Secretin (SCGN) is a cytoplasmic calcium binding protein, which has homology with calcium binding protein-D28k (CALB1) and calcium reticulum protein (CALB2). Secretin protein was isolated from Langerhans Island and insulinoma cells, and was highly expressed in pancreas, but decreased in thyroid, adrenal medulla, stomach, small intestine and colon. The cloning and sequence analysis of secretin cDNA showed that the corresponding protein included six EF hand calcium binding domain tandem repeats. The interaction between secretin and vesicular transporters (including SNAP25, SNAP23, ARFGAP2 and DOC2A) suggests that SCGN may play a role in the release of neurotransmitters and hormones. The study on the expression of secretin in fetal brain and developing brain shows that this calcium binding protein plays a role in differentiation, brain wiring and neuronal development.