlcNAc2-P-P-dolichol in microsomal vesicles from pig brain: use of the processing glucosidases I/II as latency markers.. Glycobiology 8(12):1207-13 PMID: 9858642
- 4. Parodi AJ. 2000. Role of N-oligosaccharide endoplasmic reticulum processing reactions in glycoprotein folding and degradation.. Biochem J 348 Pt 1(Pt 1):1-13 PMID: 10794707
- 5. Romero PA et al.. 1997. The yeast CWH41 gene encodes glucosidase I.. Glycobiology 7(7):997-1004 PMID: 9363442
- 6. Zeng YC et al.. 1998. Purification to homogeneity and properties of plant glucosidase I.. Arch Biochem Biophys 355(1):26-34 PMID: 9647663
- 8. Takeuchi M et al.. 1990. Inhibitory effect of pseudo-aminosugars on oligosaccharide glucosidases I and II and on lysosomal alpha-glucosidase from rat liver.. J Biochem 108(1):42-6 PMID: 2229010
