MYO5A — Myosin Va

MYO5A — Myosin Va

<div class="infobox infobox-gene">
<h3>MYO5A</h3>
<table>
<tr><th>Gene Symbol</th><td>MYO5A</td></tr>
<tr><th>Full Name</th><td>Myosin Va (Myosin-5a)</td></tr>
<tr><th>Chromosome</th><td>15q21.2</td></tr>
<tr><th>NCBI Gene ID</th><td>[4644](https://www.ncbi.nlm.nih.gov/gene/4644)</td></tr>
<tr><th>OMIM</th><td>[160777](https://www.omim.org/entry/160777)</td></tr>
<tr><th>Ensembl ID</th><td>[ENSG00000128594](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000128594)</td></tr>
<tr><th>UniProt ID</th><td>[Q9Y4P9](https://www.uniprot.org/uniprot/Q9Y4P9)</td></tr>
<tr><th>Protein Class</th><td>Unconventional myosin motor protein</td></tr>
<tr><th>Protein Size</th><td>1,855 amino acids (~205 kDa)</td></tr>
<tr><th>Associated Diseases</th><td>[Griscelli Syndrome](/diseases/griscelli-syndrome), [Parkinson's Disease](/diseases/parkinsons-disease), Alzheimer's Disease, Syndromic Intellectual Disability</td></tr>
<tr><th>Expression</th><td>Brain (neurons), melanocytes, platelets, testis</td></tr>
</table>
</div>

Introduction

MYO5A — Myosin Va

<div class="infobox infobox-gene">
<h3>MYO5A</h3>
<table>
<tr><th>Gene Symbol</th><td>MYO5A</td></tr>
<tr><th>Full Name</th><td>Myosin Va (Myosin-5a)</td></tr>
<tr><th>Chromosome</th><td>15q21.2</td></tr>
<tr><th>NCBI Gene ID</th><td>[4644](https://www.ncbi.nlm.nih.gov/gene/4644)</td></tr>
<tr><th>OMIM</th><td>[160777](https://www.omim.org/entry/160777)</td></tr>
<tr><th>Ensembl ID</th><td>[ENSG00000128594](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000128594)</td></tr>
<tr><th>UniProt ID</th><td>[Q9Y4P9](https://www.uniprot.org/uniprot/Q9Y4P9)</td></tr>
<tr><th>Protein Class</th><td>Unconventional myosin motor protein</td></tr>
<tr><th>Protein Size</th><td>1,855 amino acids (~205 kDa)</td></tr>
<tr><th>Associated Diseases</th><td>[Griscelli Syndrome](/diseases/griscelli-syndrome), [Parkinson's Disease](/diseases/parkinsons-disease), Alzheimer's Disease, Syndromic Intellectual Disability</td></tr>
<tr><th>Expression</th><td>Brain (neurons), melanocytes, platelets, testis</td></tr>
</table>
</div>

Introduction

MYO5A (Myosin Va) encodes an unconventional myosin motor protein that moves towards the plus end of actin filaments. Myosin Va is a highly processive motor protein capable of taking multiple steps along actin filaments without dissociating, making it ideal for long-distance intracellular transport. This protein plays critical roles in the nervous system, where it participates in the transport of synaptic vesicles, organelles, and other cargoes essential for neuronal function and survival [@wu1999][@wang2014].

The discovery of myosin V as a processive motor revolutionized our understanding of intracellular transport mechanisms. Unlike conventional myosins that function as simple levers, myosin V exhibits walk-like movement along actin filaments, similar to kinesin motors. This processivity is achieved through coordinated activity of the two motor domains, which take turns binding to actin filaments, allowing the protein to traverse micrometer-scale distances without detachment.

Myosin Va is encoded by the MYO5A gene located on chromosome 15q21.2. The protein is expressed in a tissue-specific manner, with highest levels in brain, melanocytes, and platelets. In neurons, Myosin Va is enriched in dendritic compartments and synaptic regions, where it functions as a critical mediator of cargo transport essential for synaptic plasticity, dendritic spine morphology, and overall neuronal health.

Protein Structure and Function

Structural Organization

Myosin Va possesses a distinctive multi-domain architecture that enables its specialized motor functions [@rose2015]:

Motor Activity

Myosin Va exhibits several unique functional properties:

• Processive movement: Can traverse >1 μm on actin filaments without detachment
• Step size: Takes ~36 nm steps, matching actin filament periodicity
• Velocity: Moves at ~300-500 nm/s in vitro
• Direction: Plus-end directed (towards actin filament barbed ends)
• Regulation: Calmodulin binding modulates motor activity in response to calcium

Cargo Transport

The globular tail domain mediates binding to diverse cargoes [@todorovic2020]:

• Synaptic vesicles: Transport of synaptic vesicle precursors
• Endoplasmic reticulum: ER network maintenance and distribution
• Melanosomes: Pigment granule transport in melanocytes
• Mitochondria: Axonal and dendritic distribution
• Lysosomes: Intracellular trafficking
• Autophagosomes: Movement during autophagy

Role in Neuronal Function

Synaptic Transmission

Myosin Va plays a critical role in synaptic transmission through multiple mechanisms [@stuart2016]:

• Transport of synaptic vesicle precursors from the soma to presynaptic terminals
• Regulation of synaptic vesicle pool maintenance at active zones
• Participation in vesicle recycling pathways
• Modulation of neurotransmitter release probability

Dendritic Spines and Synaptic Plasticity

Myosin Va is essential for proper dendritic spine formation and maintenance [@masri2021]:

• Regulates spine morphogenesis during development
• Maintains spine stability in mature neurons
• Couples synaptic activity to structural plasticity
• Links postsynaptic signaling to cytoskeletal remodeling

Axonal Transport

In axons, Myosin Va contributes to the transport of various organelles [@li2018]:

• Anterograde transport of synaptic components
• Retrograde transport of signaling endosomes
• Distribution of presynaptic proteins
• Organelle positioning within axonal compartments

Autophagy and Protein Clearance

Myosin Va participates in autophagic pathways essential for neuronal health [@korolchuk2011][@huang2021]:

• Transport of autophagosomes along dendrites
• Fusion of autophagosomes with lysosomes
• Clearance of protein aggregates
• Regulation of mitophagy

Disease Associations

Parkinson's Disease

Myosin Va has been increasingly implicated in Parkinson's disease pathogenesis [@deshpande2019]:

Genetic studies have identified variants in MYO5A that may modify PD risk, though the exact mechanisms remain under investigation. The protein's role in autophagic clearance is particularly relevant given the centrality of protein aggregation in PD pathogenesis.

Alzheimer's Disease

Myosin Va involvement in AD includes:

• Dysregulated synaptic vesicle trafficking
• Impaired autophagic-lysosomal pathway
• Altered dendritic spine dynamics
• Contribution to amyloid-beta-induced synaptic loss

Griscelli Syndrome

Biallelic mutations in MYO5A cause Griscelli syndrome type 1 [@chen2022]:

• Inheritance: Autosomal recessive
• Clinical features: Silver-gray hair, pigment accumulation in melanocytes, immune deficiency, neurological impairment
• Mechanism: Loss of myosin Va function disrupts melanosome transport
• Neurological phenotype: May include intellectual disability, seizures, and ataxia

Other Neurological Conditions

• Syndromic intellectual disability: MYO5A variants associated with neurodevelopmental disorders
• Chediak-Higashi syndrome: Related to vesicle trafficking defects
• Huntington's disease: Altered Myosin Va expression in models

Therapeutic Implications

Targeting Strategies

Myosin Va represents a potential therapeutic target for neurodegenerative diseases:

• Modulation of transport function: Small molecules to enhance transport efficiency
• Autophagy enhancement: Promoting protein clearance pathways
• Synaptic protection: Maintaining neurotransmitter balance

Challenges

• Essential functions in multiple tissues complicate targeting
• Processive movement requires specific structural features
• Blood-brain barrier delivery challenges

Preclinical Status

• Animal models of Myosin Va deficiency inform disease mechanisms
• No direct clinical trials for neurodegenerative diseases as of 2024

Key Publications

Brain Atlas Resources

• [Allen Human Brain Atlas - MYO5A](https://human.brain-map.org/microarray/search/show?search_term=MYO5A)
• [Allen Cell Type Atlas](https://celltypes.brain-map.org/)
• [BrainSpan Atlas of the Developing Human Brain](https://brainspan.org/)
• [Allen Mouse Brain Atlas](https://mouse.brain-map.org/)

References

See Also

• [Axonal Transport](/mechanisms/axonal-transport)
• [Synaptic Function](/mechanisms/synaptic-function)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Synaptic Vesicles](/entities/synaptic-vesicles)
• [Autophagy](/mechanisms/autophagy)

External Links

• [NCBI Gene: MYO5A](https://www.ncbi.nlm.nih.gov/gene/4644)
• [UniProt: MYO5A](https://www.uniprot.org/uniprot/Q9Y4P9)
• [Ensembl: MYO5A](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000128594)
• [OMIM: 160777](https://www.omim.org/entry/160777)