The IIBCGlc transmembrane subunit of the glucose transporter of E. coli containing a carboxy-terminal affinity tag consisting of six adjacent histidines was purified by nickel chelate affinity chromatography. The protein was constitutively overexpressed from a high copy number plasmid. 1.5 mg of 95% pure protein was obtained from 5 g (wet weight) cells. 70% of the phosphotransferase activity present in cell membranes was recovered. Adsorption to the nickel resin allows delipidation as well as rapid detergent exchange. The procedure was used to demonstrate exchange ofsubunits in the IIBCGlc dimer and it helds promise for the investigation of other protein-protein interactions.
