Calcium binding proteins are centrally involved in mediating intracellular calcium signals. Secretagogin (SCGN) is a recently characterized hexa-EF hand calcium binding protein which was cloned from a beta-cell cDNA library. Two full-length variants (Secretagogin-R22 and Secretagogin-Q22) and a truncated variant (Setagin), which exhibits no calcium binding capacity, have been identified so far. Full-length SCGN binds four calcium ions with a [Ca2+]0.5 of approximately 25µM and exhibits structural changes following calcium binding. Therefore SCGN was confined to be rather a calcium sensor than a calcium buffer protein. SCGN is highly and specifically expressed in neuroendocrine cells, especially in pancreatic beta cells. Additional expression was found in distinct neurons of the central nervous system and in a subgroup of colorectal cancers. Functional in vitro analysis and its interaction with the SNARE complex member SNAP-25 implicate its involvement in the insulin secretion process. Basing on its characteristic expression pattern, SCGN was implemented as neuronendocrine marker protein. Moreover, SCGN is detectable in the serum of patients suffering from cerebral hypoxia. In this context, recently developed commercial kits for the serum detection of SCGN allow its linical application. In conclusion, SCGN is a recently identified calcium binding protein with functional and clinical aspects in the field of neuroendocrinology.
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