Protein Friction causes Molecular Wear in Kinesin-Powered Molecular Shuttles

Abstract

During the operation of biological nanomachines, such as motor proteins, energy has to be dissipated to enable cycles of unbinding and rebinding leading to stepwise movement. Since the energy dissipation is, for low velocities, proportional to the velocity of movement, it can be conceptually understood as “protein friction”. At the same time, the forces generated during the unbinding steps can be expected to generate adhesive wear. Here, the degradation of microtubules gliding on surfaces covered by kinesin motor proteins is examined, a situation with relevance to biological systems as well as engineered hybrid systems, such as molecular shuttles powered by motor proteins. We find that the gliding motion leads to a detectable shortening of the microtubules that depends non-linearly on the kinesin density and the microtubule velocity. We interpret our data as a result of the sequential removal of the most weakly bound tubulin dimers from the end of the microtubule by the motors.