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A Programmable Optical Angle Clamp for Rotary Molecular Motors

Teuta Pilizota ^*, Thomas Bilyard ^*, Fan Bai ^*, Masamitsu Futai , Hiroyuki Hosokawa  and Richard M. Berry ^*

^* Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom; and Futai Special Laboratory, Microbial Chemistry Research Center, Microbial Chemistry Research Foundation, CREST, Japan Science and Technology Agency, Kamiosaki, Shinagawa, Tokyo

Correspondence: Address reprint requests to Richard M. Berry, Tel.: 44-0-1865-282559; Fax: 44-0-1865-272400; E-mail: r.berry1{at}physics.ox.ac.uk.

Optical tweezers are widely used for experimental investigation of linear molecular motors. The rates and force dependence of steps in the mechanochemical cycle of linear motors have been probed giving detailed insight into motor mechanisms. With similar goals in mind for rotary molecular motors we present here an optical trapping system designed as an angle clamp to study the bacterial flagellar motor and F₁-ATPase. The trap position was controlled by a digital signal processing board and a host computer via acousto-optic deflectors, the motor position via a three-dimensional piezoelectric stage and the motor angle using a pair of polystyrene beads as a handle for the optical trap. Bead-pair angles were detected using back focal plane interferometry with a resolution of up to 1°, and controlled using a feedback algorithm with a precision of up to 2° and a bandwidth of up to 1.6 kHz. Details of the optical trap, algorithm, and alignment procedures are given. Preliminary data showing angular control of F₁-ATPase and angular and speed control of the bacterial flagellar motor are presented.