Application of a Small EF Hand Affinity Tag for Expression, Purification and Biophysical Studies of G Protein-Coupled Membrane Receptors

Heptahelical G protein-coupled receptors (GPCR) comprise a large family of integral membrane proteins involved in a wide array of cell signaling pathways. For high resolution structural studies of these receptors, multi-milligram quantities of pure and structurally unperturbed proteins are required. Purification of recombinant GPCRs typically involves their solubilization into detergent micelles followed by chromatographic purification. Because of relatively low expression levels of these recombinant receptors, it is challenging to design an efficient strategy for selective and efficient purification with high yield. Here, we describe a recently introduced purification system employing a high affinity molecular switch based on fragment complementation, with a calcium dependent capture and EDTA mediated chelation elution. This technique was successfully applied to the purification of the recombinant cannabinoid receptor CB2, a promising target for the development of drugs for inflammation, immunological disorders and pain. It is feasible that similar strategies can be successfully employed for expression and purification of other membrane protein targets.