Secretagogin, a hexa EF-hand calcium-binding protein: High level bacterial overexpression, one-step purification and properties

• Secretagogin (SCGN) is a hexa EF-hand Ca2+-binding proteins.
• We describe one-step method for SCGN purification by refolding from inclusion bodies.
• SCGN binds Mg2+ with rather high affinity (∼13 μM).
• SCGN forms dimer in the presence of Ca2+.
• Like other Ca2+ sensors, SCGN exhibits large conformational change upon Ca2+ binding.

Secretagogin (SCGN), a hexa EF-hand calcium-binding protein, is highly expressed in the endocrine cells (especially in pancreatic islets) and in restricted neuronal sub-populations, albeit at comparatively low level. Since SCGN is predicted to be a potential neuroendocrine marker in carcinoid tumors of lung and gastrointestinal tract, it is of paramount importance to understand the features of this protein in different environment for assigning its crucial functions in different tissues and under pathophysiological conditions. To score out the limitation of protein for in vitro studies, we report a one-step, high purity and high level bacterial purification of secretagogin by refolding from the inclusion bodies yielding about 40 mg protein per litre of bacterial culture. We also report previously undocumented Ca2+/Mg2+ binding and hydrodynamic properties of secretagogin.