Final Report Summary - BIOTORQUE (Probing the angular dynamics of biological systems with the optical torque wrench)
In the field of single-molecule biophysics, it is nowadays technically possible to perform mechanical studies of individual isolated molecules of biological interest (polymers like DNA, RNA and proteins) directly stretching them one by one and observing their mechanical properties. This is important to go beyond the measurement of ensemble averages, observing each individual response to an external force. Our group advanced these techniques by adding the possibility to rotate and apply torque to a single molecule. We have achieved this by developing and improving techniques based on optical trapping of birefringent particles and tailored magnetic fields. This work is motivated by the fact that in several molecular biological systems, rotation and torque are the relevant parameters. Our model system of choice is the Bacterial Flagellar Motor, a powerful nanometer-scale rotary motor that rotates the flagella in bacteria and allows a controlled cellular movement. We have studied the internal dynamics of the units that generate torque, and proposed a model for the observed mechano-sensing property of the motor, i.e. its ability to adjust the output torque as a function of the external conditions. Our techniques have possible applications in other fields, which we are currently investigating, as in scanning microscopy, rheology, and the biophysics of other molecular motors.