Collective motor dynamics in membrane transport in vitro

Abstract

Key cellular processes such as cell division, internal cellular organization, membrane compartmentalization and intracellular transport rely on motor proteins. Motor proteins, ATP-based mechanoenzymes, actively transport cargo throughout the cell by walking on cytoskeletal filaments. Motors have been studied in detail on the single motor level such that information on their step size, ATP turnover rate, stall force, average run length and processivity are well known. However, in vivo, motors are often found working together, raising the question of how motors work together in transport. In their native environment, motors are bound to membrane material so that they can diffuse through a lipid bilayer, suggesting that their collective behavior may rely more on dynamic self-organization than experiments until now have allowed. In this thesis, an in vitro approach is presented to study collections of motors as they self-organize to actively transport membrane along microtubule tracks. Motors are specifically attached to a membrane reservoir and when they encounter cytoskeletal tracks, the motors walk on the track and extract membrane tubes from the reservoir. We find that dynamic fluctuations in motor densities and effects such as cooperative binding are key players in the collective action of motors in membrane transport.