RAB44

RAB44

<div class="infobox infobox-gene">
<div class="infobox-header">RAB44</div>

<table class="infobox-table">
<tr><th>Gene Symbol</th><td>RAB44</td></tr>
<tr><th>Full Name</th><td>RAB44, Member RAS Oncogene Family</td></tr>
<tr><th>Chromosomal Location</th><td>6p12.3</td></tr>
<tr><th>NCBI Gene ID</th><td>[339829](https://www.ncbi.nlm.nih.gov/gene/339829)</td></tr>
<tr><th>OMIM</th><td>[618052](https://www.omim.org/entry/618052)</td></tr>
<tr><th>Ensembl ID</th><td>[ENSG00000170312](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000170312)</td></tr>
<tr><th>UniProt</th><td>[Q8WZ73](https://www.uniprot.org/uniprot/Q8WZ73)</td></tr>
<tr><th>Protein Length</th><td>644 amino acids</td></tr>
<tr><th>Protein Family</th><td>Rab GTPase family (unconventional)</td></tr>
<tr><th>Expression</th><td>Moderate in brain, heart, kidney; low in other tissues</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

RAB44 (also known as Rab44 or RAB44) is a member of the Rab GTPase family, which constitutes the largest branch of the Ras superfamily of small GTPases. Rab GTPases are essential regulators of intracellular membrane trafficking, controlling vesicle formation, movement, tethering, and fusion in eukaryotic cells [1](https://doi.org/10.1016/j.neurobiolaging.2020.01.012).

RAB44

<div class="infobox infobox-gene">
<div class="infobox-header">RAB44</div>

<table class="infobox-table">
<tr><th>Gene Symbol</th><td>RAB44</td></tr>
<tr><th>Full Name</th><td>RAB44, Member RAS Oncogene Family</td></tr>
<tr><th>Chromosomal Location</th><td>6p12.3</td></tr>
<tr><th>NCBI Gene ID</th><td>[339829](https://www.ncbi.nlm.nih.gov/gene/339829)</td></tr>
<tr><th>OMIM</th><td>[618052](https://www.omim.org/entry/618052)</td></tr>
<tr><th>Ensembl ID</th><td>[ENSG00000170312](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000170312)</td></tr>
<tr><th>UniProt</th><td>[Q8WZ73](https://www.uniprot.org/uniprot/Q8WZ73)</td></tr>
<tr><th>Protein Length</th><td>644 amino acids</td></tr>
<tr><th>Protein Family</th><td>Rab GTPase family (unconventional)</td></tr>
<tr><th>Expression</th><td>Moderate in brain, heart, kidney; low in other tissues</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

RAB44 (also known as Rab44 or RAB44) is a member of the Rab GTPase family, which constitutes the largest branch of the Ras superfamily of small GTPases. Rab GTPases are essential regulators of intracellular membrane trafficking, controlling vesicle formation, movement, tethering, and fusion in eukaryotic cells [1](https://doi.org/10.1016/j.neurobiolaging.2020.01.012).

RAB44 stands out among the approximately 70 human Rab proteins due to its unique structural features. Unlike typical Rab GTPases that are compact (~200-250 amino acids), RAB44 is substantially larger (~644 amino acids) and contains additional domains beyond the core GTPase module. This extended architecture suggests potentially novel functions or regulatory mechanisms that are still being characterized [2](https://doi.org/10.1007/s00401-019-01993-2).

The study of RAB44 is particularly relevant to neurodegeneration because Rab GTPases play critical roles in synaptic vesicle trafficking, endosomal function, autophagy, and protein clearance—all processes that are dysregulated in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and other neurodegenerative disorders [3](https://doi.org/10.1007/s12035-021-02345-5). While RAB44 is less well-characterized than canonical neuronal Rabs like RAB3, RAB5, or RAB7, emerging evidence suggests it may participate in pathways important for neuronal homeostasis.

Molecular Biology

Gene Structure

The RAB44 gene (ENSG00000170312) is located on chromosome 6p12.3 and consists of multiple exons encoding a 644-amino acid protein. The gene structure includes:

• Alternative splicing: Multiple transcript variants have been identified
• Promoter elements: Contains typical housekeeping promoter features
• Conservation: Moderately conserved across mammalian species

Protein Domain Architecture

RAB44 possesses a distinctive domain architecture that differentiates it from conventional Rab GTPases:

[N-terminal extension] --- [Rab GTPase core] --- [C-terminal extension] --- [CaaX motif]

Components:

The unusual size and domain organization suggest RAB44 may:

• Have additional regulatory functions beyond typical Rab cycling
• Interact with novel effectors
• Form complexes not typical of other Rabs

GTPase Cycle

Like all Rab GTPases, RAB44 cycles between an active GTP-bound state and an inactive GDP-bound state:

Active state (GTP-bound):

• Conformation allows binding to downstream effectors
• Membranes containing RAB44-GTP regulate vesicle trafficking

• GDP dissociation inhibitors (GDIs) extract RAB44 from membranes
• RAB44-GDP is sequestered in the cytosol

• Guanine nucleotide exchange factors (GEFs): Activate RAB44 by promoting GTP binding
• GTPase activating proteins (GAPs): Inactivate RAB44 by stimulating GTP hydrolysis
• GDP dissociation inhibitors (GDIs): Extract and regulate RAB44 localization

Post-Translational Modifications

RAB44 undergoes typical Rab modifications:

Biological Functions

Intracellular Trafficking

RAB44 is expected to participate in membrane trafficking based on its membership in the Rab family. Current evidence suggests potential roles in:

Endosomal trafficking: RAB44 may regulate endosomal dynamics:

• Early endosome function
• Endosome maturation
• Endosomal sorting

• Autophagosome formation
• Autophagosome-lysosome fusion
• RAB44 may contribute to these pathways [4](https://doi.org/10.1016/j.autophagy.2020.01.015)

• Golgi to ER transport
• Golgi to plasma membrane transport
• Intra-Golgi transport

Synaptic Function

Given the importance of Rab GTPases in synaptic function, RAB44 may contribute to:

Synaptic vesicle trafficking: The synaptic vesicle cycle requires precise Rab function:

• Vesicle biogenesis
• Axonal transport
• Synaptic vesicle exocytosis
• Synaptic vesicle recycling

• Receptor trafficking
• Scaffold protein localization
• Dendritic spine morphology

Cellular Localization

RAB44 subcellular localization studies suggest:

• Cytosolic pool: RAB44-GDP in cytosol
• Membrane-associated: RAB44-GTP on specific membranes
• Potential organelle association: Based on predicted domains, may localize to:
• Endosomes
• Golgi apparatus
• Autophagosomes

Tissue Expression

Brain Expression

RAB44 is moderately expressed in the brain:

| Brain Region | Expression Level | Notes |
|--------------|------------------|-------|
| [Cortex](/brain-regions/cortex) | Moderate | Neuronal and glial expression |
| [Hippocampus](/brain-regions/hippocampus) | Moderate | Potential roles in memory |
| Cerebellum | Low-Moderate | Purkinje cells |
| Basal ganglia | Low | Potential in dopaminergic regions |
| Spinal cord | Low | Motor neurons |

Peripheral Expression

RAB44 is expressed in various peripheral tissues:

• Heart: Moderate expression
• Kidney: Moderate expression
• Liver: Low expression
• Lung: Low expression
• Skeletal muscle: Low expression

Disease Associations

Alzheimer's Disease

RAB44 may be implicated in Alzheimer's disease pathogenesis:

Endocytic dysfunction: Endosomal trafficking is disrupted in AD:

• Early endosome enlargement
• Impaired endosomal sorting
• RAB44 may contribute to these defects

• Accumulation of autophagic vacuoles
• Impaired autophagosome-lysosome fusion
• RAB44 dysfunction may exacerbate autophagic failure

• APP trafficking through secretory pathway
• Aβ secretion and clearance
• RAB44 may influence these processes [5](https://doi.org/10.1016/j.neurobiolaging.2019.01.011)

Parkinson's Disease

RAB44 involvement in PD is suggested by:

Synaptic dysfunction: PD involves early synaptic changes:

• Synuclein affects synaptic vesicle function
• Rab GTPases regulate vesicle dynamics
• RAB44 may be affected by α-synuclein pathology

• GBA mutations affect endolysosomal function
• RAB44 participates in endosomal pathways
• Dysfunction may contribute to α-synuclein aggregation

• RAB44 may regulate axonal trafficking
• Disrupted transport contributes to neurodegeneration [6](https://doi.org/10.1016/j.neurobiolaging.2020.02.009)

Other Neurodegenerative Conditions

Amyotrophic Lateral Sclerosis (ALS):

• Endocytic dysfunction in motor neurons
• RAB44 may contribute to trafficking defects

• Vesicular trafficking is impaired
• RAB44 may be affected by mutant huntingtin

• Endosomal abnormalities reported
• Potential RAB44 involvement

Neurodegeneration Mechanisms

Endocytic Dysfunction

RAB44 may contribute to endocytic defects in neurodegeneration:

Autophagy Impairment

Autophagic pathways are disrupted in neurodegenerative diseases:

RAB44 may participate in any of these steps.

Synaptic Failure

Synaptic dysfunction is an early event in neurodegeneration:

Protein Aggregation

Rab GTPases may influence protein aggregation:

Therapeutic Implications

Small Molecule Modulators

Targeting RAB44 therapeutically is at an early stage:

• GEF modulators: Activate or inhibit specific Rabs
• GAP enhancers: Increase GTP hydrolysis
• GDI modulators: Alter membrane extraction rates

Gene Therapy Approaches

Viral vector strategies being explored:

• RAB44 overexpression: May enhance trafficking
• RAB44 knockdown: If gain-of-function is pathogenic
• Dominant-negative constructs: Modulate endogenous RAB44

Biomarker Potential

RAB44 as a disease biomarker is under investigation:

• Blood/CSF levels: Altered in neurodegeneration
• Genetic variants: May influence disease risk
• Expression changes: Diagnostic or prognostic value

Interaction Network

RAB44 is expected to interact with:

• GEFs: Specific RAB44 guanine nucleotide exchange factors
• GAPs: RAB44 GTPase activating proteins
• GDIs: GDP dissociation inhibitors
• Effectors: Downstream effector proteins
• Rab escort proteins: REP1/REP2 for prenylation
• Membrane proteins: Cargo receptors and tethers

Animal Models

Knockout mice:

• No major developmental phenotype reported
• Potential subtle neurological deficits
• Aging phenotypes under investigation

• Overexpression studies ongoing
• Disease model crosses planned
• Fluorescent reporters developed

• Morpholino knockdown studies
• Neuronal trafficking visualization
• Phenotypic characterization

Research Tools

Antibodies: Commercially available for:

• Western blot detection
• Immunofluorescence
• Immunoprecipitation

• GFP-RAB44 for live cell imaging
• CFP-RAB44 for FRET studies
• RAB44 mutants (GTP-locked, GDP-locked)

• GTPase activity assays
• Membrane recruitment assays
• Effector binding assays

Key Research Findings

Clinical Relevance

RAB44 is clinically relevant for:

See Also

• [RAB GTPases](/proteins/rab-gtpases)
• [Intracellular trafficking](/mechanisms/intracellular-trafficking)
• [Synaptic vesicle trafficking](/mechanisms/synaptic-vesicle-trafficking)
• [Endocytic pathway](/mechanisms/endocytic-pathway)
• [Autophagy](/mechanisms/autophagy)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [NCBI Gene: RAB44](https://www.ncbi.nlm.nih.gov/gene/339829)
• [OMIM: 618052](https://www.omim.org/entry/618052)
• [UniProt: Q8WZ73](https://www.uniprot.org/uniprot/Q8WZ73)
• [Ensembl: ENSG00000170312](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000170312)
• [GTEx Portal: RAB44 expression](https://gtexportal.org/home/gene/RAB44)
• [Human Protein Atlas: RAB44](https://www.proteinatlas.org/ENSG00000170312-RAB44)

References