Single-molecule angular manipulation, excitability and the bacterial flagellar motor
Francesco Pedaci
CBS, Montpellier, Francia
The possibility to directly apply and measure force on microscopic objects has opened many possibilities in the field of single-molecule biophysics. Using these microscopic handles, it becomes possible to probe mechanical properties of single molecules like DNA or protein motors, with nanometer and pico-Newton resolution. Novel techniques are under development to further open the possibility to apply and measure not only force but also torque on single molecules. In several biological systems, in fact, rotation and torque are relevant physical parameters, the main example being the double helix of DNA which can be open or compressed depending of the sense of rotation. I will describe the optical torque wrench, an optical trapping technique which achieve this angular control on microscopic birefringent particles. I will show how the angular dynamics of the trapped particle is a nice and simple example of excitability, a dynamical property found in different other non-linear systems, particularly in biology. Finally I will show how this technique can be used to study torque generation of the powerful molecular motor which rotates flagella in E.coli and other bacteria