External torque application to molecular motor F₁-ATPase using optical vortex trapping

Single-molecule manipulation techniques are used to elucidate mechanisms in biological systems. Optical tweezers are powerful tools because of their ease of use in combination with optical microscopy and appropriate torque range. However, the use of optical tweezers to generate rotational motion is difficult owing to the complexity of applying constant torque to a moving molecule. The magnitude of the torque applied with optical tweezers depends on the positional relationship with the trapping particle and requires positional feedback. In this study, we found that the adaption of optical vortices (OVs) generated by phase modulation of optical tweezers enabled quantitative mechanical manipulations. Moreover, optical tweezers with an OV could be applied to measure the torque generated by a molecular motor. We used an OV to apply torque via a precise handle consisting of a DNA origami rod to a rotating molecular motor, F₁-ATPase. Using the constant torque generated by the OV, we applied torques to F₁-ATPase and succeeded in stalling and reversing its rotation. This technique is useful for applying constant torque to biomolecules.