Kompleksina

Kompleksina, often rendered as complexin in English, denotes a family of small presynaptic proteins that regulate neurotransmitter release at chemical synapses. In vertebrates this family comprises four isoforms encoded by CPLX1–CPLX4. The term kompleksina is used in several languages to reference these proteins, sometimes alongside the English name Complexin.

These proteins are soluble cytosolic factors with a molecular weight around 12–17 kDa and a predominantly alpha-helical structure. They contain a central SNARE-binding region that interacts with the core SNARE complex assembled during vesicle fusion.

Functionally, complexins bind to the SNARE complex at the active zone of presynaptic terminals. They act as a clamp to suppress spontaneous, calcium-independent fusion while enabling rapid, calcium-triggered neurotransmitter release when calcium enters the terminal via interactions with synaptotagmin and other fusion machinery. The relative effects can vary by isoform, synaptic type, and calcium conditions.

Distribution patterns differ among isoforms: CPLX1 and CPLX2 are abundantly expressed in the brain, whereas CPLX3 and CPLX4 show more restricted distribution in retina and cerebellum. All isoforms share a common role in modulating exocytosis, but may contribute differently to synaptic plasticity across circuits.

Knockout and overexpression studies in model organisms reveal that disruption of complexin alters evoked and spontaneous release, affects synaptic strength and plasticity, and can produce motor or behavioral phenotypes. Because of its central role in vesicle fusion, complexin is used as a model system for studying the regulation of neurotransmitter release and synaptic efficiency.

Discovery and nomenclature sections note that the protein family was identified in the late 1990s–early 2000s, and that the name kompleksina reflects localization in some vocabularies. It is commonly cited together with the SNARE complex as a key regulator of presynaptic exocytosis.