How Kinesin Motor Proteins Deal with Traffic Jams

Neuronal cells are highly crowded with various types of vesicles, organelles, proteins and cytoskeletal filaments densely packed inside the cytoplasm. One would expect crowding to pose challenges to motor-protein mediated transport, but in spite of the very crowded interior of the cell, motors appear to be able to deliver their cargo efficiently, overcoming traffic jams and roadblocks. The motors could be a possible source for crowding by creating traffic jams, limiting the number of motor-binding sites thus blocking the forward motion of motors. We use in vitro motility assays to take Total Internal Reflection Microscopy sequences of images of motors moving along microtubules. Here, we have developed an advanced analysis technique to obtain quantitative motor parameters from the image sequences in an automated way, using correlation of the fluorescence intensities. This new analysis method speeds up analysis and requires less data than the single-particle tracking approach. Correlating intensities allows analysis of data obtained under conditions inaccessible for single-particle tracking, including those performed at high motor densities that can provide insight into traffic-jam like interactions between motors. Apart from Kinesin-1 motors, this advanced analysis technique is used to understand the behavior of two kinesin-2 family motors in a crowded environment. These two kinesin-2 family motors, heterotrimeric kinesin-II and homodimeric OSM-3, cooperate to drive intraflagellar transport (IFT) in the sensory cilia of C. elegans. Our results based on the new analysis approach provide novel insights into the way kinesin motor proteins handle traffic-jam situations