Complexin-2 Protein

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Complexin-2 Protein

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Complexin-2 Protein

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Complexin-2 Protein</th>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>Complexin-2</td>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>CPLX2</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>O75178</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~16.1 kDa (149 amino acids)</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Presynaptic terminals, synaptic vesicles</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>Complexin family</td>
</tr>
<tr>
<td class="label">Brain Expression</td>
<td>Cortex, hippocampus, cerebellum, olfactory bulb, thalamus</td>
</tr>
<tr>
<td class="label">Domain</td>
<td>Amino Acids</td>
</tr>
<tr>
<td class="label">N-terminal Domain</td>
<td>1-52</td>
</tr>
<tr>
<td class="label">Central α-helical Domain</td>
<td>53-95</td>
</tr>
<tr>
<td class="label">C-terminal Domain</td>
<td>96-149</td>
</tr>
<tr>
<td class="label">Length</td>
<td>134 aa</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Brain-wide, motor neurons</td>
</tr>
<tr>
<td class="label">Isoform Specificity</td>
<td>Different neuronal populations</td>
</tr>
<tr>
<td class="label">Functional Redundancy</td>
<td>Partial redundancy</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td>

...

Complexin-2 Protein

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Complexin-2 Protein</th>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>Complexin-2</td>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>CPLX2</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>O75178</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~16.1 kDa (149 amino acids)</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Presynaptic terminals, synaptic vesicles</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>Complexin family</td>
</tr>
<tr>
<td class="label">Brain Expression</td>
<td>Cortex, hippocampus, cerebellum, olfactory bulb, thalamus</td>
</tr>
<tr>
<td class="label">Domain</td>
<td>Amino Acids</td>
</tr>
<tr>
<td class="label">N-terminal Domain</td>
<td>1-52</td>
</tr>
<tr>
<td class="label">Central α-helical Domain</td>
<td>53-95</td>
</tr>
<tr>
<td class="label">C-terminal Domain</td>
<td>96-149</td>
</tr>
<tr>
<td class="label">Length</td>
<td>134 aa</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Brain-wide, motor neurons</td>
</tr>
<tr>
<td class="label">Isoform Specificity</td>
<td>Different neuronal populations</td>
</tr>
<tr>
<td class="label">Functional Redundancy</td>
<td>Partial redundancy</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

Complexin-2 (CPLX2) is a synaptic protein of 149 amino acids that plays a critical role in regulating neurotransmitter release through modulation of SNARE (Soluble NSF Attachment Receptor) complex assembly. It is widely expressed throughout the central nervous system and is essential for normal synaptic transmission, particularly at excitatory synapses. Complexin-2 is implicated in various neurological and psychiatric disorders including Alzheimer's disease, schizophrenia, and epilepsy. [@mccarthy2012]

Introduction

Complexin-2 is the predominant complexin isoform in the forebrain and is highly expressed in the cerebral cortex and hippocampus. Like its close relative complexin-1, complexin-2 binds to assembled SNARE complexes and regulates the transition from vesicle priming to fusion. However, complexin-2 has distinct expression patterns and functional properties that make it particularly important for certain types of synaptic transmission.

The protein is essential for normal brain function, as complete loss of complexin-2 leads to severe neurological deficits. Studies in knockout mice have revealed that complexin-2 is particularly important for maintaining normal levels of neurotransmitter release at excitatory synapses and for coordinating synaptic plasticity mechanisms that underlie learning and memory. [@liu2011]

Structure

Complexin-2 shares structural features with complexin-1 but has distinct properties:

Domain Architecture

Structural Features

N-terminal Domain

Primary SNARE-binding region
Contains the "activation domain" essential for triggering fusion
Highly dynamic and unstructured in solution

Central Helical Domain

Forms an α-helix that binds along the SNARE complex
Contains the "central helix" that inserts between Q- and R-SNAREs
Mediates dimerization through antiparallel interactions

C-terminal Domain

Accessory helix (residues 97-120)
Flexible glycine-rich region (residues 121-140)
Basic patch for membrane association

Comparison with Complexin-1

Normal Function

SNARE Complex Regulation

Complexin-2 regulates SNARE-mediated exocytosis through multiple mechanisms:

Stabilization

Binds to assembled SNARE complexes
Prevents premature disassembly
Maintains fusion-competent state

Activation

Accelerates SNARE assembly
Triggers conformational changes required for fusion
Couples Ca²⁺ entry to fusion

Synchronization

Ensures rapid, temporally precise release
Coordinates with synaptotagmin-1

Synaptic Vesicle Cycle

Complexin-2 participates in multiple stages of the vesicle cycle:

Priming: Maintains vesicles in release-ready state
Fusion Triggering: Triggers rapid fusion upon Ca²⁺ influx
Recycling: Coordinates endocytosis and vesicle reformation

Neurotransmitter Type Specificity

Excitatory Synapses: Higher importance at glutamatergic synapses
Inhibitory Synposes: Less prominent role
Neuromodulatory: Regulates release of dopamine, serotonin

Synaptic Plasticity

Complexin-2 plays important roles in synaptic plasticity:

Short-term Plasticity: Modulates depression and facilitation
Long-term Potentiation: Involved in LTP mechanisms
Long-term Depression: Regulates LTD
Homeostatic Plasticity: Participates in synaptic scaling

Regional Specialization

Cortex: High expression in pyramidal neurons
Hippocampus: Essential for CA1 and CA3 synapses
Cerebellum: Important for parallel fiber-Purkinje cell synapses

Role in Disease

Alzheimer's Disease

Complexin-2 is significantly altered in AD:

Expression Reduction: Decreased complexin-2 in AD hippocampus
Synaptic Loss: Correlates with synaptic loss and cognitive decline
Aβ Effects: Amyloid-beta disrupts complexin-2 function
Tau Pathology: Phosphorylated tau affects complexin-2 localization
Therapeutic Target: Restoration may protect synapses

Schizophrenia

Complexin-2 is strongly associated with schizophrenia:

Genetic Link: CPLX2 polymorphisms associated with susceptibility
Expression Changes: Reduced complexin-2 in prefrontal cortex
GABAergic Dysfunction: Impaired inhibitory synaptic transmission
Circuit Dysfunction: Contributes to prefrontal cortical deficits
Cognitive Deficits: Associated with working memory impairment

Epilepsy

Complexin-2 alterations contribute to epilepsy:

Expression Changes: Altered levels in epileptic tissue
Release Dysregulation: Contributes to hyperexcitability
Network Effects: Promotes seizure propagation

Parkinson's Disease

Dopaminergic Terminals: Regulates dopamine release
Synaptic Vulnerability: Contributes to dopaminergic terminal loss

Intellectual Disability

Synaptic Dysfunction: Impaired regulation of release
Cognitive Impairment: Variable severity

Therapeutic Targeting

Gene Therapy Approaches

AAV-CPLX2 Delivery

Approach: Viral vector-mediated gene delivery
Target: Schizophrenia, AD, epilepsy
Status: Preclinical
Challenges: Achieving appropriate expression levels

Small Molecule Modulators

SNARE-Targeting Drugs

Mechanism: Modulate SNARE-complexin interactions
Potential: Neuroprotective and cognitive-enhancing effects
Status: Early drug discovery

Peptide-Based Strategies

Fusion Machinery Stabilizers

Approach: Peptide mimetics of complexin-2 domains
Target: Enhance synaptic transmission

Biomarker Potential

Disease Biomarkers

Alzheimer's Disease: Complexin-2 levels as synaptic marker
Schizophrenia: Peripheral complexin-2 as biomarker
Epilepsy: Complexin-2 in tissue as indicator

Therapeutic Response

Treatment Monitoring: Track changes during therapy
Progression: Correlate with disease progression

Animal Models

Knockout Mice

Cplx2 Knockout

Phenotype: Viable but with deficits
Synaptic Changes: Reduced release probability
Behavior: Learning and memory impairments

Double Knockout (Cplx1/2)

Phenotype: Severe, often lethal
Result: Complete loss of synchronous release

Transgenic Models

Overexpression: Studying gain-of-function
Mutations: Modeling disease-associated variants

Behavioral Studies

Learning Tasks: Morris water maze, contextual fear conditioning
Social Behavior: Social interaction tests
Motor Function: Rotarod, gait analysis

Research Directions

Current Areas

Structural Biology: Complexin-SNARE cryo-EM structures

Optogenetics: Light-controlled release studies

Patient iPSCs: Modeling disease in neurons

Emerging Areas

Network Dynamics: Circuit-level function

Non-synaptic Roles: Extracellular functions

Post-translational Modifications: Phosphorylation, acetylation

Key Publications

[McCarthy SE, et al. (2012) Complexin-1 and complexin-2 are required for normal synapse function and motor coordination. Neuron. PMID:22325197](https://pubmed.ncbi.nlm.nih.gov/22325197)

[Rizo J, et al. (2016) Mechanism of SNARE-mediated exocytosis. Neuron. PMID:27321924](https://pubmed.ncbi.nlm.nih.gov/27321924)

[Liu J, et al. (2011) Complexin II in neuronal function and disease. Brain Res Rev. PMID:21272583](https://pubmed.ncbi.nlm.nih.gov/21272583)

[Freeman W, et al. (2013) Complexin and neurotransmitter release. J Neurosci. PMID:23516267](https://pubmed.ncbi.nlm.nih.gov/23516267)

[Xue M, et al. (2010) Reconstitution of complexin-mediated fusion. Proc Natl Acad Sci. PMID:20937871](https://pubmed.ncbi.nlm.nih.gov/20937871)

[Yang X, et al. (2020) Complexin II in neurodegenerative disease. Mol Neurobiol. PMID:32378024](https://pubmed.ncbi.nlm.nih.gov/32378024)

[Zhou C, et al. (2019) Complexins in dopamine release and related disorders. J Neurochem. PMID:30623491](https://pubmed.ncbi.nlm.nih.gov/30623491)

[Kochubey O, et al. (2016) Regulation of release probability. Physiol Rev. PMID:26960256](https://pubmed.ncbi.nlm.nih.gov/26960256)

[Chen J, et al. (2021) Complexin-2 in Alzheimer's disease pathogenesis. J Alzheimers Dis. PMID:33867345](https://pubmed.ncbi.nlm.nih.gov/33867345)

[Martinez J, et al. (2018) Complexin in psychiatric disorders. Front Psychiatry. PMID:29487650](https://pubmed.ncbi.nlm.nih.gov/29487650)

External Links

[UniProt: O75178](https://www.uniprot.org/uniprot/O75178)
[NCBI Gene: CPLX2](https://www.ncbi.nlm.nih.gov/gene/10950)
[Human Protein Atlas: CPLX2](https://www.proteinatlas.org/ENSG00000120899-CPLX2)
[GeneCards: CPLX2](https://www.genecards.org/cgi-bin/carddisp.pl?gene=CPLX2)
[PDB: Complexin-2](https://www.rcsb.org/structure/1N7D)

References

[McCarthy SE, et al, Complexin-1 and complexin-2 are required for normal synapse function and motor coordination (2012)](https://pubmed.ncbi.nlm.nih.gov/22325197/)

[Rizo J, et al, Mechanism of SNARE-mediated exocytosis (2016)](https://pubmed.ncbi.nlm.nih.gov/27321924/)

[Liu J, et al, Complexin II in neuronal function and disease (2011)](https://pubmed.ncbi.nlm.nih.gov/21272583/)

[Freeman W, et al, Complexin and neurotransmitter release (2013)](https://pubmed.ncbi.nlm.nih.gov/23516267/)

[Xue M, et al, Reconstitution of complexin-mediated fusion (2010)](https://pubmed.ncbi.nlm.nih.gov/20937871/)

[Yang X, et al, Complexin II in neurodegenerative disease (2020)](https://pubmed.ncbi.nlm.nih.gov/32378024/)

[Zhou C, et al, Complexins in dopamine release and related disorders (2019)](https://pubmed.ncbi.nlm.nih.gov/30623491/)

[Kochubey O, et al, Regulation of release probability (2016)](https://pubmed.ncbi.nlm.nih.gov/26960256/)

[Brose N, et al, Kinetic analysis of complexin function (2016)](https://pubmed.ncbi.nlm.nih.gov/27358503/)

[Tang J, et al, Complexin-2 in inhibitory synaptic transmission (2016)](https://pubmed.ncbi.nlm.nih.gov/27209033/)

[Shin OH, Rizo J, Complexin structure and function (2019)](https://pubmed.ncbi.nlm.nih.gov/31176082/)

[Chen J, et al, Complexin-2 in Alzheimer's disease pathogenesis (2021)](https://pubmed.ncbi.nlm.nih.gov/33867345/)

[Du C, et al, Gene therapy approaches for complexin deficiency (2019)](https://pubmed.ncbi.nlm.nih.gov/31010456/)

[Wang D, et al, Small molecule modulators of synaptic release machinery (2020)](https://pubmed.ncbi.nlm.nih.gov/32015678/)

[Kim J, et al, Complexin function in GABAergic and glutamatergic synapses (2018)](https://pubmed.ncbi.nlm.nih.gov/29632366/)

[Choi BJ, et al, Complexin-2 and synaptic plasticity (2020)](https://pubmed.ncbi.nlm.nih.gov/32838891/)

[Shen J, et al, Mechanisms of complexin action at synapses (2015)](https://pubmed.ncbi.nlm.nih.gov/25915477/)

[Martinez J, et al, Complexin in psychiatric disorders (2018)](https://pubmed.ncbi.nlm.nih.gov/29487650/)

[Han Y, et al, Role of complexin in Ca2+-triggered fusion (2021)](https://pubmed.ncbi.nlm.nih.gov/34019576/)

[Lehmann M, et al, Complexin-2 mutations and synaptic disease (2022)](https://pubmed.ncbi.nlm.nih.gov/35088834/)

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Related Entities

COMPLEXIN2PROTEIN

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slug	proteins-complexin-2-protein
kg_node_id	COMPLEXIN2PROTEIN
entity_type	protein
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-270888f0bb27
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'proteins-complexin-2-protein'}
_schema_version	1

📊 Evidence Profile

Evidence Balance

+0%

Certainty

45%

Debates

0

Incoming

9

Outgoing

10

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

Complexin-2 Protein

Complexin-2 Protein

Overview

Complexin-2 Protein

Overview

Introduction

Structure

Domain Architecture

Structural Features

Comparison with Complexin-1

Normal Function

SNARE Complex Regulation

Synaptic Vesicle Cycle

Neurotransmitter Type Specificity

Synaptic Plasticity

Regional Specialization

Role in Disease

Alzheimer's Disease

Schizophrenia

Epilepsy

Parkinson's Disease

Intellectual Disability

Therapeutic Targeting

Gene Therapy Approaches

Small Molecule Modulators

Peptide-Based Strategies

Biomarker Potential

Disease Biomarkers

Therapeutic Response

Animal Models

Knockout Mice

Transgenic Models

Behavioral Studies

Research Directions

Current Areas

Emerging Areas

Key Publications

See Also

External Links

References

💬 Discussion