Spiral Defects in Motility Assays: A Measure of Motor Protein Force

Abstract

In a commonly used motility assay, cytoskeletal filaments are observed as they glide over a surface coated with motor proteins. Defects in the motion frequently interrupt the flow of filaments. Examination of one such defect, in which a filament adopts a spiral form and rotates about a fixed point, provides a simple measure of the force exerted by the motor proteins. We demonstrate the universality of this approach by estimating the elementary forces of both myosin and kinesin.