The gammaepsilon-c subunit interface in the ATP synthase of Escherichia coli. cross-linking of the epsilon subunit to the c subunit ring does not impair enzyme function, that of gamma to c subunits leads to uncoupling.

Mutants with a cysteine residue in the gamma subunit at position 207 and the epsilon subunit at position 31 were expressed in combination with a c-dimer construct, which contains a single cysteine at position 42 of the second c subunit. These mutants are called gammaY207C/cc'Q42C and epsilonE31C/cc'Q42C, respectively. Cross-linking of epsilon to the c subunit ring was obtained almost to completion without significant effect on any enzyme function, i.e. ATP hydrolysis, ATP synthesis, and ATP hydrolysis-driven proton translocation were all close to that of wild type. The gamma subunit could also be linked to the c subunit ring in more than 90% yield, but this affected coupling. Thus, ATP hydrolysis was increased 2. 5-fold, ATP synthesis was dramatically decreased, and ATP hydrolysis-driven proton translocation was abolished, as measured by the 9-amino-6-chloro-2-methoxyacridinequenching method. These results for epsilonE31C/cc'Q42C indicate that the c subunit ring rotates with the central stalk element. That the gamma-epsilon cross-linked enzyme retains ATPase activity also argues for a gammaepsilon-c subunit rotor. However, the uncoupling induced by cross-linking of gamma to the c subunit ring points to important conformational changes taking place in the gammaepsilon-c subunit interface during this. Blocking these structural changes by cross-linking leads to a proton leak within the F(0).