SEPTIN5 (Septin 5) encodes a member of the septin family of GTP-binding proteins essential for cytoskeleton organization, cell division, and membrane dynamics. Septins form hetero-oligomeric complexes that assemble into filaments and rings, functioning as scaffolds for protein localization and barriers in membrane trafficking. SEPTIN5 is predominantly expressed in the nervous system and is particularly important for synaptic vesicle organization, neurotransmitter release, and neuronal survival.
**Symbol:** SEPTIN5 (formerly SEPT5)
**Full Name:** Septin 5
**Chromosomal Location:** 22q11.21
**NCBI Gene ID:** [54148](https://www.ncbi.nlm.nih.gov/gene/54148)
**OMIM:** [604680](https://www.omim.org/entry/604680)
**Ensembl ID:** ENSG00000100338
**UniProt ID:** [Q9NSC5](https://www.uniprot.org/uniprot/Q9NSC5)
**Associated Diseases:** Parkinson's Disease, Alzheimer's Disease, Lewy Body Dementia
**Protein Class:** GTP-binding cytoskeletal protein
¶ Protein Structure and Function
SEPTIN5 is a 367-amino acid GTP-binding protein with:
- GTP-binding domain with P-loop motif (residues 73-80) that hydrolyzes GTP to GDP
- Septin unique element (SUE) — a conserved 30-amino acid insert unique to septins
- Central helix for protein-protein interactions
- C-terminal filament assembly domain for polymerization
SEPTIN5 forms hetero-oligomeric complexes with SEPTIN2, SEPTIN6, and SEPTIN7, creating higher-order structures essential for cellular functions.
- Synaptic Vesicle Clustering — SEPTIN5 localizes to presynaptic terminals where it organizes synaptic vesicles into functional pools, enabling efficient neurotransmitter release [1].
- Neurotransmitter Release Regulation — Through interactions with SNARE complex proteins, SEPTIN5 modulates exocytosis and synaptic plasticity [2].
- Cytokinesis in Dividing Neurons — During neurogenesis, SEPTIN5 contributes to cell division machinery in neural progenitor cells.
- Mitochondrial Dynamics — Recent research demonstrates SEPTIN5 involvement in mitochondrial fission and trafficking along axons [3].
- Membrane Trafficking — SEPTIN5 acts as a barrier at the plasma membrane, regulating vesicle trafficking and endocytosis [4].
¶ Expression and Localization
High expression in:
- Cerebral cortex — Layer V pyramidal neurons (corticospinal motor neurons)
- Hippocampus — CA3 pyramidal cells and dentate gyrus granule cells
- Cerebellum — Purkinje cells (major inhibitory output neurons)
- Basal ganglia — Striatal medium spiny neurons and substantia nigra pars compacta dopaminergic neurons
- Brainstem — Pontine nuclei and dorsal motor nucleus of the vagus
- Presynaptic terminals — Specifically localizes to synaptic vesicle clusters
- Axon initial segments — Regulates action potential initiation
- Growth cones — Guides axonal pathfinding during development
- Mitochondria — Associates with mitochondrial outer membranes
- Golgi apparatus — Involved in vesicular trafficking
SEPTIN5 expression increases during postnatal brain development, peaking in early adulthood and remaining elevated in aged brains, with particular vulnerability in regions affected by neurodegeneration.
SEPTIN5 plays a critical role in Parkinson's disease pathogenesis through multiple mechanisms:
- Alpha-Synuclein Aggregation — SEPTIN5 directly interacts with alpha-synuclein, co-localizing in Lewy bodies. This interaction accelerates aggregation and stabilizes toxic oligomers [5].
- Dopaminergic Neuron Vulnerability — SEPTIN5 is highly expressed in substantia nigra pars compacta neurons, which are selectively vulnerable in PD. Loss of SEPTIN5 function exacerbates dopaminergic degeneration [6].
- Synaptic Vesicle Dysfunction — PD-linked mutations in SEPTIN5 impair synaptic vesicle clustering, disrupting neurotransmitter release and leading to synaptic failure [7].
- Genetic Associations — Polymorphisms in the SEPTIN5 gene locus (22q11.21) have been associated with increased PD risk in genome-wide association studies [8].
In Alzheimer's disease, SEPTIN5 contributes to:
- Synaptic Dysfunction — SEPTIN5 deficiency impairs synaptic plasticity, contributing to memory deficits. Aβ oligomers reduce SEPTIN5 expression in hippocampal neurons [9].
- Tau Pathology — SEPTIN5 interacts with hyperphosphorylated tau, potentially affecting microtubule stability and axonal transport [10].
- Excitotoxicity — Septin cytoskeleton alterations contribute to dysregulated calcium homeostasis and excitotoxic cell death.
¶ Lewy Body Dementia
SEPTIN5 is a component of Lewy body pathology, where it co-aggregates with alpha-synuclein and may influence the progression of synucleinopathies.
graph TD
A["SEPTIN5 monomers"] --> B["GTP-bound SEPTIN5"]
B --> C["SEPT2/SEPT6 heterotrimer"]
C --> D["SEPT5-SEPT2-SEPT6 complex"]
D --> E["Octameric filament"]
E --> F["Higher-order structures"]
F --> G["Presynaptic scaffold"]
F --> H["Membrane diffusion barrier"]
| Partner |
Interaction Type |
Functional Consequence |
| SEPTIN2 |
Direct binding |
Filament formation |
| SEPTIN6 |
Direct binding |
Filament formation |
| SEPTIN7 |
Direct binding |
Filament formation |
| SNARE complex |
Protein interaction |
Exocytosis regulation |
| Alpha-synuclein |
Protein interaction |
Aggregation modulation |
| Synaptic vesicles |
Localization |
Vesicle clustering |
| Mitochondria |
Association |
Fission/fusion regulation |
- Synaptic Vesicle Cycling — SEPTIN5 modulates the vesicle cycle through interactions with synapsin and synaptophysin.
- Actin Cytoskeleton — Coordinates with actin filaments for membrane organization.
- Microtubule Transport — Regulates kinesin/dynactin-mediated axonal transport.
- Parkinson's Disease — GWAS signals at 22q11.21 implicate SEPTIN5 variants in PD susceptibility
- Autism Spectrum Disorder — SEPTIN5 rare variants associated with synaptic dysfunction
- Schizophrenia — 22q11.2 deletion syndrome includes SEPTIN5 haploinsufficiency
- Septin-Targeting Compounds — Small molecules modulating septin GTPase activity are in development
- Gene Therapy — SEPTIN5 overexpression as neuroprotective strategy
- Protein-Protein Interaction Inhibitors — Blocking alpha-synuclein-SEPTIN5 interaction
| Partner |
Function |
| SEPT2 |
Filament formation |
| SEPT6 |
Filament formation |
| SEPT7 |
Filament formation |
| SNARE complex |
Exocytosis regulation |
| Alpha-synuclein |
PD aggregation |
- SNCA — Alpha-synuclein
- VPS35 — Retromer component
- LRRK2 — Leucine-rich repeat kinase 2