Positively regulates a late step in exocytosis of various cytoplasmic vesicles, such as synaptic vesicles and other secretory vesicles (PubMed:23345244). Organizes the SNAREs into a cross-linked zigzag topology that, when interposed between the vesicle and plasma membranes, is incompatible with fusion, thereby preventing SNAREs from releasing neurotransmitters until an action potential arrives at the synapse (PubMed:23345244). Also involved in glucose-induced secretion of insulin by pancreatic beta-cells. Essential for motor behavior (PubMed:15126625, PubMed:16000319). Binds to the SNARE core complex containing SNAP25, VAMP2 and STX1A. Enriched at synaptic-releasing sites in mature neurons. Nervous system, and pancreatic islet cells. Present in many brain regions, including hippocampus and cerebellum. In the retina, present at conventional amacrine cell synapses (at protein level). In the brain, expression starts at P6 and increases to reach a plateau at P20. Mice have no obvious brain abnormality, but suffer from severe ataxia with dystonia starting from P7. Adult mice lacking Cplx1 are not capable of coordinated running or swimming and exhibit pronounced resting tremor. They also fail to habituate to confinement and have reduced exploration abilities in open field. Belongs to the complexin/synaphin family.