Escherichia coli F1Fo-ATP Synthase with a b/δ Fusion Protein Allows Analysis of the Function of the Individual b Subunits

The "stator stalk" of F1Fo-ATP synthase is essential for rotational catalysis as it connects the nonrotating portions of the enzyme. In Escherichia coli, the stator stalk consists of two (identical) b subunits and the delta subunit. In mycobacteria, one of the b subunits and the delta subunit are replaced by a b/delta fusion protein; the remaining b subunit is of the shorter b' type. In the present study, it is shown that it is possible to generate a functional E. coli ATP synthase containing a b/delta fusion protein. This construct allowed the analysis of the roles of the individual b subunits. The full-length b subunit (which in this case is covalently linked to delta in the fusion protein) is responsible for connecting the stalk to the catalytic F-1 subcomplex. It is not required for interaction with the membrane-embedded F-o subcomplex, as its transmembrane helix can be removed. Attachment to F-o is the function of the other b subunit which in turn has only a minor (if any at all) role in binding to delta. Also in E. coli the second b subunit can be shortened to a b' type.