Direct interaction of subunits a and b of the F0 complex of Escherichia coli ATP synthase by forming an ab2 subcomplex

The addition of a His(6) tag to the N terminus of subunit a of the F-0 complex of the Escherichia coli ATP synthase allowed the purification of an ab(2) subcomplex after solubilization of membranes with n-dodecyl-beta-D-maltoside and subsequent nickel-nitrilotriacetic acid affinity chromatography. After co-reconstitution of the ab(2) subcomplex with purified subunit c, passive proton translocation rates as well as coupled ATPase activities after binding of F-1 were measured that were comparable with those of wild type F-0. The interaction between subunits a and b, which has been shown to be stoichiometric and functional, is not triggered by any cross-linking reagent and therefore reflects subunit interactions occurring within the F-0 complex in vivo.