Measuring Collective Transport by Defined Numbers of Processive and Nonprocessive Kinesin Motors

Abstract

Molecular motors usually work together in teams within the cell. However, studying coordination among these nanomachines has posed a challenge. Here, we used experimentally defined assemblies in vitro to investigate how the functions of molecular motors depend on the motor number and arrangement. The assembly forms a linear array of motor proteins with defined number and spacing on a DNA scaffold. using this method, we linked together multiple molecules of either two different types of kinesin motors, kinesin-1 or Ncd (kinesin-14), which shows a processive and nonprocessive movement, respectively. Regardless of the motor type, their processivity scaled exponentially with the motor number at low load. While single Ncd motors showed short, diffusive movement along microtubules, the assemblies composed of two Ncd molecules moved processively for more than 1 μm. Force measurement revealed that small groups of Ncd can generate an additive force that is much larger than can single motors, while multiple kinesin-1 can rarely share an external load. Numerical simulations suggest that the coordination among Ncd motors strongly depends on the fast microtubule binding kinetics of individual motors. Moreover, we found that Ncd can exert a larger drag force when pulled backward despite its small active force. These features would make Ncd suited for one of its cellular functions to dynamically crosslink microtubules while antagonizing the opposing force. Thus, our experimental system may provide a platform to study the collective behavior of motor proteins from the bottom up.