Bcl‐XL as a fusion protein for the high‐level expression of membrane‐associated proteins

Abstract An Escherichia coli plasmid vector for the high‐level expression of hydrophobic membrane proteins is described. The plasmid, pBCL, directs the expression of a target polypeptide fused to the C terminus of a mutant form of the anti‐apoptotic Bcl‐2 family protein, Bcl‐XL, where the hydrophobic C terminus has been deleted, and Met residues have been mutated to Leu to facilitate CNBr cleavage after a single Met inserted at the beginning of the target sequence. Fusion protein expression is in inclusion bodies, simplifying the protein purification steps. Here we report the high‐level production of PLM, a membrane protein that is a member of the FXYD family of tissue‐specific and physiological‐state–specific auxiliary subunits of the Na,K‐ATPase, expressed abundantly in heart and skeletal muscle. We demonstrate that milligram quantities of pure, isotopically labeled protein can be obtained easily and in little time with this system.