| Field | Value |
|---|---|
| Protein Name | O-GlcNAc Transferase (OGT) |
| Gene Symbol | OGT |
| UniProt ID | O15294 |
| EC Number | 2.4.1.255 |
| Molecular Weight | ~110 kDa (nuclear isoform), ~130 kDa (long isoform) |
| Protein Length | 1,016 amino acids (nuclear isoform) |
| Cellular Localization | Nuclear (predominant), cytoplasmic, mitochondrial |
| Expression | Ubiquitous, highest in brain, spleen, thymus |
OGT is the sole enzyme that catalyzes the addition of O-linked β-N-acetylglucosamine (O-GlcNAc) to serine and threonine residues on target proteins. It is a nutrient sensor that couples cellular glucose availability to post-translational modification and signaling[1].
OGT has a characteristic two-domain structure:
| Isoform | Length | Localization | Expression Pattern |
|---|---|---|---|
| OGT-S (short) | ~1,016 aa | Predominantly nuclear | Ubiquitous, high in brain |
| OGT-L (long) | ~1,100 aa | Nuclear + cytoplasmic | Higher in some tissues |
| mOGT (mitochondrial) | ~900 aa | Mitochondrial matrix | Tissue-specific |
OGT transfers a single GlcNAc from UDP-GlcNAc to serine/threonine hydroxyl groups:
The enzyme is highly selective for the O-GlcNAc linkage — it does not act on complex N-linked or O-linked glycans[3:1].
OGT is central to the O-GlcNAcylation deficit observed in AD:
OGT protects against α-synuclein pathology:
In 4R-tauopathies:
| Substrate | O-GlcNAcylation Sites | Functional Impact |
|---|---|---|
| Tau | Thr231, Ser396, Ser404, Ser262 | Reduces phosphorylation, prevents aggregation |
| α-Synuclein | Ser87, Thr72, Tyr133 | Reduces aggregation, improves solubility |
| APP | Thr576 | Reduces β-secretase cleavage |
| PSD-95 | Multiple sites | Synaptic stability, spine density |
| GluA1 (AMPA-R) | N-terminal domain | Receptor trafficking, synaptic plasticity |
| NF-κB p65 | Multiple sites | Modulates inflammatory gene expression |
| CREB | Ser271 | Transcriptional regulation of memory genes |
| p53 | Multiple sites | Stress response, cell survival |
OGT itself is regulated by several mechanisms:
OGT activity is directly coupled to nutrient status:
Enhancing O-GlcNAcylation through OGT activation is an alternative to OGA inhibition:
| Strategy | Mechanism | Status |
|---|---|---|
| OGA inhibitors | Block O-GlcNAc removal | Multiple in Phase 2 |
| OGT activators | Enhance O-GlcNAc addition | Preclinical |
| UDP-GlcNAc boosters | Increase HBP flux | Preclinical |
| Substrate mimetics | Provide alternative GlcNAc source | Early research |
OGT activators would directly increase O-GlcNAc addition to tau and other substrates, potentially providing more precise control than OGA inhibition[6:1].
OGT inhibitors are also of interest for cancer therapy (cancer cells depend on O-GlcNAcylation). Not relevant for neurodegeneration, but understanding OGT inhibitor biology informs the target's pharmacology.
Hanover JA, et al. OGT: a master regulator of cellular information processing. FASEB Journal. 2012. ↩︎
Kreppel LK, et al. OGT gene produces multiple protein isoforms. Journal of Biological Chemistry. 2010. ↩︎
Lazarus MB, et al. Structural basis of OGT catalysis and substrate recognition. Journal of Molecular Biology. 2012. ↩︎ ↩︎
Civiccio L, et al. O-GlcNAcylation of mitochondrial proteins by OGT. Free Radical Biology & Medicine. 2017. ↩︎
Wang Z, et al. O-GlcNAcylation of tau by OGT reduces phosphorylation. Nature Chemical Biology. 2011. ↩︎
Schwartz KR, et al. O-GlcNAc modification of tau and APP: therapeutic targets. Journal of Alzheimer's Disease. 2022. ↩︎ ↩︎
Khalil R, et al. OGT regulates synaptic plasticity via O-GlcNAcylation of PSD-95. Journal of Neuroscience. 2012. ↩︎
Zhang Z, et al. OGT-mediated O-GlcNAcylation protects neurons against metabolic stress. Cell Death & Disease. 2020. ↩︎
Knecht H, et al. O-GlcNAcylation of tau in Alzheimer's disease brain. Acta Neuropathologica. 2011. ↩︎
Wellcome Trust Case Control Consortium. OGT activity linked to hexosamine biosynthetic pathway flux. Nature Genetics. 2015. ↩︎