None of the Rotor Residues of F1-ATPase Are Essential for Torque Generation

doi:10.1016/j.bpj.2014.04.013

None of the Rotor Residues of F₁-ATPase Are Essential for Torque Generation

Editor: Robert Nakamoto.

Ryohei Chiwata,^† Ayako Kohori,^†Tomonari Kawakami,^† Katsuyuki Shiroguchi,^† Shou Furuike,^† Kengo Adachi,^† Kazuo Sutoh,^† Masasuke Yoshida,^‡§ Kazuhiko Kinosita Jr.^†*

†Department of Physics, Faculty of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan; ^‡ATP Synthesis Regulation Project, ICORP, Japan Science and Technology Agency (JST), Aomi 2-41, Koto-ku, Tokyo, Japan; and ^§Department of Molecular Bioscience, Kyoto Sangyo University, Motoyama, Kamigamo, Kyoto, Japan
*Corresponding author

DOI: http://dx.doi.org/10.1016/j.bpj.2014.04.013

Abstract

F₁-ATPase is a powerful rotary molecular motor that can rotate an object several hundred times as large as the motor itself against the viscous friction of water. Forced reverse rotation has been shown to lead to ATP synthesis, implying that the mechanical work against the motor’s high torque can be converted into the chemical energy of ATP. The minimal composition of the motor protein is α₃β₃γ subunits, where the central rotor subunit γ turns inside a stator cylinder made of alternately arranged α₃β₃ subunits using the energy derived from ATP hydrolysis. The rotor consists of an axle, a coiled coil of the amino- and carboxyl-terminal α-helices of γ, which deeply penetrates the stator cylinder, and a globular protrusion that juts out from the stator. Previous work has shown that, for a thermophilic F₁, significant portions of the axle can be truncated and the motor still rotates a submicron sized bead duplex, indicating generation of up to half the wild-type (WT) torque. Here, we inquire if any specific interactions between the stator and the rest of the rotor are needed for the generation of a sizable torque. We truncated the protruding portion of the rotor and replaced part of the remaining axle residues such that every residue of the rotor has been deleted or replaced in this or previous truncation mutants. This protrusionless construct showed an unloaded rotary speed about a quarter of the WT, and generated one-third to one-half of the WT torque. No residue-specific interactions are needed for this much performance. F₁ is so designed that the basic rotor-stator interactions for torque generation and control of catalysis rely solely upon the shape and size of the rotor at very low resolution. Additional tailored interactions augment the torque to allow ATP synthesis under physiological conditions.

This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).

Katsuyuki Shiroguchi’s present address is Laboratory for Integrative Genomics, RIKEN Center for Integrative Medical Sciences (IMS), Yokohama 230-0045, Japan.

Shou Furuike’s present address is Faculty of Physics, Osaka Medical College, Takatsuki 569-8686, Japan.

Received: December 27, 2013; Accepted: April 7, 2014;