Breaking of bonds between a kinesin motor and microtubules causes protein friction

Abstract

Friction limits the operation of macroscopic machines. Using optical tweezers, we showed that friction also limits the operation of molecular machines by measuring the friction between single yeast kinesin-8, Kip3p, and its microtubule track. The protein friction arises from the force necessary to break the adhesive bonds that Kip3p forms with discretely, 8-nm spaced binding sites on its track. A model based on bond rupture dynamics with a single energy barrier described the data. A fluctuation analysis con firmed Kip3p stepping during diffusion. Here, we validate our experimental results and data analysis by a Monte Carlo simulation. Our data have implications for other molecular machines or actively driven proteins, and give further insight into diffusion of proteins along polymers such as microtubules or DNA.