Rapid purification of wildtype and mutant cytochrome c oxidase from Rhodobacter sphaeroides by Ni(2+)-NTA affinity chromatography.

A rapid and highly efficient method of purifying the aa3-type cytochrome c oxidase from Rhodobacter sphaeroides has been developed. This method relies upon a six-histidine affinity tag fused to the C-terminus of subunit I, which confers to the oxidase a high affinity for Ni(2+)-nitrilotriacetic acid (NTA) agarose. The histidine-tagged oxidase can be purified rapidly and with high yield by one affinity chromatography step, starting with solubilized membranes. The purified oxidase is > 95% pure and possesses structural and functional characteristics of the wildtype enzyme. The six-histidine tag can be easily added to pre-constructed site-directed mutants of subunit I, increasing the availability of purified cytochrome c oxidase mutants for biophysical and biochemical studies.