A MECHANISM OF PROTON TRANSLOCATION BY F1F0 ATP SYNTHASES SUGGESTED BY DOUBLE MUTANTS OF THE ALPHA-SUBUNIT

Three amino acid residues in the alpha subunit of the Escherichia coli F1F0 ATP synthase are essential for pro ton translocation: Arg(210), Glu(219), and His(245). In this study, the essential glutamic acid has been relocated to position 252 with retention of function. It had bee n known that Gln(252) can be replaced by Glu without significant effec t. To test whether Q252E would function in the absence of Glu(219), a ''site-directed second-site suppressor'' experiment was designed. Satu ration mutagenesis was applied to residue Glu(219), and 14 different a mino acid substitutions were isolated, five of which permitted growth on succinate minimal medium at 37 degrees C: Asp, Lys, Gly, Ala, and S er. These results indicate that Q252E can provide the essential carbox yl group normally provided by Glu(219), but that strict requirements a re placed on the residue at position 219. We interpret these results t o mean that the Q252E must occupy, at least partially, the normal posi tion of Glu(219). We present a novel mechanism of proton translocation by F1F0 ATP synthases that includes a rotating oligomer of c subunits , in which the Asp(61) of two c subunits simultaneously interact with Glu(219) and Arg(210) of the alpha subunit. This mechanism can be adap ted for both mitochondrial and sodium-driven bacterial ATP synthases.