N-terminal SNARE complex binding domain found in complexins III and IV
Complexins (CPXs) are small, cytosolic proteins that bind to the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex to regulate synaptic vesicle exocytosis. Complexins III (CPX III) and IV (CPX IV) are the only CPX isoforms present in retinal ribbon synapses. They carry an extension with a functional CAAX-box farnesylation site that is absent in CPXs I and II. Their C-terminal farnesylation regulates their synaptic targeting and modulatory function in transmitter release. They may contribute to the unique release efficacy of retinal sensory neurons. CPXs III and IV can functionally replace CPXs I and II, which regulate a late step in the release process, most likely by stabilizing SNARE complexes and thus maintaining synaptic vesicles in a highly release competent state. This model corresponds to the N-terminal SNARE complex binding domain of CPXs III and IV.
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