Rotation of a complex of the gamma subunit and c ring of Escherichia coli ATP synthase - The rotor and stator are interchangeable

ATP synthase (F0F1) transforms an electrochemical proton gradient into chem ical energy (ATP) through the rotation of a subunit assembly. It has been s uggested that a complex of the gamma subunit and c ring (c(10-14)) of F0F1 could rotate together during ATP hydrolysis and synthesis (Sambongi, Y., Ik o, Y., Tanabe, M., Omote, H., Iwamoto-Kihara, A., Ueda, I., Yanagida, T,, W ade, Y., and Futai, M. (1899) Science 286, 1722-1724), We observed that the rotation of the c ring with the cI28T mutation (c subunit cIle-28 replaced by Thr) was less sensitive to venturicidin than that of the wild type, con sistent with the antibiotic effect on the cI28T mutant and wild-type ATPase activities (Fillingame, R. H., Oldenburg, M., and Fraga, D, (1991) J, Biol . Chem. 266, 20934-20939), Furthermore, we engineered F0F1 to see the alpha (3)beta (3) hexamer rotation; a biotin tag was introduced into the alpha o r beta subunit, and a His tag was introduced into the c subunit, The engine ered enzymes could be purified by metal affinity chromatography and density gradient centrifugation. They were immobilized on a glass surface through the c subunit, and an actin filament was connected to the alpha or beta sub unit, The filament rotated upon the addition of ATP and generated essential ly the same frictional torque as one connected to the c ring. These results indicate that the gamma epsilonc(10-14) complex is a mechanical unit of th e enzyme and that it can be used as a rotor or a stator experimentally, dep ending on the subunit immobilized.