Glutamate residues at positions 219 and 252 in the α-subunit of the Escherichia coli ATP synthase are not functionally equivalent

The role of glutamate-219 in the α-subunit of the Escherichia coli F₀F₁-ATPase was examined using site-directed mutagenesis. The replacement of Glu-219 by lysine, alanine or glycine resulted in a partially functional F₀F₁-ATPase. Combining any of these mutations with the substitution of glutamate for Gln-252 did not result in any increase in function. These findings rule out a proposal that glutamate at position 252 can functionally replace glutamate at position 219 [S.B. Vik, B.J. Antonio, J. Biol. Chem. 269 (1994) 30364-30369]. All the single and double mutants grew better at 25°C than at 37°C, suggesting a role for Glu-219 in maintaining the structure of the F₀.