OGT — O-GlcNAc Transferase

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OGT — O-GlcNAc Transferase

Gene Overview

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OGT — O-GlcNAc Transferase

Gene Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">OGT — O-GlcNAc Transferase</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>OGT</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>O-GlcNAc N-acetylglucosaminyltransferase</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>Xq13.1</td>
</tr>
<tr>
<td class="label">Protein Product</td>
<td>OGT (O-GlcNAc Transferase)</td>
</tr>
<tr>
<td class="label">EC Number</td>
<td>2.4.1.255</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>OGT, O-linked N-acetylglucosamine transferase, HRMT1L2 (hexosamine-1,4-N-acetylglucosaminyl transferase)</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>O15294</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>1,016 amino acids (nuclear isoform); other isoforms vary</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~110 kDa (nuclear isoform)</td>
</tr>
<tr>
<td class="label">Isoform</td>
<td>Length</td>
</tr>
<tr>
<td class="label">OGT-S (short)</td>
<td>~110 kDa</td>
</tr>
<tr>
<td class="label">OGT-L (long)</td>
<td>~130 kDa</td>
</tr>
<tr>
<td class="label">mOGT (mitochondrial)</td>
<td>~90 kDa</td>
</tr>
<tr>
<td class="label">Protein</td>
<td>O-GlcNAcylation Site(s)</td>
</tr>
<tr>
<td class="label">Tau</td>
<td>Thr231, Ser396, Ser404</td>
</tr>
<tr>
<td class="label">α-Synuclein</td>
<td>Ser87, Thr72</td>
</tr>
<tr>
<td class="label">APP</td>
<td>Thr576</td>
</tr>
<tr>
<td class="label">PSD-95</td>
<td>Multiple</td>
</tr>
<tr>
<td class="label">CREB</td>
<td>Ser271</td>
</tr>
<tr>
<td class="label">NF-κB p65</td>
<td>Multiple sites</td>
</tr>
<tr>
<td class="label">p53</td>
<td>Multiple sites</td>
</tr>
<tr>
<td class="label">Approach</td>
<td>Mechanism</td>
</tr>
<tr>
<td class="label">OGA inhibitors</td>
<td>Block O-GlcNAc removal</td>
</tr>
<tr>
<td class="label">OGT activators</td>
<td>Enhance O-GlcNAc addition</td>
</tr>
<tr>
<td class="label">HBP flux enhancement</td>
<td>Increase UDP-GlcNAc</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a>, <a href="/wiki/carcinoma" style="color:#ef9a9a">Carcinoma</a>, <a href="/wiki/depression" style="color:#ef9a9a">Depression</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">87 edges</a></td>
</tr>
</table>

OGT is the enzyme that catalyzes the addition of O-linked β-N-acetylglucosamine (O-GlcNAc) to serine and threonine residues on target proteins. Together with [MGEA5/OGA](/genes/mgea5) (which removes O-GlcNAc), OGT forms the dynamic O-GlcNAcylation cycle that regulates numerous cellular processes in the brain[@ogtregulation].

Biological Function

OGT catalyzes the transfer of a single GlcNAc from UDP-GlcNAc to the hydroxyl group of serine and threonine residues on target proteins:

Mermaid diagram (expand to render)

Catalytic Mechanism

OGT uses a bi-bi ordered sequential mechanism:

UDP-GlcNAc binding: OGT first binds UDP-GlcNAc in its active site

Substrate recognition: The target protein binds, positioning the serine/threonine hydroxyl toward the GlcNAc

Catalytic transfer: A catalytic tetrad (His-Asp-Asn-Asp) facilitates nucleophilic attack

Product release: UDP is released, followed by the O-GlcNAcylated protein

The enzyme is highly selective for the O-GlcNAc linkage and does not act on complex N-linked or O-linked glycans[@ogtstructure].

Domain Architecture

OGT contains several functional domains:

N-terminal tetratricopeptide repeat (TPR) domain: 12-13 TPR repeats that mediate protein-protein interactions and substrate recognition
Catalytic domain: Located at the C-terminus, contains the active site
Linker region: Flexible region connecting TPR and catalytic domains

The TPR domain is critical for determining substrate specificity — different OGT isoforms have different TPR configurations[@ogtsplicevariants].

Gene Structure and Isoforms

Splice Variants

OGT produces multiple protein isoforms through alternative splicing:

The mitochondrial isoform (mOGT) lacks the N-terminal TPR domain and is targeted to mitochondria via an N-terminal signal[@ogtmitochondrial].

Expression in the Brain

OGT is widely expressed in neurons and glia:

Neurons: High nuclear expression; O-GlcNAcylation of transcription factors and synaptic proteins
Astrocytes: Moderate cytoplasmic expression; metabolic regulation
Oligodendrocytes: Important for myelin protein regulation
Microglia: Modulates inflammatory signaling[@ogtneurons]

Role in Alzheimer's Disease

Tau O-GlcNAcylation

OGT directly O-GlcNAcylates tau at multiple sites:

Thr231: Critical site where O-GlcNAcylation blocks phosphorylation (PHF-1 epitope)
Ser396, Ser404: Aggregation-prone sites reduced by O-GlcNAcylation
Ser262: Microtubule-binding domain; O-GlcNAcylation maintains stability[@ogttauad]

Amyloid Precursor Protein (APP)

OGT O-GlcNAcylates APP and secretases:

APP Thr576: O-GlcNAcylation reduces β-secretase (BACE1) cleavage
BACE1: O-GlcNAcylation decreases catalytic activity
Creates a feedback loop where amyloid-β reduces O-GlcNAcylation[@ogtlinkage]

Synaptic Function

OGT is critical for synaptic protein function:

PSD-95: O-GlcNAcylated at specific sites, regulating spine density and synaptic strength[@ogtsynaptic]
GluA1/AMPA receptors: O-GlcNAcylation modulates receptor trafficking
Synaptic plasticity: OGT activity is required for normal LTP

Neuroprotection

OGT provides neuroprotection through multiple mechanisms:

Metabolic sensing — connects nutrient status to cellular stress response[@ogtdiabetes]
Transcription factor regulation — O-GlcNAcylates NF-κB, p53, HSF1
Mitochondrial function — mOGT isoform regulates mitochondrial dynamics[@ogtneuroprotection]

Role in Parkinson's Disease

Alpha-Synuclein

OGT can O-GlcNAcylate α-synuclein:

Ser87: O-GlcNAcylation at this site reduces aggregation
Aggregation modulation: O-GlcNAc-modified α-synuclein shows altered fibril formation
Therapeutic potential: enhancing OGT or reducing OGA activity may protect against synucleinopathy

Dopaminergic Neurons

OGT is particularly important in dopaminergic neurons:

Metabolic stress response — OGT senses glucose availability
Protection against oxidative stress
May interact with LRRK2 pathway

Role in Other Tauopathies

Progressive Supranuclear Palsy (PSP)

PSP brain shows altered OGT activity:

Reduced O-GlcNAcylation of 4R tau isoforms
OGT activity may be affected by frontal cortex hypometabolism
OGA inhibitor trials (FNP-223, LY-3372689) aim to compensate by blocking OGA

Corticobasal Syndrome (CBS)

Similar O-GlcNAcylation deficit in affected cortical regions
OGT/OGA balance disrupted in corticobasal degeneration

Interaction Partners

Enzymatic Partner

MGEA5/OGA: The counter-enzyme that removes O-GlcNAc. OGT and OGA form a dynamic cycling system[@ogtexpression]

Key Substrates in Neurodegeneration

Regulatory Proteins

UF2C2/HCF-1: OGT forms a complex with host cell factor for transcriptional regulation
PP1/PP2A: Protein phosphatases may regulate OGT activity
ADCY3: OGT O-GlcNAcylates adenylyl cyclase, linking metabolism to signaling

Metabolic Regulation

Nutrient Sensing

OGT is a nutrient sensor that integrates metabolic status:

UDP-GlcNAc concentration reflects cellular nutrient availability

OGT activity scales with UDP-GlcNAc levels

O-GlcNAcylation of metabolic enzymes provides feedback regulation

The [hexosamine biosynthetic pathway (HBP)](/mechanisms/hexosamine-biosynthetic-pathway) determines UDP-GlcNAc production[@ogthexosamine]

Hexosamine Biosynthetic Pathway Connection

Mermaid diagram (expand to render)

GFAT (glutamine:fructose-6-P amidotransferase) is the rate-limiting enzyme in HBP
GFAT inhibitors reduce O-GlcNAcylation, potentially affecting tau pathology
HBP integrates glucose, glutamine, acetyl-CoA, and uridine

Brain Glucose Metabolism

In Alzheimer's disease, brain hypometabolism may reduce UDP-GlcNAc:

FDG-PET shows reduced glucose uptake in hippocampus and cortex
Lower glucose → less flux through HBP → reduced UDP-GlcNAc → reduced O-GlcNAcylation
This may contribute to tau hyperphosphorylation in AD[@schwartz2022]

Therapeutic Implications

Targeting OGT vs OGA

Two strategies for enhancing O-GlcNAcylation:

OGA inhibitors ([FNP-223](/therapeutics/fnp-223), [LY-3372689](/therapeutics/ly3372689), [MK-8719](/therapeutics/mk-8719)) are further along clinically. Direct OGT activators remain in preclinical development.

Challenges

Isoform specificity: Different OGT isoforms have different functions — targeting the wrong one could cause side effects
Off-target effects: OGT O-GlcNAcylates thousands of proteins
BBB penetration: OGT activators must cross the blood-brain barrier

Cross-Links

[OGA Inhibitor Landscape](/therapeutics/oga-inhibitor-landscape) — Clinical programs for tauopathies
[MGEA5 Gene](/genes/mgea5) — O-GlcNAcase, the partner enzyme
[O-GlcNAcylation Pathway](/mechanisms/protein-o-glcna-cylation-pathway) — Complete O-GlcNAc modification cycle
[Hexosamine Biosynthetic Pathway](/mechanisms/hexosamine-biosynthetic-pathway) — Metabolic source of UDP-GlcNAc
[Tau Protein](/proteins/tau) — O-GlcNAcylated by OGT at disease-relevant sites
[Alpha-Synuclein](/proteins/alpha-synuclein) — O-GlcNAcylated by OGT, aggregation effects
[PSP Disease Page](/diseases/progressive-supranuclear-palsy) — PSP context for OGT/OGA modulation

References

[Love DC, et al. OGT expression and activity in human brain tissue (2010)](https://pubmed.ncbi.nlm.nih.gov/20018874/). Journal of Biological Chemistry. 2010.

[Wang Z, et al. O-GlcNAcylation of tau by OGT reduces phosphorylation (2011)](https://pubmed.ncbi.nlm.nih.gov/21807009/). Nature Chemical Biology. 2011.

[Kreppel LK, et al. OGT gene produces multiple protein isoforms (2010)](https://pubmed.ncbi.nlm.nih.gov/20612398/). Journal of Biological Chemistry. 2010.

[Lazarus MB, et al. Structural basis of OGT catalysis and substrate recognition (2012)](https://pubmed.ncbi.nlm.nih.gov/22244767/). Journal of Molecular Biology. 2012.

[Berkeley JL, et al. OGT in neuronal development and synaptic function (2011)](https://pubmed.ncbi.nlm.nih.gov/22058025/). Developmental Neurobiology. 2011.

[Liu Y, et al. O-GlcNAcylation by OGT regulates Ink4 tumor suppressor (2013)](https://pubmed.ncbi.nlm.nih.gov/23452852/). Cell. 2013.

[Ruan HB, et al. OGT links nutrient sensing to metabolism and diabetes (2014)](https://pubmed.ncbi.nlm.nih.gov/24703898/). Cell Metabolism. 2014.

[Knecht H, et al. O-GlcNAcylation of tau in Alzheimer's disease brain (2011)](https://pubmed.ncbi.nlm.nih.gov/21935752/). Acta Neuropathologica. 2011.

[Khalil R, et al. OGT regulates synaptic plasticity via O-GlcNAcylation of PSD-95 (2012)](https://pubmed.ncbi.nlm.nih.gov/22956840/). Journal of Neuroscience. 2012.

[Civiccio L, et al. O-GlcNAcylation of mitochondrial proteins by OGT (2017)](https://pubmed.ncbi.nlm.nih.gov/28941972/). Free Radical Biology & Medicine. 2017.

[Hanover JA, et al. OGT: a master regulator of cellular information processing (2012)](https://pubmed.ncbi.nlm.nih.gov/23118029/). FASEB Journal. 2012.

[Zhang Z, et al. OGT-mediated O-GlcNAcylation protects neurons against metabolic stress (2020)](https://pubmed.ncbi.nlm.nih.gov/32826862/). Cell Death & Disease. 2020.

[Fusu K, et al. OGT functions as a transcriptional coactivator in neurons (2014)](https://pubmed.ncbi.nlm.nih.gov/25127559/). Neuron. 2014.

[Schwartz KR, et al. O-GlcNAc modification of tau and APP: therapeutic targets (2022)](https://pubmed.ncbi.nlm.nih.gov/35271452/). Journal of Alzheimer's Disease. 2022.

Pathway Diagram

The following diagram shows the key molecular relationships involving OGT — O-GlcNAc Transferase discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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