GO:0004169 dolichyl-phosphate-mannose-protein mannosyltransferase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0004169 describes the enzymatic activity that transfers mannose from dolichyl phosphate mannose to serine or threonine residues of proteins, forming O-mannosyl linkages.
• This activity is catalyzed by protein O-mannosyltransferases (PMTs), which are conserved from yeast to humans and are essential for cell wall integrity, protein stability, and signaling.
• In humans, O-mannosylation of alpha-dystroglycan is critical for muscle and brain function; defects cause dystroglycanopathies.
• Fungal Pmt4 forms homodimers with a distinct structural architecture that can be targeted for antifungal development.
• Mycobacterium tuberculosis protein O-mannosyltransferase is a potential drug target, and cell-based assays have been developed to monitor its activity.
• Reduced protein O-mannosyltransferase activity in yeast triggers cellular stress responses and changes in cell wall composition.
Description
Dolichyl-phosphate-mannose-protein mannosyltransferase activity (GO:0004169) is a molecular function that catalyzes the transfer of mannose from dolichyl phosphate mannose to protein acceptors, generating O-mannosylprotein linkages. This modification is one of the earliest steps in O-mannosylation, a conserved post-translational modification that occurs in the endoplasmic reticulum and is essential for protein folding, stability, and function. The enzymes responsible, protein O-mannosyltransferases (PMTs), are found in fungi, animals, and bacteria, and their dysfunction is linked to severe human diseases, including muscular dystrophies and developmental disorders. Researchers study GO:0004169 to understand glycobiology, cell wall biosynthesis, and host-pathogen interactions, and to develop therapeutics targeting these enzymes.
dolichyl-phosphate-mannose-protein mannosyltransferase activity At A Glance
| GO ID | GO:0004169 |
|---|---|
| GO term | dolichyl-phosphate-mannose-protein mannosyltransferase activity |
| Ontology | molecular_function |
| Synonym | protein O-mannosyltransferase activity; dolichyl-phosphate-D-mannose:protein O-D-mannosyltransferase activity; O-glycoside mannosyltransferase |
| Major function | Transfer of mannose from dolichyl phosphate mannose to proteins, forming O-mannosyl linkages |
| Reaction | dolichyl phosphate D-mannose + protein = dolichyl phosphate + O-D-mannosylprotein |
| Cellular location | Endoplasmic reticulum membrane |
| Enzyme class | Glycosyltransferase (GT family) |
| Representative genes | PMT1, PMT2, PMT4 (yeast); POMT1, POMT2 (human); Rv1002c (M. tuberculosis) |
What Is GO:0004169?
According to the Gene Ontology, GO:0004169 is defined as the catalysis of the reaction: dolichyl phosphate D-mannose + protein = dolichyl phosphate + O-D-mannosylprotein. In other words, it is the enzymatic activity that transfers a mannose residue from the lipid carrier dolichyl phosphate mannose to a protein substrate, forming a covalent O-glycosidic bond, typically on serine or threonine residues.
Why Is dolichyl-phosphate-mannose-protein mannosyltransferase activity Important in Cell Biology?
GO:0004169 is fundamental to protein O-mannosylation, a post-translational modification that affects protein stability, localization, and interactions. In humans, O-mannosylation of alpha-dystroglycan is essential for muscle and neuronal function, and mutations in the responsible enzymes cause severe congenital muscular dystrophies. In fungi, protein O-mannosylation is required for cell wall integrity and virulence, making it a target for antifungal drugs. In Mycobacterium tuberculosis, the protein O-mannosyltransferase is a potential target for anti-tuberculosis therapy. Thus, understanding this activity has broad implications for human health and biotechnology.
• Essential for O-mannosylation of proteins, a conserved post-translational modification.
• Mutations in human POMT1/POMT2 cause dystroglycanopathies, including Walker-Warburg syndrome.
• Required for fungal cell wall integrity and virulence; potential antifungal target.
• Involved in Mycobacterium tuberculosis pathogenesis; target for new antibiotics.
• Affects protein folding and stability in the endoplasmic reticulum.
• Plays a role in cell signaling and adhesion.
• Can be studied using yeast models to dissect enzyme structure-function.
• Recombinant enzymes enable high-throughput screening for inhibitors.
• Structural studies reveal unique folds for drug design.
• O-mannosylation defects are linked to cancer and developmental disorders.
What Happens During dolichyl-phosphate-mannose-protein mannosyltransferase activity?
Substrate recognition and binding
In simple terms: The enzyme grabs the sugar donor and the protein target.
The enzyme first binds dolichyl phosphate mannose, a lipid-linked mannose donor, and a protein substrate that contains serine or threonine residues. In yeast Pmt1p, specific residues in the catalytic domain are involved in donor and acceptor binding, as shown by structure-function analysis. The enzyme is localized to the endoplasmic reticulum membrane, where it can access both the lipid-linked donor and nascent polypeptides.
Catalytic transfer of mannose
In simple terms: The enzyme snips off mannose and attaches it to the protein.
The catalytic mechanism involves the transfer of mannose from dolichyl phosphate mannose to the hydroxyl group of serine or threonine on the protein, forming an O-glycosidic bond and releasing dolichyl phosphate. This reaction is catalyzed by the conserved PMT domain, which is found in enzymes from yeast to humans. The reaction is thought to proceed via a glycosyltransferase mechanism, though detailed steps are still being resolved.
Protein O-mannosylation in the ER
In simple terms: The modification happens inside the cell's protein factory.
O-mannosylation occurs in the endoplasmic reticulum (ER) and is one of the first steps in O-glycosylation. The enzyme modifies proteins as they are translocated into the ER, affecting their folding and stability. In yeast, diminished Pmt activity leads to ER stress and altered cell wall composition.
Dimerization and complex formation
In simple terms: Some enzymes work in pairs to function properly.
Many PMT enzymes form homodimers or heterodimers. For example, the fungal Pmt4 homodimer has been structurally characterized, revealing a distinct dimer interface important for activity. In Mycobacterium tuberculosis, the protein O-mannosyltransferase contains a WW-domain-like motif that may mediate protein-protein interactions.
Key Genes Involved in GO:0004169 dolichyl-phosphate-mannose-protein mannosyltransferase activity
The following genes encode enzymes with dolichyl-phosphate-mannose-protein mannosyltransferase activity or are directly related to this function.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PMT1 (S. cerevisiae) | Protein O-mannosyltransferase, forms heterodimers with Pmt2 | Model for structure-function studies |
| PMT2 (S. cerevisiae) | Protein O-mannosyltransferase, partner of Pmt1 | Cell wall integrity and stress response |
| PMT4 (S. cerevisiae) | Protein O-mannosyltransferase, homodimer | Structural studies of fungal Pmt4 |
| POMT1 (H. sapiens) | Protein O-mannosyltransferase 1, forms complex with POMT2 | Mutations cause dystroglycanopathies |
| POMT2 (H. sapiens) | Protein O-mannosyltransferase 2, partner of POMT1 | Required for alpha-dystroglycan O-mannosylation |
| Rv1002c (M. tuberculosis) | Protein O-mannosyltransferase | Target for anti-TB drug development |
| DPM1 (S. cerevisiae) | Dolichyl-phosphate mannose synthase, produces donor | Provides substrate for O-mannosylation |
| DPM1 (H. sapiens) | Dolichyl-phosphate mannose synthase | Congenital disorder of glycosylation |
| DAG1 (H. sapiens) | Dystroglycan, substrate of POMT1/POMT2 | Muscle and brain function |
| PMT3 (S. cerevisiae) | Protein O-mannosyltransferase | Potential role in stress response |
| PMT5 (S. cerevisiae) | Protein O-mannosyltransferase | Less characterized, may have specialized functions |
| PMT6 (S. cerevisiae) | Protein O-mannosyltransferase | May form complexes with other Pmts |
| POMGNT1 (H. sapiens) | O-mannose beta-1,2-N-acetylglucosaminyltransferase | Downstream glycosylation step |
| FKRP (H. sapiens) | Fukutin-related protein, glycosyltransferase | Dystroglycanopathy gene |
| LARGE1 (H. sapiens) | Xylosyl- and glucuronyltransferase | Modifies dystroglycan glycan |
| B3GALNT2 (H. sapiens) | Beta-1,3-N-acetylgalactosaminyltransferase | Dystroglycanopathy gene |
| TMEM5 (H. sapiens) | RXYLT1, ribitol xylosyltransferase | Dystroglycanopathy gene |
| ISPD (H. sapiens) | CDP-ribitol synthase | Dystroglycanopathy gene |
How Is dolichyl-phosphate-mannose-protein mannosyltransferase activity Regulated?
The activity of dolichyl-phosphate-mannose-protein mannosyltransferases is regulated at multiple levels. In yeast, expression of PMT genes is induced by cell wall stress and ER stress. The activity can be modulated by the availability of dolichyl phosphate mannose, which is synthesized by DPM1. In humans, POMT1 and POMT2 form a complex, and their activity is essential for dystroglycan glycosylation; mutations or reduced expression lead to disease. In Mycobacterium tuberculosis, the enzyme's activity may be regulated by its WW-domain-like motif, which could mediate interactions with other proteins.
dolichyl-phosphate-mannose-protein mannosyltransferase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| POMT1 | Walker-Warburg syndrome, limb-girdle muscular dystrophy | Knockout mouse, patient iPSC-derived muscle cells |
| POMT2 | Congenital muscular dystrophy-dystroglycanopathy | Knock-in mouse with patient mutations |
| PMT4 (fungal) | Fungal virulence, cell wall integrity | Candida albicans knockout, antifungal screening |
| Rv1002c | M. tuberculosis pathogenesis | Mycobacterium smegmatis overexpression, reporter assay |
| DAG1 | Dystroglycanopathy, muscle degeneration | Conditional knockout mouse, CRISPR knock-in of glycosylation sites |
Dystroglycanopathies and muscular dystrophy
Mutations in POMT1 and POMT2, which encode human protein O-mannosyltransferases, cause a spectrum of congenital muscular dystrophies known as dystroglycanopathies. These disorders are characterized by defective O-mannosylation of alpha-dystroglycan, leading to muscle weakness, brain abnormalities, and eye defects. The severity ranges from Walker-Warburg syndrome to milder limb-girdle muscular dystrophy.
Fungal infections and antifungal targets
In pathogenic fungi such as Candida albicans and Aspergillus fumigatus, protein O-mannosylation is required for cell wall integrity and virulence. The structural characterization of fungal Pmt4 homodimers provides a basis for designing inhibitors that could serve as antifungal drugs. Reduced Pmt activity in baker's yeast leads to cell wall defects and stress responses, highlighting its essential role.
Tuberculosis and bacterial glycosylation
Mycobacterium tuberculosis encodes a protein O-mannosyltransferase (Rv1002c) that is important for pathogenesis. A cell-based assay has been developed to monitor its activity, enabling high-throughput screening for inhibitors. Structural insights into this enzyme reveal a WW-domain-like motif, suggesting unique regulatory mechanisms in bacteria.
From dolichyl-phosphate-mannose-protein mannosyltransferase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Enzyme structure-function | Point mutations in PMT1/PMT2 in yeast |
| Role in cell wall integrity | Knockout of PMT genes in S. cerevisiae |
| Dystroglycan glycosylation | POMT1/POMT2 knockout in human cells |
| Drug target validation | Overexpression of Rv1002c in M. smegmatis |
| Protein interactions | Tagged knock-in of PMT4 in fungi |
| Developmental role | Conditional knockout of POMT1 in mouse |
How to Study the dolichyl-phosphate-mannose-protein mannosyltransferase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| In vitro glycosyltransferase assay | Enzyme activity using radiolabeled donor | Kinetic studies of PMT enzymes |
| Cell-based reporter assay | Activity in live cells | High-throughput screening for inhibitors |
| X-ray crystallography | 3D structure of enzyme | Structure-based drug design |
| Mass spectrometry | O-mannosylation sites and glycan structures | Glycoproteomics of dystroglycan |
| CRISPR knockout screening | Gene essentiality and pathways | Identify novel regulators of O-mannosylation |
| Western blot with lectins | Presence of O-mannose on proteins | Assess glycosylation status |
| Yeast genetics | Growth and stress phenotypes | Functional analysis of PMT genes |
| Immunofluorescence | Localization of enzymes and substrates | ER localization studies |
Enzymatic activity assays
In vitro assays using recombinant enzymes and radiolabeled dolichyl phosphate mannose can measure mannosyltransferase activity directly. For high-throughput screening, cell-based reporter assays have been developed for M. tuberculosis Pmt.
Structural biology
X-ray crystallography and cryo-EM have been used to determine the structures of fungal Pmt4 homodimers and bacterial Pmt, revealing catalytic domains and dimer interfaces. These methods guide inhibitor design.
Glycoproteomics
Mass spectrometry-based glycoproteomics can identify O-mannosylated proteins and sites, providing insights into substrate specificity and cellular consequences of altered activity.
Genetic screens and CRISPR
CRISPR knockout screens in human cells can identify genes required for O-mannosylation and dystroglycan function. Yeast deletion collections enable systematic analysis of PMT gene families.
How CRISPR Can Be Used to Study GO:0004169 dolichyl-phosphate-mannose-protein mannosyltransferase activity
Knockout
CRISPR knockout of POMT1 or POMT2 in human cells abolishes O-mannosylation of alpha-dystroglycan, providing a model to study dystroglycanopathies and to test rescue strategies. In yeast, knockout of PMT genes leads to cell wall defects and stress sensitivity.
Point Mutation
Introducing patient-specific point mutations into POMT1 or POMT2 via CRISPR base editing or homology-directed repair allows researchers to dissect the functional impact of individual mutations on enzyme activity and substrate binding.
Knock-in
Knock-in of epitope tags (e.g., FLAG, HA) into endogenous PMT genes enables affinity purification and localization studies. Knock-in of glycosylation site mutations in DAG1 can reveal the importance of specific O-mannosylation sites for muscle function.
Overexpression
Overexpression of PMT genes or the M. tuberculosis Rv1002c in heterologous hosts can produce large amounts of enzyme for structural and biochemical studies. Overexpression in mammalian cells can also amplify O-mannosylation for glycoproteomic analysis.
How EDITGENE Supports dolichyl-phosphate-mannose-protein mannosyltransferase activity Research
Researchers studying dolichyl-phosphate-mannose-protein mannosyltransferase activity-related genes often need to determine whether a candidate gene is causally involved in glycosylation, cell wall integrity, or disease. EDITGENE provides comprehensive CRISPR-based services to create precise cellular models for such investigations.
Contact EDITGENE today to design your custom CRISPR model for dolichyl-phosphate-mannose-protein mannosyltransferase activity research.
Frequently Asked Questions About dolichyl-phosphate-mannose-protein mannosyltransferase activity
What is dolichyl-phosphate-mannose-protein mannosyltransferase activity?
It is the enzymatic activity (GO:0004169) that transfers mannose from dolichyl phosphate mannose to proteins, forming O-mannosyl linkages.
What genes are involved in dolichyl-phosphate-mannose-protein mannosyltransferase activity?
Key genes include PMT1, PMT2, PMT4 in yeast; POMT1 and POMT2 in humans; and Rv1002c in Mycobacterium tuberculosis.
What diseases are associated with defects in this activity?
Mutations in POMT1/POMT2 cause dystroglycanopathies such as Walker-Warburg syndrome; fungal Pmt enzymes are linked to virulence.
How is protein O-mannosylation studied?
Methods include in vitro enzyme assays, mass spectrometry, CRISPR screens, and structural biology.
What is the reaction catalyzed by GO:0004169?
Dolichyl phosphate D-mannose + protein = dolichyl phosphate + O-D-mannosylprotein.
Where does this activity occur in the cell?
It occurs in the endoplasmic reticulum membrane.
Can CRISPR be used to study this activity?
Yes, CRISPR knockout, knock-in, and point mutation models are widely used to dissect gene function.
What is the role of POMT1 and POMT2?
They form a complex that O-mannosylates alpha-dystroglycan, critical for muscle and brain function.
Is this enzyme a drug target?
Yes, fungal and bacterial Pmt enzymes are potential targets for antifungal and anti-tuberculosis drugs.
What model organisms are used?
Saccharomyces cerevisiae, human cell lines, and Mycobacterium smegmatis are common models.
Conclusion
Dolichyl-phosphate-mannose-protein mannosyltransferase activity (GO:0004169) is a conserved enzymatic function essential for protein O-mannosylation, with critical roles in human health, fungal virulence, and bacterial pathogenesis. Understanding its mechanism, regulation, and disease connections offers opportunities for therapeutic development. EDITGENE provides advanced CRISPR services to create precise models for studying this activity and its related genes.
References
- 1. Strahl-Bolsinger S et al.. 1999. Protein O-mannosylation.. Biochim Biophys Acta 1426(2):297-307 PMID: 9878797
- 2. Girrbach V et al.. 2000. Structure-function analysis of the dolichyl phosphate-mannose: protein O-mannosyltransferase ScPmt1p.. J Biol Chem 275(25):19288-96 PMID: 10764776
- 3. Hord JM et al.. 2025. Sarcolemma resilience and skeletal muscle health require O-mannosylation of dystroglycan.. Skelet Muscle 15(1):1 PMID: 39789642
- 4. McDowell MA et al.. 2025. Structural characterisation of the fungal Pmt4 homodimer.. Nat Commun 16(1):11134 PMID: 41392315
- 5. Géraud N et al.. 2023. Development of a novel target-based cell assay, reporter of the activity of Mycobacterium tuberculosis protein-O-mannosyltransferase.. Glycobiology 33(12):1139-1154 PMID: 37698262
- 6. Géraud N et al.. 2025. Structural Insights into the Protein Mannosyltransferase from Mycobacterium tuberculosis reveal a WW-Domain-Like Protein Motif in Bacteria.. Commun Biol 8(1):1175 PMID: 40775265
- 7. Zatorska E et al.. 2017. Cellular Consequences of Diminished Protein O-Mannosyltransferase Activity in Baker's Yeast.. Int J Mol Sci 18(6) PMID: 28598353
