Characterization of the temperature-sensitive reaction of F1-ATPase by using single-molecule manipulation.

Rikiya Watanabe,Hiroyuki Noji

doi:10.1038/srep04962

Abstract

F1-ATPase (F1) is a rotary motor protein that couples ATP hydrolysis to mechanical rotation with high efficiency. In our recent study, we observed a highly temperature-sensitive (TS) step in the reaction catalyzed by a thermophilic F1 that was characterized by a rate constant remarkably sensitive to temperature and had a Q10 factor of 6–19. Since reactions with high Q10 values are considered to involve large conformational changes, we speculated that the TS reaction plays a key role in the rotation of F1. To clarify the role of the TS reaction, in this study, we conducted a stall and release experiment using magnetic tweezers, and assessed the torque generated during the TS reaction. The results indicate that the TS reaction generates the same amount of rotational torque as does ATP binding, but more than that generated during ATP hydrolysis. Thus, we confirmed that the TS reaction contributes significantly to the rotation of F1.

Highlights

F1-ATPase (F1) is a rotary motor protein that couples ATP hydrolysis to mechanical rotation with high efficiency
The results indicate that the TS reaction generates the same amount of rotational torque as does ATP binding, but more than that generated during ATP hydrolysis
The catalytic sites for ATP hydrolysis/synthesis are located at the interface between each a and b subunit, mainly on the b subunits; i.e., F1 possesses three catalytic sites

Summary

Introduction

F1-ATPase (F1) is a rotary motor protein that couples ATP hydrolysis to mechanical rotation with high efficiency. The results indicate that the TS reaction generates the same amount of rotational torque as does ATP binding, but more than that generated during ATP hydrolysis. According to the presently accepted scheme of the reaction (Fig. 1), hydrolysis or turnover of a single ATP molecule at each catalytic site is coupled with one revolution of the c subunit, and the angle between the three catalytic sites differs by 120u during each catalytic phase[18]. When a b subunit’s ATP-binding angle is 0u (cyan circle in Fig. 1), it executes a hydrolysis reaction after the c subunit rotates by 200u18, releases ADP between 240u and 320u, and Pi at 320u, respectively[15,24]

Methods

Results

Conclusion