ALS2 Protein (Alsin)

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ALS2 Protein (Alsin)

<div class="infobox infobox-protein">
<div class="infobox-header">ALS2 Protein (Alsin)</div>
<table class="infobox-table">
<tr><th>Protein</th><td>Alsin</td></tr>
<tr><th>Gene</th><td>ALS2</td></tr>
<tr><th>UniProt</th><td><a href="https://www.uniprot.org/uniprotkb/Q96Q42/entry" target="_blank" rel="noopener noreferrer">Q96Q42</a></td></tr>
<tr><th>Core Function</th><td>Rab5/Rac1 guanine-nucleotide exchange and endosomal trafficking control</td></tr>
<tr><th>Primary Localization</th><td>Cytosol with dynamic recruitment to endosomal and stress-responsive membranes</td></tr>
<tr><th>Disease Axis</th><td>Juvenile motor-neuron syndromes (juvenile ALS, PLS, IAHSP)</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">Amyotrophic Lateral Sclerosis</a>, <a href="/wiki/dementia" style="color:#ef9a9a">Dementia</a>, <a href="/wiki/frontotemporal-dementia" style="color:#ef9a9a">Frontotemporal Dementia</a>, <a href="/wiki/ftd" style="color:#ef9a9a">Ftd</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">105 edges</a></td>
</tr>
</table>
</div>

Overview

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ALS2 Protein (Alsin)

Overview

Alsin, encoded by ALS2, is a multi-domain trafficking regulator that coordinates membrane dynamics in vulnerable long-projecting [neurons](/entities/neurons).[@hadano2001][@yang2001] Pathogenic biallelic ALS2 variants are a validated cause of juvenile-onset motor-neuron disorders, including juvenile amyotrophic lateral sclerosis, juvenile primary lateral sclerosis, and infantile ascending hereditary spastic paralysis.[@hadano2001][@yang2001][@panzeri2006]

Mechanistically, alsin is best characterized as a Rab5 pathway activator with additional Rac1-coupled behavior that links cytoskeletal signaling to endocytic flux.[@topp2004][@kunita2007] This places ALS2 at the interface of [endolysosomal trafficking defects](/mechanisms/endolysosomal-trafficking-defects), stress adaptation, and axonal maintenance.

Domain Architecture and Functional Logic

ALS2 is a large protein with an N-terminal RCC1-like region, central Dbl-homology/pleckstrin-homology features, and a C-terminal VPS9 domain that drives Rab5 activation.[@topp2004][@yamanaka2003] The domain organization supports a recruitment-and-activation model:

upstream membrane/cytoskeletal cues recruit alsin,
alsin locally activates Rab5,
endosome maturation/fusion is promoted,
trafficking competence is restored under stress.

In neurons with long axons, this buffering of trafficking stress is likely critical because small delays in endosomal maturation can accumulate into major distal-compartment dysfunction.

Normal Cellular Function

Endosomal maturation and membrane turnover

ALS2 supports early endosomal dynamics through Rab5 activation and shapes macropinocytic/endocytic processing pathways.[@topp2004][@kunita2007] This function is particularly relevant in neurons, where membrane turnover and receptor recycling are continuous and spatially distributed.

Rac1-coupled membrane remodeling

ALS2 behaves as a Rac1-interacting effector under activated conditions, linking actin-dependent membrane remodeling to Rab5-positive vesicle handling.[@kunita2007] This coupling provides a mechanistic bridge between growth/motility cues and intracellular transport.

Stress-responsive mitochondria-endosome crosstalk

Under oxidative challenge, Rab5 machinery can relocalize to mitochondria in an ALS2-dependent manner, supporting a cytoprotective response. ALS2-deficient motor neurons show impaired adaptation and greater stress vulnerability.[@hsu2018]

Role in Disease

High-confidence genetic disease link

ALS2 mutations are among the clearest examples of recessive trafficking-pathway motor-neuron disease genes.[@hadano2001][@yang2001][@panzeri2006] The dominant molecular pattern is loss of function, often truncating variants.

Endolysosomal vulnerability model

Cell and animal models converge on impaired endosomal dynamics, altered neurite maintenance, and slowly progressive neuronal system dysfunction.[@yamanaka2003][@cai2005][@hadano2010] These models generally show subtle early phenotypes with cumulative late deficits, consistent with a long-horizon degeneration process rather than abrupt developmental failure.

Interaction with broader ALS stress biology

In SOD1-ALS background models, ALS2 loss worsens motor phenotypes, supporting the view that alsin functions as a resilience factor across convergent stress pathways rather than an isolated syndrome mechanism.[@hadano2010a]

Translational Implications

Near-term strategy: pathway compensation

Because ALS2 disease is mostly loss-of-function, immediate translational options are pathway compensation approaches:

increasing endosomal efficiency,
supporting mitochondrial stress buffering,
reducing secondary inflammatory amplification.

Mid-term strategy: genetic restoration

Gene-replacement or RNA-level correction approaches are conceptually strong for ALS2 but require motor-system-wide delivery and dose control.

Trial-design considerations

ALS2-associated syndromes are rare and slowly progressive. Efficient clinical designs likely require:

shared biomarker frameworks across juvenile motor-neuron disorders,
longitudinal digital motor metrics,
mechanistic endpoints tied to trafficking stress.

Evidence Quality Snapshot

High confidence: ALS2 mutations cause recessive juvenile motor-neuron disease.[@hadano2001][@yang2001][@panzeri2006]
High confidence: alsin is a Rab5-regulatory trafficking protein with Rac1-linked membrane dynamics.[@topp2004][@kunita2007]
Moderate confidence: stress-induced mitochondria-endosome adaptation role relevant to motor-neuron survival.[@hsu2018]
Moderate confidence: therapeutic leverage via endolysosomal pathway support, pending disease-specific intervention trials.

Brain Atlas Resources

The following resources from the Allen Brain Atlas provide expression and connectivity data for this protein/gene:

[Allen Human Brain Atlas - Gene Expression](https://human.brain-map.org/microarray/search/show?search_term=ALS2): Searchable gene expression database from adult human brain
[Allen Brain Atlas - RNA Sequencing](https://human.brain-map.org/rnasearch): RNA sequencing data across brain regions
[Allen Cell Type Atlas](https://celltypes.brain-map.org/): Single-cell transcriptomic data for cell type classification
[Allen Mouse Brain Atlas](https://mouse.brain-map.org/): Comprehensive mouse brain gene expression database
[BrainSpan Atlas of the Developing Human Brain](https://www.brainspan.org/): Developmental expression data across brain regions and ages

External Links

[UniProt: als2](https://www.uniprot.org/)
[PubMed: als2](https://pubmed.ncbi.nlm.nih.gov/?term=als2+neurodegeneration)

References

[Hadano S, Hand CK, Osuga H, et al, A gene encoding a putative GTPase regulator is mutated in familial amyotrophic lateral sclerosis 2 (2001)](https://pubmed.ncbi.nlm.nih.gov/11586298/)

[Yang Y, Hentati A, Deng HX, et al, The gene encoding alsin, a protein with three guanine-nucleotide exchange factor domains, is mutated in a form of recessive amyotrophic lateral sclerosis (2001)](https://pubmed.ncbi.nlm.nih.gov/11586297/)

[Panzeri C, De Palma C, Martinuzzi A, et al, The first ALS2 missense mutation associated with adult-onset primary lateral sclerosis (2006)](https://pubmed.ncbi.nlm.nih.gov/18223690/)

[Topp JD, Gray NW, Gerard RD, Horazdovsky BF, Alsin is a Rab5 and Rac1 guanine nucleotide exchange factor (2004)](https://pubmed.ncbi.nlm.nih.gov/15033976/)

[Kunita R, Otomo A, Mizumura H, et al, The Rab5 activator ALS2/alsin acts as a novel Rac1 effector through Rac1-activated endocytosis (2007)](https://pubmed.ncbi.nlm.nih.gov/17409386/)

[Yamanaka K, Vande Velde C, Eymard-Pierre E, et al, Unstable mutants in the peripheral endosomal membrane component ALS2 cause motor neuron disease (2003)](https://pubmed.ncbi.nlm.nih.gov/16085057/)

[Hsu F, Spannl S, Ferguson C, et al, Rab5 and Alsin regulate stress-activated cytoprotective signaling on mitochondria (2018)](https://pubmed.ncbi.nlm.nih.gov/29469808/)

[Cai H, Lin X, Xie C, et al, Mice deficient in the Rab5 guanine nucleotide exchange factor ALS2/alsin exhibit age-dependent neurological deficits and altered endosome trafficking (2005)](https://pubmed.ncbi.nlm.nih.gov/16321985/)

[Hadano S, Otomo A, Suzuki-Utsunomiya K, et al, ALS2CL, a novel ALS2-interactor, modulates ALS2-mediated endosome dynamics (2010)](https://pubmed.ncbi.nlm.nih.gov/21680709/)

[Hadano S, Otomo A, Kunita R, et al, Loss of ALS2/Alsin exacerbates motor dysfunction in a SOD1-expressing mouse ALS model by disturbing endolysosomal trafficking (2010)](https://pubmed.ncbi.nlm.nih.gov/20339559/)

AlphaFold Structure

AlphaFold DB provides a predicted structure for ALS2 / UniProt Q96Q42 (model version 6): https://alphafold.ebi.ac.uk/entry/Q96Q42.
AlphaFold reports a mean pLDDT confidence score of 74.06, indicating confident backbone placement for much of the model, with lower-confidence regions possible.
InterPro annotations highlight Dbl homology domain domain (690-885); Regulator of chromosome condensation, RCC1 repeat (60-109); VPS9 domain domain (1513-1657).
PDB coordinates: https://alphafold.ebi.ac.uk/files/AF-Q96Q42-F1-model_v6.pdb mmCIF coordinates: https://alphafold.ebi.ac.uk/files/AF-Q96Q42-F1-model_v6.cif.
Use the prediction as structural context for target assessment; local low-pLDDT segments may reflect disorder, flexible linkers, or unresolved domain orientation rather than a stable fold.

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ALS2 Protein (Alsin)

ALS2 Protein (Alsin)

Overview

ALS2 Protein (Alsin)

Overview

Domain Architecture and Functional Logic

Normal Cellular Function

Endosomal maturation and membrane turnover

Rac1-coupled membrane remodeling

Stress-responsive mitochondria-endosome crosstalk

Role in Disease

High-confidence genetic disease link

Endolysosomal vulnerability model

Interaction with broader ALS stress biology

Translational Implications

Near-term strategy: pathway compensation

Mid-term strategy: genetic restoration

Trial-design considerations

Evidence Quality Snapshot

See Also

Brain Atlas Resources

External Links

References

AlphaFold Structure