Cooperative Effects in Transport Systems Driven by Diffusively Anchored Motors

Abstract

Intracellular trafficking of membrane-bound organelles is a fundamental process essential to many cellular functions including cell growth and signaling. A variety of such organelles are transported by motor proteins such as kinesins, dyneins and myosins, walking on cellular tracks made of microtubules and actin filaments. Since studying the mechanical and biochemical functioning of these transport systems inside the cell is extremely challenging, transport is often mimicked in-vitro, for example by gliding motility assays. There, cytoskeletal filaments are propelled by motors that are conventionally immobilized on a rigid substrate. In contrast, when transporting membrane-bound organelles inside a cell the motors are diffusively anchored - either directly or via adaptor molecules - to lipid bilayers. Such resulting ‘loose’ coupling may induce motor co-ordination and is likely to change the collective motor dynamics.In this study, we investigate the collective behavior of motor proteins anchored to lipid bilayers. Using truncated kinesin-1 motors with a streptavidin-binding-peptide tag we performed gliding motility assays on streptavidin-loaded biotinylated supported lipid bilayers. Our results suggest a dependence of the microtubule gliding velocity on both, the motor density as well as the microtubule length. Based on measurements of the diffusion constants and the velocity of motors and microtubules, a theoretical model is developed to determine (i) the number of microtubule-attached motors and (ii) the force produced by an ensemble of motors.