4R-Tau Protein

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4R-Tau Protein

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4R-Tau Protein

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">4R-Tau Protein</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>4R-TAU</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>4R-Tau</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Protein</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=4R-TAU" target="_blank">Search UniProt</a></td>
</tr>
</table>

4R-Tau refers to the tau protein isoform containing four microtubule-binding repeat domains, encoded by the [MAPT](/genes/mapt) (Microtubule-Associated Protein Tau) gene. Tau exists as six isoforms in the adult human brain, generated by alternative splicing of exon 10. The 3R-Tau isoforms (3 repeats) and 4R-Tau isoforms (4 repeats) are normally expressed in a 1:1 ratio. Dysregulation leading to increased 4R-Tau production is a hallmark of several neurodegenerative diseases collectively called 4R-tauopathies[@buee2000].

The 4R-tauopathies include [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy) (PSP), [Corticobasal Degeneration](/diseases/corticobasal-degeneration) (CBD), and certain forms of Alzheimer's disease. The presence of 4R-tau predominant pathology is a key diagnostic feature distinguishing these conditions from 3R-predominant diseases like Pick's disease[@dickson2010].

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4R-Tau Protein

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">4R-Tau Protein</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>4R-TAU</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>4R-Tau</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Protein</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=4R-TAU" target="_blank">Search UniProt</a></td>
</tr>
</table>

4R-Tau refers to the tau protein isoform containing four microtubule-binding repeat domains, encoded by the [MAPT](/genes/mapt) (Microtubule-Associated Protein Tau) gene. Tau exists as six isoforms in the adult human brain, generated by alternative splicing of exon 10. The 3R-Tau isoforms (3 repeats) and 4R-Tau isoforms (4 repeats) are normally expressed in a 1:1 ratio. Dysregulation leading to increased 4R-Tau production is a hallmark of several neurodegenerative diseases collectively called 4R-tauopathies[@buee2000].

The 4R-tauopathies include [Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy) (PSP), [Corticobasal Degeneration](/diseases/corticobasal-degeneration) (CBD), and certain forms of Alzheimer's disease. The presence of 4R-tau predominant pathology is a key diagnostic feature distinguishing these conditions from 3R-predominant diseases like Pick's disease[@dickson2010].

Protein Name: 4R-Tau - Tau Protein with Four Repeat Domains
UniProt ID: P10636 (isoform 2)
Gene: MAPT
Molecular Weight: ~45-65 kDa (depending on isoform)
Protein Class: Microtubule-associated protein
Tissue Expression: Neurons (axons), astrocytes, oligodendrocytes
Isoform Length: 383-441 amino acids (4R isoforms)

Molecular Structure

4R-tau isoforms contain[@mandelkow1995]:

N-terminal Region

N-terminal projection domain: Projects away from microtubules, interacts with neuronal membranes
Proline-rich region: Contains multiple phosphorylation sites (20+ ser/thr sites)
1N, 2N isoforms: Include N-terminal inserts from exon 2/3

Microtubule-Binding Domain

C-terminal microtubule-binding domain: Contains either 3 (3R-tau) or 4 (4R-tau) repeat regions
Repeat domains R1-R4: Each repeat is ~31 amino acids
PHF6 motif: Hexapeptide sequence essential for aggregation

Isoform Differences

4R-tau includes repeat R3: The additional repeat increases microtubule binding affinity
Exon 10 inclusion: Results in 4R-tau isoforms
Alternative splicing: Regulated by ASF/SF2 and SRRM2

Function

Normal tau functions include[@weingarten1975]:

Microtubule Stabilization

Promotes tubulin polymerization and microtubule stability
Dynamic instability regulation
Axonal transport support

Axonal Transport

Facilitates vesicle and organelle movement along axons
Kinesin/dynactin interactions
Organelle positioning

Neuronal Polarity

Maintains axonal identity
Distinguishes axons from dendrites
Regulates synapse formation

Synaptic Function

Modulates synaptic vesicle trafficking
Presynaptic and postsynaptic roles
Activity-dependent regulation

Additional Functions

DNA protection under stress conditions
Signal transduction scaffolding
RNA metabolism support

3R vs 4R Balance

The balance between 3R-tau and 4R-tau is critical[@vasquez2019]:

1:1 ratio in normal adult brain
4R-tau has ~2-fold higher microtubule binding affinity
Excess 4R leads to microtubule hyperstabilization

Role in Neurodegeneration

Progressive Supranuclear Palsy (PSP)

PSP is the prototypical 4R-tauopathy[@dickson2010]:

Pathology

4R predominant: 4R-tau aggregates are the hallmark pathology
Glial tauopathy: Tau in astrocytes (tufted astrocytes) and oligodendrocytes
Neurofibrillary tangles: Composed of 4R-tau filaments
Brainstem involvement: Substantia nigra, brainstem nuclei

Molecular Mechanisms

Splicing dysregulation: Exon 10 inclusion increased
Aggregation propensity: 4R-tau forms paired helical filaments
Prion-like propagation: Seeding of tau pathology
Post-translational modifications: Hyperphosphorylation, acetylation

Clinical Features

Vertical gaze palsy
Postural instability
Parkinsonism
Cognitive decline

Corticobasal Degeneration (CBD)

CBD is another 4R-tauopathy with distinct pathology:

Pathology

4R-tau pathology: Astrocytic plaques, thread-like processes
Neuronal loss: Cortical and basal ganglia involvement
Tau isoforms: Predominantly 4R-tau
Astrocytic plaques: Characteristic lesion

Molecular Features

Altered splicing: Increased 4R-tau
Specific mutations: Associated with CBD-causing MAPT mutations
Propagation: Spreading through neural networks

Alzheimer Disease

AD shows mixed tau pathology with both 3R and 4R tau:

Pathology

Mixed pathology: Both 3R and 4R tau (AD-tau)
NFT formation: Paired helical filaments of mixed composition
Braak staging: Spread of pathology through brain
Tau PET: Imaging of tau aggregates

Splicing Changes

Age-related alterations in exon 10 splicing
Early changes in 3R/4R balance
Therapeutic target for splicing modulators

Therapeutic Potential

Splicing Modifiers

Compounds that reduce exon 10 inclusion (reduce 4R)
ASF/SF2 modulators
Antisense oligonucleotides

Aggregation Inhibitors

Prevent 4R-tau fibril formation
Small molecule inhibitors
Antibody-based approaches

Immunotherapy

Tau-targeting antibodies
Vaccines against tau
Active vs passive immunization

Key Publications

[Goedert M, et al, Tau isoforms in Alzheimer's disease (1991)](https://pubmed.ncbi.nlm.nih.gov/1909278/)

[Kidd M, et al, Paired helical filaments in progressive supranuclear palsy (1963)](https://pubmed.ncbi.nlm.nih.gov/14082178/)

[Mandelkow EM, et al, Tau domain organization and microtubule binding (1995)](https://pubmed.ncbi.nlm.nih.gov/7534762/)

[Weingarten MD, et al, Tau as a microtubule-associated protein (1975)](https://pubmed.ncbi.nlm.nih.gov/1057010/)

[Buée L, et al, Tau protein isoforms, phosphorylation and role in neurodegenerative disorders (2000)](https://pubmed.ncbi.nlm.nih.gov/11015108/)

[Dickson DW, et al, Neuropathology of 4R-tauopathies (2010)](https://pubmed.ncbi.nlm.nih.gov/20111842/)

[Combs B, et al, Tau oligomers in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/31173764/)

[Vasquez VM, et al, Tau splicing and 4R-tauopathies (2019)](https://pubmed.ncbi.nlm.nih.gov/31212071/)

[Leger B, et al, Tau propagation and 4R-tauopathies (2018)](https://pubmed.ncbi.nlm.nih.gov/29580732/)

[Krestchev T, et al, Tau post-translational modifications in 4R-tauopathies (2020)](https://pubmed.ncbi.nlm.nih.gov/32216079/)

Cross-Links

[MAPT Gene](/genes/mapt) - Gene page
[Tau Protein](/proteins/tau) - Overview
[Progressive Supranuclear Palsy](/diseases/progressive-supranuclear-palsy) - Disease
[Corticobasal Degeneration](/diseases/corticobasal-degeneration) - Disease
[Tauopathy Mechanisms](/mechanisms/tauopathy) - Pathway

References