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Complexin
In molecular biology, complexin (also known as synaphin), a eukaryotic specific protein, is a cytoplasmic neuronal protein which binds to the SNARE protein complex (''SNAREpin'') with a high affinity. In the presence of Ca2+, the transport vesicle protein synaptotagmin displaces complexin, allowing the SNARE protein complex to bind the transport vesicle to the presynaptic membrane.
Complexin acts as both an inhibitor and a facilitator of synaptic vesicle fusion and neurotransmitter release. In one conformation, it clamps ''SNAREpin'' complexes, preventing vesicle fusion, while in a different conformation it releases the ''SNAREpins'', allowing synaptotagmin to trigger fusion.
Whereas complexin is not necessary for synaptic vesicle exocytosis, it does increase neurotransmitter release by 60–70% as demonstrated by complexin gene knockout in mice. A number of human neurological diseases have been linked to a deficiency of complexin.
==Structure and Binding==
Complexin is a small highly charged cytosolic protein that is hydrophilic, rich in glutamic acid and lysine residues. Complexin's central region (amino acids 48–70) binds to the SNARE core as an anti-parallel α-helix, which attaches complexin to the SNARE complex. It interacts selectively with the ternary SNARE complex but not with monomeric SNARE proteins. Complexin binds to the groove between the synaptobrevin and syntaxin helices. Complexin promotes interaction of the transmembrane regions of syntaxin and synaptobrevin. Complexin stabilizes the C-terminal part of the SNARE complex.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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