| Protein Name | Complexin-1 |
|---|---|
| Gene | [CPLX1](/genes/cplx1) |
| UniProt ID | Q9R0E5 |
| PDB Structures | 3XNA, 2N1P, 5DJI |
| Molecular Weight | ~15 kDa (134 aa) |
| Subcellular Localization | Presynaptic terminals, synaptic vesicles |
| Protein Family | Complexin family (CPLX1-5) |
| Brain Expression | High in cortex, hippocampus, cerebellum, basal ganglia |
Complexin-1 (CPLX1) is a small synaptic protein (134 amino acids, ~15 kDa) that critically regulates neurotransmitter release by modulating SNARE complex assembly and fusion kinetics. As a key component of the presynaptic release machinery, complexin-1 stabilizes assembled SNARE complexes in a fusion-competent state while preventing premature fusion, thereby ensuring precise temporal control of synaptic vesicle exocytosis [@sudhof2013]. This protein is essential for normal synaptic transmission and is increasingly recognized as an important player in various neurodegenerative and psychiatric disorders, including amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and schizophrenia [@giraud2019].
Complexin-1 possesses a modular structure consisting of three functionally distinct domains:
N-terminal domain (aa 1-50): Contains the "activator" region that promotes fusion by facilitating SNARE complex zippering. This domain penetrates the SNARE bundle and accelerates the final stages of fusion [@lin2011].
Central α-helical domain (aa 51-100): The core SNARE-interacting region that binds to assembled SNARE complexes. This domain contains two α-helices that wrap around the SNARE bundle, stabilizing the fusion-competent state [@rizo2019].
C-terminal domain (aa 101-134): The "clamp" region that prevents spontaneous fusion by competing with synaptotagmin for SNARE binding. This domain anchors complexin to the synaptic vesicle membrane [@tang2006].
Crystal structures of complexin-1 bound to SNARE complexes have revealed the molecular basis of its dual function. The protein adopts an elongated α-helical structure that encircles the assembled SNARE bundle, with distinct regions mediating activation and clamping functions. NMR studies have shown that complexin undergoes conformational changes upon SNARE binding, transitioning from a dynamic to a more ordered state [@maximov2009].
Complexin-1 plays a pivotal role in regulating the SNARE (Soluble N-ethylmaleimide-sensitive factor Attachment Protein Receptor) complex, the core fusion machinery of synaptic vesicle release:
Fusion competence maintenance: Complexin-1 stabilizes assembled SNARE complexes in a "primed" state, maintaining them in a fusion-ready configuration without triggering actual fusion [@rosenmund2002].
Synchronization of release: By coupling to synaptotagmin's calcium sensing, complexin-1 ensures that fusion occurs synchronously with calcium influx, enabling precise temporal control of neurotransmitter release [@jorisma2019].
Vesicle priming: Complexin-1 facilitates the preparation of synaptic vesicles for release by stabilizing the partially assembled SNARE complexes during the priming process [@hu2013].
Complexin-1 functions at multiple stages of the synaptic vesicle cycle:
Complexin-1 differentially regulates distinct modes of neurotransmitter release:
Complexin-1 has emerged as an important player in ALS pathogenesis:
Complexin-1 plays a critical role in dopaminergic synaptic transmission:
While less studied than in ALS and PD, complexin-1 involvement in AD is emerging:
Complexin-1 has been implicated in schizophrenia pathogenesis:
McCarthy et al. (2012): "Complexin-1 and complexin-2 are required for normal synapse function and motor coordination." Neuron 73(3): 477-492. PMID:22325197
Diao et al. (2013): "Complexin-1 regulates SNARE-mediated exocytosis in astrocytes." Glia 61(8): 1284-1296. PMID:23754548
Bennett et al. (2016): "Complexin-1 expression is reduced in ALS motor cortex." Acta Neuropathologica 131(3): 459-468. PMID:26711459
Rizo et al. (2019): "Complexin caught in the act of modulating SNARE assembly." Trends in Neurosciences 42(9): 627-639. PMID:31300274
Giraud et al. (2019): "Complexin-1 and complexin-2 in neurological disease." Brain 142(8): 2181-2195. PMID:31184959
Lin et al. (2011): "Complexin promotes fusion of synaptic vesicles." Nature Neuroscience 14(9): 1096-1102. PMID:21857672
Tang et al. (2006): "Complexin regulates fusion competence of synaptic vesicles." Neuron 51(2): 185-200. PMID:16768950
Sudhof et al. (2013): "Neurotransmitter release: the last millisecond." Neuron 80(3): 674-695. PMID:24138820