A New Microtubule Gliding Assay Analysis of Microtubule Persistence Length

Abstract

Microtubules are cytoskeletal polymers which play a role in cell division, cell mechanics, and intracellular transport. Each of these functions requires microtubules that are stiff and straight enough to span a significant fraction of the cell diameter. As a result, the microtubule persistence length, a measure of stiffness, has been actively studied for the past 15 years. Curiously, short microtubules are 10-50 times less stiff than long microtubules. In order to study this phenomenon, we have developed a new kinesin-driven microtubule gliding assay analysis of persistence length. By combining sparse fluorescent labeling of individual microtubules with single particle tracking of individual fluorophores, we tracked microtubule gliding trajectories with nanometer-level precision. By varying the surface density of kinesin, we measured the persistence length of microtubules on length scales from 100s of nanometers to 10s of micrometers. Microtubule persistence length increased from about 200 micrometers to 3 mm across these scales, consistent with previous experiments at short or long length scales. The scale dependence of persistence length we measured supports models in which protofilaments are loosely coupled near microtubule tips, becoming tightly coupled far from the tip.