Complexin that regulates SNARE protein complex-mediated synaptic vesicle fusion (By similarity). Required for the maintenance of synaptic ultrastructure in the adult retina (By similarity). Positively regulates synaptic transmission through synaptic vesicle availability and exocytosis of neurotransmitters at photoreceptor ribbon synapses in the retina (By similarity). Suppresses tonic photoreceptor activity and baseline 'noise' by suppression of Ca(2+) vesicle tonic release and the facilitation of evoked synchronous and asynchronous Ca(2+) vesicle release (By similarity). . This is the function of CPLX4 (complexin 4, ENSG00000166569).