septin5-protein

Septin5 Protein (SEPTIN5)

<table class="infobox infobox-protein">
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<th class="infobox-header" colspan="2">septin5-protein</th>
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<td class="label">Symbol</td>
<td><strong>SEPTIN5</strong></td>
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<td class="label">Full Name</td>
<td>septin5-protein</td>
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<td class="label">Type</td>
<td>Protein</td>
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<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=SEPTIN5" target="_blank">Search UniProt</a></td>
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<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
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Overview

Septin5 (SEPTIN5) is a member of the septin family of GTP-binding proteins that play critical roles in cytokinesis, membrane dynamics, and cytoskeletal organization. In the brain, SEPTIN5 is highly expressed in neurons and is particularly important for synaptic function, mitochondrial quality control, and dopaminergic neuron survival. SEPTIN5 has emerged as a significant protein in Parkinson's disease (PD) pathogenesis due to its interaction with [alpha-synuclein](/proteins/alpha-synuclein), [parkin](/genes/parkin), and its presence in Lewy bodies [1][2][3].

Septin5 Protein (SEPTIN5)

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">septin5-protein</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>SEPTIN5</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>septin5-protein</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Protein</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=SEPTIN5" target="_blank">Search UniProt</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

Overview

Septin5 (SEPTIN5) is a member of the septin family of GTP-binding proteins that play critical roles in cytokinesis, membrane dynamics, and cytoskeletal organization. In the brain, SEPTIN5 is highly expressed in neurons and is particularly important for synaptic function, mitochondrial quality control, and dopaminergic neuron survival. SEPTIN5 has emerged as a significant protein in Parkinson's disease (PD) pathogenesis due to its interaction with [alpha-synuclein](/proteins/alpha-synuclein), [parkin](/genes/parkin), and its presence in Lewy bodies [1][2][3].

The septin family comprises evolutionarily conserved GTPases that form hetero-oligomeric complexes, assembling into filaments and rings that function as scaffolds for membrane organization and protein recruitment. SEPTIN5 is predominantly expressed in the central nervous system, with particularly high levels in dopaminergic neurons of the substantia nigra pars compacta (SNc), hippocampal pyramidal neurons, and cortical neurons [4][5].

Structure and Biochemistry

Protein Architecture

SEPTIN5 belongs to the septin family characterized by a conserved GTP-binding domain (P-loop NTP hydrolase domain) with the following structural features [6][7]:

• Nucleotide-binding domain: Core P-loop NTP hydrolase domain (~200 amino acids) that binds and hydrolyzes GTP
• Switch I and II regions: Conformational changes upon GTP/GDP binding that mediate protein-protein interactions
• Polybasic region: C-terminal membrane interaction domain that facilitates association with phospholipid membranes
• Coiled-coil domain: Mediates homomeric and heteromeric septin interactions for filament formation

GTPase Activity

The GTPase activity of SEPTIN5 is regulated by:

• Nucleotide cycling: GTP binding induces conformational changes; GTP hydrolysis to GDP resets the cycle
• Self-assembly: Septin polymerization enhances GTPase activity through allosteric mechanisms
• Phosphorylation: Post-translational modifications at serine and threonine residues modulate activity
• Membrane interactions: Phosphoinositide binding stimulates GTPase activity

Normal Physiological Function

Synaptic Vesicle Trafficking

In the nervous system, SEPTIN5 plays a central role in synaptic vesicle dynamics [10][11]:

• Synaptic vesicle release: SEPTIN5 localizes to presynaptic terminals and regulates the docking, fusion, and release of synaptic vesicles. Septin filaments form a diffusion barrier at the active zone that controls the availability of releasable vesicles.
• Exocytosis: SEPTIN5 participates in dense-core vesicle release in neurons, including neuropeptide secretion and hormone release from endocrine cells. The septin scaffold facilitates SNARE complex assembly and membrane fusion.
• Synaptic vesicle cycling: SEPTIN5 coordinates the replenishment of synaptic vesicle pools after exocytosis, ensuring sustained neurotransmission during repetitive stimulation.

Mitochondrial Quality Control

SEPTIN5 interacts with the parkin-mediated mitophagy pathway [12][13]:

• Parkin interaction: SEPTIN5 binds to parkin (PARK2), an E3 ubiquitin ligase mutated in autosomal recessive familial PD. This interaction recruits SEPTIN5 to damaged mitochondria.
• Mitophagy regulation: SEPTIN5 ubiquitination by parkin tags mitochondria for autophagic degradation. Loss of SEPTIN5 impairs mitophagy and leads to accumulation of dysfunctional mitochondria.
• Mitochondrial dynamics: SEPTIN5 influences mitochondrial fission and fusion events, affecting mitochondrial morphology and distribution in neurons.

Neuronal Polarity and Cytokinesis

SEPTIN5 contributes to [neuronal development and polarity](/mechanisms/neuronal-development) [14]:

• Axon-dendrite polarity: Septin filaments accumulate at the axon initial segment (AIS) and help maintain neuronal polarity by forming a diffusion barrier
• Cytokinesis: In neural progenitor cells, SEPTIN5 is essential for cell division and proper distribution of daughter cells
• Neuronal migration: SEPTIN5-mediated cytoskeletal dynamics contribute to neuronal migration during cortical development

Dopaminergic Neuron Function

SEPTIN5 is particularly important in dopaminergic neurons [15][16]:

• Dopamine synthesis and release: SEPTIN5 regulates the packaging and activity-dependent release of dopamine from synaptic vesicles
• Axonal maintenance: Septin filaments support axonal integrity and mitochondrial transport in long dopaminergic axons projecting from the substantia nigra to the striatum
• Neuronal survival: SEPTIN5 protects dopaminergic neurons against various cellular stressors through its role in mitophagy and synaptic maintenance

Role in Neurodegenerative Diseases

Parkinson's Disease

SEPTIN5 is strongly implicated in PD pathogenesis through multiple mechanisms [17][18][19]:

Alpha-Synuclein Interaction

SEPTIN5 directly interacts with alpha-synuclein (αSyn), the core protein of Lewy bodies:

• SEPTIN5 co-localizes with αSyn in Lewy bodies and Lewy neurites in PD brains
• αSyn aggregation disrupts SEPTIN5 filament organization and function
• SEPTIN5 can modulate αSyn aggregation kinetics in vitro and in cellular models
• The SEPTIN5-αSyn interaction may represent a therapeutic target for disease modification

Parkin Pathway Dysfunction

Mutations in the PARK2 (parkin) gene cause autosomal recessive juvenile Parkinsonism:

• SEPTIN5 accumulation is observed in parkin-deficient neurons and PD brains
• Impaired parkin-mediated SEPTIN5 ubiquitination leads to toxic SEPTIN5 aggregation
• Loss of SEPTIN5 regulation contributes to mitochondrial dysfunction in dopaminergic neurons

Aggregation Pathology

SEPTIN5 forms insoluble aggregates in PD brains:

• SEPTIN5-positive inclusions are found in the substantia nigra of PD patients
• SEPTIN5 aggregation correlates with dopaminergic neuron loss
• Aggregated SEPTIN5 may represent a seed for Lewy body formation

Therapeutic Implications

Targeting SEPTIN5 represents a promising therapeutic strategy [20][21]:

• Septin-stabilizing compounds: Small molecules that promote septin filament formation and stability
• GTPase modulators: Drugs targeting SEPTIN5 GTPase activity to restore proper function
• Gene therapy: Viral vector-mediated SEPTIN5 expression or silencing approaches
• Protein-protein interaction inhibitors: Blocking SEPTIN5-αSyn or SEPTIN5-parkin interactions

Alzheimer's Disease

SEPTIN5 alterations are observed in Alzheimer's disease (AD) [22][23]:

• Changed SEPTIN5 expression in AD brain tissue
• SEPTIN5 involvement in amyloid-β-induced synaptic dysfunction
• Potential role in tau pathology through cytoskeletal interactions

Huntington's Disease

SEPTIN5 contributes to Huntington's disease (HD) pathogenesis [24]:

• Altered septin expression and localization in HD brains
• SEPTIN5 involvement in mutant huntingtin-induced synaptic dysfunction
• Dysregulated mitophagy in HD neurons involving SEPTIN5

Amyotrophic Lateral Sclerosis

SEPTIN5 may play a role in ALS [25]:

• SEPTIN5-positive inclusions in spinal cord motor neurons of ALS patients
• Impaired axonal transport in motor neurons involving septin dysfunction
• Interactions with ALS-associated proteins (TDP-43, FUS)

Therapeutic Targeting

Small Molecule Therapies

Several therapeutic approaches target septin function [26][27]:

• Septin GTPase activators: Compounds that enhance GTPase activity to promote proper septin dynamics
• Septin filament stabilizers: Molecules that stabilize septin assemblies and prevent aggregation
• Anti-aggregatory agents: Drugs that prevent SEPTIN5 aggregation and promote clearance

Gene Therapy Approaches

Gene therapy strategies include [28][29]:

• SEPT5 overexpression: Viral delivery of wild-type SEPT5 to restore function in dopaminergic neurons
• RNAi silencing: Reducing SEPTIN5 expression in contexts where aggregation is toxic
• Septin-modifying enzymes: Expressing enzymes that regulate SEPTIN5 post-translational modifications

Biomarker Potential

SEPTIN5 shows promise as a biomarker for synucleinopathies [30]:

• Cerebrospinal fluid SEPT5: Detectable levels in CSF correlate with disease progression
• Blood-derived exosomes: SEPT5 in neuronal exosomes reflects brain pathology
• Diagnostic utility: SEPT5 measurement may aid in differential diagnosis of Parkinsonian disorders

Cross-Links

• [Alpha-synuclein](/proteins/alpha-synuclein) — PD protein, directly interacts with SEPTIN5
• [Parkin](/genes/parkin) — PD gene, regulates SEPTIN5 via ubiquitination
• [Parkinson's Disease](/diseases/parkinsons-disease) — Primary disease association
• [Mitochondrial dysfunction](/mechanisms/mitochondrial-dysfunction) — SEPTIN5 regulates mitophagy
• [Synaptic dysfunction](/mechanisms/synaptic-dysfunction) — SEPTIN5 controls vesicle release
• [Dopaminergic neurons](/cell-types/dopaminergic-neurons) — Primary cell type expressing SEPTIN5
• [Substantia nigra](/cell-types/substantia-nigra-pars-compacta) — Brain region with high SEPTIN5 expression
• [Lewy bodies](/mechanisms/lewy-body-pathology) — SEPTIN5 co-localizes with αSyn in inclusions

References

See Also

• [Parkin Gene](/genes/parkin)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Alpha-synuclein](/proteins/alpha-synuclein)
• [Mitochondrial dysfunction](/mechanisms/mitochondrial-dysfunction)
• [Synaptic dysfunction](/mechanisms/synaptic-dysfunction)
• [Dopaminergic neurons](/cell-types/dopaminergic-neurons)
• [Lewy body pathology](/mechanisms/lewy-body-pathology)