Abstract
Intraflagellar transport (IFT) in C. elegans chemosensory cilia is an example of functional coordination and cooperation of two motor proteins with distinct motility properties operating together in large groups to transport cargoes: a fast and processive homodimeric kinesin-2, OSM-3, and a slow and less processive heterotrimeric kinesin-2, kinesin-II. To study the mechanism of the collective dynamics of kinesin-II of C. elegans cilia in an in vitro system, we used Total Internal Reflection Fluorescence microscopy to image the motility of truncated, heterodimeric kinesin-II constructs at high motor densities. Using an analysis technique based on correlation of the fluorescence intensities, we extracted quantitative motor parameters, such as motor density, velocity and average run length, from the image. Our experiments and analyses show that kinesin-II motility parameters are far less affected by (self) crowding than OSM-3. Our observations are supported by numerical calculations based on the TASEP-LK model (Totally Asymmetric Simple Exclusion Process-Langmuir Kinetics). From a comparison of data and modelling of OSM-3 and kinesin-II, a general picture emerges of the collective dynamics of the kinesin motors driving IFT in C. elegans chemosensory cilia and the way the motors deal with crowding.
Highlights
Differentiated and specialized cells generate specific transport needs and encounter a variety of transport challenges
The kinesin-II motility parameters were obtained by extracting single-motor trajectories from the time-series of Total Internal Reflection Fluorescence (TIRF) images using Single-Particle Tracking (SPT)
Our results indicate that heterodimeric kinesin-II is far less affected by motor crowding than kinesin-1 and OSM-3 [7]
Summary
Differentiated and specialized cells generate specific transport needs and encounter a variety of transport challenges. Transport along cytoskeletal filaments is driven by members of the kinesin, dynein and myosin superfamilies of motor proteins, often engaged in teams and highly regulated. Unraveling the collective dynamics of different motor species is very important to understand how intracellular transport can run smoothly in a cellular environment. A key example of collective and collaborative transport by multiple, densely packed motor proteins is intraflagellar transport (IFT) driven in the anterograde direction by kinesin-2 motors. In the chemosensory cilia of C. elegans, teams of two Kinesin-2 motors: ~50 slow heterotrimeric kinesin-II (KLP-11/20 KAP-1) and ~30 fast homodimeric OSM-3 teams, work together to drive transport of IFT trains from ciliary base to tip.
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