Longitudinal and Rotational Motion of Microtubules Driven by the Kinesin-14 Motor Ncd

Abstract

In gliding motility assays, various motor proteins have been shown to drive the rotation of filaments around their longitudinal axis. Using FLIC microscopy [1], we measured the longitudinal and rotational motion of quantum-dot labeled microtubules driven by Ncd (nonclaret disjunctional, a kinesin-14 motor protein) as a function of the ATP concentration. The data show two striking features: (i) The longitudinal velocity shows a strong deviation from the Michaelis-Menten curve. (ii) The rotational pitch depends strongly on the ATP concentration.We propose a simple mechanical model which explains both findings. The underlying mechanism of the non-processive Ncd motor requires that the power stroke comprise a longitudinal, as well as a lateral (off-axis) component and that the waiting (apo) state take place before the power stroke. We note that the model is distinct from what has been proposed for actin rotation by myosin motors and microtubule rotation by kinesin-1 motors, where the rotation is a consequence of the filament structure [2, 1]. Our results are consistent with previous evidence based on cryo-EM data [3] that the Ncd power stroke is triggered by ATP binding.[1] B. Nitzsche, F. Ruhnow and S. Diez, Nature Nanotechnology 3:552-556 (2008)[2] A. Vilfan, Biophys. J. 97:1130-1137 (2009).[3] N.F. Endres, C. Yoshioka, R.A. Milligan and R.D. Vale, Nature 439:875-878 (2006).