Complexin1/2

Complexins are enriched in neurons where they colocalize with syntaxin 1 and SNAP 25. In addition, complexin 2, also referred to as synaphin 1, is expressed ubiquitously at low levels. Complexins bind weakly to syntaxin 1 alone and not at all to synaptobrevin and SNAP 25, but strongly to the SNAP receptor-core complex composed of these three molecules. They compete with α-SNAP for binding to the core complex but not with other interacting molecules, suggesting that complexins regulate the sequential interactions of α-SNAP and synaptotagmins with the SNAP receptor during exocytosis. In retinal ribbon synapses complexin 3 and complexin 4 functionally replace complexin 1 (synaphin 2) and 2. They have similar biochemical binding properties and are farnesylated at their C-terminus. 1 ) Südhof TC et al., Nature (1995) 2 ) Jahn R et al., Annu. Rev. Neurosci. (1994) 3 ) McMahon HT et al., Cell (1995)