FYN Protein (Fyn Tyrosine Kinase)

FYN Protein (Fyn Tyrosine Kinase)

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">FYN Protein (Fyn Tyrosine Kinase)</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[FYN](/genes/fyn)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[P06241](https://www.uniprot.org/uniprot/P06241)</td>
</tr>
<tr>
<td class="label">PDB Structures</td>
<td>1AZZ, 2D4Q, 4K2J, 5NPE</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~59 kDa</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Membrane, cytoskeleton, postsynaptic densities</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>Src Family Tyrosine Kinase</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Neurons, microglia, astrocytes, oligodendrocytes</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

FYN (Fyn Tyrosine Kinase) is a member of the Src family of non-receptor tyrosine kinases, expressed prominently in the brain where it plays critical roles in synaptic plasticity, signal transduction, and neuronal function[@salter2011]. Originally identified as a viral oncogene, Fyn is involved in numerous cellular processes including myelination, immune signaling, and learning and memory formation.

FYN Protein (Fyn Tyrosine Kinase)

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">FYN Protein (Fyn Tyrosine Kinase)</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[FYN](/genes/fyn)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[P06241](https://www.uniprot.org/uniprot/P06241)</td>
</tr>
<tr>
<td class="label">PDB Structures</td>
<td>1AZZ, 2D4Q, 4K2J, 5NPE</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~59 kDa</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Membrane, cytoskeleton, postsynaptic densities</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>Src Family Tyrosine Kinase</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Neurons, microglia, astrocytes, oligodendrocytes</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

FYN (Fyn Tyrosine Kinase) is a member of the Src family of non-receptor tyrosine kinases, expressed prominently in the brain where it plays critical roles in synaptic plasticity, signal transduction, and neuronal function[@salter2011]. Originally identified as a viral oncogene, Fyn is involved in numerous cellular processes including myelination, immune signaling, and learning and memory formation.

In the context of neurodegenerative diseases, FYN has emerged as a key signaling molecule that promotes amyloid-beta (Aβ) toxicity, contributes to tau pathology, and modulates NMDA receptor function leading to excitotoxicity[@eloy2019]. The kinase is therefore considered a potential therapeutic target for [Alzheimer's disease](/diseases/alzheimers-disease) and related disorders.

Protein Infobox

Structure

Fyn is a member of the Src family of non-receptor tyrosine kinases with characteristic domain architecture:

N-terminal Region

• Myristoylation site: Covalent attachment of myristic acid for membrane anchoring
• Unique domain: Mediates protein-protein interactions specific to Fyn

Src Homology Domains

• SH3 domain: Proline-rich region binding, involved in signaling complexes
• SH2 domain: Phosphotyrosine binding, regulates kinase activity
• Kinase domain (SH1): Catalytic domain with tyrosine kinase activity

Regulatory Features

• C-terminal tail: Contains Tyr527 (inhibitory phosphorylation site)
• Activation loop: Contains Tyr420 (autophosphorylation site, activating)
• Linker region: Connects SH2 domain to kinase domain

Structural Comparison

• SRC: Ubiquitously expressed, critical for cell growth
• LCK: T-cell specific, immune function
• YES: Widely expressed, redundant with Fyn
• LYN: Myeloid cell expression

Normal Function

Synaptic Signaling

NMDA Receptor Modulation

• Phosphorylates [NMDA receptor](/entities/nmda-receptor) subunits (GluN2A/B)
• Regulates channel trafficking to the plasma membrane
• Modulates synaptic plasticity (LTP, LTD)
• Controls calcium influx through NMDA receptors

AMPA Receptor Regulation

• Phosphorylates AMPA receptor subunits
• Modulates receptor trafficking and function
• Regulates synaptic strength

Postsynaptic Density

• Localizes to postsynaptic densities
• Interacts with PSD-95 and other scaffolding proteins
• Forms signaling complexes with glutamate receptors

Myelination

• Promotes oligodendrocyte differentiation
• Regulates myelin gene expression
• Supports myelin maintenance

Immune Function

• T-cell receptor signaling (via LCK redundancy)
• Microglial activation
• Neuroinflammatory responses

Learning and Memory

• LTP induction in hippocampal neurons
• Memory consolidation
• Synaptic plasticity mechanisms

Role in Neurodegeneration

Alzheimer's Disease

Fyn is strongly implicated in AD pathogenesis through multiple mechanisms[@eloy2019]:

Aβ-Induced Activation

• [Amyloid-beta](/proteins/amyloid-beta) (Aβ) oligomers activate Fyn
• Aβ binds to cellular prion protein (PrP^c), triggering Fyn activation
• Fyn activation is an early event in Aβ toxicity
• Fyn knockout mice are protected from Aβ toxicity

NMDA Receptor Phosphorylation

• Fyn phosphorylates NMDA receptor subunits
• Leads to enhanced calcium influx (excitotoxicity)
• Contributes to synaptic dysfunction
• Links Aβ to glutamate excitotoxicity

Tau Pathology

• Tyrosine phosphorylation of tau (Tyr18, Tyr394)
• Promotes tau aggregation into neurofibrillary tangles
• Mediates Aβ-induced tau pathology
• Therapeutic target for breaking Aβ-tau interaction

Therapeutic Implications

• Fyn inhibitors protect against Aβ toxicity
• Saracatinib (AZD0530) tested in clinical trials
• Challenges: achieving CNS penetration and avoiding toxicity

Parkinson's Disease

Fyn is implicated in [Parkinson's disease](/diseases/parkinsons-disease)[@zhou2018]:

Dopaminergic Vulnerability

• Fyn expression altered in PD substantia nigra
• Contributes to dopaminergic neuron vulnerability
• May regulate α-synuclein toxicity

Neuroinflammation

• Fyn in microglial activation
• Contributes to neuroinflammation in PD
• May exacerbate dopaminergic neuron loss

Multiple Sclerosis and Demyelination

Fyn plays complex roles in demyelinating diseases[@tessier2019]:

Oligodendrocyte Function

• Required for proper oligodendrocyte maturation
• Fyn deficiency leads to hypomyelination
• Role in demyelination and remyelination

Therapeutic Target

• Fyn modulators being investigated for MS
• Balancing remyelination with immune function

Other Neurodegenerative Conditions

• Huntington's Disease: Altered Fyn signaling
• Amyotrophic Lateral Sclerosis (ALS): Motor neuron vulnerability
• Frontotemporal Dementia: Tau pathology connections

Therapeutic Targeting

Src Family Kinase Inhibitors

Several approaches are being developed[@kaufman2015]:

Clinical Candidates

• Saracatinib (AZD0530): Advanced to clinical trials for AD
• Dasatinib (Sprycel): FDA-approved for leukemia, tested in CNS
• Bosutinib: Another SFK inhibitor in development

Challenges

• CNS penetration: Many inhibitors don't cross the blood-brain barrier
• Toxicity: Off-target effects due to ubiquitous Src family expression
• Selectivity: Developing Fyn-selective vs. pan-SFK inhibitors

Alternative Approaches

Antibody-Based Therapy

• Targeting Aβ-Fyn interaction
• Blocking upstream activators

Gene Therapy

• Reducing Fyn expression
• Modulating downstream effectors

Combination Therapies

• Fyn inhibitors with Aβ immunotherapy
• Combined with tau-targeted approaches

Key Publications

Cross-Links

• [FYN Gene](/genes/fyn) - Gene page
• [NMDA Receptor](/entities/nmda-receptor) - Key substrate
• [Amyloid-Beta](/proteins/amyloid-beta) - Aβ toxicity
• [Tau Protein](/proteins/tau) - Tau phosphorylation
• [Alzheimer's Disease](/diseases/alzheimers-disease) - Disease
• [Parkinson's Disease](/diseases/parkinsons-disease) - Disease

References

See Also

• [FYN Gene](/genes/fyn)
• [NMDA Receptor Signaling](/entities/nmda-receptor)
• [Amyloid-Beta Toxicity](/proteins/amyloid-beta)
• [Tau Phosphorylation](/proteins/tau)
• [Src Family Kinases](/mechanisms/src-kinase-signaling)
• [Excitotoxicity](/mechanisms/excitotoxicity)

External Links

• [UniProt: P06241](https://www.uniprot.org/uniprot/P06241)
• [GeneCards: FYN](https://www.genecards.org/cgi-bin/carddisp.pl?gene=FYN)
• [PDB: Fyn kinase domain](https://www.rcsb.org/structure/1AZZ)
• [ClinicalTrials.gov: Saracatinib](https://clinicaltrials.gov/)