RAB27A Protein (Ras-Related Protein Rab-27A)

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Introduction

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">RAB27A Protein (Ras-Related Protein Rab-27A)</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[RAB27A](/genes/rab27a)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[P51159](https://www.uniprot.org/uniprot/P51159)</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~25 kDa</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Cytoplasmic, associated with secretory granules</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>Rab GTPase family</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>Rab27A, GS2</td>
</tr>
<tr>
<td class="label">Approach</td>
<td>Description</td>
</tr>
<tr>
<td class="label">Gene therapy</td>
<td>AAV-RAB27A for GS2</td>
</tr>
<tr>
<td class="label">Small molecule modulators</td>
<td>GTPase activators/inhibitors</td>
</tr>
<tr>
<td class="label">Immunomodulation</td>
<td>For HLH management</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <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/cancer" style="color:#ef9a9a">Cancer</a></td>
</tr>
<tr>
<td class="label">SciDEX Hypoth

...

Introduction

RAB27A is a small GTPase belonging to the Rab family of proteins involved in vesicular trafficking. It plays a critical role in regulated secretion, particularly in neuroendocrine cells, immune cells, and melanocytes. Mutations in RAB27A cause Griscelli syndrome, a rare autosomal recessive disorder characterized by partial albinism, immunodeficiency, and neurological abnormalities.

:: infobox .infobox-protein
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Structure

Protein Architecture

RAB27A is a member of the Rab GTPase family with characteristic features:

GTP-binding domain: Five conserved motifs for nucleotide binding
Switch I and II regions: Conformational changes upon GTP/GDP exchange
C-terminal CAAX motif: Cysteine methylation and prenylation for membrane anchoring
Hypervariable region: Determines effector specificity

Post-Translational Modifications

Prenylation: C-terminal cysteine prenylation for membrane association
Palmitoylation: Additional lipid modification
GDP/GTP cycling: Active (GTP-bound) and inactive (GDP-bound) states

Normal Function

Vesicle Trafficking

RAB27A regulates vesicle trafficking through:

Secretory granule exocytosis: Controls regulated secretion in neuroendocrine cells

Lysosome-related organelle trafficking: Functions in melanosomes, lytic granules

Synaptic vesicle dynamics: Involved in neurotransmitter release

Autophagosome-lysosome fusion: Role in autophagy

Effector Proteins

RAB27A interacts with multiple effector proteins:

Slac2-a/MyRIP: Links RAB27A to actin filaments
Munc13-4: Regulates dense-core vesicle exocytosis
JFC1/Slp1: Scaffold protein for exocytosis
Synaptotagmin-like proteins: Calcium sensors for exocytosis

Cellular Distribution

Neuroendocrine cells (chromaffin cells, PC12 cells)
Immune cells (T cells, NK cells, mast cells)
Melanocytes
Neurons (synaptic terminals)
Platelets

Role in Disease

Griscelli Syndrome Type 2 (GS2)

RAB27A mutations cause Griscelli syndrome type 2:

Clinical features:
Partial albinism (silver-gray hair, pigmentary dilution)
Immunodeficiency (impaired T cell and NK cell function)
Hemophagocytic lymphohistiocytosis (HLH)
Neurologic abnormalities (in some patients)
Pathogenesis: Impaired secretory granule trafficking
Inheritance: Autosomal recessive

Immunodeficiency

RAB27A is essential for immune cell function:

Cytotoxic T cells: Impaired granule release
NK cells: Defective cytotoxicity
Mast cells: Altered degranulation
Platelets: Defective dense granule release

Neurodegeneration

Emerging evidence for RAB27A in neurodegeneration:

Alzheimer's disease: Altered Rab GTPase expression
Parkinson's disease: Role in alpha-synuclein trafficking
ALS: Impaired vesicle transport in motor neurons

Cancer

RAB27A is overexpressed in several cancers:

Melanoma: Promotes metastasis
Pancreatic cancer: Associated with poor prognosis
Breast cancer: Regulates exosome secretion

Therapeutic Implications

Animal Models

Rab27a Knockout Mice

Display hypopigmentation
Show immunodeficiency
Impaired platelet function
Neurological deficits

Zebrafish Models

Morpholino knockdown recapitulates GS2 phenotype
Used for drug screening

Protein-Protein Interactions

RAB27A interacts with:

GTP/GDP exchange factors (GEFs): Activate RAB27A
GTPase activating proteins (GAPs): Inactivate RAB27A
Effectors: Slac2-a, Munc13-4, JFC1
Motor proteins: Myosin Va for transport

References

[Unknown, Fukuda M. RAB27A and its role in regulated secretion (2013) (2013)](https://doi.org/10.1016/j.yexcr.2013.03.006)

[Menasche G et al., RAB27A mutations cause Griscelli syndrome (2000) (2000)](https://doi.org/10.1016/S0140-6736(00)

[Haddad EK et al., RAB27A in immune cell function (2001) (2001)](https://doi.org/10.1084/jem.194.4.471)

[Barral DC et al., RAB27A in melanosome trafficking (2002) (2002)](https://doi.org/10.1016/S0092-8674(02)

[Zhang L et al., RAB27A in cancer metastasis (2018) (2018)](https://doi.org/10.1038/s41388-018-0392-z)

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RAB27A Protein (Ras-Related Protein Rab-27A)