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Two rotary motors in F-ATP synthase are elastically coupled by a flexible rotor and a stiff stator stalk

André Wächter, Yumin Bi, Stanley D. Dunn, Brian D. Cain, Hendrik Sielaff, Frank Wintermann, Siegfried Engelbrecht, Wolfgang Junge and John E. Walker
Proceedings of the National Academy of Sciences of the United States of America
Vol. 108, No. 10 (March 8, 2011), pp. 3924-3929
Stable URL: http://www.jstor.org/stable/41061037
Page Count: 6
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Two rotary motors in F-ATP synthase are elastically coupled by a flexible rotor and a stiff stator stalk
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Abstract

ATP is synthesized by ATP synthase (F₀F₁-ATPase). Its rotary electromotor (F₀) translocates protons (in some organisms sodium cations) and generates torque to drive the rotary chemical generator (F₁). Elastic power transmission between F₀ and F₁ is essential for smoothing the cooperation of these stepping motors, thereby increasing their kinetic efficiency. A particularly compliant elastic domain is located on the central rotor (c 10-15 /ε/γ), right between the two sites of torque generation and consumption. The hinge on the active lever on subunit β adds further compliance. It is under contention whether or not the peripheral stalk (and the "stator" as a whole) also serves as elastic buffer. In the enzyme from Escherichia coli, the most extended component of the stalk is the homodimer b₂, a right-handed α-helical coiled coil. By fluctuation analysis we determined the spring constant of the stator in response to twisting and bending, and compared wild-type with b-mutant enzymes. In both deformation modes, the stator was very stiff in the wild type. It was more compliant if b was elongated by 11 amino acid residues. Substitution of three consecutive residues in b by glycine, expected to destabilize its α-helical structure, further reduced the stiffness against bending deformation. In any case, the stator was at least 10-fold stiff er than the rotor, and the enzyme retained its proton-coupled activity.

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