F1-ATPase is a rotary motor protein, and ATP hydrolysis generates torque at the interface between the γ subunit, a rotor shaft, and the α3aβ3 substructure, a stator ring. The region of conserved acidic 'DELSEED' motif of the β subunit has a contact with γ subunit and has been assumed to be involved in torque generation. Using the thermophilic α3β3γ complex in which the corresponding sequence is DELSDED, we replaced each residue and all five acidic residues in this sequence with alanine. In addition, each of two conserved residues at the counterpart contact position of γ subunit was also replaced. Surprisingly, all of these mutants rotated with as much torque as the wild-type. We conclude that side chains of the DELSEED motif of the β subunit do not have a direct role in torque generation.
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