Collective Dynamics of Cooperating Homodimeric and Heterotrimeric Kinesin-2 Motor Proteins Unraveled

Abstract

Intracellular transport takes place in the crowded environment of the cell, densely packed with proteins, cytoskeletal filaments, vesicles and organelles. In most transport systems, multiple motors team up to transport a single cargo, resulting in collective motor behavior that cannot be explained only from single-motor properties. Intraflagellar transport (IFT) in C. elegans cilia is an example of functional coordination and cooperation of two motor proteins with distinct motility properties operating together in groups to transport a single cargo: homodimeric OSM-3 (fast and processive) and heterotrimeric Kinesin-II (slow and less processive). To study the mechanism of the collective dynamics of OSM-3 and kinesin-II in cilia, we use fluorescence microscopy and high-density in-vitro motility assays. Using an advanced analysis technique based on correlation of the fluorescence intensities, we extracted the quantitative motor parameters (such as motor density, velocity and average run length) from the image sequences in an automated way with a high level of precision. Our experiments and analyses show that OSM-3 and Kinesin-II motors are affected differently by the presence of the other motor. For example, OSM-3 velocity and run length are substantially reduced in the presence of the Kinesin-II. Numerical calculations based on TASEP-LK model (Totally Asymmetric Simple Exclusion Process-Langmuir Kinetics) underline the importance of intermolecular interactions, such as the change of the OSM-3 affinity to the microtubule dependent on the Kinesin-II density. Based on this approach, a general picture of collective dynamics of OSM-3 and Kinesin-II motor proteins in IFT is formulated.