PKR Protein (Protein Kinase R)

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PKR Protein (Protein Kinase R)

Overview

flowchart TD TREM2["TREM2"] -->|"associated with"| P19589["P19589"] CAPN6["CAPN6"] -->|"associated with"| P19589["P19589"] style P19589 fill:#4fc3f7,stroke:#333,color:#000

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">PKR Protein (Protein Kinase R)</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[EIF2AK2](/genes/eif2ak2)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[P19589](https://www.uniprot.org/uniprot/P19589)</td>
</tr>
<tr>
<td class="label">PDB Structures</td>
<td>2E7O, 3UI8, 5Y36</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~62 kDa</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Cytoplasm, nucleus</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>Serine/Threonine Kinase (PKR family)</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Ubiquitous, high in brain</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">3 edges</a></td>
</tr>
</table>

...

PKR Protein (Protein Kinase R)

Overview

Mermaid diagram (expand to render)

PKR (Protein Kinase R, also known as EIF2AK2) is a serine/threonine protein kinase that plays a central role in the cellular stress response, particularly in antiviral defense and translational control["@b愛德华茲2020"]. Also known as double-stranded RNA-dependent protein kinase (DSRNA-PK), PKR is activated by various stress signals including viral RNA, cellular stress, and protein aggregates found in neurodegenerative diseases.

In the context of neurodegenerative disorders, PKR has emerged as a key player in the pathogenesis of [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and other conditions. The kinase phosphorylates the translation initiation factor eIF2alpha, leading to global protein synthesis inhibition, and is activated by various pathological protein aggregates. Understanding PKR's role may lead to therapeutic strategies for neuroprotection.

Protein Infobox

Structure

PKR contains an N-terminal regulatory domain and a C-terminal kinase domain:

N-terminal Regulatory Domain

Double-stranded RNA binding domain (DRBD): Binds dsRNA of viral origin
Zinc finger domain: Involved in protein-protein interactions
Regulatory motifs: Control kinase activation

C-terminal Kinase Domain

Kinase subdomain XI: Contains the catalytic site
Activation loop: Phosphorylation site (Thr446)
ATP-binding pocket: Target of small molecule inhibitors

Regulatory Mechanisms

Autophosphorylation: Required for kinase activation
Dimerization: Induced by dsRNA binding
Inhibitory proteins: PACT (protein activator of PKR)

Normal Function

Antiviral Defense

PKR is a key component of the innate immune response:

dsRNA Detection

Binds to double-stranded RNA (viral replication intermediate)
Activation triggers interferon-stimulated genes
Blocks viral protein synthesis

eIF2α Phosphorylation

Phosphorylates translation initiation factor eIF2α
Inhibits global protein synthesis
Reduces viral replication
Conserves cellular resources during stress

Integrated Stress Response

PKR is part of the integrated stress response (ISR)[@ong2017]:

eIF2α phosphorylation is the hallmark of ISR activation
Four kinases: PKR, PERK, GCN2, HRI
Common downstream: ATF4-mediated transcription

Translational Control

PKR regulates protein synthesis[@sadigh2017]:

Global inhibition: Through eIF2α phosphorylation
Selective translation: Some mRNAs escape inhibition
Stress granule formation: mRNA sequestration

Role in Neurodegeneration

Alzheimer's Disease

PKR is implicated in AD through multiple mechanisms[@carroll2018]:

Activation in AD Brain

PKR is activated in AD hippocampus and frontal cortex
Activation correlates with disease severity
Early activation before significant pathology

eIF2α Phosphorylation

Elevated eIF2α-P in AD brains
Leads to synaptic protein synthesis inhibition
Contributes to memory impairment

Links to Aβ and Tau

[Amyloid-beta](/proteins/amyloid-beta) can activate PKR
[Tau](/proteins/tau) pathology enhances PKR activation
Creates a feed-forward loop of neurodegeneration

ER Stress

PKR links ER stress to neuronal death[@liu2018]:

ER stress activates PKR
Contributes to the unfolded protein response
Leads to apoptosis in vulnerable neurons

Parkinson's Disease

PKR is activated in PD and contributes to dopaminergic neuron death[@sukh2020]:

α-Synuclein Activation

[Alpha-synuclein](/proteins/alpha-synuclein) aggregates can activate PKR
Activated PKR in PD substantia nigra
Contributes to protein synthesis deficits

Mitochondrial Stress

Mitochondrial toxins activate PKR
Links mitochondrial dysfunction to translational repression
Exacerbates energy deficits in dopaminergic neurons

Other Neurodegenerative Conditions

Amyotrophic Lateral Sclerosis (ALS)

PKR activation in motor neurons
Contributes to translational inhibition
Mouse models show protection with PKR deletion

Huntington's Disease

Mutant huntingtin activates PKR
Contributes to translational dysfunction
Therapeutic target

Multiple Sclerosis

PKR in demyelination and neuroinflammation
Contributes to oligodendrocyte death

Therapeutic Targeting

PKR Inhibitors

Several approaches are being developed[@yoshino2019]:

Small Molecule Inhibitors

2-aminopurine: First-generation inhibitor
C16: More potent and specific
Imidazoles: Novel inhibitors in development

Challenges

CNS penetration: Essential for neurodegenerative applications
Selectivity: Avoiding off-target effects
Timing: When to intervene in disease course

Alternative Strategies

Reducing PKR Activation

Targeting upstream activators
Preventing protein aggregate formation
Modulating stress responses

ISR Modulation

Other ISR kinases can compensate
eIF2α phosphatases as targets
ATF4 modulators

Gene Therapy

Reducing PKR expression
Dominant-negative constructs
Antisense oligonucleotides

Key Publications

[Edwards HG, et al, PKR in neurodegeneration (2020)](https://pubmed.ncbi.nlm.nih.gov/32941063/)

[Carroll EC, et al, PKR and Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29524602/)

[Sukhova K, et al, PKR activation in Parkinson's disease (2020)](https://pubmed.ncbi.nlm.nih.gov/31785023/)

[Sadigh-Eteghad S, et al, PKR and protein synthesis inhibition (2017)](https://pubmed.ncbi.nlm.nih.gov/28651208/)

[Yoshino Y, et al, PKR inhibitors as therapeutic agents in neurodegenerative disease (2019)](https://pubmed.ncbi.nlm.nih.gov/31305978/)

[Gomez ML, et al, PKR in viral infections and neurodegeneration (2018)](https://pubmed.ncbi.nlm.nih.gov/29706646/)

[Abe T, et al, PKR and translational control in neurons (2018)](https://pubmed.ncbi.nlm.nih.gov/29500538/)

[Pezzuto P, et al, PKR knockout protects against neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/31067428/)

[Ong ML, et al, PKR activation and the integrated stress response (2017)](https://pubmed.ncbi.nlm.nih.gov/28257823/)

[Duttagupta P, et al, PKR in neuroinflammation (2019)](https://pubmed.ncbi.nlm.nih.gov/31766527/)

Cross-Links

[EIF2AK2 Gene](/genes/eif2ak2) - Gene page
[eIF2α](/proteins/eif2a) - Key substrate
[Alzheimer's Disease](/diseases/alzheimers-disease) - Disease
[Parkinson's Disease](/diseases/parkinsons-disease) - Disease
[Integrated Stress Response](/mechanisms/integrated-stress-response)
[Alpha-Synuclein](/proteins/alpha-synuclein) - PD protein

References